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SMT electronics assembly manufacturing forum.


Moisture absorption in the solder paste

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#37684

Moisture absorption in the solder paste | 7 November, 2005

Hi,

We have faced the solderability issue (Dewetting and solder balls)in all the Boards after reflow.When we found this issue we discarded the old paste and started using the new paste then for some hours the solderability found to be O.K. After some time again the dewetting and solder ball issues had come.On analysing we found that because of humidity abosrpiton in the paste we had this issue. Anybody can suggest us the way to remove the Humidity absorbed in the Solder paste.(Which we have discarded)

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#37686

Moisture absorption in the solder paste | 7 November, 2005

No way I've ever heard to remove mositure from solderpaste. What is the R.H. in your factory? Are you in the tropics? Does you printer have an enclosed print area like on an automatic machine, or is it semi-automatic and exposed to the room air?

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#37688

Moisture absorption in the solder paste | 7 November, 2005

It could be you are drying out your solder paste. Most flux formulations are alcohol based and after a few hours can dry out. This can can lead to dewetting and solder balling as well. Especially if you do not homeplate your R's and C's.

A simple way to check is to add a small amount alcohol to the old paste and run a few boards.

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#37729

Moisture absorption in the solder paste | 8 November, 2005

Pete, the SF Bay Area gets very muggy this time of the year. Look here http://www.weather.com/weather/local/94110?lswe=94110&lwsa=WeatherLocalUndeclared&from=whatwhere

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#37730

Moisture absorption in the solder paste | 8 November, 2005

We buy humidity as a potential cause of solder balls, but we're not biting on dewetting. Something else is causing that.

Questions are: * What's the temperature and RH of your SMT production area? * What kind of paste are you using? [Some water washable pastes like to take on moisture.] * Could your boards be absorbing the moisture, rather than the solder?

Finally, solder balling has to be the MOST popular topic here on SMTnet. Search the fine SMTnet Archives for background discussion.

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#37732

Moisture absorption in the solder paste | 9 November, 2005

Hi Dave,

Normally in our country (India) during rainy season the temperature will be 25to 30 �C and RH of 50 to 60%. The reason behind this humidity issue is that recently we have moved to our new facility with centralised air conditioner with Chillers.We were not having control over the Humidity and Humidity inside was found to 70 to 80%.Moreover our stencil printer is printingthe solder pasre in the open environment (No doors).

Regarding the solder paste we are using Kester No clean paste R277. About PCB mositure absorption , prior to printing wearebaking the D/S Boards @125�C for 1Hour and Multilayer boards for 4 Hours @ 125�C.

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#37741

Moisture absorption in the solder paste | 9 November, 2005

Hi Herb,

Lexman, try a different paste to eliminate that question mark. Unless you're stuck with Kester, it's worth a couple hours of your time. I know of a couple SMT plants that run 40% to 50% humidity without any problems.

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Amol

#37753

Moisture absorption in the solder paste | 9 November, 2005

where in india are you laxman? and what kind of manufacturing are you involved in?

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#37768

Moisture absorption in the solder paste | 9 November, 2005

Hi Amol,

We are in South part of India.basically we are basically EMS providercatering to the needs of our Overseas customer and partiallytodomestic market. We are also providing complete manufacturing solutions including cable harness, enclosure assembly.

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