International Business Machines Corporation

David P Watson

John Saunders Corbin, Jr

John Acocella

Karl G Hoebener

Joseph Angelo Benenati

Donald R Banks

Thomas Caulfield

Joel R Anstrom

Darryl Ray Polk

Terry L Wilmoth

Francis W Bogaczyk

Robert W Kulterman

Gilbert B Nebgen

Michael A Rubsam

Robert D Hrehor, Jr

Robert A Holloway

Robert A Amos

Clifford M Wood

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

The apparatus of the present invention may be utilized for the automated bonding of electronic components to a circuit board. A placement and bonding head is attached to a manipulatable robotic arm and is utilized to select an electronic component having a plurality of conductive leads from a supply of such components and position that component adjacent a plurality of contact pads on a circuit board. While retaining the electronic component within the placement and bonding head, the component is then thermally bonded to the contact pads. In one embodiment of the present invention, an electronic component may be optically inspected while being retained within the placement and bonding head. In another embodiment, thermal bonding is accomplished utilizing a plurality of thermally activatable blades which each include a thermocouple mounted adjacent thereto. Selective low current control signals are then coupled to the placement and bonding head where transformers are utilized to amplify the current prior to coupling the control signal to individually thermally activatable blades. In yet another embodiment of the present invention, the placement and bonding head includes a plenum for supplying inert gas to the bonding site so that the use of flux is not necessary.

System for automated mounting of electronic components to circuit boards

The method and apparatus of the present invention may be utilized to support a selected mounting point on a circuit board during the mounting an electronic component. An integrated circuit device is selected and positioned adjacent a first side of a circuit board at a desired mounting point utilizing a robotic manipulator and a placement head. A support fixture is then urged into temporary contact with a second side of the circuit board utilizing a flexible mounting system such that minor variations or misalignments between the plane of the support fixture, the circuit board and the placement head are eliminated. In one embodiment of the present invention a flexible fluid filled bag is utilized in conjunction with the support fixture so that the presence of components on the second side of the circuit board may be accommodated while supporting the circuit board during component mounting. Finally, the requirement for providing a robotic manipulator and placement head capable of generating the substantial downward forces necesary to create a bond between a circuit board and an electronic component is eliminated by positioning the placement head and heated bonding tool proximate to the conductive leads of an electronic component and then forcefully urging the support fixture upward toward the heated bonding tool while maintaining the heated bonding tool in a fixed position.

Method and apparatus for circuit board support during component mounting

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Beaverton, OR, United States of America

David P Watson