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February 2001

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Subject:
From:
"Marsico, James" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 28 Feb 2001 14:24:20 -0500
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Can't for the life of me see where the solder is going.  The board design is
'pads only".  All surface traces are SMOBC (solder mask over bare copper).
I will try to get a photo.
Jim Marsico
Senior Engineer
Production Engineering
AIL/Electronics Systems Group
An EDO Company
[log in to unmask] <mailto:[log in to unmask]>

        -----Original Message-----
        From:   Kathy Kuhlow [SMTP:[log in to unmask]]
        Sent:   Wednesday, February 28, 2001 1:51 PM
        To:     [log in to unmask]
        Subject:        Re: [TN] Insufficient Solder Joints

        At the locations with the insufficient solder, Is the deposited
solder paste visible or does it look like the paste flowed out to a
via/trace that is connected?  Do you have any photo's of the joints?

        Kathy

        >>> [log in to unmask] 02/28/01 11:56AM >>>
        Ok, here's one for discussion...

        We have a 68 ceramic leadless chip carrier that routinely yields
        insufficient solder at the corner locations.  The details are:
        10 mil stencil
        1:1 apertures (stencil to board)
        Rounded apertures, rounded solder pads
        Sn63 solder paste (water soluble flux)
        Pretinned components (Sn63)
        Reflowed in air

        Observations are:
        Uniform pretinning solder volume
        Uniform HASL on boards
        Perfect solder deposits
        Perfect component placement
        Clean apertures after deposition
        Minute solder balls after reflow (nothing out of the ordinary)

        Here's the kicker...  we use this same component on another board
without
        the occurrences of insufficient solder.  The difference is that on
this
        design the solder pads and stencil apertures are rectangular, not
rounded
        ends.  I know that your first reaction is going to be "Well, it's
obvious,
        rounded apertures deposit less solder paste than rectangular ones,
thus the
        insufficient solder."   I'd say "correct" except that the
insufficient
        joints appear predominantly on the corners!  BTW, the apertures are
the same
        size throughout the component.

        Any ideas?
        Jim Marsico
        Senior Engineer
        Production Engineering
        AIL/Electronics Systems Group
        An EDO Company
        [log in to unmask] <mailto:[log in to unmask]>


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