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What is the Suggested Humidity Level for Electronics Assembly?

What is the Suggested Humidity Level for Electronics Assembly?
I am aware of the suggested humidity level for an electronics assembly facility. Do the same limits apply within a 100,000 class clean room?
Board Talk
Board Talk is presented by Phil Zarrow and Jim Hall of ITM Consulting.
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Phil Zarrow
Phil Zarrow
With over 35 years experience in PCB assembly, Phil is one of the leading experts in SMT process failure analysis. He has vast experience in SMT equipment, materials and processes.
Jim Hall
Jim Hall
A Lean Six-Sigma Master Blackbelt, Jim has a wealth of knowledge in soldering, thermal technology, equipment and process basics. He is a pioneer in the science of reflow.


And welcome to Board Talk with Jim Hall and Phil Zarrow, the Assembly Brothers, who by day go as ITM Consulting. We are here to solve your problems for free, and that is about what the advice is worth today.

Jim, today's question is from M.S. M.S. writes, I am aware of the suggested humidity level for an electronics assembly facility. Do the same limits apply within a 100,000 class clean room?

Besides ESD concerns to control solder paste what other operations or processes within an electronics assembly facility are sensitive to all of this humidity outside of the specified limit.

Well, good question. To start off, the answer to your question whether they apply to a class 100,000 clean room, yeah, why wouldn't they. Just because you are cleaning off the dirt particles and fuzz and stuff like that doesn't mean the rules of humidity don't apply. Yes, they absolutely do.

To be fair Phil, the second part of the question says besides ESD and solder paste. Perhaps this person is not doing any solder paste printing within the clean room and that is why they are thinking that the humidity only affects solder paste and ESD.

So maybe when we answer the second part of the question it will be clear. Humidity affects anything plastic that can absorb moisture, mainly your PCBs and your components.

There is a whole IPC JDEC specification for moisture-sensitivity of components. J Standard 033 tells us how to handle it. The new spec for PCBs which is, Phil you always remember this one.

I somehow recall it being 1621. Boy, if I'm wrong on that number...

There is a new IPC Spec about handling and storage of PCBs that talks about the issues with moisture absorption and gives you bake out schedules and so forth.

Basically the plastic materials can absorb moisture. If they get too much moisture in them then they can be damaged during reflowing and other high temperature processes.

Right, so in answer to your question, yeah, there is a lot going on. Definitely familiarize yourself with JDEC 033 and 020.

Yes, 020 is the component specification that defines the moisture sensitive levels for components.

And the PCB spec, and understand what best practices are for handling these.

Phil, one other thing any other material such as adhesives or conformal coatings and so forth may have humidity sensitivities. If you are using any of those materials you also have to be concerned. It is just a good idea to not let the humidity get too high or two low because ESD as you say is always there.

Well, good I think we covered that point. I hope M.S. is in better shape now.

Regardless of whether you are soldering in a clean room or in a dust bin, whatever you do please don't solder like my brother.

And don't solder like my brother.


All depends on products and circumstances. I've been in clean rooms where they assembled lithium batteries. The moisture in the room was maintained to <100ppm H2O.
Tom Salzer, Hermetric,Inc.
Typical humidity range for NASA JPL assembly is suggested to be between 40-80% RH for safety reasons. I strongly suggest following this guideline as this has served me successfully for more than 40 years. Handling of paste and fluxes have a separate specification due to working life in the manufacturing environment. Check with the manufacturer of the fluxes and pastes used as this will significantly affect the working life. it's usually 30 minutes. The processed solder joints clearly reflect this.
Jeffrey Lewis, Display Graphics
Maybe you think about IPC-1601 for PCB in this matter.
Holger Boenitz, KSG Leiterplatten

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