If I understand correctly, you deposit solder paste under the component
during the initial build.  After reflow, the paste solidifies and makes
contact with the bottom of the component for heat transfer.  Your question
is what to do when replacing the component.  How do you replace the solder
bumps under the device.

Is the body of the component ceramic or metal?  If ceramic, when you remove
the devise the solder bumps should remain intact, nice and flat.  Why not
leave these bumps as is and place the component, contacting the existing
bumps while soldering?  If the case is metal, and you disturb the bumps
during removal, how about reapplying solder paste, placing the component and
reflowing it with a hot air terminal?  Another option is to change the
drawing to allow the use of a thermal adhesive for rework.

Jim Marsico
Senior Engineer
Production Engineering
EDO Electronics Systems Group
[log in to unmask] <mailto:[log in to unmask]>
631-595-5879


        -----Original Message-----
        From:   Becerra Alejandro [SMTP:[log in to unmask]]
        Sent:   Wednesday, April 24, 2002 4:54 PM
        To:     [log in to unmask]
        Subject:        [TN] Repair of Circuit with Solder Paste below

        Hello to All,

        We have a circuit that requires solder under it because in order to
have a good thermal dissipation.
        The circuit is a QFP48. When assembled in the line, the stencil has
apertures in the body of the component in order to apply solder.

        We have tried to manually apply the solder with an iron tip, but
after cross-sectioning the repair component we have found that

        sometimes the solder is not in contact with the component.
        What could be the appropriate procedure to repair this component?

        Regards,

        Alejandro Becerra



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