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January 2003

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Subject:
From:
"Dehoyos, Ramon" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 6 Jan 2003 11:55:51 -0800
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        Joe:
        The grainy appearance of the solder indicates that its surface has
oxidized. Using the STS or soak to spike profile is one of ways to have this
problem.  The RTS or ramp to spike or the Tent profile where the temperature
is slowly raised than spiked to reflow the solder makes a smooth solder
joint.  The longer the solder stays close to 183 deg C the more oxidation (
grainy and dull) will occur. I used to work for an outfit that all their
solder joints were grainy for many years, till the RTS profile was
introduced. Components are not shocked as much either. This type of profile
(RTS) was presented on one issue of the SMT magazine sometime in the latter
part of 2000.
        Regards,
        Ramon

> -----Original Message-----
> From: Macko, Joe @ IEC [SMTP:[log in to unmask]]
> Sent: Saturday, December 28, 2002 11:44 AM
> To:   [log in to unmask]
> Subject:      [TN] 2nd side reflow problems
>
> TechNets,
>
> Many of our boards are densely populated, double sided, multilayered with
> BGAs on both sides.   Side 1 is populated and reflowed, then side 2 is
> populated and reflowed.  Side 1 therefore sees 2 reflows which appears to
> make the surface of the solder balls on the BGAs reflowed twice appear
> grainier after the 2nd reflow.   A water soluble flux based Sn 62Pb36Ag02
> solder paste is used.  We have also tried using Sn63Pb37 alloy.
>
> Has anyone else experienced similar problems with densely populated,
> double
> sided boards where one side sees 2 reflow cycles?  Is there a practical
> solution for maintaining BGA solder ball appearance thru the 2nd reflow?
> Reflowing in a nitrogen environment is not an option.
>
> Happy Holidays
> joe
>
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