Patent Application
20120023730
The present invention relates generally to the field of miniaturized spring contacts and spring probes for high density electrical interconnection systems. More particularly, the present invention relates to microfabricated spring contact methods and apparatus and associated assembly structures and processes, and improvements thereto, for making electrical connections to semiconductor integrated circuits (ICs) having increasingly higher density and finer pitch input/output connections and the next level of interconnect in applications including but not limited to semiconductor device testing and packaging.
Advances in semiconductor integrated circuit design, processing, and packaging technologies have resulted in increases in the number and density of input/output (I/O) connections on each die and as well as in an increase in the diameter of the silicon wafers used in device fabrication. With increasing numbers of I/O connections per die, the cost of testing each die becomes a greater and greater fraction of the total device cost. The test cost fraction can be reduced by either reducing the time required to test each die or by testing multiple die simultaneously.
Probe cards may be used to test single or multiple die simultaneously at the wafer level prior to singulation and packaging. In multiple die testing applications, the requirements for parallelism between the array of spring probe tips on the probe card and the semiconductor wafer become increasingly stringent since the entire array of spring probe tips are required to make simultaneous electrical contact over large areas of the wafer.
With each new generation of IC technology, the I/O pitch tends to decrease and the I/O density tends to increase. These trends place increasingly stringent requirements on the probe tips and associated probe card structures. Fine pitch probe tips are required to be smaller in width and length while continuing to generate the force required to achieve and maintain good electrical connections with the device under test. The force required to achieve a good electrical connection is a function of the processing history of the IC contact pad, such as but not limited to the manner of deposition, the temperature exposure profile, the metal composition, shape, surface topology, and the finish of the spring probe tip. The required force is also typically a function of the manner in which the probe tip “scrubs” the surface of the contact pad.
As the probe pitch decreases, the linear dimensions of the IC connection terminal contact areas also decreases leaving less room available for the probe tips to scrub. Additionally, the probes must be constructed to avoid damaging the passivation layer that is sometimes added to protect the underlying IC devices (typically 5-10 microns in thickness). Additionally, as the spring probe density increases, the width and length of the probes tends to decrease and the stress within the probe tends to increase, to generate the force required to make good electrical contact to the IC connection terminal contact areas.
There is a need for probe cards for fine pitch probing comprised of an array of spring probe contacts capable of making simultaneous good electrical connections to multiple devices on a semiconductor wafer under test in commercially available wafer probers using specified overdrive conditions over large areas of a semiconductor wafer and or over an entire wafer. To accomplish this, the array of spring probe contacts on the probe card should be co-planar and parallel to the surface of the semiconductor wafer to within specified tolerances such that using specified overdrive conditions, the first and last probes to touch the wafer will all be in good electrical contact with the IC device yet not be subject to over stressed conditions which could lead to premature failure. Additionally, any changes in the Z position, e.g. due to set or plastic deformation, or condition of the probe tips, e.g. diameter, surface roughness, etc., over the spring probe cycle life should remain within specified acceptable limits when operated within specified conditions of use, such as but not limited to overdrive, temperature range, and/or cleaning procedures.
Micro-fabricated spring contacts are potentially capable of overcoming many of the limitations associated with conventionally fabricated spring contacts, e.g. tungsten needle probes, particularly in fine pitch probing applications over large substrate areas. Micro-fabricated spring contacts can be fabricated using a variety of photolithography based techniques known to those skilled in the art, e.g. Micro-Electro-Mechanical Systems (MEMS) fabrication processes and hybrid processes such as using wire bonds to create spring contact skeletons and MEMs or electroplating processes to form the complete spring contact structure. Arrays of spring contacts can be either be mounted on a contactor substrate by pre-fabricating and transferring them (either sequentially or in mass parallel) to the contactor substrate or by assembling each element of the spring contact array directly on the contactor substrate, such as by using a wire bonder along with subsequent batch mode processes.
Micro-fabricated spring contacts may be fabricated with variety of processes known to those skilled in the art. Exemplary monolithic micro-fabricated spring contacts may comprise stress metal springs having one or more layers of built-in or initial stress that are photolithographically patterned and fabricated on a substrate using batch mode semiconductor manufacturing processes. As a result, the spring contacts are fabricated en masse, and can be fabricated with spacings equal to or less than that of fine pitch semiconductor device electrical connection terminals or with spacings equal to or greater than those of printed circuit boards, i.e. functioning as an electrical signal space transformer.
In exemplary stress metal spring contacts, an internal stress gradient created within the spring contact causes a free portion of the spring contact to bend up and away from the substrate to a lift height that is determined by the magnitude of the stress gradient. An anchor portion remains fixed to the substrate and is electrically connected to a first contact pad on the substrate. The spring contact is made of an elastic material, which provides the free portion of the spring contact with flexibility and mechanical compliance. The force generated by stress metal spring contacts can be increased by the application of one or more plated metal layers comprising metals and metal alloys with appropriate Young's modulii, such as nickel or nickel cobalt, etc. Increasing the spring force helps to establish reliable electrical contacts and can also help to compensate for mechanical variations and induced by temperature changes and other environmental factors.
Photolithographically patterned spring structures are particularly useful in electrical contactor applications where it is desired to provide high density electrical contacts which may extend over relatively large contact areas and which also may exhibit relatively high mechanical compliance in the normal direction relative to the plane of the contact area. Such electrical contactors are useful for applications including integrated circuit device testing (both in wafer and packaged formats), integrated circuit packaging (including singulated device packages, wafer scale packaging, and multiple chip packages) and electrical connectors (including board level, module level, and device level, e.g. sockets. Photolithographically patterned spring structures are also well suited for the fabrication of electrical interposers capable of providing compliant electrical connections between arrays of electrical contacts.
Interposers, having many contacts in parallel, can be subject to contamination from particulates or other contamination layers, e.g. surface contamination layers, which may cause unreliable electrical contact under use conditions, such as including repeated mechanical and thermal cycling. A controlled increase of interposer contact force is associated with an increase in the reliability of the electrical contacts under use conditions, as well as during aging and storage in environments in which surface contamination films can form. While it is desirable to increase the contact force, it is undesirable to increase contact force excessively, since the force to compress the interposer becomes too high, which may cause unacceptable mechanical deflection of the interposer and probe card structures.
It may therefore be desirable to provide interposers designed to have sufficient contact force to provide high quality low resistance electrical connections yet not so high that excessive forces are generated on adjacent structures.
Lift height non-uniformity can be caused by numerous factors including but not limited to variations in the internal stress gradient of stress metal springs, variations in the substrate thickness, and variations in lift height associated with plating processes, variations in lift height due to thermal processes, and variations in lift height due to assembly fabrication processes.
As device pitch decreases and for other reasons mentioned above, it would be desirable for micro fabricated contactors and interposers to possess contact elements having increasing higher levels planarization and/or lift height uniformity.
It would be advantageous to provide a method and structure to fabricate improved microfabricated spring contacts either directly or indirectly across the surface of substrate areas, which can provide increased strength, longevity, and planarity, as well as superior electrical contact performance, over a wide variety of operating conditions e.g. temperature, cycle life, overdrive, pad metal, etc. Such a development would provide a significant technical advance.
Furthermore, it would be advantageous to provide cost-effective assembly structures and methods for thermal processing of microcontactor assemblies. Such improvements would provide an additional technical advance.
As well, it would be advantageous to provide enhanced probe card structures and associated processes, such as to improve setup, servicing, and thermal performance. Such improvements would provide a major technical advance.
Enhanced microfabricated spring contact structures and associated methods, e.g. such as for electrical contactors and interposers, comprise improvements to spring structures that extend from the substrate surface, and/or improvements to structures on or within the support substrate. Improved spring structures and processes comprise embodiments having selectively formed and etched, coated and/or plated regions, which are optionally further processed through planarization and/or annealment. Enhanced solder connections and associated processes provide a gap between substrates for componentry, and or improved manufacturing techniques using distributed spacers. Enhanced probe card assembly structures and processes provide improved planarization adjustment and thermal stability.
Micro-fabricated spring contacts may be fabricated with a variety of processes known to those skilled in the art. Exemplary monolithic micro-fabricated spring contacts may comprise stress metal springs that are photolithographically patterned and fabricated on a substrate using batch mode semiconductor manufacturing processes. As a result, the spring contacts are fabricated en masse, and can be fabricated with spacings equal to or less than that of semiconductor bonding pads or with spacings equal to or greater than those of printed circuit boards, i.e. functioning as an electrical signal space transformer.
Fabrication of high density arrays of spring contacts are also possible using monolithic micro-fabrication processes wherein arrays of elastic, i.e. resilient, core members, i.e. spring contact skeleton structures, are fabricated directly on a contactor substrate utilizing thick or thin film photolithographic batch mode processing techniques such as those commonly used to fabricate semiconductor integrated circuits.
The spring constant of the spring is a function of the Young's modulus of the material used to fabricate the spring and the length, width, and thickness of the spring. The spring constant of the spring can be increased by enveloping the springs 40 with a coating of a metal including but not limited to electroplated, or sputtered, or CVD deposited nickel or a nickel alloy, gold, or a palladium alloy such as palladium cobalt (see
The spring constant can be varied over many orders of magnitude by controlling the thickness of the deposited coating layer, the geometrical characteristics of the spring, and the choice of metal and the thickness and number of coatings. Making the springs thicker both increases the contact force and the robustness of the physical and electrical contact between the spring and its contact pad.
As seen in
As further seen in
As also seen in
Additionally, optical signals can be transmitted through the contactor substrate 30, by fabricating openings of sufficient size through the substrate through which the optical signals can be transmitted. The holes may be unfilled or filled with optically conducting materials, including but not limited to polymers, glasses, air, vacuum, etc. Lenses, diffraction gratings and other optical elements can be integrated to improve the coupling efficiency or provide frequency discrimination when desired.
While the contacts 40 are described herein as spring contacts 40, for purposes of clarity, the contacts 40 may alternately be described as contact springs, elastic core members, spring probes or probe springs.
Preferred embodiments of the spring contacts 40 may comprise either non-monolithic micro-fabricated spring contacts 40 or monolithic micro-fabricated spring contacts 40, depending on the application. Non-monolithic micro-fabricated spring contacts utilize one or more mechanical (or micro-mechanical) assembly operations, whereas monolithic micro-fabricated spring contacts utilize batch mode processing techniques including but not limited to photolithographic processes such as those commonly used to fabricate MEMs devices and semiconductor integrated circuits.
In some embodiments of the spring contacts 40, the electrically conductive monolithically formed contacts 40 are formed in place on the contactor substrate 30. In other embodiments of the spring contacts 40, the electrically conductive monolithically formed contacts 40 are formed on a sacrificial or temporary substrate 63, and thereafter are removed from the sacrificial or temporary substrate 63, e.g. such as by etchably removing the sacrificial substrate 63, or by detaching from a reusable or disposable temporary substrate 63, and thereafter affixing to the contactor substrate 30.
Both non-monolithic and monolithic micro-fabricated spring contacts can be utilized in a number of applications including but not limited to semiconductor wafer probe cards, electrical contactors and connectors, sockets, and IC device packages.
Sacrificial or temporary substrates 63 may be used for spring fabrication, using either monolithic or non-monolithic processing methods. Spring contacts 40 can be removed from the sacrificial or temporary substrate 63 after fabrication, and used in either free standing applications or in combination with other structures, e.g. contactor substrate 30.
In embodiments of contactor assemblies that are planarized, a plane 72 of optimum probe tip planarity is determined for a contactor assembly 18 as fabricated. Non-planar portions of spring contacts 40 located on the contactor substrate 30 are preferably plated 68, and are then planarized, such as by confining the probes 40 within a plane within a fixture 140 (
The contactor assembly 18 shown in
Monolithic micro-fabricated spring contacts 40, such as seen in
An exemplary monolithic micro-fabricated spring contact comprising a stress metal spring i.e. an elastic core member, is fabricated by sputter depositing a titanium adhesion/release layer having a thickness of 1,000 to 5,000 angstrom on a ceramic or silicon substrate (approximately 10-40 mils thick) having 1-10 mil diameter electrically conductive vias pre-fabricated in the substrate. Electrically conductive traces fabricated with conventional photolithographic processes connect the spring contacts to the conductive vias and to the circuits to which they ultimately connect. A common material used to fabricate stress metal springs is MoCr, however other metals with similar characteristics, e.g. elements or alloys, may be used. An exemplary stress metal spring contact is formed by depositing a MoCr film in the range of 1-5 mm thick with a built-in internal stress gradient of about 1-5 GPa/mm. An exemplary MoCr film is fabricated by depositing 2-10 layers of MoCr, each layer about 0.2-1.0 mm thick. Each layer is deposited with varying levels of internal stress ranging from up to 1.5 GPa compressive to up to 2 GPa tensile.
Individual micro-fabricated stress metal spring contact “fingers” are photolithographically patterned and released from the substrate, using an etchant to dissolve the release layer. The sheet resistance of the finger and its associated trace can be reduced by electroplating with a conductive metal layer (such as copper, nickel, or gold). The force generated by the spring contact can be increased by electrodepositing a layer of a material, such as nickel, on the finger to increase the spring constant of the finger. In interposer applications (see
The lift height of the spring contacts is a function of the thickness and length of the spring and the magnitude of the stress gradient within the spring. The lift height is secondarily a function of the stress anisotropy and the width of the spring and the crystal structure and stress in the underlying stress metal film release layer. The spring constant of the spring is a function of the Young's modulus of the material used to fabricate the spring and the length, width, and thickness of the spring. The spring constant of the spring can be increased to the degree desired by enveloping the springs 40 with one or more electrodeposited, sputtered, or CVD metal coatings (see FIG. 1,2). Coatings can be applied with thicknesses of between 1 micron and 100 microns using metals including nickel, gold, palladium, platinum, rhodium, tungsten, cobalt, iron, copper, and combinations thereof. The spring constant can be varied by controlling the thickness of the deposited coating layers, the geometrical characteristics of the spring, the choice of metal, and the number of coatings.
The microstructure and hence mechanical properties of the resulting spring contacts are a function of the metals deposited as well as the deposition and subsequent processing conditions. The process conditions for fabricating spring contacts according to the present invention comprise, electrodeposition current densities in the range of about 0.3 to about 30 Amperes/square decimeter (typically 3 Amperes per square decimeter) and saccharine added at a concentration of greater than about 1 gram/liter or preferably greater than 4.5 grams per liter. One or more heat treatment processes are preferably included, such as to provide any of probe tip planarization relative to the support substrate and/or annealment to provide increased resistance to set and cracking through repeated cycles of deflection over the life of the spring contact.
Grain sizes for spring coating or plating layers, e.g. 68,70 (
It should be noted that methods for depositing coatings of both insulating and conductive materials are discussed in Yin et al., Scripta mater: 44 (2001) 569-574; Feenstra, et al, Materials Science and Engineering: A, Volume 237, Number 2, September 1997, pp. 150-158(9); Kumar et al., Acta Materialia 51 (2003) 387-405), and patent publications, such as U.S. Pat. No. 6,150,186. Electrodeposited layers of metals such as nickel and nickel alloys such as Nickel Cobalt are characterized as having “nanocrystalline” microstructures when the grain sizes range from less than a few tens of nanometers to an extreme upper limit of 100 nm. From this description, the materials fabricated as described above would not be characterized as having nanocrystalline microstructures.
Setting, i.e. plastic deformation, of the probes during the useful life of the product can be minimized by carrying out an annealing process at an optimal time and temperature. For example, using a 250 C anneal temperature, it was observed that a minimum set occurred for a 3 hour anneal (5 microns) whereas for 1 hour and 12 hours annealing times, set was observed to be 28 microns and 12 microns respectively. Additionally, accelerated aging studies, i.e. repeated, cycling of the spring probes on a probe card using a wafer prober have shown that the spring contacts are resistant to cracking when fabricated with an anneal time selected to reduce set such as for the annealing process described above. However, it has also been observed that resistance to cracking decreases with anneal times in excess of that required to minimize set.
The above teachings describe the manufacture of an exemplary monolithic micro-fabricated stress metal spring, however, those skilled in the art will understand that spring contacts having the characteristics required to practice the present invention can provide many possible variations in design and/or fabrication processes. Such variations may include but would not be limited to, for example, choice of processes, process chemicals, process step sequence, base spring metal, release layer metal, coating metals, spring geometry, etc. The structures and processes disclosed herein may preferably be applied to a wide variety of non-monolithic spring contacts and monolithic micro-fabricated spring contacts, such as but not limited to spring structures disclosed in D. Smith and A. Alimonda, Photolithographically Patterned Spring Contact, U.S. Pat. No. 6,184,699; M. Little, J. Grinberg and H. Garvin, 3-D Integrated Circuit Assembly Employing Discrete Chips, U.S. Pat. No. 5,032,896; M. Little, Integrated Circuit Spring Contacts, U.S. Pat. No. 5,663,596; M. Little, Integrated Circuit Spring Contact Fabrication Methods, U.S. Pat. No. 5,665,648; and/or C. Tsou, S. L. Huang, H. C. Li and T. H. Lai, Design and Fabrication of Electroplating Nickel Micromachined Probe with Out-of-Plane Deformation, Journal of Physics: Conference Series 34 (2006) 95-100, International MEMS Conference 2006.
Interposer springs 86, such as photolithographically formed probe springs 86, are generally arranged within an interposer grid array, to provide a plurality of standardized connections. For example, in the dual-sided interposer 80a shown in
Electrically conductive interposer vias 84 extend through the interposer substrate 82, from the first surface 102a to the second surface 102b. The interposer vias 84 may preferably be arranged in redundant via pairs, such as to increase the manufacturing yield of the interposer 80, and/or to promote electrical conduction, particularly for power traces.
The opposing surfaces 102a,102b are typically comprised of a release layer 90, such as comprising titanium, and a composite layer 88,92, typically comprising a plurality of conductive layers 88a-88n, having different inherent levels of stress. Interposer vias 84, e.g. such as CuW, PtAg, or gold filled, extend through the central substrate 82, typically ceramic, and provide an electrically conductive connection between the release layers 90.
The composite layers 88,92 typically comprise MoCr (however other metals with similar characteristics, e.g. elements or alloys, may be used), in which the interposer probe springs 86 are patterned and subsequently to be released within a release, i.e. lift, region 100. For example, while composite layers 88a-88n for spring probes 40 or interposer springs 86 may typically comprise MoCr, other alloys, such as comprising TiNi or CrNi, may be used for one or more of the layers 88a-88n, such as to reduce trace resistance.
In some embodiments, a seed layer 94, such as a 0.5 to 1 μm thick gold layer, is preferably formed over the composite layers 88,92. In some embodiments, a tip coating 104, such as rhodium or palladium alloy, is controllably formed at least over the tips of spring fingers 86, such as to provide wear durability and/or contact reliability. Traces 96, typically comprising copper (Cu), are selectably formed by plating over the structure 78, as shown, such as to provide reduced resistance. As well, polyimide PMID layers 98 are typically formed over the structure 78, as shown, to define the spring finger lift regions. The seed layer 94 seen in
Enhanced Lower Interface Structures and Associated Processes. In regard to the exemplary probe card assembly 42 seen in
For example, it would be advantageous to provide adequate spacing between a probe chip contactor assembly 18 and a central structure 16, such as to allow mounting 124 (
As seen in
As also seen in
The size of the solder balls 116 may preferably be optimized between shorts (too large) and opens (too small) for a given pad size 64,122, pad to pad spacing, and/or Z tolerance (gap thickness variation between the first surface 46a of the Z-block 16a and the back surface 48b of the probe chip contactor assembly 18. In some solder connection embodiments 112, an exemplary solder material chosen for low temperature soldering processes 116 comprises BiSnAg, wherein the solder balls 116 are reflowed to form bumps on the Z-block 16a and/or probe chip backside metal 64.
As further seen in
The preformed array of solder columns 118 can be provided with a laminate wafer 119, comprising a soluble material, that dissolves after assembly. The solder columns 118, such as available through Six Sigma, Inc., of Milpitas, Calif., may preferably comprise a structure, such as but not limited to an outer shell or coil, and an inner solder region, which when heated to form soldered connections 112 between the probe chip contactor assembly 18 and a central structure 16, retains planarity between the two substrates 30 and 16, and controllably defines a gap 120. The solder columns 118 can be provided by a wide variety of structures and methods such as but not limited to:
The use of solder columns 118 between substrates may attain a greater range of standoff height 120 and tighter pitch, as compared to probe chip to Z-block structures 43 that use solder balls 112, such as to increase yield. For example, if planarizing a front surface 48a of a contactor assembly 18, the height of solder columns 118 may provide a smaller pitch, e.g. for solder columns 118 that tend to expand less than a solder ball 112 for a given height 120.
The exemplary Z-block solder pads 122 seen in
Probe Chip to Z-block Solder Fixture.
As seen in
The distributed spacers 135 typically comprise any of shim dots 135, e.g. cylinders 135, having a precise height 137, or spheres 135 having a precise diameter 137, which eliminates the need for custom fabricated reference plate for a probe chip to Z-block solder fixture 130. In some embodiments, the distributable spacers comprise any of metal, ceramic, glass, and a semiconductor. The distributed spacers 135 take up fluctuations in substrate thickness that would otherwise be transmitted to the back side 48b of the probe chip contactor assembly 18. The spacers 135, e.g. shim dots or spheres are typically aligned using a stainless steel stencil 156 (
As seen in
The reference plate 136 shown in
As noted above, the spacers 135 may preferably comprise distributed shims, e.g. shim dots 135, which in some embodiments comprise shim dots that are laser cut from shim stock.
Enhanced Structures and Processes for Planarization. For many embodiments of probe card assemblies 42, it is advantageous to planarize the probe springs 40, by providing controlled thermal processing of the probe chip contactor 30.
The shim dots or spheres 135 eliminate the need for a custom fabricated reference plate for a probe chip planarization fixture 140a. The distributable spacers 135, e.g. shim dots or spheres, may typically comprise any of metal, ceramic, glass, and a semiconductor. In some embodiments, the shim dots or spheres 135 comprise a magnetic material, so that they stick to the reference plate 136, which can also be at least partially comprised of a magnetic material, such as steel or iron, or may alternately comprise other attached or associated means for creating magnetic attraction to the reference plate 136, e.g. an electromagnetic element or field embedded within a stainless steel reference plate 136.
As seen in
Therefore, for most embodiments of the planarization fixture 140b, each of the wells 162 typically are required to have a nearly identical depth 164, which may be hard to fabricate. As well, different reference plates 136a are typically required to be provided for different probe chip contactor assemblies 18, which typically have different layouts, e.g. probe spring areas 154 and spring depths 164. Therefore, the alternate planarization fixture 140a, using a more universal planar reference plate 136 and spacers 135 with different heights and/or distribution patterns, may provide advantages over a more specific planarization fixture design 140b.
As seen in
Planarization Structures and Processing.
For example, the controlled processing of spring structures can improve co-planarity of the plated metal probe tips 40, e.g. stress metal springs 40, of a probe chip assembly 18. The probe chip substrate 30 is held flat against the flat surface of a reference chuck 134, e.g. such as a vacuum or electrostatic chuck 134. In the exemplary embodiment shown in
In an alternative embodiment, the probe tips 40 are made parallel to the front surface 48a of the probe chip substrate 30, by replacing the glass substrate 136 with a chuck 136 having a flat surface and one or more recesses 162 (
Probe Assemblies Having Separable Connectors.
Upper substrate standoffs 208 are preferably used, to limit the maximum Z travel of the probe chip substrate 30, relative to the daughter card 16b, thereby providing protection for the flexible connections 206a-206n. The upper standoffs 208 may preferably be adjustable, such that there is a slight pre-load on the flexible connections 206a-206n, forcing the probe chip substrate 30 away from the daughter card 16b, thereby reducing vibrations and chatter of the probe chip substrate 30 during operation. As well, one or more standoffs 208, connected to either the back surface 48b of the probe chip contactor 18 or the opposing first side 46a of the daughter card 16b, may be substantially located in a central region of either the probe chip contactor 18 or the daughter card 16b, such as for pre-load or to prevent excessive bowing between the two substrates 30,16b.
A damping material 210, e.g. such as a gel, may also preferably be placed at one or more locations between the probe chip substrate 30 and the daughter card 16b, to prevent vibration, oscillation or chatter of the probe chip substrate 30.
The separable connector 202, e.g. such as an FCI connector 202, preferably has forgiving mating coplanarity requirements, thereby providing fine planarity compliance between the daughter card 16b and the mother board 12. A mechanical adjustment mechanism 212, e.g. such as but not limited to fasteners 216, spacers 214, nuts 218, and shims 220 (
While many of the probe card assemblies 42 described herein provide large planarity compliance for a probe chip contactor substrate 30, some probe card assemblies 42 are used for applications in which the device under test comprises a relatively small surface area. For example, for applications in which a small number, e.g. one to four, of integrated circuits 26 are to be tested at a time, the size of a mating substrate 30 can also be relatively small, e.g. such as less than 2 cm square.
In such embodiments, therefore, the planarity of the substrate 30 to the wafer under test 20 may become less critical than for large surface areas, and the compliance provided by the probe springs 40a-40n alone is often sufficient to compensate for the testing environment. While the compliance provided by the probe springs 40a-40n may be relatively small, as compared to conventional needle springs, such applications are well suited for a probe card assembly 42 having photolithographically formed or MEMS formed spring probes 40a-40n.
The probe card assembly 42b is therefore inherently less complex, and typically more affordable, than multi-layer probe card assembly designs. The small size of the substrate 30 reduces the cost of the probe card assembly 42b, since the cost of a probe chip contactor assembly 18 is strongly related to the surface area of the probe chip substrate 30.
The probe springs 40a-40n are fabricated on the lower surface 48a of a hard probe chip substrate 30, using either thin-film or MEMS processing methods, as described above. Signals from the probe springs 40a-40n are fanned out to an array of metal pads 64 (
The small test area probe card assembly 42b preferably includes a means for providing a mechanical connection 212 between the mother board 12 and the daughter card 16b. In the probe card assembly 42b embodiment shown in
Lower substrate standoffs 50, which are typically taller than other features on the probe chip substrate 30 (except for the spring tips 40a-40n), are preferably placed on the lower surface 48a of the substrate 30, preferably to coincide with saw streets on a semiconductor wafer 20 (
As shown in
Improved Probe Card Assemblies. The use of separable connectors 202 can be used in a wide variety of enhanced probe card assemblies, such as in conjunction with enhanced stiffeners 38 and/or enhanced attachment means 310 (
In the exemplary probe card assembly 42c seen in
The exemplary motherboard 12 seen in
As also seen in
As seen in
The upper electrical interface 24 between the daughter card 16b and the mother board 12 shown in
Some embodiments of the LCD platform probe card structure 42c typically comprise a three or four push-pull actuators 310 that are adjustably settable throughout the height range of the separable connectors 202, to provide control over the separation distance and planarity between the central structure 16, e.g. a daughter card 16b, and the mother board 12. The push-pull actuators 310 allow the separable connectors to be slidably controllable through their full compliance range 322.
As well, one or more of the actuators may be set, such as after adjustment of any of separation distance and planarity, to provide planarity adjustment of the assembly 42c, by deflecting the probe chip contactor assembly 42. For example, adjustment of the probe card structure 42c may comprise the steps of:
For some embodiments of lower probe card interface assemblies 43 (
In some embodiments of the enhanced lower probe card interface assembly 43a, the stiffener comprises any of ceramic and metal, e.g. titanium (Ti) or equivalent.
The size, shape, composition, mounting structure 394 (e.g. adhesive, solder or mechanical bond), and mounting location of the stiffener 392 may preferably be optimized to compensate for bow and/or other source of non-planarity of the probe tips 40. For example the lateral dimensions 393 or thickness 395 may be chosen to impart specified mechanical or thermal characteristics for the enhanced lower probe card interface assembly 43a.
In one exemplary embodiment, a stiffener 392 is attached to the daughter card 16b and is cured at solder temperature, such as to ensure that when the daughter card 16b is heated for probe chip soldering 112, the solder bonding surface will be substantially flat. Any of the size, shape, and material of the stiffener 392 may preferably be adjusted to approximately compensate for bow due to probe chip TCE mismatch. An optional mechanical adjustment 396, 397, such as a threaded post 396 adhesively attached to the stiffener 392 and adjustable in relation to another component, e.g. the mother board 12, may preferably be used to make fine correction, e.g. applying vertical tension or compression to the daughter card 16b, such as to ensure that bow is compensated to within acceptable specifications.
Probe Card Assemblies Having Thermal Stiffeners.
An exemplary embodiment of the probe card assembly 42d may typically comprise:
The stiffener 38 for the probe card assembly 42d preferably comprises a material having a low thermal expansion coefficient, e.g. less than 6×10−6/° C. @ 20-50° C., such as but not limited to Nobinite, mehanite, or Invar, to reduce soak time, i.e. pre-warming of a probe card assembly prior to use, and/or to increase thermal stability of attached mother board 12. For example, in some embodiments of the probe card assembly 42d, the stiffener 38 comprises nobinite cast iron, available through Enomoto USA, of Torrance Calif. Nobinite thermal stiffeners 38 have a thermal coefficient of expansion (TCE) that is significantly less than that of carbon steel, over a wide temperature range. For example, different Nobinite alloys typically comprise a TCE from about 0 to 5×10−6/° C. @ 20-50° C., as compared to 11 to 12×10−6/° C. @ 20-50° C. As well some varieties of Invar have a TCE of about 0 to 1×10−6/° C. @ 20-50° C. The exemplary mother board 12 seen in
The Z-block 16a in
Some embodiments of the probe card assembly 42d have a reduced number of attachment points between the Z-block flange 430 and the mother board 12, to allow the motherboard PCB 12 to float in relation to the Z-block 16a and probe chip contactor assembly 18. While the motherboard may comprise a material having a thermal coefficient of expansion (TCE) more than that of the stiffener, the points of connection between the motherboard 12 and the stiffener 38 may preferably be located toward a central region, such that the motherboard 12 may expand and contract over a range of temperatures, without significant warping.
As seen in
The design and materials chosen for the probe card assembly 42d therefore provide enhanced planar support for the mother board 12, which typically comprises a PC board. The probe card assembly 42d allows the mother board 12 to swell and shrink, while keeping the probe chip contactor assembly the same in planarity, despite temperature fluctuation.
Plated Interposer Structure and Process. Interposers that have many contacts in parallel are sometimes subject to contamination from particulates or other contamination layers that may cause the electrical contact to be unreliable under use conditions, such as including repeated mechanical and thermal cycling.
A controlled increase of interposer contact force is associated with an increase in the reliability of the electrical contacts under use conditions, as well as during aging and storage in environments in which surface films can form. While it is desirable to increase the contact force, it is undesirable to increase contact force excessively, since the force to compress the interposer becomes too high, which may cause unacceptable mechanical deflection of the interposer and probe card structures. It may therefore be desirable to provide interposers that provide high quality low resistance electrical connections without requiring excessive contact force.
The exemplary interposer plating fixture 600 seen in
The lifted fingers 86 on the first side 102a and second side 102b of the interposer 80 typically comprise stress metal springs, e.g. having a similar construction to contactor spring probes 40, comprising MoCr or equivalent materials, optionally over coated 94 with a conductive material, e.g. Au, Rh, etc., to provide low contact resistance to a planar surface, e.g. a Ti—Au coated wafer 82, e.g. comprising ceramic or silicon).
The sputtering steps 808 and 814 are performed to provide an electrically conductive layer 607 (
The plating steps 810 and 816 typically comprise the plating of one or more outer layers 892a-892g, such as to provide desirable performance characteristics for the springs 86, and/or to provide enhanced bonding for subsequent outer layers. For example, in a current exemplary embodiment:
For example, one or more of the outer plating layers 892 may preferably increase the spring rate for the interposer springs from about 0.1 g/mil to between about 0.05 g/mil to about 1 g/mil, e.g. with about 1 um to about 10 um microns Ni or between about 3 um to 6 um Ni). As well, the an probing contact layer 894 may be applied, such as comprising about 0.5 um to about 3 um, e.g. optionally either hard Au, Rh, or PdCo.
The stripping steps 812 and 818 are performed to remove the temporary plating player from the opposing side, e.g. 102a or 102b, of the interposer 80, such as by using a stripping agent comprising sodium persulfate (Na2S2O3).
Outer alignment pins 932 typically extend from the top stiffener 38 through the probe card assembly 42d,42e, such as through the motherboard 12 to the Z-block flange 430. The outer alignment pins 932 engage mechanical registration features 933, such as notches, slots, and/or holes, or any combination thereof, defined in components in the probe card assembly 42, e.g. 42d,42e, such as the motherboard 12 and the Z-block flange 430. The use of registration features 933 preferably allows for differences in thermal expansion between components in the probe card assembly 42, to allow testing over a wide temperature range.
While the exemplary plating processes and structures disclosed herein are described in regard to plating of interposers, it should be understood that the disclosed structures and processes can also be performed on other substrates, such as for probe chip contactor assemblies 18 having spring probes 40a-40n extending there from.
For example, an electrically conductive layer can similarly be applied to the back surface 48b of a probe chip contactor assembly 18 to provide electrical conduction for plating the spring contacts on the front side 48a, such as by any of sputtering electro or electroless plating 808 an electrically conductive layer 607 (
Additionally, backside plating may be performed to decrease trace resistance, while optimizing use of area of the probe chip substrate 30, such as for probing more die with a single substrate. In some embodiments, a CrCu seed layer is sputtered on the back side 48b of the probe chip contactor assembly 18. Photo resist is then deposited and patterned, such that contact is made to the base metal on the front side 48a of the probe chip contactor assembly 18, such as comprising but not limited to any of TiMoCr, TiNi and CrNi, which may preferably be selected to reduce trace resistance. Low resistance metals such as copper may also be plated on the back side interconnect layers (
Contactor Assembly Structures Having Multiple Layer Interconnections.
In addition, lateral stresses generated by heating, cooling and/or spring deflection are relieved by the stress decoupling layer 974. In embodiments where the stress decoupling layer 974 is formed from a polymer, e.g. polyimide, the structure is capable of withstanding spring fabrication temperature cycles, as well as most extreme temperatures encountered in the use case, e.g. −100 C to +350 C.
The disclosed decoupled spring and contactor structures provide numerous improvements, such as for providing improvement in any of fine pitch probing, cost reduction, increased reliability, and/or higher processing yields. For example, electrical contact between the spring probe structures, e.g. springs 40,86 and the substrate via structures, e.g. 66,84, is controllably defined with a formed fulcrum region 990.
Decoupled spring and contactor structures may therefore provide improved process temperature performance and adhesion margin. As well, key parameters are decoupled in decoupled spring and contactor structures, whereby design parameters may be independently optimized. As well, Decoupled spring and contactor structures may readily be modeled and tested, provide advantages in scalability.
In some embodiments of the enhanced sputtered film processing system 10 and method 150, measurement and/or compensation are provided for any of the lift height 262 and the X-Y position of photolithographically patterned spring contacts 246. For example, any of the spring length and angle may preferably be measured and/or adjusted on the photolithographic mask to compensate for any errors, e.g. dimensional or positional, measured in produced spring substrate assemblies.
While some embodiments of the structures and methods disclosed herein are implemented for the fabrication of photolithographically patterned springs, the structures and methods may alternately be used for a wide variety of connection environments, such as to provide mechanical compliance and/or electrical connections between any of contacts, connectors, and/or devices or assemblies, over a wide variety of processing and operating conditions.
Accordingly, although the invention has been described in detail with reference to a particular preferred embodiment, persons possessing ordinary skill in the art to which this invention pertains will appreciate that various modifications and enhancements may be made without departing from the spirit and scope of the claims that follow.
This Application is a divisional application of U.S. application Ser. No. 12/517,528, entitled Construction Structures and Manufacturing Processes for Integrated Circuit Wafer Probe Card Assemblies, filed 3 Jun. 2009, which is a U.S. National Phase entry of PCT/US2007/86394 filed 4 Dec. 2007, which claims priority to U.S. Provisional Application No. 60/868,535, entitled Construction Structures and Manufacturing Processes for Integrated Circuit Wafer Probe Card Assemblies, filed 4 Dec. 2006, to U.S. Provisional Application No. 60/898,964, entitled Structures and Processes for Fabrication of Probe Card Assemblies with Multi-Layer Interconnect, filed 31 Jan. 2007, and to U.S. Provisional Application No. 60/891,192, entitled Fine Pitch Probe Card Having Rapid Fabrication Cycle, filed 22 Feb. 2007 Each of the aforementioned documents is incorporated herein in its entirety by this reference thereto.
| Number | Date | Country | |
|---|---|---|---|
| 60898964 | Jan 2007 | US | |
| 60891192 | Feb 2007 | US | |
| 60868535 | Dec 2006 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12517528 | Jun 2009 | US |
| Child | 13253810 | US |
