On last week’s Amp Hour, Chris and Dave were discussing laser etching PCBs. I’m not sure they realized it, but this is actually a fairly hot area in PCB processing research right now, along with printed electronics.
Currently, PCBs are processed by copper-cladding a substrate material, like FR-4. There are a couple ways to get the circuit layout onto the board. The first possibility is that the circuit layout is printed onto the board using screen printing. The copper you want to keep is covered in an impermeable ink. A second method uses a photomask. The areas you want to keep are exposed to light, which will harden the mask. The unexposed areas are still soft and removed chemically. The final step in both processes involves removal of unwanted copper using a chemical such as ferric chloride or ammonium persulfate.
(Note: A third method can involve the use of a PCB mill, which will use drill bits to mechanically remove the copper. Sometimes people will use lasers to etch away unwanted copper. Both of these approaches are generally used on a very small scale, however.)
Given the expense of copper, you would think that this process would be abandoned. Unfortunately, the reason these processes are still in use is that they are very fast: they make it possible to process many boards at once. But if you think the process is wasteful, you’d be right; it also uses very nasty, dangerous chemicals.
The industry is seriously looking at alternative means of processing PCBs. There are a couple methods which are being developed. The first is directly printing traces on boards using metallic inks and something like an inkjet printer (such as was demonstrated in this paper). A second method involves laser etching traces and then printing them as in step one.
Each of these processes is significantly less wasteful than the current method of producing PCBs. However, they all suffer from the same problems: they are not generally considered fast enough for commercial production of PCBs. The problem with both printing and laser etching is that you’re limited in speed. Another problem is that metallic inks tend to have a lower conductivity than straight copper. Producing inks that work well, are sufficiently conductive, and affordable is not a trivial task.
Regardless, there is a good chance that the copper etching method of producing PCBs may be coming to its end. The replacing process(es) will hopefully reduce the amount of wasted material, making the process just a bit more green.