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January 2005

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Subject:
Re: Solder Joint Failures after Short-term Vibration
From:
Kelly Morris <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Kelly Morris <[log in to unmask]>
Date:
Thu, 6 Jan 2005 12:40:04 -0600
Content-Type:
text/plain
Parts/Attachments:
text/plain (51 lines) 
Cheryl's point on 2ndary reflow is a good one.  I"ve seen this a couple of
times.  Also, the fix of changing the wave solder parameters is good too.
Another idea for corrective action, if changing the wave parameters is not
a good choice is to add a thermal barrier to the area under the QFP on the
bottom side of the PCB.  Polyimide tape (Kapton) works good for this.  A
longer term fix may also be to mask over the vias in that area under the
QFP.  The mask can provide enough of a thermal barrier to prevent 2ndary
reflow.

Kelly


On Thu, 6 Jan 2005 12:27:31 -0600, Cheryl Tulkoff <[log in to unmask]>
wrote:

>Roger -
>
>Does this board go through the wave solder process after SMT? You could be
>seeing secondary reflow of the SMT joint at the wave. This happens when the
>temperature of the wave process is sufficient to remelt topside joints. It
>usually happens only on fine pitch QFPs(smaller joints with less solder
>volume). To avoid this, most people will run the wave solder temperature
>lower (240-250 C rather than 260C) and the conveyor faster (5.5 ft/min or
>higher).
>
>I can send more info if you're interested in checking it out.
>
>Thanks,
>
>Cheryl Tulkoff
>Phone:(512) 683-8586
>Fax: (512) 683-8847
>National Instruments
>11500 N. Mopac Expressway
>Building A
>Austin, TX 78759-3504
>
>
>
>

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