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Sunday, March 16, 2008

Part 4 Etching and Drilling

Etching.

Before I continue, I want you to give yourself a pat on your back for job well done. J The etching process is same regardless of method used to transfer the pattern on PCB. Now; for the dirtiest part of the whole PCB making process.

The etchant is FeCl3. Also know as Ferric Chloride. It can be obtained from any respectable electronic shop. Don’t get the solution. Buy the crystals and make the solution yourself. It costs less than RM5 for the crystals. WARNING: FERRIC CHLORIDE STAINS MAKE SURE IT DOES NOT SPILL ON YOUR CLOTHES, FLOOR OR ANY WHERE ELSE. The ratio for mixture is 1 to 3. You need hot water and a plastic container to mix the etchant. Use the whole packet, dissolve it. FeCl3 is very toxic. The container with ferric chloride must be labeled and store in a safe place.
For etching, pour some in a deep container (used ice-cream container) until half full. Pour the balance in a bottle and label it. Container must be large enough to fill your largest project PCB. FeCl3 is reusable, so don't dispose of it after use. Leave it in the container and cover it.

The etching process should not take too long, about 5-10 minutes. Depending on your solution strength. To speed up the process, get an aquarium air pump, air stone, some tubing and some suckers. Place the air stone in the container with the etchent. Tape a string to the top of the board. Place the board so it floats on the etchent. Then turn on the air pump. Within 5 to 10 minutes, you PCB should be ready. If left too long in the etchent, your tracks might dissolve. And if not long enough, your excess copper wont dissolve. 

It's a good idea to check the PCB every 5 minutes or so, if you are not sure. Once etching is done., Check the PCB for shorts and open circuit. The green layer of UV sensitive coating will still be on the tracks. Soldering with coating on is not recommended, because it takes the lead sometime to stick and the joint is not clean. This coating can be removed by rubbing isopropyl alcohol.






FeCl3 Anhydrous

The mixed, solution. Keep extra in bottle and label it.
 

Air pump, air stone and sucker. Is optional, but increases etching time.
Place PCB face down in and let it float. Turn on air pump.

Drilling


This is easy on the phenolic board. But a but difficult on the FR4. I use a high speed motor for RC toys and got the bits from Pasar Road (again).
You can use a 9V battery to power the drill, but i use an old PC power supply, modified, for my projects. Make sure the bit doesn't wobble when drilling. It usually does at high speed. I am using 0.8mm and 1mm bits. Couldn't find the 0.7mm bits. For double sided PCBs, drill the pads before you etch. For faster and cleaner drilling, use a Dremel high speed drill with flexi hose.


The drills used.


My PSU to drive the drills and test projects.

Next Part 5 .... The conclusion.

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