Influence of initial morphology and thickness of Cu6Sn5 and Cu3Sn intermetallics on growth and evolution during thermal aging of Sn-Ag solder/Cu joints

Abstract

Intermetallic-layer formation and growth in Pb-free solder joints, during solder reflow or subsequent aging, has a significant effect on the thermal and mechanical behavior of solder joints. In this study, the influence of initial intermetallic morphology on growth rate, and kinetics were examined in a Sn-3.5Ag solder reflowed on Cu. The initial morphology of the intermetallic was tailered by cooling in water, air, or furnace conditions. Solder aging was conducted at 100°C, 140°C, and 175°C and aged for 0-1,000 h. Cooling rate, aging temperature, and aging time played an important role on microstructure evolution and growth kinetics of Cu 6 Sn 5 (η) and Cu 3 Sn (ε) intermetallic layers. Prior to aging, faster cooling rates resulted in a relatively planar Cu 6 Sn 5 layer, while a nodular Cu 6 Sn 5 morphology was present for slower cooling. Intermetallic-growth rate measurements after aging at various times, indicated a mixed growth mechanism of grain-boundary and bulk diffusion. These mechanisms are discussed in terms of the initial intermetallic thickness and morphology controlled by cooling rate, diffusion kinetics, and the competition between Cu 6 Sn 5 and Cu 3 Sn growth.

Microstructural evolution and mechanical properties of Sn-Bi-Cu ternary eutectic alloy produced by directional solidification

“…Higher solidification rate yields a thinner IMC, which is consistent with other researchers' results 42,43 . Because of its mechanical properties, Cu 3 Sn is also more suitable than Cu 6 Sn 5 and Sn as a joint material for microbumps 44,45 .…”

Mechanical Characterization of Lead-Free Sn-Ag-Cu Solder Joints by High-Temperature Nanoindentation

“…Details of the reflow procedure can be obtained elsewhere. 15 The processing conditions were controlled in order to obtain two types of joints: (a) one with a thinner intermetallic layer but coarser solder microstructure, and (b) one with a relatively thick intermetallic layer but finer solder microstructures, as shown in Fig. 1.…”

Numerical and Experimental Investigations on the Growth of the Intermetallic Mg2Si Phase in Mg Infiltrated Si‐Foams

“…The driving force for the diffusion is the gradient of the concentration and the growth behavior follows the parabolic law, d / ffiffi t p . [35] The reaction is driven by the difference of the grand chemical potential,…”