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Questions About Humidity Indicator Cards and Baking Components?



Questions About Humidity Indicator Cards and Baking Components?
We run small jobs so a reel of MSD components could be opened a number of times. If the humidity cards are not pink, do we have to bake the components? Phil Zarrow and Jim Hall, The Assembly Brothers, share their experience.
Board Talk
Board Talk is presented by Phil Zarrow and Jim Hall of ITM Consulting.
Process Troubleshooting, Failure Analysis, Process Audits, Process Set-up
CEM Selection/Qualification, SMT Training/Seminars, Legal Disputes
Phil Zarrow
Phil Zarrow
With over 35 years experience in PCB assembly, Phil is one of the leading experts in SMT process failure analysis. He has vast experience in SMT equipment, materials and processes.
Jim Hall
Jim Hall
A Lean Six-Sigma Master Blackbelt, Jim has a wealth of knowledge in soldering, thermal technology, equipment and process basics. He is a pioneer in the science of reflow.

Transcript


Phil
And welcome to Board Talk with Jim Hall and Phil Zarrow of ITM Consulting. The Assembly Brothers. Coming to you from ITM headquarters, high above Mount Rialto.

We are here to talk to you about electronic assembly, materials, equipment, components, practices and procedures, among other things. Jim, what is the question du jour?

Jim
Okay. This is from M.B. We run small jobs so a reel of MSD components could be open and closed a number of times.

Each time we put a new desiccant pack and a new humidity indicator card in the MSD bag and seal it. If we total all of the times we open the bag it exceeds 168 hours.

Example, eight hours open then seal for one or more days, then we open the bag for ten hours and seal, etc. If the humidity indicator cards are not pink, do we still have to bake the components?

Phil
Interesting question. I will weigh in first by saying that humidity indicator cards are very helpful and useful. But in terms of finite accuracy, I think they are up there with the old temperature sensing labels.

They get you in the ballpark. Would I want to hitch my wagon to that? Put it this way, do you feel lucky?

The procedure calls for logging strictly in and when you exceed the exposure duration with the remaining components, you do the bake out. My answer to that is I wouldn't trust a humidity card, I would trust the time honored JEDEC 021 and 033.

Jim
I agree with you 100%. First off, for those of you not familiar, M.B. is talking about 168 hours. That is the floor exposure limit for a type 3 moisture sensitive device.

The MSL of level 3 is 168 hours. It is probably the most common level that we deal with. The spec says that the total exposure is greater than that.

The thing that I would point out is that the humidity indicator card is really only telling you about the integrity of the bag, the atmosphere in the bag. It is not really telling you what is going on in the heart of your little component.

Think about it, your part is out for eight hours to use this example that M.B. provided. During those eight hours, the plastic package has absorbed moisture. That moisture is inside that package.

So now you put it back in the bag and seal it up with desiccant. There is no moisture in the bag, and no moisture can get into it. But it doesn't really tell you what is going on with that moisture inside.

I would point out that for all components if they are out for short exposure, this is clearly defined in J Standard 033, which you should have in your possession. Somebody in your organization should have that spec and be intimately familiar with it so that you can plan how best to deal with these things.

It is not a big spec, it is only about 25 or 30 pages. A couple hours you can understand it pretty well. There is something in there called short-term exposure.

I don't know the exact numbers, but the numbers 8 and 12 stick in my mind. So let's say it is 8. It says that if your part is not exposed for more than eight hours.

If you put it back in the moisture sensitive bag, desiccant and seal it up, that part will reset to 0 in some long time interval. Which I think is the number ten.

Don't hold me on these numbers, read the spec. Okay, you're out for 7 hours, that's less than eight. You close the bag up.

If you keep that bag closed for 10 times 7, or 70 hours then the clock will be reset to 0. The idea being that this really dry air and desiccant does remove that little bit of moisture that you got into the bag.

So that is for these multiple jobs. You may want to read that spec and see if you can take advantage of that if your storage in between runs is long enough.

You may be resetting your clock to 0 on some of these things. But in all cases get that get that Standard 033. It is not big.

Have somebody read it and really understand it. Then define a strategy that works for you in your environment with the frequency at which you open and close these bags.

Phil
My brother brings up a very good point.

Jim
I usually do.

Phil
Yeah, usually. Yes, you do. I won't make a trite comment.

The point is, you really need to have somebody who understands the whole MSD story, as Jim was saying, in terms of 020 and 033 and understanding what it is all about. It is very important that your operators and tech understand it too so that they are diligent about replacing the bag and logging the time.

We recommend, as Jim mentioned, somebody that is actually responsible. For lack of a better word, an MSD guru. Most facilities have somebody who is the go to person for ESD. You want to have it for MSD as well.

You don't have to pay that person a lot of money extra, if anything. It would look good on their resume. We highly recommend that.

Good. I think we covered that subject.

Jim
This is one of the most important topics that we see problems with when we audit facilities. We talk to our customers, we often see lack of clarity on their handling of their moisture sensitive parts. So M.B. the fact that you understand it to this level is laudable.

Phil
Well, very good. I just want to say though Tim Jensen wants to strangle us with the real preforms every time we say it, you have been listening to Board Talk with Jim Hall and Phil Zarrow.

Whatever you do, whether you are dealing with expired MSD components or not, don't solder them like my brother.

Jim
And don't solder like my brother.

Comments

Our business is Corrosion Prevention and Mitigation. Not sure what desiccant types you all are using. Desiccant bags MUST NOT be allowed to come into contact with the components. This especially relevant to silica gel given that silica gel, upon hydration, can result in producing an acidic liquid layer (depending on grade of silica gel) Type A & B Silica Gel'have a pH range of 4 - 8 Other types of desiccants such as magnesium chloride are both acidic and release chloride ions. This is a very corrosive combination to many base metals. If you use desiccants, please ensure they are secured away from direct contact with any substrates.
Wade Rohland, Northern Technologies International Corporation
With regard to MSL I have heard that its best not to vacuum seal the bags. Is this the case? Also I would assume the bat type might have something to do with this?
Eric Rossi, EMAC, Inc.
We stopped using humidity indicator cards many years ago and now use digital temperature/humidity data loggers such as this wireless unit: https://www.lascarelectronics.com/easylog-el-wifi-th Or these USB units: https://www.lascarelectronics.com/easylog-el-usb-2-lcd
Wade Rohland, Northern Technologies International Corporation
If you are counting on the Dessicant in your resealed bag to reset the clock on your components, you need to make sure your desiccant is dry. For example, you have a can full of desiccant packs, and it is sitting around with a loose cover, you now have compromised desiccant. Cans of desiccant should be stored in a dry box once opened. Even if you put the cover on tight. If not, it will need to be baked to dry it out. The desiccant package should have instructions for baking. Now that you have dry desiccant, you put it in the bag and seal it. You use vacuum to seal it? You can, but do NOT fully evacuate the bag. You need to have space for the water vapor to be drawn into the desiccant. Not so much of an issue if you Bake out the parts first, and then vacuum seal, as you then know your parts are already dry.
Alan Woodford, NeoTech
If your humidity levels are close to 20%, uptake will be very low, and you might be able to cut corners. Conversely, high humidity needs super diligence.
Tony Stanley, Tyco
I agree with Phil, it's not good to trust a humidity card, better be adherent with JEDEC standards. About this, I'd like to share my experience about MSL control in shop floor. Years ago we faced this issue in an innovative way. Our final solution was based on software.

The IT guys developed an application (conveniently named MSL) integrated to ERP system that every time a MSD component was opened and scanned by a RF gun its moisture clock is set to run. The system had a series of alarms, green status if MSL was until 80% of time, yellow if between 80% and 99%, and red if MSL was equal or greater than 100% of MSL time.

If the component is not OK (red) to be used in production, due to expired MSL time, it was reproved and immediately sent to baking. If alarm was yellow, MSL clock time for the device was checked by production guys against total MSL time. Finished the production, the MSD component was returned to storage area and the item was scanned again. If it MSL clock was expired, the system displayed a red alarm and the item was sent to baking.

Obviously this is an automated and expensive way to control MSL. However, before this software is placed in site, we had this same control by using adhesive paper labels manually attached on MSD devices and totally controlled by the guys in the shop floor.

All the information about MSL clock time for each MSD device needed was hand written in the label and controlled by people. This is hard to do, complex and time consuming way, but it works with some discipline.
Glayson Figueiredo, Philips Medical Systems

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