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Nitrogen Storage

Dason C

#19914

Nitrogen Storage | 14 May, 2002

Recently, our customer request us to use the N2 dry cabinet and we are currently using the desiccant type dry box. My concern not only the cost. Is it any data to show if the component exposed to the floor for a while and store back into the N2 cabinet. The moisture inside the package may pentrate and close to the die due to N2 doesn't absorb any moisture from the package.

Thank!

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#19915

Nitrogen Storage | 14 May, 2002

Hi Dason,

Here is some relevant information that you might find useful :

J-STD-033, section 7.1.2.2 Dry Box : "Components may be placed in a dry box, capable of maintaining 25+/-5C and less than 10%RH. Nitrogen or dry air may be used."

In other words, as long as the correct temperature and humidity conditions are met, there is no difference between a N2 dry cabinet or a desiccant-type dry box as far as moisture is concerned. Perhaps the only additional benefit of the Nitrogen environment would be to minimize lead oxidation.

For the second part of your question the answer is yes. There is data that shows how absorbed moisture will continue to diffuse towards the die interface and potentially exceed the critical limit when previously exposed components are returned in dry storage. If you want I can e-mail you separately a technical paper from Lucent that demonstrates this phenomena really well.

Regards,

Francois Monette Cogiscan Inc. Tel : 450-534-2644 Fax : 450-534-0092 fmonette@cogiscan.com www.cogiscan.com

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Dason C

#19918

Nitrogen Storage | 14 May, 2002

Thank! Francois. I think that I also had a paper from Lucent, Handling of Highly-Moisture Sensitive Components. Is it the one which you mention above? I just would like to figure out. Per Desiccant type dry box, it claim that it can absorb the moisture from the package and we proved already by the weight of reduction on the component after placed into the desiccant box. Based on this Pros and the paper from Lucent. I think that I can convince our customer.

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#19934

Nitrogen Storage | 15 May, 2002

Hi Dason,

Yes I was talking about the same paper. This is the best technical information available to clearly explain the physics of moisture diffusion inside a plastic package. Many of the guidelines contained in the current J-STD-033 are derived from this research data.

As far as dry storage is concerned, I would be very careful about using any claims that rely on weight reduction. This is a simplistic approach that was used many years ago, before the above paper was published and before the release of J-STD-033. The basic flaw with the method is that it assumes that the weight content is uniform throughout the package. What the Lucent paper explains is that the moisture content is actually a slowly moving gradient and that the location of the moisture is more important that the overall moisture content. i.e. A large amount of moisture will be harmless if it is on the surface of the package (after a short exposure time) whereas a very small amount of moisture at the critical interface can lead to cracks and delaminations (as you would find when previously exposed components have been stored in a dry box for a long time).

That is why the standard only allows you to reset the floor life clock in very specific conditions of prior exposure followed by sufficient time in dry storage, as defined in the short duration exposure rule (Ref. J-STD-033, 7.1.2). Using any other rule to account for dry storage is not based on good science and it is not backed up by an industry standard supported by component vendors.

For this reason you might have a hard time to convince any serious customer about using rules that are different from the IPC/JEDEC standard.

Let me know if you have any questions on the above.

Regards,

Francois Monette Cogiscan Inc.

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