Abstract: Thermally enhanced plastic ball grid arrays are typically cavity down and wirebonded. The majority of heat is extracted through the back of the die, which is attached with a conductive adhesive to a metal heat sink. These packages are designed for heat dissipation on high power or high-speed chips. Typical I/O counts of these single or multi-tiered substrates exceed 300. Staggered wire bond pads with effective pitches down to 45 microns are becoming more common. The encapsulant and the encapsulation process must be optimized to eliminate voiding or “bridging” of the material over the wires. Nearly all of these packages employ a fine filler liquid encapsulant at this time. The materials have been optimized to flow through very fine spaces at atmospheric pressure. In addition various liquid dispensing nozzles, alternative dispense techniques have been developed to further increase production through put. Packages of this type have been in low volume production for over five years now. Liquid encapsulants, dispense processes and equipment have continued to improve as volumes of these packages have increased. As progress is made to increase functionality and speed of devices, the thermal problem becomes more pronounced and the use of these types of packages increases. High volume suppliers have gone from 1998 rates of about 300,000 devices per month to better than 1,000,000 per month in 1999. As semiconductor packagers increase production rates on these packages the alternative of transfer molding these devices becomes more viable. This paper addresses the advantages and disadvantages of both processes as a function of both total package cost and package reliability.
Key words: Thermally enhanced ball grid arrays, transfer molding, cavity filled packages, liquid encapsulation