In the first part of this article, we covered the extensive subject of imaging a design onto a blank board and the best way to etch that board. After completing these steps, you will have a PCB almost ready for assembly. I will now explain the remaining steps. Some are essential and some not so much. As usual, each has their own set of problems to overcome.
Now that you have a nice shiny PCB with your traces and pads imprinted on it, you need to drill the holes for thru-hole components and vias. The easiest way to do this is with a desktop drill press. Since I don’t have a dedicated PCB fabrication setup, I found another easy method for drilling holes at home. Harbor freight sells a 12v powered Dremel-type tool. While this tool is way under-powered for most tasks, it turns out to be a virtue when drilling small PCB holes. I simply chuck up a #60 bit and the hole already etched in the copper pad provides a nice indentation to hold the bit steady. The low power prevents the drill from getting squirrelly and jumping out of the indentation. You can probably get similar results with a battery powered Dremel tool.
At this point you have a PCB good enough to be assembled. Modern PCBs have some additional features that your board does not have. You can add these features yourself, but at extra cost in time and money.
Solder mask is what gives commercial PCBs their solid coloring, frequently green. However, it serves another purpose besides simply coloring the board. It constrains the flow of solder to the pads where components are to go. It also insulates the board from any stray connection. The former property is most useful for surface mount components. The latter prevents inadvertent shorts from occurring in your finished board. You can buy your own solder mask paint from e-bay for about $5. Search for ‘UV Curable Solder Mask PCB Repairing Paint Green New’.
For home use, you probably won’t want to bother with solder mask. To prevent unwanted shorting, just examine your finished board and apply liquid electrical tape, hot glue or even latex paint wherever you see a point that might be at risk.
Silk screening is the part of the process that provides those wonderful part outlines and labels for assembly. If you are making more than one board of a give design, you will probably want silkscreen. You have a few options available. The first is to buy ink-jet rub-on sheets. You can buy them here.
You can also use toner transfer for your silk screen layer and just leave the toner in place.
Those nice shiny copper traces won’t be shiny for long. When they oxidize your board will be harder to solder and may even suffer from “cold solder joints”. The commercial solution to this problem is to tin the copper traces. You can buy tinning solution from solder suppliers. For home use, there is an easier solution. Just before you assemble your board, give it a good scrubbing with a Scotch-Brite pad. If you aren’t familiar with them, they are a modern replacement for steel wool. They last a long time and don’t shed iron fragments like the former will. A minute of scouring with these pads will remove all oxidation and leave your board ready for soldering.
Vias are the dirty little secret seldom mentioned in articles on DIY printed circuit boards. Vias are another name for plated through holes. When doing double-sided boards, you must have plated through holes. Not only are they used for tunneling a trace from the one side to the other, but they are also needed for traces to run from either the top side of a component pin or the bottom side. This latter use is the most troublesome for home PCB makers.
In single-sided boards, all soldering is done on the bottom side. Ditto for through-hole components in commercial boards. In double-sided boards, in many cases a circuit trace may connect to the top side of a component pin. With a plated-through hole, the soldering can still be done on the bottom side as both sides are connected by copper going through the hole. Not only that, but the solder will wick through the hole, completely filling it and soldering the pin to the pads on both sides.
When you make your own boards, you have a problem unless they are single sided. You must solder the component pin to the pad on the side(s) where they trace connects. For most components like resistors and ICs, there is no problem except for more assembly work. For IC sockets, header pins and such, there is now a problem – a big problem. These components sit right down on the pad and cover it. You can no longer solder to the top-side pad, and solder won’t flow through the hole from the other side either. There are few solutions to this problem, and none of them are very good either.
The first solution is the one used decades ago before plated-through hole technology was developed – copper rivets. There are a couple of sources of rivet type materials described in this article, or you can try using a foil-type kit to do the same thing. Any of these solutions require a lot of time and money. I just can’t see using them, but I might try the foil type one day.
The second solution is to solder the component higher up off the board. This works so-so. Give it a go if you have nothing else to try.
The third solution I have read about is to apply a lot of heat and solder. Supposedly, given enough heat and solder, it will wick up to the top and spill over onto the pad. I have not been able to do this myself, but you might want to try it.
The best solution I have found is to use a commercial PCB service. I know that doesn’t help with home fabrication, but that is how things stand at the moment.
No matter what method you use for patterning your board, without a means of plating your holes you will run into this problem. Vias for switching trace layers are not a problem. For those you just insert a piece of wire and solder on both sides. Ditto for most component leads as well.
You might be asking (as I did) – “why not plate the holes yourself like the commercial houses do?” That is the only reliable way to deal with the issue, but the problem is it is not a DIY procedure. Not to say it isn’t possible, but that it isn’t cheap or easy. It took a long time to develop the technique in the beginning, and chemistry doesn’t change with technology. Sadly, it remains out of reach for the hobbyist. If you know a way to do it easily, prove me wrong and share your knowledge.
After writing this section, I thought some more about the problem, and have come up with a fourth possible approach. At the cost of some extra work soldering via wires to connect traces as they jump sides, it might just be a decent solution. When you route a trace on the top side to a through-hole component pin that you cannot access, simply switch your routing layer just before you reach the pin and connect to the bottom side of the pad. You will have a lot of extra vias, but it will be needed for at most 50% of the pins for those components that cover the board’s topside. You may also have to allow a little extra room on the board for all the extra vias – alongside ICs and headers.
There are many more resources and tutorials on home PCB fabrication than those mentioned in this article. I have tried to mention the more useful ones. I have also surveyed the various methods available so you can choose which one suits you the best. I have also addressed some of the most common problems and how to overcome them. The last problem – that of vias, remains unsolved. For this reason, I now favor using a commercial PCB service most of the time, but will be giving the fourth approach a try.
The main drawback of a commercial PCB service is when you need a board now. In such cases, you can either build your circuit on a perf-board and wire it up by hand, or make your own PCB. Making your own PCB is also the best option if you can’t afford even the modest cost of PCB prototyping services. I will cover these new services in another article. With a cost of less than $20, having a PCB made commercially is more available than ever.
Please share your experiences and favorite articles in the comments.