Study of Interface Reliability of PCB-UF Interface in FCBGAs under Sustained High Temperature Operation in Automotive Underhood Environments

Abstract

Electronics are increasingly being employed in automobile applications for safety-critical tasks to allow sophisticated driver-assist systems (ADAS). Lane departure warning systems, collision avoidance systems, driver alertness monitoring, park and drive assist systems, adaptive cruise control, and semi-autonomous navigation are just a few examples. The majority of the electronics are placed under the hood, where they may be exposed to temperatures in the range of 100-200°C for up to 10-years over the vehicle's lifetime. FCBGAs (Flip-Chip Ball Grid Arrays) are being used to provide safety-critical tasks in automobile underhood electronics. Underfills needed to reinforce flip-chip interconnects in FCBGAs need to operate reliably under sustained high temperature operation. Under extreme temperature conditions, the underfill-to-substrate interface is one of the most common failure sites, and it is generally a prelude to flip-chip junction failure. Understanding the damage development of the underfill-to-substrate interface as a function of running duration and operating temperature is required to assess the dependability in the end application. In this study, the Substrate-UF interface was exposed to high temperature and the interfacial fracture toughness quantified. A three-point and four-point composite beam specimen of Substrate/Underfill was fabricated to study the interface and thermally aged for periods of 10 days, 30 days, 60 days, 120 days, 360 days at temperatures ranging from 100°C to 150°C. Quasi-static bending was used to observe and determine interfacial delamination of the sample specimen. A 2D-Digital Image Correlation (DIC) method was also employed to understand the Crack tip opening displacement (CTOD), crack initiation and the fracture toughness, CTOD were compared with the aging schedule and temperature. The CZM parameter developed from the image correlation and critical load is used to make a damage model in Abaqus to rank the underfills and to validate the experimental procedure. The model is also predict the failure rather than conduct the expensive experimental to get the performance characteristics of the underfills