JP3597607B2

JP3597607B2 - Solder alloy and paste solder

Info

Publication number: JP3597607B2
Application number: JP22708395A
Authority: JP
Inventors: 嘉明田中
Original assignee: Uchihashi Estec Co Ltd
Current assignee: Uchihashi Estec Co Ltd
Priority date: 1995-08-11
Filing date: 1995-08-11
Publication date: 2004-12-08
Anticipated expiration: 2015-08-11
Also published as: JPH0952191A

Description

【０００１】
【発明の属する技術分野】
本発明ははんだ合金及びそのはんだ合金の粉末を使用したペ−スト状はんだに関するものである。
【０００２】
【従来の技術】
周知の通り、はんだ付け時、被はんだ付け金属が溶融はんだに溶解し、はんだが凝固する際に、はんだ成分のＳｎまたはＰｂと被はんだ付け金属との化合物が析出する現象、すなわち、はんだ溶食の発生が避けられず、所謂、Ａｇ食われが発生することがある。
例えば、回路基板への電子部品の実装においては、Ａｇ厚膜電極等に対するはんだ付けの際に、Ａｇが溶融はんだに溶出し、このＡｇとＳｎまたはＰｂとの化合物がはんだ付け界面に析出することがある。
この場合、Ａｇ食われにより、Ａｇ厚膜電極の消失が懸念され、導通不良等が招来される畏れがある。このためＡｇ溶食防止はんだの組成が種々提案されている。
【０００３】
周知の通り、はんだ付け界面においては、凝固はんだと被はんだ付け金属との熱膨張係数の差異に基づく熱応力の発生が避けられず、特に、ヒ−トサイクルのもとでは、その応力が繰返し応力となり、はんだ付け界面を疲労させる原因となる。このため耐疲労性改善のためのはんだ組成が種々提案されている。
特に、電子部品を実装した回路板においては、通電のオン、オフによるヒ−トサイクルを受けるので、上記した耐Ａｇ溶食性のみならず高度の耐熱疲労性が要求される。
【０００４】
上記Ａｇ溶食の防止には、はんだにＡｇを、はんだ付け温度下での飽和濃度に相当する量だけ添加することが有効であり、耐Ａｇ溶食はんだとして、Ｓｎ−ＰｂはんだにＡｇを０．５〜５．０重量％添加した組成が知られている。
この場合、Ａｇ単独の添加に代え、Ａｇ及びＩｎを添加することの有効性も知られている。
しかしながら、ＡｇまたはＡｇ及びＩｎの添加だけでは耐熱疲労性の付与が不十分であり、耐Ａｇ溶食性は勿論のこと耐熱疲労性の改善を図るために、例えば、次のような組成が提案されている。
【０００５】
（１）Ｓｎ：１５〜６５重量％，Ａｇ：０．５〜３．５重量％，Ｓｂ：０．５〜３．０重量％，残部Ｐｂ（特開昭５６−１４４８９３号公報）。
（２）Ｐｂ：１０〜９５重量％，Ａｇ：０．０１〜１０重量％，Ｉｎ：０．０１〜１０重量％，Ｓｂ：０．１〜８重量％，残部Ｓｎ（特開平３−１０６５９１号公報）。
（３）Ｐｂ：１０〜９５重量％，Ａｇ：０．０１〜１０重量％，Ｉｎ：０．０１〜１０重量％，Ｂｉ：０．１〜８重量％，残部Ｓｎ（特開平３−１０６５９１号公報）。
（４）Ｐｂ：２０〜３５重量％，Ａｇ：０．０５〜５重量％，Ｉｎ：０．１〜５重量％，Ｓｂ：０．０５〜１重量％，Ｃｕ：０．０５〜２重量％，残部Ｓｎ（特開平３−１０６５９１号公報）。
（５）Ｐｂ：３５〜５０重量％，Ａｇ：０．０５〜５重量％，Ｉｎ：０．１〜５重量％，Ｓｂ：０．０５〜１重量％，Ｃｕ：０．０５〜２重量％，残部Ｓｎ（特開平３−１０６５９１号公報）。
（６）Ｐｂ：１０〜９０重量％，Ａｇ：０．０５〜４．０重量％，Ｓｂ：０．５〜５．０重量％，Ｃｕ：０．０５〜３．０重量％，残部Ｓｎ（特公昭５２−３０３７７号公報）。
【０００６】
【発明が解決しようとする課題】
これらのはんだ組成は、Ｓｎ−ＰｂはんだにＡｇ，Ｂｉ，Ｉｎ，Ｓｂ，Ｃｕの３乃至４種を添加したものに該当し、Ａｇ，Ｂｉ，Ｉｎ，Ｓｂ，Ｃｕの全てを添加するものではない。Ａｇ，Ｂｉ，Ｉｎ，Ｓｂ，Ｃｕ等をＳｎ−Ｐｂ系はんだの添加材として使用することは公知であり（例えば、特開昭６１−２７３２９２号公報の第１表）、上記（１）〜（７）に例示したはんだ組成は、Ａｇ，Ｂｉ，Ｉｎ，Ｓｂ，Ｃｕの３乃至４種の選択とその添加量の限定により耐Ａｇ溶食性と耐熱疲労性の改善を図っている。何れの組成においても、耐Ａｇ溶食性の付与のためにＡｇまたはＡｇ及びＩｎを添加している。
【０００７】
しかしながら、ＢｉとＳｂとＣｕの三者を共に添加しているものはない。Ｂｉ、Ｓｂ及びＣｕ等においては、はんだ自体の組織を緻密化して機械的強度を増大させる点で耐熱疲労性の改善に寄与する。しかしながら、組織の緻密化ははんだの融点を上昇させ、融点上昇のもとではＡｇの溶解飽和濃度が上昇するから、Ａｇ溶食が生じ易くなり、結局耐熱疲労性を保証できなくなる。しかるに、耐熱疲労性は接合界面での安定な合金層の形成による接合強度の増加やはんだ自体への伸び性の付与によっても改善でき、本発明者の検討結果によれば、ＢｉとＳｂとＣｕの三者を共に特定の量で添加すれば、はんだの機械的強度ののみならずこれらの点からも耐熱疲労性性の改善が可能となり、Ａｇ溶食を有効に防止のうえ優れた耐熱疲労性を付与できることを知った。
【０００８】
本発明の目的は、上記知見に基づき、耐Ａｇ溶食性は勿論のこと耐熱疲労性に優れたはんだ合金を提供することにある。
【０００９】
【課題を解決するための手段】
請求項１に係るはんだ合金は、Ｓｎが５０〜７０重量％、Ａｇが０．５〜５．０重量％、Ｂｉが０．１〜２．０重量％、Ｃｕが０．０３〜０．３重量％、Ｓｂが０．１〜２．０重量％、残部がＰｂであることを特徴とする。
請求項２に係るはんだ合金は、Ｓｎが５０〜７０重量％、ＡｇとＩｎが等量でそれらの合計量が０．５〜５．０重量％、Ｂｉが０．１〜２．０重量％、Ｃｕが０．０３〜０．３重量％、Ｓｂが０．１〜２．０重量％、残部がＰｂであることを特徴とする。
請求項３に係るはんだ合金は、請求項１または２の組成１００重量部にＰが０．００２〜０．５重量部添加されていることを特徴とする。
請求項４に係るペースト状はんだは、請求項１〜３何れかのはんだ合金の粉末とペースト状フラックスとからなることを特徴とする。
【００１０】
本発明において、Ｓｎ−Ｐｂ系合金をベ−スとする理由は、はんだ付けの基本的条件である濡れ性を確保するためである。そのＳｎの量を５０〜７０重量％とする理由は、液相線温度をフロ−法又はリフロ−法に適したはんだ付け温度に設定するためであり、表面実装部品を熱衝撃損傷の畏れなく安全にはんだ付けし、また、Ａｇの飽和溶解度の上昇を排除してＡｇ溶食を効果的に防止するのに有効な要件である。
【００１１】
Ａｇを添加する理由は、前述したＡｇ溶食を防止するためであり、その添加量を０．５〜５．０重量％とする理由は、０．５重量％未満ではその効果を満足に達成し得ず、５．０重量％を越えると、液相温度が高くなり過ぎ、Ａｇの飽和溶解度が上昇して有効なＡｇ溶食防止を行い難く、また、上記適切なはんだ付け温度の設定が困難になるためである。
このＡｇ単独添加に代えＡｇ及びＩｎを使用するのは、Ａｇの添加によりＡｇ_３Ｓｎホイスカ−の発生が懸念されるためであり、この場合、Ｉｎ添加量が５．０重量％を越えると、低温域での固相間変態のためにヒ−トサイクルによる組織の脆弱化が惹起され、耐熱疲労性の保障が困難になる。
【００１２】
Ｂｉを添加する理由は、合金組織の緻密化を促し、機械的強度を増大させるためであり、その添加量を０．１〜２．０重量％とする理由は、０．１重量％未満ではその効果を満足に達成し得ず、２．０重量％を超えると、はんだ自体の粘性が低下し伸びが低下し脆くなって耐熱疲労性の保証が困難になり、またはんだ表面の光沢性が喪失されるに至るからである。
【００１３】
Ｃｕを添加する理由は、上記と同様機械的強度を増大させるためであり、その添加量を０．０３〜０．３重量％とする理由は、０．０３重量％未満ではその効果を満足に達成し得ず、０．３重量％を超えると、融点が高くなって前記適正なはんだ付け温度の設定等が困難になり、また、はんだの機械的強度が低下し耐熱疲労性の保証が困難になり、更には、はんだの流動性が低下して作業性が悪くなるからである。
【００１４】
Ｓｂを添加する理由は、上記と同様機械的強度を増大させるためとはんだの接合強度を増大させるためであり、その添加量を０．１〜２．０重量％とする理由は、０．１重量％未満ではその効果を満足に達成し得ず、２．０重量％を超えると、はんだ自体が硬く脆くなって伸びが低下し、接合強度も低下して耐熱疲労性の保証が困難になり、またはんだの流動性が低下して作業性が悪くなるからである。
【００１５】
上記Ａｇ、Ａｇ及びＩｎ、Ｂｉ、Ｓｂ並びにＣｕの添加理由や添加量との関連で述べた作用は、各添加元素単独で奏する作用であり、これ以外に相乗作用により耐熱疲労性性が向上されることは、次の実施例と比較例との対比から、何れの元素を削除しても、耐熱疲労性性が顕著に低下する事実より認識できる。
【００１６】
本発明において、Ｐを添加する理由は、酸化防止及びＣｕやＳｂの添加による濡れ広がり性の低下抑制にあり、その添加量を０．００２〜０．５重量％とする理由は、０．００２重量％未満ではその効果を満足に達成し得ず、０．５重量％を超えると、はんだ自体が硬く脆くなって伸びが低下し耐熱疲労性の保証が困難になるからである。
【００１７】
【発明の実施の形態】
本発明に係るはんだ合金においては、従来のはんだに較べて優れた耐熱疲労性性を呈する。なお、上記の添加元素以外に、ＪＩＳ−Ｚ−３２８２に規定されたＡ級に属する範囲内の不純物を含んでいても、本発明の効果は影響されずに達成される。
本発明に係るはんだ合金はフロ−法による回路基板への電子部品の実装に使用される。また、リフロ−法による回路基板への電子部品の実装にも使用され、この場合は、電子部品をペ−スト状はんだの粘着力で回路基板に仮固定し、この回路基板を加熱炉に通しペ−スト状はんだをリフロ−させることによりはんだ付けを行っていく。
本発明に係るペ−スト状はんだにおいては、はんだ粉末８５〜９５重量％、残部ペ−スト状フラックスの配合で使用され、はんだ粉末のメッシュは２５０〜５００とされる。ペ−スト状フラックスには、重合ロジン、水添ロジン、天然ロジン、マレイン化ロジン等のロジンに活性剤、例えば、シクロヘキシルアミンＨＢｒ、オクチルアミンＨＢｒ、マロン酸、コハク酸、安息香酸等を添加し、これを溶剤でペ−スト化したものを使用できる。
本発明に係るはんだ合金においては、上記粉末状の外、棒状、線状、リボン状、やに入りはんだの形態で使用することもできる。
【００１８】
【実施例】
〔実施例１〕
はんだ合金の組成に、Ｓｎ：６２重量％、Ａｇ：２．０重量％、Ｂｉ：０．６重量％、Ｃｕ：０．０６重量％、Ｓｂ：０．６重量％，残部Ｐｂを使用した。ペ−スト状フラツクスには、重合ロジン：６０重量％、水素添加ヒマシ油：５重量％、シクロヘキシルアミンＨＢｒ：１重量％、残部ブチルカルビト−ルを使用し、４００メッシュはんだ合金粉末９０重量％とペ−スト状フラツクス１０重量％とを混合撹拌してペ−スト状はんだを作成した。
【００１９】
〔実施例２〕
実施例１に対し、Ａｇ：２．０重量％に替えＡｇ：１．０重量％及びＩｎ：１．０重量％を使用した以外、実施例１と同様にしてペ−スト状はんだを作成した。
〔実施例３〕
実施例１のはんだ合金組成１００重量部にＰを０．１重量部添加した合金組成を使用した以外、実施例１と同様にしてペ−スト状はんだを作成した。
〔実施例４〕
実施例２のはんだ合金組成１００重量部にＰを０．１重量部添加した合金組成を使用した以外、実施例２と同様にしてペ−スト状はんだを作成した。
【００２０】
〔比較例１〕
実施例１に対し、はんだ合金の組成に、Ｓｎ：６２重量％、Ａｇ：２．０重量％、残部Ｐｂを使用した以外、実施例１と同様にしてペ−スト状はんだを作成した（実施例１に対し、Ｂｉ、Ｃｕ及びＳｂの省略）。
〔比較例２〕
実施例１に対し、はんだ合金の組成に、Ｓｎ：６２重量％、Ａｇ：２．０重量％、Ｂｉ：０．６重量％、残部Ｐｂを使用し以外、実施例１と同様にしてペ−スト状はんだを作成した（実施例１に対し、Ｃｕ及びＳｂの省略）。
〔比較例３〕
実施例１に対し、はんだ合金の組成に、Ｓｎ：６２重量％、Ａｇ：２．０重量％、Ｃｕ：０．０６重量％、残部Ｐｂを使用し以外、実施例１と同様にしてペ−スト状はんだを作成した（実施例１に対し、Ｂｉ及びＳｂの省略）。
〔比較例４〕
実施例１に対し、はんだ合金の組成に、Ｓｎ：６２重量％、Ａｇ：２．０重量％、Ｓｂ：０．６重量％、残部Ｐｂを使用し以外、実施例１と同様にしてペ−スト状はんだを作成した（実施例１に対し、Ｂｉ及びＣｕの省略）。
〔比較例５〕
実施例１に対し、はんだ合金の組成に、Ｓｎ：６２重量％、Ａｇ：２．０重量％、Ｂｉ：０．６重量％、Ｃｕ：０．０６重量％、残部Ｐｂを使用し以外、実施例１と同様にしてペ−スト状はんだを作成した（実施例１に対し、Ｓｂの省略）。
〔比較例６〕
実施例１に対し、はんだ合金の組成に、Ｓｎ：６２重量％、Ａｇ：２．０重量％、Ｂｉ：０．６重量％、Ｓｂ：０．６重量％、残部Ｐｂを使用し以外、実施例１と同様にしてペ−スト状はんだを作成した（実施例１に対し、Ｃｕの省略）。
〔比較例７〕
実施例１に対し、はんだ合金の組成に、Ｓｎ：６２重量％、Ａｇ：２．０重量％、Ｃｕ：０．０６重量％、Ｓｂ：０．６重量％、残部Ｐｂを使用し以外、実施例１と同様にしてペ−スト状はんだを作成した（実施例１に対し、Ｂｉの省略）。
上記何れの合金組成においても、添加元素以外の不純物は、ＪＩＳ−Ｚ−３２８２に規定のＡ級の範囲に属している。
【００２１】
これらの実施例並びに比較例のペ−スト状はんだを使用し、チップ抵抗をガラスエポキシ回路基板にリフロ−法によりはんだ付けし、−４０℃にて３０分、１００℃にて３０分を１サイクルとする熱衝撃試験を５００サイクルまで行い、その間１００サイクルごとにはんだ付けフィレットの外観を観察したところ、表の通りであった。
ただし、○ははんだ付けフィレットが正常であることを、△は皺の発生があることを、×はクラックが発生していることをそれぞれ示している。
【００２２】
【表１】

【００２３】
この表から明らかなように、本発明によれば、はんだ付けフィレットの繰返し熱応力に対する耐久性を飛躍的に向上できる。特に、本発明に対してＳｂを省略した比較例５、同じくＣｕを省略した比較例６、同じくＢｉを省略した比較例７に較べても格段の向上効果が認められることから、ＢｉとＣｕとＢｉとの予想外の相乗作用が推測される。
【００２４】
【発明の効果】
本発明によれば、耐熱衝撃試験に対して著しく安定なはんだ付けを可能とするはんだ合金及びペ−スト状はんだを提供でき、電子部品実装回路板の導通信頼性や安定性を長期にわたって保証できる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a solder alloy and a paste solder using the powder of the solder alloy.
[0002]
[Prior art]
As is well known, when soldering, the metal to be soldered dissolves in the molten solder, and when the solder solidifies, a phenomenon in which a compound of the solder component Sn or Pb and the metal to be soldered precipitates, that is, solder erosion. Is unavoidable, and so-called Ag erosion may occur.
For example, when mounting an electronic component on a circuit board, Ag is eluted into the molten solder when soldering to an Ag thick film electrode or the like, and the compound of Ag and Sn or Pb precipitates at the soldering interface. There is.
In this case, there is a concern that the Ag thick film electrode may disappear due to the Ag erosion, which may lead to poor conduction and the like. For this reason, various compositions of Ag corrosion prevention solders have been proposed.
[0003]
As is well known, at the soldering interface, the generation of thermal stress due to the difference in the thermal expansion coefficient between the solidified solder and the metal to be soldered is unavoidable, and especially, under the heat cycle, the stress repeats. It becomes stress and causes fatigue of the soldering interface. For this reason, various solder compositions for improving fatigue resistance have been proposed.
In particular, since a circuit board on which electronic components are mounted is subjected to a heat cycle by turning on and off the current, high heat fatigue resistance as well as the above-described Ag erosion resistance is required.
[0004]
In order to prevent the Ag erosion, it is effective to add Ag to the solder in an amount corresponding to the saturation concentration at the soldering temperature. A composition in which 0.5 to 5.0% by weight is added is known.
In this case, the effectiveness of adding Ag and In instead of adding Ag alone is also known.
However, the addition of Ag or Ag and In alone does not provide sufficient thermal fatigue resistance. In order to improve not only Ag corrosion resistance but also thermal fatigue resistance, for example, the following composition has been proposed. ing.
[0005]
(1) Sn: 15 to 65% by weight, Ag: 0.5 to 3.5% by weight, Sb: 0.5 to 3.0% by weight, balance Pb (JP-A-56-144893).
(2) Pb: 10 to 95% by weight, Ag: 0.01 to 10% by weight, In: 0.01 to 10% by weight, Sb: 0.1 to 8% by weight, balance Sn (JP-A-3-106591) Gazette).
(3) Pb: 10 to 95% by weight, Ag: 0.01 to 10% by weight, In: 0.01 to 10% by weight, Bi: 0.1 to 8% by weight, balance Sn (JP-A-3-106591) Gazette).
(4) Pb: 20 to 35% by weight, Ag: 0.05 to 5% by weight, In: 0.1 to 5% by weight, Sb: 0.05 to 1% by weight, Cu: 0.05 to 2% by weight And the remainder Sn (Japanese Patent Laid-Open No. 3-106591).
(5) Pb: 35 to 50% by weight, Ag: 0.05 to 5% by weight, In: 0.1 to 5% by weight, Sb: 0.05 to 1% by weight, Cu: 0.05 to 2% by weight And the remainder Sn (Japanese Patent Laid-Open No. 3-106591).
(6) Pb: 10 to 90% by weight, Ag: 0.05 to 4.0% by weight, Sb: 0.5 to 5.0% by weight, Cu: 0.05 to 3.0% by weight, balance Sn ( JP-B-52-30377).
[0006]
[Problems to be solved by the invention]
These solder compositions correspond to those obtained by adding 3 to 4 types of Ag, Bi, In, Sb, and Cu to Sn-Pb solder, and do not add all of Ag, Bi, In, Sb, and Cu. . It is known to use Ag, Bi, In, Sb, Cu and the like as additives for Sn-Pb-based solder (for example, Table 1 of JP-A-61-273292). The solder composition exemplified in 7) aims to improve the Ag corrosion resistance and the thermal fatigue resistance by selecting three or four types of Ag, Bi, In, Sb, and Cu and limiting the amount of addition. In any composition, Ag or Ag and In are added for imparting Ag corrosion resistance.
[0007]
However, none of them add Bi, Sb, and Cu together. Bi, Sb, Cu and the like contribute to improvement of thermal fatigue resistance in that the structure of the solder itself is densified to increase the mechanical strength. However, densification of the structure increases the melting point of the solder, and under the rise in the melting point, the dissolved saturation concentration of Ag increases. Therefore, Ag erosion is likely to occur, and eventually, the thermal fatigue resistance cannot be guaranteed. However, the thermal fatigue resistance can also be improved by increasing the bonding strength by forming a stable alloy layer at the bonding interface or by imparting elongation to the solder itself. According to the study results of the present inventors, Bi, Sb and Cu By adding the above three in specific amounts, it becomes possible to improve not only the mechanical strength of the solder but also the thermal fatigue resistance in these respects. We knew that we could give sex.
[0008]
An object of the present invention is to provide a solder alloy having excellent resistance to Ag corrosion as well as excellent heat fatigue resistance based on the above findings.
[0009]
[Means for Solving the Problems]
In the solder alloy according to claim 1, Sn is 50 to 70% by weight, Ag is 0.5 to 5.0% by weight, Bi is 0.1 to 2.0% by weight, and Cu is 0.03 to 0.3%. % By weight, Sb is 0.1 to 2.0% by weight, and the balance is Pb.
In the solder alloy according to claim 2, Sn is 50 to 70% by weight, Ag and In are equivalent, and the total amount thereof is 0.5 to 5.0% by weight, and Bi is 0.1 to 2.0% by weight. , Cu is 0.03 to 0.3% by weight, Sb is 0.1 to 2.0% by weight, and the balance is Pb.
The solder alloy according to claim 3 is characterized in that 0.002 to 0.5 parts by weight of P is added to 100 parts by weight of the composition of claim 1 or 2.
According to a fourth aspect of the present invention, there is provided a paste-like solder comprising a powder of the solder alloy according to any one of the first to third aspects and a paste-like flux.
[0010]
In the present invention, the reason why the Sn-Pb alloy is used as a base is to secure wettability, which is a basic condition for soldering. The reason for setting the amount of Sn to 50 to 70% by weight is to set the liquidus temperature to a soldering temperature suitable for the flow method or the reflow method. This is an effective requirement for safely soldering and effectively preventing Ag corrosion by eliminating an increase in the saturation solubility of Ag.
[0011]
The reason for adding Ag is to prevent the above-mentioned Ag erosion, and the reason for setting the addition amount to 0.5 to 5.0% by weight is that when the amount is less than 0.5% by weight, the effect is satisfactorily achieved. If it exceeds 5.0% by weight, the liquidus temperature becomes too high, the saturation solubility of Ag increases, it is difficult to effectively prevent Ag corrosion, and the above-mentioned appropriate setting of the soldering temperature is difficult. Because it becomes difficult.
The reason for using Ag and In instead of adding Ag alone is that the addition of Ag may cause the generation of Ag ₃ Sn whiskers. In this case, if the amount of In exceeds 5.0% by weight, Due to the solid-phase transformation in the low-temperature region, the structure becomes weakened by the heat cycle, and it becomes difficult to guarantee the thermal fatigue resistance.
[0012]
The reason for adding Bi is to promote the densification of the alloy structure and increase the mechanical strength. The reason for adding the amount of 0.1 to 2.0% by weight is that Bi is less than 0.1% by weight. If the effect cannot be satisfactorily achieved, and if the content exceeds 2.0% by weight, the viscosity of the solder itself decreases, the elongation decreases, the solder becomes brittle, and it becomes difficult to assure thermal fatigue resistance. For it is lost.
[0013]
The reason for adding Cu is to increase the mechanical strength in the same manner as described above. The reason why the addition amount is set to 0.03 to 0.3% by weight is that when the amount is less than 0.03% by weight, the effect is satisfied. If it cannot be achieved, and if it exceeds 0.3% by weight, the melting point becomes high, making it difficult to set the proper soldering temperature, etc., and the mechanical strength of the solder decreases, making it difficult to guarantee the thermal fatigue resistance. And further, the fluidity of the solder is reduced and the workability is deteriorated.
[0014]
The reason for adding Sb is to increase the mechanical strength and to increase the bonding strength of the solder in the same manner as described above. If the content is less than 2.0% by weight, the effect cannot be achieved satisfactorily. If the content is more than 2.0% by weight, the solder itself becomes hard and brittle, the elongation is reduced, and the bonding strength is reduced, making it difficult to guarantee the thermal fatigue resistance. This is because the workability deteriorates due to a decrease in the fluidity of the solder or the solder.
[0015]
The effects described in relation to the reasons for and addition of Ag, Ag and In, Bi, Sb, and Cu are effects exerted by each of the added elements alone, and in addition to this, the synergistic effect improves the thermal fatigue resistance. This can be recognized from the comparison between the following Examples and Comparative Examples, from the fact that, regardless of which element is removed, the thermal fatigue resistance is significantly reduced.
[0016]
In the present invention, the reason for adding P is to prevent oxidation and to suppress the decrease in wet spreadability by adding Cu or Sb. The reason for adding 0.002 to 0.5% by weight is 0.002%. If the content is less than 0.5% by weight, the effect cannot be satisfactorily achieved. If the content exceeds 0.5% by weight, the solder itself becomes hard and brittle, the elongation is reduced, and it becomes difficult to guarantee the thermal fatigue resistance.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
The solder alloy according to the present invention exhibits excellent thermal fatigue resistance as compared with conventional solders. The effects of the present invention can be attained without affecting even if impurities other than the above-mentioned additional elements in the range belonging to Class A defined in JIS-Z-3282 are included.
The solder alloy according to the present invention is used for mounting electronic components on a circuit board by a flow method. It is also used for mounting electronic components on a circuit board by the reflow method. In this case, the electronic component is temporarily fixed to the circuit board by the adhesive force of paste solder, and the circuit board is passed through a heating furnace. Soldering is performed by reflowing the paste solder.
In the paste solder according to the present invention, 85 to 95% by weight of the solder powder and the balance of the paste flux are used, and the mesh of the solder powder is 250 to 500. To the paste-like flux, an activator, for example, cyclohexylamine HBr, octylamine HBr, malonic acid, succinic acid, benzoic acid, etc. is added to rosin such as polymerized rosin, hydrogenated rosin, natural rosin and maleated rosin. A product obtained by pasting this with a solvent can be used.
The solder alloy according to the present invention can be used in the form of the above-mentioned powdery, rod-shaped, linear, ribbon-shaped, or fluted solder.
[0018]
【Example】
[Example 1]
For the composition of the solder alloy, Sn: 62% by weight, Ag: 2.0% by weight, Bi: 0.6% by weight, Cu: 0.06% by weight, Sb: 0.6% by weight, and the balance Pb were used. As the paste-like flux, polymerized rosin: 60% by weight, hydrogenated castor oil: 5% by weight, cyclohexylamine HBr: 1% by weight, and the balance butyl carbitol were used. A paste-like solder was prepared by mixing and stirring with 10% by weight of a paste-like flux.
[0019]
[Example 2]
A paste-like solder was prepared in the same manner as in Example 1, except that 1.0% by weight of Ag and 1.0% by weight of In were used instead of 2.0% by weight of Ag. .
[Example 3]
A paste-like solder was prepared in the same manner as in Example 1 except that the alloy composition of Example 1 in which 0.1 part by weight of P was added to 100 parts by weight of the solder alloy composition was used.
[Example 4]
A paste-like solder was prepared in the same manner as in Example 2 except that the alloy composition of Example 2 in which 0.1 part by weight of P was added to 100 parts by weight of the solder alloy composition was used.
[0020]
[Comparative Example 1]
A paste-like solder was prepared in the same manner as in Example 1 except that Sn: 62% by weight, Ag: 2.0% by weight, and the balance Pb were used in the composition of the solder alloy (Example 1). Omission of Bi, Cu and Sb from Example 1).
[Comparative Example 2]
In contrast to Example 1, the composition of the solder alloy was the same as Example 1, except that Sn: 62% by weight, Ag: 2.0% by weight, Bi: 0.6% by weight, and the balance Pb were used. A solder paste was prepared (Cu and Sb were omitted from Example 1).
[Comparative Example 3]
In contrast to Example 1, the composition of the solder alloy was the same as Example 1, except that Sn: 62% by weight, Ag: 2.0% by weight, Cu: 0.06% by weight and the balance Pb were used. A solder paste was prepared (Bi and Sb were omitted from Example 1).
[Comparative Example 4]
The procedure of Example 1 was repeated, except that the composition of the solder alloy used was 62% by weight of Sn, 2.0% by weight of Ag, 0.6% by weight of Sb, and the balance Pb. A solder paste was prepared (Bi and Cu were omitted from Example 1).
[Comparative Example 5]
Example 1 was repeated except that the composition of the solder alloy used was Sn: 62% by weight, Ag: 2.0% by weight, Bi: 0.6% by weight, Cu: 0.06% by weight, and the balance Pb. A paste solder was prepared in the same manner as in Example 1 (Sb was omitted from Example 1).
[Comparative Example 6]
In comparison with Example 1, the composition of the solder alloy was changed except that Sn: 62% by weight, Ag: 2.0% by weight, Bi: 0.6% by weight, Sb: 0.6% by weight, and the balance Pb were used. A paste-like solder was prepared in the same manner as in Example 1 (Cu was omitted from Example 1).
[Comparative Example 7]
In comparison with Example 1, the composition of the solder alloy was changed except that Sn: 62% by weight, Ag: 2.0% by weight, Cu: 0.06% by weight, Sb: 0.6% by weight, and the balance Pb were used. A paste solder was prepared in the same manner as in Example 1 (Bi was omitted from Example 1).
In any of the above alloy compositions, impurities other than the added elements belong to the class A range defined in JIS-Z-3282.
[0021]
Using the paste-like solders of these Examples and Comparative Examples, the chip resistors were soldered to the glass epoxy circuit board by the reflow method, and one cycle of 30 minutes at -40 ° C and 30 minutes at 100 ° C. The thermal shock test was performed up to 500 cycles, and the appearance of the soldering fillet was observed every 100 cycles during the test.
However, ○ indicates that the soldering fillet is normal, △ indicates that wrinkles are generated, and × indicates that cracks are generated.
[0022]
[Table 1]

[0023]
As is clear from this table, according to the present invention, the durability of the soldering fillet to repeated thermal stress can be dramatically improved. In particular, in comparison with Comparative Example 5 in which Sb was omitted, Comparative Example 6 in which Cu was omitted, and Comparative Example 7 in which Bi was omitted, a remarkable improvement effect was observed. An unexpected synergy with Bi is assumed.
[0024]
【The invention's effect】
According to the present invention, it is possible to provide a solder alloy and a paste-like solder which enable remarkably stable soldering for a thermal shock test, and to assure long-term conduction reliability and stability of an electronic component mounted circuit board. .

Claims

50 to 70% by weight of Sn, 0.5 to 5.0% by weight of Ag, 0.1 to 2.0% by weight of Bi, 0.03 to 0.3% by weight of Cu, 0.1 to 2.0% by weight, with the balance being Pb.

Sn is 50 to 70% by weight, Ag and In are equivalent and their total amount is 0.5 to 5.0% by weight, Bi is 0.1 to 2.0% by weight, and Cu is 0.03 to 0. 3% by weight, 0.1 to 2.0% by weight of Sb, and the balance being Pb.

A solder alloy comprising 0.002 to 0.5 parts by weight of P added to 100 parts by weight of the composition according to claim 1.

A paste solder comprising the solder alloy powder according to claim 1 and a paste flux.