JP2006508495A - Miniaturized contact spring - Google Patents

Abstract

A solution is provided for increasing the yield strength and fatigue strength of miniaturized contact springs that can be fabricated in arrays with very small pitches, and for miniaturized springs against repeated contacts. Discloses a solution to minimize the adhesion of contact pad material to the spring tip without affecting reliability, and allows relatively greater energization without significantly reducing their lifetime A solution to fabricate the spring, and a strong spring to couple the die bonding terminal to the corresponding input / output pad of the substrate, which has an inorganic or organic material for reliable package manufacturing Providing a solution to make.
The present invention provides a solution for increasing the yield strength and fatigue strength of a miniaturized spring that can be fabricated in an array having a very small pitch. It also discloses a solution for minimizing the adhesion of contact pad material to the spring tip for repeated contacts that do not affect the reliability of the miniaturized spring. Furthermore, the present invention also presents a solution for making springs that allow relatively greater energization without significantly reducing their lifetime.

Description

  The present invention generally relates to very miniaturized springs. More particularly, the present invention relates to a group of miniaturized contact springs and a group of methods for increasing the yield strength and fatigue strength of these springs.

  Miniaturized springs can be fabricated with pitches of less than 10 μm even with such miniaturized arrays of springs, so integrated circuits, PCBs, interposers, space transformers for testing, burn-in and packaging , And electrical contacts to contact pads or input / output terminals on the probe tip. Miniaturized stress metal film springs, usually patterned by photolithography, are fixed parts attached to the substrate, also called anchor parts, and the inherent stress gradient of the spring when it is first attached to the substrate and released. As a result of having lifted portions, also called free portions, that extend away from the substrate to form a three-dimensional structure. Typically, stress gradients in the film occur through sequential deposition of multiple thin film layers by sputtering or electroplating under different process conditions. An exemplary embodiment of a stress metal spring is shown diagrammatically in FIG. 1a and includes an anchor portion 101 associated with an electrical contact or terminal 102 attached to a substrate or electrical component 103, and a spring tip. And a free part 104 with 105. Specific examples of such a structure are disclosed in Patent Document 1 and Patent Document 2.

  Other types of springs are discrete solids that are fabricated individually or in groups and then mounted on a substrate, such as integrated solid state devices such as springs or semiconductor devices used in wafer testing or burn-in assemblies Including a spring. Still other types of such springs can be integrated into the substrate using photolithography, as mentioned in patent documents such as US Pat. These cantilever-type springs are manufactured. Some of these springs are fabricated individually or in groups on a sacrificial substrate and then mounted on a substrate used in wafer testing or burn-in assembly or on a substrate having semiconductor devices. FIG. 1b is a diagrammatic cross-sectional view of a cantilever spring of the type standing on a typical photolithographically patterned support that is fabricated on a sacrificial layer. This spring includes a base region 201 at one end attached to the electrical contact pad 202 of the substrate 203, a contact tip region 204 at the other end of the spring, and a spring connecting the base 201 and the contact tip region 204. A central body 205. The problem with this type of spring is that they are too long. Shorter and smaller springs are desirable for testing and burn-in of some current and next generation integrated circuits having contact terminal pads with a very small pitch, for example 20-50 μm.

  Methods for making shorter springs using a photolithographic process to add a thicker metal coating are defined in the patent literature. One method is described in Patent Document 7. This method uses electroplated photoresist and allows the metal to be plated on a standing spring. However, unsupported springs with the dimensions required to probe an IC with a pad pitch of less than 150 μm, the backside without significantly reducing the probe height required for compliance. It does not have sufficient strength to hold the photoresist. Also, any non-uniformity in the photo process translates into a non-uniform spring height that cannot meet the uniformity requirements required to remain on the IC pad during testing.

  The method described in Patent Document 7 also has an additional problem of lift height control after plating. One purpose of having a spring standing unsupported is to provide a framework or structure for supporting a thicker plated metal. If the spring is plated on only one side, the spring curves to different lift heights based on the stress of the plated film. If the membrane is tensile, it will bend up and if it is compressive it will push down. Both of these stress conditions make it difficult to control the tolerances and spring lift uniformity required to test the IC. In addition, a compressive spring is stronger than a tensile spring, and a spring with a compressive plated film is not sufficiently compliant to be a valid probe until: Reduce lift height. There is also a limit on how high a spring standing unsupported can be lifted before plating to compensate for this compression effect. The probe needs to contact the IC electrical pad at an angle of less than 90 degrees. Increasing the lift height tends to cause the spring to warp itself and form a 360 degree circle on the substrate. As a result, the process taught by this patent application does not meet the requirements for controlling the uniformity of the lift height of the spring array required for IC testing.

  One method of constructing the probe of Patent Document 7 is to assemble a tip on a plated spring and assemble a spring fabricated on a sacrificial substrate on a second interconnect substrate. This assembly process adds positional error and is expensive to manufacture from a fully integrated connection button tip as described herein.

  Another method described in U.S. Pat. No. 6,057,059 is a photoresist layer, i.e. a release layer island (release layer) to keep the mask away from the spring and allow plating of the standing part without spring support. layer island). If the release mask stops adjacent to the base (anchor part) of the spring and does not extend along the base of the spring, the thickness and width of the free part of the spring near the base is the base region Compared with, it becomes very large simultaneously with plating. As a result, the part standing without spring support is mechanically weaker near the base region. Because the bending moment is the largest in this region, applying a force to the spring tip during IC testing will cause the spring to break early and therefore meet the probe life requirements required on the IC manufacturing line. Can not. In the case of the other method described in Patent Document 8, in which the photoresist mask does not cover the part of the anchor standing without supporting the spring and the part of the anchor during plating, the width of the resist is likely to be damaged. There is still a continuum. Control of the mask alignment and spring release process also creates serious problems that result in uneven plating and variations in lift uniformity. Another major problem of this process arises from the relatively thin release layer as well as the high electrical resistivity of the stress metal film through which the plating current flows. The current density varies widely depending on the distance from the power connection point at the edge of the substrate. As a result, plated film properties, such as micro structure, thickness, stress, etc., vary widely in different areas of the spring. As a result, this process does not result in a spring array with reasonably uniform and controlled characteristics, such as lift height, which is essential for effective IC testing.

  The present invention herein provides a solution that avoids the problems associated with the two methods described above and that enables the manufacture of a spring array suitable for meeting the stringent requirements of wafer level IC testing. Have several means of providing In particular, the present invention allows for the manufacture of spring arrays with reasonably uniform lift height and characteristics, and durability. For example, it makes it possible to maintain the spring height with proper uniformity after electrodeposition, with the electrodeposited membrane on the whole spring core, both the unsupported part and the anchor part. Teaches the practice of covering with balanced stress. In another teaching, it shows a method of selectively plating a spring without using any photoresist mask.

  Miniaturized contact springs undergo a number of contact operations during tests that expose the springs to various levels of stress, including repeated stresses. Also, in packages that use contact springs to join two components, eg, a chip and a chip carrier, the springs are stressed during testing and operation. The spring is required to withstand such stress without breaking. However, we have found that miniaturized springs, e.g., about 400 μm × 60 μm × 20 μm in size, typically begin to break after 10,000 touchdowns where the contact force exceeds about 1 gf. That is, they were observed to be plastically deformed and / or broken. The main reason for failure is that the resulting alternating stress exceeds the fatigue strength of the spring material. Fatigue strength refers to alternating stress levels at which a material can withstand a specified number of repetitions. It is typically part of the material's yield strength that corresponds to the occurrence of plastic deformation, or instantaneous permanent deformation. As observed in our experiments, a spring resistance to breakage of about 1 gf is typically required to form a good reproducible contact on low contact resistance aluminum. Therefore, it must be significantly enhanced to improve the performance and quality of the spring. Although springs with larger cross-sections can withstand similar or greater forces without breaking because the resulting stress is smaller, they limit the pitch at which the splash is built.

  For some operations, such as device burn-in, the contact spring is required to contact the device terminal at elevated temperature, eg, about 100 ° C. Such contacts may also be required to allow a relatively large energization of, for example, 250-500 mA during operation. Under this condition, the contact resistance must be very small (eg 0.1 mΩ) so that the contact tip area of the spring is not damaged by overheating. One way to achieve low contact resistance is to increase the contact force by increasing the spring thickness. However, the greater contact force increases the stress generated in the spring body, particularly near the base region, and thus increases the probability of premature spring failure during repeated contacts.

  Furthermore, during repeated contacts, material from the electrical contact pads or terminals tends to adhere to the spring tips. The adhesion of the pad material to the spring tip increases the contact resistance, or if the pad material is exposed to ambient conditions and easily forms a strong compound, the electrical contact is after repeated contact. It deteriorates with. This also shortens the life of the spring. Accordingly, the contact tip structure should preferably be made of a material that does not adhere strongly to the contact pads or terminals.

  Therefore, what is needed is a mechanism for maximizing the yield strength and fatigue strength of a miniaturized spring within the requirements of miniaturization.

  What is further required is a mechanism for minimizing the adhesion of contact pad material to the spring tip for repeated contacts without substantially affecting the reliability and conductivity of the spring.

  What is needed is a method of making a spring that is highly durable against compliant stress that results in a uniform spring height and provides a durable tip structure.

U.S. Patent No. 5,613,861 International application number PCT / US00 / 21012 International Publication No. 01/48818 Pamphlet WO 97/44676 Pamphlet U.S. Patent No. 6,184,053 WO 01/09952 pamphlet International Publication No. 01/48870 Pamphlet U.S. Patent 6,528,350

  The present invention provides a solution to increase the yield strength and fatigue strength of miniaturized contact springs that can be fabricated into arrays with very small pitches. It also discloses a solution for minimizing adhesion of contact pad material to the spring tip without affecting the reliability of the miniaturized spring for repeated contacts. Furthermore, the present invention also presents a solution for making springs that allow relatively greater energization without significantly reducing their lifetime. The present invention also provides a solution for fabricating a strong spring to couple the die bonding terminals to the corresponding input / output pads of the substrate, having an inorganic or organic material for reliable package manufacturing. Bonding can be facilitated by the use of conductive adhesives including, for example, solder or anisotropic conductive adhesive films.

  The stress metal spring of the present invention has a multilayer structure. The thin film has a yield strength and fatigue strength that is substantially greater than the corresponding bulk material, so these springs are subject to repeated, if any, significant plastic deformation during testing or burn-in. Make it possible.

  The deposition of a compressively stressed film on the core film has been found to be effective to increase the spring life. This also allows for the production of stress metal springs that can apply large forces with electrical contact pads or terminals.

  The thin film crosses the interface between two different materials, either continuously or in discontinuous fine steps, so that the modulus of elasticity generally increases monotonically with the depth from the spring surface to the spring core. Deposited with a gradual transition of composition. The resulting spring exhibits a significant increase in life during repeated contact.

  Appropriate materials and / or processes have been found to be effective to increase the strength of the interface of the multilayer structure. Materials with approximately the same lattice constant are preferably used in adjacent films, and amorphous or nanocrystalline films are used as interfaces. The interface can be produced either by “phasing-in” the two adjacent layer materials or by using an alloy of the two adjacent layer materials.

  The thickness of the free part of the thin film is preferably in the range of 4 to 35 μm, which means reliable and low electrical contact between the spring tip and contact pads or electrical terminals with different materials Allows resistance.

  At least one high thermal conductivity film in a multilayer structure is preferably used to dissipate heat during testing or burn-in with a relatively large current.

  It has been found that modification of the process parameters during deposition of the film that makes up the spring structure is effective to increase the quality and reliability of the spring. For example, the thin film that makes up the coating of the spring core, with appropriate microstructural features such as very small grain size (eg <200 nm), to increase the yield and fracture toughness of the spring, Is deposited.

  The force used to make a good electrical contact between the spring and the contact pad is substantially reduced. A suitable range of force for contacts on aluminum (Al) is 0.8-10.0 gf. For contact pads made of gold, copper or solder, the force to make a good electrical contact is very small. Miniaturized photolithography patterned miniaturized contact springs form contacts with probe card assemblies containing probe tips, ie IC terminals, interposers and assembly fixtures for test and burn-in A substrate with an attached probe spring for as well as making packaging very easy. The assembly is greatly simplified by the use of these low force springs since bending, warping and alignment problems are minimized.

  Methods for improving spring life include solutions to minimize surface roughness.

  It has also been found that changes in spring dimensions, such as width and thickness, are effective to improve life.

  In one embodiment, the free part of the spring is tapered. The present invention also provides a cheaper and more effective solution for electrodepositing overlying membranes, circuit wiring and electrical contact pads onto stress metal springs without the use of any mask.

  In one embodiment, the spring tip region, also referred to as a buttoned spring tip, is a material that minimizes the deposition of contact pad material during repeated contact and is selected using a lithographic process. Coated. The thickness of the spring tip region is built prior to spring release from the substrate.

  In another embodiment, the tip is selectively coated after the spring is lifted and optionally electroplated with a material that minimizes adhesion of the contact pad material during repeated contact. To make it possible, the photoresist is applied and patterned.

  The solution for stress metal springs is applicable to other types of cantilever springs. One embodiment is applicable to other cantilever springs with or without a buttoned contact structure in the spring contact tip region. The multilayer film is selected and sequentially deposited according to specific principles that result in the manufacture of strong high performance springs with high durability and increased life. The principle is that the membrane is selected such that the elastic modulus of the outer layer of the spring is smaller than that of the inner layer and the elastic modulus gradually increases from the surface layer of the spring to the innermost layer and Require that it is to be deposited sequentially.

  In another embodiment, the thin film comprising the stress-free metal cantilever spring has a suitable microstructure such as, for example, a very small grain size (eg, less than 200 nm) to increase the spring yield and fracture toughness. It is deposited with various features.

  In yet another embodiment, the unstressed metal cantilever spring layer comprises at least one deposited film layer having an embedded compressive stress.

  According to the same principle, shorter springs with increased strength and higher strength can be produced.

  The present invention is applicable to the testing and burn-in of various types of solid state devices such as silicon and III-V devices, display devices, surface acoustic wave elements, MEMS (micro-electromechanical) devices.

  Furthermore, the present invention is also applicable to packages in which electrical terminals of electronic components are coupled to corresponding contact pads on adjacent substrates.

Miniaturized springs can be fabricated using thin film or discrete component manufacturing techniques such as wire bonding. In general, in a wide range of applications, in order for the spring to function well, the yield strength of the material is required to be greater than the stress applied to the spring during testing or burn-in, or within the assembled package. We have observed that many thin film stress metal springs deform plastically during testing because the yield strength of the spring material is less than the applied stress. Stress metal films are typically molybdenum (Mo) or its alloys, tungsten (W), with an additional overlay film coating, such as nickel or nickel-cobalt (Ni-Co) alloy films Alternatively, it has a strong core film made of a material such as an alloy thereof. Some of these membranes are relatively thick, typically 4 × 10 ³ to 10 ⁴ nm thick, which is contacted by a spring to establish a good electrical contact Required to increase the force that needs to be applied to the face. Such a high yield strength of the film is required to ensure sufficient performance of the spring.

  Since the stress metal springs made in accordance with the present invention are fabricated in bulk using thin film / IC or MEMS technology on a substrate or electrical component, the springs described herein are in particular probes. Including cards, interposers, space transformers, PCBs, wafers, electronic components and microchips with extremely miniaturized contact pads or input / output terminals with a pitch in the range of 3-100 μm, Suitable for test, burn-in and packaging applications (including 3D packaging and chip / chip carrier bonding). Existing technologies are largely unsuitable for such applications. The corresponding spring or spring terminal dimensions are also very small, typically 10 to 1,000 μm in length, 3 to 500 μm in width and 0.1 to 40 μm in thickness. The curl radius of the raised core is typically 20 to 2,000 μm. It should be noted that the teachings of the present invention can also be used to fabricate springs or spring terminals outside the indicated dimensions and pitch. It should also be noted that the teachings of the present invention can be applied to both stress metal springs and any other miniaturized spring having a thin film.

  In a preferred embodiment of the present invention, multiple layers of very thin films, each having a thickness of less than about 1.5-2 μm, are used to manufacture the springs to increase the yield strength of the thin film spring material. . This is particularly effective for building a coating layer for the core of a thin film spring. The stress-strain curve of the thin film shown diagrammatically in FIG. 2 is very different from that of the corresponding bulk material. Materials in thin films exhibit much greater yield strength compared to the same material in bulk form, i.e., the films maintain their elasticity at greater stresses and have a relatively smaller plastic deformation prior to failure. Present. In general, the yield strength of a thin film is much closer to the theoretical strength than the yield strength of the corresponding bulk material. As the film thickness increases, for example, above about 2 μm, the film gradually exhibits bulk stress-strain characteristics. As a result, the elastic limit of the thicker membrane is smaller than that of the thinner membrane. Furthermore, the grain size of very thin films is generally much smaller than relatively thick films, which also increases both yield and fracture strength. Thus, a spring with a thinner membrane is stronger.

  In this preferred embodiment, the discontinuity in atomic arrangement is 2 because the two films retain their individual mechanical properties and the interface prevents defect propagation from one film to the other. Intentionally introduced at the interface between two adjacent membranes. Changing the deposition parameters after the film has been deposited to the required thickness is one way to accomplish this. Another way to design this interface is to sequentially deposit two different materials next to each other. This involves the use of two different materials, for example Cu and Ni with close lattice constants, in two adjacent layers to enhance bonding at the interface. Note that this scheme also works if the lattice constants of two adjacent layers are not very close to each other. Using such a scheme, multiple layers of thin films can be deposited to build the desired spring film thickness. The surface of the spring is preferably a thin film structure that prevents environmental degradation during storage or operation and adhesion of the contact material to the spring surface. Examples are shown diagrammatically in FIGS. 3a and 3b, where A, B, C, etc. indicate different materials. An asterisk is used to indicate adjacent layers, eg, A and A *, when showing the same material deposition but using different process parameters to form the next adjacent layer.

  Multi-layer springs formed in this manner are relatively low, if necessary, to facilitate the coupling between adjacent layers and relaxation of the internal stresses of the membrane to convey the added strength of the spring Annealing can be done for 10 minutes at a temperature, for a short time, eg 150 ° C.

  In the case of this example variation, in order to change the deposition conditions and facilitate bonding between adjacent layers, an amorphous or crystalline thin film (less than about 200 nm), two relatively thicker films Can be fabricated between layers (about ≦ 2000 nm). Specific examples of such an intermediate material film are Au, Ag, Ni, Cu and the like.

  Various deposition techniques, such as physical vapor deposition (eg, sputtering or CVD), electrodeposition, and chemical vapor reaction can be used to deposit the multilayer film. In the case of a spring embodiment that is suitable for making good electrical contact with contact pads or terminals of various materials, the spring is stressed over thickness (from a compressive bottom to a pulling top). It consists of a sputter-deposited core of about 1-4 μm thick Mo—Cr film with a gradient. Multilayer thin films, such as core overlying Ni or alloys thereof, are about 18-35 μm using film deposition techniques such as electroplating techniques (dc and / or pulsed deposition) after the free part of the spring has been released. Is deposited on all sides of the core to a total spring thickness. Electrodeposition (both electroplating and electroless plating) is the preferred technique for coating the core film. The electrodeposition method, pulse plating, is particularly useful for coatings because it tends to produce denser films. Composition-adjusted electrodeposition methods can also be used to deposit multilayer films.

  We have a stress metal with a thickness of 1 to 45 μm for the free part, whether composed of very thin (less than about 2 μm thick) multilayers or relatively thicker films, eg, thicker than about 2 μm It has been found that springs are very suitable for making good electrical contacts with various materials having electrical contact pads or electrical terminals on different substrates or electrical components. A preferred thickness range for fabricating the free part of the spring is 4 to 35 μm. Excellent electrical contact (very low contact resistance), with the appropriate thickness in this preferred range, is mainly common with gold (Au), copper (Cu) or the tip of the free part end of these springs. Obtained between lead-free or lead-containing solder, or electrical contact pads or terminals containing aluminum (Al).

  In another equally preferred embodiment, the fracture resistance of a spring composed of a relatively thin film, e.g. 0.2 μm, or a thick film, e.g. The relatively thick overlaying film, particularly the film close to the spring surface, is substantially increased by electroplating the film onto the core film so that it is under compressive stress. This means that the completed spring is designed to be pre-stressed. In order to maintain pre-stressed conditions, both the overlaying material and the core material should have a high elastic limit that prevents plastic deformation. Furthermore, the interface between the different membrane layers must also be strong. In a typical embodiment, the overlying film with compressive stress consists of nickel having a thickness of about 10 μm on each side of the Mo—Cr core film. The use of appropriate deposition conditions (eg, electrodeposition bath additive concentration) produces such films. The resulting spring withstood numerous contacts without any breakage. One reason for spring failure is that high tensile stresses are generated on the spring surface when pressed to form contacts with electrical contact pads or terminals. The fatigue strength of a material is generally lower under tensile mean stress than under compressive mean stress. The described solution minimizes the occurrence of spring surface tensile stress when pressed into contact with a contact pad or terminal, thus increasing resistance to spring failure. This scheme and the scheme described in the following paragraphs are also relatively large, effective for generating the large contact forces required at electrical contact pads or terminals for some applications. Enables the manufacture and use of thin stress metal film springs having an overall thickness.

  Note that the completed spring is designed to be pre-stressed. The application of the preceding stress is preferably achieved by compressive stress. However, this range can be a small tensile stress relative to the compressive stress, for example, a tensile stress of 30 MPa relative to a compressive stress of 70 MPa. The stress is different for different thicknesses of Ni plating for the same additive concentration. For thinner films, the stress is higher. For example, for a 1.5 μm thick film, the stress is a compressive force of about 70 MPa. The range of compressive stress that can be generated in Ni springs plated with the same additive concentration is about 6-70 MPa (compressive force) for thicknesses in the range of 25-1.5 μm. Therefore, the stress for various Ni film thicknesses can be adjusted by changing the additive concentration.

Another effect of changing the additive concentration of the plating solution is reflected in the crystal grain size of the plated film. For springs currently plated with increased additive concentration, the grain size was found to be one fifth (20%) of the previously plated sample with lower additive concentration. Smaller grain sizes increase the yield stress of the thin film (d ^-1/2 dependence). This is an important contributing factor in increasing the life of our springs during repeated contact. A suitable range of film particle sizes, for example 3 to 500 nm for Ni overlaid spring cores, and a typical preferred value is 50 nm. It has been found that the plated overlay film becomes stronger as the grains become more equiaxed. For example, the ratio of the larger dimension to the smaller dimension of the crystal grains is less than 2.

  In another equally preferred embodiment, the film material for the deposition of a multilayer stack of films is relatively thick, for example, a film thicker than about 1.5-2 μm, or very thin (less than about 1.5-2 μm) Whichever film is constructed, a film having a smaller elastic modulus is selected to be deposited near the spring surface and a film having a coefficient that increases gradually toward the core is deposited. The In this embodiment variation, the film is selected and deposited over the core so that the modulus of elasticity increases reasonably continuously from the spring surface to the spring core, i.e., stepwise deposition in composition. The A gradual transition in composition and elastic modulus from the spring surface to the core in a continuous or fine discontinuous step across the interface between two different materials distributes the stress at critical locations As a result, it can be used to suppress the occurrence of permanent damage. For these configurations, when the spring is pressed to form electrical contact with the contact pad or terminal, the critical tensile stress that causes nucleation of damage at the surface is a greater factor below the surface, Since the stress is spread from the surface to the inside of the spring, it is reduced on the surface. This reduces the probability of crack initiation at the spring surface during repeated contact, resulting in increased spring life. As a specific example of this embodiment, the spring surface layer (ie, the outer surface of the overlying stack) has a palladium alloy (eg, an alloy having Ni, Co or Pt), a gold alloy (eg, Ni or Co). Alloy), Pt alloy, etc .; on the other hand, the membrane layer closer to the spring core, eg Mo—Cr, consists of nickel or Ni alloy, eg Ni—Co. The higher the concentration of Pd or Au in nickel, the smaller the elastic modulus. Thus, another explanation is to deposit a nickel or alloy thereof having a higher elastic constant on a core film, e.g. Mo-Cr, followed by sequential deposition of an overlying film containing Ni with increasing amounts of Pd. By depositing the layer, the spring life is increased. The outer membrane in this case contains a relatively high concentration of Pd, for example 10-50 w% Ni and 90-50% Pd. For the graded film as described above, the Pd concentration in Ni is continuously changed from the core to the surface. The latter can be achieved by changing the deposition parameters of conventional deposition techniques (eg electrodeposition) during the deposition process. The core material should be a material having a higher modulus of elasticity than that of the other membranes.

  Various material combinations can be used to fabricate the multilayer stack across the core of the stress metal spring. They are applicable to membranes with individual compositions both very thin (less than 2 μm) and relatively thick, for example 2-20 μm. Such combinations include Ni, Au, Ag, Cu, Co, Rh, Ru, Pt, Os, Pd, TiN, W, or alloys thereof, such as Ni-Co, Pd-Ni, Pd-Co, Co- It is selected from the group of materials including Pt, Au—Pt, Pd—Rh, Ni—P, Ni—Mo, Ni—Co—Pd, Ni—Mo—W, Ni—PW and the like. At least two of materials such as Ni with less than about 12% W, or Ni with 2% Mo, or Cu-Rh-Pd or Pd-Ni or Pd-Co, Ni-Co or Co-Pt, etc. Solid solutions with are particularly good candidates for making multilayer thin film stacks because they enhance the mechanical properties of the film.

  The multilayer film is particularly suitable for making electrical contact with terminals / contact pads during testing and burn-in processes that require relatively large energization. A common practice in the industry is to make probe contacts from time to time to terminal pads at current levels of 250-500 mA. This often leads to contact failure due to excessive heat generated in the contact area. Heat flow modeling indicated that the maximum temperature could be reached near the tip region of the spring. In some cases, melting of the spring tip region was also observed. It is shown in the present invention that the addition of a good thermally conductive film, for example Cu with a typical thickness of about 0.75 to 2 μm, can solve the problem within a multilayer stack of the film in which the spring is constructed. . The presence of Cu allows heat to be dissipated rapidly from the tip region, thereby minimizing damage during testing or burn-in. Of course, good thermal conductive films of different thicknesses, for example greater than 2 μm, will also work for this purpose.

  FIG. 4 is a schematic diagram showing such a spring finger including a Cu film for improved thermal conductivity. Other high thermal conductivity materials can also be used instead or in addition to Cu to improve heat dissipation from the spring tip. Specific examples are Au, Ag, Al and the like. In this solution, a film with high thermal conductivity can be deposited before or after the spring is lifted. If the film is electrodeposited after being lifted, the highly conductive film can be deposited all around the core film. If the membrane is deposited on or near one side of the spring, the deposition can take place before the spring is lifted and patterned.

  If the electrical contact resistance of the probe tip to the contact pad is minimized, the increase in high temperature near the spring tip region is minimized. Reduction of contact resistance can also be achieved by increasing the force applied on the contact pad by the probe-tip. We have found that the electrical contact resistance between the spring tip and the contact pad or terminal is less than 1π when the contact is reliable and stable. A preferred range for good electrical contact and good heat dissipation is about ≦ 0.1-0.2 Ohm.

In another embodiment of the present invention, the thin film spring is resistant to failure by strengthening the interface between different film layers against defect propagation and by enhancing good bonding between two adjacent film layers. Can be strengthened. For example, by fading-in Ni at the end of the Mo-Cr deposition, the interface between adjacent layers of the core spring material Mo-Cr and Ni film can be significantly strengthened, and at the interface The bond between the two layers can be substantially stronger. Fading-in can be achieved as follows. Ni deposition begins immediately before the end of Mo-Cr deposition. Next, the Mo-Cr deposition rate is gradually reduced to zero, and at the same time, the deposition parameters are adjusted appropriately to increase the Ni deposition rate. For other methods, such as subsequent deposition of Ni or its alloys on the core by electrodeposition, Ni or its alloys are deposited on the Ni surface of the core. This results in strong bond formation and increased interfacial strength. Such interface engineering can also be applied to enhance the quality of the interface between two adjacent electrodeposited film layers. In that case, near the end of the deposition of electrodeposited film A, the alloy of A _x B _1-x is deposited using the appropriate process parameters so that the deposition of another film B to be electrodeposited continues. Can be made.

  For another embodiment of the present invention that includes electrodeposition to deposit a thin film that coats a layer on the spring core, the deposition parameters are intermittent during deposition to improve the quality of the coating film. Can be changed. It is known that the electrodeposition of relatively thick membranes of material often exhibits increased porosity in the membrane layer near the top surface of the membrane, with thicknesses generally exceeding about 1.5-2 μm. Thus, changing film parameters, such as dc plating to pulse plating, or changing the current density during deposition significantly improves film quality. As a result, the membrane becomes stronger and prevents premature failure during testing or operation. Varying the deposition parameters during electrodeposition can change the microstructure, such as grain size and crystallographic structure of the deposit, as well as film stress.

  FIG. 5 is a schematic diagram illustrating a solution for the design and manufacture of a stress metal spring according to another aspect of the present invention. Where 501 refers to an electrical pad, 502 refers to a metal filled via, 503 refers to an insulating film such as a polymer film, 504 refers to an electrical trace, and 505 refers to a release layer. 506 refers to the plated film, 507 refers to the core of the spring, 508 refers to the surface plated film, and 509 refers to the substrate. This design allows for the establishment of good electrical contacts with less force and thus results in a substantial increase in durability against breakage during repeated contacts. The fatigue life of the structure is a strong function of load stress. Therefore, achieving a small and stable contact resistance with a small contact force that allows for smaller stresses in smaller sized structures is highly desirable to increase spring life and performance. Some of the miniaturized springs made by different means according to the present invention, which are also used for electronic component testing or burn-in, reportedly require contact forces of 2 to 150 gf. In some experiments, we have demonstrated that a stress metal spring having the basic structure of the present invention shown in FIG. 5 can form very good contacts with much less force. In these experiments, the part of the film, for example Ni or Ni alloy that covers the core film on all sides, is not very thin, for example thicker than 2 μm, and the outer surface of the spring is relatively Coated with a hard, environmentally stable material such as Pd-Co or Rh. However, with a contact between these springs and Al, one of the most difficult materials to make electrical contact, a force of only 1.4 gf resulted in good, low and stable contact resistance. In fact, we have found that the force should preferably be maintained within the range of about 0.8-10.0 gf for effective electrical contact between these springs and Al. Larger forces tend to damage the contact pads 501 and smaller forces fail to break through the surface oxide with reproducibility. When contacting other materials that do not form strong oxides such as Al, such as Au, Cu and solder, the force required to form a good electrical contact is significantly less, for example 0.2 gf It is. We have obtained good electrical contact between our probe spring and gold contact pad with a small force of 0.01 gf. As noted above, establishing a good electrical contact with low contact resistance also allows testing of a circuit or device at higher currents without significant degradation of spring quality due to high thermal problems To. Accordingly, a probe spring having the configuration shown in FIG. 5 is desirable for testing or burn-in that requires greater current passage. Similar springs having a multi-layer structure consisting of very thin membranes, for example less than about 2 μm, are also suitable for such tests or burn-ins that require greater current flow.

  As noted above, the ability to make good electrical contacts between springs and contact pads or terminals with very little force provides numerous benefits. The introduction of copper metallization and low dielectric constant materials into deep submicron integrated circuits by the microelectronics industry places substantial demands on low force probe contacts during chip testing and burn-in. Open. Low k dielectric materials are relatively fragile. Thus, the spring structure described herein is particularly suitable for circuit applications having Cu films and low dielectric constant materials. These springs can form good electrical contacts on Cu with relatively little force, eg, less than 1 gf. Therefore, the possibility of damaging circuit elements is minimized.

  Another important benefit from small force contacts is related to the manufacture of interposers. As is well known in the prior art, a probe card assembly is used to establish an electrical connection between an IC to be tested and a tester, a probe chip (or a space transformer) and a load. An interposer is often used between load-boards (PCBs connected to testers). Cantilever type springs are attached to these interposers to facilitate electrical connection. In the case of currently available probe card assemblies on the market, the force applied by each of these interposer springs is relatively large, for example 15-30 gf. Since the contact terminals are generally made of a material other than aluminum, such as gold, an interposer having a miniaturized stress metal spring made in accordance with the present invention has a much lower force, for example 0.005-2 gf, An electrical contact can be formed with the opposing contact terminal. Such small contact forces can be applied by these springs consisting only of core material without any plating, eg MoCr. Of course, a relatively thin layer of plating, for example with gold, is preferred in some applications to increase the electrical conductivity or mechanical properties of the spring, such as the wear resistance of the spring tip. As a result of low force contact springs, the overall force applied by an interposer with thousands of springs is greatly reduced. Thus, miniaturized stress metal springs patterned with photolithography of the present invention for the construction of probe card assemblies including probe tips, interposers and test and burn-in, and assembly fixtures for packaging The use of is greatly simplified by the use of these low force springs since bending, warping and alignment problems are minimized. Due to the small force exerted by the spring of the present invention on the contact to establish a good electrical connection, the assembly can save a large mechanical support for many applications as well as the interposer It is. Thus, the use of the low force spring described herein provides significant enhancements in yield and reliability, as well as cost and complexity reduction.

  It is known that by increasing the thickness of the spring, the force of the spring contact on the contact pad or electrical terminal can be increased. A mathematical expression can be used to calculate the force as a function of spring size. In stress metal springs, the thickness of the core material, e.g., Mo-Cr, is generally kept below about 5-6 μm to facilitate lifting of the free part of the spring following its patterning on the substrate. Be drunk. The film is then deposited on the spring, for example by electrodeposition, to increase its thickness for applications that require increased contact force. The deposition of selectively added films on the spring using photolithography or other methods is very complex and expensive due to the non-planar structure of the spring. In the case of the present invention, a much simpler and effective solution has been applied to deposit different films by electrodeposition on springs and, if necessary, on circuit traces. This solution does not require the use of any masking. In this case, electrical contact to the spring array is made by depositing a conductive thin film over the entire back of the substrate 509 or by patterning the back of the film to better control current density. The Electrical continuity penetrated through a substrate such as 502 filled with conductive material in electrical contact with a spring, adhesive layer 505, spring metal 507, trace, eg 504, or contact pad, eg 501 Established using vias. Thus, the film is deposited only on conductive surfaces that are electrically connected to the appropriate terminals of the power source behind the substrate. This scheme allows selective electroplating on the lifted spring, and thus all surfaces surrounding the spring, and also allows electroplating of other metal structures not covered by traces and insulation. Suitable substrates include inorganic materials such as ceramic, quartz, silicon, glass. Other substrates with organic materials such as polymers, epoxies, FR4 and polyimides can also be used within the scope of the present invention. Specific examples of later groups of boards are printed circuit boards using FR4, DuPont Thermount and Nelco N4000.

  A previous study (Patent Document 7) also reports the plating of material onto a lifted stress metal spring. However, they used complex photoresist patterning to electroplate the material on one surface of the lifted spring due to the non-planar structure. In our study, we have found that the method is completely different for the manufacturing process because the presence of stress in the film electrodeposited mainly on one surface of the core spring material affects the lift height of the spring. I found that it didn't work well. Furthermore, because the very thin spring core is made to allow for proper lifting, the photoresist deposited on the free part and base of the spring is uncontrollable, apparently due to the effect of surface tension, There is a tendency to pull the lifted part towards the base. As a result, the method is not suitable for obtaining a reproducible and controlled lift height for the spring array. In the present invention, this problem is eliminated by electrodeposition of an envelope of material covering the spring core without using any photoresist mask, as shown in FIG. Further, in this case, the stresses on the two sides of the core spring are reasonably balanced, thereby minimizing spring lift height correction due to plating. Thus, unmasked plating of the spring core uses all through-substrate vias to establish electrical contact from the substrate-surface opposite the surface on which the spring is positioned, and further requires the use of all core surfaces. Accordingly, it is highly desirable to produce a coating of electroplated membrane that covers other conductive surfaces around the spring).

  FIG. 6 shows the lifted spring before plating and FIG. 7 shows the spring after plating. In order to maintain the proper stress in the plated film, it is important to compensate for the changes that occur in the current density as the area of the lifted spring changes. The current supply must be programmed to manage the stress in the film to compensate for changes in spring thickness that reduce the current density.

  A problem often experienced with multiple contacts, eg 100,000, is the strengthening of the contact pad material on the stress metal spring tip region. This affects the contact resistance and life of the spring, especially when the contact pad is composed of aluminum. Coating the probe tip region with a metal or conductive material that does not adhere well or at all with the metal to contact, such as Al, minimizes this problem. Examples of such coating materials are rhodium (Rh), palladium and ruthenium, and two or more adducts such as palladium-nickel, palladium-rhodium, palladium-cobalt, palladium-gold-rhodium, and titanium nitride. Platinum group materials including their alloys with Ir-Au, Ir-Pt, gold-cobalt, zirconium nitride and the like. Although a thin film of such coating material is deposited on the body of the probe spring for low force and less current applications, it is only in the vicinity of the spring tip region after the stress metal spring is released from the substrate. Depositing the coating material is desirable for some applications. One reason for not depositing the coating material on the entire spring body is, for example, the flexibility in selecting the coating material for the desired elastic modulus and film thickness for selective coating of the spring tip region. That is. The presence of some coating material having a relatively large thickness on the spring body can affect the reliability of the spring. The present invention provides a new solution for highly controllable deposition of such coatings only on the tip region of a stress metal spring using techniques that are compatible with integrated circuit technology. In this solution, a “button”, preferably having a plurality of conductive films, is fabricated in the tip region of the spring for making contact with the electrical contact pads or terminals. In one embodiment of this solution, as described above, the coating material is deposited as a film that finally covers the “button” before the free portion of the probe spring is released from the substrate. As a result, only the small part of the spring is constrained by the coating material at the tip, while the rest is free to bend and lift, which is associated with lifting the free part of the next spring to the proper height. The problem is minimized. This approach is used for smaller force springs that do not require greater force or added thickness for improved spring electrical conductivity (MoCr springs are thin and durable).

  As described above, the process steps for making a spring with a “buttoned” tip are as follows. Following the deposition of the stress metal spring core film, e.g. Mo-Cr, a mask, e.g. photoresist, is deposited on the core film and patterned using a technique, e.g. photolithography, to define the shape of the spring. Is done. The spring is etched, the photoresist is removed, and an additional photo process follows, so that all of the core film remains covered with the mask except for the spring tip region. Subsequently, Rh, which is to be deposited later as an overlayer on the spring core, for example Rh, is deposited to the exposed spring tip region to the desired thickness, and the aforementioned coating materials, such as Pd-Ni, Pd- The last overlayer deposition with a suitable thickness of Rh, Pd-Co, Rh or TiN, for example about 1 to 4 μm, follows. Also, the coating layer thickness range will naturally be larger, eg, 1-20 μm, for the present invention to function. It should be noted that in a variation of this embodiment, the film deposited on the spring tip region can also be composed of materials other than those later deposited on the spring body. Once the mask is removed, the etch is used to undercut the spring and release the free part of the spring from the substrate. This is followed by deposition over the spring body to the desired thickness, while the already fabricated spring tip region is protected by, for example, a photoresist or polyimide mask.

  The resulting tip region thickness could be designed to be approximately equal to the rest of the lifted spring. Subsequently, the mask is removed and a probe spring having the desired thickness of coating material on the spring tip region is obtained. Electrodeposition is suitable for such deposition, although a number of film deposition techniques can be used to deposit the overlayer and the final coating layer. In another variation of this embodiment, the selective deposition of the overlaying film on the spring tip region prior to spring release is an alternative to patterning the spring fingers after depositing the coating film on the spring tip region. It can also be done after patterning the deposited core film into spring fingers. The remaining subsequent process steps are the same for both embodiments.

  A suitable method for fabricating a button on a raised plated spring such as that shown in FIG. 7 is described below. After the spring is lifted from the substrate, using photolithography, the spring tip region is selectively coated with one or more suitable materials (button manufacturing). In this method, the photoresist is deposited on a lifted spring using well known techniques such as spinning or spraying or plating. A preferred method is to spin on the photoresist. Unlike unplated springs, thick photoresists can be utilized for the springs because the relatively thick coating of material covering the cores substantially hardens them. Due to this enhanced stiffness, the spring height is not significantly affected by applying a photoresist. A spring covered with photoresist is shown in FIG. With regard to photoresist plating, as described above, the electrical terminals on the backside of the substrate are used to connect to a power source. The back terminal is connected to a spring on the front surface of the substrate by a metallized via. Next, the photoresist is selectively removed from the spring tip region, including the top and side portions of the tip region, using a photomask and photolithography techniques, as shown in FIG. Subsequently, as described in the previous paragraph, the coating material on the tip, eg Pd-Ni, Pd-Co, is deposited on the spring tip region using conventional techniques, preferably electroplating. Is done. Sputtering or CVD can also be used, in which case the coating material is also deposited onto the photoresist layer, followed by any unnecessary overlay using conventional solvents. Removed along with the coating material, leaving only the coating material in the tip region. Electroplating of the spring tip region that is not covered with photoresist allows for substantial coverage of the tip region. Suitable materials for the buttons consist of platinum group materials (ie Pd, Pt, Rh, Os, Ru and Ir), Ni, Co, Au and Ag. This structure is shown in FIG.

  In the process described in the previous paragraph, the tip button is plated following the deposition of a relatively thick coating of material, eg, Ni, which substantially hardens the spring. Because of this enhanced stiffness of the spring by the button and the relatively small coverage, the height of the spring lift is not significantly affected by button plating.

  After the button tip is plated, the photoresist is removed leaving the final structure as shown in FIG. Note the anchor portion 516.

  If there are no metallized through-vias in the substrate to allow backside connection, a variation of the solution described in the previous paragraph will also lift the spring core film and overlay the film. It can be used to selectively apply a coating to the spring tip region following deposition. A conductive material, such as Au, Ag or Cu, is first deposited over the entire substrate, in this case a substrate containing a stress metal spring after lifting the spring using techniques such as sputtering or electrodeposition or CVD The whole covering is made to the desired thickness including the overlying film covering the core film. This conductive layer is used to provide an electrical connection for button electroplating of the spring tip. A photoresist is then deposited over all of the conductive surface. Using photolithographic techniques, the coating material is selectively deposited only in the spring tip region, as described in the previous paragraph. Next, the thin conductive material deposited prior to photoresist deposition is removed by wet or dry etching techniques.

  FIG. 12b shows a specific example of a selectively coated spring tip region with improved spring life, where 1215 is a tip with a protective coating, such as Pd—Co or Pd—Ni alloy Point to a button. Here, the free portion 1218 of the spring is substantially tapered. As will be discussed later, in this example, the spring life is substantially enhanced and the coating material in the tip region does not show any significant degradation during repeated contact.

  FIG. 13 shows the result of tip (button) plating using photoresist application followed by selective coating of the tip region by patterning to expose the tip region and electroplating of a Pd—Co alloy. It is a drawing. All tips can be substantially covered with plated buttons, but usually only a relatively small area of the spring tip is a probe card for electrical testing or burn-in operation. • Contact IC terminals or electrical contact pads on other parts of the test assembly. The large coverage of the spring tip by the button material provides flexibility in designing the spring and test assembly. Furthermore, the joining of spring electrical components to IC terminals or contact pads for packaging applications using techniques such as soldering is greatly facilitated with the use of a button that substantially covers the spring tip. In such cases, the button plating material is a group that forms a reliable bond with solder, for example, an alloy containing Sn, Pb-Sn or commonly used in the microelectronics packaging industry It is selected from solder that does not contain Pb. Specific examples of button materials or spring coating materials for forming contacts with solder or conductive adhesives in packaging applications include platinum group materials such as palladium, platinum, ruthenium, etc., as well as cobalt, nickel, gold, copper, A multilayer stack of films with cobalt or an alloy.

  The durability of a stress metal spring against failure can also be increased by designing a spring with a varying width that increases from the finger tip region to the base. Most of the spring breaks during repeated contact occur near the base of the spring. In general, the stress generated during contact with the contact pad is greatest near the base of the spring finger, so the stress near the base is substantially reduced by increasing the width near the base region. Is possible. For example, the free part of the spring can be patterned to have a substantially trapezoidal shape. A similar increase in puncture resistance can also be achieved by making the region closer to the spring-base thicker, which for a given applied force, Nearby stresses are also reduced.

  FIGS. 12a and 12b are schematic diagrams showing an embodiment 1200 of a spring having a taper-changing width. Here, 1216 refers to the fixed spring base and 1218 refers to the free portion of the spring that is tapered due to the relatively uniform stress distribution. Having a tapered spring free portion 1218 is a significant increase in spring break resistance. In this example by tapering, the key point here is to properly shape the free portion 1218 of the spring so that the bending stress is evenly distributed along the spring 1200. Furthermore, spring compliance is increased due to the tapering. This concept thus allows a design solution to maximize the force with minimal stress for a given compliance range. It is noted that the parallel sides of the base region (ie, the anchor portion) can also extend to the raised region (ie, the free portion) to some extent, such as 1218a, before tapering. I want. FIG. 12b diagrammatically shows a buttoned and tapered spring that has been found to withstand multiple contacts without breaking.

  In an exemplary embodiment, the core member of the stress metal spring, having a free part and an anchor part attached to the substrate, is a material with a large elastic modulus, such as Mo, Mo-Cr, W, Ti-W. . The core member is selectively coated to cover all of its exposed surface after the free part of the spring is lifted. The result is that at least one deposited by electroplating without a mask, using the metallized through-hole vias in the substrate to establish electrical contact from the back of the substrate (opposite the spring surface) A film having a metal film. The coating extends to the anchor portion without any discontinuities that balances the stress in the free portion and mechanically weakens the membrane causing premature failure. Generally, Ni or Ni alloy is deposited on the core member. Additional films, such as Pd alloy films, are optionally electroplated onto Ni as needed. Selective deposition of an additional layer of palladium alloy film on the spring tip region can be accomplished using conventional photolithography and deposition techniques such as electrodeposition (electroplating and / or electroless plating) or sputtering or CVD. Executed. The typical thickness of Mo-Cr is 4 μm. The thickness of the electroplated nickel and palladium alloy film on each side of the Mo—Cr film is 2-20 μm and 1-10 μm, typically 12 μm and 4 μm, respectively. In this case, the elastic modulus of the membrane decreases from the spring core towards both surfaces. The thickness of the button with the added deposit of palladium alloy film is, for example, 1-20 μm, typically 12 μm, in the contact tip region.

  Another aspect of the present invention is to eliminate stress concentration points on the spring surface. We have observed that spring breaks, such as cracks, are often initiated at the surface during repeated contact. Therefore, the surface roughness needs to be minimized. As shown in FIG. 5, much of the roughness of the side of the lifted spring begins while patterning a core film, such as a film made of Mo-Cr, W or Zr-Ni, for example by wet etching. . The overlaying film, such as 506, subsequently deposited on the core 507 follows the rough contoured surface, resulting in a rough surface on the finished spring structure side. In accordance with the present invention, forming the spring core pattern by dry etching containing ionized species minimizes this roughness. When using electroplating to build an overlaid film, roughness is also minimized using sequential plating and deplating processes to increase the spring thickness. The reverse plating parameters are adjusted so that only a portion of the plated thickness is removed during reverse plating. Polishing the wet-etched core 507 or the fully plated spring face first by electrolytic polishing, chemical or electrochemical polishing also makes it possible to minimize roughness.

  In another embodiment, a spring covered with a film deposit, where the core film overlays everywhere, is the maximum over-ride in electrical contact pads or terminals allowed by the designed height and position of the standoffs. As limited to the drive, the standoff is provided on the substrate or electrical component.

  The solution described above can also be used in manufacturing a variety of other cantilever springs that are not partially lifted stress metal springs as a result of the presence of an inherent stress gradient in the membrane. is there. When the spring tip-end contacts the contact pad, i.e. the input / output (I / O) pad of the wafer or other substrate or component of the test or burn-in assembly, the stress in this region is maximized One of the main concerns regarding the performance of these other cantilever springs is also the tendency to breakage, for example deformation or crack formation near the base or anchored end of the cantilever spring. Mathematical expressions can be used to show the effect of spring length on stress near the base region. When the spring is pressed to form contact with the contact pad, the spring will minimize the stress in the base region while the spring is bent, and thus increase its durability against breakage during repeated contact The length of is currently designed to be relatively large, for example, about 700 to 2,000 μm. However, this limits the applicability of cantilever springs to current and future generation generation tests and burn-in of microminiaturized integrated circuits. For this circuit, the spring probe array must accommodate a much denser array of device input / output pads with a denser pitch, eg, about 20-50 μm. Therefore, it would be highly desirable to find a means to create a tighter pitch, shorter spring that is sufficiently strong, especially near the base region, to withstand greater stress without failure.

  In order to apply the required force during spring contact to the contact pad, the need for an increased spring constant requires that the free part of the cantilever type spring be made thicker. In some embodiments, a thicker spring is a spring core that stands on one or more metals or their alloys, such as nickel or nickel alloys or palladium alloys, without a photolithographically patterned support, For example, it is made by electroplating on a Mo-Cr alloy. In some other embodiments, the spring is patterned using photolithography and electroplating at least one metal or metal alloy film, such as a relatively thick layer of nickel or nickel alloy, onto the seed layer It is manufactured by doing. In many of these embodiments, a button-type contact structure is also provided in the contact chip area to improve contact characteristics and maintain contact integrity during repeated contact during wafer test and burn-in operations. Is done. However, such an embodiment still requires a relatively thick membrane that constitutes the body of the spring to apply the required contact force at the contact tip end. For relatively shorter springs that are about 100-700 μm long, increased spring thickness results in greater stress near the base end, resulting in shorter spring life.

  Solutions for producing shorter cantilever type springs with or without buttons similar to the contact structure in the spring tip region are described below. In this type of spring, the strength of the base or body region of the spring is enhanced against mechanical failure, resulting in a significant increase in the performance, strength, resistance and life of such a spring.

  Figures 14a and 14b show two cross-sectional views of a stress-free metal cantilever spring standing without a typical support according to one embodiment of the present invention. A cantilever spring standing without support is a button 1406 with a base region 1401 at one end attached to the electrical contact pad 1402 of the substrate 1403, a contact tip region 1404 at the other end of the spring, and a contact tip region 1404. And a body deposited with a Ni film 1408 and a Pd-alloy film 1409. The spring length allows it to be substantially parallel to the surface of the attached substrate, or it extends away from the substrate surface forming an oblique angle with respect to the surface. Is possible. In general, the spring base 1401, tip 1404 and body are fabricated from the same material in the same operation using, for example, thin film deposition techniques such as electroplating, sputtering or CVD.

  Contact tip region 1404 has a button-type contact structure 1406 that facilitates reliable and durable contacts. This structure can be fabricated by selectively depositing a film on the contact tip region 1404 as an integral part of the tip region, or by being fabricated separately and attached to the tip region. Similarly, the base region 1401 can be fabricated integrally with the spring, or can be fabricated separately and coupled to the base using conventional techniques such as soldering, brazing, and the like. Can be attached to the post. In the case of monolithic manufacture of the post, the film can be selectively deposited using a technique such as electroplating followed by polishing in holes within the sacrificial substrate.

  The presence of the button-type contact structure 806 in the spring tip region 1404 is effective to achieve a reliable and durable electrical contact to the opposing contact pads in a wafer test or burn-in assembly. In that case, a suitable material with the desired contact properties and thickness is not necessarily required, but it is also possible to have the same material that constitutes the spring body 1405 or base 1401 to create such a button. Can be selected. However, the choice of material for each of the three parts gives strength to each part of the spring and allows them to withstand wafer testing and burn-in processes involving repeated contact without breakage. Must be. Many of the materials that are suitable for various electroplating applications were used in making cantilever type springs. For example, such materials include nickel and its alloys, gold, rhodium, Pd and its alloys, copper, platinum group elements and their alloys, titanium, molybdenum and their alloys, and the like. However, the challenge of producing shorter springs with the required strength remains. The stress-free metal cantilever springs manufactured today remain relatively long, for example 1-2 mm. The main objective in this area is to support the microelectronics industry's continued driving force to produce deep sub-micron integrated circuits with higher circuit density and associated smaller pins between input / output terminals. And to find a way to make a much shorter and stronger spring array.

  The present invention allows such a strong contact spring array to be fabricated by applying special material selection principles for the construction of buttoned or unbuttoned springs with metal membranes Enable. The selection of the appropriate material by applying these principles provides a specific method of film deposition and thus leads to the production of contact springs with the desired strength.

  The specific material selection principles that have been found to have very significant effects in improving spring performance and reliability are as follows. A multilayer film with three parts, namely a spring base, a tip region, and a body and a button, a film with a smaller elastic modulus is deposited near the spring surface that forms a contact with the IC terminal for testing, And it should have a graded material composition so that films with progressively larger coefficients are deposited towards the opposite surface. Since it is the mechanical strength of the spring body and base region that determines the strength of the spring, the mechanical strength of the button is not a critical factor. However, in accordance with the teachings of the present invention, the button membrane also optionally has a modulus of the button face membrane that has a lower modulus of elasticity than the underlaid membrane layer, the modulus of the button face being It can be selected and deposited so as to gradually increase away from. Such a gradual transition of the composition and elastic modulus from the spring contact surface to the opposite surface, either continuously or in discontinuous steps across the interface between two different materials, is a critical position. It can be used to distribute stress and therefore suppresses damage to the spring. As a result, the life of the spring is increased. This means that the spring tip 804 is spring-loaded everywhere, including the spring base 801, when pressed against and contacts a contact pad on another substrate, such as a semiconductor wafer or other part of a test or burn-in assembly. Increase the durability of mechanical breakage in

  In accordance with the principles described above, one exemplary embodiment of a stress-free metal cantilever spring is that palladium has a modulus of elasticity greater than that of its palladium alloy, so that the overlay layer is palladium—about 20% cobalt or palladium. -Having a nickel film as a base layer with about 20% nickel alloy film. Other films can also be deposited to form a multi-layer spring, if the principle of selection is applied, generally to determine the deposition order. In addition, a very thin film layer can also be deposited between the two main film layers to improve interfacial strength or adhesion as needed. For example, as is well known to those skilled in the art, gold or nickel or rhodium strikes can be used for this purpose. In this case, the button 1406 on the tip region 1404 may have an additional layer of the palladium alloy film. The button 1406 can be fabricated as an integral part of the contact tip region 1404 or can be attached to the tip region 1404 separately. Such a spring, as illustrated in FIGS. 14a and 14b, is typically deposited on the sacrificial layer and it is subsequently removed to provide a cantilever spring standing unsupported. The substrate 1403 can also have a multilayer metallization and conductive blind vias or through vias as shown in FIG. Films 1408 and 1409 and other added layers are deposited by conventional techniques, such as electroplating. If desired, a suitable thin adhesion promoting layer and / or seed layer with a material such as titanium can also be deposited prior to the deposition of the electroplated layer. The thickness of each membrane layer is determined by the desired contact force, which can be calculated from various mathematical expressions, or the spring constant. Various spring dimensions can be used, for example 1-50 μm as the thickness range, for example in terms of force and pitch based on design requirements. As an illustration, considering an overall spring thickness of 30 μm, the nickel and palladium alloy thicknesses of this example can be 25 μm and 5 μm, respectively. In this case, the thickness of the added layer of palladium alloy in the button can be 3-20 μm. It should be understood that the above numbers are used only for examples. A wide variation in numerical values works well to ensure spring strength as long as the basic principles are met.

  In another exemplary embodiment, the core film is made of molybdenum-chromium alloy or titanium-tungsten or molybdenum-tungsten and has a sequentially deposited overlayer of nickel and palladium alloy films. In this case, as described above, the button 1406 on the tip region 1404 has an added deposited thickness of the palladium alloy. Button 1406 can be fabricated by selectively depositing an additional thickness of palladium alloy film on tip region 1404 using photolithography. The discussion of typical thickness ranges, deposition techniques, adhesion promoting layers and seed layers, etc. in the previous paragraph apply here as well.

  As noted above, the film of the above-described embodiment of a stress free metal cantilever spring can be preferentially deposited with compressive stress to further improve strength. The strength is also further improved by appropriately selecting the film deposition parameters such that the film grain size is very small, for example 3 to 500 nm. For example, specific examples of such deposition parameters include electroplating bath additive concentration, current density and temperature.

  The disclosed interconnect apparatus and associated fabrication techniques are suitable for a variety of applications including, but not limited to, electronic component testing, wafer level burn-in, and electronic device packaging. The electronic components include devices such as integrated circuits, liquid crystal displays, MEMS, and printed circuit boards or any combination thereof. Packaging includes the coupling and establishment of an electrical connection between two components or substrates using the disclosed contact spring elements, where the coupling is achieved with or without the use of solder or conductive adhesive Can.

Metric terms and abbreviations for chemical elements:
μm-micron = 10 ^-6 meters;
nm-nanometer or millimicron = 10 ^-9 meters;
Ag-silver;
Al-aluminum;
Au-gold;
Co-cobalt;
Cr-chrome;
Cu-copper;
Mo-molybdenum;
Ni-nickel;
Pb-lead;
Pd-palladium;
Pt-platinum;
Rh-rhodium;
Ru-ruthenium;
Sn-tin;
Ti-titanium;
W-tungsten.

  The present invention applies to all types of miniaturized springs. The preferred embodiments disclosed herein are illustrative only and are not intended to be limiting. Other modifications and variations to the present invention will be apparent to those skilled in the art from the foregoing detailed disclosure. While only certain embodiments of the invention have been specifically described herein, it will be apparent that numerous modifications are possible without departing from the spirit and scope of the invention.

  Accordingly, the invention should be limited only by the claims.

1 is a schematic diagram showing a typical stress metal film spring according to the prior art. FIG. 1 is a schematic diagram showing a typical cantilever spring according to the prior art. It is a diagram which shows the stress-strain curve of the bulk material corresponding to thin film. 1 is a schematic diagram showing a stress metal film spring with a multilayer structure according to the present invention. FIG. 1 is a schematic diagram showing a stress metal film spring having a multilayer structure according to the present invention. FIG. 1 is a schematic diagram illustrating a stress metal film spring with a multilayer structure having at least one high thermal conductivity film in accordance with one embodiment of the present invention. FIG. FIG. 6 is a schematic diagram illustrating a solution for spring design and manufacture in which metal filled vias, insulating polymer films and electrical traces are used in accordance with one embodiment of the present invention. FIG. 4 is a schematic diagram of a stress metal film spring formed on a via that provides electrical connection to the backside of a substrate, in accordance with the present invention. 1 is a schematic diagram of a stressed metal film spring formed and then plated to improve strength, in accordance with the present invention. FIG. 1 is a schematic diagram of a plated stress metal film spring coated with a photoresist according to the present invention. FIG. FIG. 4 is a schematic diagram of a plated stress metal spring coated with a patterned photoresist and exposing a spring tip in accordance with the present invention. FIG. 3 is a schematic diagram of a plated stress metal spring with a contact tip material plated on the exposed portion of the tip according to the present invention. FIG. 3 is a schematic diagram of a plated stress metal spring with contact tip material after photoresist removal in accordance with the present invention. FIG. 3 is a schematic diagram illustrating a stress metal film spring with a taper-shaped varying width according to one embodiment of the present invention. FIG. 6 is a schematic diagram showing a tapered stress metal film spring whose tip region is coated with a contact material, according to one embodiment of the present invention. 1 is a schematic diagram of a plated stress metal spring comprising an interleaved array contact tip material in accordance with the present invention. FIG. 1 is a schematic diagram illustrating a cross-sectional view of a typical stress-free metal cantilever spring standing according to one embodiment of the present invention. FIG. 1 is a schematic diagram illustrating a cross-sectional view of a typical unstressed metal cantilever spring standing in accordance with one embodiment of the present invention. FIG.

Explanation of symbols

501 Contact pad
502 via filled metal
505 release layer
506 plated membrane
507 spring core
509 substrate
516 anchor part

Claims (61)

In an interconnection device for establishing electrical contact between two parts,
A core member, wherein the core member is attached to a substrate with at least one through via filled with a conductive material therein and initially attached to the substrate and released when the core member is released. Having at least one elastic core member having a free portion extending away from the substrate due to an inherent stress gradient in the core;
An interconnection device, wherein the core member is covered by at least one layer covering all exposed surfaces of the core member by electrodeposition.   2. The interconnect device according to claim 1, wherein the coating has an electroplated membrane.   The interconnect of claim 1, wherein the free portion is either substantially tapered with a gradually decreasing width over a substantial length of the free portion, and is substantially trapezoidal in shape. apparatus.   The material in which the at least one layer includes at least one of nickel, palladium, platinum, rhodium, ruthenium, osmium, iridium, gold, silver, copper, cobalt, aluminum, tungsten, and alloys thereof. The interconnect device according to claim 1, wherein the interconnect device is selected from the group.   The interconnect device of claim 1, wherein the average grain size of at least one of the at least one layer ranges from 3 nm to 500 nm.   The interconnect device of claim 1, wherein at least one layer is electroplated with inherent compressive stress.   2. The interconnect device according to claim 1, wherein at least one layer near the surface of the core member covered by the electrodeposition has a smaller elastic modulus than the surrounding core.   2. The interconnect device according to claim 1, wherein the coating has a plurality of different and sequentially electrodeposited films.   The electrodeposited film generally has a gradual decrease in the modulus of elasticity of the deposited film from the innermost core to the outermost surface, and from the innermost core to the outermost surface. 9. The interconnect device of claim 8, wherein the interconnect device is deposited to be either substantially discretely reduced.   2. The interconnect device according to claim 1, further comprising a film layer selectively applied in a probe tip region on the core member covered by the electrodeposition.   11. The interconnection device according to claim 10, wherein the film layer has at least one of the group consisting of palladium, rhodium, platinum, iridium, osmium, ruthenium, cobalt, nickel, gold, and alloys thereof.   The interconnect device of claim 1, wherein the free portion has a size ranging from 10 μm to 1000 μm in length, from 3 μm to 500 μm in width, and from 0.1 μm to 40 μm in thickness.   The interconnect device of claim 1, wherein the outermost layer of the at least one layer comprises one of copper, gold, nickel, and a platinum group material comprising Pd, Pt, Ir, Rh, Ru, and Os. .   2. The interconnect device according to claim 1, wherein the substrate includes any one of ceramic, glass, silicon, quartz, and an organic material.   2. The interconnection device according to claim 1, wherein the core member includes any one of Mo, Cr, Ti, W, Zr, Mo—Cr, and Ti—W. A method for manufacturing a plurality of miniaturized springs on a substrate, each of the miniaturized springs having a conductive core member, the core member being attached to an anchor portion and initially to the substrate And when released, has a free portion that extends away from the substrate due to an inherent stress gradient in the core, the free portion comprising a tip region at the end, and the anchor portion is Fixed to a substrate having a plurality of metallized through vias,
Electroplating the spring core member with at least one membrane layer to cover all surfaces of the core member including free parts, without using a mask;
The electroplating of the core member is performed using through vias in the substrate to establish electrical contact to the core member from the substrate surface opposite the surface on which the core member is positioned; And having a method.   17. The method of claim 16, wherein at least one membrane layer is electroplated with inherent compressive stress.   The method of claim 16, wherein the at least one membrane layer is electroplated with an average grain size in the range of 3 to 500 nm.   19. The method of claim 18, wherein the grain size of at least one electroplated film is controlled by changing the additive composition of the electroplating bath and / or the current density during plating.   The at least one film layer is Pt, Pd, Rh, Ir, Ru, Os, cobalt, nickel, gold, silver, copper, or aluminum; Co, Ni, Au, Cu, Ag, Al, Pt, Pd 17. The method of claim 16, selected from the group of materials comprising: an alloy having at least one of the group consisting of Rh, Ir, Ru, Os, W. Further comprising selectively coating the tip region to form a contact button following the electroplating of the core member;
The contact button has at least one conductive material that does not adhere strongly to the opposite contact pad or terminal; and
The tip region is optionally selectively coated either before the free part is released from the substrate and after the free part is released from the substrate to form the contact button. 17. The method of claim 16, wherein:   22. The at least one conductive material comprises at least one of the group consisting of palladium, rhodium, platinum, iridium, osmium, ruthenium, cobalt, nickel, gold, silver, copper, and alloys thereof. the method of.   17. The method according to claim 16, further comprising forming a pattern of the core film by dry etching.   The method of claim 16, further comprising polishing the core film prior to depositing the layer.   The method of claim 16, further comprising polishing the outermost surface using any of electrolytic polishing, chemical polishing, and electrochemical polishing processes. In an interconnection device for establishing electrical contact between two parts,
A core member, wherein the core member is attached to a substrate having a metallized multilayer with at least one metallized via and initially attached to the substrate and released; Having at least one elastic core member having a free portion extending away from the substrate due to an inherent stress gradient in the core;
An interconnection device in which the core member is covered by at least one layer covering all exposed surfaces of the core member by electrodeposition. In an interconnection device for electrically connecting two parts,
A core member that extends away from the substrate due to an inherent stress gradient in the core when the core member is anchored to the substrate and initially attached to the substrate and released. At least one elastic core member having
At least one layer covering the core member by electrodeposition and covering all exposed surfaces of the core member; and
An interconnect device having a film layer selectively applied in a probe tip region on a core member covered by electrodeposition.   28. The interconnect device of claim 27, wherein the coating comprises an electroplated membrane.   28. The interconnect of claim 27, wherein the free portion is either substantially tapered with a gradually decreasing width over a substantial length of the free portion, and is substantially trapezoidal in shape. apparatus.   The material in which the at least one layer has at least one of nickel, palladium, platinum, rhodium, ruthenium, osmium, iridium, gold, silver, copper, cobalt, tungsten, aluminum, and alloys thereof. 28. The interconnect device of claim 27, selected from the group.   28. The interconnect device of claim 27, wherein at least one layer is electroplated with inherent compressive stress.   28. The interconnect device of claim 27, wherein the at least one layer has at least one average grain size ranging from 3 nm to 500 nm. The coating has a plurality of different and sequentially electrodeposited films; and
Either the electrodeposited membrane generally decreases gradually from the innermost core to the outermost surface, and decreases substantially discretely from the innermost core to the outermost surface. 28. The interconnect device of claim 27, wherein the interconnect device is deposited.   28. The interconnect device of claim 27, wherein the anchor portion is attached to a substrate having a plurality of through vias filled therein with a conductive material.   28. The film layer of claim 27, wherein the membrane layer comprises at least one of the group of materials consisting of palladium, rhodium, platinum, iridium, osmium, ruthenium and cobalt, nickel, gold, silver, copper and alloys thereof. Interconnect equipment.   28. The interconnection element of claim 27, wherein the free portion has a size ranging from 10 μm to 1000 μm in length, from 3 μm to 500 μm in width, and from 0.1 μm to 40 μm in thickness. A method for manufacturing a plurality of miniaturized springs on a substrate, each of the miniaturized springs having a conductive core member, the core member being attached to an anchor portion and initially to the substrate And when released, has a free portion that extends away from the substrate due to an inherent stress gradient in the core, the free portion comprising a tip region at the end, and the anchor portion is A method of being fixed to the substrate,
Electroplating the spring core member with at least one membrane layer to cover all surfaces of the core member including free parts, without using a mask;
Selectively coating the tip region to form a contact button following the electroplating of the core member;
The method wherein the contact button has at least one conductive material that does not adhere strongly to the opposite contact pad or terminal.   38. The method of claim 37, wherein the at least one membrane layer is electroplated with inherent compressive stress.   38. The method of claim 37, wherein the at least one membrane layer is electroplated with an average grain size in the range of 3 to 500 nm.   40. The method of claim 39, wherein the grain size of at least one electroplated film is controlled by changing the additive composition of the electroplating bath and / or the current density in plating. The material used for the inner layer has a higher modulus of elasticity;
The material used for the outer layer has a smaller elastic modulus; and
38. The method of claim 37, wherein the modulus of elasticity of the layer gradually decreases from the innermost layer to the outermost layer, or decreases discretely from the innermost layer to the outermost layer.   38. The at least one film layer has at least one of Pt, Pd, Rh, Ir, Ru, Os, cobalt, nickel, gold, silver, copper, aluminum, tungsten; and an alloy thereof. The method described in 1.   38. The method of claim 37, wherein the substrate comprises any of ceramic, glass, silicon, quartz and organic materials.   38. The method according to claim 37, wherein the core member has any one of Mo, Cr, Ti, W, Zr, Mo—Cr, and Ti—W.   The electroplating of the core member is performed using through vias in the substrate to establish electrical contact to the core member from the substrate surface opposite the surface on which the core member is positioned; 38. The method of claim 37, further comprising:   The tip region is selectively coated either before the free part is released from the substrate and after the free part is released from the substrate to form the contact button. Item 38. The method according to Item 37.   The at least one conductive material is at least one member of the group consisting of Pt, Pd, Rh, Ir, Ru, Os, cobalt, nickel, gold, silver, copper, tungsten; and alloys thereof. 38. The method of claim 37, comprising:   38. The method according to claim 37, further comprising the step of forming a pattern of the core film by dry etching. Polishing the core film before deposition of the layer;
38. The method of claim 37, further comprising: optionally polishing the outermost surface using any of electrolytic polishing, chemical polishing and electrochemical polishing processes. A method for manufacturing a miniaturized spring on a substrate, each of the miniaturized springs having an anchor portion and a free portion, the free portion comprising a tip region at its end, and In a method for manufacturing a miniaturized spring on a substrate, wherein the width of the spring gradually decreases from the vicinity of the anchor portion to the tip region,
Depositing a core membrane member;
Patterning the body of the core membrane member to form the anchor portion and the free portion;
Releasing the free part from the substrate;
Depositing on the core membrane member at least one overlying membrane layer covering all surfaces of the core membrane member;
Applying a photoresist film to the core film member coated with the at least one overlaying film;
Patterning the photoresist film to expose a region of the tip region that is coated with the at least one overlying film;
Coating the exposed tip region covered with the at least one overlying membrane layer with a conductive contact material that minimizes contact adhesion resulting from repeated contact;
And removing the photoresist film from the core film member.   51. The method of claim 50, wherein the electroplating is performed using through vias in the substrate to establish electrical contact to the spring from the substrate surface opposite the surface on which the spring is positioned. .   51. The method of claim 50, wherein at least one overlying membrane layer is electroplated with inherent compressive stress.   51. The method of claim 50, wherein the at least one overlying membrane layer is electroplated with an average grain size in the range of 3 to 500 nm.   54. The method of claim 53, wherein the grain size of at least one electroplated film is controlled by changing the additive composition of the electroplating bath and / or the current density in plating. The material used for the inner membrane layer has a higher modulus of elasticity;
The material used for the outer membrane layer has a smaller elastic modulus; and
The elastic modulus of the membrane layer gradually decreases from the innermost membrane layer to the outermost membrane layer, or decreases discretely from the innermost membrane layer to the outermost membrane layer. Method.   51. The method of claim 50, wherein the contact material is deposited by any of electroplating, sputtering and chemical vapor reaction methods.   51. The method of claim 50, wherein the electroplating is performed using through vias in the substrate to establish electrical contact to the spring from the substrate surface opposite the surface on which the spring is positioned. .   The at least one overlying membrane layer of the core membrane member is at least one of Pt, Pd, Rh, Ir, Ru, Os, cobalt, nickel, gold, silver, copper, aluminum, tungsten; and 51. The method of claim 50, comprising an alloy of:   51. The method according to claim 50, wherein the contact material has any one of Co, Ni, Au, Cu, Ag, Pt, Pd, Rh, Ir, Ru, and Os.   51. The method of claim 50, wherein the substrate comprises any of ceramic, glass, silicon, quartz and organic materials.   51. The method according to claim 50, wherein the core film member has any one of Mo, Cr, Ti, W, Zr, Mo-Cr, and Ti-W.

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