US 5,729,896 AGranted

Method for attaching a flip chip on flexible circuit carrier using chip with metallic cap on solder

AssigneeInternational Business Machines Corporation

InventorsHormazdyar M. Dalal, Kenneth M. Fallon, Gene J. Gaudenzi, Cynthia S. Milkovich

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Abstract

A structure and method is disclosed for directly attaching a device or package on flexible organic circuit carriers having low cost and high reliability. IC chips with a new solder interconnect structure, comprised of a layer of pure tin, deposited on the top of high melting Pb--Sn solder balls are employed for joining. These methods, techniques and metallurgical structures enables direct attachment of electronic devices of any complexity to any substrate and to any level of packaging hierarchy. Also, devices or packages having other joining technologies, eg. SMT, BGA, TBGA, etc. could be joined onto the flexible circuit carrier.

Claims37

Dependent claims

A method of directly attaching an electronic device onto a flexible circuit carrier, said method comprising the steps of:

(a) providing said electronic device with at least one at least one reflowed solder ball, wherein said, at least one reflowed solder ball has at least one coating of at least one low melting point metal to form a metallic cap,
(b) adhering at least one layer of at least one stiffener sheet with at least one thermo-plastic adhesive onto at least one surface of a flexible sheet,
(c) forming at least one electrically conductive metal line on said at least one surface of said flexible sheet,
(d) coating at least a portion of said flexible carrier with at least one insulator material, and removing selective portions of said insulator material and exposing selective portions of said metal line, and forming a flexible circuit carrier,
(e) screening eutectic solder paste to coat selective sites on said flexible circuit carrier,
(f) placing said flexible circuit carrier on an assembly fixture to hold said flexible circuit carrier,
(g) dispensing at least one solder flux at selective sites on said flexible circuit carrier,
(h) aligning and placing said electronic device onto said flexible circuit carrier, such that said at least one reflowed solder ball with metallic cap makes contacts with said solder flux, and upon heating forms an electrical connection between said electronic device and said flexible circuit carrier.

5 more elements

Dependencies are inferred from the claim text.