Drip. Drip. Drip. Drip. Drip …

Okay, water doesn’t have to actually be dripping down on to your parts to be a problem. I don’t know if you’ve heard or not, but water also comes in vapor form. Weird. I wonder if there’s a way to harness water in that vapor stage and do something useful with it. Hmmm. Ponder material for another day.

Here is something not so useful about vaporous water: It can get into your parts and make them unhappy. I was recently asked about opening and resealing moisture barrier packages for moisture-sensitive parts. This old post has a link to the IPC and Jedec standards document (J-STD-033B.1) covering this subject. It can be a complicated subject and the document is worth the read.

In sort, the best thing to do is just leave the parts sealed in their original moisture barrier packaging. If that’s not practical, look at the MSD classification. There are eight levels with one being least sensitive and six being most. (Levels are 1, 2, 2A, 3, 4, 5, 5A and 6). Most parts seem to be level 3, which can be open and exposed for a cumulative time of 168 hr. The actual safe time may vary based on your local humidity.

If you want to open and reseal, you’ll need the humidity indicator card that came with the parts, desiccant and a thermal sealing gizmo. Open the package, take out the parts you need, put the remainders, desiccant and card back in the package and reseal it. Sealing it with tape won’t do the trick. Then you would count the time that the components were in the open air toward the cumulative open time.

If there’s any doubt, just let the assembly house know that the parts need to be baked. It will probably add some time to your job, but it’s better to add a bit of time than have bad parts.

Duane Benson
Add walnuts and chocolate chips.


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