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BrianG · 08:37 PM

The FETs used in most ESCs I've seen are just a huge array of surface mounted devices (no mounting "tab"). Therefore, they mostly use the PCB traces as a heatsink. Since there are so many FETs, the PCB is nowhere near big enough.

Schulz apparently attaches heatsinks to the sides of the PCB where the traces end.

Other designs seem to have multiple FET PCBs stacked on top of each other with the heatsink on the top layer. Each layer has the PCB above it laying on top of the FETs so the heat transfers to the layer above it (that sounded confusing even to me). BKs and Quark seem to do this. They have to make sure that each PCB firmly touches the FET below it or the heat won't be conducted as effectively.

[Edit]: Personally, each design leaves room for error and some FETs aren't cooled enough. I would like to see a slab of Aluminum between each layer of FETs, maybe machined so there are little raised squares where the actual FET is to prevent shorts. Each slab is then attached to a heatsink on the sides. Each layer gets cooled more or less equally that way. Although, it would be substantially larger, weigh considerably more, and be more expensive...

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BrianG RC-Monster Admin Offline Posts: 14,609 Join Date: Nov 2005 Location: Des Moines, IA	07.29.2006, 08:32 PM The FETs used in most ESCs I've seen are just a huge array of surface mounted devices (no mounting "tab"). Therefore, they mostly use the PCB traces as a heatsink. Since there are so many FETs, the PCB is nowhere near big enough. Schulz apparently attaches heatsinks to the sides of the PCB where the traces end. Other designs seem to have multiple FET PCBs stacked on top of each other with the heatsink on the top layer. Each layer has the PCB above it laying on top of the FETs so the heat transfers to the layer above it (that sounded confusing even to me). BKs and Quark seem to do this. They have to make sure that each PCB firmly touches the FET below it or the heat won't be conducted as effectively. [Edit]: Personally, each design leaves room for error and some FETs aren't cooled enough. I would like to see a slab of Aluminum between each layer of FETs, maybe machined so there are little raised squares where the actual FET is to prevent shorts. Each slab is then attached to a heatsink on the sides. Each layer gets cooled more or less equally that way. Although, it would be substantially larger, weigh considerably more, and be more expensive... Last edited by BrianG; 07.29.2006 at 08:37 PM.