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May 2001

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Subject:
From:
"<Peter George Duncan>" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 14 May 2001 09:08:42 +0800
Content-Type:
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You have a problem with outgassing volatiles. The gas movement in the voids
keeps the solder moving until solidus, which causes poor grain structure
that weakens the joint. The poor grain structure is less reflective adn
therefore shows as grey and not shiny.

What area are you trying to solder? Why is the temperature so far above the
liquidous? (This will make the outgassing problem worse). Reduce the
temperature in stages as much as you can, and monitor the effect at each
stage to determine the best temperature versus soak time. Alternatively,
can you pull a vacuum on the soldering process while the solder is above
liquidous? This would help the outgassing of volatiles.

Pete Duncan



                    Jonathan A Noquil
                    <Jonathan.A.Noquil@FAIRCHIL        To:     [log in to unmask]
                    DSEMI.COM>                         cc:     (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
                    Sent by: TechNet                   Subject:     [TN] Solder Voiding
                    <[log in to unmask]>


                    05/11/01 05:55 PM
                    Please respond to "TechNet
                    E-Mail Forum."; Please
                    respond to
                    Jonathan.A.Noquil






Hello Everyone,

Please help,
Can Anybody explain why too much voiding
occurs when two metal is joined (Top Metal
and Bottom metal)? Eventhough the peak temp is
40 C over than the liquidus temp of the solder.
When a solder is reflowed without top metal
the solder wetting is very good and the appearance
is shiny. But when you put a top metal to be joine
and then X-ray, there are a lot of voids.
I tried to removed the top metal, and the picture
below showed a lot of voids. Another thing is the
color is not shiny but grayish.




(Embedded image moved to file: pic29915.pcx)

The paste is 85Pb/10Sb/5Sn
Peak temp is 290 C
Oven: Conduction
Time until the unit is out: 180 Seconds.


Many thanks to everybody.

Sincerely
Jonathan

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