JP2009078299A - Solder alloy, solder ball using it, and soldered part excellent in drop impact resistance - Google Patents
Solder alloy, solder ball using it, and soldered part excellent in drop impact resistance Download PDFInfo
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- 229910000679 solder Inorganic materials 0.000 title claims abstract description 109
- 229910045601 alloy Inorganic materials 0.000 title claims abstract description 49
- 239000000956 alloy Substances 0.000 title claims abstract description 49
- 229910052709 silver Inorganic materials 0.000 claims abstract description 7
- 229910052725 zinc Inorganic materials 0.000 claims abstract description 6
- 239000012535 impurity Substances 0.000 claims abstract description 3
- 230000008018 melting Effects 0.000 abstract description 11
- 238000002844 melting Methods 0.000 abstract description 11
- 230000000052 comparative effect Effects 0.000 description 13
- 150000001875 compounds Chemical class 0.000 description 10
- 238000010521 absorption reaction Methods 0.000 description 9
- 229910052797 bismuth Inorganic materials 0.000 description 6
- 229910052759 nickel Inorganic materials 0.000 description 6
- -1 Ag—Zn compound Chemical class 0.000 description 5
- 229910018100 Ni-Sn Inorganic materials 0.000 description 5
- 229910018532 Ni—Sn Inorganic materials 0.000 description 5
- 229910020816 Sn Pb Inorganic materials 0.000 description 5
- 229910020922 Sn-Pb Inorganic materials 0.000 description 5
- 229910008783 Sn—Pb Inorganic materials 0.000 description 5
- 238000005728 strengthening Methods 0.000 description 5
- 239000000758 substrate Substances 0.000 description 5
- 229910020836 Sn-Ag Inorganic materials 0.000 description 4
- 229910020988 Sn—Ag Inorganic materials 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 4
- 230000005496 eutectics Effects 0.000 description 4
- 230000001771 impaired effect Effects 0.000 description 4
- 229910000765 intermetallic Inorganic materials 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 229910001297 Zn alloy Inorganic materials 0.000 description 3
- 230000006378 damage Effects 0.000 description 3
- 239000006185 dispersion Substances 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 229910017944 Ag—Cu Inorganic materials 0.000 description 2
- 229910017980 Ag—Sn Inorganic materials 0.000 description 2
- 239000004593 Epoxy Substances 0.000 description 2
- 239000006023 eutectic alloy Substances 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 238000005476 soldering Methods 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 229910020994 Sn-Zn Inorganic materials 0.000 description 1
- 229910009069 Sn—Zn Inorganic materials 0.000 description 1
- 238000007545 Vickers hardness test Methods 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000009863 impact test Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 239000012299 nitrogen atmosphere Substances 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 229910052763 palladium Inorganic materials 0.000 description 1
- 239000011347 resin Substances 0.000 description 1
- 229920005989 resin Polymers 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
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Abstract
Description
本発明は、電子部品等のはんだ付けに使用される、耐落下衝撃性に優れたはんだ合金、およびそれを用いたはんだボール、ならびにはんだ接合部に関するものである。 The present invention relates to a solder alloy excellent in drop impact resistance, used for soldering electronic components and the like, a solder ball using the solder alloy, and a solder joint.
ＥＵのＲｏＨＳ（Ｔｈｅ ｒｅｓｔｒｉｃｔｉｏｎ ｏｆ ｔｈｅ ｕｓｅ ｏｆ ｃｅｒｔａｉｎ ｈａｚａｒｄｏｕｓ ｓｕｂｓｔａｎｃｅｓ）指令に代表される近年の環境問題への取り組みの一つとして、電子部品の接合に用いられるはんだのＰｂフリー化がある。長年に渡ってＳｎ−Ｐｂ共晶合金がはんだとして用いられてきたが、Ｐｂが人体にとって有害であることから、Ｐｂを含有しない新規のはんだ合金が各種検討されている。 One approach to environmental problems in recent years typified by EU's RoHS (the restriction of the use of ceramic hazards) directive is to make Pb-free solder used for joining electronic components. Sn-Pb eutectic alloy has been used as a solder for many years, but since Pb is harmful to the human body, various new solder alloys not containing Pb have been studied.
Ｓｎ−Ｐｂ共晶合金の代替材料として必要な特性は、融点が十分に低く、はんだ付け時に電子部品を構成する耐熱性の乏しい樹脂材料に熱的損傷を与えないことや、接合材料として十分な機械的強度を有することなどが挙げられる。現在最も広く適用が検討されているＰｂフリーはんだは、Ｓｎ−Ａｇ合金をベースにしたものである。例えば、特許文献１では、Ｓｎ−Ａｇ合金に、融点を低下させたり、機械的強度を向上させたりする目的でＣｕを添加したＳｎ−Ａｇ−Ｃｕ系合金が提案されており、中でもＳｎ−３Ａｇ−０．５ＣｕはＰｂフリーはんだとして主流となっている。
また、特許文献２および特許文献３では、Ｓｎ−Ａｇ合金にＺｎを添加したＳｎ−Ａｇ−Ｚｎ系合金が提案されている。Ｓｎ−Ａｇ−Ｃｕ系合金と同様、機械的強度を向上する目的でＺｎが使用されている。Ｓｎ−Ａｇ−Ｚｎ系合金の場合も、特許文献２および３に具体的に開示されるように、Ａｇ含有量は質量％で３％か３．５％のいずれかである。これはＳｎ−Ａｇ二元共晶が３．５％であり、はんだの融点を低くすることができるためである。
Patent Document 2 and Patent Document 3 propose Sn-Ag-Zn-based alloys in which Zn is added to Sn-Ag alloys. Similar to the Sn—Ag—Cu alloy, Zn is used for the purpose of improving the mechanical strength. Also in the case of Sn—Ag—Zn based alloys, as specifically disclosed in Patent Documents 2 and 3, the Ag content is either 3% or 3.5% by mass. This is because the Sn—Ag binary eutectic is 3.5%, and the melting point of the solder can be lowered.
また、携帯電話などのモバイル機器に搭載される電子部品が、Ｐｂフリーはんだによってマザーボードと接合される場合、融点だけでなく、はんだ接合部の耐落下衝撃性が非常に重要となる。これは、モバイル機器を使用したり持ち運んだりしている間に不注意で落としてしまい、機器に衝撃応力が加えられるためである。従来のＳｎ−Ｐｂ共晶はんだは非常に延性に富むため、このような衝撃応力をはんだ自身が変形することで吸収することが可能であった。一方、一般にＰｂフリーはんだはＳｎ−Ｐｂ共晶はんだと比較して延性に乏しいことから、衝撃応力が加えられた際に十分に変形できず、接合しているマザーボードや電子部品に物理的損傷を与えたり、はんだ接合部自体が破壊したりすることが問題となっている。特に、ＢＧＡ（Ｂａｌｌ Ｇｒｉｄ Ａｒｒａｙ）のように、リードフレームを介さず電子部品とマザーボードの電極をはんだによって直接接続する場合、衝撃応力が負荷されたときのはんだ接合信頼性がモバイル機器の落下衝撃に対する寿命を決定するうえで極めて重要となる。 Further, when an electronic component mounted on a mobile device such as a mobile phone is joined to a motherboard by Pb-free solder, not only the melting point but also the drop impact resistance of the solder joint is very important. This is because the mobile device is inadvertently dropped while being used or carried, and impact stress is applied to the device. Since conventional Sn—Pb eutectic solder is very ductile, it was possible to absorb such impact stress by deformation of the solder itself. On the other hand, Pb-free solder generally has poor ductility compared to Sn—Pb eutectic solder, so that it cannot be sufficiently deformed when impact stress is applied, causing physical damage to the bonded motherboard or electronic components. It is a problem that the solder joints themselves are destroyed. In particular, as in BGA (Ball Grid Array), when the electronic component and the electrode of the mother board are directly connected by solder without using a lead frame, the solder joint reliability when the impact stress is applied to the drop impact of the mobile device. This is extremely important in determining the service life.
特許文献２および３に開示されるＳｎ−Ａｇ−Ｚｎ系合金は、融点がＳｎ−Ｐｂ共晶はんだに比較的近いことに加え、十分な機械的強度を有するといった点で優れるものの、モバイル機器へ適用する際に非常に重要となる耐落下衝撃性についてはこれまで評価されておらず、またモバイル機器への適用の可否についても検討されていなかった。
そこで本発明者は、Ｓｎ−Ａｇ−Ｚｎ系はんだ合金の耐落下衝撃性について調査した結果、Ａｇ添加量の増加とともに耐落下衝撃性が著しく損なわれ、最も検討されてきた３％程度のＡｇを含有するはんだでは、モバイル機器へ適用するのに十分な耐落下衝撃性を有していないことがわかった。また、Ｚｎ添加量についても同様に調査した結果、Ｚｎ添加量の増加とともに耐落下衝撃性が著しく損なわれることを確認した。
The Sn—Ag—Zn alloys disclosed in Patent Documents 2 and 3 are excellent in that they have sufficient mechanical strength in addition to being relatively close to the Sn—Pb eutectic solder, but are suitable for mobile devices. The drop impact resistance, which is very important in application, has not been evaluated so far, and the applicability to mobile devices has not been studied.
Therefore, as a result of investigating the drop impact resistance of the Sn—Ag—Zn solder alloy, the present inventor significantly deteriorated the drop impact resistance as the amount of Ag added increases, and the most studied Ag of about 3% It was found that the solder contained does not have sufficient drop impact resistance to be applied to mobile devices. Moreover, as a result of investigating similarly about Zn addition amount, it confirmed that drop impact resistance was impaired remarkably with the increase in Zn addition amount.
本発明の目的は、融点や機械的強度への要求を満足するだけでなく、耐落下衝撃性に関しても優れたはんだ合金、はんだボール、およびはんだ接合部を提供することにある。 An object of the present invention is to provide a solder alloy, a solder ball, and a solder joint that not only satisfy requirements for melting point and mechanical strength but also have excellent drop impact resistance.
本発明者は、ＡｇおよびＺｎ添加量と耐落下衝撃性との関係について評価を重ねた結果、添加量をそれぞれ厳密に制御することによって、融点や機械的強度をほとんど低下させることなく、耐落下衝撃性の面でも優れたはんだ合金が得られることを見出した。さらに、ＮｉやＢｉを添加することで、耐落下衝撃性を確保しつつ、機械的強度を大幅に向上できることを見出し本発明に到達した。 As a result of repeated evaluations on the relationship between the addition amount of Ag and Zn and the drop impact resistance, the present inventor has controlled the addition amount strictly to reduce the drop resistance without substantially reducing the melting point and mechanical strength. It has been found that an excellent solder alloy can be obtained in terms of impact. Furthermore, the inventors have found that by adding Ni or Bi, the mechanical strength can be greatly improved while ensuring the drop impact resistance, and the present invention has been achieved.
すなわち本発明は、質量％で、０．１〜２．０％のＡｇと、０．０５〜２．０％のＺｎを含有し、残部Ｓｎ及び不可避的不純物からなる耐落下衝撃性に優れたはんだ合金である。 That is, the present invention contains 0.1 to 2.0% Ag and 0.05 to 2.0% Zn in mass%, and has excellent drop impact resistance composed of the remaining Sn and inevitable impurities. It is a solder alloy.
また、本発明の耐落下衝撃性に優れたはんだ合金は、質量％で、０．１〜１．２％のＡｇを含有することが好ましい。
また、本発明の耐落下衝撃性に優れたはんだ合金は、質量％で、０．１％以下のＮｉまたは２．０％以下のＢｉの何れか一つ以上を含有してもよい。
Moreover, it is preferable that the solder alloy excellent in drop impact resistance of the present invention contains 0.1 to 1.2% Ag in mass%.
Moreover, the solder alloy excellent in drop impact resistance of the present invention may contain at least one of Ni of 0.1% or less or Bi of 2.0% or less in mass%.
また、本発明は、前記はんだ合金が球状化されてなるはんだボールである。
また、本発明は、前記はんだ合金およびはんだボールがＮｉ電極に接合されてなるはんだ接合部である。
The present invention also provides a solder ball in which the solder alloy is spheroidized.
Moreover, this invention is a solder joint part by which the said solder alloy and a solder ball are joined to Ni electrode.
本発明によって、融点や機械的強度への要求を満足するだけでなく、耐落下衝撃性に関しても優れたはんだ合金、はんだボール、およびはんだ接合部が得られ、モバイル機器における耐落下衝撃性の問題も飛躍的に改善することが可能である。 The present invention not only satisfies the requirements for melting point and mechanical strength, but also provides excellent solder alloys, solder balls, and solder joints with respect to drop impact resistance, and the problem of drop impact resistance in mobile devices. Can also be improved dramatically.
上述のように、本発明の重要な特徴は、Ｓｎ−Ａｇ−Ｚｎ系合金におけるＡｇおよびＺｎ添加量と耐落下衝撃性との関係を明らかにし、最適な添加量を見出したことにある。
また、本発明のもう一つの重要な特徴は、前記はんだ合金にわずかな量のＮｉやＢｉを添加することで、耐落下衝撃性を確保しつつ、機械的特性を大幅に改善することができることを見出したことにある。以下に、詳細について説明する。
As described above, the important feature of the present invention is that the relationship between the addition amount of Ag and Zn and the drop impact resistance in the Sn—Ag—Zn alloy is clarified and the optimum addition amount has been found.
Another important feature of the present invention is that by adding a small amount of Ni or Bi to the solder alloy, the mechanical properties can be greatly improved while ensuring drop impact resistance. It is in having found. Details will be described below.
Ａｇの添加量を質量％で０．１〜２．０％とするのは以下の理由である。
ＡｇをＺｎとともにＳｎに添加した場合、金属間化合物であるＡｇ−Ｓｎ化合物あるいはＡｇ−Ｚｎ化合物を合金中に形成するため、化合物の分散強化により機械的強度を向上することができる。
しかし、その反面、Ａｇ−Ｓｎ化合物やＡｇ−Ｚｎ化合物の形成は、耐落下衝撃性において重要な特性であるはんだの延性を低下させる。２．０％を超えて添加すると、形成される金属間化合物の量が過多となり、はんだの延性が著しく損なわれる。このため、衝撃応力が負荷されてもはんだが十分に変形することができず、電子部品やマザーボードへ物理的損傷を与えたり、はんだ接合部自体が破壊したりすることになる。
Ａｇ添加量を２．０％以下とすることで、耐落下衝撃性は確保され、特に、１．２％以下の添加量とすることで、金属間化合物の形成量を十分低減することが可能であり、耐落下衝撃性が大幅に改善される。一方、Ａｇ添加量が０．１％未満の場合、延性は良好であるものの、機械的強度が不足し、はんだ合金として適さない。このためＡｇ添加量を０．１％以上とする。
The reason why the addition amount of Ag is 0.1 to 2.0% by mass is as follows.
When Ag is added to Sn together with Zn, an Ag—Sn compound or an Ag—Zn compound, which is an intermetallic compound, is formed in the alloy, so that mechanical strength can be improved by dispersion strengthening of the compound.
However, on the other hand, the formation of an Ag—Sn compound or an Ag—Zn compound reduces the ductility of the solder, which is an important characteristic in drop impact resistance. If it exceeds 2.0%, the amount of intermetallic compound formed becomes excessive, and the ductility of the solder is significantly impaired. For this reason, even if an impact stress is applied, the solder cannot be sufficiently deformed, resulting in physical damage to the electronic component or the mother board or destruction of the solder joint portion itself.
Drop impact resistance is ensured by making the Ag addition amount 2.0% or less, and in particular, by making the addition amount 1.2% or less, it is possible to sufficiently reduce the amount of intermetallic compound formation. The drop impact resistance is greatly improved. On the other hand, when the amount of Ag added is less than 0.1%, the ductility is good, but the mechanical strength is insufficient and it is not suitable as a solder alloy. For this reason, the amount of Ag added is 0.1% or more.
また、Ｚｎの添加量を質量％で０．０５〜２．０％とするのは以下の理由である。
前述のように、ＺｎをＡｇとともにＳｎに添加した場合、金属間化合物であるＡｇ−Ｚｎ化合物を合金中に形成する。これらの化合物によって分散強化されることで合金の機械的強度を向上することができる。また、Ｚｎ量がＡｇ量に対して４倍以上多く含む場合、Ｓｎ中にはＡｇ−Ｚｎ化合物に加えＺｎ単体も形成され、機械的強度が向上する。
しかし、その反面、はんだの延性が著しく損なわれ、耐落下衝撃性が大幅に低下する。Ｚｎ単体の形成を抑えるためにはＺｎ添加量を２．０％以下とする。
また、Ｚｎ添加量が０．０５％未満になると、Ｚｎ単体が形成されないばかりか、Ａｇ−Ｚｎ化合物もほとんど形成されず、はんだ接合部としての機械的強度が不足する。このため、Ｚｎ添加量を０．０５％以上とする。
Moreover, the reason why the added amount of Zn is 0.05 to 2.0% by mass is as follows.
As described above, when Zn is added to Sn together with Ag, an Ag—Zn compound that is an intermetallic compound is formed in the alloy. The mechanical strength of the alloy can be improved by dispersion strengthening with these compounds. Moreover, when Zn content contains 4 times or more with respect to Ag amount, in addition to an Ag-Zn compound, Zn single-piece | unit will be formed in Sn, and mechanical strength will improve.
However, on the other hand, the ductility of the solder is remarkably impaired, and the drop impact resistance is greatly reduced. In order to suppress the formation of Zn alone, the amount of Zn added is set to 2.0% or less.
Further, when the Zn addition amount is less than 0.05%, not only a Zn simple substance is formed, but also an Ag—Zn compound is hardly formed, and the mechanical strength as a solder joint is insufficient. For this reason, Zn addition amount shall be 0.05% or more.
また、本発明において、ＮｉやＢｉを添加することで、耐落下衝撃性を確保しつつ、機械的強度を大幅に向上することが可能である。Ｎｉは、はんだ合金中でＮｉ−Ｓｎ化合物を形成することから、その分散強化によってはんだ合金の機械的強度が向上される。
本発明において、Ｎｉ添加量は、質量％で０．１％以下が好ましい。Ｎｉ添加量が０．１％を越えると、機械的強度は向上するものの、Ｎｉ−Ｓｎ化合物の形成によって融点が上昇するため、Ｎｉ添加量は０．１以下が好ましい。一方、Ｎｉ添加量が０．０１％未満の場合、Ｎｉ−Ｓｎ化合物の形成量が少なく、その効果がほとんど得られないため、Ｎｉ添加量は、０．０１％以上が好ましい。
また、Ｂｉは、Ｓｎ中に固溶することから、固溶強化によって機械的強度を向上させる。本発明において、Ｂｉ添加量は、質量％で２．０％以下が好ましい。Ｂｉ添加量が２．０％を超えると機械的強度が向上する反面、延性が著しく損なわれ、衝撃応力を十分に吸収することができなくなるため、Ｂｉ添加量は、２．０％以下が好ましい。一方、Ｂｉ添加量が０．１％未満の場合、固溶強化による機械的強度の向上がほとんど見込めないため、Ｂｉ添加量は、０．１％以上が好ましい。
In the present invention, by adding Ni or Bi, it is possible to significantly improve the mechanical strength while ensuring the drop impact resistance. Since Ni forms a Ni—Sn compound in the solder alloy, the mechanical strength of the solder alloy is improved by the dispersion strengthening.
In the present invention, the amount of Ni added is preferably 0.1% or less by mass%. If the Ni addition amount exceeds 0.1%, the mechanical strength is improved, but the melting point increases due to the formation of the Ni-Sn compound, so the Ni addition amount is preferably 0.1 or less. On the other hand, when the amount of Ni added is less than 0.01%, the amount of Ni—Sn compound formed is small and the effect is hardly obtained, so the amount of Ni added is preferably 0.01% or more.
Moreover, since Bi dissolves in Sn, the mechanical strength is improved by solid solution strengthening. In the present invention, the Bi addition amount is preferably 2.0% or less by mass%. If the Bi addition amount exceeds 2.0%, the mechanical strength is improved, but the ductility is remarkably impaired and the impact stress cannot be sufficiently absorbed. Therefore, the Bi addition amount is preferably 2.0% or less. . On the other hand, when the amount of Bi added is less than 0.1%, improvement in mechanical strength due to solid solution strengthening can hardly be expected. Therefore, the amount of Bi added is preferably 0.1% or more.
以上に述べた本発明のはんだ合金は、球状化してはんだボールとして用いる場合に非常に有効である。これは、前述のように、モバイル機器に搭載される電子部品として多く用いられているＢＧＡでは、はんだ接合部の耐落下衝撃性が特に重要であることによる。本発明のはんだ合金からなるはんだボールを用いて電子部品とマザーボードとを接合することで、モバイル機器の落下衝撃に対する寿命を飛躍的に改善することができる。 The solder alloy of the present invention described above is very effective when used as a solder ball after spheroidizing. This is because, as described above, in the BGA that is often used as an electronic component mounted on a mobile device, the drop impact resistance of the solder joint is particularly important. By joining the electronic component and the mother board using the solder ball made of the solder alloy of the present invention, it is possible to drastically improve the life against the drop impact of the mobile device.
また、以上に述べた本発明のはんだ合金およびはんだボールは、Ｎｉ電極に接合された場合にさらに有効である。通常、Ｓｎを主体とするはんだをＮｉ電極に接合した場合、接合界面にはＮｉ−Ｓｎ化合物が形成され、衝撃応力が加えられた際、主にＮｉ−Ｓｎ化合物とＮｉ電極との界面で剥離が発生する。
一方、本発明におけるはんだ合金およびはんだボールを用いた場合、Ｎｉと相性の良いＺｎが優先的に反応するため、接合界面にＮｉ−Ｓｎ−Ｚｎ化合物が形成される。これにより、接合界面の強度が増し、より大きな衝撃応力を吸収することが可能である。この効果は、Ｎｉ電極に限定されるものではなく、Ｎｉの酸化を抑制し、はんだの濡れ性を改善する目的でＡｕやＰｄなどの金属層が形成されている場合にも同様の効果が得られる。
The above-described solder alloy and solder ball of the present invention are more effective when bonded to a Ni electrode. Normally, when a solder composed mainly of Sn is bonded to a Ni electrode, a Ni—Sn compound is formed at the bonding interface, and when impact stress is applied, peeling occurs mainly at the interface between the Ni—Sn compound and the Ni electrode. Will occur.
On the other hand, when the solder alloy and the solder ball in the present invention are used, Zn having a good compatibility with Ni reacts preferentially, so that a Ni—Sn—Zn compound is formed at the bonding interface. This increases the strength of the bonding interface and can absorb a larger impact stress. This effect is not limited to the Ni electrode, and the same effect can be obtained when a metal layer such as Au or Pd is formed for the purpose of suppressing the oxidation of Ni and improving the wettability of the solder. It is done.
表１に示すＳｎ−Ａｇ−Ｚｎ合金と、それにＮｉまたはＢｉを添加した合金からなるはんだボールを作製した。また、比較材として、Ｐｂフリーはんだとして最も主流となっているＳｎ−３Ａｇ−０．５Ｃｕ（質量％）のはんだボールも準備した。はんだボールは、直径３００μｍおよび４３０μｍの２種類を用意した。 Solder balls made of an Sn—Ag—Zn alloy shown in Table 1 and an alloy with Ni or Bi added thereto were produced. In addition, as a comparative material, a solder ball of Sn-3Ag-0.5Cu (mass%), which is most popular as Pb-free solder, was also prepared. Two types of solder balls having a diameter of 300 μm and 430 μm were prepared.
次に、作製したはんだボールをガラス・エポキシ（ＦＲ−４）基板上のＮｉ／Ａｕ電極に接合することで、はんだバンプを形成した。接合条件は、Ｐｂフリーはんだの接合として一般的な条件である、最高加熱温度２４０℃、２２０℃以上の保持時間６０ｓとし、窒素雰囲気中で行った。
また、はんだボールを接合した電極は、４３０μｍのはんだボールに対しては直径３２０μｍ、３００μｍのはんだボールに対しては直径２５０μｍのものを使用した。
接合したはんだ合金の耐落下衝撃性を評価するため、小型シャルピー衝撃試験機を用いた衝撃試験を実施した。具体的には、はんだバンプに重さ２０ｇの振り子を１ｍ／ｓの速度で衝突させ、はんだバンプが吸収した衝撃エネルギーの大きさを求めた。
衝撃吸収エネルギーは、はんだバンプを打撃したときの振り子の速度をレーザー速度計により測定し、打撃によって失われる振り子の運動エネルギーとして求めた。また、衝撃吸収エネルギーの測定に加え、試験後の破面観察を実体顕微鏡により行い、接合界面で破壊した割合を界面破壊確率として求めた。なお、実体顕微鏡により観察した結果、いずれのはんだ合金も２４０℃で接合されていたことから、はんだ合金としての使用に際し、融点に関しては問題がないことを確認できた。
Next, solder bumps were formed by joining the produced solder balls to Ni / Au electrodes on a glass-epoxy (FR-4) substrate. The joining conditions were a general condition for joining Pb-free solder, a maximum heating temperature of 240 ° C., a holding time of 220 ° C. or higher, and a holding time of 60 s, and was performed in a nitrogen atmosphere.
The electrodes to which the solder balls were joined were 320 μm in diameter for 430 μm solder balls and 250 μm in diameter for 300 μm solder balls.
In order to evaluate the drop impact resistance of the joined solder alloy, an impact test using a small Charpy impact tester was performed. Specifically, a 20 g weight pendulum collided with the solder bump at a speed of 1 m / s, and the magnitude of impact energy absorbed by the solder bump was determined.
The impact absorption energy was determined as the kinetic energy of the pendulum lost by the impact by measuring the speed of the pendulum when hitting the solder bump with a laser velocimeter. In addition to the measurement of impact absorption energy, the fracture surface after the test was observed with a stereomicroscope, and the ratio of fracture at the bonded interface was determined as the interface fracture probability. In addition, as a result of observing with a stereomicroscope, since all the solder alloys were joined at 240 degreeC, it has confirmed that there was no problem regarding melting | fusing point at the time of use as a solder alloy.
表２に、４３０μｍのはんだボールに対する衝撃吸収エネルギーと界面破壊確率を、表３に、３００μｍのはんだボールに対する値を示す。また、現在Ｐｂフリーはんだとして主流となっている比較例３の衝撃吸収エネルギーに対する相対比を表２、３に併記する。
ボール径が４３０μｍの場合、比較例３の衝撃吸収エネルギーは０．２ｍＪであり、９０％のはんだバンプが界面破壊を示した。また、比較例１および比較例２に示すＡｇ量やＺｎ量が高いはんだも同レベルの衝撃吸収エネルギーと界面破壊確率を示した。
一方、本発明例１〜３や本発明例６の衝撃吸収エネルギーは、表２の相対比に示すように、比較例３の約２倍以上の高い値を示し、界面破壊も抑制することができた。また、本発明２、３および６と比較例２との比較から、Ａｇ量を低減することで耐落下衝撃性が向上していることを確認できた。同様に、本発明例３と比較例１とを比較すると、Ｚｎ量を低いレベルに制御することによっても耐落下衝撃性が改善されている。
以上のように、Ａｇ量とＺｎ量の厳密な制御が、耐落下衝撃性の改善に非常に有効であることが確認できた。
Table 2 shows impact absorption energy and interface fracture probability for 430 μm solder balls, and Table 3 shows values for 300 μm solder balls. Moreover, the relative ratio with respect to the impact absorption energy of the comparative example 3 which is mainstream now as Pb-free solder is written together in Tables 2 and 3.
When the ball diameter was 430 μm, the impact absorption energy of Comparative Example 3 was 0.2 mJ, and 90% of the solder bumps showed interface breakdown. Moreover, the solders with high Ag and Zn contents shown in Comparative Example 1 and Comparative Example 2 also showed the same level of impact absorption energy and interface fracture probability.
On the other hand, as shown in the relative ratios of Table 2, the impact absorption energy of Invention Examples 1 to 3 and Invention Example 6 shows a high value of about twice or more that of Comparative Example 3, and also suppresses interface fracture. did it. Further, from comparison between the present inventions 2, 3 and 6 and Comparative Example 2, it was confirmed that the drop impact resistance was improved by reducing the Ag amount. Similarly, when Example 3 of the present invention and Comparative Example 1 are compared, the drop impact resistance is improved by controlling the Zn content to a low level.
As described above, it has been confirmed that strict control of the Ag content and the Zn content is very effective in improving the drop impact resistance.
ボール径が３００μｍの場合、比較例３はわずか０．０５ｍＪの衝撃吸収エネルギーしかなく、１００％の界面破壊確率を示した。また、Ｚｎ量の多い比較例１もほぼ同様であった。
これに対し、表３の相対比に示すように、本発明例３では、Ｚｎ量を制御することで衝撃吸収エネルギーがおよそ７倍まで向上し、界面破壊確率は１０％未満にまで低減することができた。また、本発明例４および５が示すように、ＮｉやＢｉが添加されたはんだについても比較例１および３と比較して耐落下衝撃性が大幅に改善されていることが確認できた。
このように、Ｓｎ−Ａｇ−Ｚｎ系はんだ合金において、厳密なＡｇ量とＺｎ量の制御により耐落下衝撃性を飛躍的に向上することができた。
When the ball diameter was 300 μm, Comparative Example 3 had an impact absorption energy of only 0.05 mJ and showed an interface fracture probability of 100%. Further, Comparative Example 1 with a large amount of Zn was almost the same.
On the other hand, as shown in the relative ratio of Table 3, in Example 3 of the present invention, the impact absorption energy is improved to about 7 times by controlling the amount of Zn, and the interface fracture probability is reduced to less than 10%. I was able to. Further, as shown in Invention Examples 4 and 5, it was confirmed that the drop impact resistance of the solder added with Ni or Bi was significantly improved as compared with Comparative Examples 1 and 3.
As described above, in the Sn-Ag-Zn solder alloy, the drop impact resistance can be remarkably improved by strictly controlling the Ag amount and the Zn amount.
モバイル機器における落下衝撃を想定した基板落下試験を実施し、本発明におけるはんだ合金の有効性を評価した。
直径３００μｍのはんだボールを用いて、３４５個のＮｉ／Ａｕ電極を有するＢＧＡにはんだバンプを形成した後、ガラス・エポキシ（ＦＲ−４）基板のＣｕ電極に接合することで、落下試験用試験基板を作製した。電極径の大きさは、ＢＧＡのＮｉ／Ａｕ電極が２５０μｍ、マザーボードのＣｕ電極が２８０μｍである。また、評価に用いたマザーボードの大きさは１３２×７７×１ｍｍである。なお、マザーボード１枚当り４個のＢＧＡが搭載されており、各はんだ組成に対して２つの試験基板、つまり合計８個のＢＧＡを接合した。
A board drop test was conducted assuming a drop impact in a mobile device, and the effectiveness of the solder alloy in the present invention was evaluated.
Using a solder ball with a diameter of 300 μm, after forming solder bumps on a BGA having 345 Ni / Au electrodes, it is bonded to a Cu electrode on a glass-epoxy (FR-4) substrate, so that a test substrate for drop test Was made. The electrode diameter is 250 μm for the BGA Ni / Au electrode and 280 μm for the Cu electrode on the motherboard. The size of the motherboard used for the evaluation is 132 × 77 × 1 mm. In addition, four BGAs are mounted on one motherboard, and two test boards, that is, a total of eight BGAs are bonded to each solder composition.
次に、ドロップテーブルに試験基板を水平に固定した後、水平姿勢を保った状態で５０回落下させた。このとき、ドロップテーブルに加えられる落下衝撃は１５００Ｇ、０．５ｍｓの半正弦波となるような高さに設定した。また、試験基板には、導通抵抗測定用の回路が形成されており、バイアス変化を試験中に測定することで導通の有無を確認し、断線したときの落下回数を寿命として求めた。
また、はんだの機械的強度としてはんだのビッカース硬さを測定し、耐落下衝撃性への影響を調査した。ビッカース硬さ試験における負荷荷重は５０ｇとした。
Next, the test substrate was fixed horizontally on the drop table, and then dropped 50 times while maintaining the horizontal posture. At this time, the drop impact applied to the drop table was set to such a height as to be a half sine wave of 1500 G and 0.5 ms. In addition, a circuit for measuring conduction resistance was formed on the test substrate, and the presence or absence of conduction was confirmed by measuring the bias change during the test, and the number of drops when it was disconnected was obtained as the lifetime.
In addition, the Vickers hardness of the solder was measured as the mechanical strength of the solder, and the influence on the drop impact resistance was investigated. The load applied in the Vickers hardness test was 50 g.
表４に、落下試験におけるＢＧＡの平均寿命と、はんだのビッカース硬さを示す。これから明らかなように、本発明におけるはんだ合金を用いて接合されたＢＧＡの平均寿命は３０回以上となっており、Ｚｎ添加量が最適化されていない比較例１や、Ｚｎの添加されていない比較例３と比較して、耐落下衝撃性が飛躍的に改善されている。
また、本発明例２および本発明例３は、それぞれＮｉまたはＢｉを添加することにより、耐落下衝撃性を確保しつつ、ビッカース硬さが向上していることから、機械的強度が向上していると推定される。
このように、本発明におけるはんだ合金、はんだボールおよびはんだ接合部は、融点や機械的強度への要求を満足するだけでなく、耐落下衝撃性に関しても優れており、モバイル機器における耐落下衝撃性の問題を飛躍的に改善することが可能であることを確認した。
Table 4 shows the average life of the BGA in the drop test and the Vickers hardness of the solder. As is clear from this, the average life of the BGA bonded by using the solder alloy in the present invention is 30 times or more, and Comparative Example 1 in which the Zn addition amount is not optimized or Zn is not added. Compared to Comparative Example 3, the drop impact resistance is dramatically improved.
Inventive Example 2 and Inventive Example 3 add Ni or Bi, respectively, to ensure the drop impact resistance and improve the Vickers hardness, thereby improving the mechanical strength. It is estimated that
Thus, the solder alloy, solder ball and solder joint in the present invention not only satisfy the requirements for melting point and mechanical strength, but also have excellent drop impact resistance, and drop impact resistance in mobile devices. It was confirmed that it was possible to dramatically improve the problem.
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