Browse Prior Art Database

Increased Solder Standoffs Using Donor Lead Frames

IP.com Disclosure Number: IPCOM000109955D
Original Publication Date: 1992-Sep-01
Included in the Prior Art Database: 2005-Mar-25
Document File: 1 page(s) / 41K

Publishing Venue

IBM

Related People

Caulfield, T: AUTHOR [+5]

Abstract

Perimeter I/O pads for MCM (multichip modules) can be connected to TAB frames or to similar structures that may be seen as a cross between a lead frame and a TAB structure. The I/O pads have been coated with solder to allow connections to be made between the MCM and lead frame. To make these solder pads thick enough for increased standoff height and to take advantage of the compliant nature of the solder column requires a vacuum-deposited solder process similar to C4 evaporations. Disclosed is a method to increase solder column heights by using the coating on the lead frame to act as a solder donor.

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Increased Solder Standoffs Using Donor Lead Frames

      Perimeter I/O pads for MCM (multichip modules) can be connected
to TAB frames or to similar structures that may be seen as a cross
between a lead frame and a TAB structure.  The I/O pads have been
coated with solder to allow connections to be made between the MCM
and lead frame.  To make these solder pads thick enough for increased
standoff height and to take advantage of the compliant nature of the
solder column requires a vacuum-deposited solder process similar to
C4 evaporations.  Disclosed is a method to increase solder column
heights by using the coating on the lead frame to act as a solder
donor.

      The carrier is held in a nest that includes a bias heater and
and a fixture to hold the lead frame in position relative to the
carrier.  The carrier is fluxed with a suitable flux for the selected
solder on the carrier and the solder that has been plated on the lead
frame.  A temperature bias will facilitate the reflow and will be
dependent on the mass of the MCM.  Using a hot air reflow tool, the
solder connection at the pad/lead interface is allowed to reflow.
Moving the lead frame fixture toward the hot air tool while the gas
remains flowing will allow the solder on the lead frame to melt and
contribute additional solder for the increased standoff height shown
in the engineering drawing below.

      Disclosed anonymously.