Aging of the Molding Compound Identification using Piezoresistive Silicon Based Stress Sensor

Abstract

Safety relevant electronics have applications in automotive field such as automated driving and electrification. The current distribution of the Electronic Control Units (ECU) will change to a centralized solution, such as Vehicle Control Units (VCU), comprising most of the car functions. Aging due to the thermal effects on molding compounds can play an important role in reliability predictions. During operation lifetime of the electronic package, the molding compound subjected to the thermal cycling and active loads can lead to changes in the mechanical material properties. These changes will make the current structural models inaccurate in evaluating reliability and durability. In this study, the oxidation effect captured by 120 piezoresistive stress sensitive cells packaged in a QFN automotive standard package is studied. The high temperature storage experiment consists of 2000h of $150^{\circ}\mathrm{C}$ of constant temperature. Considerable change during the experiment in mechanical stress are observed. Warpage measurements and cross-sections of the aged package are performed to explain the change in the stress. Cross-sections of QFN package are performed each 500h to determine the oxidation layer. Also, Finite Element Method is used to predict the mechanical stresses due to the mechanical properties changes of the oxidation layer.