How to find short on PCB

[dipmicro]

Came to my attention that approx 1 in 10pcs of our PK28 board has short between Vdd and GND. Our suppliers tell us they do electrical test, but apparently some take shortcuts. Anyway, we stopped using particular supplier who delivered last batch of PK28 some time ago and using higher quality PCB fab.

I do sometimes wave electrical test on very simple boards without narrow spacing, e.g. proto board PB1. However, PK28 uses "spilled ground" and this was exactly the problem - one of the Vdd pads touched this spilled ground (see image below)

Set your scanner to at least 1200x1200 dpi, full 24-bit color and custom size slightly larger than your PCB. I used 10 x 6cm area and when increasing resolution, 4800 dpi gave "not enough memory" warning despite 4GB in the system.

Take two scans - top and bottom. Paste each scan into it's separate layer, mirror the bottom one and align them in your favorite photo editing program (I use Paint.NET for quick jobs like this one).

Now you can zoom and move image and inspect both layers at the same time. Turn layer visibility on/off as needed.

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