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February 2014

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Subject:
From:
Wayne Thayer <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Wayne Thayer <[log in to unmask]>
Date:
Thu, 20 Feb 2014 18:10:44 +0000
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Solder mask materials are not designed to be robust in acetone!  This means that the solder mask can start to weaken or dissolve in the acetone.  Not surprising to either have the surface of the soldermask appear different or splotchy as a result of applying acetone to it.  It also wouldn't be surprising to smear dirt into the mask when it has been softened in this way.

Get hold of some of the "dirty" boards and see if the issue has to do with acetone attacking the soldermask.  Your PCB fabricator may have changed mask providers, or a mask provider could have made a process change which made it more sensitive to acetone--this is the problem with relying on subjecting materials to environments which aren't listed on the datasheet!

Similarly, fluxing system providers could have changed something which made leftover deposits sensitive to acetone.

That RF part Steve brought up is typical of RF part providers:  If they ship in a ceramic package, you can bet that they've got too much gold on the pads to reliably surface mount, and yet sell the part as an SMT part.  Few, if any, provide solder dipping services.  Not surprising they'd add a product which couldn't be handled in a standard cleaning line.  I think they are just recommending the acetone on that datasheet to make absolutely sure there is no residue between the part and the board.  How to make this work in production is the user's problem.

Wayne Thayer

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
Sent: Thursday, February 20, 2014 12:56 PM
To: [log in to unmask]
Subject: Re: [TN] Acetone as a cleaning agent for PCBA's

Hmm
I think I would like to know what their wiping procedure is and what they are hoping to achieve by doing it before making any firm comment. 
Naturally nothing has changed in your place or theirs, but something has if this has just started to appear. 
I would start from the premise that the boards can be no cleaner than the last thing that touched them.
Unless the acetone is being allowed to flush off the board the probability is that they are making the boards dirtier. If there is anything in the acetone or on the board and it dries in place then the board will be no cleaner than it was before (the soil might be redistributed slightly) and anything in the acetone or on operators gloves will be left on board. If they are applying the acetone to the wipe by holding it against the bottle then anything in the wipes will gradually accumulate in the bottle.
Quite likely they are just seeing a surface effect as you would get on any shiny surface wiped over like this. Think of cleaning a mirror. So it could be technique or the acetone is dissolving something from the wipe or softening the resist slightly. OR your boards are contaminated from packaging say and they are seeing partial removal. In this respect the boards could be ionically clean as measured by zero ion tester, but theoretically could have non ionic contamination. 
So a lot of what ifs and maybes at this point.


Regards 
 
Mike
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert DeQuattro
Sent: Thursday, February 20, 2014 5:00 PM
To: [log in to unmask]
Subject: [TN] Acetone as a cleaning agent for PCBA's

I have a customer that uses acetone to wipe down their PCBA's upon receipt.
The assemblies we make for them are cleaned using a closed loop aqueous board washer then sampled for cleanliness with our zero-ion tester per J-std-001E guidelines.
Recently this customer commented that boards appeared dirty upon cleaning with the acetone.  Does anyone have any thoughts on this acetone cleaning process.
Thanks,

Bob

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