DCC Topics


PCB DIY (Do it yourself)

One of the difficulties of modern times is that the electronic circuits have become very very small and almost impossible to prototype with them. I had to use always a breadboard or a universal PCB that only allowed DIP or big components.

I wanted to work with SMD (Surface Mount Devices) chips that usually are more powerful and are smaller, but this was the disadvantage for me and for many hobbyists.

A friend from Argentina once told me about a method to make your own PCB in home with no expensive components or complicated processes. This method is Toner Transfer.

There are a lot of resources on the Web that explains this method in deep. Here are some of the useful links that helped me in this process.

- http://www.fullnet.com/~tomg/gooteepc.htm

- http://www.michaeladams.org/Electronics/PCBs

- http://www.youtube.com/watch?v=urv6jArKp6M&feature=fvw

I first made a double side PCB for the autoreverser and block detector. It was a big (10 x 12 cm) but simple circuit. The difficulty was to align the two sides of the PCB to make the through holes match. I used for this PCB magazine paper to try something VERY inexpensive. I found that those magazines with very strong pages are more difficult to peel after the transfer is done, but worked. If you don't have photo paper you can try with magazines. If the transfer is not what you where expecting then you can wipe it out with acetone or Thinner and start over. I did this about 6 times until I was satisfied with the transfer.

Tips to align the two sides:

Mirror the top layer and print it. The bottom side is normal. Once you have the both prints face them inwards and use a bright light to look into them. Make some corner holes to match. I used in my circuit some marks outside the board area that helped me align the circuit. There where multiple crosses around the board.

Once you have matched some holes or crosses, use some masking tape. Place this tape as far from the board area as you can. That's because when you insert the unprocessed PCB between the two sheets of paper there is going to be a very low deviation due to the width of the board. Be sure to use enough tape to keep things in place.

The next step, as I mentioned earlier, is to place the PCB in the middle and pray it would match :-).

Now there is the same method as described in the links.

In many sites say that you have to move the tip of the iron for every inch of the board making a lot of pressure. I did this a lot of times but when you are working with very low pitch or gap between the pads (like TQFP or SSOP) it always ended in melted pads and a lot of shorts. I will discus this latter.

When you ironed the PCB for several minutes (depending on the size of your board) you have to wait for it to cool down. If you are like me you wont wait, but you have to because the toner could be weak in the hot copper. Once it is cold, it's time to soak it in water for about 15 to 20 minutes. If the paper you are using has many layers, you can peel the first one to let the internal layers to soak better in water.

After that you can gently remove the paper with your fingers at the beginning. Be careful not to scratch it with you nails or other hard material because you may remove the toner and you will have to start over (i did this :-(    )

To remove the remaining paper, I used an old tooth brush with soft circular movements and long runs on the tracks I wanted to clean. Always used a lot of water to do this.

Finally the etching process is to get rid of the copper. There are different chemical methods like the Ferric Chloride or the Muriatic acid and Hydrogen Peroxide. You can find a lot of information about this in Google. I used Ferric Chloride but the next time I think I will use the other method. Be careful with the disposal of the Ferric Chloride because it can damage your drain and worst.. it is dangerous to this world!!!!! After etching 3 or 4 circuits you can mix it with Caustic Soda to neutralize it and make some solid copper balls. For more information visit http://www.mgchemicals.com/techsupport/ferric_faq.html

Here are some pictures of this first attempt.

Top Layer
Bottom Layer



SDM or SMT PCB in my home

After making this PCB, I wanted to use the PIC32 I have ordered as sample to Microchip and I began to search for references to TQFP footprints and I found Michael's blog that inspired me to build this PCB and opened a big door for using edge technology keeping costs low.

I designed a circuit with two TQFP (0,5 mm - 19 mil pitch) , one SSOP (0,65 mm - 25 mil pitch) and one SOIC (1,27 mm pitch) and 10 mil (0.254mm) lines. I also tried a 8 mil (0.2032mm) lines with no problem at all.

This circuit do nothing but to demonstrate it is possible to achieve 0.5 mm (19 mil) pitch with 10 mil (0.254 mm) gaps).

For this project I had to use photo paper because the magazine paper didn't work as expected.

Also I didn't apply a lot of pressure to the iron. Just swung the iron like doing laundry.

Here is the result. I'm really happy!!!!!!.

If you have any comments or questions just send me an email



Here is a picture of the 64 pin TQFP 0.5mm pitch and a SSOP soldered. It was a difficult task but I could make it! Maybe it's not the best solder you'll ever see but before today it was impossible for me.

Here is a picture taken with magnification microscope of a 0.5mm pitch connector of other board