JP2000123637A - Lead for electronic component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide performance equal to that of a Pb-Sn alloy plated lead by constituting an inner plating layer formed on a lead base material and an outer plating layer formed on the inner plating layer, and forming one plating layer with an Sn-Ag alloy and the other plating layer with an Sn-Bi alloy. SOLUTION: A lead for an electronic component has an inner plating layer 2 made of an Sn-Bi alloy having specified thickness formed by an electrolytic process on an acid-cleaned copper alloy wire 1 having a specified outer diameter, and an outer plating layer 3 made of an Sn-Ag alloy having specified thickness formed by an electrolytic process. The Sn-Ag alloy and the Sn-Bi alloy have a property mutually diffusing Ag, Bi, and Sn by wire drawing anneal and skin pass operation, the inner plating layer 2 and the outer plating layer 3 laminated up and down have excellent performance in adhesion, solder wettability, color changing resistance, and whisker characteristics, and are effectively used as the lead for an electronic component capable of replacing an Sn-Pb alloy plated lead.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead for an electronic component, and more particularly to a lead for an electronic component suitable as a lead for a wiring of an electronic device or an outer lead of a semiconductor device.

[0002]

2. Description of the Related Art Leads used in electronic components such as diodes, resistors, capacitors, transistors, etc. are, for example, Sn-wires on copper or copper alloy wires.
Pb alloys, that is, those subjected to solder plating are known. In a semiconductor device such as an IC package, a solder plating layer is formed on the surface of an outer lead by an electrolytic method or a dissolving method in order to improve the connectivity with a printed circuit board to be connected. I have.

A lead having such a configuration is characterized by having excellent resistance to thermal oxidation and good solder wettability, and is used for wiring of electronic equipment or mounting of electronic goods on a printed circuit board. This type of lead bonding process has been fully established in the field of electronic components requiring high-density bonding technology.

However, according to the lead having such a solder plating layer formed thereon, the Pb component in the plating layer has a property of being eluted by acid rain or the like.
There is concern about groundwater pollution and, in turn, its effects on the human body.
Therefore, from the viewpoint of environmental protection, there is a tendency that the use thereof is restricted.

For this reason, development of Pb-free Pb-free solder alloys has been progressing in various fields, and a typical example thereof is a lead having an Sn plating layer formed thereon. This lead is a simple material, has good wettability with a Pb-free alloy, and is suitable for strength.

[0006]

However, according to the lead on which the Sn plating layer is formed, there is a great difficulty in that whiskers are easily generated, and it can be said that the characteristics are sufficient as an alternative plating of the Sn-Pb alloy. Absent.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a lead for an electronic component having the same performance as that of a Sn-Pb alloy-plated lead which has been widely used.

[0008]

In order to achieve the above object, the present invention provides a lead base material, an internal plating layer formed on the lead base material, and an internal plating layer formed on the internal plating layer. An internal plating layer and the external plating layer, one of which is composed of a Sn-Ag alloy and the other of which is composed of a Sn-Bi alloy. Is what you do.

As the lead base material, for example, if the target is a lead used for wiring of electronic equipment, copper,
Alternatively, a wire made of a copper alloy or the like is used. The outer lead of a semiconductor device using a lead frame can be used to constitute a lead base material in the present invention, and a tape carrier in which a copper foil wiring pattern and an insulating film are laminated in place of the lead frame is used. It is also possible to apply the present invention to the outer leads of the semiconductor device constituted by this.

The Sn—Ag alloy and the Sn—Bi alloy constituting the inner plating layer or the outer plating layer have a property that Ag, Bi, and Sn are mutually diffused by wire drawing annealing, skin pass processing, and the like. The plating layer formed by laminating these layers on top and bottom has excellent performance in adhesion, solder wettability (solderability), discoloration resistance, and whisker properties, and has a low melting point. Show sufficient attributes.

[0011]

Next, an embodiment of an electronic component lead according to the present invention will be described. FIG. 1 shows a cross-sectional structure of an electronic component lead according to the present embodiment, wherein 1 is a copper alloy wire having an outer diameter of 0.6 mm, 2 is an internal plating layer formed on the copper alloy wire 1, Indicates an external plating layer formed on the internal plating layer 2.

[0012]

Embodiment 1 An inner plating layer 2 of a 3 μm thick Sn—Bi alloy (Bi content: 10% by weight; the same applies hereinafter) is formed on a pickled wire 1 by an electrolytic method. Similarly, an external plating layer 3 of a Sn-Ag alloy (Ag content: 3.5% by weight; the same applies hereinafter) having a thickness of 3 μm was formed by the electrolytic method, and a predetermined lead for electronic parts was obtained.

An organic sulfonic acid-based plating solution is used for forming the inner plating layer 2 and the outer plating layer 3.
Films were formed under the conditions of a current density of 4 A / dm ² and a plating time of 3 minutes.

[0014]

Embodiment 2 In the embodiment 1, the inner plating layer 2 is made of Sn
-Formed by Ag alloy plating, and the outer plating layer 3 is made of Sn
-A lead for a predetermined electronic component was obtained by forming the alloy by Bi alloy plating and further setting the other conditions to the same.

[0015]

2. Prior Art Referring to FIG. 2, a Sn-Pb alloy plating layer 4 having a thickness of 6 .mu.m was formed on a copper alloy wire 1 by an electrolytic method to obtain a conventional lead for electronic parts.

[0016]

REFERENCE EXAMPLE In FIG. 2, a plating layer 4 was formed by Sn plating with a thickness of 6 μm by an electrolytic method to obtain predetermined electronic component leads.

Table 1 shows the characteristic test results of the leads for electronic parts obtained in the above Examples, Conventional Examples and Reference Examples. As test items, adhesion of the plating layer, solder wettability, discoloration resistance, and whisker occurrence frequency were selected.

The adhesion of the plating layer was determined by heating the sample at 350 ° C. for 15 minutes in a hydrogen atmosphere, subsequently heating the sample at 250 ° C. for 2 hours in the atmosphere, and then winding the self-diameter winding layer. The evaluation was based on the presence or absence of peeling.

In the self-diameter winding, one end of a sample is sandwiched between vise and the other end is bent at 90 °, and the sample is fixed at a predetermined position, and the sample is stretched at a predetermined position. Was wound several tens of times around a winding rod. The case where no peeling occurred in the plating layer was evaluated as 1, the occurrence of slight peeling was evaluated as 2, and the occurrence of complete peeling was evaluated as 3.

The solder wettability is determined by MIL-STD-202.
Based on the test method of D-208B, the evaluation was made based on the solder wetting area when the same heat treatment as in the adhesion test was performed in the state of no flux. 90 wet area
% Or less was evaluated as 1, 70 to less than 90% as 2, and less than 70% as 3.

The discoloration resistance was evaluated by the presence or absence of discoloration when the sample was allowed to stand for 10 days in an atmosphere of constant temperature and humidity of 40 ° C./95% RH. evaluated.

The presence or absence of whiskers is determined at 121 ° C./60.
The sample was allowed to stand in a constant temperature and constant humidity atmosphere of% RH for 24 hours, and was confirmed by visual judgment. No occurrence was evaluated as 1, slight occurrence was evaluated as 2, and occurrence was evaluated as 3.

[0023]

[Table 1]

According to Table 1, the lead for an electronic component according to the embodiment was found to be excellent in adhesion of the plating layer, solder wettability, discoloration resistance, and the like.
Regarding the occurrence of whiskers and the occurrence of whiskers, a rating of 1 was obtained at the same level as in the conventional example.

These items are test items for evaluating the characteristics of Sn—Pb alloy plated leads that have long been established in the joining process of electronic components for a long time.
Therefore, in these test items, the test results which are comparable to those of the Sn-Pb alloy plated lead show that the lead according to the present invention is effective as a lead for electronic parts replacing the Sn-Pb alloy plated lead. Means that it can be used. In the case of the lead of the reference example in which the Sn plating layer is formed, the test result of the presence or absence of whisker is poor, and there is a problem in practicality.

[0026]

As described above, according to the lead for electronic parts of the present invention, one of the inner plating layer and the outer plating layer laminated on the lead base material is made of Sn-Ag alloy, The other is made of an Sn-Bi alloy, thereby providing an electronic component lead having characteristics equivalent to those of a Sn-Pb alloy plating lead that has been widely used so far, and its usefulness is great.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an embodiment of an electronic component lead according to the present invention.

FIG. 2 is an explanatory view of a conventional electronic component lead.

[Explanation of symbols]

 1 Copper alloy wire 2 Inner plating layer 3 Outer plating layer

Claims (5)

[Claims] A lead base material, an internal plating layer formed on the lead base material, and an external plating layer formed on the internal plating layer, wherein the internal plating layer and the external plating One layer is Sn-
An electronic component lead comprising an Ag alloy and the other being an Sn-Bi alloy. 2. The electronic component lead according to claim 1, wherein said inner plating layer is made of a Sn—Ag alloy, and said outer plating layer is made of a Sn—Bi alloy. 3. The lead according to claim 1, wherein the inner plating layer is made of a Sn—Bi alloy, and the outer plating layer is made of a Sn—Ag alloy. 4. The electronic component lead according to claim 1, wherein the lead base material is a wire made of copper, a copper alloy, or the like. 5. The semiconductor device according to claim 1, wherein said lead base material is an outer lead of a semiconductor device.
Item 14. An electronic component lead according to any one of the above items.