Homebrew PCBs

----- Original Message ----- 
From: "Stefan Trethan" <stefan_trethan@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Thursday, February 23, 2006 10:15 AM
Subject: Re: [Homebrew_PCBs] Re: Re: Photolithography - resolution


> On Thu, 23 Feb 2006 09:09:15 +0100, Richard <metal@...> wrote:
>
>> Lyman, congrats on your first photo-board.
>>
>>
>> You didn't say what your exposure tool was; but at the
>>
>> 1-mil level, you may well be running into effects of poor
>>
>> collimation; as much as any other factor.
>
>
> Yea sure, making 1mil traces, that's 25um wide, a typical pcb has 35u of
> copper thickness.
> So anyone telling me he is making PCBs with traces that are actually
> narrower than they are high is either very, very good, or a liar. 'Cause
> without directional etching like used for ICs that's just not happening.
>
> I think industry standard is 2mil minimum, but that's on thinner copper
> and with spray etching.
>
> From my experience, anything below 6.66mil is unreliable due to
> underetching. And that's the same with toner transfer and photoprocess. 4
> or 5 mil traces i could believe with a well set-up etcher, but 1mil, come
> on! And it makes no difference if that is photoprocess or toner transfer,
> the underetching is getting you first with both methods.
>
> So, unless someone shows me a PCB that actually has 1mil traces _made_
> _at_ _home_ i'll just take this at joke value, because i've been there,
> tried that:

I think that the really fine-line stuff is made by copper deposition, not 
etching.

Leon