JP3832151B2 - Lead-free solder connection structure - Google Patents

Lead-free solder connection structure Download PDF

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Publication number
JP3832151B2
JP3832151B2 JP20721399A JP20721399A JP3832151B2 JP 3832151 B2 JP3832151 B2 JP 3832151B2 JP 20721399 A JP20721399 A JP 20721399A JP 20721399 A JP20721399 A JP 20721399A JP 3832151 B2 JP3832151 B2 JP 3832151B2
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Prior art keywords
solder
temperature
lead
free solder
melting point
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JP2001035978A (en
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太佐男 曽我
英恵 下川
寿治 石田
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Hitachi Ltd
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Hitachi Ltd
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    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/01Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/26Layer connectors, e.g. plate connectors, solder or adhesive layers; Manufacturing methods related thereto
    • H01L2224/31Structure, shape, material or disposition of the layer connectors after the connecting process
    • H01L2224/32Structure, shape, material or disposition of the layer connectors after the connecting process of an individual layer connector
    • H01L2224/321Disposition
    • H01L2224/32151Disposition the layer connector 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
    • H01L2224/32221Disposition the layer connector 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
    • H01L2224/32225Disposition the layer connector 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 non-metallic, e.g. insulating substrate with or without metallisation

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  • Die Bonding (AREA)
  • Cooling Or The Like Of Semiconductors Or Solid State Devices (AREA)

Description

【0001】
【発明の属する技術分野】
本発明はSiチップとヒートシンクもしくは絶縁基板等の熱膨張係数が異なる構造体接続用はんだ、大型構造の封止部接続用はんだ及びそれを用いた接続構造体に関する。
【0002】
【従来の技術】
従来は上記目的に対し、Sn-Pbはんだ組成の組み合わせで対応してきた。このはんだの各種の優れた特性から、プロセス、信頼性等での問題点は少なく、ほとんど解決されてきた。鉛の人体への影響が明らかにされるにつれ、鉛が水に溶けやすいことが災いして地球環境の問題に発展している状況下にある。このため、Sn-Pbはんだに代わる優れた特性、特に耐熱疲労性、はんだ付け時、温度サイクル試験時に素子、部品等をいためないで耐えられて、はんだ付け性に優れたPbフリーはんだ材料及びその構造体が求められている。
【0003】
【発明が解決しようとする課題】
上記目的に対し、鉛を使用しないはんだの製品開発が盛んに行われているものの、未だ開発途上で、絞り込まれていない段階である。これらの要求に対応できるはんだの候補に上っているSn系の鉛フリーはんだとしては、高温系はこれまで使用されてきたSn-Sb(融点:236〜240℃)が知られている。
【0004】
このはんだと温度階層をつけられる、即ちSn-Sbを溶かさないで230℃以下ではんだ付けできる、Sn-Pb共晶代替の優れたものは見いだされていない。温度特性、機械的特性、経済性に優れた材料としてSn-9Zn(融点:199℃)が知られているが、Znの酸化が顕著であるため、ぬれ性に劣り、強いフラックスを使う必要性から絶縁特性、ペーストの場合にはポットライフの問題、洗浄の問題等のため容易には使えず限定された使い方が求められている。このためSn-3.5Ag(融点:221℃)にCu,Biを入れた系が本命になっている。
【0005】
これまで各種の接続実験が行われてきたが、はんだ付け温度を下げる必要性からBiを入れて融点を下げる検討がなされてきたが、(1)接合界面の強度不足、(2)凝固時に最終凝固の部分で低温のBi相が接合界面に偏析して、信頼性を低下させること、(3)メタライズにPbが存在すると、更に低温相(Sn-Pb-Biの三元共晶:97℃)の形成により、信頼性が更に低下すること等により、特性上、Sn-Pb共晶代替になれないのが現状である。
【0006】
本案ははんだ付け時に継手が剥離を起こしにくいはんだ組成にして、かつ、素子、メタライズ等にダメッジを与えることなく、高信頼で接合可能なはんだを提案することにある。そして、-55〜125℃、-65〜150℃等の信頼性評価条件としては最も厳しい部類に入る条件に対しても保証できる継手を提案するものである。更には、高温系のSn-Sbとの温度階層をつけられるはんだを提案するものである。
【0007】
【課題を解決するための手段】
上記課題をクリアするため、Sn-Ag-Cuをベースとするはんだが正常にぬれるためには、継手温度として最低220℃を確保する必要がある。炉の温度ばらつきは中央の部品の継手と端部の部品の継手で約10℃以内である。部品の熱容量が大きいと温度ばらつきもつきやすい。従って、220〜230℃の範囲内で接合でき、しかも高信頼性を確保できるはんだである必要がある。
【0008】
この域の有力候補としてはSn-Ag-Cu系にはんだ付け温度を下げるために、Biを添加した系が知られている。Biが少ないとSn-Ag-Cu系と変わらなく、はんだ付け時に継手の温度が235℃以上になるので、Sn-Sbとの温度階層接続には使えない。Biが5%前後のSn-(2〜3.5)Ag-(0.2〜0.8)Cu (4〜6)BiならばほぼSn-Pb共晶代替の温度であり、その代表例がSn-3Ag-0.7Cu5Bi(融点:195〜215℃)である。この範囲であれば炉内の温度ばらつき、継手部のばらつきを含めて220〜230℃での接続が可能である。しかし、この範囲のBi量では接合界面の強度が小さいため、剛性の強い構造では、冷却時に熱膨張差による熱応力に耐えきれず、剥離破壊を起こすことがある。更には、-55〜125℃、-65〜150℃の温度サイクル条件では目標寿命を満たすことが出来ない場合がある。
【0009】
そこで、はんだ付け温度を下げられて、かつ、高信頼性を確保する必要性から、BiとInの添加量の制御と、信頼性と、プロセスコンパチビリテーとの関係が重要である。Biは添加量を増やすと融点は下がるが(図1)、機械的特性も顕著に低下する(図2)。従って、継手の機械的な信頼性はBi量で決まり、Inの添加は機械的特性をほとんど損ねないで、融点を下げる役目をすることが明らかになった(図3)(図4)。BiのSn-Ag-CuはんだのSn晶への固溶限が約1.5%であるため、それ以上入れると温度は下げられるものの、固溶できないBiが析出して機械的特性、特に重要な伸びの低下をもたらし、かつ、接合界面の強度低下を起こすことになる(図5)。
【0010】
Bi量のSn晶への固溶が1.5%以内では0%のSn-Ag-Cuに比べ、機械的特性で若干低下する程度である。機械的強度を損ねないで融点を下げれるBi量として0.5〜3.0%を定めた。これ以上のBi量は接合界面の強度低下につながり、実験的にこれ以上では影響してくることが分かった。特に、Bi:3%ではBiが界面に偏析しやすいが、通常は表面にNi/Auのメタライズ膜が施されるので、ある程度Biが偏析しても、BiとNiとは金属間化合物を形成しやすいので、Cuと異なりなじみが良く密着力も悪くないので耐えられる。
【0011】
次にはんだ付け温度を下げるため、即ち、融点を下げるためにIn量を3〜5%添加することにした。3%にした理由は、Inを添加しないものに対して、5〜10℃下げられる効果があるためである。これ以下でははんだ付け温度が高すぎる。5%以上では、コストの面、Inは酸化され易いため、ペーストの保管性、印刷性等の影響が出やすいこと、及びはんだ組織上の不安定さにつながる。
【0012】
即ち、固相線温度が下がり、更にPbが含まれると、低温のSn-In-Pb-Bi の低温相が出やすくなり、信頼性で問題がでてくる。Cuの組成範囲は機械的特性を損ねないで、Sn-Ag結晶の融点を数度下げる効果がある。しかし、Cu含有量は0.8%を越えると伸びが低下してくる(図6)。
【0013】
Cuを接合対象とする場合はCuの食われ防止にも効果がある。Ag量は2%以下では融点の上昇と伸び等の機械的強度特性の低下が起きる。3.5%以上でも同様に融点の上昇と機械的強度特性の低下が起こり、更にはコスト高である。よって、はんだ組成としてSn-(2〜3.5)Ag-(0.2〜0.8)Cu-(3〜5)In-(0.5〜3)Biに定めた。
【0014】
【発明の実施の形態】
Sn-Ag-Cu系の液相線温度が218℃であることから、継手部の温度は220℃以上である必要がある。炉中の約300×300内に置かれた場合、継手部の温度ばらつき(ΔT=10℃)を考慮すると、継手部では220(min)〜230 (max)℃になり、Sn-Sbとの温度階層接続が可能である。
【0015】
Sn-Ag-Cu系では220℃以上であれば、確実に端子部をぬらすこと、及び温度が上がってもぬれ広がりは増さないが、はんだを載置した箇所は確実にぬれていることが確認された。従って、はんだ箔を載せた箇所は確実にぬれることになる。
【0016】
この温度で接続できるPbフリーはんだの組成としてSn-Ag-Cu-Bi系が知られている。具体的組成として、Ag、Cuを代表的な組成に仮固定したSn-3Ag-0.7Cuを例にとると、
このはんだにBi:4〜6%位がはんだ付け可能な範囲になる。Biは6%以上では融点は下がるのではんだ付けは容易になるが、材料の伸び特性が低下し、接合界面の強度(ピール強度)は低下するので(図5)、信頼性が低下し、Biを多く入れる意味はない。従って、融点は高くなるが、信頼性が向上する方向のBi が少ない域が重要になる。この220〜230℃ではんだ付けできるSn-Ag-Cu-Biはんだの組成範囲としては、Bi:5%前後になる。
【0017】
Sn-3Ag-0.5CuはんだにBi含有量を変えたはんだを用いて、42アロイリードにSn-10PbめっきしたものとCu箔とをはんだ付けし、接合界面のピール強度の結果(図7)をみればBiが5%入ると界面の強度低下が起こることが分かる。Biに対するこの傾向は、絶対値は異なるがNiめっきでも同様な傾向を示す。この強度低下の原因はBi界面での偏析である。現状ではBi:2〜3%と少ない場合、破壊面でBi濃度の増加は認められるが、明確なBi相の存在は確認できていない。また、伸び等の機械的特性はピール強度のようにBiに対して急激な変化ではなく、幾分緩やかであることから3Biの耐温度サイクル性は優れることが予想される。
【0018】
パワーデバイスにおいて、図8に示すように、アルミナ基板3を挟むようにMo板2(低熱膨張の熱拡散板、Niめっき5)と、Cu板ヒートシンク9(Niめっき)を0.15mmtのSn-7Sb(融点:235〜244℃)はんだ箔8を用いて、不活性雰囲気でmax270℃ではんだ付けをした。その後、接合されたMoの裏面(Niめっき)に、Sn-3Ag-0.7Cu-3In-3Biはんだ箔7(0.15mmt)を用いてSiチップ1(W/Ni等でメタライズ4された)を載せてmax230℃で、同様に不活性雰囲気ではんだ付けを行った。このとき、当然のことながらSn-7Sbは溶けないので、階層接続を実現できる。6はW-Niめっきである。
【0019】
図9は大型の封止構造に、このはんだを適用した一例を示したものである。W/Niめっきセラミック容器9とNiめっきCu板10とを、Sn-3Ag-0.7Cu-3In-2Biはんだ箔12で封止たものである。ヘリウムリーク試験でも問題無いことを確認した。11はセラミックである。
【0020】
他方、比較用として、同様にSiチップの接合をSn-3Ag-0.7Cu5Bi(融点:195〜215℃) はんだでも行って信頼性評価を行った。はんだ付けしたサンプルを切り出して、断面研磨した結果、最終凝固となる側に、EDX分析ではBiがはんだ中の含有率(5%)以上に含まれている濃縮層が認められた。Niとの接合であるため、Cuのように極端に弱くはなかったが、この偏析が起こる限り正常な継手とは言えない。-55〜125℃の温度サイクル試験では、このBiの濃縮層の界面でのクラック進展がSn-3Ag-0.7Cu-3In-3Biはんだに比べて速く、問題であることが分かった。
【0021】
この結果、Sn-3Ag-0.7Cu-3In-3Bi はSn-Pb共晶と比較すると、耐熱疲労性は優れるが、他方、Sn-3Ag-0.7Cu-5Bi はSn-Pb共晶と比較して、耐熱疲労性は劣る事を確認できた。耐クリープ性はSn-3Ag-0.7Cu-3In-3Bi、Sn-3Ag-0.7Cu-5Bi共にSn系であり、Biが入っているので強度が大であることから、Sn-Pb共晶と比較して数倍優れる。また、融点も195℃以上であり、 Sn-Pb共晶の183℃より高く、強くて硬いSn晶の集まりなので耐高温に優れる。
【0022】
図10はSn-3Ag-0.7Cuはんだを例にとり、横軸の左半分はBiが0〜5%、右半分はInが0〜5%含有した場合で、縦軸に温度をとったものである。図11は横軸は同じで、縦軸に伸びをとったものである。Bi量とはんだの液相線と固相線を左半分に示し、Sn-3Ag-0.7CuにBiが2%入り、それにInを含有させたはんだの液相線と固相線を右半分に示した。Sn-3Ag-0.7Cu-2Bi-3Inは融点ではSn-3Ag-0.7Cu-5Biに近く、Sn-3Ag-0.7Cu-2Biよりは低い。これより、Sn-3Ag-0.7Cu-2Bi-3Inのはんだ付け温度はSn-3Ag-0.7Cu-5Bi並みで可能である。同様に、Bi:0.5〜3%の範囲で、In:3〜5%の範囲の組み合わせならばSn-3Ag-0.7Cu-5Bi並みのはんだ付け温度で可能である。
【0023】
これより、融点、はんだ付け温度はSn-3Ag-0.7Cu-5Bi 並みで、高信頼性のはんだ組成を得ることができた。更にInで融点を下げたSn-3Ag-0.7Cu-2Bi-5Inの場合も、同様にプロセス、信頼性をクリアできた。更に、Inを入れることは融点が下がる方向であり、コスト、印刷性(ライフタイム)、組織安定性(低温相の形成)の問題があるので、望ましくはない。Snマトリクス中へのBiの固溶は、1.2%であるが、バルク材料の特性ではBi量に比例して脆化するが、Bi が2%までは特性上優れていると言える。
【0024】
次に、Biを添加しない系であるSn-3Ag-0.7Cu-3In(融点:207〜216℃)、 及びSn-3Ag-0.7Cu(融点216〜220℃) の評価を行った。Sn-3Ag-0.7Cu-3Inの融点はSn-3Ag-0.7Cu-5Biと余り変わず、230℃で接続が可能であった。Sn-3Ag-0.7Cuの継手部温度はmax235℃をこえるため使用できないが、継手の信頼性は行った。これらのはんだ付け時における継手の剥がれはない。この理由はBiが含まれていないため、接合界面の強度が高いことによると考える。
【0025】
更に、同様に温度サイクル試験を行った結果、両者とも-55〜125℃の温度サイクル試験では目標とする2000サイクルをクリアし、クラック進展も少ない。しかし、Sn-3Ag-0.7Cuの場合、応力的に厳しい位置でのメタライズ部に破壊が起きた。他の組成ではこのような現象を起こしていないことから、Sn-3Ag-0.7Cu特有な現象と考えられる。原因は、融点が高いので、室温に冷却された時点では残留応力、歪みが高いこと、はんだの強度が高いので、はんだでは解放されず、その影響がメタライズ部にかかることが考えられる。特に、剛性の強い場合はそのことが言える。
【0026】
これらの結果から、Sn-3Ag-0.7Cu-(0.5〜3)Bi-(3〜5)Inはバランスのとれた優れた組成であることが確認された。ベースになったSn-3Ag-0.7CuはAg、Cuの範囲として、既に示したSn-(2〜3.5)Ag-(0.2〜0.8)Cuで良いので、これらの条件を満たすPbフリーはんだ組成はSn-(2〜3.5)Ag-(0.2〜0.8)Cu-(0.5〜3)Bi-(3〜5)Inである。
【0027】
【発明の効果】
以上のように、本発明によれば、鉛を使用しないことから、環境に優しい製品を供給できる。
【0028】
現用の炉で、従来の方式がそのまま適用できる。他方、従来のSn-Pb共晶はんだよりも、耐熱疲労性、耐クリープ性、耐高温に優れ、かつ高密度実装に対して高歩留まりが期待できる。
【図面の簡単な説明】
【図1】 Sn-Ag-CuにBiを添加したときの融点を示す特性図。
【図2】 Sn-Ag-CuにBiを添加したときの伸びを示す特性図。
【図3】 Sn-Ag-CuにInを添加したときの伸びを示す特性図。
【図4】 Sn-Ag-CuにInを添加したときの融点を示す特性図。
【図5】 Sn-Ag-CuにBiを添加したときのSnめっきを施した42アロイリードとの接続強度を示す特性図。
【図6】 Sn-AgにCuを添加したときの伸びを示す特性図。
【図7】 Sn-Ag-CuにBiを添加したときのCuとの接続強度を示す特性図。
【図8】本発明を利用したパワーデバイスを示す断面図。
【図9】本発明を利用した大型の封止構造を示す断面図。
【図10】 Sn-Ag-CuにBiとInを添加したときの融点を示す特性図。
【図11】 Sn-Ag-CuにBiとInを添加したときの伸びを示す特性図。
【符号の説明】
1…Siチップ、2…Mo板、3…アルミナ、4…メタライズ膜、5…Niめっき、6…W-Niめっき、7…Sn-3Ag-0.7Cu-3Bi-3In、8…Sn-Sb、9…Cu板、10…セラミック、11…Cu板、12…Sn-3Ag-0.7Cu-2Bi-3In。
[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a structure connecting solder having a different thermal expansion coefficient, such as a Si chip and a heat sink or an insulating substrate, a large structure sealing part connecting solder, and a connecting structure using the same.
[0002]
[Prior art]
Conventionally, the above purpose has been addressed by a combination of Sn—Pb solder compositions. Due to the various excellent characteristics of this solder, there are few problems in process, reliability, etc., and it has been almost solved. As the effects of lead on the human body are clarified, the fact that lead is easily dissolved in water is causing disasters and developing into global environmental problems. For this reason, Pb-free solder materials with superior characteristics that can replace Sn-Pb solder, especially heat fatigue resistance, soldering, and without damaging elements and components during temperature cycle tests, and their solderability and their A structure is desired.
[0003]
[Problems to be solved by the invention]
Although the development of solder products that do not use lead has been actively conducted for the above purpose, it is still in the process of being developed and not yet narrowed down. As a Sn-based lead-free solder that is a candidate for a solder that can meet these requirements, Sn-Sb (melting point: 236 to 240 ° C.) that has been used so far is known.
[0004]
No excellent alternative to Sn-Pb eutectic that can be soldered at 230 ° C or lower without melting Sn-Sb, that is, a temperature hierarchy with this solder, has not been found. Sn-9Zn (melting point: 199 ° C) is known as a material with excellent temperature characteristics, mechanical characteristics, and economical efficiency, but because of the remarkable oxidation of Zn, it is inferior in wettability and requires the use of a strong flux. Therefore, in the case of insulation characteristics, in the case of paste, there is a need for limited usage that cannot be easily used due to problems such as pot life and cleaning. For this reason, a system in which Cu and Bi are added to Sn-3.5Ag (melting point: 221 ° C.) is the favorite.
[0005]
Various connection experiments have been conducted so far, but due to the necessity of lowering the soldering temperature, investigations have been made to lower the melting point by adding Bi, but (1) insufficient strength at the joint interface, (2) final during solidification Low-temperature Bi phase segregates at the interface at the solidification part, reducing the reliability. (3) When Pb is present in the metallization, the low-temperature phase (Sn-Pb-Bi ternary eutectic: 97 ℃ )), The reliability is further lowered, and therefore it is not possible to substitute for Sn—Pb eutectic in terms of properties.
[0006]
The present proposal is to propose a solder that has a solder composition in which the joint does not easily peel off during soldering and can be joined with high reliability without causing damage to the elements, metallization, and the like. And the joint which can guarantee also about the conditions which enter into the severest category as reliability evaluation conditions, such as -55-125 degreeC and -65-150 degreeC, is proposed. Furthermore, the present invention proposes a solder capable of providing a temperature hierarchy with high-temperature Sn-Sb.
[0007]
[Means for Solving the Problems]
In order to clear the above-mentioned problems, it is necessary to secure a minimum joint temperature of 220 ° C. in order for the solder based on Sn—Ag—Cu to get wet normally. The temperature variation of the furnace is within about 10 ℃ at the joint of the central part and the joint of the end part. If the heat capacity of the parts is large, temperature variations are likely to occur. Therefore, it is necessary to be a solder that can be joined within a range of 220 to 230 ° C. and can ensure high reliability.
[0008]
As a potential candidate in this region, a system in which Bi is added to lower the soldering temperature to the Sn-Ag-Cu system is known. If the amount of Bi is small, it will not be different from Sn-Ag-Cu, and the temperature of the joint will be 235 ° C or higher during soldering. If Bi is around 5% Sn- (2-3.5) Ag- (0.2-0.8) Cu (4-6) Bi, it is almost the temperature of Sn-Pb eutectic substitution, and a representative example is Sn-3Ag-0.7 Cu5Bi (melting point: 195-215 ° C). If it is this range, the connection in 220-230 degreeC including the temperature variation in a furnace and the variation of a joint part is possible. However, when the amount of Bi is within this range, the strength of the bonding interface is small, so that a structure having a high rigidity cannot withstand the thermal stress due to the difference in thermal expansion during cooling, and may cause peeling failure. Furthermore, the target life may not be satisfied under the temperature cycle conditions of -55 to 125 ° C and -65 to 150 ° C.
[0009]
Therefore, since it is necessary to lower the soldering temperature and to ensure high reliability, the relationship between the control of the addition amount of Bi and In, reliability, and process compatibility is important. When Bi is added, the melting point decreases (Fig. 1), but the mechanical properties are also significantly reduced (Fig. 2). Therefore, it became clear that the mechanical reliability of the joint is determined by the amount of Bi, and that the addition of In plays a role in lowering the melting point with almost no loss of mechanical properties (FIG. 3) (FIG. 4). Since the solid solubility limit of Bi in Sn-Ag-Cu solder to Sn crystals is about 1.5%, the temperature can be lowered if more is added, but Bi that cannot be dissolved precipitates and mechanical properties, particularly important elongation As a result, the strength of the bonding interface is reduced (FIG. 5).
[0010]
When the solid solution of Bi in Sn crystals is within 1.5%, the mechanical properties are slightly reduced compared to 0% Sn-Ag-Cu. The Bi amount that can lower the melting point without impairing the mechanical strength is set to 0.5 to 3.0%. It has been found that an amount of Bi higher than this leads to a decrease in the strength of the bonding interface, and it is experimentally affected beyond this. In particular, at Bi: 3%, Bi tends to segregate at the interface, but usually a Ni / Au metallized film is applied to the surface, so even if Bi is segregated to some extent, Bi and Ni form an intermetallic compound. Because it is easy to do, it can withstand it because it is familiar and good adhesion unlike Cu.
[0011]
Next, in order to lower the soldering temperature, that is, to lower the melting point, it was decided to add 3 to 5% of In. The reason for setting it to 3% is that it has an effect of being lowered by 5 to 10 ° C. with respect to the case where In is not added. Below this, the soldering temperature is too high. If it is 5% or more, In is easy to oxidize from the viewpoint of cost, it tends to be affected by paste storability and printability, and leads to instability on the solder structure.
[0012]
That is, when the solidus temperature is lowered and Pb is further contained, a low-temperature phase of Sn—In—Pb—Bi is likely to be produced, resulting in a problem with reliability. The composition range of Cu has the effect of lowering the melting point of the Sn—Ag crystal several times without impairing the mechanical properties. However, when the Cu content exceeds 0.8%, the elongation decreases (FIG. 6).
[0013]
When Cu is a bonding target, it is also effective in preventing Cu erosion. If the Ag content is 2% or less, the melting point increases and the mechanical strength properties such as elongation decrease. If it is 3.5% or more, the melting point is increased and the mechanical strength characteristics are lowered, and the cost is high. Therefore, the solder composition was determined to be Sn- (2-3.5) Ag- (0.2-0.8) Cu- (3-5) In- (0.5-3) Bi.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Since the liquidus temperature of the Sn—Ag—Cu system is 218 ° C., the temperature of the joint portion needs to be 220 ° C. or higher. When placed in about 300 x 300 in the furnace, considering the temperature variation of the joint (ΔT = 10 ° C), the joint has a temperature of 220 (min) to 230 (max) ° C. Temperature hierarchy connection is possible.
[0015]
In the Sn-Ag-Cu system, if the temperature is 220 ° C or higher, the terminal part is surely wetted, and even if the temperature rises, wetting spread does not increase, but the place where the solder is placed is definitely wet. confirmed. Therefore, the part on which the solder foil is placed is surely wetted.
[0016]
The Sn-Ag-Cu-Bi system is known as the composition of Pb-free solder that can be connected at this temperature. As a specific composition, for example, Sn-3Ag-0.7Cu temporarily fixed to a typical composition of Ag and Cu,
Bi: About 4 to 6% of solder is within the solderable range. When Bi is 6% or more, the melting point is lowered and soldering becomes easy. However, the elongation characteristic of the material is lowered and the strength (peel strength) of the joint interface is lowered (FIG. 5), so the reliability is lowered and Bi is reduced. There is no point in putting more. Therefore, the melting point becomes high, but the region with a small Bi in the direction of improving the reliability becomes important. The composition range of the Sn—Ag—Cu—Bi solder that can be soldered at 220 to 230 ° C. is about Bi: 5%.
[0017]
Using Sn-3Ag-0.5Cu solder with different Bi content, 42 alloy leads plated with Sn-10Pb and Cu foil were soldered, and the peel strength results at the joint interface (Fig. 7) It can be seen that when 5% Bi enters, the strength of the interface decreases. This tendency with respect to Bi shows a similar tendency with Ni plating although the absolute values are different. The cause of this strength reduction is segregation at the Bi interface. At present, when Bi is as low as 2-3%, an increase in Bi concentration is observed on the fracture surface, but the existence of a clear Bi phase has not been confirmed. In addition, the mechanical properties such as elongation are not abrupt changes with respect to Bi as in peel strength, but are somewhat gradual. Therefore, it is expected that 3Bi has excellent temperature cycle resistance.
[0018]
In the power device, as shown in FIG. 8, a Mo plate 2 (low thermal expansion thermal diffusion plate, Ni plating 5) and a Cu plate heat sink 9 (Ni plating) are sandwiched between 0.15 mmt Sn-7Sb so as to sandwich the alumina substrate 3 therebetween. (Melting point: 235 to 244 ° C.) Soldering was performed using solder foil 8 at a maximum of 270 ° C. in an inert atmosphere. Then, Si chip 1 (metalized 4 with W / Ni, etc.) is placed on the back of the bonded Mo (Ni plating) using Sn-3Ag-0.7Cu-3In-3Bi solder foil 7 (0.15mmt). Similarly, soldering was performed at 230 ° C. in an inert atmosphere. At this time, as a matter of course, Sn-7Sb does not melt, so that hierarchical connection can be realized. 6 is W-Ni plating.
[0019]
FIG. 9 shows an example in which this solder is applied to a large sealing structure. A W / Ni plated ceramic container 9 and a Ni plated Cu plate 10 are sealed with Sn-3Ag-0.7Cu-3In-2Bi solder foil 12. It was confirmed that there was no problem in the helium leak test. 11 is ceramic.
[0020]
On the other hand, for comparison, the Si chip was similarly joined with Sn-3Ag-0.7Cu5Bi (melting point: 195 to 215 ° C.) solder and the reliability was evaluated. As a result of cutting out the soldered sample and polishing the cross section, a concentrated layer in which Bi was contained in the solder in a content ratio (5%) or more was found by EDX analysis on the side where final solidification occurred. Since it is a joint with Ni, it was not extremely weak like Cu, but as long as this segregation occurs, it cannot be said to be a normal joint. In a temperature cycle test at -55 to 125 ° C, it was found that the crack growth at the interface of the concentrated layer of Bi was faster than that of Sn-3Ag-0.7Cu-3In-3Bi solder, which was a problem.
[0021]
As a result, Sn-3Ag-0.7Cu-3In-3Bi has better thermal fatigue resistance than Sn-Pb eutectic, while Sn-3Ag-0.7Cu-5Bi has better resistance to Sn-Pb eutectic. It was confirmed that the heat fatigue resistance was inferior. Creep resistance is Sn-based, Sn-3Ag-0.7Cu-3In-3Bi and Sn-3Ag-0.7Cu-5Bi are both Sn-based, and since Bi is contained, the strength is high, so it is compared with Sn-Pb eutectic. And several times better. In addition, the melting point is 195 ° C or higher, which is higher than 183 ° C of Sn-Pb eutectic and is a collection of strong and hard Sn crystals.
[0022]
Fig. 10 shows Sn-3Ag-0.7Cu solder as an example. The left half of the horizontal axis contains 0 to 5% Bi and the right half contains 0 to 5% In. The vertical axis shows temperature. is there. In FIG. 11, the horizontal axis is the same, and the vertical axis is elongated. The amount of Bi, the liquidus and the solidus of the solder are shown in the left half, and 2% Bi is contained in Sn-3Ag-0.7Cu, and the liquidus and solidus of the solder containing In are contained in the right half. Indicated. Sn-3Ag-0.7Cu-2Bi-3In has a melting point close to Sn-3Ag-0.7Cu-5Bi and lower than Sn-3Ag-0.7Cu-2Bi. Thus, the soldering temperature of Sn-3Ag-0.7Cu-2Bi-3In can be as high as Sn-3Ag-0.7Cu-5Bi. Similarly, a combination of Bi: 0.5 to 3% and In: 3 to 5% is possible at a soldering temperature comparable to Sn-3Ag-0.7Cu-5Bi.
[0023]
As a result, the melting point and soldering temperature were similar to Sn-3Ag-0.7Cu-5Bi, and a highly reliable solder composition could be obtained. In the case of Sn-3Ag-0.7Cu-2Bi-5In, whose melting point was lowered with In, the process and reliability were cleared in the same way. Furthermore, the inclusion of In is not desirable because it tends to lower the melting point and has problems of cost, printability (lifetime), and structural stability (formation of a low temperature phase). Although the solid solution of Bi in the Sn matrix is 1.2%, the bulk material is brittle in proportion to the amount of Bi, but it can be said that the Bi is excellent up to 2%.
[0024]
Next, Sn-3Ag-0.7Cu-3In (melting point: 207 to 216 ° C.) and Sn-3Ag-0.7Cu (melting point: 216 to 220 ° C.), which were not added with Bi, were evaluated. The melting point of Sn-3Ag-0.7Cu-3In was not much different from Sn-3Ag-0.7Cu-5Bi, and connection was possible at 230 ° C. Although the joint part temperature of Sn-3Ag-0.7Cu exceeds max 235 ° C, it cannot be used, but the joint reliability was achieved. There is no peeling of the joint during soldering. The reason for this is thought to be that the strength of the bonding interface is high because Bi is not included.
[0025]
Furthermore, as a result of performing the temperature cycle test in the same manner, both of them cleared the target 2000 cycles in the temperature cycle test of −55 to 125 ° C., and crack progress is small. However, in the case of Sn-3Ag-0.7Cu, fracture occurred in the metallized part at a severely stressed position. Since such a phenomenon is not caused in other compositions, it is considered to be a phenomenon peculiar to Sn-3Ag-0.7Cu. The cause is that the melting point is high, the residual stress and strain are high when cooled to room temperature, and the strength of the solder is high. This is especially true when the rigidity is strong.
[0026]
From these results, it was confirmed that Sn-3Ag-0.7Cu- (0.5-3) Bi- (3-5) In has an excellent balanced composition. The base Sn-3Ag-0.7Cu can be Sn- (2-3.5) Ag- (0.2-0.8) Cu as the range of Ag and Cu, so the Pb-free solder composition that satisfies these conditions is Sn- (2-3.5) Ag- (0.2-0.8) Cu- (0.5-3) Bi- (3-5) In.
[0027]
【The invention's effect】
As described above, according to the present invention, environmentally friendly products can be supplied because lead is not used.
[0028]
The conventional method can be applied as it is in the current furnace. On the other hand, it is superior to conventional Sn—Pb eutectic solder in heat fatigue resistance, creep resistance and high temperature resistance, and a high yield can be expected for high density mounting.
[Brief description of the drawings]
FIG. 1 is a characteristic diagram showing a melting point when Bi is added to Sn—Ag—Cu.
FIG. 2 is a characteristic diagram showing elongation when Bi is added to Sn—Ag—Cu.
FIG. 3 is a characteristic diagram showing elongation when In is added to Sn—Ag—Cu.
FIG. 4 is a characteristic diagram showing a melting point when In is added to Sn—Ag—Cu.
FIG. 5 is a characteristic diagram showing the connection strength with a 42 alloy lead plated with Sn when Bi is added to Sn—Ag—Cu.
FIG. 6 is a characteristic diagram showing elongation when Cu is added to Sn-Ag.
FIG. 7 is a characteristic diagram showing the connection strength with Cu when Bi is added to Sn—Ag—Cu.
FIG. 8 is a cross-sectional view showing a power device using the present invention.
FIG. 9 is a cross-sectional view showing a large sealing structure using the present invention.
FIG. 10 is a characteristic diagram showing a melting point when Bi and In are added to Sn—Ag—Cu.
FIG. 11 is a characteristic diagram showing elongation when Bi and In are added to Sn—Ag—Cu.
[Explanation of symbols]
1 ... Si chip, 2 ... Mo plate, 3 ... alumina, 4 ... metallized film, 5 ... Ni plating, 6 ... W-Ni plating, 7 ... Sn-3Ag-0.7Cu-3Bi-3In, 8 ... Sn-Sb, 9 ... Cu plate, 10 ... Ceramic, 11 ... Cu plate, 12 ... Sn-3Ag-0.7Cu-2Bi-3In.

Claims (2)

素子を内蔵したSi等のチップを絶縁基板もしくはヒートシンク材に第一の鉛フリーはんだで接続し、更にその下にヒートシンク材もしくは絶縁基板を第二の鉛フリーはんだで接続する階層接続構造において、
前記第二の鉛フリーはんだは、Sn-Sb(236〜240℃)であり
前記第一の鉛フリーはんだは、Sn-(2〜3.5)Ag-(0.2〜0.8)Cu-(3〜5)In-(0.5〜3)Biもしくはそれに他の微量元素を添加したものであること
を特徴とする鉛フリーはんだ接続構造体。
In a hierarchical connection structure in which a chip such as Si having a built-in element is connected to an insulating substrate or a heat sink material with a first lead-free solder, and further a heat sink material or an insulating substrate is connected to the lower layer with a second lead-free solder,
It said second lead-free solder is an Sn-Sb (236~240 ℃),
The first lead-free solder is obtained by addition of Sn- (2~3.5) Ag- (0.2~0.8) Cu- (3~5) In- (0.5~3) Bi or other trace elements to it A lead-free solder connection structure characterized by that.
素子を内蔵した Si 等のチップを絶縁基板もしくはヒートシンク材に第一の鉛フリーはんだで接続し、更にその下にヒートシンク材もしくは絶縁基板を第二の鉛フリーはんだで接続する階層接続構造において、
前記第二の鉛フリーはんだは、 Sn-Sb(236 240 ) であり、
前記第一の鉛フリーはんだは、Sn-(2〜3.5)Ag-(0.2〜0.8)Cu-(3〜5)In-(0.5〜3)Bi-(0.2〜1)Sbもしくはそれに他の微量元素を添加したものであること
を特徴とする鉛フリーはんだ接続構造体。
In a hierarchical connection structure in which a chip such as Si having a built-in element is connected to an insulating substrate or a heat sink material with a first lead-free solder, and further a heat sink material or an insulating substrate is connected to the lower layer with a second lead-free solder,
The second of the lead-free solder is a Sn-Sb (236 ~ 240 ℃ ),
The first lead-free solder is Sn- (2-3.5) Ag- (0.2-0.8) Cu- (3-5) In- (0.5-3) Bi- (0.2-1) Sb or other trace amounts. lead-free solder connection structure characterized by elemental is obtained by adding.
JP20721399A 1999-07-22 1999-07-22 Lead-free solder connection structure Expired - Fee Related JP3832151B2 (en)

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US6892925B2 (en) 2002-09-18 2005-05-17 International Business Machines Corporation Solder hierarchy for lead free solder joint
US6854636B2 (en) 2002-12-06 2005-02-15 International Business Machines Corporation Structure and method for lead free solder electronic package interconnections
US6917113B2 (en) * 2003-04-24 2005-07-12 International Business Machines Corporatiion Lead-free alloys for column/ball grid arrays, organic interposers and passive component assembly
JP2005310956A (en) 2004-04-20 2005-11-04 Denso Corp Method for manufacturing semiconductor device
US8004075B2 (en) 2006-04-25 2011-08-23 Hitachi, Ltd. Semiconductor power module including epoxy resin coating
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CN102017111B (en) 2008-03-05 2013-01-16 千住金属工业株式会社 Lead-free solder joint structure and solder ball
CN103962744B (en) 2009-04-20 2016-05-18 松下知识产权经营株式会社 Soldering tin material and electronic unit conjugant
JP2011138968A (en) * 2009-12-28 2011-07-14 Senju Metal Ind Co Ltd Method for soldering surface-mount component, and surface-mount component
WO2012150452A1 (en) * 2011-05-03 2012-11-08 Pilkington Group Limited Glazing with a soldered connector
JP5732627B2 (en) * 2013-11-27 2015-06-10 パナソニックIpマネジメント株式会社 Solder material and joint structure
JP2015105391A (en) * 2013-11-28 2015-06-08 パナソニックIpマネジメント株式会社 Method for producing lead-free solder alloy powder
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