SMTA China Conference Proceedings


Authors: Brad Perkins, Alan Lewis, China Team Member
Company: ASYMTEK
Date Published: 4/22/2007   Conference: SMTA China

Abstract: Mobile electronics are offering expanded capability with decreasing package sizes making Package on Package devices (PoP) commonplace in today’s consumer products. The stacking of multiple packages require underfill, corner bond, or edge bonding processes for mechanical reliability. There are added process challenges over standard CSP/BGA due to the simultaneous dispensing of multiple package layers. Design requirements for PoP underfill should account for a slight increase in the total area required for the leading edge fillet due to the increased package height but can be also successfully accomplished with boards not designed for underfill as well. This paper discusses how the automated equipment for the underfill process can compensate for component placement, manage thermal requirements, perform dispense height registration on stacked packages, and perform software enabled process control management features. It will also show how a robust PoP underfill process encapsulates the solder interconnects of both layers while compensating for differences in bump height and layout, material mass requirements, thermal differences, and differentials in flow out times. Data is shown on how to minimize the fillet footprint, promote flow to both interconnect layers, maximize material savings, and decrease dispense time. It is also shown how dispensing can be successfully accomplished after RF Shield placement. Optimized RF Shield design considerations for dispense requirements in the placement and size of the holes as the material flow patterns is discussed. The ability to partially mechanically bond the package through corner and edge bond is also a capable process requiring less thermal management and process considerations than full underfill. Techniques for automating these processes are also discussed.

Keywords: PoP, Underfill, Jetting, BGA

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