ESD Systems - Questions And Answers

Hi. Is it mandatory to keep the humidity RH SPEC inside hygrometer similar to ANSI/ESD S20.20 requirement >30% but less than 70%? IF yes . Why? Would appreciate your comments and shared of thoughts. Many thanks - Anonymous, kulim, 00, Malaysia

As you note, the ESD Association in ANSI/ESD S20.20 Table 1 has Humidity Technical Requirement as > 30% Rh < 70%, however this is the minimum recommended technical requirement, so it is recommended. Note 6 states “This is a proposed value that has not been substantiated by any standard.”

In Malaysia, high charge generation due to low humidity isn’t likely a problem; tribocharging reduces significantly at higher humidity; however the concern is corrosive effects on electronic components.

From ESD Handbook TR 20.20 paragraph 5.3.15 Humidity
“Humidity is beneficial in all ESD Control Program Plans. Contact and separation of dry materials generates greater electrostatic charges than moist materials because moisture provides conductivity that helps to dissipate charge. For this reason, ESD effects are most noticeable in the winter since heating systems reduce building environment moisture. Geographic location (desert vs. coastland) is also a major contributor to ambient conditions inside buildings. Any circumstance that results in a low relative humidity will permit a greater accumulation of electrostatic charges. Relative humidity above 30 percent in ESD protective areas is desirable as long as other adverse conditions are not created as a result of humidity levels. Generally speaking an upper limit of 70 percent is desirable to prevent corrosive effects on the metal portions of electronic devices and assemblies.”

Your ESD Control Plan can set a different range that the recommended greater than 30% RH and less than 70%. Per S20.20 paragraph 6.0.3. Tailoring:
“This document, or portions thereof, may not apply to all applications. Tailoring is accomplished by evaluating the applicability of each requirement for the specific application. Upon completion of the evaluation, requirements may be added, modified or deleted. Tailoring decisions, including rationale, shall be documented in the ESD Control Program Plan”

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