Sauraen

Warped PCBs

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Both sets of custom boards I have ordered for my ASIDITY project (from different companies) have arrived somewhat warped. I left the first set under a stack of books for a few days but that did absolutely nothing, and I eventually soldered everything to them, at which point they are stuck in their warped shape and cannot be bent back. Now I just got another set, and they're warped too. Does anyone have any suggestions as to how I should flatten them out?

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That usually happens when there is a large ground plane on one side of the board and none on the other, and the board is above a certain size. There is nothing you can do about it, except revise the design for the next run of boards.

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For the first set, the part about the ground plane is correct, but they weren't that big, only about 4" x 5". The other has no ground planes but is huge, about 7" x 13". We're not planning to order any more of them, but if we did, what could we change in the design (other than adding a second ground plane to the first one)?

 

Edit: How about this? http://www.circuitrework.com/guides/3-2.shtml

Edited by Sauraen

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Last time i had to straighten a pcb i just used my solderstations hot air tool and put a large vent tip on and keeping the hot air tool about 15cm away and constantly moving it around in a circle for a few mins until it heated the board up, i then quickly placed a really heavy book on top of it and left it for about 15 mins to cool down, it was fine after that.

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Thanks! I'll try the same thing with a hair dryer. :)

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For the first set, the part about the ground plane is correct, but they weren't that big, only about 4" x 5". The other has no ground planes but is huge, about 7" x 13". We're not planning to order any more of them, but if we did, what could we change in the design (other than adding a second ground plane to the first one)?

 

Edit: How about this? http://www.circuitrework.com/guides/3-2.shtml

 

It might depend a little on the manufacturer, but a general procedure would be to use ground meshes instead of solid planes. You can find a fine example of this on the LPC17 board.

 

And I stand corrected, apparently heating up the whole board and letting it cool down as per the link you provided seems to cure the problem. Maybe using a heat gun if you don't have a rework station is feasible, too?

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I tried a hair dryer; it did absolutely nothing. I don't think it was hot enough. I'll keep looking for options.

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Just my thoughts; I experience the same with almost all PCB I make myself. I think the reason (just my thoughts) is that the copper is glued on, and some tension appears between the copper and the rest, and that could be the reason why it warps. I remember some of the first boards I made, I saw it was warped, and I sort of just accepted that - until I etched it - taking away much of the copper - then it was straight as never before. Seems like etching copper away takes some tension off it. That also makes sense when thinking about what Ilmenator said...

 

I don't know that it actually works this way, but it's kinda logical considering my own experiences with the warped boards.

 

Heating it up (if it is the way I concluded for myself) could probably give u different results with different pcb materials then... If it's plastic, you could probably heat it to straighten it out, but maybe it's not possible if the board material has fibers in it...

 

As I started with; just my thoughts and reasoning... :).

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I tried the baking technique and it worked great. The board is not exactly flat, but it's much better and definitely good enough. The board material was FR-4; I had it custom-made, and it was about the same quality as the boards available in the MIDIbox Shop, though maybe slightly inferior.

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a hair dryer won't nearly be hot enough... you need a heat gun or hot air smt station to heat it up enough.

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