JP4046642B2 - Metal materials for electronic parts that prevent whisker generation - Google Patents

Description

【０００９】
【発明の効果】
以上述べた様に、本発明の電子部品用金属材料は、ウイスカによる短絡不良の問題が解消され、メッキ後の成型加工においても必要な曲げ加工性もあり、また地球環境保全に適した電子部品用金属材料を提供することができる。
【図面の簡単な説明】
【図１】Ｓｎメッキ表面に発生したウイスカの一例を示す顕微鏡写真である。
【図２】Ｓｎメッキ層を施した時のＮｉ，Ｃｕメッキ層の厚さとウイスカ発生状況との関係を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a metal material for electronic parts of a semiconductor device.
[0002]
[Prior art]
A lead frame used in a semiconductor device such as a semiconductor integrated circuit or a high-density integrated circuit is manufactured through the following steps. First, after applying a conductive adhesive to a semiconductor mounting portion of a lead frame for a semiconductor device, the conductive adhesive is cured in a baking furnace after mounting a semiconductor element. Next, the electrode part on the semiconductor element and the internal lead part in the lead frame are connected by a bonding wire. Next, in order to protect the semiconductor circuit from the external environment, it is sealed with an epoxy resin. Next, external plating such as solder plating is applied to the external lead portions that are exposed to the outside of the sealing resin connected to the internal leads of the lead frame. The exterior plating is mainly performed to improve the corrosion resistance. Generally, Sn-Pb two-element electrolytic plating coating or solder plating is performed using a molten solder dip device. It is more often used than the melting solder dip device because of the advantage that a Sn—Pb plating layer having a predetermined thickness can be uniformly deposited on the surface of the external lead by a DC power source. For metal materials such as chassis, Sn plating has been performed with an electroplating apparatus for a long time. However, the internal stress in Sn is relaxed and Sn atoms self-diffusion . The two-element solder plating in which Pb is added to Sn is performed for the reason that whisker, which is called a needle-like single crystal, is generated and grows and an electrical short circuit cannot be maintained. Further, after cutting the dam bar holding the resin, it is separated into semiconductor device pieces and cut into a predetermined lead length. Finally, the external lead portion is lead-molded into a predetermined shape such as a gull wing shape or a J shape, thereby completing the semiconductor device.
[0003]
[Problems to be solved by the invention]
Metal materials used for electronic components such as lead frames and chassis used in conventional semiconductor devices include Cu alloys, 42% Ni iron alloys, iron thin plates, Al alloys, etc. with solder plating layers. in use. However, as the actions to promote international environmental conservation in the last few years are steadily becoming necessary, the regulation of Pb contained in the solder plating layer is required, and the development of a plating layer that does not use Pb has become necessary. It is an important issue. Two methods have been studied for the countermeasures. One of them is a so-called Sn—Bi plating layer that uses a Bi component instead of Pb. By using Bi, the melting point is lowered as compared with Sn without using harmful Pb, and plating without generating whiskers can be performed. On the other hand, Bi has poor workability compared to Pb, and thus has a problem of being restricted by bending workability in the forming process after plating. As another countermeasure, there is a diversion technique of the Sn single plating method that has been used for metal materials such as a chassis. This countermeasure has no problem in the above processing due to the flexible nature of Sn. However, as described above, there has been a problem that reliability of use performance is lacking due to a problem that a whisker occurs and causes a short-circuit accident.
[0004]
In view of the above problems, the present inventors have conducted various studies on the Sn plating method for the purpose of providing an electronic component metal material for a semiconductor device that prevents whisker generation. When the Sn plating layer is applied to the surface of the metal for electronic parts, Ni is applied in an amount of 1.0 to 5 μm as a base, and further Cu is applied in an amount of 1.0 to 5 μm. It has been found that further promotion of It was also found that there was no problem with the molding process after plating.
[0005]
[Means for Solving the Problems]
The present invention is configured on the basis of this finding, and the gist thereof is that when a Sn plating layer is applied to the surface of a metal for an electronic component made of an iron alloy of 42% Ni, Ni plating is used as a base at 1.0 to 5 μm, Furthermore, it is a metal material for electronic parts which prevents the generation of whiskers, which is characterized in that Cu plating is performed thereon by 1.0 μm to 5 μm.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the gist of the present invention will be described in detail.
In the present invention, Ni plating is applied to the surface of a metal (or substrate) made of a 42% Ni iron alloy used in a semiconductor device, and a Cu plating base layer is applied thereon, and then Sn plating is applied thereon. Apply. The Ni and Cu plating layers exhibit an effect of suppressing whiskers that are generated and grown from the surface of the Sn plating layer. FIG. 2 shows the relationship between Ni and Cu plating thickness and whisker generation when Sn plating is performed. The Ni layer is 0.5 to 5 μm thick as a base, and the Cu plating layer is 0. When the thickness is less than 5 μm, the effect of suppressing whisker generation is small, and when the thickness exceeds 5 μm, the suppression effect reaches supersaturation, which is economically unnecessary. The numbers in the diagram of FIG. 2 are scores indicating the degree of whisker generation, and are the same as the scores in Table 1 shown in the examples. In the present invention, the reason why the thickness of the Cu plating layer is limited to 1.0 to 5 μm is determined from such experimental results. The upper Sn plating is applied for solder wettability and corrosion resistance of the external leads. The reason for suppressing the occurrence of whisker between the two plating layers is not clear at the present time, but according to the inventor's estimation, by thinly applying Ni and Cu plating to the underlayer of the Sn plating layer, It affects the crystal orientation and grain size of the Sn plating layer, aligns the orientation of whisker that is difficult to grow, or coarsens the crystal grain to lower the grain boundary energy, or promotes the diffusion of Cu plating metal to the Sn plating layer. Thus, there are a number of reasons such as suppressing the generation and growth of whiskers, or improving the adhesion at the interface by a thin plating layer. In addition, by applying the Ni plating layer to the base of the Cu plating layer, the adhesion between the surface of the metal material for electronic parts and the Cu plating layer is enhanced through the Ni plating layer, and something is improved by the increased adhesion. It has the effect of maintaining the whisker-suppressing effect of the Cu plating layer for a long period of time without being easily peeled even when subjected to the impact of.
[0007]
【Example】
Next, examples of the present invention will be described.
Table 1 shows the plating layer after 1000 cycles of -40 ° C to 120 ° C thermal cycles of the metal material for electronic components and the comparative material of the present invention when various plating layers are applied to the metal (substrate) for electronic components. The result of having observed the whisker generation | occurrence | production state on the surface with SEM, and having performed the following scoring is shown.
1; better than Sn-Pb 2; level equivalent to Sn-Pb 3; no problem in practical use, but worse than conventional materials.
4; Applicable to about 100 pins or less 5; Difficult to apply to any device As a result, the metal material for electronic parts of the present invention in which the lower layer is plated with Ni or Cu suppresses the occurrence of whiskers. Further, the comparative material in which the lower layer was plated with Sn alone or excessively thick Cu could not suppress the generation of whiskers.
[0008]
[Table 1]

[0009]
【The invention's effect】
As described above, the metal material for electronic parts of the present invention solves the problem of short circuit failure due to whiskers , has bending workability necessary for molding after plating, and is suitable for global environmental protection. Metal materials can be provided.
[Brief description of the drawings]
FIG. 1 is a photomicrograph showing an example of whisker generated on the surface of Sn plating.
FIG. 2 is a graph showing the relationship between the thickness of Ni and Cu plating layers and the state of whisker generation when an Sn plating layer is applied.

Claims (1)

When subjected to Sn plating layer for electronic components metal surfaces made of 42% Ni iron alloy, Ni and 1.0 5 .mu.m as a base, and characterized in that the further subjected 1.0 Myuemu～5myuemu the Cu thereon Metal materials for electronic parts that prevent whiskers from occurring.

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