JP4475852B2 - High strength copper alloy lead frame material for bare bonding - Google Patents
High strength copper alloy lead frame material for bare bonding Download PDFInfo
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- JP4475852B2 JP4475852B2 JP2001343862A JP2001343862A JP4475852B2 JP 4475852 B2 JP4475852 B2 JP 4475852B2 JP 2001343862 A JP2001343862 A JP 2001343862A JP 2001343862 A JP2001343862 A JP 2001343862A JP 4475852 B2 JP4475852 B2 JP 4475852B2
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- copper alloy
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- H01L24/80—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected
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- H01L2224/45001—Core members of the connector
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- H01L2224/451—Material with a principal constituent of the material being a metal or a metalloid, e.g. boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te) and polonium (Po), and alloys thereof
- H01L2224/45138—Material with a principal constituent of the material being a metal or a metalloid, e.g. boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te) and polonium (Po), and alloys thereof the principal constituent melting at a temperature of greater than or equal to 950°C and less than 1550°C
- H01L2224/45147—Copper (Cu) as principal constituent
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- H01L2224/48247—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being metallic connecting the wire to a bond pad of the item
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- Engineering & Computer Science (AREA)
- Computer Hardware Design (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Power Engineering (AREA)
- Wire Bonding (AREA)
- Lead Frames For Integrated Circuits (AREA)
- Preventing Corrosion Or Incrustation Of Metals (AREA)
Description
【０００１】
【発明の属する技術分野】
本発明はめっきを施さない状態で使用されるベアボンディング用高強度銅合金リードフレーム材に関し、特にワイヤボンディング性に優れるベアボンディング用高強度銅合金リードフレーム材に関する。
【０００２】
【従来の技術】
従来、リードフレーム材の表面には貴金属めっきが施されており、これにより熱による表面酸化又ははんだ付性の低下が抑制されていた。このためワイヤボンディング性が問題視されることはなかったが、近年、ダイボンディング技術又はワイヤボンディング技術の発達により、リードフレームが受ける熱量が減少したため、生産性向上及びコストダウンの観点からニッケルめっき又は貴金属めっきの省略が考えられるようになり、ワイヤボンディング性の問題が重要視されるようになった。
【０００３】
【発明が解決しようとする課題】
本発明者らは、特許第２７６６６０５号明細書において、ベアボンディング用銅合金リードフレームを提案している。この銅合金リードフレームは、導電率が９０％ＩＡＣＳ以上の銅合金において、酸化皮膜の状態と防錆皮膜付着量を定量化しその値を所定範囲に規制したもので、ワイヤボンディング性に優れ、ダイボンディング及びワイヤボンディングなどの組立工程において加熱された後も酸化皮膜の密着性に優れている。
【０００４】
しかしながら、導電率９０％ＩＡＣＳ以上の銅合金では、銅合金に添加する成分が制限されるため、引張強度５００Ｎ／ｍｍ２以上、望ましくは５５０Ｎ／ｍｍ２以上の高強度を得ることが難しかった。また、導電率９０％ＩＡＣＳ以上の銅合金は成形加工性（主として打ち抜き加工性）も優れない。一方、ベンゾトリアゾールを含む酸化防止材を使用する前記特許第２７６６６０５号明細書の方法を導電率９０％ＩＡＣＳ未満の高強度銅合金素材に適用した場合、同明細書に開示の条件ではワイヤボンディングができなかった。
そこで、本発明は、導電率９０％ＩＡＣＳ未満の高強度銅合金を素材とするベアボンディング用リードフレーム材に、優れたワイヤボンディング性を付与することを目的とする。
【０００５】
【課題を解決するための手段】
本発明に係るベアボンディング用高強度銅合金リードフレーム材は、金線又は銅線を用いてベアボンディングを行うリードフレーム材であり、導電率が２０％ＩＡＣＳ以上７０％ＩＡＣＳ以下、表面の酸化皮膜厚さが１００Ａ以下、引張強度が５００Ｎ／ｍｍ２以上の高強度銅合金素材と、その表面を被覆するベンゾトリアゾールを含まない酸化防止皮膜からなる。ベンゾトリアゾールを含まない酸化防止皮膜は、アミン系防錆剤、エステル系防錆剤及びアセチレン系化合物のうち２種以上を組み合わせたものを含む。
【０００６】
【発明の実施の形態】
貴金属めっきを省略して直接ダイボンディング、ワイヤボンディング等（ベアボンディング）を行う場合に、印加された熱による銅合金リードフレーム材のワイヤボンディング性は、銅合金中の添加成分の拡散及び凝縮に影響される。すなわち、銅合金リードフレーム材がダイボンディング、ワイヤボンディング等の組立工程において加熱されると、銅合金中の種々の合金成分が表面へ拡散し、ベアボンディング性が低下する。高温であれば銅合金中の成分の拡散は急速に進むため、ベアボンディングを短時間で行っても、ワイヤボンディング部の信頼性に問題がでてくる。導電率９０％ＩＡＣＳ未満の銅合金素材の場合、もともと合金成分が多く含有されているため、導電率９０％ＩＡＣＳ以上の銅合金素材に比べてその傾向が強く、拡散を抑制してワイヤボンディングを可能にするには、ベアボンディングの間２５０℃以下の温度に維持する必要がある。なお、後述する酸化皮膜の成長抑制やコストダウンの観点からは、ベアボンディングの間２００℃以下の温度に維持するのが望ましい。
【０００７】
ただし、銅合金素材の導電率が２０％ＩＡＣＳ未満であると、ベアボンディング時の温度を２５０℃以下に規制して銅合金中の成分の拡散を抑制しても、すでに表面近くに多くの添加成分が存在するため、ワイヤボンディング部の信頼性が低い。従って、本発明において銅合金素材の導電率は２０％ＩＡＣＳ以上とする。
さらに、銅合金中の添加元素の拡散と析出強化とのバランス、スタンピング性（打ち抜き加工性）に適する範囲として、銅合金素材の導電率は４０〜８５％ＩＡＣＳの範囲が望ましい。
【０００８】
また、ワイヤボンディング性は銅合金素材表面に施す酸化防止皮膜の種類とも関係があり、前記特許第２７６６６０５号明細書のようにベンゾトリアゾール成分を含む酸化防止皮膜の場合、該酸化防止皮膜中のベンゾトリアゾール（トリアゾール類化合物）が銅表面に結合してワイヤボンディング性を低下させる。導電率が９０％ＩＡＣＳ以上の銅合金素材の場合は、前記特許第２７６６６０５号明細書に記載されたように、微量であれば、表面にベンゾトリアゾールを含む酸化防止皮膜があってもワイヤボンデイングが可能であったが、導電率が９０％ＩＡＣＳ未満の銅合金素材の場合、微量でもワイヤボンディングができなくなる。
【０００９】
一方、２５０℃以下の温度でベアボンディングを行う場合、還元ガスによる銅合金素材の表面の還元効果が低下するため、銅合金素材表面の酸化皮膜の厚さを制御するとともに、その状態をベアボンディングまで維持することが必須条件となる。従って、まず、銅合金素材の表面の酸化皮膜の厚さを１００Ａ以下とする必要がある。これは、１００Ａを超える酸化皮膜は２５０℃以下の温度で還元することが難しく、ワイヤボンディング性が低下するためである。
また、酸化防止皮膜がないと銅合金素材の表面が酸化して、保管中に酸化皮膜が１００Ａを超えてしまうため、酸化防止皮膜を施す必要がある。ただし、この酸化防止皮膜がベンゾトリアゾールを含む場合、前記のとおりワイヤボンディング性が劣化するため、ベンゾトリアゾールを含まない酸化防止皮膜とする必要がある。
【００１０】
ベンゾトリアゾール（トリアゾール系化合物）成分を含まない酸化防止皮膜としては、ジメチルエタノールアミンやトリエタノールアミンなどのアミン系防錆剤とコハク酸エステルやカプリル酸エステル、多価アルコール脂肪酸エステルなどのエステル系防錆剤、２−プロピオン−１−オールやアセチレンアルコールなどアセチレン系化合物などが挙げられ、これらを組み合わせた酸化防止皮膜が望ましい。半導体装置を２５０℃以下の温度で組み立てることにより、ベンゾトリアゾールを含まない上記成分の酸化防止皮膜でも酸化を抑制でき、ベアボンディングが可能となる。
【００１１】
なお、高強度銅合金製リードフレームでは接続数が２００個所を越えるものもあり、不活性ガス又は水素等を含む還元雰囲気中にて加熱され、金線や銅線などで接合される。ベアボンディング雰囲気中の酸素濃度は５００ｐｐｍ以下、さらには１５０ｐｐｍ以下であることが望ましい。
【００１２】
【実施例】
（実施例１）
表１のＮｏ．１〜８に示す種々の組成の銅合金板素材について、下記要領にて導電率、表面酸化皮膜の厚み及び引張強度を測定し、さらに打ち抜き加工性を評価した。また、これに表１に示す種々の酸化防止皮膜を施した後又は施さないまま１０日間保管し、ワイヤボンディングを行ってワイヤボンディング性を評価した。なお、酸化防止処理を行った場合、１０日間程度の保管では酸化皮膜はほとんど成長せず、酸化防止処理時の状態を維持する。
以上の結果を表２に示す。
【００１３】
【表１】
【表２】
＜導電率＞
ＪＩＳＨ０５０５に規定されている非鉄金属材料導電率測定法に準拠して、ダブルブリッジ法にて求めた。
＜表面酸化皮膜の厚み＞
表面酸化皮膜の測定方法はカソード還元法で行った。銅合金板を０．１Ｎ−ＫＣｌ水溶液中にて０．１ｍＡ／ｃｍ２で電解し、酸化銅が還元されるときの電位と反応に使用された電気量を測定する。得られた電気量から亜酸化銅の量を求め、酸化皮膜厚さに換算した。
＜引張強度＞
ＪＩＳＺ２２４１に規定されている金属材料引張試験方法に準拠し、ＪＩＳ５号試験片にて求めた。５００Ｎ／ｍｍ２以上のものを○（良好）、未満のものを×（不良）と評価した。
【００１６】
＜打ち抜き加工性＞
銅合金板を板厚の３％のクリアランスで打ち抜き加工を行い、打ち抜いた端面を観察して板厚みに占める剪断面の割合を測定する。剪断面が板厚に占める割合が６割以下のものを打ち抜き加工性が良好、６割を越えるものは打ち抜き加工性が悪いと判断した。
＜ワイヤボンディング性の評価＞
２００℃、水素を含む酸素濃度５００ｐｐｍの窒素雰囲気中にて、直径３０μｍの金線を用い、荷重３０ｇ、接合時間３０ｍｓ、超音波出力を０．２Ｗとして、Ｎｏ．１〜８のそれぞれについて３０本ずつワイヤボンディングを行った。２００℃で１０００時間保管後にワイヤプル試験を行い、ワイヤ破断率１００％を○（良好）とし、接合界面で剥離が起こり、１００％でなかったものは×（不良）と評価した。
【００１７】
表２に示すように、導電率及び表面酸化皮膜厚さが本発明の規定範囲内で、かつベンゾトリアゾールを含まない酸化防止皮膜を施したＮｏ．１〜Ｎｏ．３は、いずれも良好なワイヤボンディング性を有し、かつ加熱試験後の信頼性に優れていた。
一方、Ｎｏ．４は、亜鉛含有量が高く導電率が１０％と低いために、ワイヤボンディング部に亜鉛の拡散濃縮が起こり、ワイヤボンディング性が悪かった。また、亜鉛が３５％を越えた銅合金は金属組織の均一化が難しく、生産性が悪いとともに表面粗さの低減や光沢処理が難しいという問題もあった。
Ｎｏ．５は、酸化が進み表面酸化皮膜厚さが厚いため、ワイヤボンディング性及び接合部の信頼性が悪かった。
Ｎｏ．６は、酸化防止皮膜を施していないため酸化皮膜が成長しやすく、保管時に変色が発生し、ワイヤボンディング性も悪かった。
Ｎｏ．７は、ベンゾトリアゾールを含む酸化防止皮膜を施したもので、ベンゾトリアゾールが表面に結合しているため、ワイヤボンディング性が悪かった。
Ｎｏ．８は、ワイヤボンディング性は良好であったが、導電率が９０％以上で強度が低い。また打ち抜き加工性が悪かった。
【００１８】
（実施例２）
表１及び表２のＮｏ．１に示される銅合金及び酸化防止材を用い（酸化防止皮膜を施した後１０日間保持）、ベアボンディング工程での加熱を模して表３に示す温度で５分間加熱した後、前記＜ワイヤボンディング性の評価＞に記載された方法でワイヤボンディングを行い、かつワイヤボンディング性の評価を行った。その結果を表３に示す。
【００１９】
【表３】
表３に示すように、加熱温度が２５０℃以下であったものは、すべてワイヤボンディング性が良好であったが、２５０℃を越える温度に加熱したものでは、ワイアボンディング性が劣っていた。
【００２１】
【発明の効果】
本発明によれば、高い強度を持ち、保管時の変色もなく、ワイヤボンディング性に優れる高強度ベアボンディング用銅合金リードフレーム材が得られる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-strength copper alloy lead frame material for bare bonding that is used without plating, and more particularly to a high-strength copper alloy lead frame material for bare bonding that has excellent wire bonding properties.
[0002]
[Prior art]
Conventionally, noble metal plating has been applied to the surface of the lead frame material, thereby suppressing surface oxidation or deterioration of solderability due to heat. For this reason, wire bondability has not been regarded as a problem, but in recent years, due to the development of die bonding technology or wire bonding technology, the amount of heat received by the lead frame has decreased, so nickel plating or from the viewpoint of productivity improvement and cost reduction The omission of precious metal plating has been considered, and the problem of wire bonding has become important.
[0003]
[Problems to be solved by the invention]
In the specification of Japanese Patent No. 2766605, the present inventors have proposed a copper alloy lead frame for bare bonding. This copper alloy lead frame is a copper alloy with a conductivity of 90% IACS or higher, which quantifies the state of oxide film and the amount of rust-preventive film and regulates the values within a predetermined range. Even after heating in an assembly process such as bonding and wire bonding, the adhesion of the oxide film is excellent.
[0004]
However, in a copper alloy having an electrical conductivity of 90% IACS or higher, the components added to the copper alloy are limited, so that it has been difficult to obtain a high strength of tensile strength of 500 N / mm 2 or higher, desirably 550 N / mm 2 or higher. In addition, a copper alloy having a conductivity of 90% IACS or more does not have excellent moldability (mainly punchability). On the other hand, when the method of the above-mentioned Japanese Patent No. 2766605 using an antioxidant containing benzotriazole is applied to a high-strength copper alloy material having a conductivity of less than 90% IACS, wire bonding is not possible under the conditions disclosed in the same specification. could not.
Accordingly, an object of the present invention is to impart excellent wire bonding properties to a lead frame material for bare bonding made of a high-strength copper alloy having a conductivity of less than 90% IACS.
[0005]
[Means for Solving the Problems]
The high-strength copper alloy lead frame material for bare bonding according to the present invention is a lead frame material for performing bare bonding using a gold wire or a copper wire, and has a conductivity of 20% IACS or more and 70% IACS or less, and an oxide film on the surface. It consists of a high-strength copper alloy material having a thickness of 100 A or less and a tensile strength of 500 N / mm 2 or more, and an antioxidant film not containing benzotriazole covering the surface. The antioxidant film not containing benzotriazole includes a combination of two or more of an amine rust inhibitor, an ester rust inhibitor, and an acetylene compound.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
When direct die bonding, wire bonding, etc. (bare bonding) is performed without precious metal plating, the wire bondability of the copper alloy lead frame material due to applied heat affects the diffusion and condensation of additive components in the copper alloy. Is done. That is, when the copper alloy lead frame material is heated in an assembly process such as die bonding or wire bonding, various alloy components in the copper alloy are diffused to the surface, and the bare bonding property is deteriorated. If the temperature is high, the diffusion of the components in the copper alloy proceeds rapidly. Therefore, even if bare bonding is performed in a short time, there is a problem in the reliability of the wire bonding portion. In the case of a copper alloy material having a conductivity of less than 90% IACS, since there are many alloy components from the beginning, the tendency is stronger than that of a copper alloy material having a conductivity of 90% IACS or more. To be possible, it is necessary to maintain a temperature of 250 ° C. or lower during bare bonding. In addition, it is desirable to maintain at a temperature of 200 ° C. or lower during bare bonding from the viewpoint of suppressing the growth of an oxide film, which will be described later, and reducing the cost.
[0007]
However, if the conductivity of the copper alloy material is less than 20% IACS, even if the temperature during bare bonding is controlled to 250 ° C or less and the diffusion of components in the copper alloy is suppressed, many additions have already been made near the surface. Since the component exists, the reliability of the wire bonding portion is low. Therefore, in the present invention, the conductivity of the copper alloy material is 20% IACS or more.
Furthermore, the conductivity of the copper alloy material is preferably in the range of 40 to 85% IACS as a range suitable for the balance between diffusion of additive elements in the copper alloy and precipitation strengthening and stamping properties (punching workability).
[0008]
The wire bondability is also related to the type of antioxidant coating applied to the surface of the copper alloy material. In the case of an antioxidant coating containing a benzotriazole component as described in the above-mentioned Japanese Patent No. 2766605, the benzoin in the antioxidant coating is included. Triazole (a triazole compound) binds to the copper surface and lowers the wire bonding property. In the case of a copper alloy material having a conductivity of 90% IACS or higher, as described in the above-mentioned patent No. 2766605, wire bonding is possible even if there is an antioxidant film containing benzotriazole on the surface, as long as it is in a very small amount. Although it was possible, in the case of a copper alloy material having a conductivity of less than 90% IACS, wire bonding cannot be performed even with a small amount.
[0009]
On the other hand, when bare bonding is performed at a temperature of 250 ° C. or lower, the reduction effect of the surface of the copper alloy material by the reducing gas is reduced, so the thickness of the oxide film on the surface of the copper alloy material is controlled, and the state is determined by bare bonding. It is indispensable to maintain until. Therefore, first, the thickness of the oxide film on the surface of the copper alloy material needs to be 100 A or less. This is because an oxide film exceeding 100 A is difficult to reduce at a temperature of 250 ° C. or lower, and the wire bonding property is lowered.
Moreover, since the surface of a copper alloy raw material will oxidize if there is no antioxidant film | membrane and an oxide film will exceed 100A during storage, it is necessary to give an antioxidant film | membrane. However, when this antioxidant film contains benzotriazole, the wire bonding property deteriorates as described above. Therefore, it is necessary to form an antioxidant film that does not contain benzotriazole.
[0010]
Antioxidant coatings that do not contain a benzotriazole (triazole compound) component include amine-based rust preventives such as dimethylethanolamine and triethanolamine, and ester-based anticorrosives such as succinic acid esters, caprylic acid esters, and polyhydric alcohol fatty acid esters. Acetylene-based compounds such as rusting agents, 2-propion-1-ol and acetylene alcohol can be mentioned, and an antioxidant film combining these is desirable. By assembling the semiconductor device at a temperature of 250 ° C. or lower, oxidation can be suppressed even with the anti-oxidation film of the above-mentioned component not containing benzotriazole, and bare bonding becomes possible.
[0011]
Note that some high strength copper alloy lead frames have more than 200 connections, and are heated in a reducing atmosphere containing an inert gas or hydrogen and joined together by gold wires, copper wires, or the like. The oxygen concentration in the bare bonding atmosphere is preferably 500 ppm or less, and more preferably 150 ppm or less.
[0012]
【Example】
Example 1
No. in Table 1 For the copper alloy sheet materials having various compositions shown in 1 to 8, the electrical conductivity, the thickness of the surface oxide film and the tensile strength were measured in the following manner, and the punching workability was further evaluated. Further, after applying various antioxidant coatings shown in Table 1 to this or without applying it, it was stored for 10 days, and wire bonding was performed to evaluate the wire bonding property. When the antioxidant treatment is performed, the oxide film hardly grows after storage for about 10 days, and the state during the antioxidant treatment is maintained.
The results are shown in Table 2.
[0013]
[Table 1]
[Table 2]
<Conductivity>
The double bridge method was used in accordance with the nonferrous metal material conductivity measurement method defined in JISH0505.
<Thickness of surface oxide film>
The surface oxide film was measured by the cathode reduction method. A copper alloy plate is electrolyzed at 0.1 mA / cm 2 in a 0.1N-KCl aqueous solution, and the potential when the copper oxide is reduced and the amount of electricity used for the reaction are measured. The quantity of cuprous oxide was calculated | required from the obtained electric quantity, and it converted into the oxide film thickness.
<Tensile strength>
In accordance with the metal material tensile test method specified in JISZ2241, the JIS No. 5 test piece was used. 500 N / mm 2 or more of the ○ (good), those below were evaluated as × (poor).
[0016]
<Punching workability>
A copper alloy plate is punched with a clearance of 3% of the plate thickness, and the punched end surface is observed to measure the ratio of the sheared surface to the plate thickness. When the ratio of the sheared surface to the plate thickness was 60% or less, the punching workability was good, and when the shearing surface exceeded 60%, the punching workability was poor.
<Evaluation of wire bonding properties>
In a nitrogen atmosphere with an oxygen concentration of 500 ppm containing hydrogen at 200 ° C., a 30 μm diameter gold wire was used, the load was 30 g, the bonding time was 30 ms, the ultrasonic output was 0.2 W, and For each of 1 to 8, 30 wires were bonded. A wire pull test was conducted after storage at 200 ° C. for 1000 hours. The wire breakage rate was 100% (good), peeling occurred at the bonding interface, and the case where it was not 100% was evaluated as x (defect).
[0017]
As shown in Table 2, the conductivity and surface oxide film thickness were within the specified ranges of the present invention, and No. 1 was applied with an antioxidant film containing no benzotriazole. 1-No. No. 3 had good wire bonding properties and was excellent in reliability after the heating test.
On the other hand, no. No. 4 had a high zinc content and a low electrical conductivity of 10%, so that zinc was diffused and concentrated in the wire bonding part, and the wire bonding property was poor. Further, a copper alloy having a zinc content exceeding 35% has a problem that it is difficult to make the metal structure uniform, the productivity is poor, and the surface roughness is reduced and the gloss treatment is difficult.
No. In No. 5, since the oxidation progressed and the surface oxide film thickness was thick, the wire bonding property and the reliability of the joint were poor.
No. In No. 6, since the antioxidant film was not applied, the oxide film was likely to grow, discoloration occurred during storage, and the wire bonding property was poor.
No. No. 7 was provided with an antioxidation film containing benzotriazole. Since benzotriazole was bonded to the surface, the wire bonding property was poor.
No. In No. 8, the wire bonding property was good, but the conductivity was 90% or more and the strength was low. Moreover, punching workability was bad.
[0018]
(Example 2)
No. in Table 1 and Table 2. 1 was used (retained for 10 days after the oxidation coating was applied), and after heating for 5 minutes at the temperature shown in Table 3 simulating the heating in the bare bonding step, the above <wire The wire bonding was performed by the method described in Evaluation of Bondability> and the wire bonding property was evaluated. The results are shown in Table 3.
[0019]
[Table 3]
As shown in Table 3, the wire bonding properties were all good when the heating temperature was 250 ° C. or lower, but the wire bonding properties were inferior when heated to temperatures exceeding 250 ° C.
[0021]
【The invention's effect】
According to the present invention, it is possible to obtain a copper alloy lead frame material for high-strength bare bonding that has high strength, no discoloration during storage, and excellent wire bonding properties.
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