JP4665071B1 - Method and apparatus for forming tin or solder precoat film - Google Patents

Abstract

[PROBLEMS] To stably produce a solder precoat film having a uniform quality with a stable quality, hardly causing a bridge to an adjacent circuit in a hot air leveler method after solder bath immersion treatment or a solder paste reflow treatment method.
An object to be treated is brought into contact with an organic fatty acid solution in an upper layer of a processing apparatus having a storage tank containing a molten tin solution or a molten solder solution in a lower layer, and a protective film of organic fatty acid is formed on the surface. Disperse molten tin solution or molten solder particles, adhere molten tin or molten solder to the surface of the object to be processed, and then immerse the object to be processed in the lower layer of molten tin or molten solder solution to form a tin or solder film And a second step of blowing off the excessively adhered tin or solder film by spraying the heated organic fatty acid solution while pulling up the object on which the tin solution or solder film is formed. .
[Selection] Figure 8

Description

The present invention relates to an electronic circuit of an electronic component such as a semiconductor element, a semiconductor chip, a semiconductor wafer, an interposer (wiring board), a semiconductor device, a capacitor, a capacitor, an inductor, a resistor, a connector, a printed circuit board, a mounting board, and an electronic device. The present invention relates to a method and apparatus for forming a tin or solder precoat film on an upper pad or lead.
In particular, the electronic component comprising a plurality of fine electronic circuits in which a large number of pads or leads having a small area are arranged at a narrow pitch, or a strip or strip plate in which a large number of electronic components are arranged in a matrix (hereinafter referred to as electronic component connection). The present invention relates to a technique and an apparatus for forming a smooth and uniform relatively thin solder precoat film on all the pads or leads of the body.

In recent years, electronic devices are increasingly highly integrated, high density, small and light, and high quality is required for reliability. Correspondingly, electronic components such as semiconductor chips, wafers, semiconductor devices, resistors, capacitors, connectors, and the like are increasingly miniaturized, and the pads or leads on these electronic circuits are both narrow and narrow in width and adjacent pitch. Is progressing. Along with this, the pads or leads of electronic circuit boards on which these electronic components are mounted and mounted have been correspondingly reduced in size.
For example, among electronic components, in particular, semiconductor devices such as BGA (Ball Grid Array) and CSP (Chip Size Package) semiconductor chips and interposers (wiring substrates) of semiconductor devices are electrode pads arranged in a matrix with miniaturization. Alternatively, the lead area is miniaturized, and the adjacent pitch is also becoming narrower.
For this reason, the solder precoat area on the pad or lead necessary for joining the solder balls to form the bumps is becoming increasingly smaller. In addition, there are many small electronic components such as ultra-mini transistors, ultra-mini diodes, and mini-capacitors that are assembled and formed as a multi-row lead frame strip that is arranged in a matrix. The leads are also becoming increasingly narrow.
On the other hand, the pads or leads on the electronic circuit board on which these micro electronic components are mounted on the surface are naturally miniaturized and fine pitches are reduced accordingly, and these electronic components are well soldered. In addition, the area of tin or solder pre-coating necessary for facilitating the process, or the area where thin gold plating is applied on the base plating of nickel has been miniaturized.

In general, as a method of forming a solder precoat film on a pad or lead of an electronic circuit board, (A) a molten solder bath immersion treatment method, (B) a solder paste coating / melting method, (C) a tin or solder plating method, ( D) Ni / Au plating method is widely used.
However, the solder pre-coating by the conventional methods (A) and (B) can be applied to a relatively wide pad or lead without any problem. However, when the pad or lead width becomes narrow, a bridge is locally formed between adjacent pads or leads. For this reason, it is said that the minimum width is 0.15 mm and the pitch between adjacent pads or leads is 0.2 mm. It is difficult to form no solder precoat film.

That is, (A) the molten solder bath dipping method is the most widely used method since the oldest. Generally, the surface other than the pad or lead is protected by the solder resist film, and only the pad or lead part is exposed. The electronic circuit board is immersed in a flux solution, or flux is applied to the pad or lead surface, then immersed in a molten solder bath, and the pad surface is oxidized using the reducing power of the flux. In this method, a solder precoat film is formed on a pad or a lead while removing the film to improve solder wettability.
In this method, since the solder generally adheres relatively thick (several tens to 100 μm), in an electronic circuit board having a narrow pitch circuit or a through hole, a bridge is easily generated locally between adjacent pads or leads, and a minute through There is a difficulty in soldering in the hole.
Therefore, in particular, in the case of a micro-fine electronic circuit having a pad or lead width of 0.02 to 0.08 mm and an adjacent pitch of 0.04 to 0.12 mm, the solder resist has a small wetting angle. There is a drawback that it is almost impossible to form a solder film because molten solder cannot be contact-bonded to the inner bottom micropad or lead surface surrounded by the high wall of the film.

For this reason, a hot liquid leveling method in which a molten solder is sprayed on an electronic circuit surface of 0.2 mm or less to form a solder film, and then a high-temperature liquid having a large specific gravity is sprayed to blow off excess solder (Patent Document 1). Has been proposed.
However, even in this method, a circuit width of 0.1 mm is a limit. For example, in the case of a small and narrow electronic circuit having a pad or lead width of 0.02 to 0.08 mm and an adjacent pitch of 0.04 to 0.12 mm, Because the wet angle inherent to molten solder is small, almost no molten solder can contact and bond to the inner bottom micropad or lead surface surrounded by the high wall of the solder resist film, so there is no solder adhesion (hereinafter referred to as missing). It is very difficult to form a stable and uniform solder film or precoat film on the surface of the micropad or lead.

For the purpose of forming a solder precoat film, there has been proposed a hot air leveling method (Patent Document 2) in which, after forming a solder layer, high temperature air is blown onto the solder layer to blow off excess solder.
However, even in this method, a circuit width of 0.1 mm is a limit. For example, in the case of a small and narrow electronic circuit having a pad or lead width of 0.02 to 0.08 mm and an adjacent pitch of 0.04 to 0.12 mm, It is almost impossible to form a uniform and uniform solder film on all micro pads or lead surfaces without missing.

Also, (B) the solder paste coating / fusion method has been widely used for a long time, and has been widely used even today, and the surface other than the pad or lead is protected with a solder resist film, and the pad or lead portion Reflow after the solder paste (cream solder) is applied to the pad or lead by screen printing etc. using a mask with an opening corresponding to the pad or lead position. The solder paste of 20-80μmφ in the solder paste is melted and fused while improving solder wettability by removing the oxide film on the pad or lead surface using the reducing power of the flux present in the solder paste. Thus, a solder film of 30 to 80 μm is formed. (Patent Documents 3, 4, and 5)
However, in this solder paste application / fusion method, the limit of the solder paste application accuracy by screen printing or the like (the limit for forming a solder coating) depends on the viscosity of the solder paste, the solder particle diameter, and the application conditions. It is said that the minimum width at which a solder film can be formed on a lead is at most 0.1 mm and the adjacent pitch is 0.15 mm. In particular, the pad or lead width is 0.02 to 0.08 mm, and the adjacent pitch is 0.04 to 0.12 mm. It is very difficult to stably form a uniform solder precoat film having a thickness of 3 to 15 μm without bridging or missing in such a fine and fine electronic circuit.

On the other hand, the (C) tin or solder plating method and the (D) Ni / Au plating method are technologies that are particularly advantageous for pre-coating fine and fine circuits. Recently, they have been used for pre-coating micro-fine pads for semiconductor wafers and interposers. Has been applied. (Patent Documents 2, 3, 6)
Among these, the method (C) is a method in which an electronic circuit board in which the surface other than the pad or the lead is protected with a solder resist and only the pad or the lead part is exposed is desired in a plating solution containing a metal ion of a solder component. In a method of forming a solder precoat film by plating to a thickness, for example, a fine fine electronic circuit having a pad or lead width of 0.02 to 0.08 mm and an adjacent pitch of 0.04 to 0.12 mm is formed with a thickness of 3 It is possible to form a uniform solder precoat film of 15 μm.
However, since aqueous solutions are mainly used, water molecules permeate into the electronic circuit board, requiring quality problems that reduce reliability, pre-treatment, water washing, post-treatment, etc. However, the process management is long and the cost is high.

  Similarly, the purpose of Ni / Au plating in the (D) method is mainly to prevent internal diffusion of elements in the tin or solder components inside the electrode, as in the case of an aluminum evaporated electrode pad on silicon such as a wafer. In order to improve the anti-oxidation and solderability of the plated nickel surface after applying a base nickel plating or the like as a diffusion prevention film, a thin gold plating is coated on the surface. Similar to the method C), for example, a uniform solder precoat film with a thickness of 3 to 15 μm is applied to a minute fine electronic circuit having a pad or lead width of 0.02 to 0.08 mm and an adjacent pitch of 0.04 to 0.12 mm. It is possible to form. However, in the case of the (D) method, the procedure of the (B) method is further added on the gold plating to form a solder precoat film. As described in the description, the minimum pad or lead width is generally 0.1 mm and the adjacent pitch is 0.15 mm. For example, the pad or lead width is 0.02 to 0.08 mm, and the adjacent pitch is 0.04 to 0.12 mm. It is almost impossible to stably form a uniform solder precoat film having a thickness of 3 to 15 μm on such a minute and fine electronic circuit without bridging or missing.

  Furthermore, a solder precoat film formed by a hot air leveling method or a hot liquid leveling method is a tin-copper solder alloy, a tin-silver solder alloy, or a tin-silver-copper solder that has been widely used as a lead-free solder alloy in recent years. In alloys and the like, needle-like or granular tin-copper or tin-silver intermetallic crystals (IMC) of about 1 to 10 μm or more are segregated and scattered in the solder layer near the solder joint interface during solidification. The surface of the solder precoat film after leveling with a precoat thickness of 10 μm or less becomes uneven, the solder thickness varies greatly, and the surface appearance has a dull pattern.

On the other hand, in the solder joining techniques such as the methods (A) and (B) described above, it is generally essential to use a flux or a solder paste at the time of coating or joining, and therefore, it is included in the flux or the solder paste. Since the solvent and the resin component instantaneously boil, vaporize, and scatter during solder joining, there is a problem that air is engulfed in the solder joint interface or the joined solder layer, and so-called micro voids (micro bubbles or voids) are easily generated. (Non-Patent Document 1)
However, there are methods that can eliminate this micro void by various technical improvements and ideas, but even if there is no micro void at the time of custom soldering, the electronic component is soldered to the electronic circuit board by the current soldering technology. When an electronic device is exposed to a high temperature of 120 ° C. or more for a long time due to energization heat generation or the like, micro voids (minute voids) are formed with time in the IMC (intermetallic compound) layer at the interface of the solder joint. This is usually called Kirkendall void, and when this occurs many over time, it is known that there is a high risk of joint breakage when an impact force is applied by dropping an electronic device, In recent years, it has become a big problem from the viewpoint of the reliability of electronic equipment. (Non-patent documents 1, 2, 3, 4)
In addition, since flux is used in the conventional method, the flux component remains inside the joint interface or inside the solder precoat film, or the flux component scattered around it may cause corrosion over time, and the mounted electronic equipment Failures may be caused, and it is not always sufficient in terms of long-term quality reliability.

On the other hand, it is also known that solder joints undergo fatigue failure due to thermal stress due to the temperature difference generated between the semiconductor element and the printed circuit board during a thermal cycle in which the electronic device repeats high and low temperatures. In order to improve the impact deterioration, a solder alloy in which a tin-silver-copper solder alloy is melted and kneaded in a non-oxidizing atmosphere such as argon gas so that the solid solution oxygen concentration in the solder alloy is 10 ppm or less is used. Thus, a method has been proposed in which the ductility and strength of the solder itself are improved by about 10%, and the thermal fatigue characteristics and impact resistance (under simple drop test conditions) of the solder joint are improved. (Patent Document 7)
However, in recent years, semiconductor devices and electronic devices that have been miniaturized and miniaturized have an impact test by acceleration gravity far more severe than the thermal fatigue characteristics and impact resistance (under a simple drop test condition) disclosed in Patent Document 7. With the solder alloy described in Patent Document 7 alone, it is generated over time near the bonding interface after high-temperature exposure (for example, an accelerated heating aging test that is left in a high-temperature atmosphere at 120 ° C. or higher for 240 hours or longer). Kirkendall void cannot be suppressed. Therefore, the inventors have found through many years of research and development that the impact resistance due to acceleration gravity cannot be satisfied with Patent Document 7 alone.

On the other hand, as one of the techniques for joining a solder alloy to a pad or lead of an electronic circuit board that is covered with a protective film such as a solder resist other than the pad or lead part, a high-temperature organic fatty acid is formed on the upper layer of the molten solder liquid. A technique for soldering using a storage tank having an upper and lower two-layer structure in which a solution is disposed has already been disclosed. (Patent Documents 8 and 9)
This technology has been developed by the inventors through years of research. First, the work such as the electronic circuit board is immersed in an organic fatty acid solution in the upper layer, and the metal oxide on the pad or lead surface is removed by washing. Then, after forming a protective film of organic fatty acid on the cleaned metal surface, immerse it in the molten solder solution below to perform good solder bonding without microvoids on the pad or lead, A protective film of organic fatty acid is coated on the surface of the solder bonded when passing through the upper organic fatty acid solution and pulling it up.
In this soldering method, no flux is used. Therefore, the solder joint interface caused by the boiling and scattering of flux, which is the difficulty of the current (A) molten solder bath immersion method and the (B) solder paste coating / fusion method, No so-called micro voids (micro bubbles or voids) are generated in the solder layer. In addition, when solder alloys with an oxygen concentration of 10 ppm or less are used, the occurrence of Kirkendall voids after long-term, high-temperature exposure is extremely low, connection reliability is high, and solder joints with excellent impact rupture resistance are obtained. It is known that (Patent Document 9)
In addition, as a method of refining the oxygen concentration in the solder alloy to 10 ppm or less, there is a method of dissolving solder in an argon atmosphere (Patent Document 7). It was proposed to manufacture molten solder by vigorously stirring in organic fatty acid solution. (Patent Document 10)

However, with the exception of the above (C) and (D), where the manufacturing efficiency is poor and the reliability is low, even if the current solder joint technology is combined, the minimum width of an electronic circuit capable of forming a solder precoat film is currently Alternatively, the lead width is at most 0.1 mm, and the adjacent circuit pitch is limited to 0.15 mm, and the width less than that and the minute pitch solder joint electronic circuit formation of the adjacent bit can be formed by the electroplating method of (C) and (D). Other than that, it has not been fully put into practical use yet.
For this reason, in order to further reduce the size and weight of electronic circuit boards, electronic components, semiconductor devices, and electronic devices for airplanes and vehicles that require particularly high reliability, for example, the pad width is 0.08 μm or less and adjacent Although a micro-fine circuit with a pitch of 120 μm or less is desired, the current method of forming a solder film has a high probability of causing bridging even if the solder is locally attached, and most of them frequently cause solder non-bonding (missing). Therefore, it is a bottleneck for further miniaturization, miniaturization, and weight reduction.

  JP-A-8-37361   JP-A-6-252542   JP-A-11-307565   JP 10-322007 A   JP-A-9-307223   JP 2002-9425   JP 2002-239780 A   Japanese Patent No. 4203281   JP 2008-084673 A   JP 2009-197135 A

  R. Aspantiar “Void in Solder Joints” SMTA Northwest Chapter. Meeting (September 21, 2005)   C. Hillman "Long-term reliability of Pb-free electronics" Electronic Products p. 69 (September 2005)   M. Mitsuyuki, Yu Shimauchi "Electronic component reliability evaluation and failure analysis technology" JFE Technical Report Vol. 13, p. 97-102, August 2006   Shinji Ishikawa et al .: “Generation of Kirkendall Void at the Joint of High Temperature Solder and Cu Plate”, Journal of Japan Institute of Electronics Packaging, Vol. 9, No. 4, p. 269-277, 2006

  The present invention is a disadvantage of the conventional method in the method of forming a solder precoat film on a pad or lead of an electronic component, that is, a bonding interface and a microvoid in the solder layer resulting from the use of flux, deterioration of connection reliability and corrosion resistance over time, Variations in the thickness of the solder precoat film are large. In addition, microvoids and carkendal voids are generated over time after long-term high-temperature exposure, and the pad or lead width is 0.08 mm or less. Adjacent pitch is 0.12 mm or less. It is an object of the present invention to provide a technology for forming a uniform tin or solder precoat film with high quality reliability by solving problems such as difficulty in forming a solder precoat film on a narrow pitch high density electronic circuit.

The present invention immerses an electronic circuit board or electronic component assembly (hereinafter referred to as a workpiece) in which a surface other than the pad or lead is protected with a solder resist film and only the pad or lead is exposed in a high-temperature organic fatty acid solution. Or by spraying the organic fatty acid solution at a high temperature on the workpiece to remove and clean the pad or the lead surface oxide layer by the chemical action of the organic fatty acid, and to clean the pad or lead In the upper layer of the processing apparatus provided with a storage tank containing a high-temperature organic fatty acid solution in the upper layer and a molten tin solution or a molten solder solution in the lower layer after forming a protective coating on the metal surface by the chemical adsorption of organic fatty acids. In a state where the workpiece is in contact with an organic fatty acid solution heated in a horizontal or inclined manner, tin or solder particles are introduced from above into the organic After spraying in a fatty acid solution and adhering at least one or more of the tin or solder particles in a molten state to the electrode pad or the lead surface to form a nucleus, the work is used to form the molten tin solution or the lower layer. A first step of immersing in a molten solder solution to form tin or a solder film on the electrode pad or the lead surface; and the work on which the tin solution or solder film is formed by the first step is formed in the upper layer. In a second step of blowing off and removing the excessively adhered tin or solder by spraying a high-temperature organic fatty acid solution on the surface while passing it through, the pad or the lead has a thickness of 2 to 20 μm, In addition, a uniform tin or solder precoat film having a thickness variation of ± 5 μm or less is formed.
In the first step, the workpiece may be dipped in the order of the upper layer → the lower layer → the upper layer in a storage tank in which a high-temperature organic fatty acid solution is disposed in the upper layer and a molten tin solution or a molten solder solution is disposed in the lower layer. Alternatively, a hot organic fatty acid solution and a molten tin solution or a molten solder solution may be sprayed with a dedicated pump to form tin or a solder joint film on the pad or the lead surface.

More specifically, the organic fatty acids used in the first step and the second step are caproic acid, caprylic acid, 2-ethylhexic acid, nonanoic acid, capric acid, undecanoic acid, myristic acid, palmitic acid, margaric acid, Stearic acid, oleic acid, linoleic acid, linolenic acid, arachidic acid, arachidonic acid, behenic acid, lignoceric acid, serotic acid, montanic acid, melissic acid, and the like are preferable.
Among these, organic fatty acids which are desirably dissolved in a solvent used at 180 to 300 ° C. and stable without decomposition are preferred. In the case of an organic fatty acid having a low boiling point, it can be used at a high pressure, but it is not preferable in terms of safety and practicality.
Industrially more suitable for practical use in view of economy and handling, for example, organic fatty acids having 13 to 20 carbon atoms, that is, myristic acid, palmitic acid, margaric acid, stearic acid, oleic acid, linoleic acid, linolenic acid, arachidin Acid, arachidonic acid and the like, which are particularly useful because they have a great effect in accordance with the object of the present invention.
Although organic fatty acids can be used even with carbon atoms of 12 or less, they are water-absorbing and are not very desirable due to their use at high temperatures. Furthermore, even if they are coated as a protective film on the solder surface after bonding, they are water-absorbing and thus are stored for a long time. The quality of time may be hindered, which is not always desirable.
Further, although organic fatty acids having 21 or more carbon atoms can be used, they have a high melting point and poor permeability and are difficult to handle, so that the rust preventive effect on the solder surface after treatment is slightly insufficient. Particularly desirable are industrially produced in large quantities in large quantities, used in many fields, and easily available, such as 16 carbon atoms of palmitic acid and 18 carbon atoms of stearic acid, and any one or more of them are used. The effect of the present invention is also great when a solution having a liquid temperature of 180 to 300 ° C., comprising 1 to 80% by weight and the balance comprising an oil-based solvent that is stable in a high temperature region.
The purpose of using an organic fatty acid solution having a carboxyl group (—COOH) in the present invention is to remove the oxide film from the metal surface of the pad by a saponification reaction, and to activate the cleaning simultaneously. Fatty acid is chemisorbed and plays the role of an anti-oxidation protective film, and also prevents the oxidation of molten tin or molten solder solution, and coats the surface of the formed solder precoat film as an anti-oxidation chemical adsorption protective film. There is. In addition, there is an effect of washing away unnecessary dust, tin or solder fine particles incidentally attached to the surface of the workpiece. In particular, in the case of micro-fine circuits, when the work is immersed in molten tin or molten solder solution, the tin or solder is thickly attached excessively to form a bridge, but when this is immersed in a high-temperature organic fatty acid solution as it is, The surplus tin or solder is repelled to some extent by the activation force, and the bridge can also be eliminated to some extent.

The concentration of the organic fatty acid in the solution is effective even if it is 1% by mass or less, but replenishment management and the like are complicated when processing a large amount continuously. Although the effect of the invention is present and can be used, it is preferably 5 to 80% by mass because the problem of smoke generation and odor is also severe.
The liquid temperature of the organic fatty acid solution is preferably equal to or higher than the temperature of the molten tin or molten solder liquid used. The upper limit temperature is about 320 ° C in consideration of ignitability, smoke generation, and safety. However, from the viewpoint of odor and energy saving, use within the range of + 20 ° C from the temperature of the molten solder solution used. It is desirable. For example, in the case of a tin-silver-copper (Ag 3.0 mass%, Cu 0.5 mass%, remaining Sn) ternary solder alloy having a melting point near 217 ° C., the temperature of the molten solder liquid used is 240 to 260. The liquid temperature of the organic fatty acid solution is optimally 240 to 280 ° C. The soldering efficiency in this case is not significantly different from the case where the liquid temperature of the organic fatty acid solution is increased to 280 ° C to 320 ° C. Similarly, in the case of a low melting point solder having a melting point of 139 to 160 ° C. such as tin / bismuth solder, the temperature of the molten solder used is generally in the range of melting point +20 to 40 ° C., and the temperature of the organic fatty acid solution is molten solder. It is better to use it at the same temperature as the liquid temperature or within the range of + 20 ° C.
In this respect as well, the method of the present invention increases the solder bath temperature, the flow furnace, or the substantial peak temperature of the reflow furnace to 280 to 280 in order to increase the solder precoat film formation efficiency as in the current methods (A) to (D). Compared to the case where the temperature is raised to 350 ° C., the amount of energy used can be reduced by about 5 to 20%.

  The organic fatty acid solvent used in the present invention may be any of mineral oil, vegetable oil, and synthetic oil as long as it dissolves the organic fatty acid and is stable in the high temperature range. Ester synthetic oil is most suitable in terms of economy and handling. The purpose and reason for using a solvent that is stable at high temperature is that the organic compound emits high-temperature smoke and suppresses odor, and that the organic fatty acid solution that has adhered excessively after soldering treatment has good cleanability. This is because the effect of lowering the liquid viscosity and improving the permeability is large. The concentration is determined by the concentration of the organic compound.

Further, in the first step of the present invention, a method of contacting the workpiece 1 whose surface other than the pad or the lead is protected with a solder resist film and only the pad or the lead portion is exposed to a high-temperature organic fatty acid solution is illustrated in FIG. 3 may be simply immersed in a stainless steel tank 10 containing an organic fatty acid solution 4 maintained at a constant high temperature, or it may be in the lower layer as shown in FIGS. A molten tin solution or a molten solder solution 5 may be disposed and immersed in the processing tank 11 or the processing tank 12 in which the high-temperature organic fatty acid liquid 4 is contained in the upper layer. In the latter case, it is advantageous that the workpiece 1 is immersed in the upper layer organic fatty acid solution 4 and then immersed in the lower layer molten solder solution 5 to easily coat the pad or lead with tin or solder. In the former case, it is immersed in a separately prepared molten solder bath.
Alternatively, as shown in FIG. 13, the organic fatty acid solution is sprayed from the nozzle 3 to the pad or the lead surface of the work 1 by the transfer pump 6, and the molten tin solution or solder solution is also sprayed from the nozzle 38 by the transfer pump 18. Even if it processes, the effect similar to the said immersion process is acquired.
The treatment time varies depending on the relative flow velocity between the organic fatty acid solution and the molten tin solution or molten solder solution and the workpiece in any treatment, but 0.5 to 10 seconds is sufficient, and the treatment time is longer than that. However, the cleaning activation effect, the protective film forming effect, and the solder film effect are not changed.

Needless to say, the immersion treatment may be performed only on the high-temperature organic fatty acid solution or the spray treatment of the high-temperature organic fatty acid solution, and then the immersion treatment may be performed on the molten tin solution or the molten solder solution in another tank.
That is, after the workpiece is immersed or sprayed in an organic fatty acid solution, a protective coating of organic fatty acid is formed on the metal surface of the workpiece pad or lead to prevent oxidation and improve the wettability of molten tin or molten solder solution. Therefore, there is no problem even if tin or solder is adhered to the pad or the lead portion by leaving it in the air and bringing it into contact with the molten tin solution or the molten solder solution again.
However, the immersion treatment is preferably performed in the upper layer of the treatment tank 11 or 12 in which the organic fatty acid solution 4 is disposed in the upper layer and the molten tin solution or the molten solder solution 5 is disposed in the lower layer as shown in FIGS. Further, it is possible to reduce the energy loss and to improve efficiency by immersing in the lower layer of molten tin solution or molten solder solution 5 to form a tin or solder joint film on the pad or lead.

On the other hand, the method of spraying tin or solder particles in the first step of the present invention is composed of, for example, a minute fine narrow pitch high density electronic circuit having a pad or lead width of 0.08 mm or less and an adjacent circuit pitch of 0.12 mm or less. In the case of workpieces, a sieve made of fine mesh wire mesh from above, a funnel with a narrower tip and narrower as the upper part is wider and lower, or a commercially available powder spreader or spray spray nozzle at the tip A solid tin or solder particle placed in a container (FIG. 15) or the like is dispersed in the organic fatty acid solution heated to a high temperature so as to be uniformly dispersed and settled, and dropped in the high-temperature organic fatty acid solution. The particles melted while landing on the pad or lead surface form a tin or solder film (FIG. 10).
When using a spray nozzle, it is effective to spray the molten solder particles from the nozzle into a high-temperature organic acid solution and disperse and distribute it evenly. Particularly, to spray fine molten solder particles of 1 to 30 μmφ. Use ultrasound. In addition, tin or solder particles are dispersed in the upper layer horizontally or at an angle of at least one tin or solder particle from the top of the workpiece in contact with the high-temperature organic fatty acid solution on the surface of all the pads or leads. It is necessary to spray evenly so as to deposit. In order to spread widely and uniformly, it is effective to change the angle of the injection nozzle periodically and continuously, or it is preferable to scan the injector itself.
Therefore, the tin or solder particles to be dispersed may be solid particles or molten solder particles.

However, although it is usually possible to produce tin or solder particles having a diameter of 30 μmφ or less, the production efficiency is not necessarily high, so that there is a problem that the price is high.
For this reason, the inventors have studied various methods through trial and error, and as a result, as shown in FIG. 9, the ultrasonic vibration is directly applied to the nozzle 26 for injecting molten tin or molten solder through the holding booster 22 and the ultrasonic horn 23. A child 20 is attached, and ultrasonic vibration is directly applied to the molten tin or molten solder 25 in the molten tin or molten solder injection line 24, and the molten tin or molten metal is injected from the nozzle 26 into the hot organic fatty acid solution 4 in the upper layer. It has been found that when solder 25 is sprayed, molten solder particles 17 of about 1 to 20 μmφ can be stably dispersed by ultrasonic oscillation of a specific frequency.
If the method of the present invention is performed by utilizing this, even a minute pad or lead having a pitch between adjacent pads or leads of 40 μm and a pad or lead width of 20 μm can actually form a good tin or solder precoat film. Verified.
In this case, the particle size of the molten solder particles depends on the ultrasonic frequency. The higher the frequency, the smaller the particle size of the fine particles obtained. For example, at a frequency of 35 kHz, 90 mass% or more is 3%. Fine particles of -10 μmφ are obtained. In the case of a frequency of 22 kHz, the particle size distribution becomes wide and particles of 3 to 25 μmφ account for 90% by mass or more.

  As a specific structural example of the molten solder particle generating device 16 with an ultrasonic vibrator, as shown in FIG. 9, an ultrasonic vibrator 20 to which an ultrasonic output cable 19 is connected is connected via a cooling fin booster 21. An apparatus having a structure in which an ultrasonic horn 23 in which a molten solder injection conduit 25 and a nozzle 26 are connected to each other is attached to the tip of the holding booster 22 connected thereto.

  As shown in FIG. 8 and FIG. 10, tin or solder fine particles 17 are uniformly distributed from above to the surface of the work 1 installed below, so that the molten organic fatty acid liquid 4 is in a molten state. The tin or solder particles 17 are dropped and deposited on the exposed pad or lead surface 28 without the solder resist film, and are used as “cores” to successively reach the pad or lead surface. Solder particles are agglomerated and adhered to the surface to form tin or solder coating 29 on all pads or leads to a certain film thickness.

On the other hand, as for the size of tin or solder particles to be dispersed, in principle, solder particles having a particle diameter equal to or smaller than the pad or lead diameter or minimum width of the work may be dispersed. It should be at least 1/2 or less of the width. If the particle size is too small, the sedimentation rate will be slow, so the time to reach the pad or lead surface will be long and the efficiency will be poor. Conversely, if the particle size is too large, the inner bottom of the pad or lead surrounded by the solder resist protective film In this case, the pad or lead diameter or the minimum width is preferably at most 1/3 or less.
In particular, in the case of a narrow circuit having a minimum work pad or lead width of 0.08 mm or less, the electrode pad or lead surface can be reached from the opening of the solder resist protective film unless the tin or solder particles are several tens of μmφ or less. I can't. Moreover, since at least one or more tin or solder particles must be deposited in the opening, it is desirable that particles having a size of 1 to 30 μmφ enter the opening (the bottom is the pad surface). A lot of tin or solder particles need to be spread evenly. Further, the particles should have a spherical shape and a smooth surface.

The spraying may be continued until the opening is almost filled with solder, or when at least one “nucleus” adheres to all the pads or leads, the spraying is stopped and the underlying molten tin or After immersing the workpiece in the molten solder solution to form a sufficient solder film on all the pads or leads, the second step of the present invention performs the high temperature organic fatty acid solution spraying process to remove excess tin or solder. Thus, a tin or solder precoat film having a desired thickness is obtained.
If the spraying is continued until all the openings are filled with tin or solder, naturally, a local bridge will be formed, and after all the pads or leads have reached a certain thickness, they will melt. When immersed in a tin solution bath or a molten solder solution bath as it is, a bridge is usually generated locally. However, by performing the high-temperature organic fatty acid solution spraying leveler process of the second step of the present invention, excess tin or solder Are removed by blowing off, the bridge is completely eliminated, and a uniform tin or solder precoat film having a thickness variation within ± 3 μm within a range of 5 to 20 μm is obtained.

  FIG. 8 shows an example in which molten tin or molten solder particles 17 are sprayed onto the lower workpiece 1 by the molten solder particle generator 16 with an ultrasonic vibrator from directly above. The direction of the tin or molten solder particle generator 16 is to inject the molten tin or molten solder particles 17 from obliquely upward to the lower side of the work 1 while automatically changing the angle two-dimensionally continuously. Is effective. In any case, since the molten tin or molten solder particles 17 must be dispersed as uniformly as possible on the surface of the work 1 as much as possible, an ultrasonic vibrator is provided on the arm of a dedicated automatic control type three-dimensional movement device. It is preferable that the molten solder particle generator 16 is attached so that the molten solder particles spread evenly over the workpiece 1.

The work 1 is fixed to a frame-shaped dedicated holder 14 and attached to the robot arm 13 of the automatic control type three-dimensional movement apparatus, and is left in the high-temperature organic fatty acid solution 4. The stationary position may be horizontal, and in order to facilitate entry of the fine particles 17 into the pad or lead surface of the opening, it is preferable to vibrate the workpiece. Also, the probability that the work is allowed to stand at an angle of about 0 to 30 degrees with respect to the horizontal, and the fine particles that have landed on the surface other than the opening (the surface of the solder resist film) fall into the opening while being rolled down due to the inclination ( Increasing the transfer rate is also effective.
The distance between the workpiece 1 and the molten tin or molten solder particle generator 16 with an ultrasonic vibrator depends on the position and shape of the nozzle to be sprayed or the amount of molten tin or molten solder ejected (the amount of molten solder supplied). When spraying molten solder from directly above to below, when the spread angle of the molten solder particles to be sprayed is 45 to 90 degrees, about 10 to 30 mm is the time required for the fine particles to reach the pad or lead surface. Has been found to be desirable because it is short.

  When the shape of the electronic circuit board or the electronic component coupling body is a flat plate or a strip, the pilot hole of the work 1 is attached to the tip of the robot arm 13 of the automatic control type three-dimensional movement device as shown in FIGS. 8 is fixed and attached using a pilot pin 15 of a metal frame-shaped dedicated holder (work fixing jig) 14, and the robot arm 13 is operated by an automatic control type three-dimensional movement device, as shown in FIG. The workpiece 1 is immersed in the high-temperature organic fatty acid solution 4 stored in the storage tank 12 and allowed to stand. At this time, the exposed pad or lead surface of the workpiece reacts by the chemical action of organic fatty acid to remove and clean the oxidized layer on the surface, and a protective coating of organic fatty acid is formed on the cleaned metal surface Therefore, a molten tin or molten solder film is formed on the surface of the pad or lead by performing the above-described fine particle spraying / adhesion treatment. Thereafter, the robot arm 13 is again operated by the automatic control type three-dimensional movement device to carry it three-dimensionally, and the process of the second step of the method of the present invention is performed.

  On the other hand, if the electronic circuit board or the electronic component connector is a long strip, the method of the present invention can be performed while being conveyed by continuous feeding or intermittent feeding.

As the kind of tin or solder used in the present invention, ordinary solder widely used in electronic parts, that is, pure tin, tin-lead alloy, tin-silver-copper alloy, tin-zinc alloy, tin-bismuth alloy, Furthermore, there is no problem even with a solder in which nickel, germanium, indium, antimony, phosphorus or the like is added to these mother alloys.
However, in order to suppress Kirkendall voids (microvoids) that are likely to occur when exposed to high temperatures for a long period of time, the inventors have conducted various trials and errors so far. As a result, for example, solder having an oxygen concentration of 10 ppm or less was used. It has been verified that when an organic fatty acid solution is immersed in the molten solder solution disposed in the upper layer and soldered, it is very effective. (Patent Document 7)
In recent years, elemental analysis of 10 ppm or less has become possible due to the advancement of analytical instruments. As a result of quantitative analysis of oxygen concentration of 10 ppm or less and investigation of the relationship between oxygen concentration and generation of Kirkendall void after long-term high temperature exposure, oxygen concentration It was found out that the generation of Kirkendall void could be eliminated when the content was 2 ppm or less, and that it was more effective. Therefore, in the present invention, when this is applied and soldered, an electronic component, a semiconductor device, and an electronic device with high quality and reliability that are excellent in impact fracture resistance after long-term heating at a high temperature of 120 ° C. or higher can be obtained.

Explaining the reason why one or more tin or solder particles are dispersed in the first step to deposit one or more pads or leads to form “nuclei”.
In general, in a minute electronic circuit board or electronic component assembly having a pad or lead width of 0.02 to 0.08 mm and an adjacent pitch of 0.12 mm or less, there is a difference in height (step) between the solder resist film and the pad or lead. 10 to 50 μm, and in the conventional method (A) (molten solder bath dipping method), there is a problem of a wetting angle due to the surface tension of the molten tin solution or molten solder solution, or a pad or lead having a depression. Due to the problem of air bubbles staying at the top, molten tin or molten solder is extremely difficult to adhere to the pad or lead. Also, solder paste can be applied by screen printing in the conventional method (B) (solder paste application / fusion method). It is quite difficult to completely (100%) fill all the fine pads or leads.
This also means that in the present invention, the hot organic fatty acid solution in the first step is brought into contact with the workpiece to remove and clean the oxide layer on the pad or lead surface of the workpiece and to form a protective film, and then directly into the molten tin solution or Just by immersing in the molten solder solution, as in the case of the methods (A) and (B), the problem of the wetting angle due to the surface tension of the molten tin solution or the molten solder solution, or the pad that is indented Alternatively, due to the problem of air bubbles remaining on the top of the lead, it is difficult to deposit 100% of tin or solder on all the pads or leads.
For this reason, in the minute and fine electronic circuit, a “nucleus” that draws in a molten tin solution or a molten solder solution is necessary, and the formation of a deposited “nucleus” of tin or solder particles is important.

  However, if the circuit has a pad or lead width of 80 μm or more, it is not always necessary to disperse tin or solder particles in the first step, and it is omitted and immersed directly in the next molten tin or molten solder liquid layer. By simply doing, tin or solder film can be formed on the pad or lead of the workpiece.

The material of the tin or solder particles to be dispersed may be any tin or solder alloy that is normally used.
However, when importance is attached to the thermal shock resistance of the tin or solder joint, for example, the Kirkendall void that occurs over time at the joint interface when a semiconductor device or an electronic device is exposed to a high temperature of 120 ° C. or higher for a long period of time. In order to suppress (microvoids), it is desirable to use tin or a solder alloy having an oxygen concentration of 5 ppm or less.
This can also be said for the molten tin solution or the molten solder solution in the lower layer, which is subsequently subjected to an immersion treatment. Solder bonding is performed with an electronic component in which a precoat film is formed using tin or a solder alloy having an oxygen concentration of 5 ppm or less. However, even if the semiconductor device or electronic device in which the electronic device is embedded generates heat when energized and is exposed to a temperature of 120 ° C. or higher for a long period of time, almost no increase in the occurrence of Kirkendall voids (microvoids) with time It is not seen, and it has excellent impact rupture resistance and high quality reliability.

Next, the second step will be described in detail. For example, as shown in FIG. 2, a high-temperature organic fatty acid solution is sprayed from the nozzle 3 onto the work 1, and the tin or excessively attached to the pad or the lead Solder is blown off to form tin or a solder precoat film having a desired uniform film thickness on the pad or the lead.
Alternatively, as shown in FIG. 5, a high-temperature organic fatty acid solution 4 is supplied to a nozzle 7 through a transfer (feeding) pump 6 from a pipe provided on the upper side wall of the tank 12, and the workpiece 1 is supplied from the nozzle 7. The organic fatty acid solution 4 is sprayed onto the pad or lead, and the tin or solder excessively attached to the pad or the lead is blown off. A solder precoat film is formed. In FIG. 5, the spraying of the organic fatty acid solution 4 is shown as an example in the air in the upper part of the liquid, but the same thing can be said even if the nozzle 7 is installed in the upper organic fatty acid solution and spraying is performed. An effect is obtained.

The flow rate and spraying time sprayed from the nozzle 7 vary depending on the nozzle shape and spray angle depending on the desired tin or solder precoat film thickness. For example, the desired precoat film thickness is 5 ± 2 μm. In the case where the tip shape of the nozzle is a slit-shaped opening width of 0.5 to 3 mm, and the opening length is 50 to 500 mm, and the spray angle is 45 to 90 degrees with respect to the electronic circuit board or electronic component assembly 1 that is a workpiece, A flow rate of 0.5 to 4 m / second and a spraying treatment time of 0.5 to 10 seconds are sufficient.
The faster the flow rate of the high temperature organic fatty acid solution 4 to be sprayed, the thinner the precoat film obtained. In addition, the nozzle shape may be a commercially available nozzle for watering. In that case, a plurality of nozzles may be arranged so that the organic fatty acid solution to be sprayed uniformly against the width of the workpiece. Two or more nozzles may be scanned two-dimensionally or three-dimensionally.

Alternatively, as shown in FIG. 6, a reverse roll 8 (work 1 described above) installed in a liquid in an upper layer of a treatment tank 12 in which a high-temperature organic fatty acid solution 4 is disposed in an upper layer and a molten tin solution or a molten solder solution 5 is disposed in a lower layer. When the organic fatty acid solution 4 is sprayed onto the pad or the lead portion of the workpiece 1 by rotating in the direction opposite to the pulling direction of the nozzle, the same effect as in the case of nozzle spraying can be obtained.
In this case, the spraying flow rate needs to be adjusted as appropriate depending on the film thickness of the desired tin or solder precoat, and for example, when the desired precoat film thickness is 5 to 20 μm, The reverse roll diameter is preferably in the range of 60 to 200 mmφ and the rotation speed is in the range of 600 to 3000 rpm. The larger the roll diameter and the higher the rotation speed, the thinner the precoat film obtained.
In order to prevent the excess tin or solder scraped off by the rotation of the reverse roll 8 from being scattered in the organic fatty acid solution and reattaching to the pad portion. A baffle 9 may be installed on the reverse roll 8. Further, the gap between the workpiece 1 and the reverse roll 8 may be about 0, 1 to 5 mm.

However, in the above description, the high-temperature organic fatty acid solution heated in the upper layer has been described in a method using a treatment tank in which a molten tin solution or a molten solder solution is disposed in the lower layer, but of course, the organic fatty acid solution and the molten tin solution or There is no particular problem even if the molten solder liquid is made into separate processing tanks and the process is clearly divided and the separate tanks are processed. However, it is more concise, clear and efficient if the upper and lower two-layer liquid is processed in one processing tank. In particular, in the case of an electronic circuit board or electronic component assembly having a pad or lead width of 0.15 mm or more and an adjacent pitch of 0.02 mm or more, the upper and lower two-layer liquid arrangement may be efficient. The reason is that if the tin or solder film coated on the pad or the lead has a thickness of 50 μm or more, even in a circuit pattern that is easily bridged by the conventional (A) molten solder bath immersion method, The bridge is eliminated by the action of the organic fatty acid during the passage, and the organic fatty acid solution spraying leveler treatment in the second step of the present invention is not necessary. Of course, the conventional hot air leveler treatment or the hot liquid leveler treatment is necessary. Nor.
However, in the case of a precoat film that requires a tin or solder film thickness of 5 to 20 μm to be coated on the pad or lead, the conventional hot air leveler treatment or hot liquid leveler treatment is performed, or the second step of the present invention is performed. In particular, the thickness variation of the precoat film obtained by the conventional hot and leveler processing or the hot liquid leveler processing is very large, whereas the thickness variation of the method of the present invention is not large. It was verified that a much smaller and uniform precoat film was obtained, and the effect of leveling treatment with an organic fatty acid solution was extremely large.

  In addition, a solder precoat film formed by a hot air leveling method and a hot liquid leveling method is a tin-copper solder alloy, a tin-silver solder alloy, a tin-silver-copper system that has been widely used as a lead-free solder alloy in recent years. In solder alloys and the like, needle-like or granular tin-copper or tin-silver intermetallic crystals (IMC) of about 1 to several tens of μm are segregated and scattered in the solder layer near the solder joint interface during solidification. The surface of the solder precoat film after leveling with a solder precoat thickness of 10 μm or less becomes uneven, and there is a drawback that the variation in the solder thickness is large.

In order to avoid that, and to achieve a nearly completely smooth glossy surface even when the solder precoat thickness is 10 μm or less, the inventors have conducted various trial and error studies. I found a good thing. For example, pure tin contains a trace amount of nickel of 0.005 to 0.1 mass%, and a trace amount of germanium of 0.001 to 0.05 mass% or phosphorus of 0.003 to 0.01 mass% When a solder precoat film is formed by the method of the present invention using a solder alloy containing tin and the balance tin, it has been found that a precoat film with good smoothness can be obtained.
Besides, eutectic solder such as tin-lead alloy (tin 63 mass%, lead 37 mass%), tin bismuth alloy (tin 42 mass%, bismuth 58 mass%), tin antimony alloy, etc. 0.005 to 0.1% by mass and a solder added with any one or more of 0.001 to 0.05% by mass of germanium or 0.003 to 0.01% by mass of phosphorus, Even when the thickness of the precoat film is 20 μm or less, the glossy surface is almost completely smooth.
In addition, electronic components composing a pre-coating film by adding nickel and one or more of germanium and phosphorus within a proper amount range to a tin bismuth eutectic alloy which is a low temperature solder (for example, a semiconductor device) When the precoat film of each electronic component is soldered via ordinary lead-free solder (for example, tin-silver-copper solder, tin-copper solder, tin-silver solder, etc.) Since the tin bismuth solder precoat film melts at a low temperature of about 140 to 180 ° C., the bonding temperature with the normal lead-free solder is slightly lower and the bonding time is shorter than that of the conventional method. There is a merit of less thermal damage.

The reason for adding a small amount of nickel to tin is to suppress so-called "copper erosion" (a phenomenon in which copper on the pad or lead surface melts into the solder) when tin or solder is coated on the pad or lead surface of the electronic circuit. In addition, it suppresses the Kirkendall void (micro void) generated near the solder joint interface when it is exposed to a high temperature cumulatively over 120 ° C over a long period of time, and the impact resistance and thermal fatigue of the embedded semiconductor device or electronic device. This is to improve the quality reliability of the product. As the addition amount is 0.001% by mass or less, the above effect is small, and when it is 1% by mass or more, the viscosity at the time of melting is high, and it is easy to generate a bridge.
A desirable addition amount of nickel is 0.005 to 0.1% by mass.
What brings about the said effect is cobalt, iron, etc. other than nickel.

Similarly, the reason for adding germanium or phosphorus is mainly to prevent the oxidation of the solder precoat film surface over time and the deterioration of solder wettability. In the case where this is not added, if the solder pre-coated product is left in the air, it will undergo oxidative discoloration over time and solder wettability will deteriorate.
If the added amount is small, the effect is small, and if it is too large, the physical mechanical properties become brittle and it is easy to break. Therefore, desirable addition amount is 0.001-0.05 mass% of germanium or 0.003-0.01 mass% of phosphorus.

As described above, according to the method of the present invention, a pad or lead width that is “bridged” and cannot be satisfactorily formed by the conventional method is 0.08 mm or less and the adjacent pitch is 0.12 mm or less. Tin or solder precoat film that can be controlled relatively freely in an arbitrary thickness range of 5 to 20 μm for pitch high-density electronic circuits and can even control thickness variations within ± 2 μm Can be produced industrially in stable mass production.
In addition, a high-density electronic device mounted and mounted by soldering using an electronic component and an electronic circuit board having a solder precoat film manufactured by the method of the present invention has a bonding interface caused by boiling and scattering of flux, which is a drawback of the conventional method. There is no generation of microbubbles or voids in the solder layer, and solder bonding is performed in an organic fatty acid solution, so there is no oxide entanglement at the bonding interface and inside the solder layer. There is an effect that the generation of voids (microvoids) can be almost eliminated. In particular, if a solder having an oxygen concentration of 2 ppm or less is used, generation of Kirkendall voids after long-term high temperature exposure can be eliminated. Therefore, the solder-bonded component according to the method of the present invention is remarkably excellent in impact fracture resistance after long-term high-temperature exposure.
Furthermore, it is possible to form a solder precoat film for a minute / narrow pitch electronic circuit having a pad or lead width of 0.02 to 0.08 mm and an adjacent pitch of 0.04 to 0.12 mm, which is impossible with the conventional method.
In this case, since the workpiece and molten tin or molten solder fine particles are bonded in an organic fatty acid solution, the tin or solder film surface is always kept in a good wettability state without involving air. Therefore, there is no entrainment of solder oxide, and the surface of the finished tin or solder film is automatically coated with an organic fatty acid protective film, and the organic fatty acid solution is sprayed in the subsequent second step treatment. Since the surface of the finished tin or solder precoat film is automatically coated with an organic fatty acid protective film for leveler processing, the solder wettability when assembling the electronic device in the subsequent process is better than that manufactured by the conventional method. Stable and excellent.

Moreover, in the method of the present invention, one of the merits of forming a tin or solder film in an organic fatty acid solution is that a bridge between adjacent circuits is less likely to occur. This is due to the fact that the organic fatty acid solution has the effect of suppressing and preventing molten solder movement between adjacent pads or leads. For this reason, in the conventional method, there is generally no “bad solder bridge between adjacent pads” or “missing failure” (defect in which solder is missing in a part of the pad) that occurs at a frequency of 0.1 to several percent. As a result, the huge amount of rework processing that has been required in the past is completely unnecessary.
In addition, as described above, the method of the present invention can efficiently form tin or solder precoat film at a lower temperature than the current method, so that the energy efficiency is good and an energy saving effect of about 5 to 20% can be expected from the current method. .
As described above, the effects of the present invention are extremely valuable industrially.
This will be described in more detail below with specific examples.

It is sectional drawing which showed typically the embodiment example of the hot air leveler system which is a solder precoat film formation method by the conventional method, ie, the arrangement configuration example which sprays hot air from an nozzle on an electronic circuit board. It is sectional drawing which showed typically the positional relationship of an electronic circuit board or an electronic component coupling body, and a nozzle as an embodiment example in the process of spraying the organic fatty acid solution of the method of this invention with a nozzle. It is sectional drawing which showed typically a mode that the electronic circuit board or the electronic component coupling body was immersed in the high-temperature organic fatty acid solution, and pulled up as an embodiment example in the first step of the present invention. As an example of the embodiment in the first step of the present invention, an electronic circuit board or an electronic component connector is first placed in an upper layer portion in a liquid storage tank in which a high-temperature organic fatty acid solution is arranged in the upper layer and a molten tin solution or a molten solder solution is arranged in the lower layer. FIG. 2 is a cross-sectional view schematically showing a state in which the electronic circuit board or the electronic component connected body is pulled up again through the upper layer after being immersed in a lower layer molten tin solution or a molten solder solution. . As an example of the embodiment in the first step of the present invention, an electronic circuit board or an electronic component connector is first placed in an upper layer portion in a liquid storage tank in which a high-temperature organic fatty acid solution is arranged in the upper layer and a molten tin solution or a molten solder solution is arranged in the lower layer. Then, after immersing in the lower layer molten tin solution or molten solder solution, the electronic circuit board or the electronic component connecting strip is again pulled up through the upper layer, and the high-temperature organic fatty acid solution in the sky is discharged from the nozzle. It is sectional drawing which showed typically a mode that this organic fatty acid solution was sprayed on the pad or lead part of an electronic circuit board or an electronic component coupling body. As an example of the embodiment in the first step of the present invention, an electronic circuit board or an electronic component connector is first placed in an upper layer portion in a liquid storage tank in which a high-temperature organic fatty acid solution is arranged in the upper layer and a molten tin solution or a molten solder solution is arranged in the lower layer. Then, after immersing in the lower layer molten tin solution or molten solder solution, the electronic circuit board or the electronic component connected body is again passed through the two reverse rolls provided in the upper layer 2 while reverse. It is sectional drawing which showed typically a mode that this organic fatty acid solution was sprayed to the pad or lead | read | reed part of this electronic circuit board or an electronic component coupling body by the high speed rotation of a roll. In the method and apparatus of the present invention, examples of a robot arm part of a programmable automatic three-dimensional movement device used for transporting an electronic circuit board or an electronic component assembly and a jig (frame-shaped dedicated holder) part to which a workpiece is attached are shown. It is sectional drawing shown typically. In the first step of the present invention, molten tin or molten solder fine particles are applied to an electronic circuit board or electronic component assembly installed in a high-temperature organic fatty acid solution from above by using molten tin or molten solder fine particle generator with an ultrasonic oscillator. It is sectional drawing which showed typically the example which is spraying. It is sectional drawing which showed typically the example of an internal structure of the molten tin with an ultrasonic oscillator or molten solder fine particle generator used as one Embodiment in the 1st step of this invention. As one embodiment of the first step of the present invention, molten tin or molten solder fine particles dispersed by an ultrasonic oscillator-equipped molten tin or molten solder fine particle generator are applied to the pad or lead surface of an electronic circuit board or electronic component assembly. FIG. 10a is an enlarged cross-sectional view schematically showing an example of the bonding process, and 10a schematically shows how the molten tin or molten solder fine particles reach the electrode pad or lead surface of the electronic circuit board or electronic component coupling body. FIG. 10b and 10c schematically show a state example in which molten tin or molten solder fine particles reaching the pad or lead surface adhere to the pad or lead surface, and the fine particles aggregate to form a tin or solder film. It is an expanded sectional view. As an illustration of the first case of the generation mechanism (hypothesis) of Kirkendall voids (microvoids) that occur over time during long-term heat exposure, the volume ratio before and after the change of tin and copper oxide to stannous oxide and copper is shown It is the figure shown typically. As an explanatory diagram of the second case of the generation mechanism (hypothesis) of Kirkendall void (micro void) that occurs with time during long-term heating exposure, before and after the change of stannous oxide and copper oxide to stannic oxide and copper It is the figure which showed the volume ratio typically. As one embodiment in the first step of the present invention, each liquid is supplied to a nozzle with a dedicated pump from a storage tank in which a high-temperature organic fatty acid solution is disposed in the upper layer and a molten tin liquid or a molten solder liquid is disposed in the lower layer, It is sectional drawing which showed typically a mode that each liquid was sprayed on an electronic circuit board or an electronic component coupling body from a nozzle, and a solder film was formed in a pad or a lead surface. As an implementation example of the method for producing a solder alloy having an oxygen concentration of 1 ppm or less used in the examples of the present invention, each liquid is supplied from a storage tank in which a high-temperature organic fatty acid solution is disposed in the upper layer and a molten solder liquid is disposed in the lower layer with a dedicated pump. Circulating and supplying liquid to the stirrer, vigorously stirring both liquids in the stirrer, removing the oxides and impurities present inside the molten solder liquid, and repeating the process of returning the mixed liquid to the original storage tank It is sectional drawing which showed typically a mode that it refine | purifies until oxygen concentration will be 1 ppm or less. In the embodiment of the present invention, fine particles of tin or solder are uniformly sprayed toward the workpiece from a sieve having a fine mesh wire mesh or a commercially available powder spraying device to an organic fatty acid solution heated to a high temperature below. It is sectional drawing which showed the state typically. In the cross-sectional form after heat aging (150 ° C., 240 hours) of the solder precoat film produced in the inventive examples and comparative examples, a) schematically shows the state of the precoat film of Comparative Example 2, b) A cross-sectional photograph of a portion of the precoat film of Comparative Example 2, similarly c) is a diagram schematically showing the state of the precoat film of Example 7, and d) is a cross section of a portion of the precoat film of Example 7. It shows a photo

A comparative example of the embodiment of the present invention and the conventional method will be described below.
First, the following two types of electronic circuit boards were used as common sample samples.
Sample P1: External dimensions 15 mm × 15 mm × 1.2 mm, number of electrode pads 192, pad diameter 0.4 mmφ, pad diameter 0.35 mmφ not covered with solder resist protective film, BGA with pad pitch 0.8 mm is 20 mm pitch Sample circuit P2: External dimensions 10 mm × 10 mm × 1.0 mm, number of electrode pads 304, pad diameter 0.1 mmφ, pad diameter not covered with solder resist protective film 0.08 mmφ , An electronic circuit board in which four rows of BGAs with a pitch of 0.15 mm between pads are arranged in two rows and four rows each at a pitch of 20 mm. Also, a method for producing a low oxygen solder alloy with a reduced oxygen concentration in the solder is as shown in FIG. Lead-free solder alloy consisting of 2.5 mass%, copper 0.5 mass%, nickel 0.01 mass%, germanium 0.005 mass% and the balance tin A molten solder solution 5 obtained by preliminarily melting and an organic fatty acid solution 4 having a liquid temperature of 260 ° C. composed of palmitic acid 30% by weight and the remaining ester synthesis are circulated and fed into a stirrer 41 and stirred vigorously to obtain a molten solder. The metal oxide and impurities present inside are incorporated into the palmitic acid solution using the saponification action of palmitic acid, the stirred mixed solution is returned to the storage tank 12, and the specific gravity of the molten solder solution and the palmitic acid solution is increased. While separating the two liquids using the difference, this was purified by repeated circulation until the oxygen concentration reached 1 ppm or less. Using this as a master alloy, a solder alloy of the same metal composition with a known oxygen concentration (120 ppm) prior to the refining treatment is added to the master alloy and melted so that the oxygen concentration becomes 2, 5, 10 ppm. Concentration solder alloys were prepared and subjected to evaluation tests of the following comparative examples and examples.

Comparative Example 1

  In a conventional method, that is, a solder bath having a bath temperature of 260 ° C. in which a lead-free solder alloy having a composition of 2.5% by mass of silver, 0.5% by mass of copper, and the balance of tin is melted as it is, The applied samples 1 and 2 were dipped for 2 seconds and soldered to the pad, and then treated with a normal hot air leveler at a temperature of 350 ° C. and a pressure (pressure gauge gauge) of 0.2 MPa.

Comparative Example 2

  Conventional method, that is, bath temperature 265 obtained by melting a lead-free solder alloy consisting of 2.5% by mass of commercially available silver, 0.5% by mass of copper, 0.01% by mass of nickel, 0.005% by mass of germanium, and the balance tin. After immersing samples 1 and 2 in which the rosin flux is applied to the pad portion in advance for 3 seconds in a solder bath at ℃ for 3 seconds and soldering the pad portion, the temperature is set to 350 ° C. and pressure (pressure) with a normal hot air leveler (Total gauge) Processed at 0.2 MPa.

Comparative Example 3

  A widely used method, that is, a commercially available cream solder (solder paste) obtained by kneading a lead-free solder alloy powder consisting of 2.5% by mass of silver, 0.5% by mass of copper and the balance of tin with a flux component. After applying the solder paste to the pad portion by the normal silk screen printing method on samples 1 and 2, the samples 1 and 2 are passed through a normal reflow furnace having a peak temperature of 350 ° C. and soldered to the pad. A film was formed.

Comparative Example 4

  Bath temperature 260 obtained by melting a lead-free solder alloy adjusted to a composition comprising 2.5% by mass of silver, 0.5% by mass of copper, 0.01% by mass of nickel, 0.005% by mass of germanium, 10 ppm of oxygen, and the balance tin. After immersing Samples 1 and 2 in which the rosin flux was previously applied to the pad part for 2 seconds in the molten solder bath at 0 ° C. for 2 seconds and soldering to the pad part, the temperature was measured with a normal hot air leveler. It processed at 350 degreeC and the pressure (pressure gauge gauge) 0.2MPa.

Comparative Example 5

  Bath temperature 260 obtained by melting a lead-free solder alloy adjusted to a composition comprising 2.5% by mass of silver, 0.5% by mass of copper, 0.01% by mass of nickel, 0.005% by mass of germanium, 2 ppm of oxygen, and the balance tin. After immersing Samples 1 and 2 in which the rosin flux was previously applied to the pad part for 2 seconds in the molten solder bath at 0 ° C. for 2 seconds and soldering to the pad part, the temperature was measured with a normal hot air leveler. It processed at 350 degreeC and the pressure (pressure gauge gauge) 0.2MPa.

Comparative Example 6

  Bath temperature 260 obtained by melting a lead-free solder alloy adjusted to a composition comprising 2.5% by mass of silver, 0.5% by mass of copper, 0.01% by mass of nickel, 0.005% by mass of germanium, 2 ppm of oxygen, and the balance tin. After immersing samples 1 and 2 in which the rosin flux was previously applied to the pad portion for 2 seconds in the molten solder bath at 0 ° C. and soldering the pad portion, glycerin at a liquid temperature of 230 ° C. was added. The hot liquid leveler process which sprays and blows off the excess solder was performed.

For sample 1, the upper layer as shown in FIG. 5 was immersed for 10 seconds in a solution having a liquid temperature of 260 ° C. consisting of 10% by mass of palmitic acid and the remaining ester synthetic oil, followed by 2.5% by mass of silver and 0% copper in the lower layer. .2% by weight in a molten lead-free solder solution composed of tin at a temperature of 260 ° C. for 2 seconds and then pulled up by passing through the upper layer, while the palmitic acid having the above composition at a liquid temperature of 260 ° C. The solution was sprayed at a flow rate of 2 m / sec, and excess solder was blown off and removed so that the finished thickness of the solder precoat film on the pad portion was 5 μm.
On the other hand, for sample 2, the upper layer as shown in FIG. 8 was placed horizontally in a solution having a liquid temperature of 260 ° C. composed of 10% by mass of palmitic acid and the remaining ester synthetic oil, and was placed directly 30 mm above the sample. High-temperature organic fatty acid from the nozzle (2.0 mmφ diameter) at the tip of the molten solder fine particle generator using ultrasonic vibration with an output of 0.5 KW and a frequency of 35 KHz from molten tin or molten solder fine particle generator equipped with an ultrasonic oscillator Molten solder fine particles having a particle diameter of 1 to 10 μm φ injected into the solution (composed of molten lead-free solder having a liquid temperature of 260 ° C. composed of 2.5% by mass of lower layer silver, 0.5% by mass of copper, and the remainder tin) ) Was sprayed while moving so that the molten solder fine particles would fall uniformly on the workpiece. The spraying amount was sprayed about 20 times the theoretical capacity value at which all openings were completely filled with molten solder.
After that, an optical fiber scope is inserted into the upper part of the lower layer workpiece, and it is confirmed on the monitor screen that has been image-processed that one or more molten solder particles are deposited on the surface of each opening pad. Then, the palmitic acid solution having the above composition having a liquid temperature of 260 ° C. at the top as shown in FIG. 5 is immersed in the molten lead-free solder solution in the lower layer for 2 seconds and then passed through the upper layer and pulled up. Was sprayed at a flow rate of 2 m / sec, and excess solder was blown off and removed so that the finished thickness of the solder precoat film on the pad portion was 5 μm.

For sample 1, the upper layer as shown in FIG. 5 was immersed for 10 seconds in a solution having a liquid temperature of 260 ° C. consisting of 10% by mass of palmitic acid and the remaining ester synthetic oil, followed by 2.5% by mass of silver and 0% copper in the lower layer. Immerse it in a molten lead-free solder solution consisting of 0.5 mass%, nickel 0.01 mass%, germanium 0.005 mass% and the balance tin at a liquid temperature of 260 ° C for 2 seconds, and then pass it through the upper layer and pull it up. However, a palmitic acid solution having the above composition at a liquid temperature of 260 ° C. is sprayed at a flow rate of 1.4 m / sec to blow off excess solder so that the finished thickness of the solder precoat film on the pad portion becomes 10 μm. Removed.
On the other hand, for sample 2, the upper layer as shown in FIG. 8 was placed horizontally in a solution having a liquid temperature of 260 ° C. composed of 10% by mass of palmitic acid and the remaining ester synthetic oil, and was placed directly 30 mm above the sample. High-temperature organic fatty acid from the nozzle (2.0 mmφ diameter) at the tip of the molten solder fine particle generator using ultrasonic vibration with an output of 0.5 KW and a frequency of 35 KHz from molten tin or molten solder fine particle generator equipped with an ultrasonic oscillator Molten solder fine particles having a particle diameter of 1 to 10 μm injected into the solution (the composition is 2.5% by mass of lower layer silver, 0.5% by mass of copper, 0.01% by mass of nickel, 0.005% by mass of germanium) The molten lead-free solder composed of the remaining tin and having a liquid temperature of 260 ° C. was sprayed while being moved so that the molten solder fine particles would fall on the work evenly. The spraying amount was sprayed about 20 times the theoretical capacity value at which all openings were completely filled with molten solder.
After that, an optical fiber scope is inserted into the upper part of the lower layer workpiece, and it is confirmed on the monitor screen that has been image-processed that one or more molten solder particles are deposited on the surface of each opening pad. Then, the palmitic acid solution having the above composition having a liquid temperature of 260 ° C. at the top as shown in FIG. 5 is immersed in the molten lead-free solder solution in the lower layer for 2 seconds and then passed through the upper layer and pulled up. Was sprayed at a flow rate of 1.4 m / sec, and excess solder was blown off and removed so that the finished thickness of the solder precoat film on the pad portion was 10 μm.

For sample 1, the upper layer as shown in FIG. 5 was immersed for 10 seconds in a solution having a liquid temperature of 260 ° C. consisting of 10% by mass of palmitic acid and the remaining ester synthetic oil, followed by 2.5% by mass of silver and 0% copper in the lower layer. 5% by mass, 0.01% by mass of nickel, 0.005% by mass of germanium, 10 ppm of oxygen, 10% of oxygen concentration, and immersed in a molten lead-free solder solution having a liquid temperature of 260 ° C. for 2 seconds, and then the upper layer The excess solder was applied so that the palmitic acid solution having the above composition at a liquid temperature of 260 ° C. was sprayed at a flow rate of 2 m / second at the top while the finished thickness of the solder precoat film on the pad was 5 μm. Was blown off and removed.
On the other hand, for sample 2, the upper layer as shown in FIG. 8 was placed horizontally in a solution having a liquid temperature of 260 ° C. composed of 10% by mass of palmitic acid and the remaining ester synthetic oil, and was placed directly 30 mm above the sample. High-temperature organic fatty acid from the nozzle (2.0 mmφ diameter) at the tip of the molten solder fine particle generator using ultrasonic vibration with an output of 0.5 KW and a frequency of 35 KHz from molten tin or molten solder fine particle generator equipped with an ultrasonic oscillator Molten solder fine particles having a particle diameter of 1 to 10 μm injected into the solution (the composition is 2.5% by mass of lower layer silver, 0.5% by mass of copper, 0.01% by mass of nickel, 0.005% by mass of germanium) , Molten lead-free solder with an oxygen concentration of 10 ppm and the balance of tin at a liquid temperature of 260 ° C.) was sprayed while moving so that the molten solder fine particles would uniformly fall on the workpiece. The amount of application was about 30 times the theoretical capacity value at which all openings were completely filled with molten solder.
After that, an optical fiber scope is inserted into the upper part of the lower layer workpiece, and it is confirmed on the monitor screen that has been image-processed that one or more molten solder particles are deposited on the surface of each opening pad. Then, the palmitic acid solution having the above composition having a liquid temperature of 260 ° C. at the top as shown in FIG. 5 is immersed in the molten lead-free solder solution in the lower layer for 2 seconds and then passed through the upper layer and pulled up. Was sprayed at a flow rate of 2.1 m / sec, and excess solder was blown off and removed so that the finished thickness of the solder precoat film on the pad portion was 5 μm.

For sample 1, the upper layer as shown in FIG. 5 was immersed for 10 seconds in a solution having a liquid temperature of 260 ° C. consisting of 10% by mass of palmitic acid and the remaining ester synthetic oil, followed by 2.5% by mass of silver and 0% copper in the lower layer. 5% by mass, 0.01% by mass of nickel, 0.005% by mass of germanium, 5 ppm of oxygen, 5 ppm of oxygen, the remainder being immersed in a molten lead-free solder solution at a liquid temperature of 260 ° C. for 2 seconds, and then the upper layer The excess solder was applied so that the palmitic acid solution having the above composition at a liquid temperature of 260 ° C. was sprayed at a flow rate of 2 m / second at the top while the finished thickness of the solder precoat film on the pad was 5 μm. Was blown off and removed.
On the other hand, for sample 2, the upper layer as shown in FIG. 8 was placed horizontally in a solution having a liquid temperature of 260 ° C. composed of 10% by mass of palmitic acid and the remaining ester synthetic oil, and was placed directly 30 mm above the sample. High-temperature organic fatty acid from the nozzle (2.0 mmφ diameter) at the tip of the molten solder fine particle generator using ultrasonic vibration with an output of 0.5 KW and a frequency of 35 KHz from molten tin or molten solder fine particle generator equipped with an ultrasonic oscillator Molten solder fine particles having a particle diameter of 1 to 10 μm injected into the solution (the composition is 2.5% by mass of lower layer silver, 0.5% by mass of copper, 0.01% by mass of nickel, 0.005% by mass of germanium) Then, molten lead-free solder having an oxygen concentration of 5 ppm and a liquid temperature of 260 ° C. composed of the remaining tin was sprayed while being moved so that the molten solder fine particles would uniformly fall on the workpiece. The application amount was about 25 times the theoretical capacity value at which all openings were completely filled with molten solder.
After that, an optical fiber scope is inserted into the upper part of the lower layer workpiece, and it is confirmed on the monitor screen that has been image-processed that one or more molten solder particles are deposited on the surface of each opening pad. Then, the palmitic acid solution having the above composition having a liquid temperature of 260 ° C. at the top as shown in FIG. 5 is immersed in the molten lead-free solder solution in the lower layer for 2 seconds and then passed through the upper layer and pulled up. Was sprayed at a flow rate of 2.1 m / sec, and excess solder was blown off and removed so that the finished thickness of the solder precoat film on the pad portion was 5 μm.

For sample 1, the upper layer as shown in FIG. 4 was immersed in a solution of 45 mass% stearic acid and 265 ° C. of the remaining ester synthetic oil for 10 seconds, and then 2.5 mass% of silver and copper 0 5% by mass, 0.01% by mass of nickel, 0.005% by mass of germanium, 2 ppm of oxygen, 2 ppm, and immersed in a molten lead-free solder solution having a liquid temperature of 260 ° C. for 2 seconds, and then the upper layer As shown in FIG. 5, a stearic acid solution having the above composition at a liquid temperature of 260 ° C. is sprayed at a flow rate of 1.4 m / second as shown in FIG. 5 so that the finished thickness of the solder precoat film on the pad is 10 μm. The excess solder was blown off and removed.
On the other hand, for sample 2, the upper layer as shown in FIG. 8 was placed horizontally in a solution having a liquid temperature of 260 ° C. composed of 45% by mass of stearic acid and the remaining ester synthetic oil, and was placed 20 mm above the sample. High-temperature organic fatty acid from the nozzle (2.0 mmφ diameter) at the tip of the molten solder fine particle generator using ultrasonic vibration with an output of 0.5 KW and a frequency of 35 KHz from molten tin or molten solder fine particle generator equipped with an ultrasonic oscillator Molten solder fine particles having a particle diameter of 1 to 10 μm injected into the solution (the composition is 2.5% by mass of lower layer silver, 0.5% by mass of copper, 0.01% by mass of nickel, 0.005% by mass of germanium) The molten lead-free solder having an oxygen concentration of 2 ppm and a liquid temperature of 260 ° C. composed of the remaining tin was sprayed while being moved so that the molten solder fine particles would uniformly fall on the workpiece. The amount of application was about 30 times the theoretical capacity value at which all openings were completely filled with molten solder.
After that, an optical fiber scope is inserted into the upper part of the lower layer workpiece, and it is confirmed on the monitor screen that has been image-processed that one or more molten solder particles are deposited on the surface of each opening pad. Then, the palmitic acid solution having the above composition having a liquid temperature of 260 ° C. at the top as shown in FIG. 5 is immersed in the molten lead-free solder solution in the lower layer for 2 seconds and then passed through the upper layer and pulled up. Was sprayed at a flow rate of 1.4 m / sec, and excess solder was blown off and removed so that the finished thickness of the solder precoat film on the pad portion was 10 μm.

For sample 1, the upper layer as shown in FIG. 4 was immersed in a solution having a liquid temperature of 265 ° C. composed of 20% by mass of stearic acid and the remaining ester synthetic oil for 10 seconds, and then 2.5% by mass of silver and 0% copper in the lower layer. 5% by weight, 0.01% by weight of nickel, 0.005% by weight of germanium, oxygen concentration of 1 ppm or less, and immersed in a molten lead-free solder solution of 260 ° C. of the remaining tin for 2 seconds, As shown in FIG. 5, the stearic acid solution having the above composition at a liquid temperature of 260 ° C. is sprayed at a flow rate of 1.8 m / second, and the finished thickness of the solder precoat film on the pad portion is 5 μm. Excess solder was blown off and removed.
On the other hand, for sample 2, the upper layer as shown in FIG. 8 was placed horizontally in a solution having a liquid temperature of 260 ° C. composed of 45% by mass of stearic acid and the remaining ester synthetic oil, and was placed 20 mm above the sample. High-temperature organic fatty acid from the nozzle (2.0 mmφ diameter) at the tip of the molten solder fine particle generator using ultrasonic vibration with an output of 0.5 KW and a frequency of 35 KHz from molten tin or molten solder fine particle generator equipped with an ultrasonic oscillator Molten solder fine particles having a particle diameter of 1 to 10 μm injected into the solution (the composition is 2.5% by mass of lower layer silver, 0.5% by mass of copper, 0.01% by mass of nickel, 0.005% by mass of germanium) , A molten lead-free solder with an oxygen concentration of 1 ppm or less and a liquid temperature of 260 ° C consisting of the remaining tin) is sprayed while moving so that the molten solder fine particles fall on the workpiece evenly. . The application amount was about 40 times the theoretical capacity value at which all openings were completely filled with molten solder.
After that, an optical fiber scope is inserted into the upper part of the lower layer workpiece, and it is confirmed on the monitor screen that has been image-processed that one or more molten solder particles are deposited on the surface of each opening pad. Then, the palmitic acid solution having the above composition having a liquid temperature of 260 ° C. at the top as shown in FIG. 5 is immersed in the molten lead-free solder solution in the lower layer for 2 seconds and then passed through the upper layer and pulled up. Was sprayed at a flow rate of 2 m / sec, and excess solder was blown off and removed so that the finished thickness of the solder precoat film on the pad portion was 5 μm.

For sample 1, the upper layer as shown in FIG. 4 was immersed for 10 seconds in a solution having a liquid temperature of 265 ° C. composed of 20% by mass of stearic acid and the remaining ester synthetic oil, and then 0.01% by mass of nickel and 0% germanium in the lower layer. .5 mass%, oxygen concentration 2 ppm, the temperature of the upper part as shown in FIG. 5 while being dipped in a molten tin solution of 260 ° C. composed of the remaining tin for 2 seconds and then pulled up by passing through the upper layer. The stearic acid solution having the above composition at 260 ° C. was sprayed at a flow rate of 1.8 m / sec, and excess tin was blown off and removed so that the finished thickness of the tin precoat film on the pad portion was 5 μm.
On the other hand, for sample 2, the upper layer as shown in FIG. 8 was placed horizontally in a solution having a liquid temperature of 260 ° C. composed of 45% by mass of stearic acid and the remaining ester synthetic oil, and was placed 20 mm above the sample. High-temperature organic fatty acid from the nozzle (2.0 mmφ diameter) at the tip of the molten solder fine particle generator using ultrasonic vibration with an output of 0.5 KW and a frequency of 35 KHz from molten tin or molten solder fine particle generator equipped with an ultrasonic oscillator Molten solder fine particles having a particle diameter of 1 to 10 μm φ to be injected into the solution (composition is 0.01 mass% of nickel in the lower layer, 0.005 mass% of germanium, oxygen concentration of 2 ppm, and a liquid temperature of 260 ° C. consisting of the remaining tin) The molten lead-free solder) was sprayed while moving so that the molten solder fine particles would fall on the workpiece evenly. The application amount was about 40 times the theoretical capacity value at which all openings were completely filled with molten solder.
After that, an optical fiber scope is inserted into the upper part of the lower layer workpiece, and it is confirmed on the monitor screen that has been image-processed that one or more molten solder particles are deposited on the surface of each opening pad. Then, the palmitic acid solution having the above composition having a liquid temperature of 260 ° C. at the top as shown in FIG. 5 is immersed in the molten lead-free solder solution in the lower layer for 2 seconds and then passed through the upper layer and pulled up. Was sprayed at a flow rate of 2 m / sec, and excess solder was blown off and removed so that the finished thickness of the solder precoat film on the pad portion was 5 μm.

For sample 1, the upper layer as shown in FIG. 4 was immersed in a solution of stearic acid 20% by mass and the remaining ester synthetic oil at a liquid temperature of 180 ° C. for 10 seconds, and then the lower layer was 42% by mass of tin and 58% by mass of bismuth. In a tin bismuth eutectic alloy having an oxygen concentration of 3 ppm, immerse it for 2 seconds in a molten solder solution having a liquid temperature of 180 ° C. with 0.07% by mass of nickel, 0.005% by mass of germanium and the remainder tin and bismuth added. Then, while passing through the upper layer and pulling up, a stearin solution having the above composition at a liquid temperature of 170 ° C. is sprayed at a flow rate of 1.8 m / sec on the top as shown in FIG. 5 to finish the solder precoat film on the pad portion. Excess solder was blown off and removed so that the thickness became 5 μm.
On the other hand, for sample 2, the upper layer as shown in FIG. 8 was placed horizontally in a solution having a liquid temperature of 260 ° C. composed of 45% by mass of stearic acid and the remaining ester synthetic oil, and was placed 20 mm above the sample. High-temperature organic fatty acid from the nozzle (2.0 mmφ diameter) at the tip of the molten solder fine particle generator using ultrasonic vibration with an output of 0.5 KW and a frequency of 35 KHz from molten tin or molten solder fine particle generator equipped with an ultrasonic oscillator Molten solder fine particles (composition is the same as the molten solder liquid in the lower layer) having a particle diameter of 1 to 10 μmφ sprayed into the solution are sprayed while being moved so that the molten solder fine particles uniformly fall on the workpiece. The spraying amount was sprayed about 20 times the theoretical capacity value at which all openings were completely filled with molten solder.
After that, an optical fiber scope is inserted into the upper part of the lower layer workpiece, and it is confirmed on the monitor screen that has been image-processed that one or more molten solder particles are deposited on the surface of each opening pad. Then, the palmitic acid solution having the above composition having a liquid temperature of 260 ° C. at the top as shown in FIG. 5 is immersed in the molten lead-free solder solution in the lower layer for 2 seconds and then passed through the upper layer and pulled up. Was sprayed at a flow rate of 2 m / sec, and excess solder was blown off and removed so that the finished thickness of the solder precoat film on the pad portion was 5 μm.

In the evaluation test, the appearance was observed with a microscope (X20 to 100 times) for the presence of bridges and missing (solder-free).
For the copper concentration and impurity concentration in the lead-free solders of the above comparative examples and examples, the solders immediately before use were sampled prior to each prototype experiment of comparative examples 1 to 5 and examples 1 to 5, and the latest TOF- The oxygen concentration from the surface to the inside of a depth of 10 μm was measured by a SIMS analyzer.
In addition, in the production of the void observation sample and the impact resistance test sample of the solder joint portion of the semiconductor device after the heat aging of Examples 1 to 5 and Comparative Examples 1 to 5, a printed circuit for burn-in test corresponding to each sample Each sample 1 of Examples 1-5 and Comparative Examples 1-5 was mounted using the board | substrate, and it solder-joined with the reflow furnace, and used for the evaluation test as a sample for evaluation.
The evaluation method for the presence or absence of voids in the vicinity of the solder joint interface is that the sample for the evaluation test is in a normal state and left in a constant temperature heating furnace at 150 ° C. for 240 hours, and after the heating aging acceleration test, the solder joint cross section is polished, Using a scanning electron microscope (SEM) and an X-ray microanalyzer (EPMA), the number and size of microvoids near the solder joint were observed, analyzed, and compared.
In addition, as an evaluation method for evaluating the presence or absence of voids near the solder joint interface on the BGA side of each of the samples 1 of Examples 1 and 2 and Comparative Examples 1, 2 and 3 that were simultaneously subjected to the heat aging acceleration test under the same conditions, The sample was left in a constant temperature oven at 150 ° C. for 240 hours and after the heat aging acceleration test, the solder joint cross section was polished, respectively, by a scanning electron microscope (SEM) and an X-ray microanalyzer (EPMA), The number and size of microvoids near the solder joint were observed and analyzed for comparison.
On the other hand, the samples of Examples 1, 2, 3 and Comparative Examples 1, 2, 3 which were subjected to the heat aging acceleration test under the same conditions at the same time were subjected to JEDEC using a commercially available fully automatic drop test apparatus for electronic device parts such as BGA. (Joint Electron Device Engineering Council) No. According to 22-B111, the test piece was repeatedly dropped from a height of 1000 mm to about 1300 G, and a continuity test of each test sample was performed each time, and the number of drop tests until a continuity failure occurred was examined. (Table 1)

The results are as shown in [Table 1] below. In particular, in the appearance inspection of the solder forming portion in the sample 2 which is a fine circuit, between Example 1 and Comparative Examples 1 and 3, Example 2 and Comparative Example There was a clear significant difference in any of 2 and 2 in Comparative Examples 1, 2 and 3, over volume (horn, tsura), bridge, missing (solder not applied) occurred frequently.
On the other hand, the film thickness of the solder in sample 1 which is a relatively wide circuit is in the range of 5 ± 2 μm or 15 ± 3 μm in Examples 1 to 5 which are the method of the present invention, but in Comparative Examples 1 to 5. 5 was 1 to 32 μm, and it was found that the variation in thickness was overwhelming and non-uniform.

Furthermore, with respect to the relationship between the oxygen concentration in the solder used and the Kirkendall void (microvoid), it was confirmed that there were no microvoids in both the comparative example and the example in the normal state of the comparative example and the example. Aging (150 ° C., 240 hours) was performed, but as shown in Table 2, Comparative Examples 1 to 3 and Comparative Examples 4, 5, and 6 using a solder whose oxygen concentration was adjusted to 10 ppm or less were used after heating aging. It was found that Kendall voids occurred frequently and the impact resistance was low.
In contrast, in the examples of the present invention, the occurrence of Kirkendall voids was slightly observed in Examples 1 and 2 using a solder having a high oxygen concentration, but the number of occurrences compared to Comparative Examples 1 to 5 Is overwhelmingly small and the size of the void is small, it was found that the impact resistance is at a level that is practically no problem.
On the other hand, in Examples 4 to 8 using the solder whose oxygen concentration is adjusted to 5 ppm or less, the viscosity of the molten solder is clearly lowered further, so-called “solder breakage” is improved, and the generation of Kirkendall void is drastically reduced. In Examples 5 to 8 in which the oxygen concentration was 2 ppm or less, it was verified that the generation of Kirkendall voids after heat aging could be eliminated. It is presumed that the inflection point (critical point) in physical and chemical properties is in the vicinity of an oxygen concentration of 5 ppm.

This is thought to be due to the presence of a large amount of oxygen or copper oxide in the vicinity of the solder joint interface. . (hypothesis)
In other words, Kirkendall voids are generally said to be voids due to lattice defects, but Kirkendall voids (microvoids) after heat aging are caused by oxygen in the copper oxide 31 as schematically shown in FIGS. Case 1 which is combined with tin 33 to form stannous oxide 32 and copper 34, that is,
CuO + Sn → Cu + SnO
The case in which microvoids (voids) 36 are generated due to volume shrinkage of about 1.5% due to the above, or, as schematically shown in FIG. Case 2 which becomes tantalum 35, that is, CuO + SnO → Cu + SnO ₂
The inventors consider that microvoids (voids) 36 are generated by causing a deposition shrinkage of about 15% due to (a hypothesis). In addition, when germanium is added to nickel-containing lead-free solder, the effect of suppressing tin oxidation is great, so the effect of improving microvoids and impact rupture resistance after heat aging is considered to be greater.
This suggests how important it is to prevent oxygen from being involved during soldering. That is, a large amount of Kirkendall voids of Comparative Examples 1 to 5 that oxygen is entrained by the scattering of flux in a boiling state in the atmosphere as in the conventional method, and oxides are taken into the metal in the solder and the metal surface of the pad. I think it was the cause.
In addition, as shown in Table 2, the impact resistance test results are as shown in Table 2. In each of Comparative Examples 1 to 6, a failure in conduction occurs in 1 to 4 times, whereas in Examples 1 to 8, no failure occurs even in 40 times. It was confirmed. In addition, since the impact test was temporarily stopped after 40 times, it is unconfirmed to what extent the normality can be maintained. The reason is that if it has 40 times, it is practically sufficient for reliability.

In addition, in the said Example, although BGA and the printed circuit board for a burn-in test corresponding to it as an electronic circuit board were used as object, it can be easily analogized that the same effect is acquired also in other electronic circuit boards, Small electronic components such as ultra-mini transistors, ultra-mini diodes, mini capacitors, etc. are connected to each other in a matrix with multiple rows and rows of electronic components, such as lead frame strips and strips, or wire rods or plates. It can be easily inferred that the same effect can be obtained even if a solder coating or a solder precoat coating is formed by the method of the present invention on the electronic component array aligned on the holder. Therefore, these are within the scope of the present invention.
In addition, the lead frame strips arranged in a matrix with multiple rows of multi-row electronic components wound in a coil shape are processed by the moving method and continuous feeding or intermittent feeding in the method of the present invention. I can do it.

Industrial applicability

  As described above, the present invention is a problem of the conventional method and similar prior art, such as a bridge problem when forming a solder precoat film of a fine circuit, a so-called micro-layer in a joint interface or a solder layer because it contains a flux component. It avoids the phenomenon of voids (small bubbles and voids), solves the problem of connection reliability over time, the problem of corrosiveness, and the problem of Kirkendall voids that occur over time after long-term high temperature exposure. Alternatively, a tin or solder precoat film having a thickness variation of ± 3 μm within a thickness range of 3 to 20 μm is formed on a fine narrow pitch electronic circuit having a lead width of 0.02 to 0.08 mm and an adjacent pitch of 0.04 to 0.12 mm. Is a groundbreaking technology that has a very high industrial value.

1 Electronic circuit board or electronic component assembly (work)
2 Hot air leveler (HAL) nozzle 3 High temperature organic fatty acid solution spray nozzle 4 High temperature organic fatty acid solution 5 Molten tin solution or molten solder solution 6 High temperature organic fatty acid solution transfer pump 7 High temperature organic fatty acid solution spray Nozzle for attaching 8 Reverse roll 9 Baffle 10 Organic fatty acid solution storage tank 11 Organic fatty acid solution (upper layer) and storage tank for molten tin or molten solder liquid (lower layer) 12 Organic fatty acid solution (upper layer) and molten tin or molten solder liquid (lower layer) ) Storage tank 13 Robot arm 14 attached to an automatically controlled three-dimensional movement device (robot) A frame-shaped dedicated holder 15 for attaching and fixing an electronic circuit board or a connected electronic component to the tip of the robot arm 15 Pilot pin 16 Ultrasonic oscillation Molten tin or molten solder fine particle generator 17 equipped with a machine 17 Molten solder fine particles 18 Molten tin liquid or molten solder liquid transfer pump 19 Ultrasonic output cable 20 Ultrasonic vibrator 21 Cooling fin booster 22 Holding booster 23 Ultrasonic horn 24 Molten tin or molten solder liquid supply line 25 Melting Tin or molten solder injection nozzle 26 Electrode pad or lead 27 Solder resist 28 Opening 29 Tin formed by adhering and bonding molten tin fine particles or molten solder fine particles to the electrode pad or lead surface, and a plurality of fine particles cohesively bonded together Alternatively, the solder coating layer 30 is a molten solder layer 31 formed by fusing molten tin fine particles or solder fine particles bonded to the electrode pad or lead surface. Copper oxide CuO
32 stannous oxide SnO ₂
33 Tin Sn
34 Copper Cu
35 stannic oxide SnO
36 Kirkendal void (micro void, void)
37 Organic Fatty Acid Solution and Molten Tin Solution or Molten Solder Solution Reservoir 38 Molten Tin Solution or Molten Solder Solution Subsequent Nozzle 39 Organic Fatty Acid Solution and Molten Tin Solution or Overflow Liquid After Mixing (Mixed Solution) )
40 Metal receiving bowl 41 receiving overflow mixed liquid 39 Stirrer 42 Mixed liquid of organic fatty acid solution and molten tin liquid or molten solder liquid 43 Valve 44 Sieve with fine mesh wire net or commercially available powder spreader 45 Copper pad Or copper lead 46 segregated material of intermetallic compound (IMC) such as tin silver and tin copper 47 intermetallic compound (IMC) layer of tin copper nickel 48 lead-free solder layer 49 tin copper nickel intermetallic alloy layer 50 tin nickel layer metal Intermetallic layer 51 Glass epoxy board

Claims (11)

In a method for forming a tin or solder precoat film on an electrode pad or a narrow pitch lead surface of an electronic circuit board or electronic component,
A high-temperature organic fatty acid solution heated in an upper layer is formed by horizontally or tilting the electronic circuit board or the electronic component in the upper layer of a processing apparatus having a storage tank containing a molten tin solution or a molten solder solution in a lower layer. After the contact with the organic fatty acid solution and forming the protective film of the organic fatty acid on the electrode pad or the lead surface, the molten tin solution placed immediately above the organic fatty acid solution in the state of contact with the organic fatty acid solution in the upper layer Alternatively, molten solder particles are dispersed, and the molten tin or molten solder is adhered to the electrode pad or the lead surface, and then the electronic circuit board or the electronic component is immersed in the molten tin liquid or molten solder liquid in the lower layer. Forming a tin or solder film on the electrode pad or the lead surface;
The tin or solder adhered excessively by spraying a heated organic fatty acid solution on the surface while pulling up the electronic circuit board or the electronic component on which tin or a solder coating is formed in the first step through the upper layer A second step of blowing off and removing the coating;
A method of forming a uniform tin or solder precoat film on the electrode pad or the lead surface.   2. The method for forming a tin or solder precoat film according to claim 1, wherein the uniform tin or solder precoat film has a thickness of 3 to 30 [mu] m and a thickness variation of 5 [mu] m or less. .   3. The method according to claim 2, wherein the organic fatty acid solution comprises 5-80% by mass of palmitic acid or stearic acid and the remaining ester synthetic oil.   3. The method according to claim 2, wherein the molten tin or the molten solder particles are dispersed by applying ultrasonic vibration directly to the molten tin liquid or the molten solder liquid that passes through the spray nozzle portion. A method for forming a tin or solder precoat film.   3. The method according to claim 2, wherein the molten tin solution or the molten solder solution contains 0.005 to 0.1 mass% nickel, 0.001 to 0.05 mass% germanium, or 0.003 to 0 phosphorus. A method for forming a solder precoat film, comprising: one or more of 0.01% by mass and the balance tin.   3. The method according to claim 2, wherein the molten tin solution or the molten solder solution is composed of a tin bismuth master alloy of 42% by mass of tin and 58% by mass of bismuth, 0.005 to 0.1% by mass of nickel, and germanium. A method for forming a solder precoat film, comprising adding at least one of 0.001 to 0.05 mass% or 0.003 to 0.01 mass% of phosphorus. An apparatus for forming a tin or solder precoat film on a small area electrode pad or a narrow pitch lead surface of an electronic circuit board or electronic component,
An organic fatty acid solution heated in the upper layer, a processing apparatus including a storage tank containing a molten tin solution or a molten solder solution in the lower layer, and
A transfer device for gripping the electronic circuit board or the electronic component to enter and exit the storage tank;
In the upper layer of the storage tank, the electronic circuit board or the electronic component is placed immediately above the electronic circuit board or the electronic component in the state where the electronic circuit board or the electronic component is in contact with the organic fatty acid solution. A spraying device for depositing molten tin or molten solder;
After tin or solder is attached to the electrode pad or lead surface of an electronic circuit board or electronic component by the spraying device, the tin or solder is immersed in the lower layer of molten tin solution or molten solder solution and then immersed in the electrode pad or lead surface. A removal device for spraying and removing the excessively adhered tin or solder film by spraying a heated organic fatty acid solution on the surface of the electronic circuit board or the electronic component on which the film is formed. Equipment.   8. The tin or solder precoat film forming apparatus according to claim 7, wherein the upper organic fatty acid solution comprises 5 to 80% by mass of palmitic acid or stearic acid and the remaining ester synthetic oil.   8. The apparatus according to claim 7, wherein the molten tin or molten solder liquid of the lower layer contains 0.005 to 0.1 mass% nickel, 0.001 to 0.05 mass% germanium, or 0.003 to 0 phosphorus. A tin or solder precoat film forming apparatus comprising 0.01 mass% and the balance of tin.   8. The tin or solder precoat according to claim 7, wherein the spraying device for adhering the molten tin or the molten solder is sprayed by atomizing the molten tin solution or the molten solder solution from a nozzle by ultrasonic vibration. Film forming device. 8. The apparatus of claim 7, wherein the transfer device is
A tin comprising: a frame-shaped jig for fixing the electronic circuit board or the electronic component via a pilot pin; and an automatic control device for attaching the frame-shaped jig to a robot arm and moving it three-dimensionally. Or a solder precoat film forming apparatus.

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