Thermal Simulation Reduces Cost of Stacked Module Potting Compound 50%

C-MAC, an electronics design and manufacturing company based in SouthDenes, Great Yarmouth, United Kingdom, recently developed a stacked module for a critical defense application. Prior to building prototypes, C-MAC engineers performed thermal simulation on the initial concept design and discovered that junction temperatures on the module ranged up to 125oC, well above the 100oC maximum. They realized they needed a potting compound to reduce thermal resistance and wanted to select the least expensive formulation that would meet the thermal requirements of the application.

“Without simulation we would have been faced with two unattractive alternatives,” said C-MAC senior engineer Jonathan Crossley. “We could have undertaken a much lengthier and more expensive physical testing process to identify the potting compound that provided the best mix of performance and price. Or we could have foregone this process and used the best potting compound because we were fairly confident that it would have delivered acceptable thermal performance.”

Instead, Crossley performed thermal simulation on the initial design using Flotherm software. “We use Flotherm because it provides many built-in functions that reduce the time required to module complex stacked module designs,” Crossley said. “The most important of these is the Flopack web-based wizard, which quickly produces accurate models of integrated circuits and other components.”

Crossley used the Flomerics Flopack web-based wizard to generate models of each of the components. “Using the Flopack wizard all I had to do was enter basic design parameters such as the die size, die flag size and lead frame clearance. Flopack generated models of the components that were almost complete. I was able to create a thermal model for this stacked module with Flopack in a tenth of the time that would have been required using conventional modeling methods.”

Compound type Simulated junction temperature
Standard 110oC
Enhanced 85oC
Best 75oC

Crossley ran thermal simulations of the stacked module with three different potting compounds which are referred to here as: standard, enhanced and best. “Simulation demonstrated that both the enhanced and best potting compounds brought the core temperature down to acceptable levels with ample safety margin on the die junction temperatures,” Hunt concluded. “So we were able to specify the enhanced potting compound at a cost of about half of the best potting compound. Thermal simulation helped us engineer an optimized solution while minimizing our engineering costs and leadtime.”