The X2825 silica-filled reworkable board-level underfill encapsulant specifies a coefficient of thermal expansion (CTE) of 26 ppm/°C.The underfill enhances drop and shock test reliability and, compared to higher CTE underfills, allegedly provides superior thermal cycle performance. For example, in one trial, thermal cycling of a BGA between -20°C and +85°C, an unfilled version of this product with a CTE of 60 ppm/°C resulted in a first failure at 500 cycles whereas X2825 had no failures after 1,500 cycles. For more details, call ZYMET INC., East Hanover, NJ. (973) 428-5245.
