International Business Machines Corporation

Joseph Angelo Benenati

Eugene R Atwood

Horatio Quinones

John Ulrich Knickerbocker

Wayne John Howell

John Saunders Corbin, Jr

William T Chen

John Acocella

Karl G Hoebener

Donald R Banks

Thomas Caulfield

David P Watson

Claude Louis Bertin

William R Tonti

Mark Vincent Pierson

Wayne Frederick Ellis

Jerzy Maria Zalesinski

Giulio DiGiacomo

Thomas E Dinan

Karl Joseph Puttlitz

Eric J Kastberg

James J Dankelman

Lisa A Fanti

John R Behun

Thermal enhancement approach using solder compositions in the liquid state

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

An integrated circuit assembly has pads of a chip electrically connected to pads of a substrate with rolling metal balls. A pliable material bonds the balls in movable contact with pads of the chip and substrate. Because the balls are relatively free to move, thermal expansion differences that would ordinarily cause enormous stresses in the attached joints of the prior art, simply cause rolling of the balls of the present invention, avoiding thermal stress altogether. Reliability of the connections is substantially improved as compared with C4 solder bumps, and chips can be safely directly mounted to such substrates as PC boards, despite substantial thermal mismatch.

Rolling ball connector

Solder compositions are introduced to interface between an IC chip and its associated heat exchanger cover. The solder compositions have a solidus-liquidus temperature range that encompasses the IC chip operational temperature range. The solder composition has the desired property of absorbing and rejecting heat energy by changing state or phase with each temperature rise and decline that result from temperature fluctuations associated with the thermal cycles of the integrated circuit chips. A path for high thermal conduction (low thermal resistance) from the IC chip to the heat exchanger to the ambient air is provided by an electronic module cover, configured as a cap with a heat exchanger formed or attached as a single construction, and made of the same material as the substrate, or made with materials of compatible thermal coefficients of expansion to mitigate the effects of vertical displacement during thermal cycling. The cap-heat exchanger cover is constructed to be compliant, and to contact both the IC chip and substrate.

An apparatus for and method of minimizing the thermo-mechanical fatigue of flip-chip packages. The interposer of the present invention, preferably comprising an organic polymer such as polyimide, contains apertures having conductive plugs inserted therein for joining a chip to a substrate in an electronic module utilizing flip-chip packaging. The interposer is selected to provide optimum spacing between the chip and substrate having a coefficient of thermal expansion adapted to the thermal cycling temperature extremes of the module components. The interposer may comprise an inner core with two adhesive outer layers which may comprise different materials to promote adhesion at their respective interfaces within a module. Conductive plugs are disposed within the apertures of the interposer comprising of a first and second solder or comprising a conductive plug having top and bottom surfaces coated with a conductive adhesive. Preferably, the first solder is disposed within an interior of the apertures and the second solder is disposed within an exterior of the apertures such that the first solder is between a first portion and a second portion of the second solder. Upon reflow, the second solder is reflowed while the first solder remains solid.

Underfill preform interposer for joining chip to substrate

A heat sink in a heat transfer relationship with a substrate such as an integrated chip, chip carrier, or other electronic package. The heat sink is connected to a frame which is connected to a printed circuit board or other suitable support on which the substrate is positioned. The heat sink, which extends through an aperture in the frame is coupled to a surface of the substrate. The heat sink is mechanically decoupled from the substrate. Large heat sinks may be thermally connected to surface mount substrates mounted using technologies such as ceramic ball or column grid arrays, plastic ball or column grid arrays, or solder balls or columns. The heat sink is attached coaxially through the aperture to the substrate. After assembly and lead/tin or other metallic surface mount interconnects are relaxed such that the substrate and is completely supported by the frame and the heat sink imparts zero or nearly zero downward force. Because the heat sink moves freely within the aperture during assembly, the heat sink package is useful for a variety of different substrates. Preferably, the frame is a plate and a plurality of studs. The plate material are selected to match the thermal expansion of the underlying support, and the stud material matched the thermal expansion of the substrate. Thus, the frame construction allows matching expansion and contraction of the assembly to the underlying substrate and support.

Zero force heat sink

A heat sink is placed in a heat transfer relationship with a substrate such as an integrated chip, chip carrier, or other electronic package, without imparting stressful forces to the substrate by connecting the heat sink to a frame which is connected to a support such as a printed circuit board or other suitable carrier on which the substrate is positioned. The heat sink extends through an aperture in the frame and is in heat transfer relationship with a surface of the substrate; however, it is mechanically decoupled from the substrate. The invention has particular application in thermally connecting large heat sinks to substrates that are surface mounted on the support using technologies such as ceramic ball or column grid arrays, plastic ball or column grid arrays, or solder balls or columns. In order to provide intimate contact between the substrate and the heat sink, the heat sink must be depressed coaxially through the aperture of the frame against a surface of the substrate and then secured by, for example, gluing while in contact with the surface. However, this downward force imparted by the heat sink is quickly reduced via relaxation of the lead/tin or other metallic elements of the surface mount. A heat sink in a heat transfer relationship with a substrate such as an integrated chip, chip carrier, or other electronic package. The heat sink is connected to a frame which is connected to a printed circuit board or other suitable support on which the substrate is positioned. The heat sink, which extends through an aperture in the frame is coupled to a surface of the substrate. The heat sink is mechanically decoupled from the substrate. Large heat sinks may be thermally connected to surface mount substrates mounted using technologies such as ceramic ball or column grid arrays, plastic ball or column grid arrays, or solder balls or columns. The heat sink is attached coaxially through the aperture to the substrate. After assembly and lead/tin or other metallic surface mount interconnects are relaxed such that the substrate and is completely supported by the frame and the heat sink imparts zero or nearly zero downward force. Because the heat sink moves freely within the aperture during assembly, the heat sink package is useful for a variety of different substrates. Preferably, the frame is a plate and a plurality of studs. The plate material are selected to match the thermal expansion of the underlying support, and the stud material matches the thermal expansion of the substrate. Thus the frame construction allows matching expansion and contraction of the assembly to the underlying substrate and support.

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

A heatsink is provided which can be removably secured in a heat transfer relationship to an electronic module or package by an epoxy type adhesive. A screw is provided through one end of the heatsink directly over an edge of the module sealing cap. To remove the heatsink from the module, the screw is turned down to contact the cap. Continued turning causes a prying force between the cap and the module whereby the heatsink is peeled away and removed from the module. All forces are directed between the cap and the module thereby eliminating harmful stress from being transmitted through the solder ball connections and to a supporting circuit card.

Apparatus for removing a heatsink from an electronic module or package

Growing community of inventors

Hopewell Junction, NY, United States of America

Joseph Angelo Benenati