Barry M. Miles

Moisture absorption and desorption predictions for plastic ball grid array packages

Plastic electronic packages are known to absorb moisture when exposed to humid ambient conditions during storage in tape and reel in the factory. Reliability becomes a concern when packages are exposed to a humid environment for a prolonged time and then processed through a reflow oven. Thermo-mechanical and moisture induced interfacial stresses generated between the die attach and die may lead to die delamination and package cracking. Current package level moisture evaluation methods are based on experimental weight gain measurements and visual inspection after reflow for cracking or delamination. This study presents a finite element analysis (FEA) simulation of the moisture weight gain or loss in plastic ball grid array (PBGA) packages as a function of time including the effects of package geometry and material selection. Experimental weight gain and bakeout data for a 68 I/O PBGA package are shown to closely match FEA model predictions. Diffusivity and solubility property data for common packaging materials are given as a function of temperature ranging from 23/spl deg/C to 150/spl deg/C. Solder pot dip tests performed at 230/spl deg/C indicate that popcorn failures result when the moisture concentration in the die attach region exceeds 0.0048 g/cm/sup 3/ for the specific package tested.

Reliability characterization of the SLICC package

SLICC (Slightly Larger than IC Carrier) is a chip-scale ball grid array (BGA) package currently under development at Motorola. The SLICC package consists of a solder-bumped integrated circuit (IC) which is flip-chip bonded to an interposer substrate-approximately 8 mils thick-and then underfilled with an encapsulant. Chip I/Os are routed to package I/Os through plated through holes (PTHs) in the interposer substrate. Package I/Os are composed of solder bumps (approx. 22.2 mils in diameter on a 32-mil pitch) attached to the bottom side of the interposer substrate. The most apparent benefit of the SLICC package is its utilization of the area efficiency associated with direct chip attach (DCA) technology, coupled with the assembly, test, and repair simplicity afforded by BGA-type packaging.