The answer is clear. Cleaning should be carried out AS SOON AS POSSIBLE 
after soldering. The longer the time gap, the harder the residues become 
and the more difficult they are to remove. The ideal is to start the 
cleaning as soon as you can comfortably hold the assemblies. This does 
not mean that you may not be able to clean them the following day, but 
you may have difficulties.

The old 1 h limit of the MIL specs is a legacy from the days when we 
soldered with an RMA flux to MIL-F-13949 (number if my memory is OK) and 
cleaned with a CFC-113 blend. We have moved beyond these days. If you 
use a WS flux, you may find the solder is horribly matt if you wait as 
long as one hour!

So the answer is ASAP but do whatever gives you provably good results, 
whether it be 1 minute, 1 hour or 1 day. NEVER rely on specifications 
for this kind of thing because the guys who wrote them had no idea which 
flux YOU would be using, which soldering process YOU would use, which 
cleaning product YOU would use or which equipment YOU would use. Only 
YOU can prove that your process is good, by scientific qualification. 
You are really asking how long a piece of string is.

Brian

- bogert wrote:
> July 23, 2008
> 
> J-STD-001 is silent on how long a time span is acceptable between wave 
> or reflow soldering and post cleaning for instances where cleaning is 
> mandated because organic Type M or H flux was used.
> 
> I believe the historical soldering specs MIL-STD-2000 and MIl-STD-454 
> requirement 5 mandated no more than one hour between cleaning and 
> solddering.
> 
> Is there a technically necessary maximum limit and if so is there data 
> to support it?  If there is a technical supported limit why should we 
> mandate it in J-STD-001?
> 
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