JP2000123636A - Lead for electronic component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide performance equal to that of a Sn-Pb alloy plated lead by constituting a plating layer formed on a lead base material with a bed layer of Sn and an outer layer of Sn-Ag alloy. SOLUTION: A lead for an electronic component has a plating layer 2 formed on an acid-cleaned wire 1 made of copper alloy having a specified outer diameter. The plating layer 2 is constituted with a bed layer 3 of Sn plating, having specified thickness, formed by an electrolytic process, and an outer layer 4 of Sn-Ag alloy plating on the bed layer 3, formed by an electrolytic process. The Sn-Ag alloy for constituting the outer layer 4 contains a very small amount of Ag and forms the outer layer 4 so as to have specified thickness. Adhesion, solder wettability, color changing resistance, and whisker producing resistance of the plating layer are enhanced, and as the lead for an electronic component capable of replacing the Sn-Ag alloy plating lead, excellent characteristics is developed and is effectively usable. Since the amount of Ag used is very small, there is no economical disadvantage.

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-P wires made of copper or copper alloy wires.
An alloy b, that is, one subjected to solder plating is known. In a semiconductor device such as an IC package, a solder plating layer is formed on an outer lead surface by an electrolytic method or a dissolving method.

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 is completely established in the field of electronic components that require 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.
For this reason, there is a tendency that its use is restricted from the viewpoint of environmental protection.

For this reason, the development of Pb-free solder alloys has been actively promoted in various fields. In the development, it is necessary to give sufficient consideration to economics without being biased only to the characteristic surface. A representative example proposed from these viewpoints is a lead having an Sn plating layer formed thereon. This lead is a simple material system.
It has good wettability with b-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.

Accordingly, an object of the present invention is to provide a lead for electronic parts which has the same performance as Sn-Pb alloy-plated leads which have been frequently used in the past and which is economically advantageous.

[0008]

In order to achieve the above object, the present invention comprises a lead base material and a plating layer formed on the lead base material, wherein the plating layer is formed of Sn
And a lead for an electronic component characterized by comprising an underlayer and an outer layer of a Sn-Ag alloy.

As the lead base material, for example, if the target is a lead or the like used for wiring of electronic equipment,
A wire made of copper or a copper alloy 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. The present invention can be applied to the outer lead at that time.

The content of Ag in the above-mentioned Sn-Ag alloy may be minute, for example, about several percent is sufficient. The thickness of the outer layer made of the Sn-Ag alloy is S
For example, about one hundredth of the n underlayers is sufficient. Therefore, there is no concern about an increase in the economic burden due to the use of Ag.

[0011]

Next, an embodiment of an electronic component lead according to the present invention will be described.

1 shows a cross-sectional structure of an electronic component lead according to an embodiment, wherein 1 is a wire made of a copper alloy having an outer diameter of 0.6 mm, and 2 is formed on a pickled wire 1. 2 shows a plated layer that has been applied.

The plating layer 2 is composed of a 6 μm thick Sn plating base layer 3 formed by an electrolytic method,
And an outer layer 4 of Sn-Ag alloy plating formed by an electrolytic method. S constituting outer layer 4
The n-Ag alloy contains 3.5% by weight of Ag, and the outer layer 4 is formed to a thickness of 0.05 μm.

[0013]

2. Prior Art In FIG. 2, the thickness of the Sn-Pb alloy was 6 mm.
A μm plating layer 5 was formed by an electrolytic method to obtain a predetermined electronic component lead.

[0014]

REFERENCE EXAMPLE Referring to FIG. 2, a plating layer 5 was formed by a 6 μm thick Sn plating by an electrolytic method to obtain a predetermined lead for an electronic component.

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. The evaluation was based on the presence or absence of peeling.

In the self-diameter winding, one end of a sample is sandwiched between vice 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 for 24 hours in an atmosphere of constant temperature and humidity of% RH, and was visually confirmed. No occurrence was evaluated as 1, slight occurrence was evaluated as 2, and occurrence was evaluated as 3.

[0021]

[Table 1]

According to Table 1, the lead for an electronic component according to the embodiment shows that the adhesion of the plating layer, the solder wettability, the discoloration resistance,
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 suitable for evaluating the excellent characteristics of Sn—Pb alloy plating leads that have long been established in the joining process of electronic components for a long time. , Sn-Pb
The fact that the test result is comparable to that of the alloy plating lead means that the lead according to the present invention can be effectively used as a lead for electronic parts replacing the Sn-Pb alloy plating lead. . Ag used
Is very small and is not economically disadvantageous.

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.

[0025]

As described above, according to the lead for electronic parts of the present invention, the plating layer formed on the lead base material is composed of the underlayer formed by Sn plating and the outer layer formed by Sn-Ag alloy plating. By doing so, it is possible to provide an electronic component lead having characteristics equivalent to those of a Sn-Pb alloy plating lead that has been frequently used in the past, and having no economic disadvantage, 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]

 DESCRIPTION OF SYMBOLS 1 Wire 2 Plating layer 3 Underlayer 4 Outer layer

Continued on the front page (72) Inventor Osamu Yoshioka 3550 Kida Yomachi, Tsuchiura-shi, Ibaraki F-term in System Materials Research Laboratories, Hitachi Cable, Ltd. F-term 4E353 AA11 EE01 EE13 GG15 GG16 GG29 5G307 BA04 BB02 BC02 BC06

Claims (4)

[Claims] 1. A lead base material and a plating layer formed on the lead base material, wherein the plating layer comprises a Sn underlayer and an Sn-Ag alloy outer layer. For electronic components. 2. The method according to claim 1, wherein the outer layer is mainly composed of Sn and is formed thinner than the underlayer.
The electronic component lead according to the item. 3. The electronic component lead according to claim 1, wherein said lead base material is a wire made of copper, a copper alloy, or the like. 4. The electronic component lead according to claim 1, wherein the lead base material is an outer lead of a semiconductor device.