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Desiccants and pcb finish degradation?

ohboy

#6604

Desiccants and pcb finish degradation? | 15 May, 2001

Hi all, I just discovered this forum and I'm very impressed.

We have a vendor who recently stopped placing desiccants in the vacuum packaging for our pcbs. (Yes, it's on the dwg!)

His reasoning was that the desiccants can degrade the finish on the pcb. I have never heard of this, and I'm wondering if anyone has any further info about such claims. We have asked for something in writing from a reputable source to support, but have not received anything yet.

If he's correct, we may have some real issues, because we request every vendor send us pcb's with desiccants enclosed. If he's wrong, well, it'd be nice to show him something in writing.

Thanks much in advance.

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#6608

Desiccants and pcb finish degradation? | 15 May, 2001

Welcome!!! Where the hay ya been???

Sorry bud, were lining-up with your fab [it hurts me to say that, but when yer  ]

We used to dry pack with desiccants, also. Its probably an old MIL-STD-2073-1C requirement [er something like that]. We quit, because: * Cant imagine that those little bags of stuff would do anything meaningful from a moisture absorption stand-point. Theyre usually too localized to be effective. Look at page 32 on [http://www.npl.co.uk/npl/ei/presentations/storage.pdf ]. * Be careful of the desiccant you use. Some give off a silicon oxide vapor [Silicon oxide is the main ingredient in most desiccants] and may inhibit subsequent soldering operations. [No sourced documentation, just hear-say.] * Most desiccant packs are static charge generators. Check the answer to question #406 at http://www.esdsystems.com/qanda/questions/questions21.html

We just throw on of those little humidity indicator cards [hic]  [The kind that come with moisture sensitive parts. We have a coffee can full of them and just run them thru the reflow to freshen them up] in the bag to indicate if it's sealed poorly.

Id like a reference from your board fabricator describing the concern that they have.

Finally, why are you telling your supplier what to do? Why dont you just tell them what you want? [Like, give me boards with traces like this and are solderable under bla, bla, bla conditions.]

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ohboy

#6614

Desiccants and pcb finish degradation? | 16 May, 2001

I been a bunch o' places...! Some good, some bad, re-inventing the wheel in many cases.

Our specs are pretty specific in a lot of cases, but that doesn't mean they always get followed. It usually becomes a case of "It's not quite right, but we really need it anyway", so enforcing such things are not that easy.

I'm waiting for a reference myself. It'd be nice if they told us first, before they made a change, what their concerns were. That's my main beef.

It's that silicon-oxide vapor kind of thing I was looking for- ie, what is it about the desiccant that would degrade solderability?

I personally, in 8-9 years of smt mfg, have not seen issues related to moisture unless there is something grossly wrong with the design, materials, fab, or storage, or some combination of such, so I tend to agree about the (non) effectiveness of desiccants in this app.

Thanks much for writing, it helps a lot!

Bill

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#6648

Desiccants and pcb finish degradation? | 21 May, 2001

I said: "Our electronic circuit board fabricators seal the boards in moisture barrier bags [MBB]. We discontinued the use of desiccant bags in these MBB because of concerns about the desiccant releasing materials that would affect the solderability of the boards we receive. What do you think?"

Sorbent Systems said: "We have created bags that use uncoated tyvek for this reason. approved and required at major chip producers." [Kevin Cullen, Customer Service, sales@sorbentsystems.com]

Drierite said: "We thank you for your question. I'm not sure if you were using our desiccant bags or not, but I wish to provide you with complete information on our bags. Our desiccant is Calcium Sulfate, which is a natural mineral mined from the ground. The outer bag material itself is a brown Kraft crepe style paper. The desiccant bags are designed to absorb the water and/or water vapors it comes in contact with. The bags do not emit anything back off. They only absorb. If you would like to consider using our desiccant bags as an aid in fighting moisture please visit our website at http://www.drierite.com to get complete pricing and packaging data. We have 6 different sizes in our desiccant bag line, so determining which size bag you need will be based on the size of your packaging. If you have any further questions, please feel free to contact us." [Sandy at DRIERITE@aol.com]

J. Travis, Inc. said: "I'm sorry but I'm not sure who you are. Can you help?" [Jim Travis ]. When I responded, Mr. Travis sent me the following link: http://www.staticcontrol.com/desiccants.asp.

Desiccare said: "If you would be so kind to call me 800-446-6650 Ext 203." [Brad Wolk ] I called, Rochelle told me that Mr. Wolk was in Hawaii and that he would return my call, Mr. Wolk has not returned the call. [Now, that�s life as I know it!!!!]

IMTEK Environmental Corporation said: "Our desiccants should not have any emissions. However, it is best that you do a test to confirm this for your products." [D. Keller IMTEK@No-Odor.com]

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ohboy

#6656

Desiccants and pcb finish degradation? | 22 May, 2001

Wow! I'm going to apply for something at Desiccare, I think...

I found similar things about desiccants, but mostly material related stuff, also some concerns more about the indicator card than the desiccant. Nothing conclusive.

At the moment, I'm looking into getting some testing done for emmissions. We have everything but the IMTEK stuff in house at the moment.

Still waiting for something from our vendor... I think they just ran out and it was a good excuse.

Thanks Dave! I'll be sure to keep you posted about my results from the emmissions testing if I can get it done without miles of red tape.

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