Incredible new way to transfer high complexity PCB layout images using an iron and a wooden dowel! This idea is nothing short of brilliant!
One thing I did to help get an excellent image transfer on larger board sizes, using just a household iron, was to use a wooden dowel under the circuit board as a way to achieve a high pressure point. What I do is to cut out my circuit board to the exact final size (this helps me line things up on double sided boards... I do one side at a time).
I place the TTS paper down on a smooth, heat resistant surface, toner facing up.
Next, I lay the circuit board down on top of the TTS paper, copper side facing down. Line up the board edges with the board outline that is on the TTS paper (I make sure to have a board outline present on the layout).
Then, I heat the board with the iron for about 15 seconds, just long enough to get the TTS paper with the toner to "tack" adhere to the board.
Now, I place a wooden dowel down on the smooth surface (I use a 7/8 inch diameter dowel that is 8 inches long). Next place the circuit board with the "tack" attached TTS paper on top of the wooden dowel, board down, TTS paper on top.
Put the iron on top of this, and slowly move the iron, TTS paper, and circuit board back and forth several times while pressing down with a goodly amount of pressure. To help with "slowly moving" the iron, TTS paper, and circuit board, use one hand on the dowel and slowly rotate the dowel. If the circuit board you are doing is larger than the bottom surface of your iron, move the iron over a bit relative to the circuit board/TTS paper and roll the dowel some more.
Its actually not too difficult to do all of this at once, and it really makes a big improvement in getting high pressure applied for a nice clean solid toner transfer! And, its even cheap!
You can check out a bit of what we are doing, for the Oregon Coast Repeater Group, at www.ocrg.org
I have been using 0805 sized surface mount devices for most of the resistors and capacitors in these types of projects lately... they are a good trade off for the price. I could easily use 0603's with as well as the toner resist works, but 0603's are still a little more expensive than 0805's. Using surface mount devices means having to drill fewer holes, although, vias then become somewhat more important! ;-)
For the vias, I use a 0.021" drill. I take a bare piece of 30 gauge wire wrap wire and use a flat nosed pair of pliers to squish the end of the wire flat (about 0.050" worth of wire). Then I bend the squished part over at a 90 degree angle. Next, I cut the wire to about 0.2" long, drop it into the via and solder the top side, flip the board over, bend the back side over and solder it.
By using the pliers to squish the wire flat, it allows the via wire to be very low profile and that will allow a surface mount IC to sit over the top of the soldered via/wire and still touch the IC's pads. I had been using rather large 0.075 via pads to allow for any mis-registration of the top and bottom layers, but with using the board outline and an exact size board lined up to the board outline on the TTS paper one could easily go down to 0.050" via pads or even 0.040" via pads. It has been proving quite easy to get really good registration top to bottom.
This fantastic idea send in by Paul Messer "WA7ZVY"