Reliability evaluation of CIF (chip-in-flex) and COF (chip-on-flex) packages

Abstract

CIF (chip-in-flex) and COF (chip-on-flex) packages have the advantages of fine pitch capability, and flexibility. Anisotropic conductive films (ACFs) are used for the interconnection between chip and substrate. Display, mobile device, and semiconductor industry require for smaller and more integrated packages. Both CIF and COF packages are an alternative for the demands. However, there are some reliability problems of interconnection between the chip and substrate because the packages are subjected to various loading conditions. These may degrade the functionality of the packages. Therefore, reliability assessment of both packages is necessary. In this study, experimental tests were performed to evaluate the reliability of interconnection between the chip and substrate of CIF and COF packages. Thermal cycling tests were performed to evaluate the resistance against thermal fatigue. The shape and warpage of the chip of CIF and COF packages were observed using optical methods (e.g., shadow Moiré and Twyman/Green interferometry). These optical Moiré techniques are widely used for measuring small deformations in microelectronic packages. The stress distribution around the chip was evaluated through FEA (finite element analysis). In addition, we suggested modifying design parameter of CIF packages for the reliability enhancement. © 2010 SPIE.