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Old 4th Jul 2017, 10:47 pm   #5
David G4EBT
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Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 3,333
Default Re: UV Dry Film PCB technique - experiences to date.

Originally Posted by Oldcodger View Post
Reading/watching with interest, David, as I'm in the final stages of my light box. Problem I'm finding is getting small quantities of negative developer so I can play.
The negative film developer is sodium carbonate, commonly known as 'soda ash' used extensively in water softeners.

It's widely available in small quantities on ebay (from 100g upwards). You need a solution of 100 ml of water to 1 2 grams of Sodium Carbonate, so 1 Litre of water requires 10 20 grams of sodium carbonate. 1 gram is 1 level teaspoon, (which is 5ml). I usually make 250ml of developer, stirring 5 grams of crystals into 250ml of lukewarm water. I've developed a board today - it only takes about 30 secs - I keep taking it out of the developer and gently rubbing it with kitchen roll, which is slightly abrasive, till it's all dissolved, then rinse it in clear water. The dissolved UV film turns a sort of 'soapy' grey colour and texture. Being negative film, it's the unexposed areas that dissolve, and the exposed areas remain on the board as the PCB tracks - the opposite of positive resist.

Really, 100grams is all you need to start you off - that would make up to ten Litres of developer. That would only set you back 1.79, post free from a UK supplier. EG, this one will supply 100G upwards (100g 1.79, 1kG 5.99) post free:

250grams here for 2.80 post free:

It's much cheaper than positive resist developer - lab grade sodium metasilicate pentahydrate is typically 12.99 per kG post free from a reputable UK supplier.
Or the same quantity can be had from Maplin at 33.28. (I won't mention MEGA).

Hope that helps a bit - good luck in your endeavours..
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