Thermomechanical analysis and reliability performance of a semiconductor package using a single gauge leadframe design

The use of copper-based dual gauge leadframe design is proven effective in the thermal, electrical, and reliability of power devices housed in a Surface Mount Devices (SMD) packages. DPAK and D2PAK packages take preference on the use of this dual gauge leadframe design, a thick leadframe diepad or heatsink thickness up to twice as thick as their leads thickness. Reducing the copper heatsink thickness to form a single gauge leadframe, a thinner version of the dual gauge leadframe, was perceived to present various electrical, thermal and reliability failure mode and mechanisms, specifically die cracking. This study presents an in-depth simulation and analysis to determine whether the thinner heatsink leadframe version is capable of achieving the defined customer product requirements on their electrical, thermal and reliability performances in a DPAK package. The drive towards cost reductions has led these authors to evaluate the use of a single gauge or thinner heatsink leadframes in DPAK - a reduction of at most 40% on the leadframe costs. Using the single gauge leadframe design will have a tremendous cost reductions implication in the production of the DPAK package. A parametric 2-Dimensional Finite Element Model (2D FEM) with axisymmetric elements representing the DPAK package was developed using the commercially available MARC code, targeted at the failure mode of die crack. The major thermal loading conditions during manufacture and testing were analyzed, such as `diesoldering´, `moulding´ and `temperature cycling testing´ where increase and decrease in temperatures are experienced. Result on the FEM simulations was a determinant factor in the selection of the new leadframe diepad thickness. Results revealed that the safest leadframe thickness range is within 0.5 - 1.0mm. The original diepad thickness falls within the safe range. Selecting the 0.5mm as the new diepad thickness for the single gauge leadframe design was as straightforward as referring from the leads thickness of the original dual gauge design. Assembly, ambient electrical, and reliability testing were carried out for the carrier devices (non-auto and automotive types) in DPAK production line. Zero-hour electrical and reliability test results revealed that products satisfied all test specification requirements for both automotive and non-automotive devices.