JPH1052790A - Solder powder and solder paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve printability and solderability by adding a specified quantity of indium into a solder and specifying the grain size. SOLUTION: In this solder powder, by wt., 0.1-5.0%, indium is added into the solder mainly composed of a tin and lead and the grain size is specified to be 10-40μm. And a solder paste is manufactured by mixing the solder powder with a paste-like flux. This solder powder is characterized by the point that the oxidation of the solder powder is restrained to oxidize by adding a suitable quantity of indium. This is reason why the indium is oxidized earlier than the tin and lead mainly composing of the solder. At this time, the system added a third element such as Ag, Sb, Bi, Zn or the like into a Sn-Pb alloy is also effective. By this way, the effect is extremely large for promoting a fine pitch mounting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solder powder having good printability and solderability, and a solder paste produced using the solder powder.

[0002]

2. Description of the Related Art Recent electronic devices are particularly required to be smaller and lighter. However, in order to achieve this, it is essential to reduce the size and weight of the printed circuit board, which is a main component of the electronic device. The idea was to use SMT (Surfase Mounting Tec) to solder the leads of electronic components (LSI, etc.) to the pads provided on the surface of the printed circuit board.
hnorogy = surface mounting technology).

In the SMT mounting method, the mounting density can be improved as compared with the conventional through-hole mounting method. In recent years, this mounting method has been widely used for mounting on printed circuit boards. In this SMT mounting, a reflow method using a solder paste is mainly used.

In this reflow soldering, a solder paste in which cream is formed by kneading a solder powder and a flux is printed on a pad of a printed circuit board by a method such as metal mask printing or screen printing, and electronic components are placed thereon. After mounting, the printed circuit board is heated to the melting temperature of the solder and the solder paste is reflowed to solder the electronic component to the printed circuit board.

Hereinafter, a process of soldering and mounting an electronic component on a printed circuit board using the SMT method will be described. (1) Solder paste manufactured by kneading solder powder and resin (this resin is a rosin-based resin) using a printing plate or the like on the part where the electronic components are mounted on the printed circuit board (hereinafter called the pad) Print.

(2) Position the leads of the electronic component on the pad on which the solder paste is printed. (3) This is heated by batch reflow to melt the solder paste. As a result, the electronic components are mounted on the printed circuit board by soldering.

[0007]

The SMT mounting technique is applied when electronic components are mounted on a fine-pitch type printed circuit board having a small pitch between pads. At present, the mainstream of fine pitch is 0.5 mm (mm). ) With the pitch, a 0.4 mm pitch is beginning to appear. However, it is considered difficult to obtain a fine pitch smaller than that.

[0008] This is because when the pitch between the pads is further reduced, the width of the pads formed on the printed circuit board becomes narrower, and the width of the opening of the printing plate also becomes narrower.
This is because it becomes difficult for the solder powder contained in the solder paste to pass through the opening of the printing plate, and the printability deteriorates.

As means for improving the printability, it is conceivable to reduce the particle size of the solder powder. The idea is "Isn't it necessary to reduce the particle size of the solder powder according to the size of the opening?"

However, since the solder powder has a substantially spherical shape (although not a perfect spherical shape), the volume increases and decreases with the cube of the radius, whereas the surface area increases and decreases with the square of the radius. . Therefore, when the particle size is reduced to, for example, 1/2, the volume reduction rate is 1/8, whereas the surface area reduction rate is 1/4.

This means that the smaller the diameter of the solder powder, the greater the amount of oxidation per unit volume (this is based on the assumption that the thickness of the oxide film is constant). FIG. 3 is a diagram showing the relationship between the amount of oxygen and the particle size of the solder as calculated values.

FIG. 3 shows that, assuming that the oxidized amount of a solder powder having a particle size of 35 μm is 100 ppm, the oxide film thickness becomes 11 ppm.
It shows a value calculated on the condition that it becomes nm (110 °). As is clear from FIG.
At 0 μm or less, the oxygen amount sharply increases. It is well known that the higher the oxygen concentration of the solder powder, the lower the solderability and the higher the degree of occurrence of solder balls. In addition, solder ball refers to the phenomenon that the solder remains in a granular state after soldering,
The quality of the solderability is determined by the degree of occurrence of the solder balls.

An object of the present invention is to provide a solder powder and a solder paste which can be applied to a pad having a fine pitch.

[0014]

The solder powder according to the present invention contains 0.1 to 5.0 watts in a solder containing tin and lead as main components.
It is characterized by adding t% of indium to reduce the particle size to 10 to 40 μm.

[0015] The solder paste according to the present invention comprises:
It is characterized by being manufactured by kneading the solder powder and a paste-like flux. The first feature of the solder powder according to the present invention is that oxidation of the solder powder is suppressed by adding an appropriate amount of indium to a solder containing tin and lead as main components.

The reason that the addition of indium to the solder powder suppresses the oxidation of the solder powder is that this indium is oxidized before tin or lead which is a main constituent material of the solder. . At this time, Sn-Pb
It is also effective for a system obtained by adding a third element such as Ag, Sb, Bi, Zn to a system alloy.

As described above, when the oxidation of indium takes a leading form, the oxide film formed on the surface of indium serves as a barrier to suppress the formation of an oxide film on the surface of tin or lead. . In this case, the oxide film formed on the surface of indium is more fragile than the oxide film formed on the surface of tin or lead. Does not adversely affect sex.

The solder powder has a particle size range of 10
The second feature is that the thickness is set to μm to 40 μm. The reason why the upper limit of the particle size is limited to 40 μm is based on the consideration that the solder powder can easily enter the opening of the printing plate, and the lower limit of the particle size is set to 10 μm. This is based on consideration that the oxidation amount per unit volume of the solder powder does not increase.

An object of the present invention is to provide a solder powder and a solder paste having excellent printability and solderability.

[0020]

FIG. 1 is a view showing one embodiment of the present invention. The "solder paste component" manufactured by changing the particle size of the solder powder and the compounding ratio of indium contained therein is changed. And a diagram showing evaluation results. " The solder powder disclosed in FIG. 1 is composed of a eutectic solder containing 63% of Sn and the balance of Pb.

The "column of items" in FIG. 1 is divided into "Examples" and "Comparative Examples". In Examples 1 to 4, the "particle size of solder powder" is fixed (10 μm to 40 μm). And "In
Of the solder powder was changed in the range of 0.1 Wt% to 5.0 Wt%, and Comparative Examples 1 to 3 show the “particle size of the solder powder” and the “In content” in the above Examples. The evaluation results when different are shown.

In FIG. 1, In indicates the content of indium (Wt%) in the solder powder, Sn indicates the content of tin, and Pb indicates the content of lead. The particle size is the diameter (μm) of the solder powder, and the printability is a percentage of the filling rate of the solder paste filled in the opening of the printing plate (filling rate% =% of the printed paste). (Volume / volume of the opening of the printing plate × 100), and the solderability was determined based on the state of occurrence of solder balls. . The evaluation of the solderability is based on JIS Z 3284 (solder paste).

Example 1 is a solder paste produced by kneading a solder powder having a particle size of 10 to 40 μm to which 0.1 Wt% of indium is added and a paste-like flux. Since the particle size of the solder powder is 10 to 40 μm, this solder paste has a good filling rate of 86%, and the addition amount of indium is 0.1 Wt%.

Example 2 is a solder paste manufactured by kneading a solder powder having a particle size of 10 to 40 μm to which 0.5 Wt% of indium is added and a paste-like flux. Since this solder paste has a particle size of 10 to 40 μm, the filling rate is as good as 83%, and the amount of indium added is 0.5 W.
Since it is t%, the solderability is also good.

FIG. 2 is a diagram showing the effect of inhibiting oxidation by indium, and is a diagram schematically showing the relationship between the temperature and the oxygen concentration in the case where the second embodiment is applied. As is clear from FIG. 2, the oxidation amount of the solder powder rapidly increases when the temperature exceeds 100 ° C.
% Of indium, the rate of increase in the amount of oxidation is suppressed as shown.

Example 3 is a solder paste manufactured by kneading a solder powder having a particle size of 10 to 40 μm to which 2.5 Wt% of indium is added and a paste-like flux. This solder paste has a particle size of solder powder of 10 to 40 μm
Therefore, the filling rate is as good as 85%. Also, since the amount of indium added is an appropriate amount of 2.5 Wt%, the solderability is good.

In the fourth embodiment, since a solder powder having a particle size of 10 to 40 μm to which 5.0 Wt% of indium is added is used, the filling factor is as good as 81% and the solderability is good.
As is clear from the above, in Examples 1 to 4, the amount of indium contained in the solder powder was 0.
1 Wt% to 5.0 wt%, and the particle size of the solder powder is 10
Since the thickness is about 40 μm, both printability and solderability are good.

On the other hand, in the case of Comparative Example 1, 0.5 Wt
% Indium, but the filling rate is not good because the particle size of the solder powder is large. However, in the case of Comparative Example 1, the incidence of solder balls was unexpectedly low. This is probably because the formation of an oxide film was suppressed by indium.

Each of the two examples disclosed in Comparative Example 2 was 0.05
Wt% indium was added, one of which had a particle size of 10 to 40 μm. The printability (filling rate) of the particles having a particle size of 10 to 40 μm is as good as 86%, but the solderability is not good. This is because the amount of indium added is 0.1 Wt%
It seems to be due to too little below.

The other of Comparative Example 2 has poor printability and poor solderability. This is presumably because the particle size is too large, 40 to 60 μm, and the amount of indium added is too small at 0.1 Wt% or less.

In each of the two examples disclosed in Comparative Example 3, no indium was added.
4040 μm. The printability (filling rate) of the particles having a particle size of 10 to 40 μm is as good as 83%, but the solderability is not good. This is presumably because indium was not added, and the oxidation concentration of the solder powder was increased.

The other of Comparative Example 3 has poor printability and poor solderability. This is because the particle size is too large, 40 to 60 μm, and indium is not added to the solder powder.

The first feature of this solder paste is that the solderability is improved by adding an appropriate amount of indium to the solder powder, and the particle size of the solder powder is in the range of 10 to 40 μm. The second feature is that the printability is improved by setting the inside.

[0034]

As is clear from the above description, the solder paste according to the present invention has the effect of suppressing the oxidation concentration by adding an appropriate amount of indium to the solder powder, and the filling rate by controlling the particle size of the solder powder. The printability and the solderability are improved by the synergistic effect of the improvement effect, and the effect is extremely large in promoting the fine pitch mounting.

[Brief description of the drawings]

FIG. 1 is a diagram showing components of a solder paste and evaluation results.

FIG. 2 is a graph showing the effect of inhibiting oxidation by indium.

FIG. 3 is a diagram showing a relationship between an oxygen amount and a solder particle size.

Claims (2)

[Claims] 1. A solder containing tin and lead as main components.
To 5.0 wt% of indium, and the particle size is 10 to 40%.
Solder powder characterized by having a size of μm. 2. A solder containing tin and lead as main components.
Particle size of 10 to 40 to which 5.0% by weight of indium is added.
A solder paste produced by kneading a μm solder powder and a paste-like flux.