Reactive cold sintering of dense barium sulfate ceramics for high-reliability chip packaging in integrated circuits

Abstract

Reactive cold sintering (RCS) is an innovative ceramic consolidation technique that combines a low-temperature reaction with the cold sintering process. In this work, equimolar (CH3COO)2Ba and (NH4)2SO4 were homogeneously mixed to obtain a reactive activator abbreviated as RA and then added to barium sulfate (BaSO4) powder obtaining BaSO4–xwt%RA (x = 5, 7.5, 10, 12.5, and 15). Dense (>96 % theoretical) BaSO4 ceramics were successfully fabricated via RCS of BaSO4–xwt%RA at 200℃ with a constantly applied pressure of 250 MPa. The Woolfrey-Bannister method provided quantitative insights into the activation energy, indicating that RA effectively reduced the energy required for densification. The Vickers hardness (1.76 GPa) and coefficient of thermal expansion (CTE, 18.8 ppm/°C) of the RCSed BaSO4 ceramics were comparable to the high-temperature (850 °C) sintered counterparts. Moreover, finite element analyses confirmed the high CTE value of the RCSed BaSO4 ceramics holds great promise for high-reliability chip packaging applications.