Circuit Board Moisture Sensitivity and Baking

Phil
Welcome to Board Talk. This is Phil Zarrow and Jim Hall. Wat is the question today?

Jim
This is a question from B.D. It's on PCB handling and storage concerns.

"I'm looking for information concerning IPC 1601 Guidelines for Handling and Storage of Printed Circuit Boards. Does anyone have a feeling for how well this is being accepted, and/or how many companies are implementing these new policies?"

Well, I think that we need to say that the spec has not been published as of the time of this broadcast. I believe it is in final approval. The final draft has been reviewed, and there's just the procedure, so it's publishing is imminent.

But then, what happens with any IPC spec?

Phil
There are some people who treat all IPC specs as holy scripture, and there are others that just go their merry way doing anything they want. However, in terms of whether this should be adhered to, we think it's very important. It's been a long time coming.

We get this question asked alot when we're doing process audits. There's moisture specifications for components. What about boards?

Jim
We should say for those of who are not familiar, IPC 1601 is the final, formal definition for dealing with moisture absorption in printed circuit boards.

It's very similar to IPC/JEDEC J-STD-033 Moisture Sensitivity and Handling in Components. This is the same kind of specifications for circuit boards.

Phil
Moisture in circuit boards, either the way they've been stored, the way they've been shipped, the way they're handled at incoming and receiving, and in the storage room. We think this is a good guideline, and there's some really good wisdom in this one. This is not superfluous at all.

Jim
And it defines formal baking schedules. People in the past have felt, "Jeez, my board has been exposed. I'm going to bake it... how much... at what temperature... how long?

This spec will define that for you. You will have a formal reference to go and answer how long should you bake a board and at what temperature.

Before you go into the reflow, or wave, or selective, or conformal coating - whatever your downstream process is, this will formalize it. It's a concern because of the newer laminates for lead-free, which tend to absorb more moisture, coupled with the higher temperatures for lead-free soldering. So there are many reasons we feel people should pay attention to this spec.

Phil
So on behalf of Phil and Jim, the only other advice I can offer is... don't solder like my brother.

Jim
And don't solder like my brother. And keep those kids away from the flux pot.

Responding to comments by Jeff Yearly.

Misconceptions concerning the proper handling of MSD's is virtually universal. You seem to be more knowledgeable than most.

The issues of drying requirements with MBB's and dry cabinets is presented in Section 4.1 of J-Std 033 (the "Bible" for assemblers handling MSD's.) Our general advise is that someone in any organization handling MSD's must get a copy of this spec and spend the time (the
whole spec is only 15 pages long) to understand it completely. THEN decide what the best program is for your manufacturing environment.

On the inconsistent MSL spec from component manufacturers, we are not surprised. Is there intelligent life in these companies.

I am a component Engineer at Libra Industries in Mentor, Ohio. I enjoy listening to your board talk segments, and I was fortunate to attend Phil's lecture at a SMTA meeting in Ohio recently "Low Volume-High Mix SMT Manufacturing."

Topics of MSD are of interest to me because I am working on improving our current system for storing moisture sensitive devices. I am wondering if you ever came across the situation I am facing right now. I have a Infineon component (QFN 160) SAB82538H-10 V3.2 that we bought and it came in marked as MSL 3 and when we bought more of the same part for our next build approx. a month or two later, that very same MPN came to us marked as MSL 5.

Between MSL 3 and 5 there is a significant difference in the allotted floor time. This has happened numerous other times with multiple types of components from different manufacturers. I have contacted the manufacturers to try to get some answers of why this is happening and I never seem to get a straight answer; answers like "it depends on the type of material we used for that particular lot." To be safe I have been treating these suspect components as if they are the higher MSL rated device (MSL 5).

With the example I shared with you on the Infineon component we were unknowingly processing the parts as if they were MSL 3 not knowing they came in again marked as MSL 5. This part was falling off the board during reflow and the popular answer at my company was to secure the part down with epoxy prior to being reflowed. I stepped in and noticed the part had an ever so slightly bulge on the bottom of the device. I baked the parts at the recommended bake times and temps and the problem has left.

Also we have McDry storage cabinets, and I heard Phil state that by putting MSD components back in the dry cabinets that it stops the clock on moisture absorption. Does this process ever reset the clock so to speak? I hear from others in our company and from the manufacture of the cabinets that over a period of time the dry cabinets will draw out any moisture, I would imagine if this were true then the parts would definitely need to be out of the bags right? (I’m not talking about sealed bags but the parts being put back in the bags that are left open.) Are either of you aware of such claims? Or is baking the only real true way to reset the clock?

Phil and Jim, with reference PCB MSD and baking. You said that IPC 1601 is in final draft. However I use IPC HDBK-001 with amendment 1 and 2, page 97, section 7.3.2 and table 7-1. PCB bake out.

120 C (248 F) 3.5 - 7 hrs
100 C (212 F) 8 - 16 hrs
80 C (176 F0 18 - 48 hrs

What is your take on this? Thanks for all your help and recommendations.