Device for measuring impedance of electronic component

The present invention relates to a device for measuring an impedance, such as a low impedance, of an electronic component.

Surface-mounted capacitors having a low equivalent series resistance (ESR) and a low equivalent series inductance (ESL) have been recently used in power supplies for central processing units (CPUs) used in computers in order to prevent voltage drop due to load fluctuation.

A surface-mounted capacitor has plural external terminals provided on a lower surface thereof. These external terminals are close to each other, hence providing a low ESL.

In order to perform circuit simulation for designing a precise and stable power supply, it is necessary to measure the ESR and ESL accurately. Accordingly, a device for measuring an impedance of the surface-mounted capacitor having the low ESR and the low ESL precisely is required.

A conventional device for measuring an impedance disclosed in Japanese Patent Laid-Open Patent Publication No. 8-110366 includes an elastic anisotropic conductive sheet. This sheet is provided between an external terminal of a surface-mounted component and a measuring probe in order to connect the external terminal of the surface-mounted component to the measuring probe.

In this conventional device, a pressure applied to the electronic component is uniformly applied to the anisotropic conductive sheet. This sheet cannot connect the external terminal stably to the measuring probe according to various surface flatness and surface configurations of the external terminal and the measuring probe, accordingly preventing the low ESR and the low ESL of the surface-mounted component from being measured accurately.

A device measures an impedance of an electronic component with using an impedance measuring apparatus. The electronic component includes first and second external terminals exposing on a surface. The impedance measuring device includes first and second probes to be connected to measuring terminals of the impedance measuring apparatus, an anisotropic conductive sheet, and a pressing member for pressing the electronic component toward the first and second probes. The first probe has a first contact surface. The second probe has a second contact surface flush with the first contact surface. The anisotropic conductive sheet has a first surface contacting the first and second contact surface, and a second surface opposite to the first surface. The pressing member causes the first and second external terminals of the electronic component to contact the anisotropic conductive sheet. The conductive sheet includes an insulating elastic sheet and plural conductive wires penetrating the elastic sheet to expose from the first surface and the second surface. The conductive wires electrically connect the first and second external terminals to the first and second contact surfaces, respectively.

This device can measure a low impedance of the electronic component accurately.

FIG. 1 is an exploded perspective view of a device for measuring an impedance of a surface-mounted electronic component according to Exemplary Embodiment 1 of the present invention.

FIG. 2 is a perspective view of the surface-mounted electronic component to be measured by the impedance measuring device according to Embodiment 1.

FIG. 3 is a schematic perspective view of a measuring probe of the device according to Embodiment 1.

FIG. 4A is a perspective view of an anisotropic conductive sheet of the device according to Embodiment 1.

FIG. 4B is a cross-sectional view of the anisotropic conductive sheet shown at line 4 B- 4 B shown in FIG. 4A .

FIG. 4C is a side view of the anisotropic conductive sheet shown in FIG. 4A .

FIG. 5A is a cross-sectional view of an essential part of the device according to Embodiment 1.

FIG. 5B is a side view of an essential part of the device according to Embodiment 1.

FIG. 6 is a cross-sectional view of an essential part of a device for measuring an impedance according to Exemplary Embodiment 2 of the invention.

Exemplary Embodiment 1

FIG. 1 is an exploded perspective view of device 1001 for measuring an impedance according to Exemplary Embodiment 1 of the present invention. FIG. 2 is a perspective view of surface-mounted electronic component 1 to be measured by device 1001 .

In device 1001 , measuring probes 5 A and 5 B that are electrically connected to impedance measuring apparatus 13 face each other at fixing stand 4 for fixing measuring probes 5 A and 5 B. Device 1001 includes anisotropic conductive sheet 6 and guard plate 12 provided between measuring probes 5 A and 5 B. Anisotropic conductive sheet 6 covers respective upper surfaces 105 A and 105 B of measuring probes 5 A and 5 B. Measuring probes 5 A and 5 B are arranged along direction D 3 . Surface-mounted electronic component 1 , an object to be measured, is inserted into through-hole 2 A formed in positioning member 2 and is mounted on anisotropic conductive sheet 6 . Surface-mounted electronic component 1 includes insulating case 7 made of insulating material, such as resin, and external terminals 8 A and 8 B exposing from lower surface 7 A of insulating case 7 . Surface-mounted electronic component 1 is pressed in direction D 1 toward measuring probes 5 A and 5 B with pressing member 3 . External terminals 8 A and 8 B are electrically connected to measuring probes 5 A and 5 B via anisotropic conductive sheet 6 , respectively.

FIG. 3 is a perspective view of measuring probes 5 A and 5 B. Measuring probe 5 A includes current-measuring probe 10 A and voltage-measuring probe 10 B separate from each other. Measuring probe 5 B includes current-measuring probe 10 C and voltage-measuring probe 10 D separated from each other. Current-measuring probes 10 A and 10 C are connected to current-measuring terminals 13 A and 13 C of impedance measuring apparatus 13 , respectively. Voltage-measuring probes 10 B and 10 D are connected to voltage-measuring terminals 13 B and 13 D of impedance measuring apparatus 13 , respectively. Measuring probes 10 A to 10 D are surrounded by shields 9 A to 9 D that have shielding effect against noise, respectively. Shields 9 A to 9 D are connected to guard plate 12 made of conductive material. Guard plate 12 eliminates stray impedance between measuring probes 5 A and 5 B. Measuring probes 10 A to 10 D have contact surfaces 110 A to 110 D contacting anisotropic conductive sheet 6 , respectively. Contact surfaces 110 A to 110 D expose upward from shields 9 A to 9 D, respectively, and are flush with each other, that is, are provided in upper surface 11 of fixing stand 4 . Shields 9 A to 9 D are connected to a ground of impedance measuring apparatus 13 . Fixing stand 4 connected to the ground of impedance measuring apparatus 13 is made of metal, and suppresses stray impedance.

Anisotropic conductive sheet 6 will be described below. FIG. 4A is a perspective view of anisotropic conductive sheet 6 . FIG. 4B is a cross-sectional view of anisotropic conductive sheet 6 at line 4 B- 4 B shown in FIG. 4A . FIG. 4C is a side view of anisotropic conductive sheet 6 shown in FIG. 4D seen from direction D 2 . In FIG. 4A to FIG. 4C , no pressure is applied to anisotropic conductive sheet 6 .

As shown in FIG. 4A , anisotropic conductive sheet 6 has elastic sheet 14 having an insulating property. Elastic sheet 14 has upper surface 14 A and lower surface 14 B opposite to upper surface 14 A. Plural contacts 16 A protrude from upper surface 14 A of elastic sheet 14 while plural contacts 16 B protrude from lower surface 14 B.

As shown in FIG. 4B , plural conductive wires 15 are provided in elastic sheet 14 that penetrate from upper surface 14 A to lower surface 14 B. Each of conductive wires 15 is connected to contacts 16 A and 16 B. Direction D 2 is perpendicular to direction D 3 along which measuring probes 5 A and 5 B are arranged. Direction D 2 crosses direction D 3 . Conductive wires 15 extend from upper surface 14 A of elastic sheet 14 toward lower surface 14 B and incline at angle Φ with respect to thickness direction D 4 which directs from upper surface 14 to lower surface 14 B of elastic sheet 14 . Conductive wires 15 have stiffness.

As shown in FIGS. 4B and 4C , conductive wires 15 extend in thickness direction D 4 without inclining in direction D 3 , and are aligned at constant intervals without inclining to the left and right seen from direction D 2 crossing direction D 3 . Conductive wires 15 incline toward direction D 2 crossing direction D 3 along which measuring probes 5 A and 5 B are arranged, and are not perpendicular to upper surface 14 A of elastic sheet 14 . When anisotropic conductive sheet 6 is pressed in direction D 1 , elastic sheet 14 elastically deforms more easily in direction D 2 than in direction D 3 . Conductive wires 15 are arranged at the constant intervals and incline in single direction D 2 , hence providing conductive sheet 6 with uniform elasticity and high conductivity.

Inclining angle Φ of conductive wires 15 ranges preferably from 0° to 45°, and reduces an increase of equivalent series impedance, namely, an equivalent series resistance (ESR) and an equivalent series inductance (ESL), of anisotropic conductive sheet 6 .

Elastic sheet 14 is preferably made of silicone rubber. The thickness of elastic sheet 14 ranges preferably from 0.1 mm to 3.0 mm. Elastic sheet having a thickness greater than 3.0 mm causes conductive wires 15 to be long, accordingly causing anisotropic conductive sheet 6 to have a large resistance. Elastic sheet 14 having a thickness smaller than 0.1 mm prevents elastic sheet 14 from deforming elastically according to surface configurations of external terminals 8 A and 8 B of surface-mounted electronic component 1 and contact surfaces 110 A to 110 D of measuring probes 10 A to 10 D.

In order to easily remove dust attached onto anisotropic conductive sheet 6 with an adhesive sheet or air, the surfaces of elastic sheet 14 may be preferably processed with surface treatment, such as fluorine-resin processing.

Conductive wires 15 are made of conductive metal, such as platinum, tungsten, silver, copper, copper alloy, or tin alloy as to reduce connection resistance between contacts 16 A and 16 B to increase connection strength. Conductive wires 15 may be made preferably of material, such as non-oxidizing metal, having a low resistance. Conductive wires 15 may be made of material plated with tin or bismuth which hardly has an insulating property by oxidation.

The diameter of conductive wire 15 ranges preferably from 30 μm to 500 μm. The diameter of each of conductive wires 15 may be determined appropriately according to the rigidity of the metal of the wires in order to be prevented from breaking or deforming due to repetitive elastic deformation of anisotropic conductive sheet 6 . The shapes and the intervals of conductive wires 15 may be determined according to the sizes of external terminals 8 A and 8 B and to the interval between the terminals.

Contacts 16 A and 16 B protrude from upper surface 14 A and lower surface 14 B of elastic sheet 14 , respectively, accordingly being connected electrically to measuring probes 5 A and 5 B and external terminals 8 A and 8 B, respectively. Contacts 16 A and 16 B preferably have dome shapes or substantially-hemispherical shapes. These shapes allow contacts 16 A and 16 B to contact external terminals 8 A and 8 B and measuring terminals 5 A and 5 B at certain points on the surfaces of contacts 16 A and 16 B according to the deformation of elastic sheet 14 , thereby securely providing electrical connection.

Each of contacts 16 A and 16 B preferably has a maximum external widths ranging from 30 μm to 500 μm. The maximum external width smaller than 30 μm may prevent contacts 16 A and 16 B from being bonded firmly to conductive wires 15 . The maximum external width greater than 50 μm may cause contacts 16 A adjoining each other to contact each other and may cause contacts 16 B adjoining each other to contact each other if conductive wires 15 incline too much, hence preventing elastic sheet 14 from deforming.

Contacts 16 A and 16 B are preferably made of wear-resistant and low contact resistance conductive material, such as nickel and platinum. Contacts 16 A and 16 B may be plated with tin or bismuth which hardly has an insulating property due to oxidation. Contacts 16 A and 16 B may be formed unitarily with conductive wires 15 rather than separated from conductive wires 15 .

Positioning member 2 is made of an insulating plate and has through-hole 2 A formed therein. Positioning member 2 regulates the position of surface-mounted electronic component 1 as to cause external terminals 8 A and 8 B to be connected electrically to measuring probes 5 A and 5 B, respectively. Positioning member 2 prevents surface-mounted electronic component 1 from being displaced upon being pressed with pressing member 3 . Through-hole 2 A may be a notch.

A method of measuring impedance of surface-mounted electronic component 1 with using impedance measuring device 1001 will be described below. FIGS. 5A and 5B are a cross-sectional view and a side view of essential parts of impedance measuring device 1001 during measurement, respectively.

First, surface-mounted electronic component 1 is mounted on anisotropic conductive sheet 6 , while being placed in through-hole 2 A of positing member 2 provided on anisotropic conductive sheet 6 .

Then, as shown in FIGS. 5A and 5B , surface-mounted electronic component 1 is pressed with pressing member 3 in direction D 1 with a predetermined pressure. Upon being pressed, anisotropic conductive sheet 6 (elastic sheet 14 ) deforms elastically to contact external terminals 8 A and 8 B and contact surfaces 110 A to 110 D of measuring probes 10 A to 10 D.

As shown in FIG. 5A , conductive wires 15 incline further in direction D 2 crossing direction D 3 according to the deformation of anisotropic conductive sheet 6 (elastic sheet 14 ). As shown in FIG. 5B , the inclining of conductive wires in direction D 3 is smaller than the inclining of the wires in direction D 2 . External terminal 8 A is electrically connected to contact surfaces 110 A and 110 B via conductive wires 15 and contacts 16 A and 16 B. External terminal 8 B is electrically connected to contact surfaces 110 C and 110 D via conductive wires 15 and contacts 16 A and 16 B. External terminal 8 A is not electrically connected to contact surface 110 C or 110 D. External terminal 8 B is not electrically connected to contact surface 110 A or 110 B.

Conductive wires 15 penetrating in thickness direction D 4 allows anisotropic conductive sheet 6 to have a small loss at high frequencies of anisotropic conductive sheet 6 , and accordingly enables the impedance of surface-mounted electronic component 1 to be measured accurately even if the impedance is low.

Conductive wires 15 incline according to the deformation of pressed elastic sheet 14 , and thereby, allows external terminals 8 A and 8 B to be electrically connected stably to measuring probes 10 A and 10 B even when external terminals 8 A and 8 B have variations in processing or even when external terminals 8 A and 8 B incline due to the inclining of surface-mounted electronic component 1 .

Measuring probes 5 A and 5 B are connected to external terminals 8 A and 8 B, respectively. Conductive wires 15 are inclines more in direction D 2 crossing direction D 3 than in direction D 3 , accordingly preventing measuring probe 5 A from being connected electrically to external terminal 8 B and preventing measuring probe 5 B from being connected electrically to external terminal 8 A.

A surface-mounted solid electrolytic capacitor as the surface-mounted electronic component 1 has a resonant frequency ranging from 100 kHz to 10 MHz and an impedance of several milli-ohms at the resonant frequency. A balanced-bridge type impedance analyzer as impedance measuring apparatus 13 can measure such a low impedance of the surface-mounted solid electrolytic capacitor accurately.

Exemplary Embodiment 2

FIG. 6 is a cross-sectional view of an essential part of impedance measuring device 2001 according to Exemplary Embodiment 2 of the present invention. In FIG. 6 , components similar to those of impedance measuring device 1001 shown in FIG. 1 according to Embodiment 1 are denoted by the same reference numerals, and their description will be omitted. Impedance measuring device 2001 according to Embodiment 2 includes pressing member 17 A instead of pressing member 3 of impedance measuring device 1001 shown in FIG. 1 according to Embodiment 1.

FIG. 6 is a cross-sectional view of pressing member 17 A along direction D 2 crossing direction D 3 shown in FIG. 1 . Pressing member 17 A includes pressing frame 17 made of insulating material. Pressing frame 17 is formed to have a recess formed therein. The upper portion of surface-mounted electronic component 1 is arranged to be inserted into the recess. Pressing frame 17 having the recess prevents surface-mounted electronic component 1 from being displaced when pressing the component. Further, a load pressure is produced in a direction crossing direction D 3 from a side or an edge of an upper surface of surface-mounted electronic component 1 . This load pressure causes a pressure applied to anisotropic conductive sheet 6 in direction D 2 crossing direction D 3 , and accordingly, causes conductive wires 15 to incline reliably in direction D 2 , thus enabling a low impedance of surface-mounted electronic component 1 to be measure accurately.

Pressing member 17 A includes shield member 19 made of conductive material, such as metal mesh, provided on its inner surface opposite to surface-mounted electronic component 1 . Pressing member 17 A further includes elastic insulating member 18 provided on the inner surface of shield member 19 .

Shield member 19 surrounds surface-mounted electronic component 1 as to reduce noises existing around surface-mounted electronic component 1 , and accordingly, improves accuracy of the impedance measurement. Shield member 19 is connected to a ground of impedance measuring apparatus 13 , thereby eliminating stray impedance.

Elastic insulating member 18 allows pressing member 17 A to uniformly press surface-mounted electronic component 1 from above.

Pressing frame 17 may be made of conductive material. In this case, pressing frame 17 functions as a shield member to be connected to the ground of impedance measuring apparatus 13 .