Double sided PCB fabrication tour

This is a tour of home fabrication of printed circuit boards using MG Chemicals presensitized board. Supplies are at Fry's or through Mouser. Featured is a double-sided board; this is much harder than single-sided because you have to align the front and back "artwork."

Ed at CSRA Makers made Youtube videos of some of the process. Search for youtube csramakers etch part 1 and youtube csramakers etch part 2.

The tour starts after the schematic is set and the artwork has been drawn on computer. (CorelDRAW works well, but steep learning curve.) Also, the .pdf files have been taken to a copy shop and printed on transparency, with scaling "none." (Do not fit to page.) Make sure the toner is going to be in contact with the blue photosensitive film on the PCB material, otherwise UV light is going to sneak in from the sides and make the exposure fuzzy on the edges.

The next photo shows the PCB behind both layers as I am about to insert it between the transparencies. You see the white liner that protects the photosensitive film from light.

Above, the spacer has been taped to both transparencies after carefully aligning "through holes." The following photo shows excellent registration.

The next photo shows how bad registration could be if you aren't careful. If you expose this way and etch it, then drill the holes that have solder pads on both sides, the drill will come through way off center.

My personal preference is that, for boards over 3" across, I drill a hole in the middle and put a large needle through with accessories (not shown) to pinch the transparencies onto the PCB so that "focus" is good. If you only pinch on the edge of the board, the middle is likely to bulge and the focus will be awful in the middle. (I use .092" acrylic to "weight" the transparencies, like MG Chemicals says.)

After photo above, you pull the PCB back out, strip off the white liner to see the blue film, slip the PCB back between transparencies, align the pinch hole, tape one transparency to the board somewhere on the edge, and develop in NaOH as MG Chemicals says.

Next photo shows exposed and "developed" boards. Top one is single sided, bottom is double sided. When you have double sided, it is going to slide around in your etch dish and get scratched on the bottom, spoiling it. You could put plastic screws through to space it up in the ferric chloride, but I prefer fastening boards onto a plastic mat, using #26 magnet wire. This way, you can develop and etch more than one board at once without the boards sliding under one another. (The ferric chloride is opaque, you can't see your boards when they are submerged.)

Next photo shows how the exposed blue has washed away, leaving copper that is going to be etched by ferric chloride. When you are developing and the blue starts washing away, it is pretty exciting to see all your hard work bearing fruit. Note: developing is the hardest chemistry to get right. 100 degrees F is OK, not much higher. I get bad results from running two boards through the same developer--works better to make small quantity of the 10:1 dilution, throw it out after one board and make new for the next board.

Next photo shows etching almost complete. Etch is slowest away from the edges. Whereas developer is done around 100 degrees F, etchant can be 110 degree F, with agitation (rock the etch dish gently, don't slosh the ferric chloride out), it takes 15 minutes. Ferric chloride has lots of iron ions and should not be ingested (it would give you an iron overdose which is toxic), and the solution picks up copper ions which are toxic, too. You reuse etchant until it is green, not brown or yellow, then you dispose of it by taking it to a recycle center. (You can't evaporate it down to a solid, it pulls water from the air and never becomes solid.)

Next photo shows good resolution (good focus).