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Electronics => Projects, Designs, and Technical Stuff => Topic started by: Gothenlor on October 14, 2021, 06:46:43 pm

Title: PowerSSO-36 heatsink fastening
Post by: Gothenlor on October 14, 2021, 06:46:43 pm

Hi,

I'm designing a pcb for a TDA7498MV, which is a PowerSSO-36 package with exposed pad up.
Most of the designs I see are with glued heatsink or this kind of sketchy heatsink + fan https://ae01.alicdn.com/kf/HTB1EfqStMmTBuNjy1Xbq6yMrVXae/1-PCS-Computer-PC-Cooler-Northbridge-Chipset-Aluminium-Cooler-Heatsink-40mm-Fan-For-3D-Printer-Cooling.jpg
Some designs uses screws to fasten the heatsink, like the Sure boards https://trevormarshall.com/class-d-tutorial/

My design is made to be portable, so I suppose the most reliable approach is to fasten the heatsink with screws.
Now what is the best method to do it ? Is there special types of spacers to put between the pcb and the heatsink for this type of IC package ?
How to be sure the heatsink contact with the IC is even ?

Another constraint is to drill and thread the heatsink for the screws.

Any insight is welcome.

Thanks

Title: Re: PowerSSO-36 heatsink fastening
Post by: thm_w on October 14, 2021, 10:02:31 pm

Is the case going to be plastic or aluminum? Could be possible to heatsink to the case.
Have you calculated the dissipation?

LCSC has a few with two holes: https://lcsc.com/products/Heat-Sinks_441.html
Then you'd have to either use screw + nut to secure it, or soldered in PCB nuts. Even contact would occur if the screws are alternately tightened until some reasonable torque is reached.

If its low dissipation I would consider the thermal epoxy, and maybe a silicone fill around that if you are worried about coming loose. I have some boards where they used glue/epoxy and its impossible for me to remove the heatsink by hand.

Title: Re: PowerSSO-36 heatsink fastening
Post by: Gothenlor on October 15, 2021, 07:22:01 am

Thanks,

Dissipated power at full power is 10W, so not much. I will use a metal case and I thought of using it as a heatsink. But it would imply that the IC would be on the bottom of the board, and other bigger (taller) elements (like filtering selfs) on top of the board. Is this a good idea for a class D design ?

Thermal epoxy sounds like an option, I didn't know it was so strong, I'll give it a try.

Title: Re: PowerSSO-36 heatsink fastening
Post by: thm_w on October 15, 2021, 10:28:19 pm

It might make layout a little harder, but if its done right should be fine.

This is how my alientek amplifier looks.