Effect of Under Bump Metallurgy and Reflows on Shear Strength and Microstructure of Joint between Cu Substrate and Sn-36Pb-2Ag Solder Alloy

Abstract

The interfacial reaction between Sn-36Pb-2Ag (numbers are all in mass% unless specified otherwise) solder balls and Ni, Ag and Ni/Ag electroplated on a Cu substrate was investigated and the joint bonding strength was measured using a ball shear tester. The intermetallic Ag 3 Sn was observed at the interface of the Cu/Ag/solder joint and Ni 3 Sn 4 was found at the Cu/Ni/solder joint. In the case of Cu/Ni/Ag substrate, the layer sequence was observed to be Cu/Ni/Ni 3 Sn 4 /Ag 3 Sn/solder. The Ag layer was completely consumed by formation of Ag 3 Sn but the Ni layer remained. Environmental tests showed that the Cu/Ni/Ag substrate retained better solder joint reliability than either Ni or Ag single plated Cu substrate. Two types of reflow profiles were tested and the specimen reflowed by a higher temperature profile showed a higher solder joint strength. Solder joint strength and microstructural change were observed with several reflow cycles in considering the real board mounting conditions. There was significant evolution of solder and joint microstructures with reflow cycles and it explained well the change of solder joint strength.

Flip-Chip Bonding of MEMS Scanner for Laser Display Using Electroplated AuSn Solder Bump

“…There are some reports on the correlation between growth of IMC and shear strength. They reported that the initial formation of the IMC at the interface means a good metallurgical bonding [17]- [19]. However, an overgrown IMC is known to be detrimental to the joint strength due to the brittle nature of IMCs.…”

Under bump metallurgy study on copper/low-k dielectrics for fine pitch flip chip packaging

“…8 In order to study the interfacial reaction with diffusion at the interface, the solder-bumped samples were subjected to a thermal aging test at 250°C for 10, 20, and 30 min, respectively, in a N 2 atmosphere box oven in order to evaluate the UBM stability and solder bump integrity. The initial formation of the IMC at the interface indicates good metallurgical bonding.…”