Package thermal challenges due to changing mobile system form factors

Mobile platforms have driven semiconductor package form factors from several times the die area to sizes approaching die size. To make matters even more challenging, the package thickness, traditionally on the order of 1-3 mm, has been reduced to thicknesses less than 0.40 mm. In mobile applications, it is size that drives package design. There has been a price paid for the package shrinkage in terms of its thermal performance. Copper, previously used for power and ground planes, and multiple layers of traces, has been replaced with extremely fine traces built in fewer layers. The body size previously used to promote the spreading of heat from the die is now left with two options for heat flow: either out the top (immediately above the die) or through the bottom (below the die) of the package. Improvements to the chip architecture in terms of power efficiency is one of the few remaining options for thermal enhancement at the package-level. Further thermal enhancement should focus on the system level, as this is where the greatest opportunities exist. While many papers have focused on the thermal challenges associated with the system-level, few have translated these constraints to challenges at the package level. This study investigates the historical evolution of mobile platforms and their impact on packaging thermal challenges. Metrics for evaluating the optimization of packages for the mobile space will also be discussed.