Sodium Carbonate also known as Soda Ash used for adjusting swiming pool PH.
Don VK3YV....
----- Original Message -----
From: "leon Heller" <leon355@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Saturday, October 11, 2008 8:34 PM
Subject: Re: [Homebrew_PCBs] Dry film woes, maybe the developer is at fault
> ----- 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
>
>
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4:08 PM