TW200952587A - Solder bonding method and solder joint - Google Patents

Abstract

Generation of voids is suppressed by means of a conventional apparatus without using attached apparatuses, such as a pressure reducing apparatus, in solder bonding wherein a BGA ball solder and a cream solder are used. The ball solder and the cream solder have a relationship where the liquidus temperature of the ball solder alloy is lower than the solidus temperature of the solder alloy in the cream solder. The ball solder and the cream solder are bonded by a reflow method. The liquidus temperature of the ball solder alloy and the solidus temperature of the solder alloy in the cream solder is 1 DEG C or higher. The ball solder and the solder alloy used for the cream solder have a eutectic composition.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder bonding method and a solder bonding structure using spherical solder and solder when electronic components are mounted on a surface of a printed circuit board. [Prior Art] It is known that the soldering method for mounting electronic components on the surface of a printed substrate is to use an axial component having a long lead, but it is used in accordance with the miniaturization or multifunction of the electronic device. Electronic components that are highly integrated, SIP or DIP, QFP, etc. In recent years, multi-functionality has progressed, and for high-density mounting, it has become a BAG package or a CSP package. In such a BAG package or a CSP package, in order to be placed on a printed substrate, a small spherical solder is used for solder bonding. As such a method, a method of setting a bag package or a CSP package after soldering a printed circuit board or a BGA ball-shaped solder, and performing solder bonding by a reflow process is known. φ However, various bonding failures occur in the BGA package or the CSP package joined by the above method. Among the joint failures, especially those having a large influence on the joint reliability, are referred to as small voids formed in the interior of the solder joint. If the inter-pore occurs, the solder joint strength is lowered and the crack is also caused. Therefore, various methods for suppressing the occurrence of voids are reviewed. ^ In the case of solder bonding such as BG A package, the height of BGA ball solder after mounting on the BGA package substrate varies. Therefore, BGA ball solder and solder cannot be used in the mounting process of the required micron unit. It is also a problem that joint failure occurs. -5-200952587 Patent Document 1: JP-A-2006-272397 Patent Document 2: International Publication No. 2005/035180 pamphlet Patent Document 3: JP-A-2005-205418 Patent Document 4: JP-A-2006-159266 Japanese Patent Publication No. Hei 8-293670 discloses a method for suppressing the occurrence of a hole. In Patent Document 1, it is necessary to ensure the gas generated from the solder in order to increase the time for solder melting in the connection portion. A proposal for a flux of solder powder having two different heat capacities of 0 is included in the time of discharge to the outside air. In the special document 2, there is proposed a composition for suppressing the occurrence of pores when a small-sized B G A spherical solder is used. In addition, in Patent Document 3, there is a proposal for a pressure reducing device that adjusts the pressure of the joint portion to a reduced pressure state during solder bonding, and Patent Document 4 performs soldering for suppressing the occurrence of voids by high-temperature solder bonding. Proposal for alloy composition. Patent Document 5 proposes to suppress the occurrence of voids by using two kinds of solder alloys having different melting points. ❹ In the solder bonding using BGA solder and flux, the spherical solder and the flux at the joint BGA are separately melted by heating in the reflow furnace. At this time, the gas generated in the flux or at the joint interface is shielded by the molten BG A spherical solder, and the gas is prevented from being released to the outside air. The gas is sealed by the solidified solder and becomes pores. It may be a cause of 'pore'. However, Patent Document 1 is only a proposal for a flux, and Patent Document 2 is only a proposal for a BGA spherical solder. Patent Document 4 is a proposal for a composition of high-temperature solder, and Patent Document 5-6-200952587 is The proposal to use two kinds of solder alloys, in general, is not effective in suppressing pore generation in the combination of BGA spherical solder and flux in each case. Further, in the proposal of using the pressure reducing device of Patent Document 3, it is necessary to additionally install a device on the reflow furnace, and it is also an indispensable problem for the shape or temperature profile of the nine pieces of solder. Further, the technique for precisely controlling the height of the BGA spherical solder attached to the BGA package substrate has been improved by the improvement of the mounting technique, but the bonding failure has occurred at a practical level of φ. SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art. The object of the invention is to prevent the occurrence of suppression by conventional equipment without using an accessory device such as a decompression device in solder bonding using BG A spherical solder and flux. The invention of the pores, the present inventors, is a basic way to achieve the above object, and focuses on the technique of pore generation, and focuses on the change of the molten state of the BGA spherical solder and the flux or the relative melting temperature. the same. That is, the alloy in which the liquidus temperature of the B G A spherical solder is selected to have a relationship lower than the solidus temperature of the flux is remarkably reduced by the reflow. Further, the liquidus temperature of the BGA spherical solder alloy and the solidus temperature of the solder alloy in the flux are selectively at least 1 °C. The liquidus temperature of the BGA spherical solder and the solidus temperature of the solder alloy in the flux are better than a certain degree, but the phase difference of 1 °C is the case of the general temperature formula of the reflow method. The BGA solder can also be liquefied first by heating. Also, the solder alloy used for BGA spherical solder and flux uses a eutectic composition. In the case of eutectic, the liquidus temperature and the solidus temperature are the same, so that the melting of each solder is fast, and the gas causing the pores can be extruded from the inside of the solder to reduce the occurrence of voids. Further, as the BGA spherical solder, a solder alloy containing Sn-Ag-Cu as a main component is used as an example, and a solder alloy containing Sn-Cu-Ni as a main component is used as an example of the solder alloy in the flux. Both are widely used as lead-free solder alloys, and have high reliability on the characteristics of solder. As is well known, when the alloy is not at the eutectic point, the liquidus temperature at which the alloy completely becomes a liquid, and the solidus temperature at which it is completely solid. In the solder alloy using the BGA spherical solder having the above relationship and the solder alloy used for the solder, the solder which is sandwiched between the printed substrate and the semiconductor package and the BGA spherical solder are exposed to the reflow. The high temperature in the furnace @ first, the BGA spherical solder with a low liquidus temperature melts into a liquid, and the surface is maintained in a curved surface by surface tension. Thereafter, for the solder particles in the flux having a solidus temperature higher than the liquidus temperature of the BGA spherical solder, thermal energy from the printed substrate is supplied, and heat is also supplied from the portion where the BGA spherical solder is in contact. In the vicinity of the BGA spherical solder, the evaporation of the flux starts to generate gas. The gas generated is prevented from intruding into the BGA spherical solder by the surface tension of the molten BGA spherical solder, and most of it is released into the outdoor air from -8 to 200952587. On the one hand, the solder particles in the flux are compared with the mass of the BGA spherical solder. For the extremely small mass of each unit, when it comes into contact with the liquid BG A spherical solder with large heat, it will melt in a very short time. It was introduced as part of BG A spherical solder. As described above, in the present invention, the BGA spherical solder is first melted to complete the liquid state in which the shape is maintained by the surface tension, and then the solder particles in the flux having a very small melting mass are introduced by the heat of the BG A ball φ-shaped solder. BGA spherical solder. On the one hand, in order to have a flux function for the solder paste component of the flux, it is known that the evaporation temperature is relatively lower than the melting temperature of the solder alloy, and although the component effectively wets the surface of the bonding object, it occurs. Gases are not introduced into the BGA spherical solder interior. In order to further enhance the understanding of the above-described effects of the present invention, the relationship between the liquidus temperature of the solder alloy in the flux and the solidus temperature of the BGA spherical solder is described as being contrary to the relationship of the present invention. At this time, Φ first evaporates the solder paste component in the flux, and then begins to melt the solder particles in the flux. The melting of the BGA spherical solder begins from the contact portion of the molten flux with the BGA spherical solder. On the other hand, the bubble gas generated in the flux floats on one side of the central portion of the flux. In the same way, as the B G A spherical solder melts, the solder particles in the previously melted flux are integrated with the BGA spherical solder, and the bubble gas is also introduced into the BG A spherical solder by buoyancy to cause voids. This series of processes is a technique for generating pores with the focus on the melting of the two solders. Further, in this relationship, when a part of the flux is initially melted, -9-200952587 raises the BGA spherical solder by the surface tension of the molten flux so that the unmelted flux of the other portion is separated from the BGA spherical solder. Even if the flux which becomes a non-contact part and the BGA spherical solder are melted after it is melted, it is difficult to fuse with each other and cause a joint failure. In the solder bonding method of the present invention and the weld bead formed by the method, conventional reflow soldering equipment can be used, and the occurrence of voids is suppressed as much as possible in comparison with conventional solder bonding. [Embodiment] Hereinafter, preferred embodiments of the present invention will be described based on the drawings and examples. Generally, when electronic components are to be mounted on the surface of a printed circuit board, BGA ball solder and flux are mounted as shown in Fig. 1 before being heated by the reflow furnace. Here, 1 is a BGA package substrate, 2 is a BGA ball solder, 3 is a flux, and 4 is a printed substrate. In the figure, the flux 3 is printed on the printed circuit board 4 in advance, but the combination of the solder 3 and the printed circuit board 4 in this state is used even if the solder 3 is attached to the lower end of the BGAQ spherical solder 2, The effect achieved by the invention is that the composition of the same BGA spherical solder 2 is not particularly limited. For example, as a lead-free solder alloy, a known Sn-Ag alloy, or a Sn-Cu alloy or a Sn-In alloy, Sn can be used. -Bi alloy, Sn-Zn alloy, Sn-Ag-Cu alloy, Sn-Cu-Ni alloy, and the like. Further, the present invention is not intended to be used as a BGA spherical solder for a Sn-Pb alloy having a lead solder alloy. Further, -10-200952587 The size and shape of the BGA spherical solder are not limited, and even if it is sold on the market, the structure of the BGA spherical solder of the present invention is widely included in the structure of the first embodiment. Read. The flux used in the present invention is not limited to the composition and composition, and is generally defined as a flux composed of a solder powder and a resin component, an active agent, a thixotropic agent, a solvent, or the like. Solder composition. φ The solder powder used in the flux of the present invention is preferably a lead-free solder powder which is generally a component containing no lead in view of the worldwide trend of lead-free solder, but the effect achieved by the present invention is not limited thereto. Specifically, 'for example, Sn, Ag, Cu, Bi, In, Zn, Al, Sb, Ni, Au, Pt, Ca, Ge, Co, Fe, P, Si, Mn, Te, or the like. Further, the content of the solder powder is not particularly limited, but it is generally about 70 to 95 by weight in the flux. The shape of the solder particles is not particularly limited to a spherical shape, an amorphous shape, or the like, but in order to uniformly supply heat or the like, the crucible is most suitable for the spherical shape, and the particle diameter is a powder having a particle range of 0.1 to ΙΟΟμηη. The body is taken as an example. Hereinafter, a resin component used for the flux is exemplified as a rosin-based resin. The rosin-based resin is a derivative such as rosin and its modified rosin, and can also be used. Specifically, there are, for example, gum rosin, wood rosin, polymerized rosin, phenol-modified rosin or derivatives thereof, but propylene-based resins may also be used. Further, the content of the resin is generally from about 25 to 75% by weight in the flux, but is not limited. The active agent used in the flux of the embodiment is exemplified as an organic amine -11 - 200952587 hydrogen halide, such as diphenyl hydrazine hydrobromide, cyclohexylamine bromate chlorate, diethylamine hydrochloride, Triethanolamine hydrobromide, monoethanolamine hydrobromide, etc., and, as organic acids, such as malonic acid, acesulfonic acid, maleic acid, glutaric acid, suberic acid, adipic acid, naphthalene Acid, etc. Further, the content of the active agent is generally from about 0. 01 to 30% by weight in the flux, and is not limited. Further, examples of the thixotropic agent used for the flux include hydrogenated castor oil, fatty acid decylamines, hydroxy fatty acids, castor wax and the like. Further, the content of the thixotropic agent is not particularly limited, but it is generally about 0 to 1 to 15% in the flux, but it is not limited. The solvent used in the flux of the present invention is, for example, hexyl carbitol, butyl carbitol, ethylene glycol monobutyl ether. Further, the content of the solvent is not particularly limited, but it is usually about 20 to 80% by weight in the flux, but it is not limited. In the present embodiment, the composition of the BGA spherical solder and the flux is specifically disclosed as described above, but in the present invention, it is necessary to be a physical property, and the liquidus temperature of the BGA spherical solder alloy is a ratio as the solder particles contained in the flux. The solidus temperature of the solder alloy is also low, and combinations of alloys that can achieve this are all included in the scope of the present invention. EXAMPLES Hereinafter, examples will be described. [Sample] -12- 200952587 The conditions of the composition of the spherical solder and the flux used for the test are shown in Table 1. Table 1 spherical solder

Spherical solder A Spherical solder B Composition Sn-3.0Ag-0.5Cu Sn-0.7Cu-0.05Ni Average particle size 0.5mm 0.5mm Liquidus temperature 219〇C 227〇C

Composition flux C flux D solder powder composition Sn-0.7Cu-0.05Ni Sn-3.0Ag-0.5Cu average particle size 25μηι 25μιη flux composition and compounding amount (leiden modified rosin 50 50 castor wax 10 10 adipic acid 2 2 1, 3-Diphenylhydrazine hydrochloride 3 3 Diethylene glycol mono-n-hexyl ether 35 35 Solidus temperature 227〇C 218〇C ❿ The conditions of the printed substrate model and the BGA package model used for the test are shown in Table 2. 13- 200952587 Table 2 External dimensions 25x35mm, t=l_6mm Printed substrate bump spacing: 〇.8mm, convex track diameter: 0.42mm (model) Material glass epoxy substrate solder coating thickness 0.1mm outer dimension 15x15mm > t= 1.6mm BGA package bump spacing: 〇.8mm, bump diameter: 0.42mm (model) Material glass epoxy substrate spherical solder installation number 100

[test device]

•Reflow oven: TNP25-53 8EM made by Tamura Co., Ltd.

• X-ray transmission type inspection device: SMX-1 60CT manufactured by Shimadzu Corporation

[Test method] 1. The spherical solder shown in Table 1 was attached to the BGA package shown in Table 2, and after heating in the reflow furnace, it was washed with a support oxide. 2. The solder shown in Table 2 was printed on the printed boards shown in Table 2, the BGA package was mounted on a spherical solder, and the solder joint was formed in the reflow oven under the conditions shown in Table 3 to produce the spherical solder shown in Table 4. Examples and comparative examples of combinations of fluxes. 3. The welds obtained in the above 2 were evaluated for the occurrence of voids using an X-ray transmission type inspection. -14- 200952587

Table 3 Temperature profile P 250 227 200 150 100 50 0

50 100 150 (sec) 200 250 300 In combination with each of the above samples, it can be seen from the respective liquidus temperature and solidus temperature that only the combination of spherical solder A and flux C, the liquidus temperature of the spherical solder alloy is The solidus temperature of the flux alloy is also low. [Test Results] The test results are shown in Table 4 and Figure 2. Example 1 Comparative Example 1 Comparative Example 2 Type of spherical solder AAB Type of flux CDD Spherical solder liquidus temperature and flux solidus temperature difference (fluid solidus temperature - spherical solder liquidus temperature) 8 °c - L °c -9 ° C Porosity (calculated as Comparative Example 1 as 100%) 20.2% 100% 106.4% From Table 4, Example 1 of the present invention is compared with Comparative Example 1 and Comparative Example 2, The incidence of voids is low. Further, as shown in Fig. 2, the void portion of the white spot can be confirmed by X-ray transmission -15-200952587, and it is understood that the occurrence of voids is small. Thus, in the relationship of the above embodiment, it is understood that the occurrence of voids inside the weld bead is reduced. That is, the liquidus temperature of the spherical solder is lower than the solidus temperature of the flux. Only the first embodiment reduces the occurrence of voids. For this, the liquidus temperature for the spherical solder is higher than the solidus temperature of the flux. In the high comparative example 2, pores were more likely to occur than in Comparative Example 1 in which the liquidus temperature was the same as the solidus temperature. From the relationship of the three, it is also possible to derive the conclusion that the occurrence of voids can be derived by using a phase in which the liquidus temperature of the BGA spherical solder is lower than the solidus temperature of the solder particles used for the solder. Further, in the above test, the state in which the BGA spherical solder and the flux were separately melted was observed. After the reflow furnace was heated, the embodiment of the present invention first melted the BGA spherical solder 2, and then the latitude and longitude which was melted by the flux 3, but At the time of melting the flux 3, there is no case where the gas is concentrated near the center and floated up, and the effect of raising the molten BGA spherical solder 2 in a moment does not act, and the side of each solder is melted together. The process of forming a solder joint. In addition, it was confirmed that all of the solder Qs of 100 were not bonded. Therefore, even if the height of the BGA spherical solder attached to the BGA package substrate 1 is somewhat different, a solder joint portion is formed on both the BGA package and the printed substrate when the solder bonding is completed. Therefore, according to the present invention, it is possible to exhibit the effect of preventing the joint failure due to the height deviation of the B G A spherical solder which is a problem. The solder bonding method of the present invention not only has a remarkable effect of suppressing the occurrence of voids but also has an effect of preventing solder joint failure. Therefore, it can be expected to be widely used in a BGA package or a CSP package which is particularly required for reliability. Electronic parts are joined. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing a state before soldering of a flux and a BGA spherical solder of the present invention. Fig. 2 is a photograph showing the state of occurrence of voids after the solder joints were photographed using an X-ray transmission type inspection apparatus. (The black circle is the solder cross section, and the white spotted shape is the generated pores). [Main component symbol description] 1 : BGA package substrate 2 : BGA spherical solder 3 : Flux 4 : Printed substrate ❹ -17-

Claims (1)

200952587 X. Patent application scope 1. A solder bonding method is a solder bonding method using spherical solder and flux when mounting electronic components on a surface of a printed substrate, characterized in that the stomach: a reflow method is used to bond the spherical solder alloy liquid Spherical solder and flux with a phase line temperature that is lower than the solidus temperature of the solder alloy in the solder. 2. The solder bonding method according to claim 1, wherein the liquidus temperature of the spherical solder alloy and the solidus phase temperature of the solder alloy in the flux are at least 11: or more. 3. The solder joint method of claim 2 or 2, wherein the solder alloy used for the spherical solder and the flux has a eutectic composition. 4. The solder bonding method according to any one of claims 1 to 3, wherein the spherical solder is a solder alloy containing Sn-Ag-Cu as a main component, and the solder alloy in the solder is Solder alloy with Sn-Cn-Ni as a main component. ❹ 5 . — A weld seam characterized by the use of any of the methods 1 to 4 of the patent application. -18- 200952587 VII designated representative map: (1) The representative representative of the case is: (1) (2), the representative symbol of the representative circle is a simple description: 1 : BGA package substrate 2 : BGA spherical solder 3 : Flux 4: Printed substrate 8. If there is a chemical formula in this case, please disclose the chemical formula that best shows the characteristics of the invention: