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Abstract: As the interconnect density of semiconductors packaging increases rapidly with the use of ball grid array (BGA) and chip-scale packages (CSP), the standard electrical routing methods and design rules for printed wiring boards (PWB) are being challenged. The use of High Density Interconnect (HDI) or microvias fabricated by non-mechanical means (i.e., laser, plasma or photo definition) is an alternative to through-hole drilled vias to meet the routing requirements [1,2]. Also, the technique of via in pad, whereby the via pad is also used as the BGA attachment pad, can be employed to further increase BGA routing density associated with both micro and through-hole vias. This paper will outline a study using laser fabricated microvias and through-hole drilled vias in BGA solder pads to evaluate the assembly and design ramifications as well as the resulting reliability of both the vias and the BGA solder joints. Daisy-chain BGA packages were assembled onto boards containing 0.075 and 0.200 mm diameter microvias and 0.250 mm through-hole vias in pad. The test board was designed so that the reliability of the vias with and without the influence of the BGA as well as the reliability of the BGA solder joints could be evaluated independently. The boards were subjected to Accelerated Thermal Cycling (ATC) in both 0 to 100°C and -40 to 125°C while being continuously monitored for failure. Additionally, cycling was performed in -55 to 125°C liquid-to-liquid thermal shock. Details of the assembly ramifications of these configurations, the results of the reliability testing and failure analysis will all be included in the paper.
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