The Best Storage Method to Protect Against Corrosion



The Best Storage Method to Protect Against Corrosion
Which storage method will better protect against corrosion, nitrogen or super dry? Regardless of the methodology you use, you want to do it in compliance with IPC 1602, which covers storage and handling of circuit boards. Jim Hall and Phil Zarrow, The Assembly Brothers, answer this question.
Board Talk
Board Talk is presented by Phil Zarrow and Jim Hall of ITM Consulting.
Process Troubleshooting, Failure Analysis, Process Audits, Process Set-up
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Phil Zarrow
Phil Zarrow
With over 50 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.

Transcript


Phil
And welcome to Board Talk with Jim Hall and Phil Zarrow, the Assembly Brothers Pick and Place. We’re here to attempt to answer your process questions regarding materials, methodology, and all of the happy stuff that makes our day go by so fast. Today, Jim, what do we have? I think we have a storage question.

Jim
It comes from L.N. It says which storage method will better protect against corrosion, nitrogen or super dry?

Phil
I would start off by saying that regardless of the methodology you use, you want to do it in compliance with IPC 1602, which covers the storage and handling of circuit boards. Also, with regard to your assemblies, you are basically treating them as a level 3 MSD. But with regard to the question, he said specifically corrosion. Correct Jim?

Jim
Yes. Chemically speaking, nitrogen excludes oxygen, so that would preclude any corrosion that requires oxygen in the reaction. So, from that standpoint, I have to say yes, nitrogen is more fool-proof. But the question in my mind, and I don’t know the answer, is that in super-dry, you have so little moisture; how many corrosion reactions can take place if there is absolutely no moisture available? And I don’t know the answer to that question. I suspect very few, but I don’t know for sure.

Phil
I believe that is the whole idea. Nitrogen is very dry, by the way also.

Jim
It has a lot of oxygen in the atmosphere that is not there in nitrogen. So any corrosion reaction that requires oxygen should be precluded of nitrogen but possibly could happen in super dry.

Phil
Well, I definitely agree with my brother on that. Make sure that regardless of your storing, if you are bare boards, if you are not putting them in the cabinet, nitrogen, or dry cabinet, they should be repackaged in a moisture barrier bag with a humidity indicator and a desiccant. Which is the way you should have received them in the first place. But again, we are talking about 1602.

If we are talking about the actual assemblies, yeah. We’ll let our listeners weigh in on that as well. I suppose we will be hearing from the vendors of both super dry and nitrogen cabinets. Gee, why do I think that? I guess we know our audience. But it will be very interesting to see. My guess is that it is probably six of one, half a dozen of another to be very non-commercial about it.

Jim
Jim We should ask the fundamental question. What materials are on these boards or components, whatever it is you are putting in this nitrogen or super dry environment, what is on there that could cause corrosion? My feeling is that there shouldn’t be anything. Materials should be clean and free of things that can cause corrosion.

Phil
Yeah, I would like to think you are not storing them with flux residue on there. Not a good idea. Very, very good point, Jim. What is the worry about corrosion unless you have the moisture element that you mentioned.

Jim
If we were talking about oxidation on solderable surfaces, then obviously nitrogen is better. But they specifically say corrosion, so we did not mention that.

Phil
Hope we answered L.N.’s question and certainly opened it up for discussion. Again, you have been listening to Board Talk with Jim Hall and Phil Zarrow. Regardless of how you are storing your boards, please don’t solder like my brother.

Jim
And don’t solder like my brother.

Comments

Over-all Nitrogen is the best. But, if the boards have contamination as from Sulfuric acid, H2SO4, residue the chemical contains oxygen which will cause local reaction, even in a nitrogen atmosphere. I have received sample circuit boards, with electrolysis nickel gold, from an offshore supplier which had a distinct order of sulfuric acid. When placed in a nitrogen purged bag, then left to sit at room temperature for two weeks, the plated via's all showed a green color (colour) from copper corrosion.

In this case, I suspect the contamination would render most any storage efforts unless. Make sure no contaminates are present immediately upon arrival, and if clean, then store them in Nitrogen.
Jaye Waas, Renkus-Heinz

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