Make high-quality double-sided PCBs – at home
Why make your own printed circuit boards when you can get them commercially made for low cost? For one, it can take one to four weeks to receive the boards. For prototyping, this can be a major hurdle. Each design iteration will then take a month or more, and a project may need many months to get done. The DIYer can fab the board and assemble everything in one evening. That advantage is really hard to beat.
Besides time, there are other reasons to make your own board. Commercial services charge by board size, not complexity. Larger boards will cost more even if they are completely blank. I once had to make an oversized PCB because the parts had to be spaced far apart. It was a very sparse board, but getting it made from even the cheapest commercial source would have been expensive.
Having said that, this is not really about saving time or money. If the phrase “building your own” does not excite you, then read no more. Building a board may not take two whole weeks, but it will take many hours. Like in everything, there is a learning curve. It’s not going to work the first time. Remember, we are talking about building a near-professional quality board, not something that is thrown together to check the functionality of a circuit. If the process itself is an unpleasant experience then it will not be worth any amount of time or money saved. The reason people build instead of buy is because they enjoy learning and perfecting new skills. If you are detail-oriented, have lots of patience, and take pride in craftsmanship, then this might be for you.
Now on to the details…
Laser printed toner transfer method
The laser printed toner transfer method is by far the easiest and the best quality for the home builder, even compared to UV exposure of pre-sensitized boards. Why this is so requires some explanation. PCB manufacturers use UV exposure of photoresist using a photoplotted (not laser printed) mask. The resolution of photoplots can exceed 50,000 DPI, whereas a laser printer tops out at about 2,400 DPI. In order to exploit the advantages of photoplotted masks, you need a very uniform UV source and alignment capability, which is far beyond the average home shop. Most home builders who use UV use a laser printer to make the transparency and use that as a mask to expose a photoresist coated board. This doesn’t make much sense. Why? Laser toner is not fully opaque to UV since it has a large number of pin holes. UV wavelength is only 365nm, so it is very difficult to seal these pinholes and make it opaque. Combined with optical diffraction and scatter in the film, it is not difficult to see that the resulting image will be worse than the original print. On the other hand, a direct fusion of the toner does not suffer from any of these effects. I can get 5mil lines with the toner transfer, which is about as good as any commercial PCB service.
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