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Has anyone looked into Vacuum storage on moisture sensitive devi

D Peter

#25494

Has anyone looked into Vacuum storage on moisture sensitive devi | 19 August, 2003

After a few problems and time constraints on baking moisture sensitive devices, we are looking at solutions to storage rather than going after a rebaking solution. One thing that always bothered me about baking was the oxidation on the lead finish, and the propensity for placing 85 C rated trays in a 105C oven about every 6 months , and the subsequent deformed trays and damaged leads. At any rate we are looking at storage solutions. The first thing that came to my mind before further research was vacuum storage to pull moisture and reduce oxidation, and as a bonus we already have the vacuum equipment in house. The only electronics references I find though relate to vacuum sealing of shipping packages rather than as a long term storage solution.

Although we have the capabilities to pull a hard vacuum (.5 Torr or less), it really doesn't take alot to reduce the RH to a quite low level, and not a whole lot more to reduce the boiling point to room temperature.

Has anyone else looked into the practicality and/or effectiveness of vacuum storage.

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Hussman

#25496

Has anyone looked into Vacuum storage on moisture sensitive devi | 19 August, 2003

Nitrogen cabinets work well if you already have nitro.

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D Peter

#25497

Has anyone looked into Vacuum storage on moisture sensitive devi | 19 August, 2003

No, we don't have nitro. We may go that way if we can't find decent data from anyone other than the food industry on vacuum drying. I'm just more comfortable with low water/O2 content by removal rather than displacement.

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#25498

Has anyone looked into Vacuum storage on moisture sensitive devi | 19 August, 2003

JEDEC standard EIA/JEP124 Section 5.2.1 Packing Moisture-Sensitive Components has words to the effect: "...Partially or lightly evacuate the bag to reduce packaging bulk and heat seal the bag as close to the end as possible following the heat sealing equipment manufacturer's guidelines. The bag should not be completely evacuated since this will reduce the effectiveness of the desiccant and possibly damage the content..."

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D Peter

#25499

Has anyone looked into Vacuum storage on moisture sensitive devi | 19 August, 2003

Again, that is for packaging, rather than moisture removal or storage. Those guidlines are for several reasons, preventing low pressure outgassing or disassociation of the dessicants, damage to parts or wafer tray due to forces on the evacuated packaging, and the ability to actually pull water vapor through the bags under hard vacuum. We were looking more along the lines of a vacuum storage vessel to allow outgassing from the chip carriers, not unlike a standard oven bake procedure, without the oxidation problems. The main reason for baking is for a given weight of water vapor in the air, raising the temperature reduces the RH, and promotes the water vapor leaving the chip carrier. It's an equilibrium reaction, just like in organic chemistry, removal of a product of a reaction drives it further toward completion. Why not just remove the water vapor in the first place, when it can be done feasibly without the use of expendable materials like dessicants or compressed nitrogen?

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#25500

Has anyone looked into Vacuum storage on moisture sensitive devi | 19 August, 2003

What are you going to fill the chamber with when it needs to be opened? If you use air, will the evacuated components suck up any available moisture?

I've never done anything like this with electronic components, but some of the more porous materials we used for some implantable med. devices would suck up well beyond the allowable moisture if we just pumped the chamber full of room air to open them. We purged with nitrogen when we evacuated them, and also flooded the chamber with nitrogen to open them.

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D Peter

#25501

Has anyone looked into Vacuum storage on moisture sensitive devi | 19 August, 2003

D Peter

#25502

oops, a bit quick on the post | 19 August, 2003

Good point, I don't know if it will pull moisture from the atmosphere without a dry nitrogen purge. There's another thing to find out.

Thank you

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