UV Curable Urethane Encapsulant for Ceramic Chip Carriers
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A new acrylated methane encapsulant has been formulated for use on ceramic chip carriers. This encapsulant has been implemented on pin grid array (PGA) ceramic carriers and on peripheral leaded surface mount (SMT) ceramic carriers for IBM''s C4 chips. The encapsulant is a UV curable material and is used to cover the thin-film circuitry on the ceramic carrier. The encapsulant offers a low-cost alternative to the metal caps that were used on the pin grid array ceramic carriers or to the ceramic cap that was used on the peripheral leaded surface mount carrier. UV curing was chosen as the preferred curing process in order to improve the manufacturing process flow. The packages used with this encapsulant all employ IBM''s C4 chips. The C4 joints to the ceramic carrier are strengthened with a silica-filled epoxy encapsulant. The new UV curable urethane encapsulant is used to protect the remaining exposed circuitry from mechanical and environmental damage. The urethane encapsulant covers everything from the chip edge to the outer edge of the package. The backside of the chip is intentionally left uncovered. When thermal enhancement is needed the heatsink is bonded directly to the chip. Significant improvement in internal thermal resistance is realized with this design.