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Chassis cooling of thermal pad on stepper driver ground plane

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maker8122

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A stepper driver (TMC5130) is mounted on a 4 layer PCB with thermal vias under the part.

The bottom layer is a GND plane.

The PCB is mounted on a machined aluminium block that carries various mechanical parts and effectively forms a part of the chassis.

I'd like to machine the aluminium block so that a short column contacts the underside of the thermal pad, thereby effectively drawing away the heat. Am considering machining the column so that it is 0.1mm taller than the PCB standoffs and then relying upon the elasticity of the PCB to assure contact.

Are there best practices to observe for such a setup?

And what about the electrical perspective? Am concerned about making unplanned electrical contact between the ground plane and the chassis where the aluminium block touches the thermal vias (GND plane).

Any suggestions most welcome.

thermal_contact.png
 

barry

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What do you mean by 'unplanned electrical contact'? If the metal of your chassis touches grounded vias, you've got PLANNED electrical contact. Anyway, counting on the 'elasticity of the PCB to assure contact' is a really, really, really bad idea. About the only thing you can assure is failure. You may want to consider adding some fasteners, e.g., screws, to assure contact. Maybe add a silicone thermal pad.
 

maker8122

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What do you mean by 'unplanned electrical contact'? If the metal of your chassis touches grounded vias, you've got PLANNED electrical contact. Anyway, counting on the 'elasticity of the PCB to assure contact' is a really, really, really bad idea. About the only thing you can assure is failure. You may want to consider adding some fasteners, e.g., screws, to assure contact. Maybe add a silicone thermal pad.

Silicone thermal pad. Yes that's it! Thanks a lot, hadn't heard of those and was wondering what could be used.

You're right, could find a way to include a bo such that there are screws on both sides of the driver chip. Until now hadn't wanted to lose any (radiating) copper pour to screw holes but once there's direct contact with the chassis that won't matter.

Thanks again.
 

KlausST

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Hi,

There are some other thermal conductive pads. Some are with silicone some without. Some are ceramics filled some not.

There are thermal glues. (also with and without silicone).
You may use mould release agent or cling film to avoid that both sides stick together.

Klaus
 
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