Fabrication and performance of embedded matrix indium thermal interface materials for advanced FCBGA packaging

Abstract

Indium (In) has been used as a thermal interface material (TIM1) in high-performance central processing unit (CPU) for better heat dissipation. However, leakage or pump-out of liquid indium during the multiple reflow cycles limits its application in advanced flip chip ball gray array (FCBGA) packaging. Former researchers place a seal or dam structure to prevent In leakage, leading to the risk of In explosion, thermal degradation, or require additional keep-out zones. In this work, a copper foam (CF) matrix was embedded in In to absorb the liquid In and eliminate the leakage of In TIM1 during the multiple reflow cycles, as the CF capillary force. Au/Ni/Cu-Au/Ni/Cu joint was fabricated by soldering with the composite solder at 190 °C for 2 min. After reflow cycles, good metallurgical bonding was formed at interfaces of joint. Rod-like Cu₁₁In₉ formed at the CF and In interface, due to the re-dissolved of Cu₁₁In₉ crystal. Small amount of Cu atoms from CF can reduce the activity of In, which inhibits the growth of Ni₃In₇ intermetallic compound (IMC) at the interface of In and Au/Ni/Cu substrate. The CF matrix also improved the shear strength (22.9%) and thermal conductivity of the solder joints. Besides, the fracture behavior of solder joints without CF matrix was classified to be ductile type while that with CF matrix was changed to be ductile-brittle mixed type.

Keywords

indium / TIM1 / leakage / flip chip ball gray array / copper foam matrix / mechanical and thermal performance

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Central South University