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Concentration of PCB Developer

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mikeb
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Username: mikeb

Post Number: 1133
Registered: 02-2008

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Posted on Monday, 16 February, 2015 - 12:10 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I am trying to reduce the cost of pcb developer that I have used for many years - PDN from Electrolube. Its about £4.00 and gives me about 10 large boards, say 15 small boards.

I have been given some powered Sodium Hydroxide 39.99 g/mol.

Can any of the chemists among the CZ'ers tell me what dilution to mix? Does anyone have a cheaper solution (sorry for that one - could not resist).

rgds

mb
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chippie
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Post Number: 345
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Posted on Monday, 16 February, 2015 - 12:33 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

From my O level chemistry....

Mass (g) = Concentration (mol/L) x Volume (L) x Molecular Weight (g/mol)
You do the maths....-:-)
eccentric millionaire financed by 'er indoors
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mark_r_abcd
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Username: mark_r_abcd

Post Number: 28
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Posted on Monday, 16 February, 2015 - 01:11 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Just to add a reminder when mixing NaOH solutions, always add the powder to the water, add it slowly and bear in mind that the solution will heat up as the solid dissolves. Also don't use any aluminium containers or utensils because they will react and release Hydrogen gas.
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gordon
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Post Number: 1053
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Posted on Monday, 16 February, 2015 - 01:48 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Most of the photoresist boards seem to work with about 7 to 14 grams of sodium hydroxide per litre of water. You will probably need to experiment on a small board, starting at the lower concentration, to find the concentration of sodium hydroxide that works well with your boards and process.
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joe
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Post Number: 1484
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Posted on Monday, 16 February, 2015 - 02:28 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I always use two level caps (red caps from a WD40 spray can) of hydroxide to 5L of water.

Not very scientific but works a treat for me.


Regards,
Joe
My projects, technical info and ramblings at www.hobbyelectronics.net/
There are two types of people... those who design aeroplanes, and those who design parachutes.
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mikeb
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Post Number: 1134
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Posted on Monday, 16 February, 2015 - 09:07 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks all - that will get me started - I will CAREFULLY add powder until I get some action (thanks for reminder mark_abcd).

rgds

mb
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zeitghost
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Post Number: 1941
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Posted on Tuesday, 17 February, 2015 - 11:42 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

And don't forget to use proper eye and hand protection.

You can't feel hydroxide burns until it's too late.
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mark_r_abcd
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Post Number: 29
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Posted on Wednesday, 18 February, 2015 - 11:42 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

The powder is horrid. If you spill just one grain and then lean on it, it sticks to you and (being hygroscopic) makes a tiny drop of concentrated liquid. As zeitghost says, the first you know of it is when it feels like someone is poking a hot needle through your skin!

I have a badly plumbed shower that needs flushing out with caustic once a month or so, and familiarity breeds contempt - been there, seen it, got a tee shirt full of holes (it eats cotton too).
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mikeb
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Username: mikeb

Post Number: 1135
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Posted on Wednesday, 18 February, 2015 - 08:00 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks for the wealth of information and advice.

I have been a bit thick here - I was concerned that I would strip my boards which I did in the early days and it cost quite a bit.

Of course, I can simply add the powder slowly (at a reasonably controlled temperature) until I start to get development. I don't know what was going on in my mind.
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joe
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Post Number: 1485
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Posted on Thursday, 19 February, 2015 - 06:12 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Mike,

I personally wouldn't take that approach as it assumes there is a caustic concentration trigger point for when the development process starts. No matter what the caustic concentration, with the board sitting in solution the development process will start.

Also as you add caustic to the water, the solution temperature will increase which helps speed up the development process.

The upshot is that as you add caustic and the development appears to start the board has actually been sitting for some time in a caustic solution of varying temperature and increasing concentration.

My development tank holds 5L of water and I use 30g of caustic or 6g per litre of water.

This works ok for me on both fibreglass and economy laminate I get from Rapid Electronics.

The tank is heated to 42deg and development starts in around 5 to 10 seconds.

Over the years I've developed a little trick to see when the board has developed properly. When you can see the image on the board surface, if you remove the board and hold it so a corner is just above the caustic solution, you can watch the drops of liquid running off the board.
If they are purple or you can see the colour dissipating as the drop hits the solution surface, then the board needs further developing. As soon as the drops are clear, another dunk for a few seconds for luck (very scientific I know) and the board can be washed and etched.

Regards,
Joe
My projects, technical info and ramblings at www.hobbyelectronics.net/
There are two types of people... those who design aeroplanes, and those who design parachutes.

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