[SOLVED] Thermal Relief, To Use or Not on 15A High Temperature PCB

[ling4ever]

I am designing a 1.6mm thick 6-layer pcb to be used continous at high temperature (+125C) and will have one 15-Ampere supply (3.3V). This 15A will be distributed to the whole board with a two layer 1 oz copper plane (L3 and L4). However, the weakest link between the outside supply and the copper plane is thru-hole fuse connection. Do I really need to have spoke connection on the fuse leads? Four 25-mil spoke will not be enough to carry 15A.

I am thinking of providing copper connection on three layers from the pcb terminal (interface between the outside ower supply and the PCB) to one pin of the fuse. Namely, top, L3 and L4 will have a copper shape of about 1000 mils by 500 mils connecting the terminal to the fuse.

The three layer connection will provide about 300 mil spoke? Is this enough? Or is it better if I will not use spoke and will directly connect the thru-hole fuse pin to the shape?

Please also consider that my ambient temperature will be +125C during the board operation.

I included a snapshot of the top layer layout of the connection from the pcb terminal to one of the fuse pin.

 

[marce]

https://www.saturnpcb.com/pcb_toolkit.htm
have a look at current capacity and fusing currents. Done 16A with PTH relays with spokes, no problem.
What I would question is the 125 degC, presume you are using a high temp laminate as FR4 will struggle, also component sourcing will be fun, even mil designs rarely run that hot.

 

[DeLorean]

I don't use thermal relief on my two layer 2 oz. copper traces and can easily hand solder wires to a through hole. Maybe a short trace to the power plane would be better for you. Board house builds have no problems without thermal relief on power planes, it's just any rework that is hard to hand solder.

 

[ling4ever]

Hi Marce,

Thanks! I used saturn toolkit, considering my allowed design parameters, the total combined current of the spokes is only 12.8A.

Hi DeLorean,

Thanks! I will now consider full-contact connection of the fuse pin to the plane considering the initial soldering will not be a problem. My group here already deviced a method to take care of possible rework, it's not really a conrern for our case.