Tuesday, April 26, 2011

Freshly etched PCB

This phenolic paper board measures 3x2 inches. It was cut using the score-and-snap method from a 6x10 inch board. The presensitized board was exposed for just 60 seconds. Ten more seconds wouldn't have hurt. Not sure how much less I could've shaved off without compromising the exposure quality. Copper has already been etched away but the photoresist is still on it (it's really metallic blue-green in color but it looks black in this pic). I've already drilled out the holes but this image was taken right before drilling.

As I said in my previous entry, as a substitute to silkscreen on the component side and in lieu of just painting the empty spaces with copper or laying a ground plane (which isn't necessary here or is it that rational on a single sided board), I try to cram as much textual info as I can on the copper side since that doesn't cost extra at all. I would've wanted to label most of the components (put labels adjacent to them) and their pads but there just isn't enough space. So I just listed the major components at the bottom of the board. Hardly standard or industry practice. But these boards are for my own use and I'm tailoring them to my needs.

The connectors (2 x 2-pin and 1 x 4-pin) are all on the right side and the labels refer to what each pin of those connectors are for. There's an ICSP header for the PIC MCU in the middle of the board. You might be able to make out the "VPP" label marking pin 1 of the header. That label will come in handy if I ever re-program the MCU in the (far) future since the PICkit 2 or 3 will go either way into the header. Plugging the programmer the wrong way around is, needless to say, a no-no.

You'll probably be able to make out the "MOC3021" near the top left hand side. That's a 6-pin triac optoisolator. There's going to be 220VAC on this board so I've placed all 5VDC components and tracks on the DC side of the optoisolator. The left side is dedicated to high voltage power circuitry. Nice clean, copious electrical isolation, eh?

The circles with crosshairs on each of the corners of the board are of course for mounting holes. The traces for those crosshairs are 10mils wide. And they're still very distinct and without any visible breaks. So I can probably get away with tracks as narrow as this if I don't bungle anything all the way to etching.

Given my breathtaking shoddiness in soldering I try to keep as large a space around pads as I can so as not to short anything. The smallest pitch I specify on my board layout is 100mils. So for TO-92s I have to physically spread the three legs apart before dropping them into the board. With my now extremely poor vision and unsteady hands I doubt I'll be able to solder anything with a smaller pitch. Right now the board looks pristine and immaculate. But the copper side won't be quite as pretty when I'm through soldering the components.

1 comment:

  1. Etching is the method used to produce printed circuit boards. A temporary mask protects the laminate from acid and leaves the etched copper layer. Acid removes the unwanted copper from the laminate. Thanks a lot.