Time above liquidus

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Re: 63/37 paste reflow Is there a standard reccomended ti... - May 09, 2007 by Jim Z

30 to 90 seconds TAL is typical. ... - May 10, 2007 by PeteC

There is no standard for time above liquidus. It is describ... - May 10, 2007 by davef

I have been TAL around 45 to 90 seconds. I prefer the longe... - May 18, 2007 by Ed Faranda

TAL Too Long - dull solder joints, dewetting. TAL Too Short... - May 25, 2007 by mfgengr

Look here: ... - May 28, 2007 by davef

Jim Z

#50161

Time above liquidus | 9 May, 2007

Re: 63/37 paste reflow

Is there a standard reccomended time (ball park) above liquidus? What are the negative ramifications if the TAL is too short or too long?

Thanks in advance

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PeteC

#50164

Time above liquidus | 10 May, 2007

30 to 90 seconds TAL is typical.

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davef

#50165

Time above liquidus | 10 May, 2007

There is no standard for time above liquidus. It is described rather broadly by the solder paste supplier.

Reflow Zone: If the temperature is too high, boards may char or burn. If the temperature is too low, cold and grainy solder joints will result. Extended duration above the solder melting point will damage temperature sensitive components. It also results in excessive intermetallic growth that makes the solder joint brittle and reduces solder joint fatigue resistance. [R Prasad]

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Ed Faranda

#50297

Time above liquidus | 18 May, 2007

I have been TAL around 45 to 90 seconds. I prefer the longer TAL so, I set my profiles around 80 seconds. In the old days (Before RoSH), the longer times would help with wetting. But, since Lead-Free, well. We all know the story about wetting now. I just kept the longer TAL just out of habbit. Been working great for me.

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mfgengr

#50395

Time above liquidus | 25 May, 2007

TAL Too Long - dull solder joints, dewetting. TAL Too Short - cold solder, insufficient wetting.

You want TAL to be as short as possible (but not lower than 30 seconds), but long enough for every solder joint to be above TAL for at least 30 seconds. Variance in thermal mass of the board, and heating uniformity of the oven govern this. Essentially, the low mass stuff reflows first, and stays in TAL longer, while the opposite applies to the high mass areas. Best way to set up is the mount a few thermocouples to you high mass areas, and set the recipe to them, shooting for the 30 second TAL. All the low mass parts will reflow with a longer TAL. With some of the other themocouples on the low mass parts, you can make sure they do not exceed the 90 second TAL.

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davef

#50404

Time above liquidus | 28 May, 2007

Look here: http://www.aimsolder.com/techarticles/Time%20Above%20Liquidus.pdf

We have no relationship, nor receive benefit from the company referenced above.

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