Home Construction Techniques

Circuit boards

When you're talking self-designed home electronics, you obviously don't have the luxury of using ready-made printed circuit boards.  With one-off projects, it's hardly worth designing and making your own PCB.  For the home constructor, it is a whole different ball-game.

For what it's worth, here are a few techniques I use to make one-off boards and still end up with a professional result.  I have worked on both low-end and high-end equipment and "borrowed" some ideas from various manufacturing techniques I have seen.

• I use Veroboard (or similar), with 0.1" (2.54mm) hole spacing.
• I design the board layout in a CAD program, laid out on a 0.1" grid.  For things like op-amp stages, I try to use a standard layout.
• When designing the layout, I make no attempt to isolate tracks which are connected to ground or to a de-coupled power rail, since when such tracks pass between tracks carrying sensitive signals, they act as shields.  In critical situations, I go to the trouble of connecting unused tracks to ground to help form a crude ground plane.
• I use the drawing to cut the tracks in the correct position, before installing the components.  You can get a special tool for this purpose, or use a standard twist drill.
• I mount the board on threaded M3 metal spacers and screws.  Veroboard is brittle and solid mounting like this helps to strengthen the board.
• For short links on boards, I use wire off-cuts from components.
• For longer links and colour coded links on boards, I use insulated single strand copper telephone wire.  This is much easier and neater than trying to use flexible stranded hookup wire.
• In the example at right, two open collector outputs on a quad IC are connected together.  It is no co-incidence that I picked two sectors that have their output pins opposite each other on the IC!  All I had to do for my trouble was not cut the track between pins 2 and 13.
• In the example at right, pins 4, 6 and 10 are connected together.  By offsetting the track cuts, all I had to do was install a simple link on the solder side of the board, saving valuable real-estate on the top side of the board.  Once again, I considered sector designations to achieve this.
• Sometimes, you might want to link a number tracks together vertically (for example, you want to connect every second pin to ground on a connector).  I save the wire off-cuts of components and wrap these around the common wire.  I temporarilly place the links in holes in the board to hold them in position, solder them, remove them from the board and trim off the excess.  Presto - an above-board link!
• I avoid any situation where heavy currents (say >1A) flow in a circuit board.  For high current, high voltage or mains, I always use conventional wiring and tagstrips.
• If a board is connected to a high power rail such as the +12V rail of a computer power supply, a short on the board would probably vapourise the track, or could even cause a fire.  Therefore, I use a small carbon resistor, spaced off the board, mounted as close as possible to the input pin to act as a fuse.  The value is calculated so that its rated power dissipation is exceeded by a factor of at least 10 under short-cicuit conditions, to ensure that it will quickly burn out.  Metal film resistors are not suitable, as they are more likely to get very hot before finally burning out.  The value of the resistor must be also chosen so that under normal operation, the voltage drop is negligible and its power dissipation is well within its limits.  In cases where this is not possible, another trick is to partially drill out the track so that you create a "weak spot" in the track, which will burn out under short circuit conditions.
• Apart from special situations such as above where I intentionally space a component which may burn out off the board to avoid damage to the board, I normally make sure that all components sit firmly on the board.  The reason for this is that if a component sitting off the board is hit from above, it could break the track underneath.
• When construction of the board is complete, I use a sharp tool to run down between the tracks to ensure there are no accidental solder bridges.  If there is not enough room between the tracks, this is probably due to excess solder or an overhanging component lead.  I will sometimes go to the trouble of desoldering and resoldering a joint to correct this problem.  Whilst doing this, I closely inspect all connections for dry joints or broken tracks.  I also check the track cuts.  After this, I clean the board with a solvent (acetone is best but WD40 with a stiff brush works at a pinch) to remove excess flux.
• I never attach external wires directly to the board.  This is difficult to do and they often snap off with repeated movement, leading to potentially dangerous situations.  I consider board connectors essential and they make it much easier to remove and work on the board.  These days, the 0.1" PCB connector system is readily available from places like Jaycar Electronics.  I place the male headers on the board and try to design the pinout to simplify the board layout.  In a home environment, you are often dealing with different types and guages of wire.  I both solder and crimp the wire to the female pin.  A crimping tool is a must, but this does not cost much.  Some suppliers sell pre-made leads, which might be suitable for some projects.