I have been using a desktop pnp for a couple of years and one thing that my pnp is bothering me is its inability to automatically identify fiducial points on a board on a panel of boards. I would move its head to one board on the panel, snap a photo of two fiducial points. Then it can automatically adjust with the rest of the boards on the panel, in theory. In reality, it starts to fail after a few boards. I suspect that it was due to the fact that my fiducial points are shiny tin-plated discs from the leadfree HASL process. The downward camera on my pnp has an array of about 4 LEDs so the illumination on the board is less than uniform, which causes the mirror-like fiducial points on each board to reflect light differently from the next, causing comparisons to fail. My thinking is, if I either cover the fid with solder paste (add to cream layer), which is going to be a diffuse scatter of light instead of specular reflection like a mirror, then it would be easier to auto identify the fid pts. Or maybe I should use silk screen or exposed copper instead. What do you all do when it comes to making fid pts and using pnp to auto identify them? Thanks.
BTW, my PCB camera also randomly goes into black-white video but luckily I almost exclusively use black PCB so I don't always notice.