JP2539445Y2 - Printed board - Google Patents

Description

[Detailed description of the invention] [Industrial application field] This invention uses reflow soldering equipment, etc.
The present invention relates to a printed circuit board to which a surface-mount type electronic component is attached using paste solder in which low-melting-point solder particles and high-melting-point solder particles are mixed at a predetermined mixing ratio.

[Prior Art] In a hybrid IC or the like, in order to increase the mounting density, electronic components mounted on an IC substrate tend to use light, thin and small surface mount components such as chip capacitors. .

In addition, there are various sizes of surface mount components, and even the same electronic component has various sizes.

In order to mount such a surface mount component, a reflow soldering apparatus is usually used in many cases.

This is because the surface mount component 1 is temporarily fixed between the conductive layers 6 and 7 formed on the predetermined printed circuit board 5 by the paste solders 8 and 9 as shown in FIG. The printed circuit board 5 is transferred into a reflow furnace (not shown).

As the paste solders 8, 9, for example, Sn-Pb eutectic solder (melting point: 183 ° C.) is used.

When the printed circuit board 5 passes through the high-temperature atmosphere (reflow temperature of 183 ° C. or more) in the reflow furnace, the paste solders 8 and 9 are melted, and the printed circuit board 5 is cooled by subsequent conveyance. As a result, the melted solder is solidified and the surface mount component 1 is joined to the printed circuit board 5.

[Problem to be Solved by the Invention] By the way, when the surface mount component 1 is mounted on the printed circuit board 5 using the reflow soldering device as described above, the component 1 passes through a high-temperature atmosphere in the reflow soldering device. Not all surface mount components 1 always show a uniform temperature distribution.

This is because the shape, size, etc. of the electronic components to be mounted vary, and small surface-mounted components, etc., adjacent to a large surface-mounted component are affected by this large surface-mounted component, and the left and right of the same component are affected. This is because, even between the electrode portions 3 and 4, a temperature difference may occur.

If there is a difference in temperature, the paste solder
Naturally, the melting states of 8 and 9 are also different, which means that even when the paste solder on the high temperature side is completely melted, the other paste solder is not completely melted temporarily.

Thus, for example, when the left-side paste solder 8 is completely melted and the right-side paste solder 9 is in an incompletely melted state, the completely melted solder 8 side has a lower surface tension of the solder 8 than the other side. The effect is increased.

The effect of the surface tension is expressed as a difference in the moment (vertical component of the rotational moment) in the height direction between the two electrode portions 3 and 4 as shown by the arrow in FIG. The moment applied to the electrode part 3 is much larger than the moment applied to the incompletely fused electrode part 4 side.

This causes a so-called Manhattan phenomenon in which the surface mount component 1 rises as shown in FIG.

The Manhattan phenomenon is more likely to occur because the effect of the surface tension of the solder on the weight of the component increases as the size of the component decreases.

In today's electronic components, there is a tendency to reduce the size of the components themselves in order to improve the packaging density, and therefore, it can be said that the conditions are such that the Manhattan phenomenon easily occurs.

In addition, the vapor phase soldering method (VPS method), which has been recently developed
In this case, the Manhattan phenomenon is particularly likely to occur, which is a major problem.

Poor bonding due to the Manhattan phenomenon is a factor that significantly reduces the yield and reliability of reflow soldering.

Also, for surface mount electronic components such as chip-type ceramic capacitors, which also have external electrodes on the side surfaces of the components, if the solder on one of the electrodes first heats up and melts, the electrodes on the side will become wet with the solder. In some cases, the moment due to the surface tension of the solder acts in the lateral direction, causing the components to shift laterally. This also causes poor bonding, similar to the Manhattan phenomenon.

Furthermore, in an atmosphere heating method such as a VPS method,
When reflow-bonding an IC that has surface-mount leads, the temperature of the lead with a smaller heat capacity rises first than that of the printed circuit board, creating a temporary temperature difference between the printed circuit board and the leads. . In this case, as a property of the molten solder, there is a property of moving to a higher temperature, and from the joint portion between the lead and the printed circuit board, the molten solder may migrate to the lead portion and cause a joint failure. . This phenomenon is called a wicking phenomenon.

In order to prevent the Manhattan phenomenon and eliminate soldering defects, it is conceivable that the paste-like solder is not composed only of solder particles of one composition, but is mixed with solder particles of another composition having different melting points.

This is because the effect of the surface tension during the melting of the solder particles having different melting points does not become too large based on the mixing ratio, and it is considered that the Manhattan phenomenon or the like is unlikely to occur.

However, when there is a temperature difference between the left and right electrodes of the component due to the components placed on the printed circuit board, and when the low melting point solder in the higher temperature electrode melts out first, The same phenomenon as described above may occur.

In view of this, the present invention proposes a printed circuit board that does not cause such a rising (Manhattan) phenomenon, a lateral displacement, and a wicking phenomenon of the surface-mounted component.

[Means for Solving the Problems] In order to solve the above-mentioned problems, in the present invention,
A predetermined amount of two kinds of solder particles, a high melting point solder particle melting at a temperature higher than the reflow temperature and a low melting point solder particle melting at a temperature lower than the reflow temperature, and a liquid flux or the like are mixed in a predetermined amount. The average particle size of the high melting point solder particles is made larger than the average particle size of the high melting point solder particles, and the mixing ratio of the low melting point solder particles to the high melting point solder particles is 20% to 80%. The electronic component is mounted on a printed circuit board.

[Operation] The average particle size of the high melting point solder particles 10b is selected to be close to or smaller than the average particle size of the low melting point solder particles 10a.

Then, the low melting point solder particles 10a are melted first before reaching the reflow temperature, and the high melting point solder particles 10b are slightly diffused into the molten solder by this melting (FIG. 7).
A, B).

When the temperature reaches the reflow temperature, the high-melting-point solder particles 10b begin to melt due to metal diffusion, even if the melting point of the high-melting-point solder particles 10b or less. In this case, since the average particle size of the high melting point solder particles 10b is close to or smaller than the average particle size of the low melting point solder particles 10a, they are almost completely diffused (FIG. 7C).

With such a particle size, low melting point solder particles 10
As a melts, the high-melting-point solder particles 10b can be reliably diffused even at a temperature lower than the temperature at which the high-melting-point solder particles 10b melt.

[Example] Subsequently, an example of the paste solder according to the present invention is described below.
A case in which a surface mount component is mounted on a printed circuit board using a reflow furnace as an example applied to the soldering of the surface mount electronic component described above will be described in detail with reference to FIG.

Also in this invention, as shown in FIG. 1, the surface mount components 1 mounted on predetermined conductive layers 6 and 7 formed on the printed circuit board 5 are joined by the paste solders 10 and 11. Thus, a substrate device is configured.

In the present invention, a special solder as shown below is used as the paste solder for joining the surface mount component 1.

That is, in the present invention, as shown in FIG. 2, the paste solder 10 (11) is composed of the low melting point solder particles 10a, the high melting point solder particles 10b, and the liquid flux 12.

The average particle size of the high melting point solder particles 10b is selected to be close to or smaller than the average particle size of the low melting point solder particles 10a, and these solder particles 10a and 10b are uniformly dispersed and mixed using the liquid flux 12. When the high melting point solder particles 10b are selected to have a particle size of about 1/5 of the low melting point solder particles 10a, the state is as shown in FIG.

Although the solder particles 10a and 10b may be simply mixed, in this example, the high-melting-point solder particles 10b are uniformly attached to the outer periphery of the low-melting-point solder particles 10a as described later, so that both are evenly distributed in the liquid flux 12. The production method has been devised in order to disperse them into a mixture and to ensure that the mixing ratio of the two is as set.

Specific examples of the low melting point solder particles 10a and the high melting point solder particles 10b that can be used in the present invention will be described below.

The level of the melting point of each solder constituting the paste solder 10 differs depending on the reflow temperature and is relative.

FIG. 3 shows an example. Here, (1) Composition of solder A: high melting point solder particles 10b: Sn 100% low melting point solder particles 10a: eutectic solder As is well known, eutectic solder has a composition of 63 wt% of Sn and 37 wt% of Pb (hereinafter abbreviated as wt%). It is.

(2) Composition of solder B: high melting point solder particles 10b: Sn95 / Pb5 low melting point solder particles 10a: eutectic solder (3) Composition of solder C: high melting point solder particles 10b: Sn85 / Pb15 low melting point solder particles 10a: common (4) Composition of solder D: High melting point solder particles 10b: Sn75 / Pb25 Low melting point solder particles 10a: Eutectic solder (5) Composition of solder particles E: High melting point solder particles 10b: Eutectic solder Low melting point solder particles 10a: Low-temperature solder As the low-temperature solder, for example, Sn43 / Pb43 / Bi14-based low-temperature solder can be used.

FIG. 3A shows the relationship between the liquidus temperatures (indicated by white circles) when the above five types of paste solders are used, and FIG. 3B shows the relationship between these paste solders and the bonding failure rate.

In the liquidus temperature in FIG. A, the white circle on the upper side indicates the melting point of the high melting point solder particles 10a, and the white circle on the lower side indicates the melting point of the low melting point solder particles 10a.

The case where the reflow temperature is 215 ° C. (shown by a broken line) is exemplified. At this reflow temperature, the solders A and B contain solder particles having a high melting point and a low melting point with respect to the reflow temperature, so that at this reflow temperature, the paste solders A and B according to the present invention are obtained.

Therefore, when the reflow temperature is about 190 ° C., the solders A, B, C, and D belong to the category of the present invention. When the reflow temperature is about 178 ° C. (shown by broken lines), only the solder E is the paste-like solder according to the present invention. It belongs to the category of.

 In the figure, the case where the solder F is only the eutectic solder is shown.

The curve shown in FIG. 3B represents the defective bonding rate of the solder in which the mixing ratio of the low melting point solder particles 10a and the high melting point solder particles 10b is selected to be 1: 1. The chip type electronic component used is a 1608 type multilayer ceramic capacitor. When the bonding defect rate exceeds 0.2%, there is a practical problem. Preferably, it is 0.05% or less.

FIG. 4 shows the use of solder B in which the mixing ratio of the low-melting-point solder particles 10a and the high-melting-point solder particles 10b was selected to be 1: 1. At a reflow temperature of 215 ° C., the low-melting-point solder particles 10a and the high-melting-point solder particles were used. It is a characteristic curve when the joint failure rate is measured while changing each particle diameter of 10b.

As is clear from this characteristic diagram, in order to secure a bonding failure rate of 0.2% or less, the average particle size of the high melting point solder particles 10b must be close to or smaller than the average particle size of the low melting point solder particles 10a. There is.

This is because if the average particle size of the high melting point solder particles 10b becomes large, it takes some time to diffuse,
This is because the high-melting-point solder particles 10b do not completely diffuse into the molten low-melting-point solder, and are unlikely to be in a completely molten state.

However, if the average particle size of the high melting point solder particles 10b is close to or smaller than the average particle size of the low melting point solder particles 10a,
The probability of complete metal diffusion increases.

FIG. 5 shows the relationship between the mixing ratio of the low-melting-point solder particles 10b to the high-melting-point solder particles 10b when the reflow temperature is selected to be 215 ° C. and the bonding failure rate.

In this case, B is used as the paste solder, and a multilayer ceramic capacitor is used as the electronic component as described above. The average particle size at this time is 50 μm for the low melting point solder particles 10 a and 10 μm for the high melting point solder particles 10 b.

As is clear from this figure, in order to suppress the bonding failure rate to 0.2% or less, the mixing rate of the low melting point solder particles 10a is set to 20 to 80.
%. In particular, it can be understood that about 40% to 50% is preferable for reducing the content to 0.05% or less.

FIG. 6 is also a characteristic diagram similar to FIG. 5, and shows the relationship of the bonding failure rate at a reflow temperature of 178 ° C. The solder used was E. In this figure, a mixing ratio of 30 to 70% may be used to secure a bonding failure rate of 0.05% or less.

As described above, while being composed of two kinds of solders having different melting points, the average particle diameter of the high melting point
When the surface mount component 1 is soldered as shown in FIG. 1 using a paste-like solder 10 having a mean particle size close to or smaller than the average particle size 0a, the surface of the printed circuit board 5 is subjected to a process as shown in FIG. The mounting component 1 is joined.

First, let it pass through the reflow furnace in a high temperature atmosphere,
In the paste solder 10 (for example, solder B) in FIG. A, low-melting-point solder particles 10a are first melted as shown in FIG.

As described above, when the electrode portion 3 is melted first, a slight surface tension acts on the electrode portion 3 due to the melting. However, since the effect of the surface tension is very weak, the surface mount component 1 hardly rises up or slides.

When the temperature of the printed circuit board 5 further increases, a part of the high-melting-point solder particles 10b of the electrode portions 3, 4 also diffuses into the metal, and both the electrode portions 3, 4 are lightly joined.

When the printed circuit board 5 is transported to the reflow area (main heating area) of the reflow furnace, the ambient temperature has increased to a predetermined reflow temperature.

Therefore, the high melting point solder particles 10b are completely diffused into the metal (C in FIG. 3), and the electrode portions 3 are completely joined by the paste solder 10.

By the way, as shown in FIG. 8A, in order to attach the high melting point solder particles 10b to the outer periphery of the low melting point solder particles 10a, for example, the low melting point solder particles 10a are positively charged as shown in FIG.
The high melting point solder particles 10b may be negatively charged and mixed in a semi-molten state. Then, both are attracted by the electric force, and the two are brought into a connected state as shown in FIG. 8A.

FIG. 9 shows an example of the manufacturing apparatus 20 for that purpose.
24 is a feed pipe for the high melting point solder 16, and 22 is a low melting point solder 18
The inner diameters of the nozzles 22a and 24a formed at the respective leading end portions are selected to values described later.

Air nozzles 28 and 30 for air injection are provided near the nozzles 22a and 24a, respectively, so that the molten solder exiting the nozzles 22a and 24a is scattered as solder particles. Accordingly, the low melting point solder 18 scatters as the low melting point solder particles 10a, and the high melting point solder 16 scatters as the high melting point solder particles 10b.

Then, using the charger 26, the nozzle 22a is positively charged, and the nozzle 24a is negatively charged. as a result,
The low melting point solder particles 10a become positively charged particles and the high melting point solder particles 10b become negatively charged particles.
If the 2a and 24a are opposed to each other with a predetermined gap as shown in the figure, the scattered semi-molten solder particles 10a and 10b attract each other by their own electric force (Coulomb force), and FIG. A is obtained as in A, and then solidifies in this state.

When a liquid flux is mixed with the mixture, a paste solder 10 as shown in FIG. 2 is obtained. In addition, although the above described the method of mixing the low melting point solder particles 10a and the high melting point solder particles 10b by electric force (Coulomb force),
The same effect can be obtained by simply mixing.

[Effects of the Invention] As described above, in the present invention, the use of a solder having a high melting point and a solder having a low melting point with respect to the reflow temperature and the appropriate selection of the particle size reduce the probability of causing a joint failure. It decreases significantly.

Therefore, if this paste-like solder is used for a mounting board for a surface-mounted component as described above, the Manhattan phenomenon, lateral displacement, wicking phenomenon, and the like of the surface-mounted component can be reliably eliminated.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a main part showing an example of a substrate device to which a surface-mounted electronic component is fixed using the paste solder according to the present invention, FIG. 2 is an explanatory view of the paste solder according to the present invention, FIG. 3 to FIG. 6 are characteristic diagrams for explaining the operation,
FIG. 7 is a view showing a joining process of the paste solder, FIG. 8 is a view showing a relationship between the low melting point solder particles and the high melting point solder particles,
FIG. 9 is a view of the manufacturing apparatus, FIG. 10 is a view showing the relationship between the surface mount component and the printed board, and FIG. 11 is a view showing the occurrence of the Manhattan phenomenon due to the conventional paste solder. 1 ... Surface mount component 3,4 ... Electrode part 5 ... Printed circuit board 6,7 ... Conductive layer 10,11 ... Solder paste 10a ... Low melting point solder particles 10b ... High melting point solder particles 12 ... Liquid flux

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takashi Usaba 1-112-18 Iizuka, Kawaguchi-shi, Saitama Aiwa Corporation Kawaguchi Center (72) Inventor Shigemi Yokoi 2--20-11 Yokokawa, Sumida-ku, Tokyo In Tartin Co., Ltd. (72) Inventor, Policy Oki 2-20-11 Yokogawa, Sumida-ku, Tokyo Tartin Co., Ltd. (56) References JP-A 1-271094 (JP, A) JP 1-2241395 (JP, A) JP-A-2-117794 (JP, A)

Claims (1)

(57) [Scope of request for utility model registration] 1. A predetermined amount of two kinds of solder particles, a high melting point solder particle melting at a temperature higher than the reflow temperature, a low melting point solder particle melting at a temperature lower than the reflow temperature, and a liquid flux or the like are mixed. A paste wherein the average particle size of the low melting point solder particles is larger than the average particle size of the high melting point solder particles, and a mixing ratio of the low melting point solder particles to the high melting point solder particles is 20% to 80%. Printed circuit board on which electronic components are mounted using solder solder.