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July 2000

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Subject:
From:
"Furrow, Robert Gordon (Bob)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 18 Jul 2000 13:41:40 -0400
Content-Type:
text/plain
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text/plain (164 lines)
Tom,

Another thing to check is finish metallization of the leads. Is it Alloy 42
or palladium? If so, that could contribute to wetting issues.

Thanks,
Robert Furrow
SMT Process Engineer
Lucent Technologies
978-960-3224    [log in to unmask] <mailto:[log in to unmask]>

        -----Original Message-----
        From:   Jeffery L. Hempton [SMTP:[log in to unmask]]
        Sent:   Tuesday, July 18, 2000 11:56 AM
        To:     [log in to unmask]
        Subject:        Re: [TN] (TN) Reflow Issue

             Tom, I agree with Ioan, check to see if pins are not bent "up"
and are
             able to touch the paste before reflow. Almost every instance I
have
             had with "pillowing", i.e. leads sit on top of solder and
solder has
             good reflow, but forms under the lead (looks like, you know, a
             pillow!) has been due to old/oxidized leads that are not
wetting. Some
             tests I ran in the past demonstrated that solder pastes with 2%
silver
             actually increased the wetting properties of these oxidized
leads, but
             that is a longer term fix (requalification of paste). We use
paste
             with 2% silver partly for this reason. I would perform some
             solderability tests, then push this problem back to your device
             supplier if they are within shelf life.
             good luck,
             Jeff Hempton
             United Technologies Electronic Controls


        ______________________________ Forward Header
__________________________________
        Subject: Re: (TN) Reflow Issue
        Author:  "Tempea; Ioan" <SMTP:[log in to unmask]> at CARMAIL
        Date:    07/18/2000 12:31 PM


        Tom,

        the first thing to check is the date code on the components. Most
likely
        they are old and the leads are oxidized, hence the dewetting you
describe.

        What to do with the bad components, this is the question. I dont
think you
        should try tinning them, since with their fine pitch you'll end up
with tons
        of shorts.
        If you are using more sorts of solder paste, try one with a stronger
flux
        for these assemblies.

        Or maybe the leads are not oxidized, but only not coplanar, so some
of them
        don't even touch the paste, so they will not form a joint.

        Good luck,
        Ioan

        > -----Original Message-----
        > From: Thomas Han [SMTP:[log in to unmask]]
        > Sent: Tuesday, July 18, 2000 12:17 PM
        > To:   [log in to unmask]
        > Subject:      [TN] Reflow Issue
        >
        > Hi all,
        >
        > I have been noticing on our last batch of boards that we ran, some
of the
        > tsop flash chips were not reflowing properly.  I am not getting
very good
        > toe fillets on the chips and some appear as though they are just
sitting
        > on
        > top of the reflowed solder.  This board has a good component
mix(i.e. BGA,
        > QFPs, PLCCsocket, SOICs, total(325-350)).  Other components reflow
fine,
        > but for some reason these TSOPS are not.  Is there something that
we are
        > overlooking?
        >
        > Your input would be greatly appreciated.  Thanks in advance
        >
        > Tom
        >
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