Obviously it is necessary to have a printed circuit board (PCB) before constructing any of the projects described in this book, and building your own printed circuit board is a reasonably easy task provided it is tackled in the right way.
Before proceeding to the projects we will therefore ﬁrst consider the home-production of printed circuits for the benefit of readers who are unfamiliar with the techniques employed in this process.
There are actually a number of similar ways of producing your own printed circuit boards, and the method that is described below is the one usually utilized by the author, and one that is also very simple and easy in practice.
Step #1: PCB Tracing
First it is necessary to have a full size drawing giving the positions of the holes in the board, and this drawing must be actual size as it will be used as a drilling template. This can be traced just like as shown in example PCB Figure 1 using either proper tracing paper or any thin paper such as typing copy paper, after cutting the paper down to the same size as the board. Some double-sided tape can be used to keep the paper in place while the tracing is being made.
Next a board of the appropriate size (approx. 78 X 42mm) must be cut out. Various types of copper laminate board are available, and in this non-critical application any single sided board should be perfectly suitable (i.e. any board coated with copper on one side, not one having both sides coated).
For the home-constructor SPBP board is probably better than one having a fibre-glass base since the glass in fibre-glass tends to blunt drills, saws and files used to work the material, and the extra strength of this type of board is not usually needed in home- constructor projects. The board is cut to size using a hacksaw, and if necessary a ﬁle can be used to tidy up the sawn edges.
Step#2: Drilling Holes on PCB
Now the holes in the board should be drilled, and in order to achieve this the tracing is ﬁxed to the copper side of the board using double-sided tape. The holes are then drilled through the drilling point marks on the tracing being as accurate as possible.
Ideally a miniature drill ﬁtted in a stand should be used to do this, but a hand drill can also be used, as can a full-size electric drill (although the latter is not recommended unless it is mounted in a stand).
Accurately positioning the holes is likely to be very difficult without a stand for the drill, and one way around this problem is to use a bradawl or similar tool to make small indentations in the board at the points where the holes must be made.
These will then tend to keep the drill bit in the correct place while each hole is drilled. However, be careful not to press too hard when making the indentations or the board could be damaged.
The ideal size for the holes for the component leadout wires is about lmm or 3/64in. Using a diameter much larger than this is likely to make it difﬁcult to solder the components into place neatly and reliably, while a diameter much less than this is quite possibly going to be too small to take the leadout wires of some of the components!
Drills of such a small diameter are inevitably rather brittle and easily broken when compared to the larger types with which most people are more familiar. Treat them reasonably gently so as to avoid unnecessary breakages. The two larger holes in the board are the mounting holes and are 3.3mm in diameter. GBA or M3 mounting bolts can be used.
The next step is to thoroughly clean the copper side of the board, and a simple way of doing this is to use a scouring pad, being sure to rinse off any soap from the board by running it under hot water (which will also help to remove any grease as well).
The point of cleaning the board is that this helps to speed up the etching process, and it might otherwise be found that the etch resist will not take to the board properly. Once the board has been cleaned try not to handle the copper surface as this would tend to make the board greasy again.
Step#3: Applying Resist on Tracks and Pads
The board is now ready for the etch resist to be applied, and the resist is simply paint or ink which is applied to the board over the areas where copper tracks are required. The board is then placed in the etchant which removes the copper from . other areas of the board, leaving only the required copper tracks.
You can use virtually any paint as the etch resist but it must of course be a water resistant type, and a quick drying type is preferable. The etch resist can be applied with a small brush, or an exhausted ﬁbre-tip pen can be used in the same way as a brush. As the track pattern is fairly complex, on this PCB it is essential to apply the etch resist with a very ﬁne brush or pen.
Etch resist pens are available at quite low prices, and using one of these is almost certainly the easiest and most convenient way of applying the resist to the board.
The copper track pattern is simply copied from Figure 1, and the finished result does not have to look as neat as the diagram. Provided there is a small pad of copper around each hole, and the tracks connect the holes together in the correct fashion the finished board should be perfectly usable.
Make quite sure that the resist covers the appropriate areas properly and that the tracks are not excessively thin, otherwise on the etched board it is possible that there will be breaks in the tracks.
If the resist should bridge two points that should not be bridged, simply let the resist dry and then scrape off the unwanted resist using a compass point or something of this nature.
Step#4: Preparing the Etchant
The etchant normally used by home-constructors is ferric chloride, and this is available from a number of the larger component suppliers and it comes in three forms.
The easiest way of obtaining it is as a ready made solution which is almost ready for use as supplied. If only needs to be diluted with water in a one to one ratio (or, at least, the solutions obtained by the author have always been of this type if the solution is supplied with instructions stating other than this then these instructions should obviously be followed).
Anhydrous ferric chloride powder is available, but is not recommended as it is hard to make it into a solution. Ferric chloride is also available in crystalline form, and in this form it looks like chunks of yellow-brown rock. 500grms of ferric chloride crystals is sufficient to make about 1 liter of solution, and it is quite likely that the crystals will not dissolve very quickly.
Using warm water and stirring the mixture will considerably speed up the process. One or two points must be borne in mind here, and the most important of these is that ferric chloride ls poisonous.
It should therefore be treated carefully, wiping up immediately any that is spilt and disposing of the paper or rag used to soak it up. If you get any on your skin always wash it off at once using plenty of water.
Do not use containers that are used for food when mixing or using the etchant. Another important thing to remember about ferric chloride is that it attacks many metals, and not just copper.
In practice this means that you should not use or store it in a metal container. or even in one having a metal lid or cap. Use tweezers when manipulating boards in the solution, but plastic tweezers not metal ones.
Do not place the board in the ferric chloride solution until the resist has dried properly. Make sure that the etchant properly covers the copper side of the board with no air bubbles on the board.
The board will etch more quickly if it is held upright or up-side-down in the solution, although it might be difficult to achieve this in practice. The board can usually be positioned upside down if the solution is held in a round bowl of a suitable size.
When using this method it is essential to have some clearance between the underside (copper side) of the board and the container used to hold the etchant or the etching process will be severely slowed down rather than speeded up. Using warm etchant and occasionally agitating it also helps to speed up the etching process.
The time taken for the etching to take place depends on numerous factors, but usually takes between about 5 minutes and an hour.
Do not leave the board in the etchant any longer than necessary as this could result in the wanted copper being slowly removed along the edges of the resist and at any points where the resist is weak.
Rinse the etched board to remove any ferric chloride solution and then remove the resist.
It is possible to obtain resist remover, but a scouring pad is also suitable and will also make sure that the copper track is very clean so that good soldered joints can be made easily when ﬁtting components onto the board.
Your homemade PCB is ready for use
It is not essential to buy the items needed to produce printed circuit boards one at a time, and a few etching kits and printed circuit kits are available and worthy of consideration.