As sort of a follow-up to my Inket Photolithography article, I have some more pictures of the process, from start to finish.
Using paintshop pro, I take individual PCB layouts and combine them into a composite panel, which is the exact size of the PCB I’m going to expose. Often I’ll repeat the same design a few times, in case there’s some glitch in one of them, or the board is damaged during the depanelizing process. I like to start with a black background for the panel, to mask out any unused sections of copper… this helps cut etching times and helps save the etchant life.
The inkjet transparency comes with a sheet of white paper attached, to protect the transparency and give the printer something extra to grab onto with the feed rolls. It takes about 30 min for the ink to fully dry.
This is my darkroom which also doubles as my house’s furance room. The exposure system is two cheap-o under cabinet lights, with “daylight” bulbs loaded in them. The timing is completely manual and is just an extension cord I unplug when time’s up.
After exposure, the PCB takes a bath in a sodium hydroxide solution to develop the resist layer. Within a few minutes resist that was softened from exposure to light is dissolved away. I rinse the board in hot water (per manuf. spec) to check for complete removal of the resist – sometimes a thin film remains and another dip in developer is required. After all is well, a rinse in cold water sets the resist and halts the developing process.
Here is the transparency used to expose the photosenstive printed circuit board. It is actually laying on top of the board which as already been etched.
The resist is a blue color when it’s “active” and turns green after it has cured, and is no longer photosensitive.
Protecting eyes, ears and lungs is a very important step.
My drilling station is a basic dremel mototool (single speed) mounted in a drill mini-press. I have two 20 watt halogen lamps to illuminate the panel, one is a flood/fill light, the other a tight focus spot right on the cutting head. Using expensive aluminum titanium oxide coated solid carbide drill bits (designed for drilling fiberglass and non ferrous metals like titanium), the dremel easily pierces the board, spinning at 35000 RPM.
Lots of holes!
Make sure your safety gear is still on!
A visit to the impromptu depanelizing saw aka a Skill Jigsaw turned upside down and secured in a bench vice. With the blade installed backward, the foot of the saw provides a nice table for resting the panel on. This arrangment will gladly take a finger or at least mess you up, so make sure you have no distractions and always know where your fingers are while the blade is moving. Sometimes you’ll end up with pieces that are pretty small, but it’s not worth the risk of serious injury trying to do them on the saw… scoring both sides of the pcb with a drywall knife should let them snap cleanly… also I’ve heard large sheer-type paper cutters work.
The end result, a pile of little PCBs.
Sometimes the saw doesn’t leave the cleanest edge or your line is a bit wavey – a visit to mr belt-sander will clean things up nicely.
editors note: some of the pictures for this article didn’t come out as well as I had hoped, or have yet to be taken, so the [image missing] tag is a place holder to remind me to reshoot.