Homebrew PCBs

----- Original Message ----- 
From: "Andrew" <andrewm1973@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Tuesday, April 10, 2007 2:27 AM
Subject: [Homebrew_PCBs] Re: who does SMD ?


>> Adam Seychell wrote:
>>
>> I'm wondering what other people are doing
>> out there for PCB that use SMD.
>> <SNIP>
>> I use photomasks from a inkjet printer.
>> <SNIP>
>> I can just get away with 0.008"(0.20mm)
>> lines/spacings. 18um foil instead 36um
>> makes etching fine traces a lot better.
>
> I do pretty much the same as you do
> except I use a large colour laser printer
> instead of the inkjet.
>
> Routinely get 8/8 thou across a large
> board (150x300mm).  Will do 6/6 but will
> try limit PCB size to 50x75mm so I can
> fit 4 boards on small blank to make sure
> I get one of the 4 that does not look too
> thin.  That is mainly due to uneven etch
> I think.

It might be due to the board being bowed, so that the transparency isn't in 
contact with the resist over the whole board. I had that problem recently, 
with 12 mil tracks and a largish board - some of the tracks disappeared. I 
thought it was uneven etching and made three boards before I realised the 
cause.

Leon