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Un-Reflowed Paste

Chris C

#29662

Un-Reflowed Paste | 26 July, 2004

We are seeing un-Reflowed paste along the IC leads. There is only a very small amount imbedded in the flux, typically there is about 10 beads per lead. But on most leads. We are using no-clean Kester 256 paste (Easy Profile)We have not encountered this until this summer. Any Ideas?

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#29669

Un-Reflowed Paste | 26 July, 2004

How do you know that those specks of solder have not been reflowed? Could it be that what you are seeing is reflowed solder ejacta from a poorly controled reflow process?

While not as prevalent problem with NC as with water soluable, moisture in the air can lead to solder balling. Search the fine SMTnet Archives for other drivers to solder balling.

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Chris C

#29695

Un-Reflowed Paste | 27 July, 2004

By looking at the solder balls they have not joined with the other particles that are alongside them. suggesting that they did'nt reflow. But they could very well be as you suggested, reflowed and ejacta from the process.

We have been experiencing very high humidity, which is difficult to control.

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#29696

Un-Reflowed Paste | 27 July, 2004

Hello , I agree with the solder ball theory, we used to have an issue with high humidity and it produced the results you�re describing. Our solution to this since adding dehumidifiers was too costly was to increase the quantity of intake ducts for the A/C and spread them around the room, basically using the a/c to dehumidify. One thing I do suggest is to invest in a logging meter one that does temp and humidity OMEGA is a good source for these, it�s very helpful to track the temp/humd and cross check against the product.

Hope this helps

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NTV

#29709

Un-Reflowed Paste | 28 July, 2004

It would be uncontrolled reflow process. Solder paste smeared, outdate solder paste, contamination, and many else could lead to this issue. A longer time reflow window would help elimating it (make it max. of 60 seconds liquid time).

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NTV

#29710

Un-Reflowed Paste | 28 July, 2004

It would be uncontrolled reflow process. Solder paste smeared, outdate solder paste, contamination, and many else could lead to this issue. A longer time reflow window would help elimating it (make it max. of 60 seconds liquid time).

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NTV

#29711

Un-Reflowed Paste | 28 July, 2004

It would be uncontrolled reflow process. Solder paste smeared, outdate solder paste, contamination, and many else could lead to this issue. A longer time reflow window would help elimating it (make it max. of 60 seconds liquid time).

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NTV

#29713

Un-Reflowed Paste | 28 July, 2004

> We are seeing un-Reflowed paste along the IC > leads. There is only a very small amount imbedded > in the flux, typically there is about 10 beads > per lead. But on most leads. We are using > no-clean Kester 256 paste (Easy Profile)We have > not encountered this until this summer. Any > Ideas?

It would be uncontrolled reflow process. Solder paste smeared, outdate solder paste, contamination, and many else could lead to this issue. A longer time reflow window would help elimating it (make it max. of 60 seconds liquid time).

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NTV

#29714

Un-Reflowed Paste | 28 July, 2004

It would be uncontrolled reflow process. Solder paste smeared, outdate solder paste, contamination, and many else could lead to this issue. A longer time reflow window would help elimating it (make it max. of 60 seconds liquid time).

This message was posted Add this forum to your site! Click to learn more. the Electronics Forum @

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NTV

#29715

Un-Reflowed Paste | 28 July, 2004

It would be uncontrolled reflow process. Solder paste smeared, outdate solder paste, contamination, and many else could lead to this issue. A longer time reflow window would help elimating it (make it max. of 60 seconds liquid time).

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Steve Stach

#29724

Un-Reflowed Paste | 28 July, 2004

Both temperature and humidity can cause solder paste to behave in a way to cause these formations.

Temperature can cause slumping, slumping spreads out the paste, upon reflow perimeter paste does not join the bulk, and because of insuffient oxide removal on the balls and insufficient ball density, the perimeter balls do not join together.

Humidity effects the thixotropic properties of the solder paste, thinning out the liquid/semi-solid beyond where it should. This then also results in solder balls at the perimeter for the same reasons.

Something to consider, Steve Stach www.aat-corp.com

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