This paper addresses implementation of a heating and cooling temperature ramp rate requirement and its impact on packaging processes. A complex multi-chip module packaging design includes a printed wiring board, solder attachment of a AlSiC-9 back plate, solder attachment of a multi-room seal frame, soldered surface mount components, power die soldered directly to a heat sink, epoxy attached chip-and-wire die, a welded lid and ribbon cable. Because of complex material interactions that exist in the design, concerns arose about cracking and other thermally induced damage that might occur during temperature excursions. The assembly challenge that resulted was a product requirement to limit the heating and cooling temperature ramp rates during packaging processes. Working together, the design agency and production agency ultimately came to an agreement on what the temperature ramp rate requirement should be and how to qualify the processes and the periodic determination of compliance. The requirement was implemented on all packaging processes that saw a heating and cooling cycle. Epoxy cure after die attach and wire bonding were modified most significantly and are specifically addressed in this paper. Solutions were implemented to minimize impact to assembly flowtime and to minimize the chance of processing errors. Temperature profiles had the ramp rates calculated then documented and qualified based on the process parameters (set point temperatures and dwell times) and the assembly machines, ovens, hot plates and tooling used. Compliance is proved through thermal profiling and calculation of ramp rate. Deviation from the set process will require approval from the design agency.

This paper addresses work to minimize voiding and die tilt in solder attachment of a large power die, measuring 9.0 mm × 6.5 mm × 0.1 mm (0.354″ × 0.256″ × 0.004″), to a heat spreader. As demands for larger high power die continue, minimizing voiding and die tilt is of interest for improved die functionality, yield, manufacturability, and reliability. High-power die generate considerable heat, which is important to dissipate effectively through control of voiding under high thermal load areas of the die while maintaining a consistent bondline (minimizing die tilt). Voiding was measured using acoustic imaging and die tilt was measured using two different optical measurement systems. 80Au-20Sn solder reflow was achieved using a batch vacuum solder system with optimized fixturing. Minimizing die tilt proved to be the more difficult of the two product requirements to meet. Process development variables included tooling, weight and solder preform thickness.