Pin-in elastomer electrical contactor and methods and processes for making and using the same

A contactor card assembly for use with a semiconductor substrate. An upper keeper plate and a lower keeper plate each include a number of conductive pins extending therethrough, situated in vias filled with an elastomeric material and extending beyond the keeper plates to contact a substrate for testing. An intermediate keeper plate is situated between the upper and lower keeper plates and includes conductive pivot bars in channels filled with elastomeric material. Each conductive pin contacts a pivot bar on one side thereof to electrically communicate with a corresponding pin on the opposite side. Under compression, variations in the height of contacts on the substrate under test are adjusted for by the movement of the pins and pivoting of the pivot bar in the elastomeric material. Methods and process for creating the keeper plates and semiconductor and testing assemblies are also included in the present invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to methods and apparatus in the field of probe cards and contact cards for testing semiconductor substrates. More specifically, the present invention relates to methods and apparatus in the field of probe and contact cards that compensate for variation in the height of contacts on the semiconductor substrate under test.

2. State of the Art

For burn-in testing of semiconductor substrates, an electrical connection must be established from the contacts on the substrate to the testing device. Often a section of printed circuit board (PCB) with contacts corresponding to the substrate under test is connected to the testing device and used to make contact with the substrate. Typically the PCB is made of low cost PCB material, which creates difficulties in making it planar and also has different thermal expansion properties than the substrate under test. Typically, probe cards, or contact cards have been used to make contact from the PCB to the substrate under test to compensate for such problems.

Variation in height of the contacts of the semiconductor substrate under test, such as where the semiconductor substrate includes mounting or interconnect structures, including under bump metallization, redistribution lines, solder balls, or other connections, can result in probe cards having difficulty making and maintaining good contact. For example, as described in U.S. Pat. No. 6,535,012, in a reusable test fixture for burn-in testing, the variation in the height of contacts of a semiconductor substrate is compensated by a portion of the reusable test fixture that uses contact tips or flexible contact tips for contacting the contacts on semiconductor devices and contacts on a wafer. If desired, an elastomeric mat having conductive patterns thereon corresponding to conductive pads or contact areas on the wafer may be used with flexible contact tips on a portion of the reusable burn-in fixture.

In another example, the variation in the height of contacts of a semiconductor substrate is compensated by a probe card used in a test assembly that may have a number of contact pins or needles extending from it on one side that contact the PCB and an opposite set that contact the semiconductor substrate under test. The individual pins or needles are typically co-planar. In compressing the testing assembly to make contact with the semiconductor substrate under test, the probe card may lose co-planarity to make contact with either the semiconductor substrate under test, resulting in poor alignment with the opposite set resulting in the problems during testing of current leak, poor connections, missing connections, etc.

One attempt to deal with these problems has been the use of “pogo” or spring loaded pins in a probe card. In the testing assembly, a keeper plate has a plurality of pogo pins, each pogo pin having a top side, a bottom side and a central sleeve containing the springs, inserted into holes in the keeper plate. One end of each pogo pin corresponds to a contact on the semiconductor substrate under test, while the opposite end corresponds to contact on the PCB. Such a keeper plate can adjust for some variation in the height of the contacts. However, each pogo pin has a cost of approximately $1.00, and must be assembled in the keeper plate. For a wafer-sized keeper plate, between 11,500 and 12,000 or more pogo pins may be needed. As such, the costs in materials and labor to manufacture such a keeper plate for a test assembly are significant.

Accordingly, a test apparatus or test system must have the pins in a probe card capable of compensating of any height variations of the contacts of a semiconductor substrate under test. Preferably, such a test apparatus or test system needs to be readily manufactured using standard micromachining or wafer handling techniques. Such a test apparatus or test system must be conveniently scalable from single semiconductor die testing to wafer-level testing.

BRIEF SUMMARY OF THE INVENTION

The present invention comprises a contact card for contacting the contacts of a semiconductor substrate, such as a semiconductor die or wafer having a plurality of semiconductor dice for testing and burn-in.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The present invention comprises a method and apparatus for a contactor card assembly for the probe testing and burn-in testing of semiconductor dies and wafers. It will be appreciated that the invention is illustrated by the various embodiments of the invention described herein. It will be understood that various combinations or modifications of the disclosed embodiments of the invention may be made without departing from the scope of the invention.

Illustrated in drawingFIG. 1is an embodiment of a contactor card assembly1000of the present invention. An upper keeper plate100includes a plurality of vias102therethrough. Each via102contains an electrically conductive upper connector or contact pin104having a shaft105, a portion (not shown) of which is surrounded by a resilient, flexible upper elastomer106that retains the upper connector pin104therein, yet allows the pin104to move in any direction along its longitudinal axis as the elastomer106flexes. Upper connector pin104and the upper elastomer106are described in more detail herein. Upper keeper plate100may contain holes108for visual and mechanical alignment of semiconductor substrates or other structures in using the assembly1000, including alignment of the upper keeper plate100to intermediate keeper plate140and lower keeper plate120, as well to external testing device fixtures.

Similar to the upper keeper plate100, a lower keeper plate120includes a plurality of vias122therethrough. Each via122containing an electrically conductive lower connector or contact pin124, which is surrounded by a resilient, flexible lower elastomer126that retains the lower connector pin124therein while allowing the connector pin124to move in any direction along its longitudinal axis as the lower elastomer126flexes. The lower keeper plate120may contain lower alignment holes128for visual and mechanical alignment of semiconductor substrates or other structures in using the assembly1000. Lower keeper plate120and upper keeper plate100are manufactured in the same manner from the similar or the same materials, differing only in the placement of the upper and lower connective pins104and124.

An intermediate keeper plate140may be disposed between the upper keeper plate100and lower keeper plate120. An electrically conductive pivot bar142is contained in a resilient, flexible elastomer144disposed in a channel146passing through the intermediate keeper plate140. At least a portion of the top surface145and bottom surface147of the electrically conductive pivot bar142remain exposed from the elastomer144.

An upper connector pin104extending from the upper keeper plate100contacts the pivot bar142on its upper surface145, at a point along its horizontal axis away from the midpoint of the pivot bar142. A lower connector pin124extends upward from the bottom keeper plate120to contact the lower surface147at a point along its horizontal axis away from the midpoint of the pivot bar142, in a direction opposite the contact of the upper connector pin104on the upper surface145. The support structure1002for supporting the keeper plates and maintaining the relationship therebetween is illustrated in dashed lines in drawingFIGS. 2 and 3.

Turning to drawingFIGS. 2 and 3, the contactor card assembly1000is shown in relationship to a semiconductor substrate220to be tested in a testing device1050. A printed circuit board200or other testing substrate is mounted on an upper backing plate204and contains at least one contact202on the surface thereof. An upper connection pin104aligns with the contact202in an uncompressed position. The semiconductor substrate220undergoing testing or burn-in is disposed on a backing plate226located beneath the lower keeper plate120. Semiconductor substrate220may be a semiconductor die, a semiconductor assembly (such as a packaged die), a semiconductor wafer containing multiple die sites or another substrate containing an integrated circuit to be tested. An electrical contact222, such as a solder ball on a semiconductor assembly or a bond pad on a semiconductor die, is aligned with the lower connective pin124corresponding to the upper connective pin104aligned with the appropriate contact202on the PCB200.

As the testing device is compressed to bring the connector pins104and124in contact with the electrical contact222and the contact202, the contactor card assembly1000conforms to the contacts as illustrated in drawingFIG. 3. The upper and lower connector pins104and124are able to move in a direction along their longitudinal axes to engage the contact202and electrical contact222with sufficient force to establish and maintain electrical communication therebetween. Where the electrical contacts222on the substrate220are of different heights, such as an array of solder balls disposed on the under bump metallization (UMB) of a wafer or die having variations in height across the array, contact may be maintained in an effective manner. In some embodiments, appropriately sized upper and lower electrical contact pins104and124may be used to allow proper contact to be made to electrical contacts222on a substrate220that includes contact pads that have conductive bumps, such as solder balls, attached thereto and non-bumped pads, such as wire bond pads. Additionally, in some embodiments, appropriately sized upper and lower electrical contact pins104and124may be used to allow proper contact to be made to electrical contacts222on a substrate220, that is a stacked semiconductor die package having electrical contacts222on different levels of the package corresponding to the differing semiconductor dice.

Pivot bar142moves within the channel146in response to the forces placed upon it by the upper and lower connector pins104and124. The elastomer144flexes to allow the pivot bar142a range of motion while retaining it in the channel146. As illustrated in drawingFIG. 3, the pivot bar142can twist, yaw, tilt or roll, in reaction to the forces placed upon it. Where a number of pivot bars142are used, each corresponding to an individual contact of an array, the ability of each pivot bar142to act independently of the others allows contact to be made from contact202to the electrical connection222across a varying distance. Compression sufficient to allow testing and burn-in of an integrated circuit can be established, while neither PCB200nor semiconductor substrate220need be maintained in exactly parallel planes to avoid problems from non-co-planarity of the contacts. In some embodiments of the invention, variation of up to about 100 μm can be tolerated across an array of contacts. It will be appreciated that for embodiments where appropriately sized upper and lower electrical contact pins104and124are used to allow proper contact to be made to electrical contacts222on a substrate220with bumped and non-bumped contact pads, or substrates220that are stacked semiconductor packages, this variation may refers to variations from the theoretically expected position of such contacts, and, even larger variations may be tolerated.

Turning to drawingFIGS. 4 through 8, one embodiment of a process in accordance with the present invention for creating a keeper plate420with conductive contact pins430extending therethrough is illustrated. A plate substrate400having a generally planar shape and including upper surface402and lower surface404may be used, as illustrated in drawingFIG. 4. Plate substrate400may comprise any material capable of supporting the additional structures. For example, a substrate comprising primarily silicon, as formed in the art by growing a single crystal wafer in the form of a cylinder, which is then segmented or sliced, such as a wafer, may be used. Alternatively, another bulk semiconductor substrate may be employed, such as silicon-on-sapphire (SOS) substrate or a silicon-on-glass (SOG) substrate, or other type of silicon-on-insulator (SOI) substrate. Other substrates that may be used as the plate substrate400include printed circuit board (PCB), metallic plates, ceramics or polymeric materials formed into a substrate. Additional suitable substrates may include photosensitive and metallizable patterned glass materials, such as FOTURAN® photo-etchable glass available from SCHOTT North America, and copper-coated Invar™ alloy (which may be finished with gold coating). In any event, the selected plate substrate400may have a coefficient of thermal expansion similar to the testing substrate or substrate under test, to reduce the possibility of damage during a testing and burn-in procedure.

In order to allow processing with currently available equipment, plate substrate400may be a wafer or may be sized as a conventional semiconductor wafer, allowing for handling and processing. The plate substrate400may have any suitable shape, so long as a substantially planar top surface402and a substantially planar bottom surface404are maintained. Plate substrate400may thus be formed as a planar disk or a planar polygonal substrate. All such alternative structures are within the scope of the present invention.

At least one via406may be formed through the plate substrate400, extending from the top surface402to the bottom surface404, as illustrated in drawingFIG. 5. The at least one via406may be formed in any suitable fashion known to those of ordinary skill in the art. For example, the at least one via406may be formed by laser ablation. Laser ablation may be effected using any suitable equipment, such as the Model 5000-series lasers, offered currently by ElectroScientific Industries (ESI) of Portland, Oreg. One specific, suitable piece of equipment is a 355 nm wavelength UV YAG laser, ESI Model 2700, which may be used to form vias as little as 25 μm in diameter. One hundred pulses using this laser will form a 750 μm deep via through silicon. Another suitable laser is the Model 200, offered by Xsil Limited of Dublin, Ireland. Alternatively, one or more vias406may be formed by etching (comprising wet etching, dry etching and either isotropic etching or anisotropic etching), by drilling or boring with a mechanical drill bit, or otherwise as known to those of ordinary skill in the art. Guide holes (such as those illustrated as108and128in drawingFIG. 1), and any other desired structures, may be formed in the plate substrate400at this time.

Once via406is complete, and if necessary cleaned, it may then be filled with an elastomeric material410, as illustrated in drawingFIG. 6. Any suitable elastomeric material, which may be dispensed into via406and retain an inserted connector pin therein may be used. The technique for filling via406will vary based on the elastomeric material410chosen. For example, a liquid elastomeric material may be dispensed directly into a via406and then cured. A liquid or gelatinous elastomeric material may be dispensed on the upper surface402of the plate substrate400and a squeegee or other scraper pulled across the surface to push the elastomeric material410into the vias406. Once the vias406are filled with the elastomeric material410, the elastomeric material may be cured by baking, by photo curing or any other type of curing appropriate for the selected material.

Suitable elastomeric materials410may include electrically insulative material to isolate the connective pin from the plate substrate400. One example of a suitable material is liquid silicone, which may be cured to a flexible state. The cured hardness of the elastomeric material410, as well as the thickness and cross-sectional area, may be selected to result in a spring force on the connective pin sufficient to ensure good contact. Via406may be filled with the plate substrate400attached to an underlying chuck plate to provide a bottom to the via406, or may be performed with via406openings exposed to allow for over-deposition of the elastomeric material410, where desired. In embodiments of the invention where the plate substrate400is constructed of a non-conductive material, a conductive elastomer may be used to facilitate current flow across the substrate400, while preventing leakage between vias406. It will be appreciated that in embodiments where the plate substrate400is a conductive material, the conductive material may be used to electrically bias the final assembly to improve performance (i.e., the material may be shorted to a ground to act as a ground plane, or biased with voltage to facilitate testing).

As illustrated in drawingFIG. 7, a pin hole412may then be bored through the elastomeric material410contained in the via406. As with via406, formation may be accomplished with a cutting laser by ablation. A micromachining laser, such as an Xsil laser, may be useful for performing this operation. Where appropriate, the pin hole412may be formed by other suitable means, such as by etching, drilling or boring with a mechanical drill bit, punching, by combining any of these means with each other or laser ablation, or as otherwise known to those of ordinary skill in the art. The bore of pin hole412has a width W. In embodiments where pin hole412has a circular cross section, width W will correspond to the diameter of the pin hole412.

As illustrated inFIG. 8, a conductive contact pin430may then be inserted into the pin hole412, and may serve as the connector pins104and124illustrated in drawingFIGS. 1 through 3. The conductive contact pin430may be an elongated conductive shaft424, which will extend out from the plate substrate400to contact the structure under test and a pivot bar142. The proximal end422(designated as the end that will contact the pivot bar142) may be rounded to facilitate the movement of the pivot bar142during operation. The distal contact end of the conductive contact pin430may be flat, rounded, crowned, pointed, or have any other shape that is desired and suitable for the intended application. The shaft424of the contact pin430may have a cross-sectional width greater than the width W of the bore of pin hole412, allowing the elastomeric material410to retain the conductiye contact pin430in the pin hole412. Placement of the conductive contact pin430may be facilitated by use of a jig J to retain a conductive contact pin430in proper position during placement. Where a number of conductive contact pins430are used, the jig J may hold the conductive contact pins430in correct alignment, allowing the insertion of the entire plurality at one time. The protrusion of the conductive contact pin430from the substrate400may also be controlled by the use of the jig J, or through machine placement of the pin.

The conductive contact pin430may be constructed of any suitable electrically conductive material. For example, a section of copper wire that is plated with gold or a gold wire that is plated with nickel then flash coated with a thin layer of gold may be used. In certain embodiments of the invention, the conductive contact pins430may be constructed by patterning vias in a wafer or a thick resist layer and then coating the vias with a seed layer, followed by plating the vias with a conductive material, such as copper. The vias may be plated until conductive material is added to form pins of sufficient depth.

One advantage of placing the conductive contact pins430into a bore of a pin hole412in cured elastomeric material is that the conductive contact pins430may be removed and replaced should failure occur. Additionally, the chance of pin contact areas becoming contaminated is lessened compared to placing the conductive contact pins430in the vias406, followed by filling the vias with an elastomer that is then cured. It will, however be appreciated that keeper plates created using such a process may be used in the contactor card assembly1000of the present invention, and as such fall within the scope of the present invention.

Illustrated in drawingFIGS. 9 through 11is a procedure for manufacturing an intermediate keeper plate140including a pivot bar142in accordance with the principles of the present invention. It will be appreciated that while illustrative of one embodiment of the present invention, other methods and procedures may also be used and all such methods are within the scope of the present invention.

An electrically conductive substrate500is illustrated in drawingFIG. 9. The electrically conductive substrate500may be a planar substrate having a top surface502and a bottom surface504. Suitable electrically conductive planar substrates may be constructed from metals. For example, a section of a metal foil may be provided. Other electrically conductive substrates500may be constructed from electrically conductive polymers, conductor-filled polymers, other electrically conductive materials and combination thereof.

As illustrated in drawingFIG. 10, a channel506may be cut through electrically conductive substrate500to substantially surround a bar508. The bar508may remain attached to the substrate500through a small tab510of material, with channel506surrounding the remainder of the bar508. Bar508may have any desired shape and any desired longitudinal axis. For example, bar508may be circular, oval, rectangular, square, a regular polygon, or irregularly shaped, as is desired for the specific usage. The upper surface507and lower surface509of bar508may remain substantially planar, or a rounded divot517(FIG. 11) may be placed therein for an electrically conductive contact pin430(FIG. 8) to slide along in a guided manner.

Channel506may be cut through substrate500in any suitable manner. For example, where a metal foil is provided as the substrate500, channel506may be cut with a micromachining laser, such as the aforementioned Xsil micromachining laser, or formed by etching the foil with a suitable etchant. Where needed, the channel506may be cleaned to remove any debris that would interfere with the motion electrical isolation of the bar508. At this point the bar508(and substrate500, if desired) may be plated to improve surface hardness or conductivity. A solder mask material may be used to selectively plate the bars508.

A non-conductive elastomeric material512may then be disposed in the channel506around the bar508attaching it to the substrate500. The upper surface507and lower surface509of bar508may remain free of the non-conductive elastomeric material512. The non-conductive elastomeric material512electrically isolates the bar508from the surrounding substrate, reducing current leaking during testing and burn-in. Any suitable non-conductive elastomeric material may be used. For example, liquid silicone may be dispensed into the channel506. Other suitable non-conductive elastomers may include flexible polymeric materials with electrically insulative properties and flexible insulative epoxies.

The non-conductive elastomeric material512may be dispensed in channel506in any suitable fashion. For example a liquid material may be dispensed directly into the channel506, where the substrate500is placed on a support plate providing a bottom for the channel. For example, a Teflon-coated plate would provide a bottom that liquid silicone would not adhere to, allowing release. In another example, tape may be applied over the channel and the contact portion of the bar508, which may be removed upon dispensing or curing of the elastomeric material512. Where the non-conductive elastomeric material512is of suitable viscosity, no support may be required. Where the non-conductive elastomeric material512is gelatinous, or a higher viscosity fluid, the material may be dispensed on the upper surface502of the substrate500and then disposed in one or more channels506by a squeegee or other scraper.

Once the non-conductive elastomeric material512is disposed in the channel506, it may be cured in any suitable fashion. For example, the part may be heated to cure the material, or exposed to a specific wavelength of light to photoset a photoactive material. Once the elastomeric material512is cured, the tab510may be removed to allow the bar508to pivot. Tab510removal may occur by laser ablation, etching or as otherwise known to those of ordinary skill in the art. Where tape is applied to protect the pivot bar508through dispensing or handling, the tape may be left on during tab510removal to protect the pivot bar508and elastomeric material512from slag and damage incurred during tab510removal and then removed.

It will be appreciated that modifications to the process outlined above may be made by those of ordinary skill in the art. For example, a non-conductive substrate500may be used with vias formed therein and a conductive bar508placed therein to further reduce the possibility of current leakage. In other embodiments, the substrate500may be provided by building up a substrate500containing the channel through a plating process, such as nickel plating an appropriate mandrel, or stacking of thick-film tab tape or fab metal. A three dimensional plated build up process, such a photolithography, or a controlled plating process may be used.

An entire contactor card assembly, such as that illustrated as1000in drawingFIGS. 1 through 3, may be assembled from an intermediate keeper plate140, and upper and lower keeper plates100and120. The contact force of the electrically conductive contact pins104and124may be controlled for the desired application by varying the thickness of the keeper plates, the diameter of the pins104and124, the diameter of the pin holes412, the shape of the bar508and the resiliency of the cured elastomeric materials.

In other embodiments of the invention, a keeper plate420may be attached to a wafer or die that has solder disposed on the electrical contacts thereof, or an assembly of wafers or dice with solder disposed on the electrical contacts thereof to form a stacked assembly with resilient contacts. This may also be accomplished with the complete assembly, including upper, lower and intermediate keeper plates to avoid the need to form insulated vias in a package. Such an assembly may be able to undergo testing and burn-in through the attached contactor assembly. The flexible compliant contacts, formed as discussed previously herein, may be used in other semiconductor related structures. This may be useful in any application where contact is to be made with a array of contacts that may have variations in contact height. For example, the contacts currently used in burn-in and test head sockets may be replaced by the compliant connectors to add a degree of flexibility to the contacts.

It will be apparent that details of the apparatus, processes, and methods herein described can be varied considerably without departing from the concept and scope of the invention. The claims alone define the scope of the invention as conceived and as described herein.