Resilient composite of silicone and foamed tin as a new material for electrical and thermal contacts

Abstract

Silicone-infiltrated tin foam containing 14 volume % metal is a new composite material that is resilient up to a compressive stress of 2 MPa and a strain of 13%. Its volume electrical resistivity is 5 × 10 −4 ω cm and remains below 1 × 10 −3 ω cm up to 1700 compressive loading cycles (0.075 MPa). Its contact resistivity (with copper) decreases with pressure and levels off at 0.22 ω cm 2 at a pressure of 0.07 MPa. Beyond 1000 compressive loading cycles (0.08 MPa), the contact resistivity rises, reaching 0.48 ω cm 2 at 1700 cycles. The thermal expansion coefficient is 215 × 10 −6°C −1 at 45°C, compared with a value of 282 × 10 −6°C −1 for silicone. This composite is attractive as a material for electrical and thermal contacts in electronic packages. Compared with silicone-infiltrated tin foam, silicone-infiltrated tin-lead foam exhibits a lower volume electrical resistivity, a lower contact resistivity (with copper) and a higher fatigue resistance, but it is resilient only up to a compressive stress of 0.4 MPa and a strain of 0.8%. The bonding between silicone and tin is stronger than that between silicone and tin-lead.