IBM, Endicott second year annual report. Executive summary
PMSP (Polymer Metal Solvent Paste) material must be deposited on a five inch wafer with 100% bump survival. The target geometry is 0.010{double_prime} diameter, and 0.004{double_prime} high with a flat surface. Accomplishments: The photobumping process has been refined to yield bumps that are 0.010{double_prime} in diameter and greater than 0.0035{double_prime} 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{double_prime} 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 PM SP 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 PM SP. 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 photorcsist that was more solvent resistant. Flat surface bumps are made with 100% yield on five inch wafers. Double layers of 0.002{double_prime} photoresist are used to define the nearly 0.004{double_prime} high bumps. Work is in progress to use single layers of 0.003{double_prime} and 0.004{double_prime} photoresist. A single layer should eliminate perturbations from a straight side wall profile that exist near the interface of a double photoresist layup.
- Research Organization:
- International Business Machines Corp., Endicott, NY (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- FC04-94AL98817
- OSTI ID:
- 399728
- Report Number(s):
- DOE/AL/98817-8-Pt.2; ON: DE97000847; TRN: 96:006398
- Resource Relation:
- Other Information: PBD: [1996]
- Country of Publication:
- United States
- Language:
- English
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