Effects of β-Sn grain orientation and temperature on the interfacial reaction in Cu/SAC305/Cu micro solder joints during aging
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摘要: 为了探究不同等温时效温度下β-Sn晶粒取向及晶界特征对界面反应的影响，采用准原位观测手段对不同Sn取向的Cu/Sn3.0Ag0.5Cu/Cu(Cu/SAC305/Cu)微焊点进行研究. 结果表明，在不同温度下时效时，微焊点两侧界面IMC(Cu6Sn5 + Cu3Sn两相)自始至终呈现对称性生长，表明时效过程中β-Sn晶粒取向及晶界的存在不会影响界面反应. 但是随着时效温度的升高，界面IMC的形貌和厚度发生明显变化. 在100 ℃时效后，界面处生成扇贝状的Cu6Sn5和较薄的不连续的Cu3Sn层；在125 ℃时效后，界面处生成扇贝状的Cu6Sn5和较薄的连续的Cu3Sn层；而在150 ℃时效后，界面IMC由层状Cu6Sn5和层状Cu3Sn双层结构组成. 时效温度的升高促使Cu和Sn原子扩散加快，促进了扇贝状Cu6Sn5向层状转变并造成Cu3Sn的快速生长. 同时，基于界面IMC厚度随时效时间的演变规律，获得了不同时效温度下微焊点界面IMC生长曲线，可为Sn基微焊点的可靠性评价提供依据.Abstract: Quasi-in-situ method was carried out to study the effects of β-Sn grain orientation and grain boundary feature on the growth behavior of interfacial intermetallic compounds (IMCs) in Cu/Sn3.0Ag0.5Cu/Cu(Cu/SAC305/Cu) micro solder joints under different aging temperatures. The results showed that the IMCs containing Cu6Sn5 + Cu3Sn phases at both interfaces of the micro solder joints grew symmetrically under all the aging conditions, proving that β-Sn grain orientation and grain boundary played no obvious effect on the interfacial IMCs growth either between the two interfaces of a same joint or those from different joints. While with increasing aging temperature, the morphology and thickness of the interfacial IMCs were changing apparently. Scallop-type Cu6Sn5 and thin discontinuous Cu3Sn formed at the interfaces after aging at 100 ℃; scallop-type Cu6Sn5 and thin continuous Cu3Sn formed at the interfaces after aging at 125 ℃ and bilayer structured IMCs containing Cu6Sn5 and Cu3Sn formed at the interfaces after aging at 150 ℃. The increasing aging temperature accelerated the diffusion of Cu and Sn atoms, which could promote the transition of Cu6Sn5 from scallop to layer and the rapid growth of Cu3Sn. Finally, based on the variation of interfacial IMCs thickness with aging time, the growth curves of the interfacial IMCs layers under different aging conditions were obtained which may be helpful for reliability assessment of Sn-based micro solder joints.
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图 1 Cu/SAC305/Cu初始微焊点微观组织及EBSD取向图
Figure 1. Microstructure and EBSD maps of Cu/SAC305/Cu as-reflowed micro solder joints. (a) EPMA image of No.1 solder joint; (b) EPMA image of No.2 solder joint; (c) EPMA image of No.3 solder joint; (d) EBSD maps of No.1 solder joint; (e) EBSD maps of No.2 solder joint; (f) EBSD maps of No.3 solder joint
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图 2 Cu/SAC305/Cu微焊点在100 ℃不同时效时间后的微观组织形貌
Figure 2. EPMA images of Cu/SAC305/Cu micro solder joints during aging at 100 ℃ for different durations. (a) No. 1 solder joint after aging for 50 h; (b) No. 2 solder joint after aging for 50 h; (c) No. 3 solder joint after aging for 50 h; (d) No. 1 solder joint after aging for 200 h; (e) No. 2 solder joint after aging for 200 h; (f) No. 3 solder joint after aging for 200 h; (g) No. 1 solder joint after aging for 400 h; (h) No. 2 solder joint after aging for 400 h; (i) No. 3 solder joint after aging for 400 h
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图 3 Cu/SAC305/Cu微焊点在100 ℃时效400 h后EBSD图
Figure 3. EBSD maps of Cu/SAC305/Cu micro solder joints after aging at 100 oC for 400 h. (a) No. 1 solder joint; (b) No. 2 solder joint; (c) No. 3 solder joint
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图 4 Cu/SAC305/Cu微焊点在100 ℃时效后界面IMC厚度与时效时间的关系
Figure 4. Interfacial IMC thickness in Cu/SAC305/Cu micro solder joints vs aging duration at 100 ℃. (a) IMC thickness at each interface and absolute IMC thickness difference between top and bottom interfaces in each joint; (b) total IMC thickness from both interfaces in each joint
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图 5 3号Cu/SAC305/Cu微焊点时效400 h后界面IMC晶粒形貌图
Figure 5. Morphology of the interfacial IMC of the No. 3 Cu/SAC305/Cu micro solder joint after aging for 400 h. (a) top interface; (b) bottom interface; (c) overall view of the top interface; (d) enlarged image of A zone in Fig.5c; (e) enlarged image of B zone in Fig.5c; (f) enlarged image of C zone in Fig.5c; (g) enlarged image of D zone in Fig.5c
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图 6 Cu/SAC305/Cu初始微焊点微观组织及EBSD取向图
Figure 6. Microstructure and EBSD maps of Cu/SAC305/Cu as-reflowed micro solder joints. (a) EPMA image of No.4 solder joint; (b) EPMA image of No.5 solder joint; (c) EPMA image of No.6 solder joint; (d) EPMA image of No.7 solder joint; (e) EBSD maps of No.4 solder joint; (f) EBSD maps of No.5 solder joint; (g) EBSD maps of No.6 solder joint; (h) EBSD maps of No.7 solder joint
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图 7 Cu/SAC305/Cu微焊点在125 ℃不同时效时间后的微观组织演变图
Figure 7. Microstructural evolution of Cu/SAC305/Cu micro solder joints during aging at 125 oC for different durations. (a) No. 4 solder joint after aging for 50 h; (b) No. 5 solder joint after aging for 50 h; (c) No. 6 solder joint after aging for 50 h; (d) No. 7 solder joint after aging for 50 h; (e) No. 4 solder joint after aging for 200 h; (f) No. 5 solder joint after aging for 200 h; (g) No. 6 solder joint after aging for 200 h; (h) No. 7 solder joint after aging for 200 h; (i) No. 4 solder joint after aging for 400 h; (j) No. 5 solder joint after aging for 400 h; (k) No. 6 solder joint after aging for 400 h (l) No. 7 solder joint after aging for 400 h
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图 8 Cu/SAC305/Cu微焊点在125 ℃时效后界面IMC厚度与时效时间的关系
Figure 8. Interfacial IMC thickness in Cu/SAC305/Cu micro solder joints vs aging duration at 125 oC. (a) IMC thickness at each interface and absolute IMC thickness difference between top and bottom interfaces in each joint; (b) total IMC thickness from both interfaces in each joint
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图 9 8号Cu/SAC305/Cu微焊点微观组织及取向图
Figure 9. Microstructure and orientation maps of No.8 Cu/SAC305/Cu micro solder joint. (a) initial EPMA image of solder joint; (b) EPMA image of solder joint after aging at 150 ℃ for 50 h; (c) EPMA image of solder joint after aging at 150 ℃ for 200 h; (d) EPMA image of solder joint after aging at 150 ℃ for 400 h; (e) initial rolling direction EBSD map of solder joint; (f) initial transverse direction EBSD map of solder joint; (g) initial normal direction EBSD map of solder joint
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