The Experiment Research And Theory Analysis Of The Effect Of Element On Properities Of Intermetalic Compound Between Sn-based Solder And Cu Substrate

So far, most connect of electronic devices is carried out by interface react between Sn-based lead-free solder alloy and Cu substrate. Duiring soldering, intermetalic compound(IMC) with different thickness is formed at the interface. With the ever increasing demands for miniaturization of electronic devices, the IMCs volume fraction of the solder joint is increasing, and its IMC will be more and more important to effect the relibility of the solder joint. Element addition is a main way to adjust the growth of interface IMCs. Therefore, it is necessary and valuable to deeply research the essence of effect of element addition on inerface IMC growth and shear strength of the solder joint.In this paper, Sn-xNi/Cu(x=0, 0.1, 0.3, 0.5, 0.8, 1.2, 1.6), Sn-xCo/Cu(x=0, 0.1, 0.3, 0.5,0.8, 1.2, 1.6), Sn-xIn/Cu(x=0, 0.3, 0.6, 0.9, 1.2, 1.5), Sn-xZn/Cu(x=0, 0.3, 0.6, 0.9, 1.2, 1.5)solder alloy were prepared by metallurgy method. The effect law of Ni, Co, In, Zn on the growth of IMC between Sn-rich solder and Cu substrate was investigated and the first-principle method was employed to study the effect reason of Ni, Co, In, Zn on the growth of interface Cu6Sn5-based IMC. Meanwhile, The effect of Ni, Co, In, Zn on the shear strength of solder joint formed between the doped solder and Cu substrate was studied by experiment method, and the observation of solder metallographic phase and fracture morphology and the component analysis of the interface phase were carried out to explore the reason of the influence.The results show that Cu6Sn5 and Cu3 Sn IMCs were formed between pure Sn solder and Cu substrate after reflow and aging at 423 K(150℃), while the formation of Cu3 Sn IMC was suspressed between Ni, Co, In, Zn added Sn-based solder and Cu substrate. In addition, the thickness law of IMC doped with Ni, Co, In, Zn is as follow:Ni Co non In Znd ?d ?d ?d ?d, that is to say, with the same content of doped element in Cu6Sn5,Ni and Co promote the growth of Cu6Sn5 IMC, while In and Zn restrain the growth of Cu6Sn5 IMC. Meanwhile, the thickness of Cu6Sn5 IMC increases with the content of Ni or Co and decreases with the content of In or Zn. The thickness of the Cu6Sn5-based IMC at the interface of Sn/Cu, Sn-0.8Ni/Cu, Sn-0.8Co/Cu, Sn-0.9In/Cu, Sn-0.9Zn/Cu increases closely linearly with the aging time, and the grain size at the interface increases after aging,so the growth of Cu6Sn5-based IMC is controled by bulk diffusion.The first-principle method was employed to calculate the formation energy E of Cu6Sn5-based IMC in different configurations doped with Ni, Co, In, Zn, and to confirm the occupy position and the corresponding stable structure. When the content of doped element is 2.77 at.%, Ni, Co, In, Zn prefer to occupy Cu(4e), Cu(4e), Sn(4e) and Sn(4e) site respectively, and Ni, Co, In, Zn prefer to occupy Cu(4e), Cu(4e), Sn(8f1) and Sn(4e) site respectively with the doping content of 4.55 at.%. In Cu6Sn5 IMC, the formation energy of void in different Cu and Sn sites and migration energy battier of neighbour sites of Cu or Sn was calculted, and it is showed that Cu is the main diffusion element in Cu6Sn5. Comparing the migration energy barrier of Cu sites along different directions, we find the path with the lowest migration energy barrier in Cu6Sn5, which is parallel to [2,0,1] direction in Cu6Sn5.Furthermore, the migration energy barrier of Cu atoms along [2,0,1] direction and other directions in Ni, Co, In, Zn doped Cu6Sn5 was calculated and it is showed that minor addition of Ni, Co, In, Zn won`t change the most possible migration path direction which is the [2,0,1] direction with the lowest migration energy barrier. Comparing the migration energy barrier of Cu atoms along the difussion path in Ni, Co, In, Zn doped Cu6Sn5, with the same content of doping element, the trend of the corresponding migration energy barrier is as follow:Ni Co non In Zn a a a a aQ ?Q ?Q ?Q ?Q, which is to say that relative to the migration energy barriernon aQ of Cu6Sn5 IMC without doping, the migration energy barrier decreases with the Ni and Co doping and increases with the In and Zn doping. The Cu atom migration energy barrier along [2,0,1] direction of Cu6Sn5-based IMC with more Ni or Co doped is smaller, while that with more In or Zn is larger. The calculated results are identical to the experiment results and it gives a good explanation to the effect of element addition on the growth of interface IMC.The grains of interface IMC were refined with the addition of Ni, Co, In, Zn, and it can improve the strength of solder alloy. Combining with the analysis of the morohology and component of fracture, we find that the shear strength of solder joint has relative with solder alloy and the interface IMC, in which the strengh of the solder alloy play the main role. When the strength of alloy is higher, the shear strength of solder joint is bigger.