Effect of Underfill Additive Agents on Crack Prevention in Large Fan-Out Multichip Module Packages

This study aimed to explore the effect of additive agents on the application of underfills in large fan-out multichip module (FOMCM) packages. The experimental results of a high-temperature storage test (HTSL) demonstrated that the commonly used in assembly industrial underfill developed cracks. These cracks resulted from the generation of an oxidation layer in the underfill under high temperatures. The addition of an antioxidation agent to the underfill prevented the formation of an oxidation layer and also prevented underfill cracking resulting from thermal oxidation. When an underfill without a flexibilizer was used in a large FOMCM package and subjected to a temperature cycling test, cracks were observed in fixed areas at the chip corner, which formed because of the excessive stress in the package. The addition of both an antioxidation agent and a flexibilizer to the underfill prevented the generation of thermal-oxidation-induced and stress-induced cracks in the package.