Phil
Welcome to Board Talk. We're the Assembly Brothers, Jim Hall and Phil Zarrow of ITM Consulting, and we're here to answer your questions on SMT processes, equipment, materials, procedures, or anything else you have on your mind. Well, probably not anything but to do with circuit board assembly and related issues, yeah, but we're not gonna solve your problems with your love life, God only knows.

Our question today is from GK. The question is, "I understand from some EMS industry sources that the PCB baking is not necessary if the PCB is vacuum packed by the PCB supplier. Is this true or do we still need to consider baking for our process?" Well, now.

Jim
This is a really interesting and pertinent question, isn't it?

Phil
Timely. Very timely.

Jim
Timely, cause the concept of the moisture sensitivity of printed circuit boards is really getting a lot of attention. In fact, the SMTA, which has had a Moisture Sensitivity Device Council for several years is now focusing most of its attention not on components, as has been the tradition, but on printed circuit boards.

In fact, if you go to the SMTA website, SMTA.org, and go to the Moisture Sensitive Device Council and go to their meeting notes from SMTAI last year in August, you will find that most of the text of the notes is devoted to the moisture sensitivity level control for printed wiring boards.

And what we're seeing is that they are – the IPC is proposing to establish some specs. They have a council, an IPC D-35 Printed Board Storage and Handling subcommittee and they are preparing a draft spec, IPC 1601 Guidance Document for Storage and Handling Issues for PWB's and Assemblies.

And from reading the notes here, you can go to the website and check it out, what they're moving to is exactly the same kind of handling procedures both for suppliers, in this case PCB fab suppliers, and for assemblers in how you have to handle this.

Phil
And this is long overdue because what we see a lot in the field is a lot of unnecessary baking and other times when baking should take place and isn't.

Jim
Well, what happens if you don't bake the board? What would cause a person to bake a board?

Phil
It's going to be that moisture gets trapped in the board and that moisture may cause delamination.

Jim
I think is biggest thing.

Phil
Also, the moisture can also pollute, dilute your solder, your fluxes, and so you‟re gonna see incidents of bad soldering, whether it's – it could be as radical as dewetting solder balls.

Good old solder balls are everywhere. The other side of the coin is we always advise not to do any unnecessary baking if you don't have to of component or boards.

Jim
Solderability issues.

Phil
Solderability issues, depending on what the finish is –

Jim
I mean you can bake in nitrogen but that‟s another expense and so forth.

Phil
Exactly, so this is good that finally we‟re being led away from the seat of pants approach on this.

Jim
Just to quote a couple of notes from this Moisture Sensitivity Council notes, they're talking that printed circuit boards should be treated as an MSL Level 4 classification and not left open to the floor for more than 72 hours. But most PWB suppliers guarantee a shelf life for six months for an unopened package.

So going back to the original question, yeah, if you keep them sealed in their vacuum bags, they're good as long as you don't expose them on the floor for more than 72 hours. Now that's a very general statement. In the notes, they also talk that different laminates are gonna be more sensitive than newer high T sub g laminates for specifically developed for lead-free assemblies are gonna be more sensitive.

They're going to absorb moisture faster and they would get an MSL rating that would be higher. But again, this is just theory so it sounds like if you can guarantee that your boards aren‟t exposed more than 72 hours before their final reflow, you'll probably be in good shape.

Phil
So yeah, so you want to keep in tune to see what the IPC when they, again, the committee is being formed now, the IPC D-35 Printed Circuit Board Storage and Handling subcommittee. So you want to keep an eye on that and watch for their forthcoming specification coming out of that.

Jim
IPC 1601.

Phil
Right, and I think that's basically it. Anybody else? Yeah, that's basically it. So that‟s it for this session and you‟ve just wasted probably less than five minutes of your very precious time with us, the Assembly Brothers. Send in your questions, comments or pronouncements or whatever else or things politically correct correction statements here by clicking on the little statement at the bottom there where it tells you to send in your questions.

And thank you for listening to Board Talk and though Circuitnet virtually stops their printing presses when they hear us say it, this has been Phil and Jim, the Assembly Brothers of ITM Consulting, and remember –

Jim
Don't solder like my brother.

Phil
And don‟t solder like my brother, either.

Jim
Keep the kids away from the solder pot.