Homebrew PCBs

----- Original Message ----- 
From: "David Hopkins" <davhop@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Saturday, October 11, 2008 3:49 AM
Subject: [Homebrew_PCBs] Dry film woes, maybe the developer is at fault


>I wonder if the resist is anything like the Riston blue -Ve acting
> dry film. This film is the main one used by the manufactures here.
> It sounds a lot like it.
>
> I have used this resist for many years.
>
> The exposure for this film requires a strong UV light source. A
> standard light would do little in the way of exposing it.
>
> I use a 300W mercury vapor street light at about 300mm. This gives an
> exposure of two minutes. The mercury vapor light produces a fair bit
> of UV light.
>
> With this light source I never have a failure.
>
> I notice you use Calcium carbonate to develop. The Riston uses Sodium
> Carbonate. I wonder If this would work on your resist. Sodium
> Carbonate is also known as washing soda and is very cheap. I think I
> paid about $25 for 25 Kilos. The mixture ratio is about 8 teaspoons
> to 4 liters of water (not the least bit critical). 25KG will last
> longer than I will.

The OP must have been wrong about calcium carbonate haveing been supplied. 
It's chalk, and won't dissolve in water. It musr have been sodium carbonate.

Leon