Method and apparatus for providing positive contact force in an electrical assembly

An electrical contact assembly includes a first module having a first set of electrical contacts, a second module having a second set of electrical contacts, a shape-generating module, and a clamping arrangement. The second set of electrical contacts is aligned with the first set of electrical contacts and the shape-generating module is arranged to impart a shape to the second module such that the second set of electrical contacts is driven toward the first set of electrical contacts. The clamping arrangement is arranged to clamp the first, the second, and the shape-generating modules together, thereby resulting in a positive contact force between the first and second sets of electrical contacts. The positive contact force is equal to or greater than a predefined value.

BACKGROUND OF THE INVENTION

The present disclosure relates generally to a method and apparatus for providing positive contact force in an electrical contact assembly, and particularly to an electrical contact assembly having an Electronic Module (EM), such as a Single-Chip Module (SCM) or a Multi-Chip Module (MCM) for example, that may have a non-planar back that electrically mates with a Printed Circuit Board (PCB).

The continuous development in the electronics and computer industry has resulted in larger Electronic Modules (such as Multi-Chip Modules) being packaged in smaller spatial environments. Coupled with this density increase is a need to connect an increased number of processing module input/output terminals to PCBs. One device for interconnecting a high number of input/output terminals on a processing module to a PCB is a Land Grid Array (LGA) interconnect. Typically, a LGA interconnect is sandwiched between the processing module and the PCB to provide electrical connection between the terminals on the processing module and interconnects (such as pads and plated vias for example) on the PCB.

Some designs use clamping techniques to apply force to the processing module to maintain electrical contact between the processing module, the LGA interconnect and the PCB. However, the bottom mating surface of the EM and the top surface of the PCB may be non-planar, with a surface camber that may vary significantly, such as about +/−75 micrometers for example. In addition to a non-planar EM bottom surface, the LGA interconnect may not have sufficient compressive compliancy to absorb the effects of surface irregularities and structural deflections with the clamping techniques employed. Increasing the global clamping force may not be an option due to the increase in stress that the substrate of the EM may encounter, thereby possibly resulting in reduced life expectancy of the EM. Accordingly, it would be advantageous to have a method and apparatus for providing positive contact force in an EM assembly, as well as other face-to-face contact assemblies, without incurring undue component stress.

SUMMARY OF THE INVENTION

In one embodiment, an electrical contact assembly includes a first module having a first set of electrical contacts, a second module having a second set of electrical contacts, a shape-generating module, and a clamping arrangement. The second set of electrical contacts is aligned with the first set of electrical contacts and the shape-generating module is arranged to impart a shape to the second module such that the second set of electrical contacts is driven toward the first set of electrical contacts. The clamping arrangement is arranged to clamp the first, the second, and the shape-generating modules together, thereby resulting in a positive contact force between the first and second sets of electrical contacts. The positive contact force is equal to or greater than a predefined value.

In another embodiment, a method of providing positive contact force in an electrical contact assembly is provided. A first set of electrical contacts is arranged in opposition to a second set of electrical contacts to provide an electrical contact arrangement. A shape-generating component is arranged proximate to and clamped toward the electrical contact arrangement. In the clamped assembly, one set of contacts is shaped in the direction of the other set to provide a positive contact force between the first and second sets of contacts.

In a further embodiment, a multi-chip module assembly includes a layered assembly having a multi-chip module, a printed circuit board and an interconnect disposed therebetween, wherein the multi-chip module, printed circuit board, and interconnect have mating sets of electrical contacts. The assembly includes means for clamping the layered assembly together and means for producing a shape in the printed circuit board such that a portion of the printed circuit board is driven toward the multi-chip module. In response to the shaping, a positive contact force results between the mating sets of electrical contacts.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention provides a Processing Module (PM) assembly, such as an Electronic Module (EM) assembly that includes a Land Grid Array (LGA) interconnect between the EM and a Printed Circuit Board (PCB), with a positive contact force between the EM and the mating surface of the PCB, the contact force being equal to or greater than a predefined value. While embodiments described herein depict an EM assembly as an exemplary mating contact assembly having a positive contact force arrangement, it will be appreciated that the disclosed invention is also applicable to other mating contact assemblies, such as PM-to-PCB, or PCB-to-PCB, for example.

FIG. 1is an exploded assembly view of an exemplary embodiment of an EM assembly100having an EM110(also herein referred to as a first module), an interconnect120(also herein referred to as a second module), a PCB130(also herein referred to as an intermediate surface), a Shape-Generating Module (SGM)140, to be discussed in more detail below, and a support base150(also herein referred to as a stiffening surface) made of aluminum, but which may be made of any material suitable for providing a stiffening surface, such as stiff plastic or other metallic for example. In an exemplary embodiment, interconnect120is a LGA including an array of contacts (for example, inter-twined balls of gold wire) arranged in a pattern matching a pattern of terminals on the bottom of EM110for providing an electrical connection between EM110and PCB130. Interconnect120may employ any area array compression contact-based electrical connection technique.

EM110includes a set of electrical contacts112, best seen by referring toFIG. 2, on the bottom (side facing interconnect120). In an embodiment, electrical contacts112are configured as surface pads, thereby providing contact faces for a face-to-face contact arrangement with a mating set of contacts. WhileFIG. 2depicts an array of electrical contacts112having a defined number of contacts, the artisan will appreciate that this is illustrative only and that EM110may have thousands of electrical contacts arranged in a variety of columns and rows. An exemplary EM110has an overall dimension of about 120 mm (millimeters) by about 160 mm, and has about 72 columns by about 72 rows of electrical contacts. The artisan will also appreciate that the term “a set of contacts” is not limited to an array of contacts of a given dimension, and may be a one-dimensional array, a two-dimensional array, or arranged in any structured or non-structured pattern. Also, the artisan will appreciate that a contact pad typically has a two-dimensional face, thereby resulting in a one-dimensional array having two dimensions with respect to the contact pad structure itself. As shown, EM110includes a base113and a cover114. Housed between base113and cover114are a plurality of electronic component(s) (EC)200, each EC200having input/output leads202that are electrically connected to EM electrical contacts (input/output terminals)112. Electrical contacts112may be implemented using a variety of structures such as pads, balls, pins, for example. The pattern of contacts on interconnect120corresponds to the pattern of terminals112on EM110. Each EC200may be in thermal communication with cover114through thermally conductive compounds204. In this manner, heat from each EC200may be dissipated through the thermally conductive compound204and cover114. Such dissipation may occur by placing heart sinks on cover114. More sophisticated cooling devices, such as refrigerant based coolers, may be placed in thermal communication with cover114.

PCB130has a mating set of contacts, depicted generally as132, which are configured to mate with electrical contacts112of EM110. Interconnect120also includes a mating set of contacts, depicted generally as122, which are configured to mate with electrical contacts112and132of EM110and PCB130, respectively. Electrical contacts122of interconnect120are arranged to provide a desired pattern of electrical connections between EM110and PCB130, which may be but is not necessarily in a one-to-one correlation. Interconnect120is arranged between EM110and PCB130, thereby providing the desired electrical path between the two. PCB130may include leads from electrical contacts132to other portions of PCB130for interfacing with EM110.

SGM140includes an insulator142, that prevents circuit traces on the bottom of PCB130from making electrical contact with support base150to prevent shorting, and a set of Shape-Generating Patches (SGP)144, best seen by now referring toFIGS. 3A-4B.FIGS. 3A and 4Adepict plan views, andFIGS. 3B and 4Bdepict respective side views, of alternative SGMs140.FIGS. 3A-Bdepict a SGM140having a set of two SGP144, whileFIGS. 4A-Bdepict a SGM140having a set of three SGP144. Alternative embodiments may have other quantities of patches in SGP144. In an embodiment, SGP144includes patch146having a diameter of 60 mm, patch147having a diameter of 42 mm, and patch148having a diameter of 24 mm, as depicted inFIGS. 4A-B. In an alternative embodiment, SGP144includes patch147having a diameter of 42 mm and patch148having a diameter of 24 mm, as depicted inFIGS. 3A-B. In an embodiment, patches146,147,148are made of 0.0015-inch thick high-temperature insulative material having an adhesive backing and have a circular shape, however, embodiments of the invention are not limited to such constraints. For example, patches146,147,148may be non-circular, such as oval or rectangular, may be of a different overall dimension, may be of a different thickness, may be of a non-uniform thickness, such as domed, and may be of a different material, adhesive-backed or not, providing the desired shape and contact force as herein disclosed results. By arranging patches146,147,148of differing diameters on top of each other, a generally dome-shaped set of SGP144can be achieved, which results in a dome-shape at PCB130. Also, SGM140is not limited to just one set of SGP144, but may include a plurality of SGP144, depending on the bottom contour of EM110and the desired contact force thereat.

Referring now back toFIG. 1, SGM140is arranged between PCB130and surface154of support base150, thereby positioning SGP144on the side of PCB130opposite to the side having electrical contacts132. In the assembled state, spring-equipped screws170(having screw172and spring174) pass through holes152on base150and holes134on PCB130into threads (not shown) of EM110, thereby creating a sandwiched EM assembly100. Interconnect120and SGM140may also include holes124,149, respectively, for receiving screw172. A sleeve156may be incorporated and assembled through holes152,149,134, and124, to further isolate screw172from electrical traces. In an embodiment, spring174is constrained at one end by structural detail (not shown but known in the art) at EM110, and at the other end by a shouldered head on screw172, thereby providing an arrangement that elastically clamps EM assembly100together. Other techniques for providing an elastic clamp having other biasing means, such as a leaf spring or a compressible material, for example, may be employed. In the assembled state and with screws170torqued to their predefined value, SGP144on SGM140presses against the underside (side opposite contacts132) of PCB130thereby imparting a shape to PCB130that drives electrical contacts132in the direction toward interconnect120and EM110. In an embodiment, the resulting shape produces a positive contact force between electrical contacts112and132that is greater than 0-grams (gms), that is preferably equal to or greater than 10 gms, and that is more preferably equal to or greater than 20 gms. Alternative connection systems may employ other minimum positive contact forces that are different from the exemplary predefined minimum positive contact forces of 10 gms or 20 gms.

FIGS. 5 and 6represent load profiles500,600, respectively, between electrical contacts112and132as a function of the surface camber of EM110(also referred to as the co-planarity characteristics of the as-sintered bottom-surface-metallurgy (BSM) of EM110) and board thickness of PCB130.FIG. 5depicts the load profile500in the absence of SGP144, whileFIG. 6depicts an embodiment of the minimum load profile600in the presence of an embodiment of SGP144. The x-axes represent the variation in surface camber in mils (0.001-inches) about a nominal zero point, and the y-axes represent the variation in board thickness in mils about a nominal zero point. The plotted contour lines depict an embodiment of the minimum electrical contact force in grams, as indicated by numerals at the contour lines. In an embodiment, the variation in surface camber varies from about −2 mils to about +2 mils, and the variation in board thickness varies from about −2 mils to about +2 mils, depicted by dashed-line boxes502,602inFIGS. 5 and 6. As discussed above, within these ranges of variation it is more preferable to have a contact force of equal to or greater than about 20 gms. Within dashed-line box502ofFIG. 5(in the absence of SGP144), the contact force is depicted as varying from less than 10 gms (in the upper left hand corner) to greater than about 40 gms (in the lower right hand side). Within dashed-line box602ofFIG. 6(in the presence of SGP144), the contact force is depicted as varying from greater than about 20 gms (in the upper left hand and lower right hand corners) to greater than about 60 gms (toward the center). As depicted, the presence of SGP144provides a contact force of greater than about 20 gms, while the absence of SGP144does not.

While an embodiment of the invention is depicted inFIG. 1as having electrical contacts112,132on EM110and PCB130, respectively, with Interconnect120disposed therebetween, it will be appreciated that alternative arrangements having face-to-face pressure contacts (alternatively force actuated contacts) may benefit from the shape-generating advantages of an embodiment of the invention. For example, in an alternative embodiment, EM110is assembled to PCB130absent Interconnect120, with SGM140disposed between PCB130and base150. Here, SGM140produces a shape at PCB130in the vicinity of contacts132in the direction of EM110, thereby driving contacts132against contacts112for positive contact engagement.

In another alternative embodiment, EM110may be replaced with a second printed circuit board (not shown) having a second set of contacts for mating with contacts132of PCB130. In this alternative embodiment, Interconnect120may or may not be used depending on the application needs. Here, and in the assembled state, SGM140, disposed between PCB130and base150, would produce a shape at PCB130in the vicinity of contacts132in the direction of the second printed circuit board, thereby driving contacts132against the second set of mating contacts on the second printed circuit board.

In yet another alternative embodiment, support base150is made of an insulative material, such as plastic, and SGP144is molded integral with base150. Here, customizing base150with SGP144to match the surface camber of a particular EM110may be accomplished by oversizing the geometry of integral SGP144and using automated micromachining techniques to remove material from SGP144as needed.

Other alternative embodiments involving force actuated contact assemblies, and specifically face-to-face contact assemblies, may benefit by having a shape-generating arrangement that produces a positive contact force across mating sets of contacts.

Some embodiments of the invention have some of the following advantages: compensation for the structural deflection that typically results during the assembly of an EM to a PCB; positive contact engagement above a predefined value between mating sets of contacts of a PCB and an EM; a contact force on a set of face-to-face contacts uniformly greater than about 10 gms, and preferably uniformly greater than about 20 gms; localized shape in a layered contact arrangement that does not overburden a clamping arrangement; ability to customize the shape of a contact assembly to compensate for or match the general shape at an EM mating surface, thereby providing increased contact force at the contact assembly; an increase in contact force at the EM without an unnecessary increase in stress at the EM substrate; effective contact engagement on an EM having an as-sintered concave bottom surface; and, improved component life expectancy.