JPH0647577A - Solder material and method for joining - Google Patents

Abstract

(57) [Summary] [Purpose] The heat treatment time for raising the melting point of the eutectic solder layer 7a is extremely shortened. [Structure] A semiconductor element 1 having a thin Sn layer 5 formed by vapor deposition or a sputtering method and a die pad 2 having a Pb layer 6 formed thereon are superposed and heated to a temperature equal to or lower than the melting points of the Sn layer and the Pb layer. After forming the eutectic solder layer 7a, the eutectic solder layer is heat-treated for an extremely short time in order to have a high melting point.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder material and a joining method used for joining one member to be joined, such as a semiconductor element, and the other member to be joined, such as a base material.

[0002]

2. Description of the Related Art FIG. 2 is a sectional view showing a structure of a conventional semiconductor device similar to that disclosed in, for example, Japanese Patent Application No. 3-4832. In the figure, 1 is a semiconductor element as one member to be joined, 2 is a base material such as a die pad as the other member to be joined, 3 is these semiconductor element 1 and die pad 2
A three-layer solder for joining and
High melting point of 5Pb-5Sn and thickness of 50μm (305 ℃)
The solder 3a and the 95Pb-5Sn solder 3a are formed on both upper and lower surfaces by plating. For example, the composition is 37Pb-63.
The eutectic solder 3b is made of Sn and has a thickness of 10 μm. Reference numeral 4 denotes a heat block for heating the mounted die pad 2, which is not a part of the semiconductor device.

In such a semiconductor device, the semiconductor element 1
And the die pad 2 are overlapped with each other with the three-layer solder 3 interposed therebetween, and heated in a reducing atmosphere to a temperature of, for example, 200 ° C. which is a melting point of the eutectic solder 3b of 183 ° C. or more and a melting point of the solder 3a of 305 ° C. or less in the heat block 4. , The eutectic solder 3b alone is melted to bond the semiconductor element 1 and the die pad 2 together. Then, by maintaining the above-mentioned temperature of 200 ° C.
Pb and Sn interdiffuse between b and the solder 3a, and solidify when the Sn concentration in the eutectic solder 3b becomes 18% or less, as can be seen from the Pb-Sn system state diagram of FIG.
Then, when the temperature is increased so as to reach a temperature just below the solidus temperature as the Sn concentration decreases, the diffusion rate of Sn is further accelerated. As shown in FIG. 3, finally, the compositions of the solder 3a and the eutectic solder 3b become the same, and the melting point of the three-layer solder 3 becomes higher than that of the eutectic solder 3b in the initial state. Therefore, it is possible to obtain a semiconductor device having a heat resistance higher than the heating temperature of 200 ° C. at the time of joining, in addition to the effect of maintaining the gap by not melting the solder 3a.

The melting point of the three-layer solder 3 is eutectic solder 3b.
And P of the entire three-layer solder determined by the thickness of the solder 3a
It can be determined and controlled by the composition ratio of b and Sn. After that, the semiconductor device is picked up from the heat block 4, a wire bonding step of connecting an electrode (not shown) on the semiconductor element 1 and an external lead (not shown) with a gold wire (not shown), a mold for sealing the semiconductor device. A semiconductor device is completed through various steps such as a resin sealing step.

[0005]

In the conventional semiconductor device as described above, the eutectic solder 3b of the three-layer solder 3 is replaced by the solder 3a.
It is very difficult to control the thickness of the eutectic solder 3b very thinly and accurately because it is formed on the surface of
When the target thickness was 10 μm, the thickness varied from 5 μm to 20 μm, and the thickness tended to become thicker than the target value.
Therefore, there is a problem that the heat treatment time required for raising the melting point of the three-layer solder 3 is not only varied as shown in FIG. Note that FIG. 4 is a diagram showing a simulation result that is well correlated with the actual measurement value.

The present invention has been made in order to solve such a problem, and it is possible to almost eliminate the variation in heat treatment time required for raising the melting point of a two-layer solder and to shorten the heat treatment time itself. An object of the present invention is to obtain a solder material and a joining method for joining a semiconductor device that can be used.

[0007]

A solder material according to the present invention comprises a thin first solder layer formed on one member to be joined by vapor deposition or a sputtering method and another thin member to be joined. A second solder layer having a higher melting point and a larger thickness than the first solder layer.

In the joining method according to the present invention, a step of forming a thin first solder layer on one joined member by vapor deposition or a sputtering method and a melting point higher than that of the first solder layer on the other joined member. And a step of forming a second solder layer having a large thickness, and superposing both members to be joined,
Forming a eutectic solder layer by heating to a temperature equal to or lower than the melting points of the first and second solder layers, and heating the two-layer solder layer including the eutectic solder layer to increase the melting point and And a step of joining the members to be joined.

[0009]

With the solder material of this invention, the first solder layer can be formed thin. According to the joining method of the present invention, since the first solder layer and thus the eutectic solder layer can be formed thin, the high melting point treatment time of the two-layer solder including the eutectic solder layer can be extremely shortened.

[0010]

【Example】

Example 1. The present invention will be described below with reference to an embodiment thereof. FIG. 1 is a cross-sectional view for explaining a process of manufacturing a semiconductor device using an embodiment of the present invention. In FIG. 1A, reference numerals 1, 2, and 4 are the same semiconductor elements, die pads, and heat blocks as in the conventional example. Reference numeral 5 is a first solder layer, for example, a Sn layer of about 1 μm formed on the back surface of the semiconductor element 1 by vapor deposition or sputtering. When the Sn layer 5 is formed by vapor deposition or sputtering in this way, its thickness is 1 μm.
Not only can it be made extremely thin at m
It could be suppressed to about 10%. Reference numeral 6 denotes a second solder layer, for example, a Pb layer having a thickness of 10 μm to 20 μm, for example, 20 μm, which is formed on the surface of the die pad 2 by plating.

In such a semiconductor device, the semiconductor element 1 on which the Sn layer 5 is formed and the die pad 2 on which the Pb layer 6 is formed are overlapped with each other, and the melting point of the Sn layer 5 is 232 ° C. and Pb is Pb in a reducing atmosphere. When the melting point of the layer 6 is 327 ° C. or lower, Pb-
The eutectic temperature in the Sn solder system is heated by the heat block 4 to a temperature of 183 ° C. or higher, for example, 190 ° C. Then,
A reaction occurs between the Sn layer 5 and the Pb layer 6, and a Pb-Sn eutectic solder layer 7a is formed at the interface. More specifically, when the Sn layer 5 having a thickness of 1 μm and the Pb layer 6 having a thickness of 20 μm are heated to 190 ° C., the eutectic solder layer 7a having a thickness of 1 μm is formed as shown in FIG. No. 6 has its thickness reduced from 20 μm to 19 μm (this reduced Pb layer is represented by reference numeral 7b). Since the eutectic solder layer 7a is generated by the mutual diffusion of Pb and Sn, it is extremely thin as 1 μm. After that, heat treatment is performed in the same manner as in the conventional example to further promote the mutual diffusion of Pb and Sn, so that the melting point of the two-layer solder 7 composed of the eutectic solder layer 7a and the Pb layer 7b having the reduced thickness is increased, resulting in high heat resistance. A semiconductor device having properties is obtained. Since the heat treatment time required at this time is uniquely determined by the thickness of the eutectic solder layer 7a, as is apparent from FIG.

Example 2. In the first embodiment, S is added to the semiconductor element 1.
Although the n layer 5 and the Pb layer 6 are provided on the die pad 2, the same effect can be obtained by vice versa.

Embodiment 3. In the first embodiment, the Pb layer 6 is formed by plating, but it may be formed by vapor deposition, sputtering, pressure welding, or the like.

Example 4. In Example 1, Pb was used as the solder layer.
-Sn system was used, but In-Pb system, Pb-Sb system, S
An n-Bi system, a Sn-Au system, etc. are considered.

[0015]

As described above in detail, the solder material of the present invention is formed on one of the members to be joined by a thin first solder layer formed by vapor deposition or sputtering and the other member to be joined. And a second solder layer having a higher melting point and a larger thickness than the first solder layer, and the joining method of the present invention is a thin first layer formed by vapor deposition or sputtering on one member to be joined. Forming a solder layer of
Forming a second solder layer having a melting point and a thicker thickness than the first solder layer on the other member to be joined, and superposing both members to be joined,
Forming a eutectic solder layer by heating the solder layer to a temperature equal to or lower than the melting point of the solder layer, and heating the two-layer solder layer including the eutectic solder layer to increase the melting point and joining both members to be joined. The first solder layer and thus the eutectic solder layer can be thinly formed, and as a result, the high melting point treatment time of the two-layer solder including the eutectic solder layer can be extremely shortened.

[Brief description of drawings]

FIG. 1 is a cross-sectional view for explaining an embodiment of the present invention.

FIG. 2 is a sectional view showing a conventional semiconductor device using three-layer solder.

FIG. 3 is a state diagram illustrating a solidification process of three-layer solder.

FIG. 4 is a graph showing the relationship between the thickness of eutectic solder and the heat treatment time.

[Explanation of symbols]

 1 semiconductor element 2 die pad 5 Sn layer 6 Pb layer 4 two-layer solder 7a Pb-Sn eutectic solder layer

Claims (2)

[Claims] 1. A thin first solder layer formed on one of the members to be joined by vapor deposition or sputtering, and a melting point and a thickness thicker than the first solder layer formed on the other member to be joined. And a second solder layer having the solder layer. 2. A step of forming a thin first solder layer on one of the members to be joined by vapor deposition or a sputtering method, and a step of forming a thin first solder layer on the other member to be joined, which has a higher melting point and a greater thickness than the first solder layer. A step of forming a second solder layer, a step of forming a eutectic solder layer by superposing both members to be joined and heating to a temperature equal to or lower than a melting point of the first and second solder layers; And a step of heating the two-layer solder layer including the solder layer to raise the melting point and joining the both members to be joined together.