JP2004031771A - Solder junction - Google Patents
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Abstract
Description
【0001】
【発明の属する技術分野】
本発明は、電子部品等のはんだ付け部に形成されるCu−Sn化合物の形状を規定したはんだ接合体に関する。
【0002】
【従来の技術】
昨今の電子機器実装面積の減少に伴って半導体パッケージも小型化傾向にあり、半導体パッケージをマザーボードに接続する実装形態も、従来のリードを用いた周辺端子型から格子状に端子を形成したタイプへ変遷しつつある。代表的なものがBGA(Ball Grid Array)であり、端子部ははんだボールや、はんだペーストを用いて基板に接続されている。
BGAはリード部品のようにリード部で外力などを緩和できず、はんだ接続部に直接負荷が加わる構造であるため、機器落下等の衝撃や、機器の使用環境、機器温度の上昇等に伴う熱応力に対して非常に敏感である。また、はんだバンプの接続部ははんだの表面張力で樽型になっているため、はんだ接続部の金属間化合物が形成された接合界面近傍に応力が集中しやすい。
【0003】
加えて、近年の環境問題への取り組みの一つとして、はんだのPbフリー化が世界的に進められており、従来用いられてきたSn−Pbはんだは使用禁止になりつつある。代替合金の主たるものはSn−Ag系やSn−Ag−Cu系等多数あるが、基本的にSn主成分であるためSn−Pb共晶はんだに比べると延性に乏しく、外力をはんだの変形で緩和することが困難になっている。
【0004】
【発明が解決しようとする課題】
以上の状況から、はんだ接合強度は、はんだと電極との間に形成される金属間化合物である化合物層自体の強度に大きく左右されると考えられる。半導体パッケージに代表されるような電子部品や、マザーボードなどの実装基板の導通端子部分には、Cu電極が広く使われている。これと他の電子部品や基板とを接続するためにSn系のはんだをはんだ付けすると、多くの組成においてはんだを溶融させた液相Snと、Cu電極の固相Cuとの間には、優先的にη相(Cu6Sn5相)が生成する。
しかしながら金属間化合物であるCu6Sn5相の破壊じん性値(KIC=1.4程度)は、母材であるはんだ等の金属(KIC=102〜103)のそれに比べると格段に小さいため脆く、粗大に成長したものは内部欠陥を起点として粒内破壊を起こしやすい。したがって、化合物中での破断ははんだ接合部の信頼性を著しく低下させる問題となっている。
【0005】
本発明の目的は、はんだ付け時に形成されるCu6Sn5相の破断を抑制した、はんだ付け部の接合強度に優れた、はんだ接合体を提供することにある。
【0006】
【課題を解決するための手段】
本発明者らは、はんだ付け時に形成されるCu6Sn5相の形状が接合強度に与える影響を調査した結果、ある粒径の範囲において、はんだ付け部の接合強度が最も優れることを見出し、本発明に到達した。
【0007】
すなわち本発明は、Cu電極上に形成されたはんだ接合体において、Cu電極とSn系はんだ部との接合界面に形成するCu6Sn5相のCu電極に対する水平面における平均粒径DがD≦2.0μmであるはんだ接合体である。平均粒径Dは1.0μm≦D≦2.0μmであることが好ましい。
また、上記Sn系はんだ部は、0.1質量%以上5質量%以下のAgと、0.1質量%以上5質量%以下のCuの内少なくとも1種を含有し、残部実質的にSnからなることが好ましい。
【0008】
【発明の実施の形態】
上述のように本発明の重要な特徴は、はんだ接合部に形成されるCu6Sn5相の粒径を制御し、接合強度を向上させる点にある。以下に詳細を説明する。
【0009】
はんだ接合部に外力が加わり、Cu6Sn5相近傍にクラックを生じた場合、粒径が大きい場合は、クラックは粒界を通らずに粒内を伝播し、へき開破壊を起こしやすい。特にCu6Sn5相の粒径が平均で2.0μmより大きいとこの傾向が強く現れる。これに対し、粒径が平均で2.0μm以下になると、本来強度が低い粒界をクラックが伝播しやすくなり、粒界破壊が優勢になる。一方、はんだ接合部におけるCu6Sn5相は、Cu面に垂直方向には結晶粒1つ分しか生成しないため、粒界を伝播するクラックの行き着く先ははんだとCu6Sn5相の界面か、Cu6Sn5相とCuとの界面になり、粒界を通って破断する場合はクラックは凹凸に伝播する。したがって破断面の形成に要するエネルギーは大きくなり、はんだやCuが塑性変形によるクラック先端の応力緩和も加わって、Cu6Sn5粒内での破壊モードよりも接合強度は向上すると考えられる。
【0010】
なお、上記のクラック伝播を妨げて接合強度を上昇させる働きは、Cu6Sn5粒径が平均で1.0μmより小さいと、クラックの経路自体がCu面に水平に近づくため効果が低減することが考えられる。また前述したように、じん性の低いCu6Sn5粒内破壊が支配的になると、低い外力でもクラックは高速に伝播しやすくなり、その結果接合強度は低下する。従って、1.0μm≦D≦2.0μmとすることが好ましい。より好ましくは1.0μm≦D≦1.5μmである。
【0011】
本発明においてCu6Sn5相のCu電極に対する水平面における平均粒径Dは、以下のように測定する。
まず、はんだ接合部における母相である金属間化合物ではないはんだ合金をエッチングにより除去し、Cu6Sn5相を表面に露出さる。露出したCu6Sn5相を走査型電子顕微鏡にてCuパッド面に対して垂直方向から観察し、一辺が50μmの正方形の測定面積内に形成している結晶粒数(最大径が0.25μm以下の結晶粒を除く)を計測する。この正方形の面積2500μmを計測した結晶粒数で除することで結晶粒の平均の断面積Saveを算出し、2(Save/π)1/2を平均粒径Dとする。
【0012】
Cu6Sn5相の平均粒径を本発明の範囲とするにおいて、Cu6Sn5相を微細化する方法としては、例えばはんだ凝固時の冷却速度の制御や、はんだにおける特定の微量元素含有量の調整等が挙げられる。
冷却速度の制御により結晶粒を微細化する場合、核生成温度から凝固完了温度までの冷却速度が粒成長速度に対して十分大であれば、粒成長が抑制できる。通常のベルトコンベア式リフロー炉における、はんだ溶融時のピーク温度から、凝固完了温度すなわち固相線温度までの冷却速度は2〜2.5℃/s程度であるが、結晶粒の微細化のためには3℃/s以上の冷却速度が望ましい。
【0013】
また、微量元素含有量の調整による結晶粒の微細化は、以下のように行うことができる。
Cu6Sn5相はCu電極上で溶融した、はんだにおける液相SnにCuが溶出して形成されるが、この際に、核になりうる化合物等が存在すればCu6Sn5核発生数が増加するため粒径を微細にできる。基本となる合金組成、冷却速度にもよるが、例えば、Snと化合物を形成するNi、Feを数10ppm〜数100ppm添加すると前述の効果が得られ易い。また、Cu6Sn5相生成時に界面に析出するような物質であれば、界面に濃化することでCu6Sn5の成長を抑えることができるため、粒微細化に有効であると考えられる。例えば、PbなどはSnに固溶するが、Cu6Sn5形成時に界面に押し出され濃化する。これははんだ中に数100ppm程度存在すると効果を発揮すると考えられる。
【0014】
本発明において、Sn系はんだ部を形成するSn系はんだには、純Sn以外のはんだも用いることが出来るが、0.1質量%以上5質量%以下のAgと、0.1質量%以上5質量%以下のCuの内少なくとも1種を含有し、残部実質的にSnからなるSn系はんだが好ましい。
AgはSn系はんだの融点を低下させてはんだ接合性を向上させ、かつSn−Bi系やSn−Zn系等のように接合部界面近傍にSn、Cu以外の相を形成してCu6Sn5相の健全な形成を阻害するようなことがない。一方、多すぎるとはんだ中に過剰なAg3Snを形成して合金強度を著しく上昇させ、界面への過多な応力集中を招くため、その含有量は0.1質量%以上5質量%以下がよい。またCu電極と接続する際にはんだを溶融させると、その溶解限まではんだ中にCu電極のCuが溶け込むことになり、その結果Cu電極量が減少して強度が低下する。従って、はんだ中にあらかじめCuを含有させておくことが望ましい。Cuの添加もはんだの融点を低下させる効果があるが、過剰に添加すると融点をいたずらに上昇させるため、その含有量は0.1質量%以上5質量%以下がよい。
【0015】
【実施例】
(実施例1)
はんだ付け部のCu6Sn5粒径と、接続強度の相関性を以下に示す。
相関性の調査には表1に示す組成のφ0.5mmのはんだボールを用いた。はんだボールの組成はグロー放電質量分析法により定量分析で特定した。また、はんだボールは、はんだ溶湯からの液滴を不活性ガス中で直接ボールとする均一液滴噴霧法で製造した。均一液滴噴霧法とは、るつぼ内で金属を溶解し、溶融金属をるつぼから排出することにより微小球を製造する方法であり、排出する際に溶融金属に振動を付与することで、排出された溶融金属を体積の均一な微小球とする方法である。この方法は、例えば特開2001−262204号公報に記載されている。
【0016】
【表1】
【0017】
上記はんだボールを防錆処理済みCuランドに窒素雰囲気、ピーク温度250℃ではんだ付けを行い、はんだバンプを形成した。上記Cuランドは、厚さ1.0mmのテスト用ガラスエポキシ基板上に形成されたもので、レジスト開口径φ0.4mmの、オーバーレジストタイプである。はんだ付け時の冷却速度は、はんだ溶融時のピーク温度から、凝固完了温度すなわち固相線温度までで3℃/sとした。
【0018】
はんだとCuパッドとに生成するCu6Sn5相粒径は、以下のように測定した。まず、上記はんだバンプをメルテックス社製メルストリップHN−843を用いてエッチングして除去し、Cu6Sn5相を表面に露出させた。その後、走査型電子顕微鏡にて倍率 ×5kにてCuパッド面に対して垂直方向から観察し、Cuパッドに水平な面でのCu6Sn5相粒径を測定し、平均粒径Dを算出した。図1に本発明の一例を示す組成(a)におけるCu6Sn5相の写真を、図2に比較例である組成(d)にけるCu6Sn5相の写真を示す。mass%でFeを0.015%、Niを0.008%、Pbを0.032%含有する(a)はこれらを殆ど含まない(d)に比べCu6Sn5相が微細化されている。組成(a)〜(d)における平均粒径を表1に併せて示す。
【0019】
次に、上記ランドが形成されたテスト用ガラスエポキシ基板とはんだバンプとの接続強度を万能ボンドテスタ(デイジ社製Dage4000)を用いて、バンプシア試験を行い測定した。データは化合物層で破断したものだけを有効なものとし、各10点計測して組成(a)〜(d)のCu6Sn5平均粒径と接続強度(シア強度)との相関性を調べた。図3に平均粒径と接続強度との関係を示す。
平均粒径が1.22μmである(a)が特に高い接続強度を有することがわかる。はんだバンプのシア試験後の破断面を走査型電子顕微鏡で観察したところ、粒径が小さく破断強度の高かった(a)は、主にCu6Sn5粒界と、はんだとCu6Sn5相の界面で破断していた。粒径が大きく接続強度の弱かった(d)は、Cu6Sn5粒内破壊が主であった。
【0020】
【表2】
【0021】
(実施例2)
実施例1で用いた(a)〜(d)と同じ組成を持つはんだボールを15mm角の半導体パッケージに搭載・リフローしてバンプを形成した。リフロー条件は実施例1と同様にして行った。パッケージの電極パッドは防錆処理されたCuであり、リフローによってCu6Sn5相が形成された。次に、テスト用ガラスエポキシ基板に千住金属製Sn−3Ag−0.5Cuペーストを印刷し、パッケージを実装した。実装のリフロー条件は、バンプ形成条件と同等とした。これら実装基板に携帯機器を模擬するため150gの錘を貼り付けた後、基板を高さ1m〜2mから水平落下させ、落下時の衝撃力に対する接合部の破断の程度を評価した。
評価に際し、予め、落下させる高さと落下時の衝撃力との相関を求めておき、目標の衝撃力となる高さから実装基板を落下させた。落下時の衝撃力は、基板のパッケージ隅のバンプ付近に貼り付けた歪みゲージの最大基板歪みによって評価した。
【0022】
表2は落下高さに対応する最大基板歪み(落下時の衝撃力)と、はんだバンプの破断との関係を示している。実施例1でCu6Sn5粒径が1.22μmである(a)では最大基板歪み0.25%でも唯一接合部が破断せず、実施例1において図1に示した接合強度の高い結果を反映している。
したがって、はんだ付け時に形成されるCu6Sn5粒径を制御することにより、はんだ接合部の強度を高める効果のあることが示された。
【0023】
【発明の効果】
本発明によって、はんだ付けされた電子部品におけるCu−Sn反応層近傍の接合強度を高めることができ、電子機器の様々な使用環境における動作信頼性を向上させることができた。
【図面の簡単な説明】
【図1】本発明である平均粒径D≦2.0μmのCu6Sn5相の一例を示す走査電子顕微鏡写真である(組成(a))。
【図2】比較例である平均粒径D>2.0μmのCu6Sn5相の一例を示す走査電子顕微鏡写真である(組成(d))。
【図3】Cu電極上に形成したCu6Sn5相の平均粒径と、接続強度の関係を示す図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a solder joint in which the shape of a Cu—Sn compound formed on a soldered portion of an electronic component or the like is specified.
[0002]
[Prior art]
With the recent decrease in the mounting area of electronic devices, semiconductor packages are also becoming smaller, and the mounting form for connecting the semiconductor package to the motherboard has changed from the conventional peripheral terminal type using leads to a type in which terminals are formed in a grid pattern. It is changing. A typical example is a BGA (Ball Grid Array), and the terminal portion is connected to a substrate using a solder ball or a solder paste.
BGA has a structure in which external force cannot be reduced at the lead part like lead parts and a load is directly applied to the solder connection part. Very sensitive to stress. In addition, since the connection portion of the solder bump has a barrel shape due to the surface tension of the solder, stress tends to concentrate near the bonding interface of the solder connection portion where the intermetallic compound is formed.
[0003]
In addition, Pb-free solder is being promoted worldwide as one of the recent approaches to environmental issues, and Sn-Pb solder, which has been conventionally used, is being banned. There are many alternative alloys, such as Sn-Ag and Sn-Ag-Cu, but they are basically Sn-based and have poor ductility compared to Sn-Pb eutectic solder. It is difficult to ease.
[0004]
[Problems to be solved by the invention]
From the above situation, it is considered that the solder bonding strength is greatly affected by the strength of the compound layer itself, which is an intermetallic compound formed between the solder and the electrode. 2. Description of the Related Art A Cu electrode is widely used for a conductive terminal portion of an electronic component typified by a semiconductor package or a mounting substrate such as a motherboard. When soldering Sn-based solder to connect this with other electronic components or substrates, there is a priority between the liquid phase Sn in which the solder is melted in many compositions and the solid phase Cu of the Cu electrode. An η phase (Cu 6 Sn 5 phase) is generated.
However, the fracture toughness value (K IC = about 1.4) of the Cu 6 Sn 5 phase, which is an intermetallic compound, is significantly higher than that of a metal such as solder (K IC = 10 2 to 10 3 ) as a base material. Because of their small size, those that are brittle and coarsely grown tend to cause intragranular fracture starting from internal defects. Therefore, fracture in the compound is a problem that significantly reduces the reliability of the solder joint.
[0005]
An object of the present invention is to provide a solder joint having excellent bonding strength at a soldered portion, in which fracture of a Cu 6 Sn 5 phase formed at the time of soldering is suppressed.
[0006]
[Means for Solving the Problems]
The present inventors have investigated the influence of the shape of the Cu 6 Sn 5 phase formed at the time of soldering on the bonding strength, and found that the bonding strength of the soldered portion is most excellent within a certain particle size range. The present invention has been reached.
[0007]
That is, according to the present invention, in the solder joint formed on the Cu electrode, the average particle diameter D in the horizontal plane with respect to the Cu 6 Sn 5 phase Cu electrode formed at the joint interface between the Cu electrode and the Sn-based solder portion is D ≦ 2. 0.0 μm. The average particle size D is preferably 1.0 μm ≦ D ≦ 2.0 μm.
The Sn-based solder portion contains at least 0.1 mass% and at most 5 mass% of Ag and at least one of 0.1 mass% and at most 5 mass% of Cu, and the balance is substantially from Sn. Preferably.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
As described above, an important feature of the present invention is that the grain size of the Cu 6 Sn 5 phase formed at the solder joint is controlled to improve the joint strength. The details will be described below.
[0009]
When an external force is applied to the solder joint and a crack is generated in the vicinity of the Cu 6 Sn 5 phase, and when the particle size is large, the crack propagates inside the grain without passing through the grain boundary and is liable to cause cleavage fracture. This tendency is particularly pronounced when the particle size of the Cu 6 Sn 5 phase is greater than 2.0 μm on average. On the other hand, when the average particle size is 2.0 μm or less, cracks are likely to propagate through grain boundaries that are originally low in strength, and grain boundary destruction becomes dominant. On the other hand, since the Cu 6 Sn 5 phase in the solder joint generates only one crystal grain in the direction perpendicular to the Cu plane, the crack that propagates through the grain boundary reaches the interface between the solder and the Cu 6 Sn 5 phase. , The interface between the Cu 6 Sn 5 phase and Cu, and when the fracture occurs through the grain boundary, the crack propagates to the irregularities. Therefore, it is considered that the energy required for forming the fractured surface increases, and the bonding strength is improved more than in the fracture mode in the Cu 6 Sn 5 grains due to the stress relaxation at the tip of the crack due to the plastic deformation of the solder and Cu.
[0010]
The function of increasing the bonding strength by hindering the above-described crack propagation is that if the average particle diameter of Cu 6 Sn 5 is smaller than 1.0 μm, the crack path itself becomes closer to the Cu surface horizontally and the effect is reduced. Can be considered. Further, as described above, if the intragranular fracture of Cu 6 Sn 5 with low toughness becomes dominant, cracks are easily propagated at high speed even with low external force, and as a result, the bonding strength is reduced. Therefore, it is preferable that 1.0 μm ≦ D ≦ 2.0 μm. More preferably, 1.0 μm ≦ D ≦ 1.5 μm.
[0011]
In the present invention, the average particle diameter D in the horizontal plane with respect to the Cu 6 Sn 5 phase Cu electrode is measured as follows.
First, a solder alloy which is not an intermetallic compound which is a mother phase in a solder joint is removed by etching to expose a Cu 6 Sn 5 phase on the surface. The exposed Cu 6 Sn 5 phase was observed from a direction perpendicular to the Cu pad surface with a scanning electron microscope, and the number of crystal grains (the maximum diameter was 0.25 μm) formed in a square measuring area of 50 μm on a side was 50 μm. The following crystal grains are excluded). The average cross-sectional area S ave of crystal grains is calculated by dividing the area of the square 2500 μm by the number of measured crystal grains, and 2 (S ave / π) 1/2 is defined as the average particle size D.
[0012]
In the average particle diameter of the Cu 6 Sn 5 phase and scope of the present invention, as a method of refining the Cu 6 Sn 5 phase, for example, control of the cooling rate during solder solidification, certain trace elements content in the solder And the like.
When crystal grains are refined by controlling the cooling rate, grain growth can be suppressed if the cooling rate from the nucleation temperature to the solidification completion temperature is sufficiently higher than the grain growth rate. In a normal belt conveyor type reflow furnace, the cooling rate from the peak temperature at the time of solder melting to the solidification completion temperature, that is, the solidus temperature is about 2 to 2.5 ° C./s. The cooling rate is preferably 3 ° C./s or more.
[0013]
The refinement of the crystal grains by adjusting the content of the trace element can be performed as follows.
The Cu 6 Sn 5 phase melts on the Cu electrode and is formed by elution of Cu in the liquid phase Sn of the solder. At this time, if there is a compound that can be a nucleus, the number of Cu 6 Sn 5 nuclei generated Particle diameter can be made finer due to an increase in the particle size. Although it depends on the basic alloy composition and the cooling rate, for example, when several tens ppm to several hundred ppm of Ni and Fe which form a compound with Sn are added, the above-described effects are easily obtained. Further, it is considered that a substance that precipitates at the interface when the Cu 6 Sn 5 phase is formed is concentrated at the interface, thereby suppressing the growth of Cu 6 Sn 5 , and thus is considered to be effective for grain refinement. . For example, Pb or the like dissolves in Sn, but is extruded to the interface when Cu 6 Sn 5 is formed and is concentrated. This is considered to be effective when about several hundred ppm is present in the solder.
[0014]
In the present invention, as the Sn-based solder forming the Sn-based solder portion, a solder other than pure Sn can be used, but Ag of 0.1% by mass or more and 5% by mass or less, and Ag of 0.1% by mass or more and 5% by mass or less. A Sn-based solder containing at least one of Cu by mass% or less, and the balance substantially consisting of Sn is preferable.
Ag lowers the melting point of the Sn-based solder to improve solder jointability, and forms a phase other than Sn and Cu near the joint interface, such as Sn-Bi-based or Sn-Zn-based, to form Cu 6 Sn. It does not interfere with the sound formation of the five phases. On the other hand, if the content is too large, excessive Ag 3 Sn is formed in the solder to significantly increase the alloy strength and cause excessive stress concentration at the interface, so that the content is 0.1% by mass or more and 5% by mass or less. Good. Further, when the solder is melted at the time of connection with the Cu electrode, Cu of the Cu electrode dissolves into the solder to the dissolution limit, and as a result, the amount of the Cu electrode decreases and the strength decreases. Therefore, it is desirable to include Cu in the solder in advance. Addition of Cu also has the effect of lowering the melting point of the solder, but if added excessively, raises the melting point unnecessarily. Therefore, the content is preferably 0.1% by mass or more and 5% by mass or less.
[0015]
【Example】
(Example 1)
The correlation between the Cu 6 Sn 5 particle size of the soldered portion and the connection strength is shown below.
For the investigation of the correlation, a solder ball of φ0.5 mm having the composition shown in Table 1 was used. The composition of the solder ball was identified by quantitative analysis by glow discharge mass spectrometry. The solder balls were manufactured by a uniform droplet spraying method in which droplets from a molten solder were directly formed into balls in an inert gas. The uniform droplet spraying method is a method of manufacturing microspheres by dissolving a metal in a crucible and discharging the molten metal from the crucible. This is a method of turning the molten metal into microspheres having a uniform volume. This method is described in, for example, JP-A-2001-262204.
[0016]
[Table 1]
[0017]
The solder balls were soldered to a rust-proofed Cu land at a nitrogen atmosphere at a peak temperature of 250 ° C. to form solder bumps. The Cu land is formed on a test glass epoxy substrate having a thickness of 1.0 mm, and is an over-resist type having a resist opening diameter of 0.4 mm. The cooling rate at the time of soldering was 3 ° C./s from the peak temperature at the time of solder melting to the solidification completion temperature, that is, the solidus temperature.
[0018]
The particle size of the Cu 6 Sn 5 phase formed on the solder and the Cu pad was measured as follows. First, the solder bumps were removed by etching using Melstrip HN-843 manufactured by Meltex Co., Ltd. to expose the Cu 6 Sn 5 phase on the surface. Thereafter, observation is performed with a scanning electron microscope at a magnification of × 5k from a direction perpendicular to the Cu pad surface, and a Cu 6 Sn 5 phase particle size is measured on a surface horizontal to the Cu pad, and an average particle size D is calculated. did. Interested in Cu 6 Sn 5 phase in the composition (a) showing an example of the present invention in FIG. 1 shows a photograph of the kick Cu 6 Sn 5 phase composition is a comparative example in Figure 2 (d). 0.015% of Fe in mass%, 0.008% of Ni, and Pb containing 0.032% (a) compared to not include these little (d) Cu 6 Sn 5 phase is miniaturized . Table 1 also shows the average particle size of the compositions (a) to (d).
[0019]
Next, the connection strength between the test glass epoxy substrate on which the lands were formed and the solder bumps was measured by a bump shear test using a universal bond tester (Dage 4000, manufactured by Dage). The data is assumed to be valid only for those fractured in the compound layer, and each point is measured at 10 points to examine the correlation between the average particle diameter of Cu 6 Sn 5 of the compositions (a) to (d) and the connection strength (shear strength). Was. FIG. 3 shows the relationship between the average particle size and the connection strength.
It can be seen that (a) having an average particle size of 1.22 μm has particularly high connection strength. When the fracture surface of the solder bump after the shear test was observed with a scanning electron microscope, it was found that the grain size was small and the fracture strength was high (a) mainly due to the Cu 6 Sn 5 grain boundary, the solder and the Cu 6 Sn 5 phase Was broken at the interface. In (d), in which the grain size was large and the connection strength was weak, Cu 6 Sn 5 intragranular fracture was mainly involved.
[0020]
[Table 2]
[0021]
(Example 2)
Solder balls having the same composition as (a) to (d) used in Example 1 were mounted on a 15 mm square semiconductor package and reflowed to form bumps. The reflow conditions were the same as in Example 1. The electrode pads of the package were made of rust-proof Cu, and a Cu 6 Sn 5 phase was formed by reflow. Next, a Sn-3Ag-0.5Cu paste made by Senju Metal was printed on a glass epoxy substrate for testing, and a package was mounted. The reflow conditions for mounting were equivalent to the bump forming conditions. After attaching a weight of 150 g to simulate a portable device on these mounting substrates, the substrates were dropped horizontally from a height of 1 m to 2 m, and the degree of breakage of the joint with respect to the impact force at the time of falling was evaluated.
At the time of evaluation, the correlation between the drop height and the impact force at the time of drop was determined in advance, and the mounting board was dropped from the height that was the target impact force. The impact force at the time of drop was evaluated based on the maximum substrate strain of a strain gauge attached near a bump at a package corner of the substrate.
[0022]
Table 2 shows the relationship between the maximum substrate distortion (impact force at the time of drop) corresponding to the drop height and the breakage of the solder bump. In the case of (a) in which the Cu 6 Sn 5 particle size is 1.22 μm in Example 1, the only joint does not break even at the maximum substrate strain of 0.25%, and the result of Example 1 is that the bonding strength is high as shown in FIG. Is reflected.
Therefore, it was shown that controlling the particle size of Cu 6 Sn 5 formed at the time of soldering has the effect of increasing the strength of the solder joint.
[0023]
【The invention's effect】
According to the present invention, the bonding strength in the vicinity of the Cu—Sn reaction layer in the soldered electronic component can be increased, and the operation reliability of the electronic device in various use environments can be improved.
[Brief description of the drawings]
FIG. 1 is a scanning electron micrograph showing an example of a Cu 6 Sn 5 phase having an average particle diameter D ≦ 2.0 μm according to the present invention (composition (a)).
FIG. 2 is a scanning electron micrograph showing an example of a Cu 6 Sn 5 phase having an average particle diameter D> 2.0 μm as a comparative example (composition (d)).
FIG. 3 is a diagram showing a relationship between an average particle size of a Cu 6 Sn 5 phase formed on a Cu electrode and connection strength.
Claims (3)
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JP2002187792A JP2004031771A (en) | 2002-06-27 | 2002-06-27 | Solder junction |
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Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2004154865A (en) * | 2002-10-17 | 2004-06-03 | Senju Metal Ind Co Ltd | Lead-free solder ball alloy and solder ball |
WO2013002112A1 (en) * | 2011-06-29 | 2013-01-03 | 株式会社日本スペリア社 | Process for producing solder joint with improved reliability |
US8587116B2 (en) | 2010-09-30 | 2013-11-19 | Infineon Technologies Ag | Semiconductor module comprising an insert |
US9214442B2 (en) * | 2007-03-19 | 2015-12-15 | Infineon Technologies Ag | Power semiconductor module, method for producing a power semiconductor module, and semiconductor chip |
WO2021024568A1 (en) * | 2019-08-05 | 2021-02-11 | 日立オートモティブシステムズ株式会社 | Electronic control device |
-
2002
- 2002-06-27 JP JP2002187792A patent/JP2004031771A/en active Pending
Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2004154865A (en) * | 2002-10-17 | 2004-06-03 | Senju Metal Ind Co Ltd | Lead-free solder ball alloy and solder ball |
US9214442B2 (en) * | 2007-03-19 | 2015-12-15 | Infineon Technologies Ag | Power semiconductor module, method for producing a power semiconductor module, and semiconductor chip |
US8587116B2 (en) | 2010-09-30 | 2013-11-19 | Infineon Technologies Ag | Semiconductor module comprising an insert |
WO2013002112A1 (en) * | 2011-06-29 | 2013-01-03 | 株式会社日本スペリア社 | Process for producing solder joint with improved reliability |
JPWO2013002112A1 (en) * | 2011-06-29 | 2015-02-23 | 株式会社日本スペリア社 | Method for manufacturing solder joints with improved reliability |
WO2021024568A1 (en) * | 2019-08-05 | 2021-02-11 | 日立オートモティブシステムズ株式会社 | Electronic control device |
JP2021027178A (en) * | 2019-08-05 | 2021-02-22 | 日立オートモティブシステムズ株式会社 | Electronic control device |
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