Development of flex stackable carriers

CSP's and /spl mu/BGA's are becoming more common in the market place and present new challenges for stacking of devices. An investigation into possible methods of stacking these devices was undertaken. New materials such as z-axis epoxies and combination flux/underfill epoxies were considered as well as the possibilities of adhesiveless copper on flex for fine line etching. This paper describes the basic approach and the results of combining the new technologies into a versatile and novel stacking approach.