Development of solder replacement flip chip using anisotropic conductive adhesives

With the continual drive towards package miniaturization, flip chip assembly using anisotropic conductive adhesives (ACAs) is fast emerging as one of the potential interconnect technology solutions in the fine pitch application space. In this paper, we report the process development of solder replacement flip chip at 120/240μm bump pitch using ACAs for mid I/O applications. Optimized ACA cure profiles were derived based on die shear test results. The cure time for anisotropic conductive paste (ACP) was found to be 2× longer than anisotropic conductive film (ACF) to achieve the same die shear strength for a given curing condition. Prolonged curing at 220°C was found to enhance the die shear strength. Consistent resistance reading was used as a criterion for ACA bond force selection. Generally, uncoined Au bumps was found to have lower and more stable resistance due to contact between the Au bump and substrate pad. As compared to unfilled ACF, silica filled ACP exhibited better contact resistance stability during temperature cycling (TC) and temperature humidity (TH) tests.