Transcript
Phil
Today's question is from a T.S.Y, we don't know where, but T.S.Y. asks, Is there a specification for proper conditions for the storage of PCBs?
Well the answer to your question is YES. Thank you for listening to Board Talk. We'll be back - actually, let's elaborate on this a bit, right Jim?
Jim
This is the second question we've had on this subject recently. The last one was on baking, but the answer is basically the same. The proper way to store your raw boards is in a moisture barrier bag that's vacuum packed and sealed. Otherwise, moisture can seep in, be absorbed by the circuit boards; and then when they get into the soldering operations, bad things can happen like delamination, cracking, and other things. So you don't want to expose your boards to moisture.
There aren't any real "hard" specs yet; although, the industry is realizing this. The IPC has formed a committee- D35 - to study it and is producing a draft document, spec IPC 1601, which is going to outline handling parameters. And what is being proposed or debated right now is that they're going to treat them just like moisture sensitive devices and components.
That means the PCBs will come sealed in a bag; and when you take them out of the bag, you will only have so much time to put them through all of the soldering operations. If you exceed that time, you have to bake them.
So I guess not having that spec cast for us yet, we could say, "Keep it in the bag. Keep them sealed. Don't take them out of the bag any longer then you have to." And if you know that you've got an open bag of boards, a partial bag left over after a build, and you need to - - you know you're not going to be able to assemble them for some time, either quickly reseal them into a moisture barrier bag just as you would MSD components or put them in a dry box.
Again, we don't have any hard numbers to compare that to. Some people have initially said, well I'm just going to treat a board like a Level 4 MSL, which would give you 72 hours out of the bag exposure time at nominal temperature and humidity conditions.
So it's a good point. The concern has been brought up, and I think the concern is because of the laminate materials for lead-free in the higher reflow and soldering temperatures. Lead-free is just making all the problems with delamination worse, so the moisture issue becomes more critical and now we're going to have to define it.
Jim
So keep it in the bag. And remember, don't solder like my brother.
Phil
And don't solder like my brother.
Jim
Keep those kids away from the flux pot.
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