Homebrew PCBs

On Thursday 22 May 2003 12:17, Marty Grove scribbled:
> Hello Neal.
>
> I'm assuming that you are asking how clean the lines are after etch (as
> opposed to how clean the etchant is after you have etched some boards).  I

Yes, exactly.


> you are using the "swish the board around in the solution" method, I cannot
> say how the lines will turn out (I have practically no experience with that
> method of etching).  I would imagine they would be okay down to a certain
> width, but at some point I would think that the "swish" method would
> produce ragged, uneven, and/or broken circuits for a number of reasons.
> poor chemistry distribution, chemistry out of range (out of specification),
> chemistry getting up-under the resist, etc.

I had been using a flat tray, with the board sitting flat on it, and I'd 
heat/stir with a small hairdryer aimed so that the solution swirls in 
circles.  And I flip the board every few minutes. Got better results than 
shaking manually every few minutes.  Recently picked up an air pump for my 
new PCB "system" so I expect better results.


> Our equipment was applying the chemistry to the board by spray.  If all of
> the nozzles were properly clean, and the oscillation system that sprayed
> the chemistry was operating correctly (and the chemistry was in
> specification), the application of etchant was very evenly applied to the
> board(s).  The impact of the spray on the board (the impingement) speeds up
> the etching process considerably.  When using a high quality photo-resist
> and everything was working properly (including artwork, imaging, applying
> the resist, and developing), we were able to achieve line spaces and widths
> as small as 5 to 3 mil's with typically nice straight lines, and the

Interesting you mention spray.  I was looking into this for rinsing my boards 
(thinking ouf using spray nozzles from a car windshield washer) and thought a 
about it for etchant, but decided to choose an etchant before investigating 
if the etchant would corrode/damage the pump.  I would ask what spray system 
you use, but my guess is that anything industry-specific will be $$$.


> industry is currently trying to get even tighter tolerances.  I once read
> that in another 8 to 10 years, the industry wants to consistently achieve 1
> mil lines and spaces. <whew>

Heard similar as well.  I went to a PCB trade show late last year, and saw 
some 3-mil boards, and 40-layer boards .... holy #$%*&#@* !!!

Luckily I only need 10 mil for now, but need to get it consistent.  I'd like 
to make my system a "science" rather than an "art".


> I'm curious as to whether anyone has built their own home spray etcher (a
> small bench-top machine)?  It would be fairly easy (albeit the time and
> components required).

Someday.


> Cheers to you too!  I'm guessing you're in the U.K.  I'll be visiting the
> U.K. in about two months.  Although I've made several business trips over
> there, this will be my first vacation (holiday).  I'm looking forward to
> it!
>
>
>
> Marty
>

Actually, I'm in the US, but not sure where I got cheers from.  I lived in 
London for a year a few years ago, but I was using cheers before that.  And I 
doubt that I got it from my original home in the Caribbean.

Cheers,
-Neil.