Design analysis and optimization of metal core BGAs for warpage

The increasing demands for electronic package miniaturization and better thermal management have prompted the design of thermally enhanced Ball Grid Arrays (BGAs). The ball grid array technology having the advantages of being lighter, denser, less expensive, simpler for structural design and easier to align for soldering, has been widely used in various industries. The metal core BGAs are gaining acceptance in the market for its excellent thermal conductivities. They have attractive features of better thermal performance with small footprint, which cannot be achieved with conventional BAG packages [1]. However, the coplanarity problem caused by assembling with the printed circuit board (PCB) has a significant impact on the system reliability of an electronic device, and is thus critical in package design and qualifications. The greatest concern in electronic package coplanarity is warpage, which is induced by thermal excursion during the manufacturing process. In a thin package, the coefficient of thermal expansion (CTE) mismatch between materials is primarily attributed to warpage and the plasticity of the metal core is the cause of increasing the package warpage. In this paper, firstly the accuracy of current simulation method is examined for the package warpage. Warpage of a seven layered metal core BGAs is modeled for elevated temperatures with modifying the effective material properties of epoxy molding compound (EMC) layer. Secondly, simulation based DOE analysis is performed to quantitatively study the effect of design and material impact on metal core package. Thirdly, optimal design and material optimization of the metal core BGAs is recommended based on the design of experiments (DOE) analysis for warpage improvement of package-on-package (PoP) bottom package, which is more critical for successful PoP stacking and SMT.