One way to mitigate the problem of solder balling is to bake the boards for 30 minutes at 70 deg C or store them in a dry room or box prior to processing. Also slow down the reflow process to, once again, dry the board and components to prevent the steaming of the humidity in vias or in the paste which is believed to create solder balls. The ideal environment that I have heard the most is 70 deg F, 70% humidity. That much humidity lessens ESD. Based on the records that we keep, air conditioning does not allow more than 68% humidity in the building we work during the summer and a lot less in the winter. That is due to the fact that when air is cooled, humidity condenses on the air conditioning system. On J-Std-001D 4.2.2 it says: Temperature and Humidity/ When humidity
decreases to a level of 30% or lower, the manufacturer
shall verify that electrostatic discharge control is
adequate, and that the range of humidity in the assembly
area is sufficient to allow soldering and assembly materials
to function correctly in the process, based on vendor recommendations
or documented evidence of process performance.
****For operator comfort and solderability maintenance***,
the temperature should be maintained between 18°C
[64.4°F] and 30°C [86°F] and the relative
humidity should not exceed 70%.
For process control, more restrictive
temperature and humidity limits may
be required.
So if you are in an air conditioned building, keep the material dry and adjust the reflow process, the problem should be very small.
Ramon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
Sent: Wednesday, February 07, 2007 2:58 AM
To: [log in to unmask]
Subject: Re: [TN] Max Humidity allowed
Surely that depends on the chemistry of the paste, the hold time before and after the component assembly and before reflow, as much as the RH?
Brian
Sklenar Vit (RBAU-AE/MFE3) wrote:
> Hi Techneters,
>
> Please is anybody aware or can you refer me to any standard which
> addresses the maximum allowed humidity in electronic production in
> order to prevent microballs creation during reflow process?
>
> Thank you fro your reply
>
> Vit Sklenar
> Robert Bosch (Australia) Pty. Ltd.
> RBAU/MF33 - VS, Process Eng.)
> www.bosch.com.au
>
> Tel. +613 9541 7734
> Fax +613 9541 3909
> [log in to unmask] 2
>
>
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