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Interfacial Reaction of SnAgCu-Xni Composite Solders on Cu and Ni

Tuesday, April 24, 2012: 9:00 AM
Red Rock B (Red Rock Casino Resort and Spa)
Mr. Liu Ping , Zhejiang Metallurgical Research Institute, Hangzhou, China
Xiaolong Gu , Zhejiang Metallurgical Research Institute, Hangzhou, China
Xiaogang Liu , Zhejiang Metallurgical Research Institute, Hangzhou, China
Xia Jin , Zhejiang Metallurgical Research Institute, Hangzhou, China
Yu Zhang , Zhejiang Metallurgical Research Institute, Hangzhou, China
Zhengyi Long , Zhejiang Metallurgical Research Institute, Hangzhou, China
Abstract: The present work prepared composite lead free solders by adding 0.5, 1, and 2wt.% of Ni micro-particles to Sn3.8Ag0.7Cu solder paste (SAC-xNi, therein x presents the weight percentage of Ni). The interfacial microstructure and evolution of SAC-xNi solders on organic solderability preservative (OSP) and Ni/Au finished Cu pads were investigated at a temperature of 150oC aging up to 1000 h. It was found that the interfacial scallop shape (CuNi)6Sn5 intermetallic compound (IMC) grain was refined significantly at the interface of composite joints on Cu substrate. After 50h aging, duplex IMCs layers were formed as the well-known structure of a layer of (CuNi)6Sn5 close to the solder and a layer of Cu3Sn adjacent to Cu substrate. It was observed that the (CuNi)6Sn5 layer in SAC-2Ni/Cu joint was entrapped by a small mount of solder. The growth of Cu3Sn layer was suppressed largely on the joint of SAC-xNi/Cu during aging, and SAC-2Ni/Cu joint presented the thinnest Cu3Sn. In the case of SAC-xNi/Ni joints, the interfacial IMC morphology and composition were affected by the weight percentages of added Ni-particles and aging time. The intermetallic compound shifted from the needle-like (CuNi)6Sn5 on the non-composite joint to dual layers of facet-like (CuNi)6Sn5 and boomerang shape (NiCu)3Sn4 with 0.5 wt.% Ni addition, and only boomerang shape (NiCu)3Sn4 was formed at the interface between the composite solder and Ni layer when Ni addition exceeded 1 wt.%. After aging for 200 h, the solder joints of SAC, SAC–0.5Ni and –1Ni presented duplex intermetallic compound (IMC) layers regardless of the initial interfacial structure on as-reflowed joints, whose upper and lower IMC layers were comprised of (CuNi)6Sn5 and (NiCu)3Sn4, respectively. Only a single (NiCu)3Sn4 IMC layer was ever observed at the SAC–2Ni/Ni interface on whole aging process. Compositional analysis indicated that the amount of Ni within the IMC regions increased as the proportion of Ni addition increased.

Keywords: Composite solders, Intermetallics, Sn3.8Ag0.7Cu, Microsctructure

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