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This may be an off topic question, but I'm sure many of you have the knowledge and experience to help out here.

A quite complicated motherboard was flexed. The resulting symptoms include cross-talk or noise on some data lines going out to the display. The symptoms get worse when lots of video data is transferred. This could be due the fact that more data is getting transferred and therefore more data is getting corrupted by the noise or it could be due to the SMPSs working harder to power the GPU resulting in more noise. It could be a combination of the two, but at the moment I suspect a bypass capacitor on one of the SMPSs on the motherboard either cracked or the solder holding it on cracked.

Question: Besides a visual inspection with a microscope, is there a way to test for a faulty capacitor/solder joint that likely failed in an open state on a PCB? A hairline crack in a SMD capacitor or in the solder joint somewhere on a large PCB seems difficult to find through visual inspection.

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  • \$\begingroup\$ Not sure why someone thinks this is off topic \$\endgroup\$ – placeholder Jul 15 '14 at 22:35
  • \$\begingroup\$ Do you have any test configurations or loopback modes to test the board? For complex designs, you typically need some method to test the board. \$\endgroup\$ – Whistle1560 Jul 16 '14 at 1:33
  • \$\begingroup\$ Unfortunately, I do not. The main test is power-on and functionality of it. \$\endgroup\$ – horta Jul 16 '14 at 2:15
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Don't flex your boards. A cracked solder joint on a rigid part is possible. Look for rigid parts with the along axis aligned across the "bow" of the flex.

There is very little chance you will catch this visually since the fracture is just a tiny crack, and with the board returned to its normal shape it probably mostly closed up such that it will be very hard to see.

The easiest fix is probably to run the whole board thru a reflow oven if you have access to one. Barring that, going around and re-melting all the solder joints might work, but will be tedious. The cheapest solution is to buy another motherboard, and then not abuse it this time.

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Other issues on top of solder joints being damaged ...

The flexing creates shear forces within the board, depending upon your via count and size and amount of plating, you can easily shear your vias and even tear them loose from the traces. Since this can happen deep within the board and the probably will return back to "normal" - i.e. no gap when not flexed, you may not be able to see this even under x-ray inspection.

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  • \$\begingroup\$ Ugh, how depressing, but good point. \$\endgroup\$ – horta Jul 15 '14 at 22:46

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