Transient Thermal Characterization of Junction to Case Thermal Resistance for 2.5D Packages

Package-level thermal characterization suffers from the difficulty such as accurate determination of the junction to case thermal resistance. In the present work, thermal characterization of the 2.5D packages was conducted, with emphasis on the junction to case thermal resistance. For purpose of accurate determination of thermal metrics, the commercially off-the-shelf thermal test chip was assembled, which has been built in with resistors and thermal diodes to act as heaters and sensors. The package were fabricated in either bare-die or molded format. The thermal test chip was assembled on the interposer wafer through microbump and underfill processes. The transient dual interface (TDI) method was utilized to determine Theta JA under natural convection condition and Theta JC with a heat sink. The obtained Theta JC for both bare-die and molded packages are compared with the steady-state measurements based on the cold plate method in previous work. The obtained Theta JC data by the TDI method, without counting in the cold plate thermal resistance, were lower than the cold plate method. Advantages and disadvantages of the TDI method are also discussed.