IBM, Endicott second year annual report. Executive summary Page: 1 of 34
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IBM, ENDICOTT SECOND YEAR ANNUAL
REPORT EXECUTIVE SUMMARY
by Michael A. Gaynes
IBM Endicott, Assembly Process Design has completed the second year of development activity on
DARPA TRP No. DE-FC-04094AL98817 for High Performance, Low Cost Interconnections for Flip
Chip Attach. The second year of Endicott activity focused heavily on
1. Paste Deposition Process Development
2. Bonding Process Development
The bonding process development includes studies on flip chip encapsulation, thermal process modeling
A brief summary of the objectives and key accomplishments follows for these two process efforts.
Attached are detailed reports for deposition and bonding process development.
PASTE DEPOSITION PROCESS DEVELOPMENT
Objective: PMSP (Polymer Metal Solvent Paste) material must be deposited on a five inch wafer with
100% bump survival. The target geometry is 0.010" diameter, and 0.004" high with a flat surface.
Accomplishments: The photobumping process has been refined to yield bumps that are 0.010" in
diameter and greater than 0.0035" high. The surface is flat and bonding results in a strong bond with
no air entrapment between the chip bump and card pad.
Initial work with photobumping yielded a bump surface that was concave. In photobumping, 0.004"
thick photoresist is imaged to create apertures. These apertures are filled with PMSP in two passes with
a solvent drying process that occurs between the first and the second pass After the first pass filling,
solvent from the PMSP interacted with the photoresist and caused the top surface, at the circumference
of the aperture, to shrink. On the second pass filling, this slightly depressed surface fills up with PMSP.
We call this blooming because the diameter of the bump is extended at the surface. When the
photoresist is stripped, the thin surface extension of the bump diameter is folded over on top of the
bump. This fold created a ridge at the circumference of the bump that would make initial contact with
the card surface during bonding. The result was a high probability of air entrapment at the joint
interface. The blooming problem was corrected by changing from an aqueous to a semiaqueous
photoresist that was more solvent resistant. Flat surface bumps are made with 100% yield on five inch
wafers. Double layers of 0.002" photoresist are used to define the nearly 0.004" high bumps. Work is
in progress to use single layers of 0.003" and 0.004" photoresist. A single layer should eliminate
perturbations from a straight side wall profile that exist near the interface of a double photoresist layup.
MASTER -STRIBUTION OF THIS dOCUME IS UNLIMrTED
IBM, ENDICOTT SECOND YEAR ANNUAL REPORT EXECUTIVE SUMMARY
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Gaynes, M.A. IBM, Endicott second year annual report. Executive summary, report, November 1, 1996; United States. (https://digital.library.unt.edu/ark:/67531/metadc688626/m1/1/: accessed April 18, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.