A circuit board response was used to characterize five chassis that were manufactured by five different suppliers to two form factors: slim and mid-tower designs. The board responses were compared to that in a reference test chassis. All the chassis were shocked to the same input. The board response was characterized by strain gauges mounted on the PCB around critical BGA components. The board strains measurements were able to detect the manufacturing variability of the chassis fabricated and was used to identify the second level interconnection (SLI) risk for BGA placement at the measured location. This paper presents an empirically driven methodology comparing supply line chassis variation and their direct affect on BGA SLI reliability and the need to revise the procurement specification to ensure repeatable and predictable BGA or any critical SLI performance.
Numerical experiments based on the three-dimensional (3-D) nonlinear finite element method (FEM) has been conducted to understand goveming damage mechanisms during the die attachment for the ball grid array (BGA) packages. The parametric studies for various designs of the BGA package and material properties have been performed. A wide range of the modulus (IMVPa30GPa) and the coefficient of thennal expansion (CTE) (lOppm -300ppm) were evaluated to see feasibility of a new class of material set in the die attach adhesive. Effects of thenmo-mechanical properties, particularly glass transition temperature (Tg) of selected die attach adhesives on the damage and warpage of the die and substrate of BGA are analyzed. The warpage of substrate and Si die cracking due to the material properties of the die attach adhesive are demonstrated. Classification of modes of deformation in the BGA package with material sets will shed light on novel material development for better reliability. In addition, the optimum thermo-mechanical properties of die attachment materials and molding compounds will be selected based on the parametric studies.1-4244-01
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