Phil,

This is a problem.  

We mostly use CMs and we have had to insist that they use DI only as we found that wetting agents damaged the windows of alphanumeric LED displays (the clear plastic appeared to have crazing cracks.  HP (now Avago) analyzed the part and told is no agents can be used (it;s in the app data sheet).  Unfortunately not all manufacturers will tell you there’s a potential problem.  

Grayhill makes pushbutton modules with clear caps that are removable. They offer no advice on washing their switches.  The switch itself has gold plated electrodes plated on a pc board.  Over it is an elastomeric conductive rubber membrane. We have always removed the clear caps and then installed them after wash/dry because we are concerned about water getting under the caps.  We take the caps of as extra insurance in case the CM does not follow instructions to install after wash/dry.

Relays thus far have not been a problem as we only use sealed relays.  Nor have ALCO slide DIP switches (which come with a Kapton seal tape that you remove after reflow solder/wash/dry).

Fiberoptic components are only installed after reflow/wash/dry.  Its likely that the plastic caps prevent water from getting into the ports but we don’t trust them. A 3 micron particle in front of an 8 micron single mode fiber reduces light input by ~40%.

Bob Landman



On Jul 31, 2014, at 10:38 AM, Nutting, Phil <[log in to unmask]> wrote:

> Over the past years we have had relays, optos and pots fail due to corrosion being found inside the parts after post soldering wash.  The quick solutions have been to use other manufacturer's parts or install after wash with hand solder "no-clean" cored flux.  One manufacturer said it was because of halides in the flux.  Our primary CM's and our flux contains halides, but we haven't seen as many failures with in-house processed PTH boards as with CM built boards.  Recent pot failures have been explained  by component manufacturers as too much wash pressure or bad flow direction from the wash jets.  Opto failures were similarly diagnosed.
> 
> Our in-house process, all PTH, is foam flux with OA flux, wave solder with 63/37 or SC995e followed by a closed loop DI wash with no chemicals.  This has been a great process since 2006 when we switched from a no-clean foam flux, 63/37 wave and terpene/alcohol wash to our listed system above.
> 
> We do not dictate flux/wash process to our CMs, but we do specify cleanliness to J-STD-001 C-22 using the 1.56 μgm / cm2 NaCl equivalent contamination value.  Forcing the CM to change fluxes for our product met great resistance and added cost so no change in flux was made.
> 
> Our business is high voltage from 30 kV to 240 kV so clean with NO residue is very important.  The DI wash has provided that in-house.
> 
> We are using different CMs going forward, but not necessarily for this reason.
> 
> Is this a problem unique to us or do other suffer from similar problems?
> 
> Phil Nutting  |  HVP Development Engineer   |  Excelitas Technologies Corp
> 
> Lab: +1 978.224.4332   |  Office: +1 978.224.4152
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