Electronics > Manufacturing & Assembly

Thin FR4 PCB's and high current

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OwenH:
Hi,

In the past I've only used 1.6mm thick PCB's but I now need more clearance in a tight enclosure.  I'm thinking of using a board that's 0.5mm thick FR4 but I've never worked with anything this thin in the past.  This design will need to handle 12 amps so there will be wide 2oz copper and 4 layers. The board will be taped with a thermal adhesive tape to an aluminium enclosure so I don't think the rigidity of the board should be an issue.  I don't see why high current with a thin pub should be any worse with a thin pcb? Maybe its even better? How flexible is a thin pcb and is this an issue for staying flat while reflowing?

Thanks,
Owen

mikeselectricstuff:
on 0.5mm, flatness/warping when reflowing may well be an issue. I'd stick to 0.8 if you can, if only because it's more common so you have more choice of suppliers. 0.5mm with heavy copper is a bit of an oddball combination.
Something you should try to do is balance the amount of copper on each layer, as unbalanced copper can cause warping.
I had this really bad on a 2-layer 0.2mm thick board, not sure how bad it would be on 0.5m but balancing can't hurt.
I'd also avoid solid pours, and use a mesh pour instead -  tweaking the line width of the mesh is a useful way to balance the copper between layers.


OwenH:
Hopefully my copper is relatively well balanced since I'm maximising the planes for thermal disapation however I will have another look.  Do you think that because this board will be only 25mm x 35mm that will help reduce any warping? Also what's your feeling on high current in a thin PCB?

Thanks!

T3sl4co1l:
I wouldn't worry about warpage on something that size, and as long as copper will be fairly even.

They might not do 0.5mm total with 4 x 2oz anyway, you need enough resin in the prepreg to fill in gaps between traces -- but 0.8 and 1mm should be fine (and reasonably priced still).

12A isn't exactly high current, you might even be able to do it in 2 layers, unless that's driven more by complexity or component density.  I would just worry if you're trying to get more than a couple watts out of that.  Which, probably with high-K thermal pads on both sides, clamping it between heatsinks, something that size could do 10W or so, maybe even a bit more, but that's also a fairly demanding assembly.  Say 3-5W with a single side thermal pad would probably be more practical.

Tim

jayx:
0.5mm is very thin and will be very flexible. Also at this size you'll need them on a panel. Most likely it will be problematic for paste print, P&P and reflow, unless you add some stiffener.

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