Reliability analysis and design for the fine-pitch flip chip BGA packaging

The geometry of solder joints in the flip chip technologies is primarily determined by the associated solder volume and die/substrate-side pad size. In this study, the effect of these parameters on the solder joint reliability of a fine-pitched flip chip ball grid array (FCBGA) package is extensively investigated through finite element (FE) modeling and experimental testing. To facilitate thermal cycling (TC) testing, a simplified FCBGA test vehicle with a very high pin counts (i.e., 2499 FC solder joints) is designed and fabricated. By the vehicle, three different structural designs of flip chip solder joints, each of which consists of a different combination of these design parameters, are involved in the investigation. Furthermore, the associated FE models are constructed based on the predicted geometry of solder joints using a force-balanced analytical approach. By way of the predicted solder joint geometry, a simple design rule is created for readily and qualitatively assessing the reliability performance of solder joints during the initial design stage. The validity of the FE modeling is extensively demonstrated through typical accelerated thermal cycling (ATC) testing. To facilitate the testing, a daisy chain circuit is designed, and fabricated in the package for electrical resistance measurement. Finally, based on the validated FE modeling, parametric design of solder joint reliability is performed associated with a variety of die-side pad sizes. The results show that both the die/substrate-side pad size and underfill do play a significant role in solder joint reliability. The derived results demonstrate the applicability and validity of the proposed simple design rule. It is more surprising to find that the effect of the contact angle in flip chip solder joint reliability is less significant as compared to that of the standoff height when the underfill is included in the package.

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