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One of the items in this shipment is (allegedly) a Xilinx XCKU5P that was cheap on AliExpress. The guy who sent it to me did some preliminary dead bug proof of life testing so now it's got bypass caps and missing solder balls stuck to the bottom.

Let's clean it up.

Doing a full chip bottom side substrate scan of the XCKU5P-2FFVB676I on the Labsmore X1.

I don't have a proper darkfield setup but find that pure metallurgical brightfield illumination works poorly on chip packages and PCBs. Here's the low angle LED lamp setup I'm experimenting with.

Hard to get good uniformity on larger samples but it works decently.

Bottom side substrate photo, mirrored so it lines up with the top-down view in the datasheet. Ball A1 in top left corner. Slightly overexposed on the top left but it'll do.

A few of the lands look to have small amounts of solder residue that I didn't quite clean off fully, so before I reball I'll inspect and possibly clean them up. Hard to tell exactly how much solder there is in this lighting.

There's also a scratch in the soldermask around the T-U 12-13 region. Shouldn't be a big problem but I might try to touch it up just to make sure I don't get any problems.

The substrate matches the ballout perfectly (further evidence the chip is real) although there are a few interesting things:

* The GTY refclks don't have ground plane cutouts around them for impedance matching, only the high speed SERDES

* There's a tiny single-pin ground island next to the VCCAUX_IO island. Why not just fill with VCCINT there?

* Most interestingly, the VCCO zone fills don't line up with the IO banks!