Reliability of ACA interconnections on microvia HDI PCBs in thermal cycling conditions

New packaging technologies require new high density substrates. In built up high density interconnect (HDI) printed circuit boards (PCB) high density is achieved by using built up microvia layers. 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 and requires often also HDI PCBs. Anisotropic conductive adhesives (ACA) are especially well suited interconnection materials for high density flip chip applications. In this study the reliability of flip chip ACA attachments on several 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 ACA film (ACF). The reliability of the interconnections was tested using fast thermal cycling between the temperatures of -40?C and 125?C. Several failures were seen with all PCB materials during the 2,000 cycles of testing. The differences in the reliability of the different microvia layers were found to be relatively small and the microvia layer composition did not seem to be critical for the thermal cycling reliability of the ACF interconnections.