Title: "PCB's Made Simple"
Published: Aug 1993
Author: Peter Murtagh


The method that we use here at Silicon Chip to make our PCB's involves making a photographic negative of the PCB pattern (as given in all our construction articles), laying it on the surface of a piece of resin coated PCB material in a darkroom, and then exposing it to UV light. The copper immediately under the tracks - the only area exposed to the UV - is 'fixed' with a chemical developer, which then allows the excess copper to be etched away.

This photo-etching system is widely used, so any method which could eliminate the necessity to make a photographic negative, then use UV exposure followed by a chemical developer, would obviously have great appeal. This is precisely the attraction of the Toner Transfer System (TTS).

The idea behind TTS is that laser printers and photocopiers heat their toner image so that it melts and adheres to the paper surface - TTS simply re-heats the toner so that is can be transferred again, this time to the copper surface of the PCB.

However, after this is done, the toner image is fused to both the original and the new surfaces. How to separate them? This problem is solved by producing the image on a water-soluble coating on the surface of the TTS paper. This means that, when the board and paper are immersed in water, the soluble layer separates from the original substrate (the paper), leaving the toner pattern adhering only to the PCB.

IRON AN IMAGE!

To actually make the transfer, the method recommended is to use an ordinary domestic iron as the heat source. You place the PCCB (copper side down) on top of the paper (toner image up), and iron the image for several minutes.

Fortunately, once the toner has set (after immersion in water to remove the TTS , and drying), the pattern is etch resistant. Hence, the excess copper on the PCB can be removed in the normal fashion. Then, once the board is dry, the toner outline can be scrubbed off. [The easiest method is to use a paper towel wet with acetone.]

[The rest of the article goes into how to flip the artwork provided in the magazine and step-by-step process for making the PCB project.]

SUMMARISING

We were quite impressed with the results of the Toner Transfer System - once we had mastered it. It offers a very easy method for home constructors to make their own boards. However, you must be prepared for a reasonable amount of experimentation before you perfect the method. This is because different toners, different irons and different ironing techniques all effect the rate and efficiency of the transfer. But once mastered, you can quickly and easily turn out your boards.