Warpage Prediction of Fine Pitch BGA by Finite Element Analysis and Shadow Moiré Technique

摘要

Warpage is one of the major concerns in manufacturing BGA, CSP, POP or QFN based array packages because a reasonably flat package is critical to successful singulation and board level assembly processes. Warpage of a package is a result of curing shrinkage of encapsulated mold compounds (EMC) and CTE mismatch between various packaging materials. In a completed package, all components are bound together by the crosslinked polymers, i.e. EMC and dieattaching adhesive (D/A). No component can expand or shrink freely. In a typical array package, warpage is in the form of either a ‘crying' face (corners facing downward) or a ‘smiling' face (corners facing upward), depending on the correlations of the packaging materials' mechanical, physical and chemical properties. Fine pitch ball grid array (fpBGA) is a chip scale package offering a competitive solution for mobile applications. Package thickness ranges from 1.4mm down to 0.6mm with ball pitches as small as 0.4mm. Since the package is very thin, warpage control is a big challenge. In this study, an accurate finite element model, incorporated appropriate material properties was developed to predict the warpage of fpBGA under reflow condition. The experimental measurements of the warpage behavior of the fpBGA under solder-reflow condition were conducted using an Akrometrix TherMoire PS200.The experimental results were compared with the results of FE analysis, which provides feedbacks for modeling optimization. Effects of material properties and geometric parameters on thermal warpage were then studied using the optimized models.