Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With housing mount
Reexamination Certificate
2000-10-31
2003-07-29
Lebentritt, Michael S. (Department: 2824)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
With housing mount
C257S678000, C257S686000, C257S782000
Reexamination Certificate
active
06600224
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to thin film bonding to a carrier, such as either as a glass ceramic or to an organic laminate substrate, and to a method for attaching a thin film wiring package to the substrate. More particularly, the invention relates to the utilization of joining materials, such as adhesives that may be processed at temperatures sufficiently low so as to avoid damaging electronic components, the wiring package and interconnection joints. Moreover, pursuant to specific aspects of the invention, the joining of the thin film to the substrate may be implemented with the novel and unique utilization of dendrites.
Currently, considerable drawbacks and limitations are being encountered in the technology with regard to the joining of thin film wiring packages to different kinds of substrates, particularly such as thin film transfer joining. Thin film wiring layers are well known as a means to provide additional wiring density on the outer layer of a glass ceramic module. This is a sequential build up process, using a material set that is compatible with relatively high temperature processing that is associated with the use of high melt solders such as 90/10 Pb/Sn.
Pursuant to the invention, this technology is improved through means intended to adapt the use of thin film wiring layers to 1) a parallel process and 2) a material set compatible with relatively low temperature processing associated with eutectic solder (63 Pb/37Sn). Thus, the invention facilitates the attachment of a thin film wiring layer (providing additional wiring density) on a organic wiring board in parallel (or independent) processes.
A fundamental motivation for joining a thin film to a laminate is presented in a number of aspects, as set forth hereinbelow.
a) The thin film, in general, may be produced with finer circuit lines and higher density packaging versus the organic laminate printed wiring board. Selectively locating high density regions of wiring atop the printed wiring board using the thin film in a glued-on fashion, similar to the appliance of a postage stamp, provides localized high density wiring, without requiring the entire printed wiring board to be processed through the more expensive higher density manufacturing processes of the thin film.
b) Building the laminate and the thin film separately (in parallel) is preferred as opposed to building the thin film directly on the laminate (in serial). This is advantageous because it is less costly due to manufacturing yield concerns.
c) The printed wiring board can be produced with widely known processes. The thin film can be produced with any number of known processes, and it could be of a wide range of packaging density. The present invention shows it to be of a much more dense circuitization than the printed wiring board.
d) The use of a thin film joining technique applied to an organic laminate printed wiring board is fundamentally different than a joining technique applied to a glass ceramic substrate. This is due to the maximum permissible processing temperature. For an organic laminate such as a printed wiring board, the maximum temperature is typically around 190 to 240 C. for short durations. This is a requirement because the widely employed eutectic solder (63 Pb/37 Sn) melts at 183 C., so to attach components, this temperature must be exceeded. For a glass ceramic substrate, the temperatures can be much higher, and typically solders of higher melting point are used, such as 90 Pb/10 Sn, requiring the use of different materials.
2. Discussion of the Prior Art
Various methods and apparatus are presently disclosed in the state-of-the-art concerning the attachment of adhesives or thin films to different types of substrates.
Gaynes et al., U.S. Pat. No. 5,910,641 discloses the forming of an electrical connection by the utilization of a conductive adhesive film containing dendritic particles. These dendritic particles contain sharp edges which penetrate the oxide coatings on the metal pads of a module in which the film is adhered to a substrate.
Merritt et al., U.S. Pat. No. 5,805,426 discloses a conductive film containing nanopores which are filled with nanoscopic fibers or tubules, and wherein the film possesses an anisotropic electrical conductivity or Z-axis conductivity.
MacDonald, Jr. et al., U.S. Pat. No. 5,905,638 discloses an elastomeric connector system which is applied to provide for the interconnection of microelectronic devices. The elastomer is generally constituted of silicone or fluorosilicone gels, and does not possess any similarities with the present inventive arrangement or method of providing dendritic connections between a thin film and a substrate.
Kwon et al., U.S. Pat. No. 5,187,020 discloses a structure for integrated circuits which provides a compliant metal contact pad for electrical testing by means of probes. The structure, which is built on top of I/O pads consists of a compliant conductive layer of conducting adhesive and a metal bump, and essentially differs in vital aspects from the present inventive concept.
Farnworth U.S. Pat. No. 5,893,765 discloses a Z-elastomeric connection system for a semiconductor package and does not direct itself to the thin film attachment to a laminate or other type of substrate using the inventive interconnections.
Pennisi et al. U.S. Pat. No. 5,136,365 discloses an adhesive material consisting of a fluxing agent, metal particles, a thermoset resin and a curing agent, whereby the metal is selected from a group of materials consisting of lead, tin, indium, bismuth, antimony and silver. The metal particles are melted in order to form a metallurgical bond with the electrical components and the substrate during-reflow soldering. Although possessing some similarities to the inventive concept in terms of a metallurgical bond which is to be formed during joining, the present invention is related more closely to the filler material particles which are coated with a low melting point metal alloy, and also the use of new conducting adhesive materials, and consequently provides for an improvement over the art.
Moreover, also of general interest are the IBM Technical Data Bulletin Volume 32, Number 10b, March 1990, Page 476; and the IBM Technical Data Bulletin Volume 35, Number 3, August 1992, Page 130, which are not unduly applicable to the invention inasmuch as they are primarily representative of the current state-of-the-art providing for thin film attachments to laminates.
SUMMARY OF THE INVENTION
Accordingly, pursuant to the present invention there is disclosed the aspect of providing a novel method and structure which are adapted for the joining of a thin film to a printed wiring board (PWB) or suitable substrate. Pursuant to a particular aspect of the invention, the thin film is provided with solder balls at each connection, which could conceivably span a range of alloys and melting temperatures, and wherein the printed wiring board would be provided with matching copper pads. Various means of now forming the required electrical interconnections between the thin film and the printed wiring board are possible. One such means is to use a solder paste, selectively patterned onto the copper pads of the printed wiring board, in combination with an adhesive spacer material that contains apertures corresponding to electrical connections. Upon aligning the three elements (thin film, spacer adhesive, and printed wiring board), and subsequently applying heat and pressure, a unitary structure is formed with electrical interconnections formed by the solder paste and a mechanical reinforcement provided by the spacer adhesive.
A second means of forming the interconnection avoids the use of solder paste. Instead, a special metallurgy is created on the copper pads of the printed wiring board, consisting of Pd (Palladium) dendrites. The thin film may be positioned above the printed wiring board, and a predrilled spacer material utilized as an adhesive layer.
Thereafter, upon an application of heat and pressure, while not necessarily excee
Farquhar Donald S.
Galasco Raymond T.
Kang Sung Kwon
Poliks Mark D.
Prasad Chandrika
International Business Machines - Corporation
Lebentritt Michael S.
Menz Douglas
Samodovitz, Esq. Arthur J.
Scully Scott Murphy & Presser
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