If you start tinkering with electronics, eventually you will want to make your own printed circuit board, or PCB as it is generally called. In the olden days, this subject was pretty straightforward. You went down to your local RadioShack, and bought an etching kit. You drew your single sided design using a marking pen and some supplied stickers. The board was fairly big, and it had only a few simple through-hole components.
Those days are now pretty much gone. Now most electronic projects are much more complex, the boards are much smaller, and you need to deal with 2 layers, surface mount components and vias. In this overview, I will tackle the different problems you may encounter and the methods available. I won’t cover PCB layout software or commercially made boards. I’ll deal with those topics in separate articles.
Making a PCB involves several steps. Today’s PCBs require a lot more steps than they used to, but for your own use, these later amenities can be omitted. The steps involved are:
- Imaging your design onto a blank PCB
- Amenities – solder mask, silk screen, tin plating
As I mentioned before, simple circuits can be drawn with a sharpie marker, but these days, you will need to print out something called a mask using CAD software. There are several ways to transferring this mask to your blank PCB. Commercially, this process is done using a photo transfer process, which is also one of the ways available to you at home. The point of this process is to add a coating to your PCB in the shape of your circuit. This coating will permit the copper to be etched away from the blank board everywhere except where you want it. The coating that prevents parts of the board from being etched is called a mask. Because of the fine pitch features often required, this step is not as easy as it would seem.
Photo transfer is the most accurate way to image your design and is used commercially. It will easily provide the fine pitches needed for modern designs. It is also the most expensive method for home use. You must buy specially photo-sensitive coated boards and print your image onto clear plastic sheets. After printing the negative of your design, you lay it on your PCB and expose it to ultra-violet light to develop the coating which now becomes your mask.
Because of the extra expense and special boards required, I have never used this method. If you need fine features, using a commercial PCB service is really the way to go. If you would like to know more here are a few articles that describe the process:
The toner transfer method involves printing out a positive image of your circuit using a laser printer, and then using heat to transfer that image to your board. The pros including being quick, cheap and produces fairly good results. It is the method I prefer to use. The downside is that it is a little tricky to get good results and you often have some areas that need touching up with a sharpie. It can handle fairly fine features, but is definitely limited as compared to the photo transfer method.
Toner transfer uses the same basic process as the laser printer does. When a laser printer prints, it deposits the toner particles onto your paper and uses heat to fuse them to the paper. When you want to transfer this image to your PCB, you again use heat to lift the toner particles and fuse them to your board.
There are two ways to make the transfer – using an iron (like you iron clothes with) or a laminate machine. I have found the iron works well enough for occasional use. If you start making a lot of PCBs, then you should invest in a laminate machine. This company sells a laminator specifically for PCBs. You can also buy a cheap laminator from amazon for $35 and modify it as specified in this article.
The main problem encountered with this process is getting all the toner off the paper and onto the PCB. The type of paper you print on is the most critical part of the process. There are several resources available for buying (here or here)or making this paper. It seems to me that buying or making special transfer paper would be just as involved as photo imaging. If I were to need to make that many PCBs, I would go with the latter route instead.
For the quick, occasional home PCB, there is a surprisingly simple and cheap alternative to special papers – glossy, magazine pages. To use them, just tear out a page that is light on the printing and print your PCB onto it. The existing printing doesn’t transfer, so it is not a problem (the lightly printed pages are needed for YOU to see your design). The toner tends to not stick very well to the glossy pages which makes it ideal for toner transfer.
For more details, I have not found a better article on the subject than this one.
One last detail on this method involves registering double-sided boards. The problem is that the mask on both sides of the board much align with each other. The easiest way to do this is to hold the two masks up to the light (using thin magazine paper here helps) and aligning them together. Once aligned, tape them together. Then slip the board in between them and transfer using an iron or laminator. This article describes the technique in perfect detail.
While I was writing this article, a new how-to article appeared that uses parchment paper from the grocery store for the toner transfer paper. It sounds like a winner to me – I will be trying it on my next board.
A third way to get your design onto a board is to print directly onto the board. This method sounds like the ideal one for home use, but it is not quite mainstream yet. The basic method uses a modified ink-jet printer. This website gives a lot of useful information on how to do it. There is also an instructable on doing it.
An alternative to etching PCBs also exists with ink jet printing – skip the copper clad board altogether, and print conductive traces directly onto a substrate. A new conductive ink that is a true solution as opposed to particles in suspension has now been developed making it ideal for this method. If you want to experiment yourself with either of this techniques, you should head over and join the yahoo group dedicated to making PCBs with inkjets.
The last way to transfer your design to a board actually eliminates the next step as well – direct milling of the copper using a CNC machine. While formerly the only available to wealthy corporations, with the advent of cheap 3D printers and DIY CNC machines, this method is now cheap enough to be available to everyone.
You can check out some of these popular designs and kits (here and here) if you want to explore more. I don’t have a desktop CNC machine myself yet, but I plan to get one eventually. When I do, direct milling PCBs will be my preferred method.
Etching MethodsEtching is fairly simple in its most basic form – you immerse the copper clad board into an etchant solution, agitate some and when you see the exposed copper dissolved, you remove the board and rinse. As with most things worth doing, there are many techniques to try to obtain a faster, better etch. The basic principles involved are temperature and agitation. The etchant needs to be warm and flowing across the copper. If it isn’t, the etching takes a long time and is more uneven.
There are two great tank construction articles I have found for making a really good etching tank. The first describes a thin vertical tank using an airstone for agitation. It looks simple and inexpensive. The second describes a spray technique that is really effective. While the build is more involved, it seems like a really great way to do it.
For the quick and dirty method that saves etching solution, I use the sponge technique. While wearing rubber gloves, rub the etchant solution onto the board with a sponge. It takes a bit of labor, but works quickly and well.
After you have successfully etched your board, you must remove your mask. The best way to do this is to use fingernail polish remover. The toner or photo resist comes off easily with a little bit of rubbing.
The traditional etching solution is Ferric Chloride. It is available from most electronics suppliers. For many people, they do not like working with this chemical. Apart from its ability to stain, I don’t have much problem with it. While I wouldn’t want to touch it, it doesn’t burn or emit noxious fumes.
There are some who favor using Cupric Chloride which begins as a mixture of hydrogen peroxide and hydrochloric acid. The raw ingredients are cheap and readily available. Hydrochloric acid is available where pool supplies are sold under the name muriatic acid. I don’t know if this solution is any safer than the traditional one, but I like the fact that the ingredients can often be found either at home or in a nearby store. Here is a great article on the subject if you want to learn more.
You are now armed with the knowledge necessary to successfully image and etch your PCBs. In part two of this article, we will explore the other steps to making a working PCB as well as some extra features common on commercial boards.