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A study of self- and mutual-heating in wafer level packaging systems

A detailed investigation of the self- and mutual-heating of today's wafer level packaging system has been characterized in terms of the ambient temperature, air flow, and presence of Cu planes in the board and an attached die. For self-heating measurements, interconnects in the board and die were individually powered. For mutual-heating measurements, the traces in the board were simultaneously powered, a trace and die were powered, or all traces and die were powered. Of these effects, mutual-heating at product-like conditions led to the largest temperature rise, while ambient temperature, fan on or off, and passive die led to less impact. The presence of Cu planes in the board led to large increases in thermal dissipation thus reducing temperature rise by about half for all scenarios. The results from this study were compared to a long-standing industry specification for a common condition, for which large margins were observed in the measured results. Therefore, an explicit thermal study of wafer-level packaging system can alleviate design constraints and improve thermal management.