Reliability of embedded wafer level ball grid arrays in automotive applications

Abstract

A general trend in automotive electronics is the development of customized products with the focus on system integration, increased reliability, and lower costs. For Continental's transmission control units (TCUs), this means a minimum of available space with extended functionalities and high operating temperatures. As a result, small package solutions with a sufficient number of interconnects and excellent thermal, electrical, and mechanical performance and reliability are needed. The family of Wafer Level Packages (WLP) was developed to provide very small packages down to the outline of the chip size. The embedded Wafer-Level Ball Grid Array (eWLB) is a WLP with a fan out area beside the chip edge, which enables a greater number of external contacts. These packages were successfully introduced and widely established in consumer electronics and mobile applications. The high volume production has been globally established for years and makes the eWLB package an interesting candidate for future automotive applications with minimized space requirements. A key issue in automotive applications is the 2nd-level reliability due to high numbers of temperature cycling at higher temperature ranges. In this paper, the board level reliability for eWLB packages is investigated. This includes the influence of selected underfill materials on the solder joint fatigue of lead-free solder during high temperature storage (150 °C) and during temperature cycles between −40 °C and 150 °C. An integrated daisy chain chip allows electrical in-situ measurements for the detailed statistical failure analysis.