International Business Machines Corporation

U.S. Philips Corporation

Olin Corporation

Cyrix Corporation

Thomas Caulfield

John Saunders Corbin, Jr

John Acocella

Karl G Hoebener

Joseph Angelo Benenati

Donald R Banks

David P Watson

Paul R Hoffman

Keshav B Prasad

Susan McGee

Sean T Crowley

Hemant S Betrabet

Otmar H Boser

Robert H Kane

High melting temperature Pb/Sn 95/5 solder balls are connected to copper pads on the bottom of a ceramic chip carrier substrate by low melting temperature eutectic Pb/Sn solder. The connection is made by quick reflow to prevent dissolving Pb into the eutectic solder and raising its melting temperature. Then the module is placed on a fiberglass-epoxy circuit board with the solder balls on eutectic Pb/Sn solder bumps on copper pads of the board. The structure is reflowed to simultaneously melt the solder on both sides of the balls to allow each ball to center between the carrier pad and circuit board pad to form a more symmetric joint. This process results in structure that are more reliable under high temperature cycling. Also, to further improve reliability, the balls are made as large as the I/O spacing allows without bridging beam on balls; the two pads are about the same size with more solder on the smaller pad; the pads are at least 75% of the ball diameter; and the eutectic joints are made as large as possible without bridging between pads. For reliability at even higher temperature cycles or larger substrate sizes columns are used instead of balls.

Solder ball connections and assembly process

Two substrates are produced each with a planar, mirror-image matrix of metal contacts in a surface wiring layer. The substrates are positioned with the matrices in parallel confrontation which defines pairs of confronting contacts. A metal ball is positioned between each pair of contacts with a respective volume of joining material between the ball and each of the two respective contacts. The volumes of joining material are simultaneously melted to allow surface tension to align the substrates and to accurately center the balls between each respective pairs of contacts in a plane defines by the matrix of balls.

Solder ball interconnected assembly

An electronic package with a semiconductor chip, a lead frame, a metal casing, and a redistribution interposer. The chip is mounted on the interposer and wirebonded to first ends of redistribution leads of the interposer. The redistribution leads have second ends orientated in a general flipped orientation relative to their corresponding first ends. The second ends are wirebonded to pads of the lead frame. The interposer allows smaller chips to be used in the package without changing the lead frame. The interposer also allows the chip to be flip-mounted in the package without changing the lead frame or casing, this allows redirection of the chip's thermal path.

Semiconductor package with chip redistribution interposer

An improved dispersion strengthened lead-tin alloy solder is provided in which there is dispersed in the solder up to about 5 vol. percent of small particles, of a metal sulfide or a nickel-tin intermetallic.

Dispersion strengthened lead-tin alloy solder

Growing community of inventors

Croton Falls, NY, United States of America

Thomas Caulfield