ABRASIVE MATERIAL FOR THE NEEDLE POINT OF A PROBE CARD

Abstract: An abrasive material for the needle point of a probe card which can effectively remove foreign matter adhering to the needle point of the probe, protect the needle point from damage and deformation, and prolong the life of the probe. The abrasive material for the needle point of a probe card comprises an abrasive layer including a layer of micro-powdered abrasive grains applied to a substrate and a cushion layer having a buffer action and elasticity.

Description: ABRASIVE MATERIAL FOR THE NEEDLE POINT OF A PROBE CARD BACKGROUND OF THE INVENTION Field of the Invention The present invention generally relates to an abrasive material for cleaning the needle point of a probe card and particularly relates to an abrasive material, which is capable of removing foreign matter adhering to the needle point of the probe card that is used to measure the electrical characteristics of a semiconductor chip formed on a semiconductor wafer. Description of the Background Art The probe of a probe card for measuring the electrical characteristics of a semiconductor chip formed on a semiconductor wafer is pressed against and contacted with the pad of the semiconductor chip. At this time, aluminum powder scraped from the pad of the semiconductor chip adheres to the tip (needle point) of the probe. If the aluminum powder is not removed from the needle point, aluminum remaining on the needle point is oxidized to aluminum oxide, allowing the resistance between the probe and the pad to be increased. Because the electrical contact is impaired, a continuity defect occurs so that the electrical characteristics cannot be exactly determined. For this, there are methods by which the needle point is cleaned every prescribed number of probes to remove the aluminum powder. The following methods are used to remove the aluminum powder. (1) Methods using a grinding stone (see Japanese Patent Applications Laid-open No. 209896/1993, No. 96342/1992, and No. 2657/1988, and Japanese Utility Model Application Laid-open No. 11167/1992). (2) Methods using a sanding plate (see Japanese Patent Applications Laid-open No 166893/1993, No. 177849/1992, No.105940/1991, No. 10176/1991, and No. 152034/1986, and Japanese Utility Model Application Laid-open No. 26772/1995). (3) Methods using a ceramic plate (see Japanese Patent Applications Laid-open No. 4969/1986 and No. 282829/1989, Japanese Utility Model Application Laid-open No. 55338/1986 , Japanese Patent Applications Laid-open No. 2939/1990, No. 55835/1989, and No. 170933/1988). (4) A method using abrasive grains (Japanese Utility Model Application Laid-open No. 97840/1986). (5) A method using a frosted glass (see Japanese Patent Application Laid-open No. 199141/1995). (6) A method using a glass coating (see Japanese Patent Application Laid-open No. 76242/1991). In these methods, the needle point is pressed against the pad in the same manner as in the probing operation to remove the aluminum powder. However, there are the following problems in these methods. (1) The needle point breaks. (2) Aluminum powder adhering in clearance gaps cannot be removed because the intervals between the concave and convex parts of the surface of the ceramic plate are in the range of 1-12 μm, while those of the needle point (contact surface) are 0.35 μm approximately. (3) The needle point is worn down so that the life of the probe is short. (4) The shape of the needle point tends to be deformed under the same load (about 2.5 kgf) as in the probing operation. Also, a method using a cleaning material in which micro-powdered abrasives are compounded in a base material is disclosed (see Japanese Patent Application Laid-open No. 244074/1995). In this method, the cleaning material can prolong the life of the probe. However, the above problems (1), (2), and (4) cannot be solved by the use of the cleaning material. The present invention has been achieved in view of this situation and has an object of providing an abrasive material for the needle point of a probe card which is capable of effectively removing foreign matter adhering to the needle point of the probe, of avoiding damage to and deformation of the needle point, and of prolonging the life of the probe. SUMMARY OF THE INVENTION The above object can be attained in the present invention by the provision of an abrasive material for the needle point of a probe card comprising: an abrasive layer including a layer of micro-powdered abrasive grains applied to a substrate, and a cushion layer having a buffer action and elasticity. In preferred embodiments of the present invention, the surface of the abrasive layer contacting the needle point of the probe card has an irregular pattern corresponding to the pattern of the needle point of the probe card; and the cushion layer consists of a modacrylic resin. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic sectional view of an embodiment of the abrasive material for the needle point of a probe card of the present invention. Figure 2 is a schematic sectional view showing the relation between the shape of the abrasive layer and the shape of the needle point of the probe card in the present invention. DETAD ED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENT The present invention will be explained in detail by way of an embodiment of the present invention with reference to the drawings. As shown in Figures 1 and 2, the abrasive material for the needle point of a probe card in the present invention includes an abrasive layer 3 provided with micro-powdered abrasive grains 5 arranged on a substrate 1, and a cushion layer 4 having a buffer action and elasticity. Abrasive Layer The abrasive layer 3 used in the present invention includes an abrasive grain layer 2 applied to the substrate 1. Substrate It is desirable that the substrate 1 give a specific stiffness to the abrasive grain layer 2 because the abrasive material of the present invention is mounted on a specific machine together with the probe card and is automatically moved, mounted, and dismounted. Specifically, given as materials for the substrate 1 are polyethylene terephthalate (PET), polyethylene naphthalate, vinyl chloride, polypropylene, and pulp cloth. It is desirable that the thickness of the substrate 1 be, for example, in a range of from 12 to 250 μm although there are no limitations to the thickness. Abrasive Grain Layer As the abrasive grains 5 used in the abrasive grain layer 2, it is preferable to select and arrange grains having such an average particle diameter that the shape of the needle point is in accord with the irregular shape of the needle point 6 to promote lapping and cleaning efficiencies. It is preferable to use grains having an average particle diameter of the same or smaller magnitude as the intervals between the concave part and convex part (hereinafter called "irregular intervals") of the needle point 6. When using a needle point 6 having irregular intervals of 0.35 μm, the surface roughness (Sm) of the abrasive layer is preferably less than 0.35 μm. Also, it is desirable that the average particle diameter of the abrasive grains 5 be 0.5 μm-3 μm. By this structure, as shown in Figure 2, the tip of the abrasive grains 5 can be inserted into the convex part of the needle point in accordance with the irregularity of the needle point to effectively remove foreign matter. The following materials may be used for the abrasive grain layer 2 though there are no limitations to the materials: alumina, silicon carbide, chromium oxides, CBN, diamond powder, cerium oxide, silicon oxide (SiO 2 ), and zirconium oxide (Zr 2 O 3 ). Though there are no limitations to the application of the abrasive grain layer 2 on the substrate 1, for example, slurry coatings such as a gravure coating, knife coating, and the like, electrostatic coatings, drop coatings, and the like may be used. It is desirable to arrange the density distribution of the abrasive grains in the abrasive grain layer 2 according to the average particle diameter of the abrasive grains so that the surface shape of the abrasive layer 3 corresponds with the irregular shape of the needle point 6. The thickness of the substrate 1 is preferably in a range of from 15 to 300 μm. If the thickness is less than 15 μm, the strength of the abrasive layer 3 is so reduced that the abrasive layer 3 tends to be broken. Also, if the thickness exceeds 300 μm, the handling characteristics are impaired. Cushion Layer For the cushion layer 4 used in the present invention, elasticity and buffer action are required to avoid damage to and deformation of the needle point when the abrasive layer 3 contacts the needle point 6, and to prolong the life of the probe The following material characteristics are required for the cushion layer 4. 3 For example, the preferable bending elastic modulus is in a range of from 1.2 x 10 3 2 to 9.0 x 10 kg/cm when using foamed materials as the cushion layer, and the preferable shore hardness A is in a range of from 30 to 90 when rising rubbers or modacrylic materials as the cushion layer. Specific examples of materials for the cushion layer 4 are acrylic resins, synthetic rubbers, and foamed materials. By this construction, forced pressure (load by pressure) between the cushion 2 layer 4 and the needle point 6 can be in a range of from 0.3 to 0.5 kg/cm . The thickness is preferably in the range of 300 μm to 500 μm. If less than 300 μm, the load by pressure becomes overloaded, and if more than 500 μm, it becomes difficult to handle the cushion layer itself. Though there are no limitations to the method for laminating the abrasive layer 3 to the cushion layer 4, a method using a pressure sensitive adhesive or bond, e.g., hotmelt, may be used. The abrasive material of the present invention has a two-layer structure consisting of the abrasive layer 3 and the cushion layer 4. Therefore, the abrasive material of the present invention possesses appropriate stiffness, elasticity, and buffer action. Also, the present invention can effectively provide desirable abrasive materials by independently providing the abrasive layer 3 and the cushion layer 4 and combining them according to the characteristics or specifications required for the probe card. EXAMPLES The present invention will be explained in more detail by way of examples, which are not intended to be limiting of the present invention. Provided as the abrasive layer was a superfine film abrasive (Imperial Lapping Film™ (aluminum oxide 1 mil 1 μm type DH) manufactured by Sumitomo 3M Ltd.), which was produced by compounding abrasive grains consisting of aluminum oxide with an average diameter of 0.1 μm with a polyester resin in a ratio of 4:1 and applying the resulting mixed material to a polyethylene terephthalate film with a thickness of 24 μm by a slurry coating. Also, provided as the cushion layer was a structural bonding tape with a thickness of 1.0 mm (VHB Y-4910J™, manufactured by Sumitomo 3M Ltd.) which contained an acrylic resin as a major component and had an appropriate stickiness and a shore hardness of 50. The superfine film abrasive and the structural bonding tape were laminated and pressed to prepare the abrasive material of the present invention. Using this abrasive material, the needle point of a probe was lapped and cleaned. As a result, the intervals between the concave and convex portions of the abrasive layer were reduced to less than 0.35 μm and the pressure load could be reduced to about 0.3 kgf. By using this abrasive material for lapping and cleaning the needle point of the probe card, it was possible to lap and clean the needle point without deformation of the shape of the needle point, to reduce the wear of the needle point, to prolong the life of the probe, and to reduce the contact resistance. As shown by the above explanations, the present invention can provide an abrasive material for the needle point of a probe card which can effectively remove foreign matter adhering to the needle point of the probe, efficiently protect the needle point from damage and deformation, and prolong the life of the probe.

Claims: WHAT IS CLAIMED IS: 1. An abrasive material for the needle point of a probe card comprising: an abrasive layer including a layer of micro-powdered abrasive grains applied to a substrate, and a cushion layer having a buffer action and elasticity. 2. The abrasive material for the needle point of a probe card according to claim 1, wherein the surface of the abrasive layer contacting the needle point of the probe card has an irregular pattern corresponding to the pattern of the needle point of the probe card. 3. The abrasive material for the needle point of a probe card according to claims 1 and 2, wherein the cushion layer consists of a modacrylic resin.

Inventors: KAMATA NAOYA, MAEDA TOSHIRO, TANAKA KAZUO, YOSHIZUMI REIJI, KAMATA, NAOYA, MAEDA, TOSHIRO, TANAKA, KAZUO, YOSHIZUMI, REIJI
Applicants: KAMATA NAOYA, MAEDA TOSHIRO, MINNESOTA MINING & MFG, NIPPON ELECTRIC CO, TANAKA KAZUO, YOSHIZUMI REIJI, KAMATA, NAOYA, MAEDA, TOSHIRO, MINNESOTA MINING AND MANUFACTURING COMPANY, NEC CORPORATION, TANAKA, KAZUO, YOSHIZUMI, REIJI
Application year: 1998
Main classification: B24D15
IPC codes: B24B19, B24D3, B24D11, B24D15, G01R1, H01L21