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Thermal Characterization of Copper Contact Interconnect for DRAM Package Stacking
Keywords: ìBGA®, ìPILR™, Reliability
With the transition to DDR2 and DDR3, the trend for increased memory density is driving the DRAM industry to provide devices that have faster data rates, lower voltage and improved thermal solutions. The demand for high density in small form factors has driven the industry to adopt various stacking solutions. Current packaging solutions use microBGA® as the package to substrate and package to package interconnect. Tessera’s recently introduced microPILR™ interconnect technology platform uses copper contacts to replace the traditional CSP (Chip Scale Package) solder balls. These copper contacts are fabricated as part of the package substrate with standard photolithography and etching technology. For package stacking, the microPILR interconnect benefits include: unprecedented finer pitch, lower profile, improved electrical and thermal performance and higher reliability. In addition to DRAM, the microPILR platform also provides significant benefits in package stacking applications such as NAND flash stacking and PoP (Package-on-Package) Logic + Memory. This presentation will review two interconnect technologies, ìBGA and ìPILR. The discussion begins with a review of how CFD simulation is performed to quantify the thermal resistance associated with interconnect only. Due to the high thermal conductivity and low profile of the Cu post, microPILR increases the thermal conduction of the first level interconnect by more than ten fold, over solder balls. The thermal resistance of the microPILR layer decreases further at reduced pitch. The calculation of thermal resistance of single package and stacked packages is then discussed. microPILR demonstrates improved thermal performance over microBGA at both the package and stacked level. In conclusion, a system level study is conducted on air cooling of an array of dual in-line memory modules (DIMM) modules in high density servers. microPILR enables lower profiles for the module with stacked packages, which significantly improves the air cooling efficiency of the tightly placed modules.
Hongyu Ran, Senior Thermal Engineer
Tessera, Inc.
San Jose, CA

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