Mail to Robert DeHate
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I thought I would detail how I etch PC boards to help others create their own designes.
Creating the pattern:
I use Visio to create my trace pattern. It is a vector drawing program so
when I create a box that is .025in it will print that same size.
It
doesnt really matter what you use as long as you can controll the line size that
is printed on the printer.
You will notice that the traces I post on my page are PDF files. This is because PDF reproduces the file exactly as the program that created it. And since I create the PDF from Visio it is sized correctly on the printer. Just be sure that your printer properties don't have scaling turned on.
Putting the pattern on the circuit board:
The hardest part in making a circuit board is transfering the trace pattern from your computer(or your head) to the circiut board. Certanly you can use an etchant pen and draw it on or you could use the tape/dry transfers. There is even etchant paint These all have their uses but if you want a fast, easy way to make quality traces you have to try another technique.
Toner Transfer:
I researched this technique and found all kinds of tips and tricks to transfer toner to a circuit board. The toner comes from a laser printer or a photo copier. Gets printed on some medium. And you use heat to transfer it to the circuit board. There are several mediums that can be used. There are even special papers you can buy that have a water soluable coating so the toner wont stick. Toner is just a type of plastic. The printer melts it onto the paper when it prints. On regular paper the toner melts into the fibers of the paper so this is no good for transfering. There is special paper, at a special price, that has a coating that prevents the toner from soaking in. Then you just iron it onto the circuit board and soak in water. Some photo quality papers are able to do this also. I was looking for a cheaper way to get this done. Others use transparencys to do the transfer so this is where my testing began.
In my limited testing I found that photo copiers dont laydown enough toner
and even some laser printers are stingy. The key here is to get a thick coat of
toner printed out.
If you have several different printers at work
then print the pattern on a transparency on each printer. Hold the transparency
up to the light and compair which one layed down the most toner. I also print as
many patterns on one page as will fit. I have found that some printers dont
print so evenly and if you print multiple patterns on the same page you can pick
the best one.
Oh and make sure that you reverse the pattern before printing it. Any patterns you find on my web page are already reversed but any you make will need to be reversed. There is nothing worse than putting the components on and realizing that the pattern is backward.
One note about transparencys. They are not all equal. Generally the transparencys for laser printers can stand higher heat than the ones for ink jet printers and if you put the wrong one in the printer the owner of the printer wont be happy to find a transparancy melted to the drum. Also I have heard of transparencys that have a smooth side. If you come across this type try to use the smooth side. Also be careful of the way you handle the transparency. I try not to get any oil from my hands on the trace pattern or on the place where I will print the pattern. Also once you have a pattern try not to bend it too much.
Once you have a nice pattern printed on a transparency your half way there. Cut out your trace pattern and grab some copper clad PC board. I usually cut the PC board a little oversize so that I have something to hold and a place to tape. Clean the board with steel wool and wipe away any residue Now position the pattern, verify the toner is against the copper, and tape it in place with one piece of masking tape along one edge. Dont let the masking tape go over where the traces are on the transparancy or you wont be able to get even pressure on them and they wont stick well where the edge of the tape is. Be carefull that the transparency isnt sticking off the end of the board because if the roller goes off the end it will press down on the transparency and cause it to pop up off the board. PIC
Now you need an iron , some sort of gripper to hold the board(it gets real hot) and a roller. I recommend buying your wife a new iron and using the old one. I usually use a vice grip to hold the PC board when working because it gets too hot to hold. The roller I use I got from a craft store called AC More. It is used when making Tee shirts. PIC
Clamp the iron down to the bench so the metal side is flat and up. Set it to high and let it come up to temperature. Put the PC board, traces side up, on the iron and slowly roll the roller from the tape side across to press the transparency down. PIC Continue rolling with firm pressure for 5 min. If you look carefully you will see the traces widen a little as they are smashed onto the board. This tells you it is working.
Now take the board and set it aside on the wood to cool. PIC Don't let it cool too much. I usually let it cool untill I can comfortably hold it(maybe 1min). I then pick it up and from the tape side peal up the tape and transparancy and in one smooth movement peal the transparancy off. If you stop while pealing you will get a line where the toner doesnt stick to the board. PIC
Touch up the traces with an etchant pen( or a sharpie). Fill in the large areas with the pen or some etchant paint. If this is the first side of a double sided board then you will need to protect the other side. I have had good luck just covering it with electrical tape. As long as the etchant cant get under it to the copper it will be fine. But dont use masking tape as it will soak through. Here is picture of the board ready to dip. Its dark because the 'handle' part is covered with black electrical tape. I also covered the back with electrical tape. I cut the 'handle' off after etching because I need it for the other side and also if I tried to cut it now I could damage the pattern. I protected the 'handle' with tape because etchant can only hold so much copper before you have to replace it. Also if etching by hand it etchs faster if there is less copper to take off.
Etching:
Using your favorite brand of Ferric Chloride etch the board. There are other copper etchants out there but I have never used them.
If you don't have a fancy etchant tank, like mine , just use a glass dish that will fit the board. Pour about a 1/2in of etchant in and agitate till the copper is gone.
I have started doing mostly surfacemount components because I hate drilling holes. If you have ever built a board with over 10 14pin ICs you know the pain.
By now you should have a fully funcioning PC board all etched and ready for parts.
Let me know what you think, and if I need to clarify anything.
Notes:
I use an HP4500 laser printer that is at my work. It seems to lay down the most toner. And thats the key to have the most amount of toner on the transparency so if some doesn't transfer its OK.
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