storage of humidity sensitive SMD devices?

[jwhitmore]

I'm fairly organised with my electronic components, having created a little web based application which tells me where they are. So most of my components are in drawers, something like this:

http://ie.farnell.com/webapp/wcs/stores/servlet/ProductDisplay?catalogId=15001&langId=353&urlRequestType=Base&partNumber=1367091&storeId=10163

My only problem is humidity sensitive devices, which I've never really found a great way to store. At present they're all in a zip lock plastic bag with some of those Silica Gel packets that you get. I had a look, but trying to find "air tight" didn't really get too many hits at all. I'm just glad that not much is actually sensitive so the zip lock bag is just about holding it all together.

[Tomorokoshi]

Are you installing these parts yourself, and have you had issues with soldering them, or are you kitting them for a board manufacturer and they are having issues?

I'm thinking that humidity exposure is somewhat less of a problem when the parts are soldered on, because you can adjust your process. The manufacturing lines are expecting parts with a certain amount of solderability because they can't process control at the individual pin level. They can only do it for the solder temperature, etc.

[rdl]

Parts I've ordered in the past were moisture sensitive came in sealed and dated bags with a humidity indicator inside. If the package is left sealed they're supposed to be good for 1 year. Once opened the parts must be soldered within one week (as long as the humidity isn't too high) otherwise they have to be pre-baked. I figured the best way to store them is probably in the package they came in, at least until the date expires or the package is opened. after that it doesn't seem to matter much because they'll need baking first no matter what.

[jwhitmore]

I'm soldering these parts myself. I usually order up a couple of extra things then I need just in case I have problems, and sure I have them about the place if I decide to reuse the part. I guess I've not got many parts that would be sensitive so I'll just leave them in the moisture proof packaging that they came in and stick them in a lunch box.

I'm not at my lab at present and all I can think of that is sensitive is a 0603 LED and a stepper motor driver chip.

[Tandy]

You could use an impulse heat sealer such as this http://www.ebay.co.uk/itm/Impulse-Heat-Sealer-Sealing-200mm-For-PP-PE-Plastic-Bags-Spare-Element-Teflon-/311383466845 to re-seal the foil bags that the components usually come in.

[tggzzz]

I have heard stories that if you preheat the components at, say, 100C for a few hours before using, they can be soldered thereafter. Obviously I have not tried that myself and it will probably be component dependent.

[Gribo]

For MSL > 1, you have bake the components for a certain period before assembly, otherwise you will have popcorn components. AFAIK, most standard SMD LED are MSL 0, so no baking.
For the drawers, You can use some silica gel or similar hygroscopic material (Usually found in component packages or other sensitive equipment such as hard drives).

[MartinX]

Moisture in components can be a real problem in production when the component passes through a complete SMD oven cycle, we have had some issues at work when correct MSL procedures were not followed. Also some some component manufacturers have changed the MSL rating without warning! This is usually smaller manufacturers making low volume parts without their own manufacturing facilities, probably they moved from one factory to another.

Baking components helps but it is difficult to remove moisture in components on reels because the tape does not like high temperatures and the reel does not work in the component feeder after the heat treatment, typically the protective film comes loose and components spill out when the reel rotates. At my company they got a special component dryer, it only heats up to 45 degrees and pumps out the air to help moisture to evaporate though low pressure, this preserves the tape but it takes a long time to work.

[jc101]

This is an interesting area, normally I just order what I need so things are used before they 'expire', where I have some left over (or I order a few extra just in case) I just re-pack them with new desiccant and seal the bags as best as I can.  It would be handy to order some bits larger quantities to get price breaks, but the storage is a concern, no room (or funds) for a dedicated storage chamber.

An extension to the suggestion by Tandy above, how about using one of the cheap food vacuum sealer units?  They suck out most of the air before heat sealing the end of the bag.  Something along the lines of one of these http://www.ebay.co.uk/itm/New-Andrew-James-Food-Kitchen-Vacuum-Sealer-Packing-Bag-Machine-/260833634592