SMTA International Conference Proceedings


FLIP CHIP UNDERFILL: VOID DETECTION AND CORRECTION

Author: Kris Slesinger et al.
Company: Solectron Technology
Date Published: 9/22/2002   Conference: SMTA International


Abstract: Bumped silicon die mounted to epoxy-glass carriers generally require underfill to enhance interconnect reliability, increasing mechanical robustness and solder joint fatigue resistance.i Air pockets known as "voids" can significantly reduce underfill effectiveness, especially if adjacent to a solder joint. This paper describes a voiding problem that was detected during routine monitoring of an established flip chip product in a contractmanufacturing environment.

The engineering team designed a series of experiments to identify the failure mechanism. Test hardware was then assembled and subjected to a variety of standard and novel analysis methods to determine the root cause of voiding. The results indicated that the customer requirement for printed circuit board (PCB) pre-bake was insufficient - apparently due to modifications to the board fabrication process. Corrective actions with the customer and board suppliers were then implemented to restore production quality to expected levels.

Acoustic microscopes can be used for non-destructive void detection (Figure 2), however most equipment cannot keep pace with a high-volume assembly line. So it’s critical to fully develop the dispense process and characterize each particular product before volume production begins. Then acoustic scanning and/or other inspection methods can be used for offline periodic monitoring.



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