High Relative Humidity and Blistering Issues in Assembly

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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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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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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