Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


PCB wash chlorine

Michael Nguyen

#25927

PCB wash chlorine | 2 October, 2003

We are using a Trek board washing system with 2 deionizer tanks hooked up to the 2 final rinse tanks and the first tank is directly connected with the city water. We are having problems with a vendor board on some tranformer/chokes. The part manufacturer said that we have chlorine contamination on the magnetic wire coils that is corroding the wires. I am curios how much chlorine is suppose to be in the water? We bought a pool water test kit and we tested it and the reading is 1 ppm of chlorine? Is that ok? If not what can we do to reduce the chlorine level or a better method in testing the pH and chlorine levels? any assistance in this would greatly be appreciated. Thanks!

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#25928

PCB wash chlorine | 2 October, 2003

Who says the chlorine comes from your tap water? Our PTOW dumps boat loads of chlorine into our water periodically. Sometimes it's so bad you can smell it. We doubt that it is the source of your problem. This chlorine will volitize very quickly, be cleaned by your carbon bed, and probably will not cause a reaction to form salts on your boards.

What are the halide levels of the fluxes you use in soldering?

Consider that a better direction for your efforts to be to understand the residues left on your boards and components [shipped to you] by your suppliers.

Ion chromatography [IPC-TM-650, Method 2.3.38] is a reasonable method for measuring chlorine. CSL says, "We recommend maximum chloride levels of 4.5 � 5.0 micrograms per square inch for final assemblies processed with water soluble fluxes and 2.0 � 3.0 micrograms per square inch for a bare board (tin-lead coated) intended for a water soluble flux process. These recommended maximums do not presently appear in any nationally accepted specifications or standards, but are based on our failure analysis efforts with numerous customers."

How does your customer measure chlorine? What level of chlorine do they find unacceptable?

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Truett H.

#25929

PCB wash chlorine | 3 October, 2003

I would discourage the use of city water at all - where rinsing electronic parts is concerned, it contains too much contamination. If practical, route DI water to your first tank and implement some aggitation (either nitrogen bubbles from the bottom or up and down motion of the board carrier).

To optimize the process, run a multi-variate analysis. Meet with everyone available to you who has experience with the process and gather as many ideas from everyone present. Choose the "top 4 or 5" suggestions and run a matrix of every combination. For example, if you choose the top 4 suggestions, your test matrix will be 2^4 (16) parts and will include a control group. If you're interested, email me and I will explain further. Good luck.

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Dean

#25949

PCB wash chlorine | 4 October, 2003

It would help to run a carbon, anion, cation, mixed-bed configuration with pure DI as the final rinse.

IF your incomming water is really bad you can run a RO unit to "prepare" the water for ion exchange.

Do you run omega meter or ionograph testing of your wash process?

I would hold little faith in pool testing kits. What flux type are you using? Is it halide free? How did your customer determine it was clorine? Ion chromatography? Did they test raw samples (x-fmrs)...

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