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SMT electronics assembly manufacturing forum.


Steve LeCour

#11770

Moisture sensitive device processing | 23 April, 1999

At Sanders (Military manufacturer), we have only started using plastic parts within the past few years. After being tasked with reviewing the new J-Std-033, it became obvious to me our process for controlling device exposure is weak. We build very low quantities (5-100 bds) and procure many parts from distributor. Our experience pushing back on Suppliers to meet our needs has been poor. What I would like is information on the typical control process used (ex. max floor exposure times, how class 5a and 6 parts are dealt with, requirements placed on suppliers/stockroom, use of dryboxes and/or in-process baking). I was also told the issues are two fold, popcorning during reflow and long term reliability degradation. Popcorning is obviously a concern, can anyone lead me to information on reliability degradation or is this bull. I appreciate the feedback. Steve

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Earl Moon

#11771

Re: Moisture sensitive device processing | 25 April, 1999

| At Sanders (Military manufacturer), we have only started using plastic parts within the past few years. After being tasked with reviewing the new J-Std-033, it became obvious to me our process for controlling device exposure is weak. We build very low quantities (5-100 bds) and procure many parts from distributor. Our experience pushing back on Suppliers to meet our needs has been poor. What I would like is information on the typical control process used (ex. max floor exposure times, how class 5a and 6 parts are dealt with, requirements placed on suppliers/stockroom, use of dryboxes and/or in-process baking). I was also told the issues are two fold, popcorning during reflow and long term reliability degradation. Popcorning is obviously a concern, can anyone lead me to information on reliability degradation or is this bull. I appreciate the feedback. | Steve | Steve,

It's no bull, but it does invite chaos. We are actively pursuing the moisture sensitive issue at H-P. I am not the resident expert. He declined my invitation to answer your questions as he is not too sociable - though a good guy.

What I know is this: We use IPC moisture sensitive guidelines (I didn't have time to get the numbers) and currently are installing moisture removal, baking, vacuum sealing, dessicant, and moisture labels in all BGA and other moisture sensitive device types.

We, and many others, have discovered the adverse affects of moisture sensitivity. They are present in most plastic types including BGA's, super BGA's, and uBGA's. To combat these effects, as often observable with X-Ray (internal connection disruption) and SEM, we are setting incoming and ongoing procedures. They consist of using supplier moisture sensitive specifications for reading indicators, when to open moisture sensitive/ESD protective bags, how long parts may be exposed to atmosphere, when to bake after over exposure, and how to re-seal parts in new bags with dessicants and moisture detection cards.

I am particularly interested as a process improvement, new process introduction, and rework/repair manufacturing engineer. I see the effects from stencil printing through reflow and through having to remove and replace these parts.

I will try to get my good friend John Hall, here, to give you more information. It actually is quite basic, but somewhat involved as it is necessary to change a culture not noing anything about this issue and how to implement the process from receipt to shipment. Also, a clearly defined database must be setup to administer the process from identifying the moisture sensitive parts and ensure they are carefully processed (this is the hard part - getting management to understand)

Earl Moon

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#11772

Re: Moisture sensitive device processing | 26 April, 1999

Steve,

Moisture sensitivity needs to be taken seriously. Being in the commercial end of electronics now, I am using many plastic packages. Unfortunately, moisture sensitivity processing is not black and white and it does require procedures and disipline. I constantly deal with distributors that don't follow the manufacturers' specs for drypacking and we end up having to bake parts before assembly. And, of course, they are always the parts that are late and we needed to build them yesterday. I am not surprised with your experience with your suppliers. If you buy direct from the manufacturer you will have properly packaged parts, but I know that is difficult when not buying in volume. It is kinda like solderability. The manufacturer should be the one guaranteeing a solderable part, yet it seems the user always ends up doing the testing and living with the questionable finishes.

To get you started on processes, get a copy of IPC-SM-786, Procedures for Characterizing and Handling of Moisture/Reflow Sensitive IC's. It has the details on classification, packaging, baking, etc. Also, Motorola has a technical data sheet on Drypacked Devices. It is #AN1260. Your Motorola rep. can get it for you or it may even be available from their web site.

By the way, baking isn't just for the initial assembly. If you have a failed sensitive component you want to do failure analysis on, you will have to bake the board (at a lower temperature for a longer time) before removing the component or else you may popcorn it depending on your reflow temperature. I learned that the hard way on some PBGA's we sent back to Motorola for FA. They couldn't do anything because the laminate separated and many wire bonds broke. So, as you can see, moisture sensitivity is real.

Bob

| At Sanders (Military manufacturer), we have only started using plastic parts within the past few years. After being tasked with reviewing the new J-Std-033, it became obvious to me our process for controlling device exposure is weak. We build very low quantities (5-100 bds) and procure many parts from distributor. Our experience pushing back on Suppliers to meet our needs has been poor. What I would like is information on the typical control process used (ex. max floor exposure times, how class 5a and 6 parts are dealt with, requirements placed on suppliers/stockroom, use of dryboxes and/or in-process baking). I was also told the issues are two fold, popcorning during reflow and long term reliability degradation. Popcorning is obviously a concern, can anyone lead me to information on reliability degradation or is this bull. I appreciate the feedback. | Steve |

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