|Ask the Experts|
March 2, 2009
What Is the Ideal Humidity for PCB Assembly?
Some experts say that a circuit assembly production facility's temperature should ideally be set between 70 and 78 degrees Fahrenheit and humidity of 40 to 70% when working with electronic assemblies. The facility I work in has a current temperature of 76 degrees and a humidity level of only 16%. Would that humidity level affect the solderability of our assemblies?
|Expert Panel Responses|
If your facility's ambient RH is only 16% then you are more prone to ESD (Electro Static Discharge) related defects. Humidity in the air helps to increase surface conductivity, which subsequently aids in dissipating electrostatic charges throughout your facility. ESD literature commonly recommends a MINIMUM RH of 40%, provided that this will not promote corrosion or delamination of the materials used in your products. For a MAXIMUM RH level I would never suggest going higher than 60% RH, for a variety of reasons including the impact of RH on Moisture Sensitive Devices. MSD floor life is dramatically reduced above 60% RH (Ref: Table 7-1 in IPC/Jedec J-STD-033B.1). The bottom line is that you want enough humidity to maintain ESD control, but not so much that you induce damage to MSDs. I would generally recommend 40% to 60% RH.
Sales Manager (Americas)
Capital Equipment Operations Manager
Specialty Coating Systems
Solder pastes react differently to temperature and humidity levels. Low humidity levels can exacerbate the driving off, or drying of solvents in solder pastes which in turn affect variables such as:
The low humidity could cause the solder paste to dry out prematurely, but your bigger concern with the low humidity is static control. Make sure your operators are using heel and wrist straps and testing them daily.
Regional Sales Manager
OK International Inc.
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