michaeladams.org / Electronics
Often when making embedded computer systems you'll need to connect a bunch of devices such as resistors, external memory, USB plugs, analogue sources, power supplies and so forth to your microcontroller.

How you do this is up to you, however if you're like me and using advanced devices that come only in surface mount form then a PCB is the only way to go!

Designing a custom PCB is simple. However getting it made can be complicated. If you're lucky you know someone at university who can slide your project under the table when no one is watching. If you're less lucky you have to pay someone to make it and prices for one-off boards can be prohibitive.

But if you have access to a laser printer, some glossy photo paper and a domestic iron then you're in luck! Just follow my step by step guide!

Recommendations for making artwork
Oddly enough, the finer your board, the more likely it is to succeed!

Highly recommended is a polygon plane (aka a ground plane), created with 45° cross hatching, 12-15mil lines at 25-30mil spacing. Don't turn on the option to remove "dead copper". Net-to-net spacing should be 12-20mil, although I have successfully etched boards with 0.5mm track pitch.

Any text should be mirrored (if on the bottom layer) but the final pattern should be printed without mirroring or negative options enabled.

The choice of paper is important; I'm using Kodak "Picture Paper" which at 190gsm is horrible! What is important is that the paper is shiny and smells funny. This allows us later on to remove the paper while leaving the toner attached to the board.

Why is a finer pattern better?
I've found that when transferring the toner to a PCB, areas without any toner don't stick to the paper. Once the iron is removed the expanding gases and different expansion/contraction rates of the paper & board cause areas without toner to buckle and produce bubbles. The upwards pressure of these bubbles on the surrounding toner can act to lift surrounding tracks, causing annoying voids on the completed board!

By making the space between tracks very fine and using a ground plane, this can easily be avoided.

Another point is to use a cross hatched ground plane rather than a solid one, as the individual tracks in the cross hatching appear to grip better than one solid area of toner. They also seem to print better on older priters. I've found that if for any reason part of a solid ground plane should fail to stick to the copper and is lifted with the paper when removed, it will tend to take surrounding areas of the toner with it as well. By using a cross hatched ground plane I suspect this would be less likely.

Step by step guide

Part way through removing the paper.
Although quite an involved process it can all be done in a night and the result can be very good indeed! It just takes a bit of patience and some experimentation to determine the best process.

An example of what is possible — the finest tracks here are 0.25mm wide with even less space between them!

Completed SMT board