Backside Die-Edge and Underfill Fillet Cracks Induced by Additional Tensile Stress from Increasing Die-to-Package Ratio in Bare-Die FCBGA

Changes in die-to-package ratios could introduce some additional harmful tensile stress. If material sets to build the packages are identical, and with only slight tweaks in dimensions of the package; the common assessment is larger die size or larger package size could yield worse reliability results. This school of thought could lead to wrongly qualifying by similarity or extension. This study demonstrates that the die-to-package ratio should not be neglected. And as a result, it will reshape the practice of qualification by similarities.

I. Introduction

The well-known backside die-edge chip outs and underfill cracks are reported to be associated with tensile stress in many works [1]-[6]. In this work, how changes in die-to-package ratios could introduce some additional harmful tensile stress are demonstrated. Since the use of flip-chip Ball-Grid-Array (FCBGA) has increased largely because of the demands of performance in integrated circuits (ICs), studies of integrity and reliability of this type of package are needed. Furthermore, based on the results of this study, the thoughts of qualifications by similarities or extensions should be reviewed and be used carefully.