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High Relative Humidity and Blistering Issues in Assembly

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#72580

High Relative Humidity and Blistering Issues in Assembly | 17 August, 2014

Hi All,

I have been looking in to some failures of PCB's in Assembly. After SMT the boards are stored for different periods of time in high humity environment (72% RH and 21.4 degrees Celsius) before being sent to Assembly to be handsoldered/put through a wave machine.

Is there anyway to work out how long say a FR4 board can sit in 72% RH at 21.4 degrees Celsius absorbing moisture without blistering by handsoldering/going through the wave machine?

I have seen a few articles on moisture absorption but no linear/non-linear data that correlates moisture absorbed over time and blistering from handsoldering/using a wave machine.

Thanks,

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#72586

High Relative Humidity and Blistering Issues in Assembly | 18 August, 2014

Off hand, I can't recall a "formula" for how long boards could sit in a specific RH environment. I've done a couple of quick Google searches, and can find a bunch of information on the dispersion rate of moisture in various PCB materials, but, nothing that indicates a standard of time/allowability.

From experience, I'd say that storing boards in a high RH environment for a period of time is, generally, a bad idea. I've had some that survive fine, and others that immediately delaminate. IPC notes that any moisture intrusion into PCB materials is potentially damaging, even if it doesn't cause delamination, as it can affect connection quality and impedence, as well as thermal characteristics and performance.

This paper is a pretty good information source: http://www.ipcoutlook.org/pdf/best_practices_controlling_moisture_ipc.pdf

Anecdotally, if you're experiencing moisture related delamination, and are concerned about the amount of time the boards are stored at the 72% RH, then I'd assume that it's too long, and needs to be shortened...or, augmented with a baking step prior to wave soldering.

Cheers, ..rob

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#72601

High Relative Humidity and Blistering Issues in Assembly | 21 August, 2014

This links to a NPL presentation on moisture removal from PCB http://www.npl.co.uk/upload/pdf/20140318_effect_baking.pdf

Consider: * Focusing on preventing moisture contamination of boards, rather than removing moisture * There will be no standard method for removing moisture due to the wide variation in board design makes it impossible to quantify

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#72681

High Relative Humidity and Blistering Issues in Assembly | 4 September, 2014

Hi all:

Interesting question you have raised as it concerns the rate of absorption by the board material. I represent http://www.EurekaDrytech.com and could assist in resolving the blistering problems you're facing. First some questions.

1. Is the high RH environment consistently at 72% RH and 21.4 degrees Celsius? Or does the temperature fluctuate through different times of the year? (perhaps a country location so we could check the yearly average) 2. Do you manufacture your own boards or do you purchase them from a vendor? 3. If you are manufacturing your own boards, are there any types of baking or dehumidifying storage for the boards post-manufacturing? 4. How much loss are you encountering due to blistering? 5. How many boards and how long are they sitting in the high humidity environment prior to being hand soldered or going through the wave machine?

Thanks for your time, hope to assist in resolving this moisture control issue.

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#72704

High Relative Humidity and Blistering Issues in Assembly | 7 September, 2014

1. Is the high RH environment consistently at 72% RH and 21.4 degrees Celsius?

No, over the past 2 weeks I have recorded the highest at the moment: 67% RH at 22.6 degrees C and lowest (it is Spring not summer yet): 31.9% RH at 19.0 degrees C.

Or does the temperature fluctuate through different times of the year?

It sure does, we are in Auckland, New Zealand (gets really humid here over Spring/Summer months).

2. Do you manufacture your own boards or do you purchase them from a vendor?

We purcahse boards from multiple vendors mostly in China.

3. If you are manufacturing your own boards, are there any types of baking or dehumidifying storage for the boards post-manufacturing?

N/A

4. How much loss are you encountering due to blistering?

Last most about 4 grand worth plus some that had passed the test and gone in to units in to the field (unknown number at this stage). I have a sneaky suspicion that the high humidity conditions are not only causing blistering but quite a few chip/part failures I have seen in Repairs.

5. How many boards and how long are they sitting in the high humidity environment prior to being hand soldered or going through the wave machine?

Thousands of boards can sit for 2 to 3 months depending on BOM changes/customer requirement etc. The longest period of time I have seen the boards sit idle in racks (no bags or decisscant) was approximately 6 months. Most boards are only sitting in racks for a month or less.

Thank you for your quick reply. I hope my answers make sense to you.

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#72715

High Relative Humidity and Blistering Issues in Assembly | 8 September, 2014

Hello,

Manufacturing process with high moisture and humidity environments and long term storage will definitely see pop corning effects once high temperature from soldering and/or re-flow process. The moisture that has been adsorbed is likely the root cause since you are storing the boards in such environment for a long period of time. Eureka Dry Tech can assist in eliminating these problems. Our service will allow you to meet IPC/JEDEC J-STD-033C Standards certification and creating additional value for your products, increase your yield and eliminate waste.

Please see our product application below for further detail information.

http://eurekadrytech.com/high-tech-manufacturing-and-rd-labs

For further details, please contact me at marketing@eurekadrytech.com

Truly yours,

Mike Tsai

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