JP4307038B2 - Method for producing metal material for electronic parts which prevents whisker generation during use - Google Patents
Method for producing metal material for electronic parts which prevents whisker generation during use Download PDFInfo
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- JP4307038B2 JP4307038B2 JP2002267387A JP2002267387A JP4307038B2 JP 4307038 B2 JP4307038 B2 JP 4307038B2 JP 2002267387 A JP2002267387 A JP 2002267387A JP 2002267387 A JP2002267387 A JP 2002267387A JP 4307038 B2 JP4307038 B2 JP 4307038B2
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- plating
- electronic parts
- metal material
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
- H01L2924/0001—Technical content checked by a classifier
- H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
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- Other Surface Treatments For Metallic Materials (AREA)
- Lead Frames For Integrated Circuits (AREA)
Description
【0001】
【発明の属する技術分野】
本発明は、使用時のウイスカの発生を防止した電子部品用金属材料の製造方法に関するものである。
【0002】
【従来の技術】
半導体集積回路、高密度集積回路などの半導体装置に使用されるリードフレームは、次のような工程を経て製造される。先ず半導体装置用リードフレームの半導体搭載部に導電性接着剤を塗布した後、半導体素子を搭載した後に導電性接着剤をベーク炉で硬化させる。次に、ボンディング線で半導体素子上の電極部とリードフレームにおける内部リード部を接続する。次に半導体回路を外部環境から保護するため、エポキシ樹脂で封止する。次にリードフレームの内部リードと接続している封止樹脂の外部に出ている外部リード部に半田めっき等の外装めっきを施す。外装メッキは、主に耐食性向上のために行うもので、一般的にはSn−Pb二元素の電解メッキ塗装または、溶融ハンダディップ装置を用いてハンダメッキが施されるが、電解メッキ装置は、溶融ハンダディップ装置よりも、直流電源により外部リード表面に所定の厚さのSn−Pbメッキ層を均一に析出させやすい利点から多く使用されている。シャーシなどの金属材料に対しても以前から電解メッキ装置で、Snの単独メッキがおこなわれていたが、Sn中の内部応力が緩和されてSn原子が自己拡散し、図1で示すひげ結晶と呼ばれる、針状の単結晶であるウイスカが発生、成長し、電気的な短絡を起こして信頼性を保持できない理由からSnにPbを添加した二元素のハンダメッキがおこなわれている。さらに樹脂を堰きとめているダムバーを切断した後、半導体装置個片に分離し、所定のリード長に切断する。そして最後に外部リード部をガルウィング形、J型等の所定の形状にリード成形して半導体装置は完成する。
【0003】
【発明が解決しようとする課題】
従来の半導体装置に使用されるリードフレーム、シャーシなどの電子部品に使用される金属材料は、Cu合金、42%Niの鉄合金、鉄の薄板、Al合金などにハンダメッキ層を施した部品が使用されている。しかしながら、ここ数年で国際的な地球環境保全を進めていくための行動が着実にしつつあるなかで、ハンダメッキ層に含まれるPbの規制が必要になり、Pbの使用しないメッキ層の開発が重要な課題となっている。その対策法に二つの方法が検討されている。その一つはPbの変わりにBi成分を使用する、いわゆるSn−Biメッキ層である。Biを使用することによって、有害なPbを使用することなくSnと比較して融点が低下し、ウイスカの発生しないメッキを施すことができる。その反面、BiはPbと比較して加工性が悪いため、メッキ後の成形加工において曲げ加工性に制約を受ける問題があった。他の対策法として、従来からシャーシなどの金属材料に使用されているSn単独メッキ法の転用技術がある。この対策法は、Snの柔軟な性質から上記の加工上の問題はないが、前記したように、ウィスカが発生し短絡事故を引き起こす問題から使用性能の信頼性を欠く問題があった。
【0004】
本発明者らは上記したような問題に鑑み、ウイスカの発生を防止した半導体装置用の電子部品金属材料を提供する事を目的にSnメッキ方法について種々検討した結果、Cuのプレメッキを施してSnメッキを施す事によって、ウイスカの問題が解消されることを知見した。またメッキ後の成型加工についても何ら支障がないことも判った。
【0005】
【課題を解決するための手段】
本発明はこの知見に基づいて構成したもので、その要旨は、42%ニッケル入鉄合金からなる電子部品用基板の表面に厚さ0.05〜3μmのCuメッキの下地層を施し、その上に外装メッキとして、Snメッキ層を電解メッキにより施す事を特徴とする使用時のウイスカの発生を防止した電子部品用金属材料の製造方法である。
【0006】
【発明の実施の形態】
以下、本発明の要旨について詳細に説明する。
本発明は、半導体装置に使用される金属材料例えば銅および銅合金、鉄および鉄合金(含42%Niの鉄合金)、Al合金など一般に使用される電子部品用金属(または基板)の表面に、Cuメッキの下地層を施し、その上にSnメッキを施す。Cuメッキ層は、Snメッキ層の表面から発生し成長するウイスカを抑制する効果を発揮する。図2は、Snメッキを施した時のCuメッキの厚さとウイスカ発生との関係を示したもので、Cuメッキ層が0.05μm未満の薄い厚みではウイスカ発生の抑制効果が小さくまた3μmを超える過剰な厚みではその抑制効果が過飽和に達する。本発明において、Cuメッキ層の厚みを0.05〜3μmに限定した理由はこの様な実験結果から定めたもので、好ましくは、0.1〜1μmである。上層のSnメッキは、外部リードのハンダ濡れ性、耐食性のために施す。尚、両者のメッキ層間においてウイスカの発生を抑制する理由は、現時点で明確ではないが、本発明者らの推測によれば、Snメッキ層の下地層にCuメッキを薄く施すことによって、Snメッキ層の結晶方向や結晶粒径に影響を与えてウイスカの成長し難い方位にそろえるか、結晶粒を粗大化して粒界エネルギーを低下させるか、Snメッキ層にCuメッキ金属の拡散を促して、ウイスカの発生と成長を抑制するのか、あるいは薄いメッキ層によって界面の密着性が向上するなど、幾多の理由が考えられる。
【0007】
また、本発明において、Cuメッキ層の下地層にさらにNiメッキを施しても、得られるウイスカ抑制効果を損なうものではない。
【0008】
【実施例】
次に、本発明の実施例について説明する。
表1は、電子部品用金属(基板)に各種メッキ層を施した場合の本発明の電子部品用金属材料と比較材料を−40℃〜120℃の熱サイクルを1000回繰り返した後のメッキ層表面におけるウイスカ発生状況をSEMで観察し、下記の評点付けを行った結果を、比較して示したものである。
1;Sn−Pbと同等レベル
2;実用上問題ないが、従来材よりは悪い。
3;300ピン以下程度のデバイスには適用可能
4;100ピン以下程度なら適用可能
5;どのデバイスにも適用が難しい
その結果、下層にCuメッキを施した本発明の電子部品用金属材料は、ウイスカの発生が抑制される。またSn単独メッキあるいは過剰な厚みのCuメッキを下層に施した比較材は、ウイスカの発生を抑制することができなかった。
【0009】
【表1】
【00010】
【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、ウィ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ィスカの一例を示す。
【図2】Snメッキ層を施した時のCuメッキ層の厚さとウイスカ発生状況との関係を示す。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a metal material for electronic parts, which prevents whisker generation during use .
[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 line. 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 for promoting global environmental conservation have been steadily taking place in the last few years, 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 is a problem in that the reliability of the use performance is lacking due to the problem of causing a whisker and causing a short-circuit accident.
[0004]
In view of the above problems, the present inventors have made various studies on Sn plating methods for the purpose of providing an electronic component metal material for a semiconductor device in which whisker is prevented from being generated. It has been found that the problem of whiskers can be solved by plating. 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 a surface of a substrate for electronic parts made of 42% nickel- containing iron alloy is provided with a Cu plating base layer having a thickness of 0.05 to 3 μm. A method for producing a metal material for electronic parts which prevents whisker generation during use , characterized in that an Sn plating layer is applied by electrolytic plating as exterior plating .
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the gist of the present invention will be described in detail.
The present invention is applied to the surface of a metal material (or substrate) generally used for electronic components such as copper and copper alloy, iron and iron alloy (including 42% Ni iron alloy), Al alloy, etc. Then, an underlayer of Cu plating is applied, and Sn plating is applied thereon. The Cu plating layer exhibits an effect of suppressing whiskers that are generated and grown from the surface of the Sn plating layer. FIG. 2 shows the relationship between the thickness of Cu plating and the occurrence of whisker when Sn plating is performed. When the Cu plating layer is thinner than 0.05 μm, the effect of suppressing the generation of whisker is small and exceeds 3 μm. If the thickness is excessive, the suppression effect reaches super saturation. In the present invention, the reason why the thickness of the Cu plating layer is limited to 0.05 to 3 μm is determined from such experimental results, and is preferably 0.1 to 1 μm. 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 guess, the Sn plating can be performed by thinly applying the Cu plating to the underlayer of the Sn plating layer. It influences the crystal direction and grain size of the layer to align the whisker in a direction where it is difficult to grow, or coarsens the crystal grain to lower the grain boundary energy, or promotes the diffusion of the Cu plating metal in the Sn plating layer, 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.
[0007]
In the present invention, even if Ni plating is further applied to the underlayer of the Cu plating layer, the obtained whisker suppressing effect is not impaired.
[0008]
【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; level equivalent to Sn—
3; Applicable to devices of about 300 pins or less 4; Applicable to devices of 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 with Cu plating on the lower layer is Whisker generation is suppressed. 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.
[0009]
[Table 1]
[00010]
【The invention's effect】
As described above, the metal material for electronic parts according to the present invention eliminates the problem of short circuit failure due to whiskers, has a bending workability required for molding after plating, and is suitable for global environmental protection. Metal materials can be provided.
[Brief description of the drawings]
FIG. 1 shows an example of a whisker generated on a Sn plating surface.
FIG. 2 shows the relationship between the thickness of the Cu plating layer and the state of whisker generation when the Sn plating layer is applied.
Claims (2)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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JP2002267387A JP4307038B2 (en) | 2002-08-08 | 2002-08-08 | Method for producing metal material for electronic parts which prevents whisker generation during use |
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JP2002267387A JP4307038B2 (en) | 2002-08-08 | 2002-08-08 | Method for producing metal material for electronic parts which prevents whisker generation during use |
Publications (3)
Publication Number | Publication Date |
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JP2004197111A JP2004197111A (en) | 2004-07-15 |
JP2004197111A5 JP2004197111A5 (en) | 2005-02-17 |
JP4307038B2 true JP4307038B2 (en) | 2009-08-05 |
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JP2002267387A Expired - Fee Related JP4307038B2 (en) | 2002-08-08 | 2002-08-08 | Method for producing metal material for electronic parts which prevents whisker generation during use |
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JP (1) | JP4307038B2 (en) |
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