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Bama Slamma 21st November 2006 02:44 AM

transistor mounting
 
Are there any advantages to drilling and tapping threads in heatsinks versus drilling untapped holes and using nuts & bolts to mount transistors? I want to make sure there is a minimum of thermal resistance between transistor and heatsink.

ROVSING 21st November 2006 04:48 AM

It doesn,t matter how you make it - in most cases the transistors have to be electrically isolated from the heatzink anyway...

DCPreamp 22nd November 2006 08:12 PM

The choice of drilling/tapping vs. drilling/bolting depends on the heatsink and fins. The biggest problem is the distortion of the heatsink's mounting surface. When drilled, the aluminum tends to warp forming a subtle "bump" around the drilled hole. Pay close attention to this as it can limit the effectiveness of heat transfer.

So, depending on the project and heatsink, you have several options including using a "bar" to clamp plastic devices to the heatsink. With TO-3's, you're limited to direct mounting.

Also remember, when mounting devices, more force is not better. Always follow the data-sheets for the proper mounting torque, otherwise you can warp the device, or cause damage, or cause part of the device to lift greatly limiting thermal contact.

There's lots of good information on the Internet and on this forum.

anatech 22nd November 2006 08:52 PM

Hi DCPreamp,
Quote:

Also remember, when mounting devices, more force is not better. Always follow the data-sheets for the proper mounting torque, otherwise you can warp the device, or cause damage, or cause part of the device to lift greatly limiting thermal contact.
Oh yeah!
Thank you for posting that.

On drilling, take your time and use pilot holes. I don't have problems if I work slow and methodically.

Old Motorola app notes on transistor mounting are an excellent read. Very worthwhile.

-Chris

Chartal 22nd November 2006 09:10 PM

There is a good article on Esp site about Heatsink design.

The Design of Heatsinks


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