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Multilayer PCB X-ray inspection

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Multilayer PCB X-ray inspection | 1 April, 2010

We've got prototype 6-layer PCB's and I suspect that mfg. swapped some internal layers. Would it be possible to use some form of x-ray inspection to verify that? Any ideas?

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Multilayer PCB X-ray inspection | 5 April, 2010

Hi Deni,

X-ray will not be able to see through Power and Grn planes.

Your only way to find out is: 1) ask your board supplier to supply stack up used. 2) surface grind layer by layer to validate if it is correct stack up.

What is making you think that it is stacked up incorrectly?



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Multilayer PCB X-ray inspection | 6 April, 2010

You would be suprised what you can see with even a simple Xray machine. The engineers upstairs wanted to see if the xray could confirm there was an open via on a thin dense board with several layers. I thought (but didn't say) no way. But with carefull manipulation of the board and xray settings I found open via where they suspected one. With another board you could see the barrel shadow clearly, with the suspect board the shadow was about 20%.

I think with some boards you would be able to tell if the stack up is on the wrong order. But you would have to be able to rotate the board and have some place where you knew the routings. And ground planes and power layers would make it more difficult, and impossible on some boards.

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Multilayer PCB X-ray inspection | 8 April, 2010

Having no real experience with x-ray inspection, this answer helped a lot. What I actually want is to check top 3 layers and it should be pretty straightforward, as the second layer from the top should be almost empty and the third one should be a ground plane. I suspect that the factory swapped those two layers, so the ground plane is on the second layer. PCB mfg. claims they made it correctly, but measurements don't confirm that (it's a RF board with some microstrip TL's). Actually, measurements confirm that the second layer is GND plane, but that's indirect method. I would like to present them a solid proof of the error, to be able to force them to fix it.

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Multilayer PCB X-ray inspection | 15 April, 2010

Dumb question maybe but does the board have a layer count window? Usually each layer has it's number visible in copper somewhere on the board and the shop will leave the solder mask clear of this window. If the layers were stacked incorrectly it would be obvious. If however they put the wrong number on the layer during layout it would look correct but could still be wrong.

As for X-ray, the others are correct, it's difficult but possible depending on the layout of the card. you will need to be able to rotate the board in the X-ray to see how the layers move relative to each other.

Good luck!

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