JP2012200759A - Au-Sn BASED ALLOY SOLDER - Google Patents
Au-Sn BASED ALLOY SOLDER Download PDFInfo
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Abstract
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本発明は、電子部品を基板に接合する際に用いるはんだに関し、特に高温用PbフリーのAu−Sn系合金はんだに関する。 The present invention relates to a solder used when bonding an electronic component to a substrate, and more particularly to a high-temperature Pb-free Au—Sn alloy solder.
近年、環境に有害な化学物質に対する規制がますます厳しくなってきており、この規制は電子部品などを基板に接合する目的で使用されるはんだ材料に対しても例外ではない。はんだ材料には古くから鉛が主成分として使われ続けてきたが、すでにRohs指令などで規制対象物質になっている。このため、鉛(Pb)を含まないはんだ(鉛フリーはんだ、Pbフリーはんだ或いは無鉛はんだ)の開発が盛んに行われている。 In recent years, regulations on chemical substances harmful to the environment have become stricter, and this regulation is no exception for solder materials used for the purpose of joining electronic components and the like to substrates. Lead has been used as a main component in solder materials for a long time, but it has already been a regulated substance under the Rohs Directive. For this reason, the development of solder (lead-free solder, Pb-free solder or lead-free solder) that does not contain lead (Pb) has been actively conducted.
電子部品を基板に接合する際に使用するはんだは、その使用限界温度によって高温用(約260℃〜400℃)と中低温用(約140℃〜230℃)に大別され、それらのうち、中低温用はんだに関してはSnを主成分とするものでPbフリーが実用化されている。例えば、Snを主成分とし、Agを1.0〜4.0質量%、Cuを2.0質量%以下、Niを0.5質量%以下、Pを0.2質量%以下含有する無鉛はんだ合金組成が記載されており(例えば、特許文献1参照。)、Agを0.5〜3.5質量%、Cuを0.5〜2.0質量%含有し、残部がSnからなる合金組成のPbフリーはんだが記載されている(例えば、特許文献2参照。)。 Solders used when bonding electronic components to a substrate are roughly classified into high temperature (about 260 ° C. to 400 ° C.) and medium / low temperature (about 140 ° C. to 230 ° C.) depending on the limit temperature of use. The medium / low temperature solder is composed mainly of Sn and Pb-free is put into practical use. For example, lead-free solder containing Sn as a main component, Ag of 1.0 to 4.0% by mass, Cu of 2.0% by mass or less, Ni of 0.5% by mass or less, and P of 0.2% by mass or less An alloy composition is described (for example, refer to Patent Document 1), containing 0.5 to 3.5% by mass of Ag, 0.5 to 2.0% by mass of Cu, and the balance consisting of Sn. Pb-free solder is described (for example, see Patent Document 2).
一方、高温用のPbフリーはんだ材料に関しても、さまざまな機関で開発が行われている。例えば、Biを30〜80質量%含んだ溶融温度が350〜500℃のBi/Agろう材が開示されている(例えば、特許文献3参照。)。また、Biを含む共晶合金に2元共晶合金を加え、さらに添加元素を加えたはんだ合金が開示されており(例えば、特許文献4参照。)、このはんだ合金は、4元系以上の多元系はんだではあるものの、液相線温度の調整とばらつきの減少が可能となることが示されている。 On the other hand, development of various high-temperature Pb-free solder materials is also being conducted. For example, a Bi / Ag brazing material containing 30 to 80% by mass of Bi and having a melting temperature of 350 to 500 ° C. is disclosed (for example, see Patent Document 3). Further, a solder alloy is disclosed in which a binary eutectic alloy is added to a Bi-containing eutectic alloy and an additional element is further added (see, for example, Patent Document 4). Although it is a multi-component solder, it has been shown that the liquidus temperature can be adjusted and variations can be reduced.
高価な高温用のPbフリーはんだ材料としてはすでにAu−Sn合金やAu−Ge合金などがMEMS水晶デバイス等で使用されている。例えば、Au:5〜15質量%を含有し、さらにBi:0.1〜10質量%、In:0.1〜10質量%およびSb:0.1〜10質量%のいずれかを含有し、残りがSnおよび不可避不純物からなる成分組成を有するSn−Au合金はんだ粉末とフラックスとの混合体に関して記載されている(例えば、特許文献4参照。)。
また、接合後の接合部のSn濃度が20.65〜23.5重量%となるようにAu−Sn系ろう材の組成及び厚さ又は体積を調整して接合する接合方法が示されている(例えば、特許文献5参照。)。
As an expensive high-temperature Pb-free solder material, an Au—Sn alloy, an Au—Ge alloy, or the like has already been used in a MEMS crystal device or the like. For example, Au: 5 to 15% by mass, Bi: 0.1 to 10% by mass, In: 0.1 to 10% by mass and Sb: 0.1 to 10% by mass, It describes a mixture of a Sn—Au alloy solder powder having a component composition consisting of Sn and inevitable impurities and a flux (see, for example, Patent Document 4).
Also, a joining method is shown in which the composition and thickness or volume of the Au—Sn brazing material is adjusted so that the Sn concentration of the joined part after joining is 20.65 to 23.5% by weight. (For example, refer to Patent Document 5).
高温用のPbフリーはんだ材料に関しては、上記、引用文献以外にもさまざまな機関で開発されてはいるが、未だ低コストで汎用性のあるはんだ材料は見つかっていない。すなわち、一般的に電子部品や基板には熱可塑性樹脂や熱硬化性樹脂などの比較的耐熱温度の低い材料が多用されているため、作業温度を400℃未満、望ましくは370℃以下にする必要がある。しかしながら、例えば特許文献3に開示されているBi−Ag系ろう材では、液相線温度が400〜700℃と高いため、接合時の作業温度も400〜700℃以上になると推測され、接合される電子部品や基板の耐熱温度を超えてしまうことになる。 The Pb-free solder material for high temperature has been developed by various organizations other than the above cited references, but a low-cost and versatile solder material has not yet been found. In other words, since materials having relatively low heat resistance such as thermoplastic resins and thermosetting resins are generally used for electronic parts and substrates, the working temperature must be less than 400 ° C., preferably 370 ° C. or less. There is. However, for example, in the Bi-Ag brazing material disclosed in Patent Document 3, since the liquidus temperature is as high as 400 to 700 ° C, the working temperature at the time of joining is estimated to be 400 to 700 ° C or more, and the joining is performed. It will exceed the heat resistance temperature of electronic components and boards.
そして、高価なAu−Sn系はんだの場合、水晶デバイスやMEMSなどのとくに信頼性を必要とする箇所のはんだ付けに使用されるが、その融点はAu−Sn共晶温度付近の280℃程度である。それよりも高い温度、例えば300〜340℃付近の融点を有するAu系はんだは実用化されておらず、この領域のはんだ付けをするためのPbフリーはんだは現在存在しない。
例えば、特許文献4の組成ではSn−Au共晶組成付近にBiやInといった融点の低い元素(Biの融点:271℃、Inの融点:156℃)を入れる組成範囲が示されており、この場合、共晶温度からさらに融点が下がってしまう。一方でSbを含有させた組成範囲が示されているが、Sbのように比較的融点の高い元素(Sbの融点631℃)を10重量%程度含有させた場合、Au−Sbの2元系合金において状態図から分かるように液相温度が約800℃、固相温度が約370℃となり、高融点合金が生成してしまうことになり実用的な材料とは考えられない。
And in the case of expensive Au-Sn solder, it is used for soldering particularly in places that require reliability, such as crystal devices and MEMS, but the melting point is about 280 ° C. near the Au—Sn eutectic temperature. is there. Au-based solder having a higher temperature, for example, a melting point in the vicinity of 300 to 340 ° C. has not been put into practical use, and there is currently no Pb-free solder for soldering in this region.
For example, the composition of Patent Document 4 shows a composition range in which an element having a low melting point such as Bi or In (Bi melting point: 271 ° C., In melting point: 156 ° C.) is present in the vicinity of the Sn—Au eutectic composition. In this case, the melting point is further lowered from the eutectic temperature. On the other hand, although the composition range containing Sb is shown, when an element having a relatively high melting point such as Sb (melting point 631 ° C. of Sb) is about 10% by weight, a binary system of Au—Sb is used. As can be seen from the phase diagram of the alloy, the liquid phase temperature is about 800 ° C. and the solid phase temperature is about 370 ° C., which results in the formation of a high melting point alloy and is not considered a practical material.
また特許文献5についても接合後の接合部のSn濃度が20.65〜23.5質量%となるようなAu−Sn系ろう材では融点は固相温度が280℃、液相温度はそれより若干高くなる程度である。
以上のようにPbフリーはんだにおいて、300〜340℃程度の融点を有する材料は見当たらず、MEMSや水晶デバイス等のとくに高信頼性を必要とする接合に際して支障をきたしている場合がある。
As for Patent Document 5, the Au—Sn brazing material in which the Sn concentration in the joined portion after joining is 20.65 to 23.5% by mass has a melting point of 280 ° C. and a liquidus temperature of A little higher.
As described above, in the Pb-free solder, there is no material having a melting point of about 300 to 340 ° C., and there is a case where a particularly high reliability such as a MEMS or a quartz device is hindered.
本発明は上記課題に鑑みてなされたものであり、MEMSや水晶デバイス等の非常に高い信頼性を要求される接合において、300〜340℃程度の融点を有し、十分な濡れ性や信頼性等に優れる高温用PbフリーのAu−Sn系合金はんだを提供することであり、さらには本発明のPbフリーはんだ合金を用いて接合された高信頼性を有する電子部品を備えた電子基板、および該電子基板が搭載された各種装置を提供することを目的としている。
ここで十分な濡れ性とは、接合作業の際にボイド(空孔)を生じることなくはんだ合金が溶融して、接合面に適度な面積に拡がることを意味し、これにより被接合物との接触面積が確保され、被接合物を強固に固着して信頼性の高い接合を達成できることとなる。また、高信頼性とは、強固な接合の結果、使用環境の温度変化にも耐えて長寿命で安定した接合を維持できることを意味する。
The present invention has been made in view of the above problems, and has a melting point of about 300 to 340 ° C. and has sufficient wettability and reliability in bonding that requires extremely high reliability such as MEMS and crystal devices. A high-temperature Pb-free Au—Sn-based alloy solder, and an electronic board including a highly reliable electronic component joined using the Pb-free solder alloy of the present invention, and An object of the present invention is to provide various devices on which the electronic substrate is mounted.
Sufficient wettability here means that the solder alloy melts without causing voids (voids) during the joining operation and spreads to an appropriate area on the joining surface. A contact area is ensured, and an object to be bonded can be firmly fixed to achieve highly reliable bonding. In addition, high reliability means that, as a result of strong bonding, it is possible to withstand a temperature change in a use environment and maintain a long-life and stable bonding.
本発明のAu−Sn合金はんだは、Snを18.5質量%以上23.5質量%以下含有し、0.02質量%以上0.5質量%以下のW、または0.02質量%以上4.3質量%以下のMoのうち少なくとも1種を含有し、残部がAuからなるAu−Sn合金はんだである。 The Au—Sn alloy solder of the present invention contains 18.5% by mass to 23.5% by mass of Sn, 0.02% by mass to 0.5% by mass W, or 0.02% by mass to 4%. It is an Au—Sn alloy solder containing at least one of Mo in an amount of 3% by mass or less and the balance being made of Au.
本発明により、電子部品と基板の接合に必要な強度を有する高温用の鉛フリーはんだ合金を提供することができる。すなわち、Au−Sn共晶組成付近にWまたはMoのうち少なくとも1種の金属元素を所定の含有率となるように添加することによって、電子部品やリードフレーム等に対する接合温度がAu−Sn共晶合金よりも高く、Au−Ge共晶合金やAu−Si共晶合金の融点(約360℃)よりも低い温度領域で接合が可能であって、十分な濡れ性を有し接合性、接合強度等に優れ、信頼性の高い接合を達成できるAu−Sn合金はんだを提供することができる。これにより高温での鉛フリーのはんだ付けの接合温度領域を広めることが可能となり、接合温度のほぼ全域を鉛フリーはんだで網羅することが可能となって汎用性が格段に高まる。 According to the present invention, it is possible to provide a high-temperature lead-free solder alloy having strength necessary for joining an electronic component and a substrate. That is, by adding at least one metal element of W or Mo in the vicinity of the Au—Sn eutectic composition so as to have a predetermined content, the bonding temperature for electronic parts, lead frames, etc. can be reduced to Au—Sn eutectic. It can be bonded in a temperature range higher than that of the alloy and lower than the melting point (about 360 ° C.) of the Au—Ge eutectic alloy or Au—Si eutectic alloy, and has sufficient wettability. It is possible to provide an Au—Sn alloy solder that is excellent in the above and can achieve highly reliable bonding. This makes it possible to widen the joining temperature region for lead-free soldering at high temperatures, and to cover almost the entire joining temperature with lead-free solder, so that versatility is greatly enhanced.
接合性が良く接合強度等に優れた信頼性の高い接合を得るためには、はんだが溶融した時に基板との間に適度な濡れ性を有することが重要である。はんだ溶融時に十分な濡れ性が確保できれば接合面積も十分確保でき、接合強度も高まり耐久性にも富んだ高信頼性のはんだ接合が得られる。適度な濡れ性とは、はんだ溶融時に接合面積の110%以上に広がることが目安となる。また、強固で確実な接合を得るためには、溶融はんだ内部にボイドを生じないようにしなければならない。ボイドの発生率は5%以下に抑える必要がある。 In order to obtain a highly reliable bond with excellent bondability and excellent bonding strength, it is important to have appropriate wettability with the substrate when the solder is melted. If sufficient wettability can be ensured when the solder is melted, a sufficient bonding area can be ensured, the bonding strength is increased, and highly reliable solder bonding with high durability can be obtained. The appropriate wettability is a standard that spreads to 110% or more of the joint area when the solder is melted. Further, in order to obtain a strong and reliable joint, it is necessary to prevent voids from being generated inside the molten solder. It is necessary to suppress the void generation rate to 5% or less.
上記目標を達成するために、本発明のAu−Sn合金はんだの組成は、Snを18.5質量%以上23.5質量%以下含有し、0.02質量%以上0.5質量%以下のWまたは0.02質量%以上4.3質量%以下のMoのうち少なくとも1種以上を含有し、残部がAuからなる組成とした。
Au−Sn共晶組成付近をベースとして、WまたはMoを所定量添加することにより、Au−Sn合金の液相温度が上昇し、さらには粘性も上昇するため接合温度を高くすることができる。具体的には、従来、接合が困難であったはんだの融点よりも30℃〜50℃高い350〜390℃程度での接合作業が可能となる。つまり、この温度領域はAu−Sn系合金(共晶温度:280℃)では温度が高すぎ、Au−Ge系合金(共晶温度:361℃)では温度が低すぎるのである。これらのはんだの高融点化に大きな効果を示すWとMoについて以下、説明をする。
In order to achieve the above goal, the composition of the Au—Sn alloy solder of the present invention contains Sn of 18.5% by mass to 23.5% by mass, and 0.02% by mass to 0.5% by mass. It was set as the composition which contains at least 1 sort (s) among W or 0.02 mass% or more and 4.3 mass% or less Mo, and the remainder consists of Au.
By adding a predetermined amount of W or Mo based on the vicinity of the Au—Sn eutectic composition, the liquidus temperature of the Au—Sn alloy increases and the viscosity also increases, so that the bonding temperature can be increased. Specifically, it is possible to perform a joining operation at about 350 to 390 ° C., which is 30 ° C. to 50 ° C. higher than the melting point of solder, which has conventionally been difficult to join. That is, this temperature region is too high for an Au—Sn alloy (eutectic temperature: 280 ° C.) and too low for an Au—Ge alloy (eutectic temperature: 361 ° C.). Hereinafter, W and Mo which have a great effect on increasing the melting point of these solders will be described.
まず、Wの効果について述べる。Wは融点が3422℃であり、高融点金属の代表である。本発明は、このWが有する高融点という特性を活かすことにある。つまり、WはAuとの2元系合金において、互いにほとんど固溶しないため、合金の溶融状態から冷却するとAuとWとの2相の金属から形成される合金となり、脆い金属間化合物を生成しないのである。従って、比較的柔らかい金属になり、加えて前述のようにWの有する高い融点によってWを少量含有するだけで液相線温度を高め、よって接合温度を容易に高められるのである。Au−Sn系はんだは元々金属間化合物を有し、Pb系などのはんだに比較し、硬くて脆い性質を有する。Wを含有させることは、融点を上げることはもちろんであるが、Au−Sn系はんだを柔らかくし、応力緩和性を持たせることもできるのである。その結果、使用環境の温度変化にも影響を受けない、強固で長寿命の信頼性の高い接合を達成できるようになる。 First, the effect of W will be described. W has a melting point of 3422 ° C. and is a typical high melting point metal. The present invention is to make use of the high melting point characteristic of W. In other words, since W is hardly dissolved in a binary alloy with Au, when cooled from the molten state of the alloy, it becomes an alloy formed from a two-phase metal of Au and W, and does not produce a brittle intermetallic compound. It is. Therefore, it becomes a relatively soft metal, and in addition, the liquidus temperature can be increased simply by containing a small amount of W due to the high melting point of W as described above, and thus the bonding temperature can be easily increased. Au—Sn solder originally has an intermetallic compound, and is harder and more brittle than Pb solder. Inclusion of W not only increases the melting point, but also makes it possible to soften the Au—Sn solder and to provide stress relaxation properties. As a result, it is possible to achieve a strong, long-life and highly reliable bond that is not affected by temperature changes in the use environment.
但し、Wは融点が高いため、多く添加すると接合時に溶融しない高融点相が生成されてしまうために、その含有量には注意を要する。具体的なWの含有量は0.02質量%以上0.5質量%以下である。Wの含有量が0.02質量%未満だと添加量が少なすぎてWの高融点化や応力緩和性の効果は実質的に表れず、0.5質量%以上だと接合時にも溶融しない高融点相ができてしまい、接合強度を下げたり、ボイド率が急に高くなったりしてしまう。 However, since W has a high melting point, if it is added in a large amount, a high melting point phase that does not melt at the time of bonding is generated. The specific W content is 0.02% by mass or more and 0.5% by mass or less. If the W content is less than 0.02% by mass, the added amount is too small, and the effect of increasing the melting point and stress relaxation of W is not substantially exhibited. If the content is 0.5% by mass or more, it does not melt even during bonding. A high melting point phase is formed, and the bonding strength is lowered or the void ratio is suddenly increased.
次にMoについて述べる。Moの効果もWと同様にはんだの高融点化と応力緩和性の向上であるが、Moの場合は応力緩和性に大きな効果を期待できる。Moも融点が2623℃の高融点金属であるため、当然、融点を上げる効果を有するが、この高融点化効果よりも応力緩和性の効果の方が大きい理由は次のとおりである。MoはAuにある程度固溶し、MoのAuへの固溶量はAu融点付近で4.2質量%である。Auに固溶したMoは溶融状態から冷却される過程において析出し核となり、これによってAu−Sn合金が微細化し、応力緩和性が向上するのである。 Next, Mo will be described. The effect of Mo, like W, is to increase the melting point of solder and improve stress relaxation, but in the case of Mo, a great effect on stress relaxation can be expected. Since Mo is a high melting point metal having a melting point of 2623 ° C., it naturally has the effect of increasing the melting point. The reason why the stress relaxation effect is greater than the effect of increasing the melting point is as follows. Mo is dissolved to some extent in Au, and the amount of Mo dissolved in Au is 4.2% by mass near the melting point of Au. Mo dissolved in Au precipitates and becomes nuclei in the process of cooling from the molten state, whereby the Au—Sn alloy is refined and stress relaxation is improved.
このMoの許容含有量は0.02質量%以上4.3質量%以下である。Moの含有量が0.02質量%未満だと添加量が少なすぎてMoの応力緩和性の効果は期待できず融点は実質的に上がらない。4.3質量%より多いとMoの含有量が共晶組成を超えてしまい合金が粗粒化してしまうとともに高融点相が生成され、接合性等を落とし信頼性を著しく低下させてしまうため好ましくない。 The allowable content of Mo is 0.02 mass% or more and 4.3 mass% or less. If the Mo content is less than 0.02% by mass, the amount of addition is too small, and the effect of Mo stress relaxation cannot be expected, and the melting point does not substantially increase. If the amount is more than 4.3% by mass, the Mo content exceeds the eutectic composition and the alloy is coarsened, and a high melting point phase is generated. Absent.
なお、濡れ性が不足する場合などは更にPまたはGeの添加が有効である。これらの元素を1種以上含有することにより還元効果を発揮しはんだ等の酸化膜を除去でき、濡れ性を改善することが可能である。これらの元素は少量添加で効果を発揮するため、多量には添加しない。例えば、Pであれば0.5質量%以下、Geであれば1.5質量%以下である。これより多く添加すると脆い相を生成したり、逆にPやGeの強固な酸化膜が多量に発生しボイド率を高くしたり接合強度を下げたりするなどの問題がでてきてしまう。 In addition, when wettability is insufficient, addition of P or Ge is effective. By containing one or more of these elements, it is possible to exhibit a reducing effect, remove an oxide film such as solder, and improve wettability. Since these elements exert their effects when added in small amounts, they are not added in large amounts. For example, P is 0.5 mass% or less, and Ge is 1.5 mass% or less. If it is added more than this, a brittle phase is generated, or on the contrary, a strong oxide film of P or Ge is generated in a large amount, resulting in an increase in the void ratio or a decrease in bonding strength.
まず、原料としてそれぞれ純度99.9質量%以上のAu、Sn、W、およびMoを準備した。大きな薄片やバルク状の原料については、溶解後の合金においてサンプリング場所による組成のバラツキがなく均一になるように留意しながら切断、粉砕等を行い、3mm以下の大きさに細かくした。 First, Au, Sn, W, and Mo having a purity of 99.9% by mass or more were prepared as raw materials. Large flakes and bulk-shaped raw materials were cut and pulverized, etc. so as to be uniform with no variation in composition depending on the sampling location in the alloy after melting, and were reduced to a size of 3 mm or less.
次に、高周波溶解炉用グラファイトるつぼにこれら原料から所定量を秤量して入れた。
原料の入ったるつぼを高周波溶解炉に入れ、酸化を抑制するために窒素を原料1kg当たり0.7L/分以上の流量で流した。この状態で溶解炉の電源を入れ、原料を加熱溶融させた。金属が溶融しはじめたら混合棒でよく攪拌し、局所的な組成のばらつきが起きないように均一に混ぜた。十分溶融したことを確認した後高周波電源を切り、速やかにるつぼを取り出し、るつぼ内の溶湯をはんだ母合金の鋳型に流し込んだ。鋳型にははんだ合金の製造の際に一般的に使用している形状(厚さ5mmの板状)と同様のものを使用した。
Next, a predetermined amount of these raw materials was weighed into a graphite crucible for a high-frequency melting furnace.
The crucible containing the raw material was placed in a high-frequency melting furnace, and nitrogen was flowed at a flow rate of 0.7 L / min or more per kg of the raw material in order to suppress oxidation. In this state, the melting furnace was turned on to heat and melt the raw material. When the metal began to melt, it was stirred well with a mixing rod and mixed uniformly so as not to cause local compositional variations. After confirming sufficient melting, the high frequency power supply was turned off, the crucible was quickly taken out, and the molten metal in the crucible was poured into the mold of the solder mother alloy. The mold used was the same shape (plate shape with a thickness of 5 mm) that is generally used in the manufacture of solder alloys.
このようにして試料1のはんだ母合金を作製した。原料の混合比率を変えた以外は試料1と同様にして試料2〜13のはんだ母合金を作製した。これら試料1〜13のはんだ母合金の組成をICP発光分光分析器(SHIMAZU S−8100)を用いて分析した。
その分析結果を下記の表1に示す。
In this way, the solder mother alloy of Sample 1 was produced. Solder mother alloys of Samples 2 to 13 were produced in the same manner as Sample 1 except that the mixing ratio of the raw materials was changed. The compositions of the solder mother alloys of Samples 1 to 13 were analyzed using an ICP emission spectroscopic analyzer (SHIMAZU S-8100).
The analysis results are shown in Table 1 below.
次に、上記試料1〜13の各はんだ母合金について、下記のごとく圧延機でシート状に加工した。また、シート状に加工した各Au−Sn系はんだ合金について、下記の方法により濡れ性の評価、ボイド率の評価及びヒートサイクル試験による信頼性の評価を行った。なお、はんだの濡れ性ないし接合性等の評価は、はんだ形状に依存しないためワイヤ、ボール、ペーストなどの形状で評価してもよいが、本実施例においてはシートの形状で評価した。得られた結果を下記表2に示す。 Next, each of the solder mother alloys of Samples 1 to 13 was processed into a sheet by a rolling mill as described below. Moreover, about each Au-Sn type solder alloy processed into the sheet form, the wettability evaluation, the void ratio evaluation, and the reliability evaluation by the heat cycle test were performed by the following methods. The evaluation of solder wettability or bondability does not depend on the shape of the solder, and may be evaluated by the shape of a wire, a ball, a paste, or the like, but in this example, it was evaluated by the shape of a sheet. The obtained results are shown in Table 2 below.
<シート形状への加工>
表1に示す試料1〜13の各はんだ母合金(厚さ5mmの板状インゴット)を、圧延機を用いて厚さ0.10mmまで圧延した。その際、インゴットの送り速度を調整しながら圧延していき、その後スリッター加工により25mmの幅に裁断した。このようにシート形状にした試料を金型プレス機を用いて、10mm角の形状に打ち抜き、以下の評価用試料として用いた。なお、一般的にAu−Snはんだが使用される場合、はんだ厚みは0.020〜0.050mm程度で使用されることが多いが、ここでは濡れ広がりの評価を行う際、濡れ性が濡れ広がり面積に反映され易いようにはんだ厚みを故意に厚くした。
<Processing into sheet shape>
Each solder mother alloy (plate-shaped ingot having a thickness of 5 mm) of Samples 1 to 13 shown in Table 1 was rolled to a thickness of 0.10 mm using a rolling mill. At that time, rolling was performed while adjusting the feed speed of the ingot, and then it was cut into a width of 25 mm by slitting. The sample thus formed into a sheet shape was punched into a 10 mm square shape using a die press machine and used as the following sample for evaluation. In general, when Au—Sn solder is used, the solder thickness is often about 0.020 to 0.050 mm. However, here, when evaluating wet spread, wettability spreads. The thickness of the solder was intentionally increased so that it was easily reflected in the area.
<濡れ性評価(濡れ広がり性)>
この濡れ性評価は、上記プリフォーム材を用いて行った。まず、濡れ性試験機(装置名:雰囲気制御式濡れ性試験機)を起動し、加熱するヒーター部分に2重のカバーをしてヒーター部の周囲4箇所から窒素を流した(窒素流量:各12L/分)。その後、ヒーター設定温度をはんだの融点よりも高い370℃にして加熱した。
370℃に設定したヒーター温度が安定した後、Niメッキ(膜厚:2.0μm)、さらに最上層にAuメッキ(膜厚:1.0μm)をしたCu基板(板厚:0.3mm)をヒーター部にセッティング後、25秒加熱した。次に、はんだ合金をCu基板の上に載せ、25秒加熱した。加熱が完了した後はCu基板をヒーター部から取り上げてその横の窒素雰囲気が保たれている場所に一旦設置して冷却した。十分に冷却した後、大気中に取り出して接合部分を確認した。溶融前の面積を100%として、溶融・冷却後の面積を光学顕微鏡(株式会社キーエンス製VHX−900)の面積測定機能を用いて測定した。
<Evaluation of wettability (wet spreadability)>
This wettability evaluation was performed using the preform material. First, a wettability tester (device name: atmosphere control type wettability tester) was started, a double cover was applied to the heater part to be heated, and nitrogen was flowed from four locations around the heater part (nitrogen flow rate: each 12 L / min). Thereafter, the heater was set to a temperature of 370 ° C. higher than the melting point of the solder and heated.
After the heater temperature set at 370 ° C. was stabilized, a Cu substrate (plate thickness: 0.3 mm) with Ni plating (film thickness: 2.0 μm) and Au plating (film thickness: 1.0 μm) as the uppermost layer was used. After setting in the heater part, it was heated for 25 seconds. Next, the solder alloy was placed on the Cu substrate and heated for 25 seconds. After the heating was completed, the Cu substrate was picked up from the heater part, and once installed in a place where the nitrogen atmosphere next to it was maintained, it was cooled. After sufficiently cooling, it was taken out into the atmosphere and a joint portion was confirmed. The area before melting was set to 100%, and the area after melting and cooling was measured using the area measuring function of an optical microscope (VHX-900 manufactured by Keyence Corporation).
<ボイド率の評価>
接合性を確認するため、上記濡れ性評価と同様にして得たはんだ合金が接合されたCu基板のボイド率を、X線透過装置(株式会社東芝製 TOSMICRON−6125)を用いて測定した。試料(はんだ)とCu基板接合面をはんだ上部から垂直にX線を透過し、取り込んだ画像データを処理して以下の式(1)を用いてボイド率を算出した。
<Evaluation of void fraction>
In order to confirm the bondability, the void ratio of the Cu substrate to which the solder alloy obtained in the same manner as in the wettability evaluation was bonded was measured using an X-ray transmission device (TOSMICRON-6125 manufactured by Toshiba Corporation). The sample (solder) and the Cu substrate bonding surface were transmitted with X-rays perpendicularly from the upper part of the solder, the captured image data was processed, and the void ratio was calculated using the following equation (1).
<ヒートサイクル試験>
はんだ接合の信頼性を評価するためにヒートサイクル試験を行った。なお、この試験は、上記濡れ性評価と同様にして得たはんだ合金が接合されたCu基板を用いて行った。
まず、はんだ合金が接合されたCu基板に対して、−40℃の冷却と150℃の加熱を1サイクルとして、これを所定のサイクル繰り返した。その後、はんだ合金が接合されたCu基板を樹脂に埋め込み、断面研磨を行い、SEM(日立製作所株式会社製 S−4800)により接合面の観察を行った。接合面にはがれやはんだにクラックが入っていた場合を「×」、そのような不良がなく、初期状態と同様の接合面を保っていた場合を「○」とした。
<Heat cycle test>
A heat cycle test was conducted to evaluate the reliability of solder joints. This test was performed using a Cu substrate to which a solder alloy obtained in the same manner as the wettability evaluation was bonded.
First, with respect to the Cu substrate to which the solder alloy was bonded, cooling at −40 ° C. and heating at 150 ° C. were taken as one cycle, and this was repeated for a predetermined cycle. Thereafter, the Cu substrate to which the solder alloy was bonded was embedded in the resin, cross-section polishing was performed, and the bonded surface was observed with SEM (S-4800, manufactured by Hitachi, Ltd.). The case where the joint surface was peeled or cracked in the solder was indicated as “×”, and the case where there was no such defect and the same joint surface as in the initial state was maintained as “◯”.
上記表2から分かるように、本発明の要件を満たしている試料1〜8のはんだ母合金は、各評価項目において良好な特性を示している。つまり、Au蒸着しているCu基板への濡れ性は十分であり、接合面での溶融が進みすぎることもなく、適度な濡れ広がりであった。ボイド率については全て2%以下であり良好な接合性を示した。さらに信頼性に関する試験であるヒートサイクル試験においても良好な結果が得られており、ヒートサイクル試験では500サイクル経過後も不良が現れなかった。 As can be seen from Table 2 above, the solder mother alloys of Samples 1 to 8 that satisfy the requirements of the present invention show good characteristics in each evaluation item. That is, the wettability to the Cu substrate on which the Au was deposited was sufficient, and the melting at the joint surface did not proceed too much, and the spread was moderate. The void ratios were all 2% or less, indicating good bondability. Furthermore, good results were obtained in the heat cycle test, which is a test related to reliability, and no defects appeared after 500 cycles in the heat cycle test.
一方、本発明の要件を満たしていない比較例の試料9〜13のはんだ母合金は、少なくともいずれかの特性において好ましくない結果となった。濡れ性の試験に関しては試料10、11がはんだ面積180%程度であり非常に濡れ広がっているが、この理由は試料の融点が接合温度に比較し低すぎて溶融が進みすぎためだと考えられる。このように濡れ広がり過ぎると電子部品の接合面積よりはんだが大きく広がってしまい十分な強度を有する接合ができなくなるため好ましくない。
また、ボイド率に関しては、全ての比較例において7%以上と高い値であり、この原因は融点に比較し接合温度が高すぎたり、WやMoの添加量が適当でなかったなどが考えられる。ヒートサイクル試験の結果においては全て500回までに不良が発生しており、この原因ははんだが濡れ広がり過ぎたり、ボイド率が高かったり、さらにははんだの応力緩和性が不十分であったためだと考えられる。
On the other hand, the solder mother alloys of Comparative Samples 9 to 13 that did not satisfy the requirements of the present invention had undesirable results in at least any of the characteristics. Regarding the wettability test, the samples 10 and 11 have a solder area of about 180% and are very wet and spread. This is considered to be because the melting point of the sample is too low compared to the bonding temperature and the melting proceeds too much. . If it is so wet and spread, the solder spreads larger than the bonding area of the electronic component, and bonding with sufficient strength cannot be performed, which is not preferable.
In addition, the void ratio is a high value of 7% or more in all the comparative examples, and this may be due to the fact that the bonding temperature is too high compared to the melting point or the addition amount of W or Mo is not appropriate. . In the results of the heat cycle test, all the defects occurred up to 500 times, and this was because the solder was too wet and the void ratio was high, and the stress relaxation property of the solder was insufficient. Conceivable.
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