JPH07273263A - External terminal of electronic component - Google Patents

Abstract

PURPOSE:To obtain a external terminal of electronic components such as an IC which does not cause ICs or other electronic components or a printed wiring board itself to be damaged, makes it difficult to oxidize the external terminal of ICs. and achieves a high-quality solderability. CONSTITUTION:Tin - lead alloy with 61.9%, or higher tin within a melting point of 183-231.9 deg.C or an alloy whose melting point is reduced by adding other metals (for example, bismuth) to tin and lead is coated on the surface of a lead 4 of an IC 1 as an intermediate layer 5 and further tin- lead alloy with 60%, or higher lead within a melting point of 231.9-327.4 deg.C melting at a higher temperature than the melting point of tin or an alloy whose melting point is increased by adding other metals (for example, silver) to tin and lead is coated on the coated surface as an outermost layer 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to solder plating of external terminals such as resin-sealed semiconductor devices, slide switches and connectors.

[0002]

2. Description of the Related Art First, an external terminal of a conventional electronic component will be described with reference to FIGS. In the following description, a resin-sealed semiconductor device (“I
(Abbreviated as “C”) will be described as a representative, but it should be added that the present invention is not limited to the IC. 3 is a partial cross-sectional side view showing an example of a conventional art IC, and FIG. 4 is a partial cross-sectional side view showing another example of a conventional art IC.

As shown in FIG. 3, a conventional IC of this type is used.
After forming the semiconductor integrated circuit, 11 is sealed with a sealing resin 12 so that the plurality of external terminals 13 are led out to protect the semiconductor integrated circuit. These external terminals 13 have a melting point of 183 ° C. or more containing a large amount of tin as a solder layer on the surface of the lead 14 in order to improve solderability when mounted on a printed circuit board or the like.
Of the tin-lead alloy and tin-lead alloy containing 61.9% or more of tin falling within the range of less than 9 ° C and another metal (for example, bismuth) added to the alloy layer and the metal layer of tin to further lower the melting point. Either one of the solder layers 15 was covered.

The solder layer 15 on the surface of the external terminal 13
As described above, the melting point is 183 ° C. to the melting point 231.9.
Because of the low melting point of ° C, when the work is performed at a temperature higher than the melting point of the solder layer 15, the solder layer 15 melts, and the solder layer 15 originally covered with a uniform thickness becomes non-uniform. As a result, the thickness of the external terminal 13 is increased, which causes an undesirable phenomenon in the work process and the quality of the IC.

Therefore, the work process of coating the solder layer 15 on the leads 14 is restricted to be brought after the work exposed to a high temperature higher than the melting point, and it is not possible to freely change the procedure of the manufacturing process. It is possible, and there is a drawback that the work efficiency cannot be improved. Further, there is an idea of forming a metal layer of only lead or tin having a high melting point, but there is a drawback that high quality solderability cannot be obtained when the external terminal is mounted on the printed board.

An IC for the purpose of eliminating these drawbacks is disclosed in, for example, Japanese Unexamined Patent Publication No. 1-1110754, "Resin-sealed semiconductor integrated circuit device". This I
C is shown in FIG. External terminal 13A of this IC 11A
In order to improve the solderability when mounting on a printed circuit board or the like, the lead 14 has a metal layer of tin as a solder layer or a tin-lead alloy containing a large amount of tin on the intermediate layer 16 and a lead layer. The outermost metal layer 17 is covered with a double layer.

[0007]

However, in the structure of the external terminal 13A, since the outermost layer 17 is a lead metal layer, the IC, other electronic components, or the printed wiring board is heated to a high temperature during the soldering process. Have to be exposed to (327.4 ° C or higher), have an unfavorable adverse effect on their quality, and have to work at high temperatures,
It is not preferable in terms of work safety.

Further, it is necessary to control the thickness of each of the intermediate layer 16 and the outermost layer 17. The outermost layer 17
If the lead has a thickness of 90% of the total, the film after melting has a tin content of only 10% at the maximum, has a high melting point, and does not only provide high-quality solderability during mounting. However, a lead oxide film is formed, and the formation of this oxide film is faster than that of solder and is thicker, so that higher quality solderability cannot be obtained. Therefore, it is difficult to obtain a desired ratio of the external terminal of the tin-lead alloy layer at the time of mounting, and there is also a drawback that high quality solderability cannot be obtained at the time of mounting the external terminal 13A on the printed board.

[0009]

Therefore, I of the present invention
C is a tin-lead alloy containing a large amount of tin with a melting point of 183 ° C. or more and a melting point of less than 231.9 ° C. and containing 61.9% or more of tin. (For example,
Bismuth or the like) to lower the melting point of the alloy or an intermediate layer formed of either one of tin and the melting point of tin 23
Higher than 1.9 ° C and melting point of lead 327.4 ° C
A tin-lead alloy with 60% or more lead in the lower temperature range,
Other metals (for example, silver) are added to tin and lead, and the alloy is coated with the outermost layer formed by one of alloys having a higher melting point.

[0010]

Therefore, when this IC is mounted on a printed wiring board, the melting point of the coating layer should be 231.9 ° C. or less after the intermediate layer and the outermost layer coating the external terminals are melted. And high quality solderability can be obtained during mounting. Furthermore, when mounted on a printed wiring board, the melting point of lead is 3
It is possible to work at temperatures below 27.4 ° C.

[0011]

Embodiments of the present invention will be described below with reference to FIGS. 1 is a partial sectional side view of a first embodiment of an IC of the present invention, and FIG. 2 is a second side view of an IC of the present invention.
It is a partial cross-sectional side view of the Example of FIG. In addition, I of the conventional technique
The same components as those of the configuration C will be described with the same reference numerals.

In the IC 1 of the first embodiment, the external terminal 3 led out from the sealing resin 2 is formed on the surface of the lead 4 with a tin-lead alloy of 70% tin and 30% lead having a thickness of about 9 μm. Then, as the intermediate layer 5, a tin-lead alloy of 10% tin and 90% lead was coated on the surface as the outermost layer 6 in a thickness of about 1 μm. The alloy ratio after melting of the tin-lead alloy layers of the intermediate layer 5 and the outermost layer 6 is 64% tin and 36% lead.
% Alloy film with a melting point of 183 ° C to 23
When the temperature falls within the range of 1.9 ° C, a film having excellent solderability can be obtained.

The melting point of the intermediate layer 5 is 183 ° C. or higher 23
Instead of a tin-lead alloy coating containing a large amount of tin of 61.9% or more falling within the range of less than 1.9 ° C, tin, an alloy in which another metal (for example, bismuth) is added to lead to lower the melting point Alternatively, the tin-lead alloy film having the above component ratio may be formed as the intermediate layer 5 and the outermost layer 6 as the film. These middle layer 5 and outermost layer 6
And can be formed by electroplating.

In the IC 1A of the second embodiment, as shown in FIG. 2, the external terminal 3A derived from the sealing resin 2 is provided on the surface of the lead 4 with, for example, a tin metal film having a thickness of 6 μm as an intermediate layer. As a layer 7, a further outermost layer 8 is formed thereon,
At a temperature higher than the melting point of tin 231.9 ° C, the melting point of lead 32
10% tin and 90% lead, which are in the temperature range below 7.4 ° C
Of tin-lead alloy was coated to a thickness of about 4 μm. The alloy ratio after melting of the tin-lead alloy layers of the intermediate layer 7 and the outermost layer 8 becomes an alloy film of 64% tin and 36% lead, and the melting point thereof is in the range of 183 ° C to 231.9 ° C. Upon entering, a good film with excellent solderability can be obtained. The melting point of the outermost layer 8 was lowered by adding another metal (for example, silver) to tin or lead instead of the tin-lead alloy falling within the range of 231.9 ° C to 327.4 ° C. Alloys may be used.

[0015]

As described above, the IC of the present invention
In the external terminal of, the coating layer, including the intermediate layer and the outermost layer, contains a large amount of tin and has a melting point of 183 ° C.
From 231.9 ° C to 231.9 ° C, a tin-lead alloy with a tin content of 61.9% or more, or an alloy layer in which another metal is added to tin or lead to further lower the melting point. When mounted on a printed wiring board, high quality solderability can be obtained without adverse effects such as heating of the IC, other electronic components, or the printed wiring board.

Further, since the outermost layer is not lead, the oxide film is produced slowly and the film thickness is thin. Therefore, when this IC is mounted on a printed wiring board, high quality solderability can be obtained. Similar to the IC of the prior art, the outermost layer does not melt and the surface does not become non-uniform during the work, and the procedure of the work process can be freely changed, so that the work efficiency can be improved. It goes without saying that you can get it.

[Brief description of drawings]

FIG. 1 is a partial sectional side view of a first embodiment of an IC of the present invention.

FIG. 2 is a side view, partly in section, of a second embodiment of the IC of the present invention.

FIG. 3 is a partial cross-sectional side view showing an example of a conventional IC.

FIG. 4 is a partial cross-sectional side view showing another example of a conventional IC.

[Explanation of symbols]

 1 Resin-Encapsulated Semiconductor Device (IC) 1A of First Example 1A Resin-Encapsulated Semiconductor Device (IC) of Second Example 3 External Terminal 3A External Terminal 4 Lead 5 Intermediate Layer 6 Outermost Layer 7 Intermediate Layer 8 Outermost layer

Claims (1)

[Claims] 1. The external terminal of an electronic component has a melting point of 183 ° C.
Is a tin-lead alloy containing a large amount of tin of 61.9% or more falling within the range of less than 231.9 ° C, or an alloy having a melting point lowered by adding another metal (such as bismuth) to tin or lead, or An intermediate layer formed of one of tin and a melting point of tin 23
Higher than 1.9 ° C and melting point of lead 327.4 ° C
A tin-lead alloy with 60% or more lead in the lower temperature range,
An external terminal for an electronic component, characterized in that it is covered with an outermost layer formed by adding tin or lead to another metal (for example, silver) and either one of alloys having a higher melting point.