gEDA-user: footprints -- novice`s problems

[Dan McMahill]

Dave McGuire wrote:
> Igor2 wrote:
>> Someone sells special film for this purpose, and that costs much. I am
>> not an expert, so I may be wrong on the mechanism, but I think the idea
>> is that the laser printer doesn't use ink but some sort of polimer that is
>> melted on the media. If the media is paper, some of the polimer paint
>> works off in the paper. If you try your good old non-ball-point pen with
>> normal paper, it 'drinks' the ink. However, if you use the special film,
>> it has a shiny surface which won't 'drink' the ink or paint. The trick is
>> not to buy that special film, but use some shiny paper with similar
>> surface. This kind of paper is used for magazines and printed spam. It's
>> usually thicker than normal paper. (I can't translate the name of the
>> paper, my dictionary lacks this word.)
>>
>> I could buy some in a local decoration shop, in my experience most
>> printers can handle ones between 100 and 130 gram/m^2. The critical part
>> is when the printer tries to feed the paper and it slips.
>>
>> Someone reported that he was too lazy to buy such paper and used some spam
>> or magazine. I haven't tested this, it may be an urban legend. 
>>
>> I hope this helps; if my description was not useful enough, I could
>> snail mail you a sample.
> 
>   Very interesting...Yes I think I understand what you're describing.
> I've not tried anything like that; I would like to do so at some point.
>  Perhaps soon.  Thanks for the info (everyone else too!)
> 
>         -Dave
> 

Hi Dave,

Here are the 2 things I've used for the toner transfer method.  One is 
called "Toner Transfer System".  Interestingly nothing in the 4 pages of 
documentation in my leftover stash of it indicates who makes it. 
Doesn't matter because I didn't think it worked very well.  Basically it 
is a shiny paper.  The important bit is if you use regular laser printer 
paper you'll get these little paper fibers which will be stuck to the 
toner and they'll transfer to your board and its pretty easy to get tiny 
little shorts.

The other stuff I've used is called "Press-n-Peel Blue".  It is made by 
Techniks Inc.  Ringoes, NJ.  This stuff is some sort of plastic sheet 
which feels like a transparency sheet.  One side is coated with some 
blue stuff that gives sort of a matte finish.  You print onto the blue 
stuff.  When you iron it on and then peel it off, the blue stuff that 
had toner on it peels off to which gives an extra layer of etch resist. 
  My notes from about a decade ago read:  "Set iron on edge between 
wash+wear and wool.  Let the board cool before peeling."  They claim you 
can get 5 mil traces with this stuff but I'll believe that when I see 
it.  I did get reasonably good results.  My biggest complaint is that 
its really only good for 1 layer as it is rather difficult to align 2 
layers.  Also I don't have a chemical sink and hood in my garage along 
with convenient and environmentally friendly ways of dealing with the 
etchant.  Also I never had a decent heater or agitator both of which 
seemed to be important.

What I've settled on is that for quick prototype builds I like to use 
this checkerboard material I have.  I used to use a pattern of 90x90 mil 
squares on 1 100 mil pitch.  Since then I've moved to 40x40 mils on a 50 
mil pitch.  This is on the top of the board and the bottom is solid 
ground.  I've found that I can very quickly prototype things with 1206 
and 0603 passives, sot-23 and similar sized transistors and DIP or SOIC 
parts.  You can do a suprisingly good job of placing the parts so you 
don't need to add a bunch of wirewrap wire for jumpers.  For ground 
connections, I just drill down and stick in a bit of 30 AWG wire and 
solder the top and bottom.  FWIW I have prototyped a complete TV tuner
frontend with this method and had no problems with signals in the
several 100's of Mhz range.  I find this method to be very fast with no 
real speed penalty for circuits which work up to close to a GHz. 
Obviously microstrip is a bit more work although at one point one could 
buy copper tape of varying widths.  That worked better in the days of 62 
mil dielectrics and not as well with a 10 mil dielectric.

For a lot of stuff though, I can wait the 2-3 days for a quick turn 
board house.  I usually have plenty of stuff to fill the intervening 
hours with!

-Dan