Thermal Performance Enhancement for CSP Packages

Attaching heat spreader into the IC package is a known and common solution for devices with specific thermal requirement. This is usually seen on medium to big size packages such as PBGA where space is not a constraint. However, for chip-scale package (CSP) where the chip is occupying most of the area of the package, placing a heat spreader is evidently the biggest challenge. There are few packaging solutions explored to boost package thermal capability without compromising the package size but the accompanied challenges and barriers seem inevitable; difficulty in manufacturing, quality issues, reliability failures and high assembly cost. For a chip scale FBGA package that is built in a matrix or panel type mold layout, attaching heat spreader to the package transpires as the top most challenge. Placement accuracy for the individual unit and preventing mold bleed on heat-spreader surface during molding are equally challenging. There are few established ways to address those assembly issues but mostly require additional non-standard process steps, jigs, fixtures and new machines, which is obviously not favorable for manufacturing. Unit cost can be high as well. UTAC developed a simple yet effective method that can embed a heat-spreader into a CSP FBGA package without compromising the package size, no additional assembly process steps, low quality and reliability risk and best of all, low cost. The unique package structure and the way it is built were developed in consideration of all the known challenges and barriers. The new FBGA package with embedded heat-spreader, labeled XP-FBGA (eXtra Performance FBGA), can improve junction-to-ambient temperature (Theta ja) by 30% at 3mm/sec air speed for a 2W device in a 15x15 body size. Further in this paper discusses the unique solutions to overcome challenges in embedding heat-spreader for CSP package and the thermal simulation studies demonstrating the performance of different package structures. The effect of each IC packa- ge component in thermal capacity of the package was also studied and will be discussed further in this paper.