Patent Application
20070075717
The present invention relates generally to the testing of semiconductor chips, and specifically to the design of an interposer for use in probe card assemblies.
Typically, semiconductor chips are tested to verify that they function appropriately and reliably. This is often done when the semiconductor chips are still in wafer form, that is, before they are diced from the wafer and packaged. This allows the simultaneous testing of many semiconductor chips at a single time, creating considerable advantages in cost and process time compared to testing individual chips once they are packaged. If chips are found to be defective, they may be discarded when the chips are diced from the wafer, and only the reliable chips are packaged.
Generally, modem microfabricated (termed MEMS) probe card assemblies for testing semiconductors have at least three components: a printed circuit board (PCB), a substrate to which thousands of probe contactors are coupled (this substrate hereinafter will be referred to as the “probe contactor substrate” and the probe contactor substrate together with the attached probe contactors hereinafter will be referred to as the “probe head”), and a connector which electrically interconnects the individual electrical contacts of the PCB to the corresponding electrical contacts on the probe contactor substrate which relay signals to the individual probe contactors. In most applications, the PCB and the probe head must be roughly parallel and in close proximity, and the required number of interconnects may be in the thousands or tens of thousands. The vertical space between the PCB and the substrate is generally constrained to a few millimeters by the customary design of the probe card assembly and the associated semiconductor test equipment. Conventional means of electrically connecting the probe contactor substrate to the contact pads of the PCB include solder connection, elastomeric vertical interposers, and vertical spring interposers. However, these technologies have significant drawbacks.
In the early days of semiconductor technology, the electrical connection between the probe contactor substrate and the PCB was achieved by solder connection. Solder connection technology involves electrically connecting an interposer to the PCB by means of melting solder balls. For instance, U.S. Pat. No. 3,806,801, assigned to IBM, describes a vertical buckling beam probe card with an interposer situated between the probe head (probe contactor substrate) and a PCB. The interposer is electrically connected to the PCB, terminal to terminal, by means of melting solder balls (see
In both of these patents, an array of individual probe contactor springs is assembled to the interposer, either mechanically or by solder attachment, which use solder area array technology. However, this method has a number of significant disadvantages, particularly when applied to large area or high pin count probe cards. For instance, probe cards with substrate sizes larger than two square inches are difficult to solder attach effectively because both the area array interconnect yield and reliability become problematic. During solder reflow, the relative difference in thermal expansion coefficients between the probe contactor substrate and PCB can shear solder joints and/or cause mismatch-related distortion of the assembly. Also, the large number of interconnects required for probe cards make the yield issues unacceptable. Furthermore, it is highly desirable that a probe card assembly can be disassembled for rework and repair. Such large scale area array solder joints can not be effectively disassembled or repaired.
An alternative to solder area array interposers is the general category of vertically compliant interposers. These interposers provide an array of vertical springs with a degree of vertical compliance, such that a vertical displacement of a contact or array of contacts results in some vertical reaction force.
An elastomeric vertical interposer is an example of one type of a vertically compliant interposer. Elastomeric vertical interposers use either an anisotropically conductive elastomer or conductive metal leads embedded into an elastomeric carrier to electrically interconnect the probe contactor substrate to the PCB. Examples of elastomeric vertical interposers are described in U.S. Pat. No. 5,635,846, assigned to IBM (see FIG. 3), and U.S. Pat. No. 5,828,226, assigned to Cerprobe Corporation (see FIG. 4).
Elastomeric vertical interposers have significant drawbacks as well. Elastomeric vertical interposers often create distortion of the probe contactor substrate due to the forces applied on the probe head substrate as a result of the vertical interposer itself. Additionally, elastomers as a material group tend to exhibit compression-set effects (the elastomer permanently deforms over time with applied pressure) which can result in degradation of electrical contact over time. The compression-set effect is accelerated by exposure to elevated temperatures as is commonly encountered in semiconductor probe test environments where high temperature tests are carried out between 75° C. and 150° C. or above. Finally, in cold test applications, from 0° C. to negative 40° C. and below, elastomers can shrink and stiffen appreciably also causing interconnect failure.
A second type of vertical compliant interposer is the vertical spring interposer. In a vertical spring interposer, springable contacting elements with contact points or surfaces at their extreme ends extend above and below the interposer substrate and contact the corresponding contact pads on the PCB and the probe contactor substrate with a vertical force. Examples of such vertical spring interposers are described in U.S. Pat. No. 5,800,184, assigned to IBM (see FIG. 6) and U.S. Pat. No. 5,437,556, assigned to Framatome (see FIG. 5) (the Framatome patent does not describe a vertical probe card interposer but is a more general example of a vertical spring interposer).
However, vertical spring interposers have significant disadvantages as well. In order to achieve electrical contact between the PCB and the substrate with probe contactors, the interposer springs must be compressed vertically. The compressive force required for a typical spring interposer interconnect is in the range of 1 gf to 20 gf per electrical contact. The aggregate force from the multitude of vertical contacts in the interposer causes the Probe Contactor substrate to bow or tent since it can only be supported from the edges (or from the edges and a limited number of points in the central area) due to the required active area for placement of probe contactors on the substrate. The tenting effect causes a planarity error at the tips of the probe contactor springs disposed on the surface of the probe contactor substrate (see
This planarity error resulting from vertical interposer compression forces requires that the probe contactor springs provide a larger compliant range to accommodate full contact between both the highest and the lowest contactor and the semiconductor wafer under test. The increase in compliant range of a spring, which such increase is roughly equal to the planarity error, requires that the spring be larger, with all other factors such as contact force and spring material being constant, and hence creates a deleterious effect on probe pitch.
Furthermore, probe contactor scrub is often related to the degree of compression, so the central contactors in the tented substrate will have different scrub than the outer contactors which are compressed less. Consistent scrub across all contactors is a desirable characteristic, which is difficult to achieve with vertical compliant interposers.
Thus a new design for an interposer is needed to overcome the deficiencies of the prior art.
Embodiments of the present invention are directed to a laterally-compliant spring-based interposer for testing semiconductor chips that imparts minimal vertical force on a probe contactor substrate in an engaged state. Instead, the interposer contactor spring elements engage contact bumps in a lateral manner and thus exert lateral force against the contact bumps on the PCB and the probe contactor substrate when in an engaged state. Because the interposer springs impart minimal vertical force, they do not appreciably distort or tent the interposer substrate, thus enabling improved planarity of the probe contactors and better electrical connections with the contact bumps built on the PCB and probe contactor substrate.
Embodiments of the present invention, generally include an interposer substrate with at least one laterally compliant spring element (i.e. the resilient contact element) having an upper and a lower portion. The upper portion extends vertically above the upper surface of an interposer substrate or holder assembly and the lower portion extends vertically below the lower surface of interposer substrate or holder assembly. It should be noted here that the term “substrate” is meant to include any type of structure from which a laterally compliant spring element extends. As will be discussed below, the structure may be a monolithic substrate, with or without vias, a ceramic strip to which laterally compliant elements are attached, a holder assembly, or any other type of structure from which laterally compliant spring elements may extend. The upper and lower portions may be electrically connected by an electrically conductive via that extends through an interposer substrate, or the resilient contact element may be a monolithic structure having an upper and lower portion which are joined together by a middle portion, the whole of which extends through a hole in the substrate or holder assembly. In the latter embodiment the middle portion may pass through the substrate. The upper and lower portions of the resilient contact element are designed to be laterally resilient. In an embodiment of the present invention, the laterally compliant spring element may be substantially vertically rigid, and in other embodiments, the laterally compliant spring element may be vertically compliant. The spring elements have contact regions (which engage the contact bumps) on a side of the spring element, as opposed to the spring element's vertical extremity as is the case with vertical spring interposer elements.
In semiconductor test probe card construction, the interposer is disposed between a PCB and a probe contactor substrate. In an unengaged state, an upper contact region of the upper portion of the resilient contact element and a lower contact region of the lower portion of the resilient contact element are not in contact with the protruding contact bumps on the PCB or probe contactor substrate. Thus, in the unengaged state, the interposer may not electrically interconnect the PCB and the probe contactor substrate.
In an engaged state, the interposer electrically interconnects the PCB and the probe contactor substrate by contacting the sides of the bumps on both substrates with a substantially lateral force. Because the force involved is substantially lateral (horizontal in a direction substantially parallel with the probe contactor substrate and the PC B) instead of vertical, they do not appreciably distort or tent the substrate, and they ensure greater planarity and better electrical connections with the contact bumps built on the substrate.
Another embodiment of the proposed invention utilizes a flexible wiring board technology (commonly known as “flex circuit”) or its functional equivalent as a foundation for forming linear arrays of lateral contact elements. The contact elements are formed from conductive metal traces on or in a flexible substrate (usually a plastic). The plastic laminate material itself forms the base or substrate on which the conductor is formed and also provides part of the resiliency required in the lateral interposer contact element. The metal conductor also provides resiliency and compliance, which in combination with the flex substrate forms the complete lateral spring. Strips of lateral contacts may be combined in an assembly to form a two dimensional array of lateral contacts. These strips may be mounted into a carrier plate such as a slotted ceramic substrate which holds the strips in their correct aligned position and also provides mechanical support to engage the lateral springs against their corresponding contact bumps. This embodiment incorporating flex circuitry allows for simplified and reduced cost manufacturing, improved signal shielding, impedance control, and supply and ground isolation from signal transients.
While the preferred embodiment of the present invention is directed to an interposer for use in a probe card assembly for testing semiconductor chips, the present invention may be used in many applications wherein an interposer substrate is used to connect two substantially parallel electrical wiring substrates.
FIGS. 25A-C illustrate a process for forming an embodiment of the present invention as illustrated in
FIGS. 26A-E illustrate a process for forming an embodiment of the present invention as illustrated by
The upper portion 110A and the lower portion 110B have the quality of being substantially compliant in a lateral (horizontal) direction. The upper portion 110A of the laterally compliant spring element 110 may have an upper contact region 140A, and the lower portion 110B of the laterally compliant spring element 110 may have a lower contact region 140B. The contact regions 140A, 140B make lateral contact with the sides of the contact bumps 130 of the upper 300 and lower 200 substrates when in an engaged state (as seen in
The upper 110A and lower 110B portions may be coupled to the via 120 by means of lithographically plating the portions 100A, 100B to the via 120. Alternatively, the upper 110A and lower 110B portions may be soldered to the via 120 with solder balls 120. Yet another embodiment is for upper portion 110A and lower portion 110B to be coupled to the via using any other bonding mechanism or retaining feature known in the art such as thermosonic and thermocompression bonding, conductive adhesive attachment, laser welding, or brazing. Such upper 110A and lower 110B portions may be made in any suitable fashion such that they have the properties of being laterally resilient. They may be formed by wire bonding and overplating, or by lithographic electroforming techniques known in the art. Examples of lithographic techniques are disclosed in U.S. patent application Ser. Nos. 11/019,912 and 11/102,982, both of which are assigned to Touchdown Technologies, Inc and are incorporated herein.
The laterally compliant spring element 110 may also be monolithic. In this case, as shown in
A monolithic laterally compliant spring element 110 may be formed from a stamped spring. Such a spring may be made of any formable spring material including Beryllium Copper, Bronze, Phosphor Bronze, spring steel, stainless steel, wire or sheet stock, etc. Monolithic laterally compliant spring elements 110 may also be formed by lithographic electroforming techniques. Lithographically electroformed elements 110 may be fabricated to very precise tolerances. Materials which can be electroformed conveniently include Ni, grain stuffed Ni, Ni alloys including Ni and NiCo, W, W alloys, bronze, etc. A further advantage of lithographic electroforming is that the contact regions 140A, 140B (or alternatively the entire element 110) can be well defined and conveniently coated with an appropriate contact metal, such as gold, silver, Pd—Co, Pd—Ni, or Rh. The contact regions 140A, 140B may also be coated by means other than plating (for example, vacuum coated) with a conductive contact material such as TiN or TiCN.
A further technique of fabricating a monolithic laterally compliant spring element 110 is by a hybrid of conventional machining and lithographic electroforming techniques whereby part of the laterally compliant spring element 110 is lithographically electroformed on spring stock material which is subsequently further shaped and released by stamping, punching, laser cutting, abrasive jet cutting or similar techniques. Such a hybrid technique allows the use of sheet spring stock (which has excellent mechanical spring characteristics) as the spring material and microformed metals for further refinement of contact shape and micro-alignment features.
The contact regions 140A, 140B may have different surface configurations as shown in
A contact feature 500A-500H may be selected to provide stable and low electrical contact resistance to the particular bump geometry (different bump geometries as discussed below) and metallurgy with a minimum of lateral force. These contact features 500B-500H may be applied to the surface by stamping, mechanical processing, chemical etching, electrochemical machining, and lithographic microfabrication including electroforming, laser machining, bump bonding, wire bonding and the like. The contact feature 500A-500H may be coated with an appropriate contact material as already described and/or the features may be made of a separate material selected for its contact characteristics.
In an embodiment of the present invention, the interposer substrate 100 (or interposer array assembly 800) is used to create a probe card assembly 1000 as seen in
In the unengaged state as shown in
To engage the interposer substrate 100, a lateral or sideways force is applied by a lateral engagement element 1100 to the interposer substrate 100, causing the interposer substrate 100 to move in a lateral fashion and engage the contact regions 140A, 140B with their corresponding bumps 130. This lateral engagements element 1100 may be screws, differential screws, cams, or other appropriate machine elements known in the art of mechanical assembly and alignment, as shown in
Because the contact regions 140A, 140B contact the bumps 130 of the upper 300 and lower 200 substrates at a side of the bumps 130, and thus only substantially impart lateral forces to the bumps 130, this interposer design does not create substantial vertical deflection (or tenting) of the substrates as shown in
The upper 110A and lower 110B portions should be made to an appropriate length such that the finished assembly meets the design requirement. For example, the design requirement may call for a maximum distance of 10 mm between a bottom surface of the upper substrate 300 and the tips of the probe contactors 720. In this case, if the probe contactor substrate is 5 mm thick and the probe contactors 720 are 0.25 mm tall, the distance between the bottom of the upper substrate 300 and the top of the probe contactor substrate should be 4.75 mm. The upper 110A and lower 110B portions then are selected such that the contact regions 140A, 140B will touch the bumps 130 in an appropriate location while still providing enough clearance between the ends of the upper 110A and lower 110B portions and the opposing substrates. This clearance may be 100 um on each end leaving the total laterally compliant spring element length (including upper portion 110A and lower portion 110B) at about 4.55 mm. The bumps 130 may be 25 um to 750 um tall and preferably about 250 um tall. In this example, a bump 130 may have a bump contact region (where the contact regions 140A, 140B of the laterally compliant spring element 110 contacts the bump 130) of about 100 um from its base on the substrate 200, 300, and the additional height is intended to accommodate manufacturing and alignment tolerances.
Another embodiment utilizes laterally compliant spring elements 110 which are designed to initially engage the bumps 130 vertically, but once engaged, the laterally compliant spring elements 110 impart only a lateral force to the bumps 130. An embodiment of such a design is illustrated in
The use of laterally compliant spring elements 110 which initially vertically engage the bumps 130 provides for the possibility of forming an assembly which once engaged has balanced lateral forces and therefore requires no net lateral restraint (i.e. does not impart the force X shown in
The same idea of a balanced lateral force may be applied to the case of a single monolithic laterally compliant spring element 110, as opposed to two laterally compliant spring elements 110. In this case, the laterally compliant spring elements 110 resemble a pin-and-socket type of connector such as those shown in
A further embodiment is illustrated in
The embodiment of the
Any of the above-mentioned embodiments of laterally compliant spring elements 110 may be assembled into an array 800 as seen in
Preferably the interposer substrate 100 has the property of a thermal expansion coefficient that is matched or close to that of the two wiring substrates 200, 300 to be interconnected. In the case where the two wiring substrates 200, 300 have dramatically different thermal expansion coefficients, the interposer substrate 100 may have a thermal expansion coefficient selected to match that of one or the other wiring substrates 200, 300, or it may have an intermediate thermal expansion coefficient so as to “share” the thermal mismatch effect between the two wiring substrates 200, 300. Using such an array 800, allows the assembly of laterally compliant spring elements in essentially arbitrary patterns and provides design flexibility in placement of the contact bumps 130 on the wiring substrates 200, 300.
As discussed before, the interposer substrate 100 and the laterally compliant spring elements 110 may have additional features designed to capture and hold the laterally compliant spring elements 110 in place within the interposer substrate 100. Such features may comprise retainer tabs, springs on the middle portion 110C of the laterally compliant spring element 110, stepped holes in the interposer substrate 100, etc. The laterally compliant spring elements 110 may also be freely placed in the interposer substrate 100 or they may be bonded in place with adhesives, solder or any other suitable bonding agent.
Another way of forming an array 800 is to attach the upper 110A and lower 110B portions of a laterally compliant spring element 110 to either side of the interposer substrate 100, as shown in
The laterally compliant spring elements 110 may alternatively be assembled into an array 800 by first assembling them into strips 1800 or linear arrays on holders as shown in
The assembled strips 1800 are then mounted together to a supporting frame 1900 to form an array 800 of laterally compliant spring elements 110, as shown in
The alignment frame 1900 and strip holders 1800 may include features designed to accurately align the strips 1800 to one another and to the frame 1900, and to fix the strips 1800 in position to the frame 1900 and to one another 1800. These features may include dowel pins and holes, slots, shoulders, threaded holes for screws, weld tabs, alignment fiducial marks, etc.
Strips 1800 of laterally compliant spring elements 110 may also be microfabricated lithographically. In such an arrangement, the laterally compliant spring elements are lithographically fabricated in batch directly to a substrate, for example, by patterned plating techniques. Then the substrate is cut into strips 1800 by dicing, Deep Reactive Ion Etching (DRIE), laser cutting, anisotropic etching, etc., and any sacrificial material is etched away to release the springs.
FIGS. 26A-E illustrate a method of lithographic fabrication of laterally compliant spring elements 110 on lateral contactor strips 1800. In FIGS. 26A-E, (a) is the strip substrate, (b) is the first sacrificial layer (photoresist or a sacrificial metal), (c) is the second photoresist layer, (d) is the structural layer, (d2) is the contact metal coating, (e) is the second sacrificial layer (sacrificial metal). The process sequence would be:
1. Provide a substrate with a platable seed layer on its surface.
2. Pattern a first photoresist to form a footing pattern.
3. Plate structural metal in the footing pattern.
4. Strip the photoresist and plate a first layer of sacrificial metal over the entire substrate.
5. Planarize the metals so as to expose the footing structural metal.
6. Pattern a second photoresist to form the lateral contactor spring structure.
7. Plate a second layer of structural metal in the spring pattern.
8. Strip the photoresist (dry ashing) 75% to 90% of the way down.
9. Plate a contact metal over the exposed spring structure.
10. Strip the remaining photoresist.
11. Plate a second layer of sacrificial metal thick enough to support the substrate segments through the separation process.
12. Separate the strips from one another by diamond abrasive sawing (dicing).
13. Selectively dissolve the sacrificial metal to completely free the resilient portions of the lateral spring contactors.
Such lateral contactors could also be fabricated with additional layers of structural metal (per U.S. patent application Ser. Nos. 11/019,912 and 11/102,982 incorporated herein) for added design freedom.
The strip 1800 preferably has the appropriate thermal matching characteristics as described above. The strip 1800 should also have sufficient strength and dimensional stability to maintain positional tolerances of the laterally compliant spring elements 110 when subjected to the lateral compression force and thermal environmental effects. The resulting strips 1800 of laterally compliant spring elements 110 could be pre-fabricated in standard pitches and lengths and assembled to a frame 1900 as needed. The supporting frame 1900 may be ceramic, metal, glass, or plastic, as required by its particular application. A preferred frame 1900 may be an Electric Discharge Machining (EDM) formed metal that is thermally matched to the strips 1800.
The contact bumps which are engaged by the contact regions 140A, 140B may be one of many configurations. Various possible configurations for the contact bumps 130 are shown in
All of the configurations in
In an alternative embodiment of the present invention, the laterally compliant interposer may consist of conductive traces on a flexible wiring board (also commonly called flex-circuit technology, flexible substrate, or simply “flex”).
Flex circuits provide a convenient technology platform which is well suited to producing electrical interconnects with excellent design freedom, shielding and impedance control characteristics. Such flex circuits are available in various configurations such as single metal layer, double metal layer, double metal layer with vias, and multi-layer. The conductive traces 3000 are most typically copper though other metals such as gold silver, palladium, platinum, nickel, and other conductive metals may be used, particularly in “build-up” or “additive” process technologies where the metal is electroformed rather than etched. It is also possible to apply a high quality spring metal on the trace to improve the mechanical spring performance. Such a metal could be from the group: Ni, NiMn, NiCu, CuZn, or NiCo. The spring metal could be plated directly on a conventional laminated flex conductor such as copper, thus forming a multi-layer conductive trace. Other resilient materials such as polymers and composites which impart a spring-like property may also be used. The base material of the flexible substrate 3010 is typically polyimide (Kapton™) or similar plastics, although other base films are available with different mechanical and electrical properties (such as Teflon™ or liquid crystal polymer or fiber reinforced resins). For the purpose of this embodiment, a base substrate film should be dimensionally stable, springable (meaning that it should have good spring resiliency characteristics with minimal creep, thermal set, and mechanical hysteresis) and have desirable electrical characteristics including stable dielectric constant and stable low loss tangent at high frequencies. Polyimide is such a suitable material and possesses exceptional spring characteristics in the class of polymer materials. A common supplier of flex circuit technology is the Sheldahl Corporation of Northfield, Minn. A typical flex substrate may have a height of 1 mm to 10 mm and a thickness of 10 um to 75 um. In certain preferred embodiments, the flex substrate may have a height of less than 5 mm and is more preferably between 2 mm and 4 mm. The flexibility of the flex is a function of both the height and the thickness, and the material properties of the base substrate and the metal layers, as well as the shape of any cutout or paddle areas (as described below). Additional springable support elements may be added to the structure as well. The conductive traces generally are between 10 um and 100 um wide, but may vary depending on the thickness of the flex. In certain preferred embodiments, the widths may be about 25 μm, 50 μm, or 100 μm with a margin of approximation being +/−20%. The contact areas generally have widths between 50 um and 500 um wide. Conventional technology allows for the distance between contact areas (the pitch) to be as small as 50 μm, but is more typically 500 μm to 1 mm. However, advances in lithographic techniques may be used to create pitches as small as 5 μm to 10 μm. The contact areas 3020 may be tailored so as to mate effectively to the bumps 130 which they are contacting and the same design elements that were described above regarding the previous embodiment may be utilized. Additionally, another possible configuration is for the conductive trace 3000 to extend beyond the flexible substrate 3010 to create a “tail,” as is illustrated in FIGS. 36 A-B. Such a tail may be only metal (for example the conductive copper overcoated with Au) or may be metal with polyimide backing. The tail configuration is particularly well suited for engagement directly into Printed Circuit Boards via holes.
FIGS. 28A-C illustrate a laterally compliant interposer utilizing a flexible substrate 3010 in an engaged state. In the engaged state, the contact areas 3020 are in contact with the contact bumps 130.
Another embodiment of the present invention utilizes cutouts on the flexible substrate to form a flexible paddle to provide even further bump-to-bump compliance (the ability to absorb bump position variance).
So far, the drawings have only displayed a simple conductor pattern without any special attention given to high frequency signal integrity considerations. However, the same materials and processes may be employed to form co-planar waveguides and/or multi-level stripline or microstrip waveguides. These advanced planar waveguide configurations provide unparalleled control over line impedance and cross-talk, both of which are critical parameters in high-speed test applications such as DRAM, microprocessor and system-on-chip test. FIGS. 30A-B illustrate a grounded coplanar waveguide. In addition to the conductive traces 3000, the flexible substrate 3010 also has a plurality of grounding strips 4000 in between the conductive traces. The grounding strips 4000 have vias 4020 which connect the grounding strips to a grounding plane 4010 (see
FIGS. 31A-B illustrates a multi-level fully shielded planar waveguide (G-S-G on the middle plane with ground planes on top and bottom). The multilevel waveguide is similar in construction to the co-planar stripline except that it has another insulating polymer layer 3010 on the front of the conductive traces 3000 and another ground plane 4010 on top of that second insulating layer. The ground planes are connected by vias 4025, or alternatively they may be connected by the holder 5000 or at a special bump location, thus providing a ground path. Dual ground planes provide more complete shielding and thus better crosstalk performance. It also isolates the traces 3000 from the holder 5000 which is an advantage if the holder is constructed from metal.
If multiple layers of metallization are employed in a flexible lateral interposer's construction, further additional signal wiring and interconnection can be accommodated within the strip itself (i.e., with more layers, the conductive traces do not need to be 1 to 1 connections from the PCB to the probe contactor substrate, rather a single point on the PCB can be fanned out to multiple points on the probe contactor substrate). For example, a common voltage could be distributed to multiple contact areas from a single source. Such a signal distribution could be accommodated using a construction employing only one metal layer (in this case only adjacent contacts can be connected), and two metal layers with vias (in which case more complex networks can be formed with or without shielding, and more than two metal layers. Components can be added to such wiring networks as noted below.
Individual flexible lateral interposers may be assembled into a 2-D array in order to form a complete lateral interposer contactor assembly as shown in FIGS. 32A-C. The individual flexible lateral interposers (including the flex substrate 3010, the conductive traces 3000, and any ground planes 4010 or grounding strips 4000) are assembled into a holder 5000 which supports the strips near their middle along their long axis. Such a holder may be a thin metal plate with machined slots 5010. The holder 5000 may also be made from a laser machined ceramic or molded plastic or any other suitable material with sufficient machinability, mechanical properties and electrical properties. If the holder 5000 is conductive, it may be grounded so as to form a shield.
The holder 5000 may also incorporate additional wiring (distribution wiring) 5020 on the surface of the holder 5000 for the distribution of common or shared power and signals, as shown in FIGS. 33A-C. Such wiring may be of a single or multi-layer construction and may be formed directly on either or both surfaces of the holder 5000 (for example, by screen printing, thin film metallization or other methods well known in the art), or by adding an additional substrate(s) to the surface(s) of the holder 5000. These additional substrate(s) may be another flex substrate or other wiring board with slots in it to allow the flexible lateral interposers to extend through them. The advantage of using an additional wiring substrate attached to the holder 5000 is that this method allows for the decoupling of mechanical requirements and wiring requirements (the mechanical function is performed by the holder 5000, while the wiring is handled by the wiring substrate). Interconnects 5040 may be formed between the flexible lateral interposers and the distribution wiring by soldering, wire bonding, spring contact, or Tab bonding flying leads built into the flexible lateral interposer to corresponding nodes on the holder 5000 or distribution substrate. Such interconnects to the flexible lateral interposer provide a means of accessing the distribution wiring from the connections to the interposers. For example, in a probe card, a few pins at the end of the array may be dedicated to the provision of power supply and timing signals to the distribution wiring from which said signals and supplies may be connected to additional contacts.
The distribution wiring 5020 may be connected to other elements of the probe card or system components by using discrete “off-board” wiring 5030 which may be directly attached to the distribution wiring. Such “off-board” wiring may be in the form of individual wires, wire bundles, coaxial cables, shielded cables or flex circuits, all of which would extend laterally from the holder 5000. Alternatively, auxiliary spring pins may be used to extend vertically from the distribution wiring to either the PCB or the probe contactor substrate. Electronic components (including passive components such as capacitors and resistors, as well as active components such as transistors, semiconductors, integrated circuits, electro-optical devices, etc.) may be attached to the holder 5000 or wiring substrate to form a more complex network. Other features may also be designed into the interposer strips or the carrier plate so as to provide accurate registration of the various components to one another. These features can include shoulders, notches, and guide pin holes among other commonly used methods. The interposer strips may be attached to the holder 5000 by any convenient means including mechanical clips, solder, or adhesives.
In cases where the flexible interposers do not provide sufficient spring force (for example, very tall strips may not be stiff enough with practical limits on the polyimide thickness) or spring stability (for example, in high temperature applications where the polyimide or the metallic conductive traces could creep or set under load eventually losing spring force in the deflected state), a spring backing 6000 may be applied to support the strip. Such a backing 6000 takes a shape similar to the paddles 3070 or may be shaped like the conductive traces 3000 and is either bonded or electroplated on the back of the strip or simply placed behind strip in the interposer assembly. In the case of bonded or assembled backing 6000, the backing is made of a suitable spring material such as stainless steel, beryllium copper, phosphor bronze, etc. If the backing 6000 is electroplated, it may be made of NiCo, NiMn, Hard Ni, or other electroplatable spring material and may be plated directly on a backing ground plane if such a plane is incorporated. In either case, the backing material is chosen (in terms of material properties and dimensions) so as to dominate the combined spring in terms of stiffness so that the non-ideal spring behavior of the flexible interposer is small in comparison the backing 6000 spring. Such backing 6000 may be electrically isolated from the flexible interposer or distribution wiring 5020 or may be electrically attached to the network and can thus act as a shield or signal path. Although
A variety of electrical components 6050 may be attached to the flexible interposers, as shown in
While particular elements, embodiments, and applications of the present invention have been shown and described, it is understood that the invention is not limited thereto since modifications may be made by those skilled in the art, particularly in light of the foregoing teaching. It is therefore contemplated by the appended claims to cover such modifications and incorporate those features which come within the spirit and scope of the invention.
This application is a continuation-in-part of U.S. patent application Ser. No. 11/226568, filed Sep. 14, 2005, titled “Lateral Interposer Contact Design and Probe Card Assembly,” the disclosure of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11226568 | Sep 2005 | US |
| Child | 11633324 | Dec 2006 | US |
