I used negative etch resist, with boards I coated myself. I used a vertical
etching tank w/ a heater and aerator (aquarium items). That kept the etchant
active and circulating/mixed. My etchant was ammonium persulfate. Sodium
persulfate works too, and it is compatible with etch resist pens. Either type
remains transparent (blue) as it gets used, so you can see when the board is
done.
After getting my process down, I was able to produce fine pitch artwork. Now,
decades later, I can't see it!
Today, if a design was at all complicated and/or had fine-pitch stuff, I'd just
have a board house "burn it".
vy 73,
Bryan WA7PRC
Date: Sun, 03 Aug 2014 09:16:21 -0700
>
>From: Jim Lux
>Subject: Re: [TowerTalk] How do you get a good looking trace when etching?
>
>On 8/3/14, 8:38 AM, Roger (K8RI) on TT wrote:
>> Over the years I've tried etching boards with various methods. I have
>> never gotten a good looking trace. Whether the trace area is cleaned and
>> painted on, or photo sensitive, the edges are always irregular. They
>> are not straight and taper to a thin edge. Just what you don't want.
>>
>> Temp, chemicals (Typically Ferric Chloride IIRC), chemical dilution,
>> agitation: All according to directions with the same results. I finally
>> gave up.
>>
>>
>
>Kind of straying a bit, but since we're building LC tuning networks and
>antenna switches, and "tapered edges" are bad from breakdown standpoints..
>
>There's a huge amount of difference between how commercial boards are
>made and how home boards are made. You may not be able to get
>"commercial fab" quality.
>
>The etching process is a tricky one, and they adjust the chemistry and
>process to get a straight down edge, neither tapered out (like you have)
>or undercut. I'd venture that none of the commercial houses use a
>chloride etchant, the primary virtue of which is that it's "safe".
>Given the reek of ammonia at the last fab I visited, I'm going to guess
>that they use some ammonia complex in their etching. They also spray
>the etchant onto the panel, with filtering and reprocessing of the
>etchant (probably to insure that the chemistry *at the etch point*
>remains consistent).
>
>I think they also use a multi step process commercially, where they put
>a photo resist on, expose it, then electro plate something ONTO the
>copper (tin?), then strip the resist, and etch the copper that isn't
>plated, using the other metal as the resist.
>
>
>30 years ago, a friend and I were fooling with using nitric acid as an
>etchant when making nitrogen laser panels.. very fast, but there are
>some handling issues. But we got real nice edges with very simple resist.
>
>These days, there are so many quick turn prototype board houses out
>there that it's almost not worth trying to make your own boards. After
>all, it's not the etching that is the hard part: it's doing the holes,
>plating through, etc.
>
>Much easier to send a file to a fab and get your board back a couple
>days later.
>
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|