This is essentially a problem of component selection, not of the washing 
process. How many times have I seen specifications of hermetic 
components unilaterally replaced by the purchasing manager because 
non-hermetic components may be one or two cents cheaper? Many more times 
than I care to reflect on! This is especially true of trimmer 
potentiometers and wound components.

Brian

On 31/07/2014 17:38, Nutting, Phil 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 �gm / 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
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