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Storage conditions (temperature and humidity) for Printed-Circuit-Board-Assembly (PCBA)

Posted on 2006-07-13
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Would like to know storage conditions (temperature and humidity) for PCBA (especially with BGA and mirco BGA chips mounted on it by reflow-soldering). I already searched thru JEDEC for answers but they have recommendation only for solid states device BEFORE reflow-soldering.

More background - our factory manufactures VGA card with SMT process (Screen-Printing - Pick-N-Place - Reflow-soldering). Recently we had VGA cards returned from our end-customer with failure symptom of no boot-up. We can fix these returned VGA cards by just baking them with 125C@6 hrs - then it will boot-up and function ok. It seems that there is moisture coming inside the VGA cards and caused problem. We would like to close this case by recommending storage condition (temperature and humidity range) for our end-customers - it will be better if the recommended storage condition is supported by common industrial standard but I just can't find it.
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Question by:Tinsony
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by:grg99
ID: 17098367

You might also want to look at your card-washing procedures.  It's unusual for IC's to absorb much moisture, but any residual fluxes on your boards may be doing so.  Look underneath any high-impedance nodes in your circuitry, such as the crystal oscillators.  Flux tends to get trapped below small capacitors and lead to humidity problems later on.

or you may find the problem happens in shipping, long before it ever gets to your end users.  So specifying storage temperatures for the end users isnt going to help in this case.

 Shipping by sea will subject your cards to very high humidity and high temperatures.  You can't control that.

The common solutions are to enclose your product in an guaranteed impermeable shrink wrap, and place a small packet of silica gel inside the package to absorb any residual humidity.   Cost is just a few cents per item.   This has been done for at least 50 years for items coming from overseas.
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by:Tinsony
ID: 17100640
ThankX, grg99.

Totally agree below -

"or you may find the problem happens in shipping, long before it ever gets to your end users.  So specifying storage temperatures for the end users isnt going to help in this case. Shipping by sea will subject your cards to very high humidity and high temperatures.  You can't control that."

However, this cards were made ~3 yrs ago and returned by end-customers. Our OEM SQE also understand above but they need sth that sound reasonable to close the case. My original plan was to bring the same point as yours -

Moisture can be incuded during shipping and handling. Please try to store them under certain "temp/hum range."

That's why I need storage temp/temp range suggested by known industrial standard - it is more for political reason.

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by:grg99
ID: 17102124

I would go look at the specs for a good piece of equipment, say a Hewlett-Packard PC.  Unfortunately those specs say up to 80% or 90% relative humidity!

http://docs.hp.com/en/A5191-96018/apbs06.html?jumpid=reg_R1002_USEN


If possible, I'd have the "bad" cards carefully evaluated as to WHY they failed due to high humidity.

"Moisture can be incuded during shipping and handling. Please try to store them under certain "temp/hum range.""

Unfortunately that doesnt help your OEM or end users-- by the time they get the card it may have already been subjected to extremes.  And once the card is on land, it's unlikely they'll stress it as much as the sea voyage did.

I think you need to investigate the exact causes.  Just suggesting the innocent parties follow some rules they are already following is not likely to help things much.





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by:public
ID: 17135772
>Recently we had VGA cards returned from our end-customer with failure symptom of no boot-up. We can fix these returned VGA cards by just baking them with 125C@6 hrs

You are making unsupported conclusions. Boards may be defective when assembled, and the baking temporarily restores bad solder joints.
Humidity is even more important before soldering, especialli fine pitch BGAs.
I suggest you spend some money to isolate the root cause of the failure by destructively analyzing the failed boards

Cleaning may be another problem leaving hygroscopic ionic residue on the board.
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by:doraiswamy
ID: 17136996
It is important to understand why the moisture created the problem in the first place. The moisture could have combined with the residual flux of the soldering process to create a conductive path between two connection points. When baked to 125 C, the moisture evaporated, and along with it the conductive path disappeared.

One of the ways I have solved similar problems is to clean the PCBs in Iso Propyl Alcohol (IPA). Ensure that this is high grade, as inferior quality IPA itself has plenty of moisture dissolved in it. Preferably use an ultrasonic cleaning tank. After the cleaning, dry the PCBs by blowing a stream of dry air over them. Then spray an inert coating (also called conformal coating) over the boards, both solder and component side. This seals the exposed surfaces and contacts. The spray I used was called CRC Acryform.

IMO the baking does not restore the bad solder points, since the melting point of solder is > 125 C.

HTH.
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public earned 500 total points
ID: 17139952
>IMO the baking does not restore the bad solder points, since the melting point of solder is > 125 C

Baking restores bad joints by distorting the board just enough for incompletely reflowed balls to make contact.
Alcohol cleaning is not compatible with many fluxes. Have the boards properly analyzes before ill advised "solution" makes the problem worse.
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