Custom Case Study
An onboard charger (OBC) customer developed a design with a custom power module from a competitor but was dissatisfied with the electrical and thermal performance of the LLC resonant converter’s output stage. Simulation results showed very high peak junction temperatures for some of the silicon die during operation.
Although the system had built-in mechanical features to improve thermal dissipation, these were not fully functional across the full dimensional area of the module. In particular, a cooling channel with coolant liquid only efficiently covered a small portion of the whole power module area.
Due to the late stage in the overall design, duplicating the existing pinout was a key requirement to avoid costly and time-consuming redesign costs for the custom aluminum heatsink and chassis of the OBC.
The overall objective was to reduce peak junction temperature without compromising the mechanical design and make the design function more efficiently.
Vishay’s EMIPAK 1B package option utilizes a pin matrix structure with the potential for 89 PressFit pin locations. These are available in a grid format with a fixed pitch of 3.2 mm in the x and y dimensions.
In the original design, the concentration of the die locations resulted in some specific hotspots where some of the die thermally affected each other inside the module. Integrating the latest Vishay FRED Pt® GEN 5 silicon technology provided superior electrical and thermal performance during operation. This ultrafast technology is optimized for LLC output stage applications and provides lower power losses, and therefore less heat to dissipate.
The integrated cooling channel was positioned in a fixed mechanical location. Due to the EMIPAK 1B pinout options, it was possible to spread out the silicon die over a larger area of the direct bond copper (DBC). This improved efficiency by removing, reducing, and specifically locating areas of heat concentration inside the module relative to the cooling channel location.
The mechanical flexibility of the EMIPAK 1B due to its customizable PressFit pins and internal layout enables the optimization of silicon die locations inside the module to maximize electrical and thermal performance. Utilizing the latest Vishay FRED Pt® GEN 5 Silicon technology ensures excellent thermal performance and reduced junction temperatures during operation.
Combining these technologies enabled our customer to avoid a costly redesign or the need to use larger and much more expensive silicon die in their OBC.
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