Various Levels of Drop Analysis for BGA in Mobile Phones

To final product quality of mobile phones, key reliability requirements are drop, bend and thermal cycling. Especially in terms of IC-device, drop reliability is the most significant of the three, and also difficult to optimize since it is a dynamic phenomenon in high speed and drop reliability is influenced by 1) system-level factors, 2) board-level and 3) micro-level. In this paper, system-level is defined as phone-level drop, specifically simplified mono-block phone including multiple devices on PWB. System-level enables to evaluate various factors, drop height, drop directions, materials to drop on, phone weight and phone mechanics. Board-level indicates IC-package, PWB and solder joints connecting in between. The board-assembled PWB is fixed onto fixture at 2∼6 points. Drop direction is flat drop only. This paper defines micro level as more detailed model than board level. PWB is modeled as composite structure consisting of dielectric materials with orthotropic properties, copper layers and micro via. IC-package is modeled as well. System level drop shows significant differences in drop directions and also the interactions between drop direction and component location. Micro level simulation results are well-correlative with experimental in failure mode. This paper will discuss overview of 3 levels of drop modeling and will focus on micro level and system level analysis in conjunction with board level.