Multilayer structure with interlocking protrusions

Details Multilayer structure with interlocking protrusions Multilayer structure with interlocking protrusions

1998-06-09

2001-02-13

Gaffin, Jeffrey (Department: 2841)

Electricity: conductors and insulators

Conduits, cables or conductors

Preformed panel circuit arrangement

C174S262000, C174S255000, C174S267000, C439S066000, C029S830000, C361S785000, C361S791000

Reexamination Certificate

active

06188028

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the field of electrical circuitry, for example, the electrical and mechanical interconnection of layers in a multilayer structure, and more particularly, relates to layered circuit structures such as multilayer circuit panels, to components and methods utilized in fabrication of such structures and to methods of making the same.
BACKGROUND OF THE INVENTION
Electrical components are commonly mounted on circuit panel structures such as printed circuit panels. Circuit panels ordinarily include a generally flat sheet of dielectric material with electrical conductors disposed on a major, flat surface of the sheet or on both major surfaces. The conductors are commonly formed from metallic materials such as copper and serve to interconnect the electrical components mounted to the board. Where the conductors are disposed on both major surfaces of the panel, the panel may have via conductors extending through the dielectric layer so as to interconnect the conductors on opposite surfaces.
Multilayer circuit panel assemblies have been made heretofore which incorporate plural, stacked circuit panels with additional layers of dielectric materials separating the conductors on mutually facing surfaces of adjacent panels in the stack. These multilayer assemblies ordinarily incorporate interconnections extending between the conductors on the various circuit panels in the stack as necessary to provide the required electrical interconnections.
Electrical components which can be mounted to circuit panel structures include so-called “discrete”, components and integrated circuits which include numerous transistors on a single chip. Chips of this nature can be mounted to elements commonly referred to as “chip carriers” which are specialized circuit panel structures. A chip carrier may be incorporated in a package which is mounted to a larger circuit panel and interconnected with the remaining elements of the circuit. Alternatively, the chip can be mounted directly to the same circuit panel which carries other components of the system. This arrangement is ordinarily referred to as a “hybrid circuit”. Relatively large circuit panels are commonly made of polymeric materials, typically with reinforcement such as glass, whereas very small circuit panels such as those used as semiconductor chip carriers may be formed from ceramics, silicon or the like.
There have been increasing needs for circuit panel structures which provide high density, complex interconnections. These needs are addressed by multilayer circuit panel structures. The methods generally used to fabricate multilayer panel structures have certain serious drawbacks. Multilayer panels are commonly made by providing individual, dual sided circuit panels with appropriate conductors thereon. The panels are then laminated one atop the other with one or more layers of uncured or partially cured dielectric material, commonly referred to as “prepregs” disposed between each pair of adjacent panels. Such a stack ordinarily is cured under heat and pressure to form a unitary mass. After curing, holes are drilled through the stack at locations where electrical connections between different boards are desired. The resulting holes are then coated or filled with electrically conductive materials, typically by plating the interiors of the holes to form what is called a plated through hole. It is difficult to drill holes with a high ratio of depth to diameter. Thus, the holes used in assemblies fabricated according to these prior methods must be relatively large and hence consume substantial amounts of space in the assembly. These holes ordinarily extend from the top or bottom of the stack. Even where interconnections are not required in the top or bottom layers, space must be provided for holes to pass through these layers so as to provide needed interconnections in the middle layers. Accordingly, substantial amounts of the available surface area on the panels must be allocated to the holes and to accommodate tolerance zones around the holes. Moreover, the electrical interconnections formed by depositing conductive materials in such drilled holes tend to be weak. The drilling method and the general nature of the laminates used therein is described, for example in Doherty, Jr., U.S. Pat. No. 3,793,469; and Guarracini, U.S. Pat. No. 3,316,618.
Various alternative approaches have been proposed. Parks, et al., U.S. Pat. No. 3,541,222; Crepeau, U.S. Pat. No. 4,249,302; Luttmer, U.S. Patent No. 3,795,037; Davies, et al., U.S. Pat. No. 3,862,790, Fox, U.S. Pat. No. 4,954,878 and Zifcak, U.S. Pat. No. 4,793,814 all relate generally to structures which have metallic or other conductive elements arranged at relatively closely spaced locations on a dielectric sheet with the conductive elements protruding through the dielectric sheet in both directions. Such a sheet may be sandwiched between a pair of circuit panels and the circuit panels may be clamped or otherwise held together so as to provide mechanical engagement between conductive elements on the adjacent faces of the circuit panels and the conductive elements of the composite sheet. In each of these arrangements, the conductive elements, the composite sheet or both is resilient or malleable so as to provide for close engagement between the conductive elements of the composite sheet and the conductors on the circuit panels.
Beck, U.S. Pat. No. 3,616,532 and Dube, et al., U.S. Pat. No. 3,509,270 describe variants of this approach in which resilient elements are used with a fusible solder. These elements are mounted on insulating boards which are then stacked between printed circuit layers. The assembly is heated so as to melt the solder, thereby freeing the resilient elements so that the resilient elements and solder cooperatively form an interconnection between the adjacent circuit panels.
Evans, et al., U.S. Pat. No. 4,655,519 describes a connector with numerous strip-like contact springs disposed in holes in a flat dielectric body, together with other spring elements. The ends of the strips protrude from opposite surfaces of the body. These are adapted to compress when electronic elements are engaged with the body surfaces, so that the ends of the strips engage pads on the electronic elements. Walkup, U.S. Pat. No. 5,167,512 discloses a further system using springs disposed in holes in a dielectric body.
Grabbe, U.S. Pat. No. 5,228,861 describes a connector having a sheet-like dielectric body with numerous generally X-shaped spring contact elements, each having four arms, lying on a first side of the sheet. Two arms of each X-shaped element are bent inwardly toward the sheet, and extend through holes in the sheet so that the tips of these arms protrude above the second, opposite face of the sheet. The other two arms are bent away from the sheet, and hence protrude from the first surface. When the connector is placed between circuit panels, each X-shaped element is compressed between mating pads of the circuit panels, causing the bent arms to flatten and causing the tips of the arms to wipe the surfaces of the pads. After engagement, the contact is maintained by the resilience of the arms.
Bernarr, et al., U.S. Pat. No. 4,548,451 describes a connector or interposer having a sheet-like elastomeric body with crushable protrusions extending outwardly from oppositely-directed surfaces. Tabs formed from a metal-coated flexible film extend on both surfaces of the body, and overlie the protrusions. The tabs on opposite sides are connected to one another by vias. When the interposer is engaged between circuit panels, the tabs and posts are crushed between contact pads on opposing panels, and the tabs assertedly wipe the pads for more effective contact. The tabs are maintained in engagement with the pads by the resilience of the elastomeric sheet and the posts; there is no permanent bond formed.
Patraw, U.S. Pat. Nos. 4,716,049; 4,902,606; and 4,924,353, describe microelectronic connection schemes using deformable contacts protruding upwardly from a substrate. Each c

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