I have pulled out an old Technet thread regarding profiling as I need to
understand the impacts of exceeding 90 seconds over liquidus for Sn63Pb37
solder connections.
My experience in reflow profiling tells me that 90 seconds maximum is very
difficult to achieve if the relative thermal masses on the board vary a lot.
In particular, I am interested in hearing what the impact of running
approximately 105 seconds over 183 C will have, provided none of the
connections exceed the 220C maximum.
And even in the KIC paper
"http://www.kicthermal.com/library/tsbcotp.html#time_above_reflow, times up
to 120 seconds are referenced.
Please help me understand the facts regarding the gray area.
I am hearing that the time over liquidus for lead free is going to have to
be shorter due the inability of flux to withstand the higher reflow
temperatures.
Thanks in advance.
At 03:55 PM 11/8/2001 -0500, Alan Kreplick wrote:
>Nancy,
>
>Check out the paper "A Comparison of Methods for Attaching TCs to PCBs for
>Thermal Profiling" which is on KIC's web page:
>http://www.kicthermal.com/press/articles.html along with several other
>good articles on reflow profiling.
>
>We were using Kapton, but recently found that it was masking the
>temperature by 5-10 C. The methods of attachment, in order of accuracy and
>repeatability that I've heard/read about are: temp-probes (or similar),
>hi-temp solder, aluminum tape, and Kapton/glue at the bottom.
>
>As for the questions:
>1. where to put the thermocouple: board and/or paste as a minimum
>2 typical or maximum profile: typical, but each assembly gets profiled.
>3. specify typical condition: based on the solder paste suppliers
>recommendations and the board design (layers, thickness, size/mix
>components, etc).
>
>Well, that's my two cents,
>
>Al Kreplick
>Sr. Mfg. Eng.
>Teradyne, Inc.
>978-370-1726
>
>
>
> (Embedded
> image moved TechNet <[log in to unmask]>
> to file: 11/08/2001 03:25 PM
> pic08573.pcx)
>
>
>
>
>Please respond to "TechNet E-Mail Forum." <[log in to unmask]>
>
>To: [log in to unmask]
>cc:
>Subject: [TN] Reflow Process Profiling Methods
>
>
>Hi Technet,
>
>I need some help to identify the most common methods of thermocouple
>placement when profiling reflow processes. And while we are on the
>subject, I would also like to collect information on targeting for typical
>or recommended profiles versus absolute min/max boundaries. Just three
>easy multiple choice questions....
>
>1. Where do you put the thermocouple?
> a. Embedded in a solder joint?
> b. On top surface of a component? (If so - how do you attach the TC to
> the part?)
> c. On surface of the PWB?
> d. In air?
>
>2. Do you target reflow profiles to fit a "typical" curve or do you just
>try to stay below a maximum?
> a. Target for typical?
> b. Stay below maximum?
>
>3. How do you specify that Typical or Maximum condition?
> a. Peak Temperature and Maximum Time at that Peak? (Please define
> conditions.)
> b. Total time above a fixed value (usually 183°C or 200°C)? (Please
> define conditions.)
> c. Solder Paste Alloy composition for above values? (If you are running
> both SnPb and Pb-free, please reply for both)
>
>If any of you would like to share soft copies of actual time/temp profiles
>that you use for targeting or specifying an acceptable range of reflow,
>please email to me off-line.
>
>Thanks in advance for your help.
>Nancy Reynolds
>KEMET Electronics
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Qualcomm Incorporated
5775 Morehouse Drive
San Diego, CA 92121
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