JPH09323189A - Solder paste composition, production of printed circuit board having solder pad, and production of electronic part package circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve packaging yield of a part by not generating solder bridge to a pad having narrow pitch of a printed circuit board mounting a narrow pitch part and forming a solder coated layer having uniform film thickness and composition. SOLUTION: The solder paste composition is a mixture of solder alloy powders having plural compositions different in melting temp. range and an eutectic temp. of 183±10 deg.C or its neighborhood temp. at fusing, further containing a ratio of flux in the total of the solder powder and flux of 10-50wt.%. It is the printed circuit board having a pad and the production method with using the composition. By this method, the productivity is good and cost is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called solder pad solder paste composition, in which a solder coat layer is formed in advance on a narrow-bitch pad of a surface mounting blind printed wiring board, and is formed using this solder paste composition. The present invention relates to a method for manufacturing a printed wiring board having a solder pad and a method for manufacturing an electronic component mounting circuit board using the same.

[0002]

2. Description of the Related Art In electronic equipment, a circuit board on which electronic parts are mounted is used as a part constituting a circuit having one function. To obtain this, a printed wiring board having a circuit wiring pattern is provided with a capacitor and a resistor. Body, QFP, SO
Electronic components such as P are mounted, but these components are soldered and connected and fixed to a copper foil land of the circuit wiring pattern, that is, a pad as a soldering land.
In order to solder electronic parts to the printed wiring board in this way, so-called chip-shaped electronic parts having electrodes at both ends at predetermined locations of the printed wiring board and electronic parts having leads on a flat surface are soldered. The pads are provided, the solder paste is applied to each pad, the electrodes of these electronic components and the leads of the flat surface are positioned on the pads, and temporarily fixed by the adhesive force of the applied solder paste film, and then air reflow, A so-called reflow soldering method is used in which the solder powder of the solder paste film is melted and heated by heating with a reflow device such as IR reflow.

In recent years, technological advances have been made in the fields of computers and communications, especially with the progress of advanced information technology, and electronic devices have been made smaller, lighter and more multifunctional. The technological improvement of electronic parts, especially of semiconductor devices has been remarkably improved, and the recent increase in the number of pins of IC packages and the narrowing of the pitch of their leads are remarkable.
Correspondingly, the surface mounting of electronic components on a printed wiring board is achieved by so-called high density mounting of electronic components at a high density. Some of the surface mounting components have a narrow pitch of 0.3 mm pitch or less. Parts have also appeared, and it is required to solder the narrow pitch leads to the corresponding narrow pitch pads of the electronic circuit board with high precision. When the solder paste is screen-printed on such a narrow pitch pad by using the metal mask which is usually used as described above, when the thickness of the metal mask is large, the supply of the solder paste is likely to be excessive, and the metal If the mask is thin, fading is likely to occur. In the former case, there is a case where the solder paste film is printed across the pads, or there is a case where it is simply protruding the pad, but if reflow soldering is performed without changing it,
A so-called solder bridge, which causes bridging of solder between the pads, causes a short circuit, which is a problem in that a soldering failure occurs.
In the latter case, the soldering strength is insufficient due to the shortage of the amount of solder placed on the pad, which causes a fatal problem such as peeling of the soldered portion from the component. When the leads are placed on the solder paste film printed on the adjacent pad and the weight of the mounted component is added, this solder bridge causes the solder paste film to lose its shape and easily stick out, so that they are easily fused to each other. , It is easy to happen from this point. In particular, it is necessary to volatilize the solvent after applying the solder pes when forming the solder paste film, and also when the mounted component is soldered to the pad on which the solder paste film is formed, the melting temperature of the solder rapidly. In order to avoid the heat stress that occurs in the part when it is heated above 200 ° C, it is preheated to around 150 ° C before heating to the melting temperature of the solder, so it is applied to the pad. In addition, the solder paste is in a state where its shape is likely to be lost due to the decrease in its viscosity and the exudation of the solvent, and the solder bridge is more likely to occur.

In order to improve the problem of solder bridging caused by applying solder paste to the narrow pitch pads as usual and soldering the components, a solder coat layer is previously formed on the pads of the printed wiring board. Form a solder pad in advance, apply flux to the printed wiring board when mounting the component, form a flux film on the solder pad, temporarily fix the lead of the component by its adhesive force, and then reflow A method of heating with an apparatus has been proposed. As a so-called solder precoating method of forming a solder coat layer on this pad in advance,
There are a solder leveler method, an electroless plating method, an electrolytic plating method, and other methods.

[0005]

However, according to the method of (1), a printed wiring board having a pad is coated with a water-soluble flux, and the printed wiring board having the flux film formed thereon is dipped in molten solder to melt the pad. After attaching the solder, hot air is blown onto the printed wiring board to blow off excess solder, and a solder coat layer is formed on the pad.The thickness of the solder layer is controlled by the pressure of hot air. Since a solder coat layer having a uniform thickness cannot be obtained due to a difference in how air is applied to molten solder, the thickness of the solder layer formed on the pad of the same printed wiring board is 25
A variation of about μm may occur. Generally 0.2
When mounting components such as QFP and TCP with a narrow pitch of 5 mm to 0.3 mm, a solder coat layer thickness of at least about 20 μm is required. On the other hand, if the solder coat layer is too thick, the space between adjacent pads will be large. The solder coat layers are easily fused to each other, and even if there is no such fusion, it is likely that the solder coat layers will be fused to each other due to protrusion due to melting at the time of soldering. Further, when the printed wiring board has through holes, solder hole filling inside the printed wiring boards is likely to occur. From this,
For example, when a solder layer having a thickness of about 30 μm is to be formed, a portion having a thickness of 20 μm or less may occur in the solder layer, which causes a decrease in soldering strength, and the thickness is substantially reduced. There is a problem that the solder coat layer cannot be designed. Also, the method of
The printed wiring board is immersed in the electroless plating bath, and the surface of the copper metal of the pad is replaced with solder.Therefore, if the surface of copper is replaced with solder, the deposition rate of solder decreases, As a result, there is a problem that only a solder layer having a thickness of about 1 μm can be formed, a required solder layer thickness cannot be obtained, and a large amount of capital investment is required. In addition, the method is to attach the solder to the pad by electrolytic plating, but since the current density differs depending on the density of the circuit including the pad arranged on the printed wiring board, the density of the circuit is the thickness of the solder, Affects composition. Therefore, there are problems in that the thickness and composition of the solder layer are likely to vary depending on the type of printed wiring board, it is difficult to obtain a constant value, and it is difficult to control soldering performance such as soldering strength. As the method, as described in Japanese Patent Application Laid-Open No. 1-157, a metal having a low ionization tendency, such as lead rosinate, and a metal having a high ionization tendency, such as tin powder, among solder alloy components are used. Although a method using a substitution reaction can be mentioned, there is a problem that a large amount of capital investment is required.

A first object of the present invention is to provide a solder paste composition capable of forming a solder coat layer having a constant thickness and composition on a pad having a narrow pitch so as not to generate a solder bridge, and a printed wiring having a solder pad. It is intended to provide a method for manufacturing a board and a method for manufacturing an electronic component mounting circuit board. A second object of the present invention is a solder paste composition which can be applied even when the method of screen-printing a solder paste on a pad does not have good printing accuracy, and the solder paste film is likely to lose its shape due to heating due to the printing. Provided is a method for manufacturing a printed wiring board having a solder pad and a method for manufacturing an electronic component mounting circuit board. A third object of the present invention is to provide a solder paste composition capable of forming a solder coat layer that has a good electronic component mounting yield, is industrially easily performed, and does not increase the cost, and a printed wiring board having a solder pad. It is to provide a manufacturing method and a manufacturing method of an electronic component mounting circuit board.

[0007]

In order to solve the above-mentioned problems, the present invention provides (1) a solder paste containing a solder powder and a flux, wherein (a) the solder powder has a melting point in a temperature range different from each other. It is a mixture of alloy powders having a plurality of compositions and the mixture has a high liquidus temperature of 227 ° C.
Up to the eutectic temperature of 183 ± 10 ° C. or a temperature in the vicinity of the eutectic temperature at which the solid phase at the time of melting all becomes a liquid phase, and (b) the total of the solder powder and the flux. The present invention provides a solder paste composition in which the proportion of the flux is 10 to 60% by weight. Further, the present invention provides (2) a solder paste containing a solder powder and a flux, wherein (a) the solder powder has a grain size of 5 to 150 μm and alloy powders of different compositions having melting point temperature ranges. And the liquidus temperature of the mixture is up to 227 ° C., and the liquidus temperature at which all the liquid phase is changed from the state of having the solid phase at the time of melting is 1
A eutectic temperature of 83 ± 10 ° C. or a temperature in the vicinity thereof,
(B) The solder paste composition in which the ratio of the flux to the total of the solder powder and the flux is 10 to 60% by weight, (3), the pad with a narrow pitch of a printed wiring board according to claim 1 or 2. Of a printed wiring board having a solder pad for forming a solder coat layer by having a screen printing step of screen printing using the solder paste composition and a step of melting the solder paste film obtained through the screen printing step. Production method,
(4) The pad having a narrow pitch of the printed wiring board is formed.
Or a screen-printing step of screen-printing using the solder paste composition according to 2 and a step of melting the solder paste film obtained through the screen-printing step, thereby having a solder pad on which a solder coat layer is formed. Provided is a method for manufacturing an electronic component-mounted circuit board, which includes a step of reflow-soldering an electronic component on a pad including a pad having a solder coating layer formed on a printed wiring board, thereby manufacturing a circuit board on which an electronic component is mounted. Is. The inventions of (3) and (4) above are "production methods", but they are also methods of using the solder paste composition of the invention of (1) or (2) above. "The method for producing a printed wiring board having" is defined as "a method for using a solder paste composition for producing a printed wiring board having a pad", and in the above (4), "electronic component-mounted circuit board for producing a circuit board having electronic components mounted thereon". Manufacturing method "," method of using solder paste composition for manufacturing circuit board on which electronic components are mounted "
It can also be.

In the present invention, one of the features obtained by the above configurations (a) and (b) is that the surface tension of the molten solder can be lowered in the process of melting the solder paste film when forming the solder pad. However, this makes it possible to reduce solder bridges, as will be apparent from the following principle described with reference to FIGS. 1 to 3. That is, in FIG. 1, 1 and 2 are pads made of copper pieces,
1a and 2a are the molten solder on the pad produced by melting the solder paste film formed on each pad, and 3 is the molten solder bridge formed between the two, and the radius of curvature of the bridge is If R ₁
The distance between the pads 1 and 2 can be approximated to 2R ₁ , but the internal pressure ΔP _B of the molten solder when the bridge is melted is ΔP _B = − (γ when the surface tension of the molten solder is γ. / R _1), and the molten solder in the internal pressure of the bridge portion whereas a negative pressure, the internal pressure [Delta] P _l of the molten solder on the pad, as shown in FIG. 2, the curvature radius of the molten solder and R ₂ Then, ΔP _l = γ / R ₂ and a positive pressure is obtained. From these equations, once the molten solder bridge occurs, the internal pressure of the molten solder in the bridge portion is low and the internal pressure of the molten solder in the pad portion is high, so the molten solder flows from the pad portion to the bridge portion, and the bridge Grow more and more.

Further, paying attention to the cross section of the edge portion of the molten solder that spreads wet on the pad, as shown in FIG. 3, when the radius of curvature of the edge portion is R ₃ , the molten solder of the wet spread portion is Since the internal pressure ΔP _C is a negative pressure ΔP _C = − (γ / R ₃ ), the molten solder in the pad portion tends to spread around the pad. From these equations, the smaller the pitch R ₁ between the pads and the smaller the curvature R _{2 of the} molten solder deposited on the narrower pad, the more likely the bridge is to occur. However, if the surface tension γ of the molten solder is reduced here, the pressure difference between the positive pressure and the negative pressure is reduced, the bridge is less likely to occur, and the generated bridge is easily cut. Further, when the wettability of the molten solder to the pad surface is increased, R ₃ becomes larger, and accordingly, the molten solder in the bridge portion receives a force such that it is torn from its equilibrium state to the pad sides on both sides thereof. Since R ₁ becomes large, the internal pressure ΔP _B of the molten solder in the bridge portion and the internal pressure Δ of the molten solder in the pad portion Δ
The difference in P _l becomes smaller, and the molten solder in the bridge is more likely to be cut. The remaining portion of the cut molten solder bridge is easily absorbed by the molten solder on the pad.
From these things, it is required to reduce the surface tension γ of the molten solder and to improve the wettability to the pad surface, but for the former, the entire liquid phase is changed from the state of having a solid phase. It is conceivable to temporarily reduce the surface tension γ of the liquid phase until that time by widening the temperature range in which the liquid phase and the solid phase coexist, and making all of it against the temperature change when the solder paste film melts. It is conceivable to have a time margin so that the time it takes to melt can be extended. Further, since the surface tension of the molten material of the flux is smaller than the surface tension of the pure molten solder, the surface tension of the mixture can be reduced if the amount of the flux component mixed in the molten solder is large. For the latter, it is conceivable to increase the flux component so that the molten solder wets the pad surface well. With respect to these points, conventionally, for example, 63
Since the eutectic solder of Sn37Pb solidifies at 183 ° C., the molten solder is solidified in a short time, and is solidified while the surface tension of all the molten solder is working, so that a solder bridge is likely to occur. Also, since the amount of flux is less than 10% with respect to the total of solder powder and flux,
From this point as well, the action of the molten solder having a large surface tension becomes dominant, a solder bridge is likely to occur, and the wettability of the molten solder to the pad surface has room for improvement.
The flux has the function of preventing oxidation of the copper surface of the pad, reducing the copper oxide, and bringing molten solder into contact with the clean copper surface. It is clear that the wettability of the molten solder in 1 can be improved.

In the present invention, “having a temperature range of melting point” in the above (a) means having a temperature range of a state in which a solid phase and a liquid phase coexist, and in a state diagram showing a phase change. This is the temperature range between the liquidus line, which is all liquid, and the solidus line, which is all solid. A mixture of alloy powders of two or more different compositions having such a melting point temperature range is used. As the mixture, a liquid phase temperature of 183 ± The composition of the alloy powder to be mixed is selected so as to be “10 ° C.”. For example, when the weight ratio of the solder alloy powder of Sn and Pb is Sn: Pb = 63: 37, it is 18
Since it has a eutectic point of 3 ° C., when the solder alloy powder having the composition before and after the composition is mixed at a predetermined ratio,
The mixture can be brought to the eutectic point at 183 ° C. where it is all solid and all liquid. In the present invention, "the liquidus temperature at which a solid phase is wholly a liquid phase is 183 ± 10 ° C." means that the temperature of the eutectic point is 183 ° C.
In fact, there are slight deviations in the composition, impurities, and differences in temperature control, so
The purpose is to set the temperature to ± 10 ° C including before and after that. When the liquidus temperature is 183 ± 10 ° C. in this manner, the above eutectic solder composition or a composition similar thereto can be obtained in a state where the molten solder is solidified, thereby making the solder metal structure uniform. Therefore, the strength can be strongly maintained. Specific examples of such alloy powders having two different compositions include those listed in Table 1. However, in the case of those listed in Table 1, the alloy powders have melting point temperature ranges corresponding to them. The liquid phase temperature of the mixture is 183 ° C. (eutectic point) (No. 1 to 5) and 176 ° C. (eutectic point) (No. 6). The mixing ratio of these two kinds of alloy powders is determined so that the liquid phase temperature at which all of them become a liquid phase can be set to the temperature described corresponding to each. From Table 1, in the present invention, "the liquidus temperature of the mixture of the solder alloy powder is high up to 227 ° C., and the liquidus temperature at which all the liquidus is changed from the state of having the solid phase at the time of melting is 183 ± 10". A eutectic temperature of ℃ or a temperature in the vicinity thereof can be obtained as a basis. However, "a plurality of solder alloy powders have a liquidus temperature to a solid phase temperature of 224 to
183 [deg.] C. (or melting point temperature range is 7 to 41 [deg.] C.), and another liquidus temperature to solid phase temperature is 227 to 183 [deg.] C. (or melting point temperature range is 20 to 44 [deg.] C.) (the former is No. ．
Nos. 3, 4 and No. 5 and 2), "The difference in the melting point temperature range of a plurality of solder alloy powders is 15 ° C (Table 1
Is 13 ° C. but the range of the same effect is expanded) and is smaller (or the temperature range of the melting point is almost the same) ”. If the difference between the melting point temperature ranges of the plurality of solder alloy powders is small, the difference in melting time is small, and the melts of the two are quickly mixed, so that they are likely to be uniform.

[0011]

[Table 1]

In the present invention, the solder powder preferably has a particle size of 5 to 150 μm. If the particle size is smaller than this, solder balls are likely to be generated, and if it is larger than this, variations in the thickness of the solder layer and the alloy composition ratio are likely to occur.

The "flux" contained in the solder paste composition of the present invention means one that can function as a flux in the state where the solder powder is removed. Means a resin that can be used for flux, such as rosin, rosin ester-based rosin-based derivatives, petroleum resin,
There may be mentioned terpene compounds and other resins.
Additives may be used in combination with this resin for flux,
For example, it is preferable to add at least one of an organic acid salt and an inorganic acid salt of a polyamine such as ethylenediamine or an amine such as cyclohexylamine as a reducing agent (activator). Other activators such as organic acid compounds may be used. A thixotropic agent may be used, and examples thereof include hydrogenated castor oil. A solvent described below can also be used for the flux. The composition of the flux is preferably 40 to 60% by weight of resin for flux, 1 to 5% by weight of activator, 2 to 10% by weight of thixotropic agent, and 30 to 50% by weight of solvent,
The solid content is preferably 50 to 70% by weight. The viscosity of the obtained solder paste is preferably 20 to 200 P _as (Malcol viscometer). In the present invention,
The ratio of the flux to the total of the solder powder and the flux is 10 to 60% by weight. If it is less than this, the amount of the solder powder compounded becomes relatively large, it is easy to form a solder bridge between the narrow-pitch pads, and the solder paste film formed on the pad is melted against the pad surface of the molten solder. The degree of improvement in wettability also decreases,
Further, it becomes difficult to secure the uniformity of the thickness of the solidified solder layer. On the other hand, if it exceeds 60% by weight, the blending amount of the solder powder is relatively reduced, resulting in a film thickness of, for example, 20 μm or less, and the thickness of the solder layer required for soldering strength may not be secured. From these facts, the proportion of the flux in the total of the solder powder and the flux is preferably 20 to 50% by weight. In order to produce the solder paste composition of the present invention, in addition to the solder alloy powder and the resin for the flux, at least a suitable one is selected from glycol ether solvents, alcohol solvents, aromatic solvents, ester solvents and the like. One kind of solvent is used, and other additives such as activator, thixotropic agent, and precipitation separation inhibitor are also used as necessary. However, these flux resins, additives such as activators, solvents, etc. are mixed. A flux is prepared, and the flux and the solder alloy powder are stirred and mixed.

The solder paste composition thus obtained is applied onto a pad of a printed wiring board by printing using a metal mask or the like, dried, or as it is, by a reflow device such as an ordinary air reflow. The solder coat layer may be formed by heating and cooling to obtain a solder pad, but as shown in FIG. 4, the solder paste film is transversely (single letter) across the pads 11, 11 ... May be formed by printing using a metal mask and processed in the same manner. By doing so, not only when the solder paste film is formed across the adjacent pads in the former case, but also in the latter case, the solder paste film between the adjacent pads is formed during the process in which the solder paste film is melted. When a part of the liquid phase becomes a liquid phase and then all become a liquid phase, the solder powder has a temperature range of melting point, so that the solder powder gradually becomes liquid phase, and as a result, the surface tension of the liquid phase is temporarily kept small, Moreover, since there are many flux components, the surface tension of the melt also becomes small, and even if the molten solder between adjacent pads tries to maintain the bridge,
As is clear from the above-mentioned principle, the balance is lost, and the surface tension of the molten solder on the pad is overwhelmingly large, and it is separated and sucked onto the pads on both sides. This occurs each time a liquid phase is generated, and it is possible to prevent or suppress the generation of solder bridges in the solidified state. Then, the molten solder sucked onto the solder pad is cooled in a mixed state where it is entirely in a liquid phase, but this time it is made to have a eutectic solder composition. It can be solidified before and after turning. At this time, since the solder paste contains 10 to 60% by weight of flux, by improving the wettability of the pad surface, the generation of solder bridges and solder balls can be suppressed, and the film thickness of the coating film can be made uniform. It is also possible to secure the uniformity of the thickness of the solder layer that is completed by the property. From these facts, the solder coat layer having an average thickness of 25 μm can be formed even on the pad having a narrow pitch of 0.15 mm, and even in that case, the variation in the film thickness can be made to such an extent that it does not hinder practical use. In this way, a printed wiring board having a solder pad is obtained, and in order to solder the narrow-pitch leads of the electronic component to this, it is not necessary to wash, but generally, after washing, applying flux,
The lead may be temporarily fixed to this, and a normal reflow process may be performed thereafter.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of the present invention will be described with reference to the following examples.

[0016]

【Example】

Example 1 As the solder powder, 33 wt% Sn / Pb = 90/10 (melting point temperature range 31 ° C.) was used as the first solder alloy powder, and Sn was used as the second solder alloy powder in the weight ratio.
A mixed powder in which 67% by weight of / Pb = 50/50 (melting point temperature range: 32 ° C.) is mixed is used. Next, a solder paste having the following composition is prepared. Flux resin (rosin) 25 parts by weight Solvent (glycol ether) 20 parts by weight Activator (cyclohexylamine hydrobromide and succinic acid) 3 parts by weight Thixo agent (hardened castor oil) 2 parts by weight Solder alloy powder (particle size) 10 to 25 μm) Total 50 parts by weight In actual production, the above-mentioned resin for flux, solvent, activator, and thixotropic agent are mixed by stirring in the predetermined parts by weight to produce a flux. The above predetermined parts by weight are mixed by stirring (weight ratio of both: 50; 5
0), a solder paste having a viscosity of 50 _Pas (Malcolm viscometer) is obtained. This solder paste is printed wiring board (using a copper-clad glass epoxy board with a thickness of 1.6 mm) 1
0 on a pad of copper foil of 1 mm x 0.15 mm with a 0.3 mm bitch, using a metal mask of 0.10 mm thickness, as shown in Fig. 4, across the pads 11, 11 ... Printing (single character printing) is performed to form a solder paste film 12 having a film thickness of 100 μm. Next, using an air reflow soldering device, heating was carried out at a peak temperature of 220 to 240 ° C. and a conveyor speed of 80 cm / min, followed by natural cooling. Thus, as shown in FIG. 5, the solder coat layer 13a,
A printed wiring board 14 having a solder pad having 13a ... Was obtained, but the thickness of the solder coat layer on the pad was 40 ± 10 μm (the maximum film thickness portion in FIG. 5) and was uniform. No solder bridge was found between them. Further, when the map of the solder alloy of the solder coat layer was examined by EPMA (X-ray microanalyzer), the Sn / Pb ratio was 63/37, which was the same as the eutectic solder alloy composition.

The solder bridge was not observed in this manner because the solder paste film was heated and melted,
By the time 215 ° C everything is in the liquid phase, the solder powder is the first
The solder powder has a melting point of 31 ° C. and the second solder powder has a melting point of 32 ° C., so that it gradually becomes a liquid phase, and as a result, the surface tension of the liquid phase is temporarily kept small and there is a large amount of flux. The effect of lowering the surface tension due to this also overlaps with this, and as described above, the molten solder between adjacent pads separates and is sucked onto the pads on both sides, and this occurs each time a liquid phase is generated, which causes the solidified state in the solidified state. It is possible to prevent the occurrence of solder bridges. The molten solder sucked onto the solder pad is entirely cooled in a liquid phase and mixed, but since it is made to have a eutectic solder composition this time, it may solidify at 183 ° C. Thus, a uniform eutectic alloy structure can be obtained. At this time, since the solder paste contains 50% by weight of flux, by improving the wettability of the pad surface as described above, it is possible to suppress the occurrence of solder bridges, and the film thickness uniformity of the coating film. As a result, it is possible to secure the uniformity of the thickness of the completed solder layer.

Regarding a printed wiring board having this solder pad, an aqueous cleaning agent (containing a surfactant, alcohol, etc.)
After cleaning the residue of the flux by washing with, the flux is applied, and the electronic component (QFP) of the lead of 0.3 mm pitch is temporarily fastened by holding the lead by the adhesive force of the flux film. The electronic component surface-mounting circuit board was manufactured by performing the reflow process. When the soldering strength of the soldered electronic component was measured, it was at the same level as when a normal solder paste was used. Actually, since the printed wiring board has a pad for soldering on which other mounting components are mounted, after the flux is applied, the component is also temporarily fixed in the same manner, and then the reflow process is performed to perform the actual electronic component. Manufactures surface mount circuit boards. It should be noted that, even with the combinations of the solder alloy powders listed in Table 1, almost the same good results as in Example 1 were obtained.

Comparative Example A eutectic alloy powder having a weight ratio of Sn / Pb = 63/37 (eutectic point 183 ° C.) was used as the solder powder, and the ratio of the solder powder to the liquid flux was 92: 8. A solder paste was manufactured in the same manner as in Example 1, and a printed wiring board having a solder pad was manufactured in the same manner as in Example 1 using this. As a result, the thickness of the solder layer of the solder pad was varied from 10 to 100 μm, and three solder bridges were recognized between the six pads in FIG. 5 and frequently occurred.

[0020]

According to the present invention, a solder paste having a plurality of different compositions having different melting point temperature ranges is used in the solder paste, and the amount of the flux is increased. It is possible to form a solder coat layer having a constant thickness and composition on the pad, and thereby to provide a printed wiring board having a solder pad on which the solder coat layer is formed and an electronic component mounting circuit board using the same. In addition, the printing accuracy is not good with the method of screen printing the solder paste on the pad,
Further, even when the solder paste film is likely to lose its shape due to the heating due to the printing, it is possible to provide the solder paste composition having the above performance. Then, a printed wiring board having a solder pad having a good soldering yield of electronic parts, which is industrially easily performed, and which does not increase the cost, and a solder pad having the solder coat layer formed, and the same are used. An electronic component mounted circuit board can be provided with good productivity and at low cost industrially.

[Brief description of drawings]

FIG. 1 is an explanatory view mainly illustrating a molten solder bridge portion for explaining a solder bridge generation mechanism.

FIG. 2 is an explanatory diagram of molten solder of the pad portion.

FIG. 3 is an AA of FIG. 1 of the wet spread portion of the molten solder.
It is sectional drawing.

FIG. 4 is an explanatory diagram showing a printing step of one step of an embodiment of the method of the present invention.

FIG. 5 is a cross-sectional explanatory view of a printed wiring board having solder pads according to an embodiment of the method of the present invention.

[Explanation of symbols]

 1, 2, 11, ... Pads 1a, 2a Molten solder on pad 3 Melted solder bridge 4 Chip component 10 Printed wiring board 12 Solder paste film 13a, 13a ... Solder coat layer 14 Printed wiring board having solder pad

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Takanori Kakuda 560, Irizen, Irizen-cho, Shimoshinagawa-gun, Toyama Prefecture Toyama Nippon Electric Co., Ltd. In-house (72) Inventor Takao Ohno 16 Sayamagahara, Ima, Saitama Prefecture 2 Tamura Kaken Co., Ltd. (72) Inventor Shoichi Saito 16 Sayamagahara, Iruma-shi, Saitama 2 Tamura Kaken shares In-house (72) Inventor Tomohiko Kasahara 16 Samuragahara, Iruma-shi, Saitama 2 Tamura Kaken Co., Ltd.

Claims (4)

[Claims] 1. A solder paste containing a solder powder and a flux, wherein (a) the solder powder is a mixture of alloy powders having different compositions having a melting point temperature range, and the liquidus temperature of the mixture is high. A liquidus temperature of 183 ± 10 ° C. or a temperature in the vicinity of the eutectic temperature, which is up to 227 ° C. and has a solid phase at the time of melting, and (b) the solder powder and the flux. A solder paste composition in which the proportion of the flux in the total is 10 to 60% by weight. 2. In a solder paste containing solder powder and flux, (a) the solder powder has a particle size of 5
A mixture of alloy powders of different compositions having a melting point temperature range of ˜150 μm and having a high liquidus temperature up to 227 ° C. and having a solid phase upon melting, The liquidus temperature which becomes a phase is 183 ± 1
A solder paste composition having a eutectic temperature of 0 ° C. or a temperature in the vicinity thereof, and (b) the ratio of the flux to the total of the solder powder and the flux is 10 to 60% by weight. 3. A screen printing step of screen printing the pad having a narrow pitch of a printed wiring board using the solder paste composition according to claim 1 or 2, and a solder paste film obtained through the screen printing step. A method of manufacturing a printed wiring board having a solder pad for forming a solder coat layer by including a melting step. 4. A screen-printing step of screen-printing the pad having a narrow pitch of a printed wiring board using the solder paste composition according to claim 1 or 2, and a solder paste film obtained through the screen-printing step. An electronic component is mounted by having a step of reflow soldering an electronic component to a pad including a pad having the solder coat layer formed on a printed wiring board having a solder pad having a solder coat layer formed by having a melting step. A circuit board manufacturing method for manufacturing a circuit board.