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How to connect “ Daughter” PCBs to “Mother” PCB?

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Flyback

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Hello, We have a 40cm by 30cm PCB on which we need to place sixteen 13.5W Buck converters (All have vin=28vdc, vout=1v5, iout=9A). All Bucks operate in parallel and feed into the same load. All Bucks are comprised of only SMT components.

The problem is that the only heatsink we have for this is a cold plate which must be situated 5mm above this PCB, (separate from it, and above it). The problem is then how to heatsink the Buck SMPS power components to this PCB?

The other problem is that the 40cm by 30cm PCB has some microprocessors on the back of it, so therefore there is no space for thermal copper pouring on the back surface of the PCB. Therefore, we cannot have thermal vias going down from the SMT power components to bottom layer thermal copper, and obviously cannot have a heatsink on to the back PCB layer.

Therefore, we wish to put the Buck SMPS’s on their own little 4cm by 3cm PCBs, which will comprise filled thermal vias going down from the power components’s pads down to bottom layer thermal copper. This copper will then be covered in insulating sil-pad, and then an aluminium “tablet” heatsink will be attached to the back of this.

…..these little Buck PCBs will then be attached “upside down” onto the 40cm by 30cm PCB, and their heatsinks will be connected via gap-pad to the cold plate (which is above the PCB, as discussed).

Do you know of any surface mount “headers” or stand-offs which we could use to connect the little 4cm by 3cm PCBs to the main 40cm by 30cm PCB?
 

AnalogKid

Well-Known Member
Most Helpful Member
POLA and other non-isolated buck modules use 0.025" square post, 0.1" pitch pin headers, at about 2-3 amps per pin. Molex Mini-Fit and AMP MTA-156 parts are rated for 9 A per pin, but the min. pin length is pretty long for your density.

PEM makes press-fit and SMT standoffs and studs specifically designed for pc board use. 0.220" dia might be their smallest one, and it would handle way more than 9 A as a combo mounting standoff and output conductor. Same for a 4-40 stud.
http://www.pemnet.com/fastening-products/fasteners-for-mounting-into-printed-circuit-boards-2/

ak
 
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