smt solder paste printability goes down with high humidity.  some of  
the low cost paste explode if you have high humidity and let the  
printed board sit around too long prior to reflow.  paste after print  
may have sag problem if your process window is very wide.  you get  
more solderballs and solder fines (depend upon what paste you use)-  
flux activity degraded.   If you know your paste well, you might be  
able to cut down your work life by x% if your un-intentionally got  
hit by high humidity... otherwise, you run a risk (if it is qualified  
line with regulated RH, I would not accept the relax RH just because  
someone think it would have no impact... unless you have data to  
prove it within the whole process window - that including the paste  
at end of the shelf life). My 1.5 cents.  (if you are in amazon, make  
sure you control the humidity on the floor).
                jk
On Oct 28, 2015, at 7:38 PM, Gregg Owens wrote:

> Juan:
>
> For a "It depends." (I hate saying that.)
>
> From a compliance side, It depends on what would fly in the face of  
> an audit. If you check level daily and record the level, would that  
> be "good enough?" That would depend on your area. In southern  
> California where I live and work, weather of any kind beyond  
> sunshine is an anomaly and a daily verification may be sufficient.  
> However, in other locations where weather can change by the minute  
> it likely would not be considered sufficient. It also depends on  
> what you are manufacturing. For high reliability (e.g. space)  
> applications a (recording) continuous monitoring would be the  
> expected norm and would prove that an assembly area has no  
> potential ESD concerns caused by low humidity. Most companies I  
> have worked at (high reliability) stop work at 30% humidity for ESD  
> issues. Some internal standards I have worked to allow working up  
> to 70% humidity. Above that level mechanical assembly could be  
> impacted due to the issue of rust.
>
> From a metallurgical perspective, I have no direct knowledge of a  
> humidity affecting soldering operations, but that is not my area of  
> expertise. But I am thinking of sailors soldering on the high seas  
> performing rework on shipboard electronics and naval avionics. But  
> from a process control perspective any environmental change can  
> affect soldering process (e.g. barometric  pressure). Now that I  
> said something I am sure more knowledgeable folks will chime in.
>
> Gregg
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Juan T. Marugan
> Sent: Wednesday, October 28, 2015 1:36 PM
> To: [log in to unmask]
> Subject: [TN] J-STD-001: Humidity control
>
> I am a little confused regarding the requirement stated in J- 
> STD-001 for the humidity level in the facility.
>
> Reading the standard, I understand that the value of 30% RH  
> (minimum) is only referred to prevent damages induced by an  
> electrostatic discharge, but not for soldering. Is it correct? Of  
> course, the soldering process shall meet all the requirements and  
> also the solder joints.
>
> And a last question. Does the J-STD-001 require keeping records of  
> the readings of temperature and humidity in the assembly workshop?  
> Is it acceptable a system that starts to work when the humidity  
> drops to a certain level (for example 40%) even if that system does  
> not have the possibility to save these data?
>
>
> Thank you.
>
>
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