Reliability Evaluation for Flip-Chip Electronic Packages under High Temperature and Moisture Condition using Moiré

The use of anisotropically conductive Film (ACF) for the direct interconnection of flipped silicon chips to printed circuits (flip chip packaging) offers numerous advantages such as reduced thickness, improved environmental compatibility, lowered assembly process temperature, increased metallization options, cut downed cost, and decreased equipment needs. Its wide application to glass displays through chip on glass (COG) process has accelerated interest in using this technology on rigid/flexible substrates or even on paper substrates as novel ACFs are being developed. A primary factor of the ACF package failure is delamination between the chip and the adhesive at the edge of the chip. This delamination is mainly affected by the shear strain at the edge of the chip. Therefore, the shear strain of each specimen was measured using portable engineering Moire interferometry (PEMI) experiments. PEMI experiments cannot acquire many data points of the shear strain. Accordingly, a phase-shifting method was utilized to obtain many exact data values of the shear strain. In the study of moisture effect, the reliability performance of the adhesive flip chip in the moisture environment test conditions was investigated. The failure modes were found to be interfacial delamination and bump/pad opening which may eventually lead to total loss of electrical contact. Different geometric size specimens in the interconnections were discussed in the context of the significance of mismatch in coefficient of moisture expansion (CME) between adhesive and other components in the package, which induces a hygroscopic swelling stress. The effect of moisture diffusion in the package and the CME mismatch were also evaluated by using the Moire interferometry. In this study, it is concluded that hygroscopic swelling assisted by loss of adhesion strength upon moisture absorption is responsible for the moisture-induced failures in these adhesive flip chip interconnects. Therefore, fully moisture induced ACF specimen and dried specimen are performed for calculating the interfacial fracture toughness. From Moire results, we can also get the stress intensity factor K. Through the analysis of the deformations by thermal and moisture environment, a damage model for adhesive flip chip package is proposed.