Homebrew PCBs

Phil wrote:

> I get a quart of acetone for like $2.50 from home depot so its a 
> truely minimal expense.  I think its even cheaper in gal quantities. 
> I've used maybe 1/4 of it and washed about 20 boards. So it costs 
> litterally pennies per washing.  I just use a thin dribble on the 
> board and scrub with an old toothbrush.  voila!  clean and ready to 
> scrub for the next test run.
> 
> I'm really beginning to appreciate how much variability paper imparts 
> to the process.  
> 
> Alan, I hear your point on the difficulty of getting pressure right 
> but I'm even more convinced that its the critical factor.  Laminators 
> will give even pressure so that's a good reason to get one.   maybe 
> I'll break down and buy one...  

   No, you shouldn't need one.  With magazine paper you may as well have been 
printing on solid acetate or glass.  Toner on glass or acetate and press against 
copper and of course the toner is going to smash.  With this paper you have some 
thickness, the toner and coating bond and are pushed into the paper more.  I can 
look at the printed page and see that the toner is more pushed into the paper 
which it's not on acetate etc, it's basically flat with the unprinted coating. 
This helps lock things together and the toner doesn't smash when ironing.  I was 
just giving a reasonable example, I just dial my arm to 'plenty' and have no 
problems.  I could probably do 10 pounds, or do 50 without significant spreading 
of the toner, it is non-critical.  It is so easy the thought of getting a 
laminator never ever enters my head, no need for extra hassle or equipment 
sitting around for little reason when this works great.  The 50 cent paper isn't 
enough to drive me to wanting one for cheap or free paper for moderate use.  My 
point on difficulty getting the pressure right was for the magazine paper.  It 
is easy or more correctly doesn't matter so much with these other papers, the 
main reason to use them is to get good prints easily without extra equipment.

   It did take some experimentation for me to start getting an initial feel for 
it, but it'll come fast.  And the extra fusing makes it even easier than when I 
started without that.  But you're fighting other habits from the other paper, 
may take you a few more tries to be getting the idea.  This takes more heat and 
a little more time, and moderate pressure.  Tack the corner down and iron the 
rest on.  Then put the iron on and heat things up, just with light pressure for 
2-3 minutes for heating up.  Then with hard as you can being full, give about 
1/2 to 2/3 full pressure for 30 seconds or so, then move the iron around some 
pressing a bit, then another 30 seconds or so good pressure.  Then keep 1/2 on 
for another 2-3 minutes, that should be enough.  This should really be a bit 
overkill for a small board, but enough to make sure you get an ok transfer, you 
can cut the last heating time down to whatever works after you get a good 
transfer or two.  And with a good transfer you should notice that the traces are 
all about even, when you of course still put more pressure in some places than 
others.  This paper should be a lot less sensitive to exactly how much pressure 
was where as long as you got at least enough heat and pressure to get the 
bonding everywhere.  I have to go out of my way and actually try to press really 
hard in one spot to get any smashing of the toner.

   Also note that your toner could easily be 20 degress off from mine in melt 
temperature.  So I'm describing what works well for me, you may have to vary it 
a little to get good results for you.  Should be doable though the temperature 
difference isn't that extreme.  Different toners can be very different overall 
though not just temp, but the paper should help mitigate that.


> 
> By the way, are people preheating their boards?  I put them in the 
> oven at 250 F to dry them out and then go straight to the transfer 
> stage.
> 

   I tried it some, but tend to just iron a minute longer or two now.  Doesn't 
seem to make too much difference either way.  It's technically better, since you 
for sure won't have water trapped and making steam to keep the toner from 
sticking.  But I don't get much of that type of problem so don't bother with the 
oven.  I think hair drying the board a bit after the final wash probably does 
about as well.

Alan