Carrie,
This parameter has always been at this temperature for as long as I can
remember. Basically, the general guideline that I follow is that I leave my
pot set at this temperature and my conveyor speed at 4.0 feet per minute. I
adjust my preheat temps so that I see top side board temps of 90 - 100 C
just prior to the wave. This is the point where flux activity is maximized.
Profiles that I have run have indicated that I achieve 3 to 6 second topside
joint exposure above the liquidus temp of the 63/37. This gives me great top
side wetting on thru hole components without causing reflow of existing SMD
joints. That is why 260C is a good temp for the typical PC usual typical PC
board. That's why I use this temperature and conveyor setting. Then all is
needed is adjustment of the preheat parameters.
I did have one instance where a PCB vendor recommended a 220C solder
temperature to prevent a delam from occurring at a flex junction. That's
what we did. We were able to do this because the board was on the thin side
(.045"). But we did have to schedule these boards for specific time periods
so the solder pot could stabilize at 220C. Changing the temperature of 2000
lbs. worth of solder takes time. Hence another reason for the 260C, it just
seems to be a good universal temperature to keep this massive amount of
metal set for good general soldering.
I would have to think that lower pot temps would affect the quality of
topside fillets on some of my backplane boards. I would have to offset the
lower pot temperature with higher preheat temps or slower conveyor speeds. I
think that doing this would reduce the flux activity. So the benefits of
lower pot temps would have to be quantified before I start messing with the
260C setting.
Most component specs, (that I can recall), specify 260C as the exposure
temperature. (e.g. 260C for 10 sec.) This would be another reason for the
260C temp selection.
Should be interesting to see if anyone does something different and why.
Bill Kasprzak
Moog Inc. Manufacturing Engineering, Electronics
> -----Original Message-----
> From: Morse, Carrie [SMTP:[log in to unmask]]
> Sent: Friday, January 10, 2003 3:15 PM
> To: [log in to unmask]
> Subject: [TN] Wave Temperature
>
> As I sit here on a Friday afternoon with little time to start thinking
> about questions that would be great for a "PCB Assembly Trivial Pursuit"
> game, I thought of something.
>
> At what temperature does everyone run their Sn63Pb37 wave machine....and
> Why?
>
> We run ours at 260C, but, don't know why. We started to get into the
> discussion as to why, and, some of the reasons were: 1) That's what was
> recommended, 2)It's hot enough to burn off the flux, 3)It reduces surface
> tension.
>
> Can someone enlighten us?
>
> Thanks,
> Carrie
>
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