The most difficult hurdles in IC packaging stand at the intersection of greatest cost sensitivity, high volumes, smallest form factor, and increasing package density and power dissipation. Cost sensitivity severely constrains the packaging choices available. High volumes are found in consumer products like mobile phones and mobile PCs. And, rapid change in consumer tastes for features has shrunk design time.
Rapidly decreasing prices in small, lightweight mobile system sizes, increasing functionality, and any increase in power dissipation intensify those design challenges. Yet higher-frequency mobile processors in notebook PCs dissipate more than 30 W. Mobile-phone unit volumes for voice and messaging communications are estimated at 450 million units worldwide for 2003, and in computing, mobile PCs are growing more rapidly than desktop systems.
Linda Matthews of TechSearch Inter-national recently illustrated trends in mobile applications at the IMAPS Advanced Technology Workshop on Thermal Management for Computing and Wireless Applications. Demand for small form-factor packages in cost-sensitive mobile applications is large, with as many as eight chip-scale packages (CSPs) in certain handsets. Unfortunately, the increasing importance of thermal issues in these applications isn't easily resolved with the weight, space, or cost flexibility implied by the addition of any metal mass acting as a heatsink.
Four-layer boards don't offer significant mass for heat dissipation. Moves to the Amkor MicroLead Frame (MLF) and other packages with an exposed pad for heat dissipation represent potential solutions. Stacked-die CSPs are another option for handset applications described by TechSearch, foretelling an increase in the use of SRAM and flash memory and logic die within stacked-die CSPs.
The importance of thermal management in lightweight mobile systems requires greater attention to the analysis of each element that contributes to thermal resistance. Low-density, high thermal-conductivity materials with good coefficient-of-thermal-expansion (CTE) compatibility and low relative cost are needed. The right materials, package types, and accurate thermal and EMI modeling and testing are critical.