Who does no know the problem, when playing with electronics one wants to use more and more advanced parts. Quickly comes the point where parts are not longer available as Dual in-line package (DIP) and one needs SMD packages with many pins. Also “Prototype PCB Experiment Matrix Circuit Board”s reach their limits. It comes the point where one wants to produce its own PCB via etching.
I came also to this point when playing with more and more advanced microelectronics. So I decided to investigate the possibilities of etching.
I think some things are essential:
* A PCB (with photo sensitive coating)
* Some chemical to etch ( I choose sodium persulfate)
* Developer for photosensitive resits (Sodium hydroxide NaOH)
Some people prefer a transfer method where they transfer the toner of a laser printer via heat onto the PCB before etching.
I decided to expose the photo coating of the PCB via a light source and then develop the whole thing and after this etch it.
There are may instructions out there often requiring expensive UV light sources and special transparent paper.
This is very expensive specially if one is unsure if it will work and if one wants to continue with these kind of production of electronics components.
But there is also a cheep way which actually works pretty good.
The only thing one needs is:
* A laser printer or copy machine
* normal paper (This gives really the possibility to use printers in copy shops, at work or any where else)
* A halogen light around 500 W
* Some oil ( for ex. cooking oil)
* Something to drill
With this it is possible to produce structure of the size of 10 mil or less!
The first thing was to build a light board. For this one needs a construction lamp, a picture frame (IKEA) and something to hold the whole construction.
I mounted the picture frame 20 cm above the construction lamp, in the way that one can put the PCB layout onto of the glass and on top of this the PCB. The safety glass of the construction lamp should be removed since it is absorbing too much UV light. So the light from the construction lamp goes through the picture fame glass, though the paper with the PCB printout and exposes the photosensitive resit. It should be noted that the printed site of the paper should be closes to the PCB, which also means that it needs to be mirrored in order to have the right direction.
The Light board looks like this:
In order to expose the PCB I was creating with eagle a PCB design and printed it.
Here an example of an Arduino layout:
Now comes the part where the cooking oil comes into the game.
The problem of normal paper is that it is not transparent enough… so lets make it transparent… put it in oil.
After the paper is completely filled with oil one can remove with some paper towel the rest of the oil and will see that the paper became transparent.
Now the paper only needs to dry for a while (if one is in a hurry it works also with the wet paper) and one can start to expose.
The exposure time in my case was about 300 to 330 seconds.
After this the PCB needs to be cleaned with some dish washing liquid in order to remove the oil which stick on the exposed PCB.
This can be done by moving it through some water with cleaning liquid. Then wash it under normal water and put it into the NaOH mixture to develop it.
Now the photo sensitive coating is not sensitive any longer and one can make a break. The next step is to put the PCB into the sodium persulfate to etch away the cooper.
It is good if the liquid is warm but for me it worked also with cold liquid… it just takes forever (30 to 90 min) with warm water and air bubbles running through it is supposed to be much faster.
I will not go into too many details here there are a lot of explanations out there about the etching… I just want to show that one needs not much advanced equipment.
After etching comes the drilling, one needs to drill a lot of holes. It has shown that if one etches a small hole 0.5mm in the middle if the soldering eye it is much easier to dill a hole in the middle since one has already some kind of stirring.
In Eagle there is a ULP called drill-aid which makes all holes of the size one wants by adding a circle in the hole. Very useful when drilling by hand.
I do the drilling with drill holder a very cheep drilling machine from the local construction marked and a PCB drill.
With some skill it’s no problem to drill holes of the size of 1mm. For me it turned out that drilling with a lower speed works much better then with high speed what is often recommended. As a drill I use a PCB drill of 1 mm which fits into a chuck of 3 mm.
All in all I payed for the equipment:
* Chemicals around 10 Euro
* Construction lamp 8 Euro
* Picture frame 2 Euro
* Drill machine 16 Euro
* PCB Drill 2 Euro (cheaper on ebay)
So less then 40 Euro… which is I think worth to try etching PCBs
Even with this poor equipment one can produce reasonable results:
A simple Atmel Mega ATMeGA328P-PU (Arduino) breakout board
A breakout board for the ATMEL AT 91SAM7S64-AU, the board is approx 60 x 60 mm, the PCB track is 11 mil (279 um).
Even double sided PCBs are possible! Even though a very good alignment is needed! A hard part are the vias, but these can be soldered with a piece of cooper wire.
The board size is 80 x 80 mm and the tracks are produced in 11 mil (279 um).