Comparison of microvia HDI PCBs with ACF interconnections in accelerated life testing

New packaging technologies require high density substrates. In built up high density interconnect (HDI) printed circuit boards (PCB) high density is achieved by using microvias. Such HDI PCBs may be used in many applications. In flip chip technology, a bare chip is attached directly to a substrate which enables very high density. Anisotropic conductive adhesive films (ACF) are often used as interconnection materials in high density flip chip applications, since they enable very high density. In this study, the reliability of flip chip ACF attachments on four different HDI PCBs was studied. The PCBs had similar core layers, but the microvia layers of the PCBs were different. Test chips were attached on these PCBs using an ACF. The reliability of the interconnections was tested using two fast thermal cycling tests and a constant humidity test. Several failures were seen with all PCB materials during the tests. However, no significant differences in the reliability of the different microvia layers was seen. Consequently, the composition of the microvia layer was not found to be critical to the reliability of the ACF interconnections.