JPH0342377Y2 - - Google Patents

Description

[Detailed description of the invention] (Field of industrial application) This invention performs electrical measurement and inspection of printed circuit boards and electronic components by contacting the test points of electronic components such as printed circuit boards and ICs. The present invention relates to contact probes for

(Prior Art) A contact probe already proposed in U.S. Pat. No. 3,435,168 has a plunger slidably provided in the opening of a conductive holding cylinder to prevent it from falling out, and the rear end of the plunger is tilted at an angle. A metal sphere is interposed between the bias cut surface and a coil spring enclosed in a holding cylinder. Then, the elasticity of the coil spring brings the sphere into elastic contact with the bias cut surface of the plunger, elastically biasing the plunger in the direction of protruding in the sliding direction, and at the same time, the component force acting on the bias cut surface perpendicular to the sliding direction The rear end of the plunger is brought into contact with the inner wall of the holding cylinder to ensure electrical connection between the plunger and the holding cylinder.

Therefore, when a contact probe is brought into contact with an inspection point on a printed circuit board, etc., a normal conductive path is formed through which current flows from the tip of the plunger to the rear end, through the holding tube, and then to the measuring device via a cable, etc. .

(Problems to be solved by the invention) By the way, in the conventional contact probe described above, the coefficient of friction of the metal sphere (for example, μ = about 0.18 even if it is made of iron and has a mirror finish) is relatively large. It is likely that the metal sphere cannot rotate smoothly between the coil spring and the bias cut surface, and a sufficient component force perpendicular to the sliding direction cannot be applied to the bias cut surface. In such a case, the rear end of the plunger cannot be brought into reliable contact with the holding tube, and dust and flux that have entered the holding tube are likely to get caught in the contact area between the plunger and the protective tube, causing damage to the plunger and the protective tube. The conductive path of the plunger is interrupted, and current tends to flow from the plunger to the metal sphere and then to the coil spring. As a result, the resistance value of about 20 milliohms in a normal conductive path increases to a resistance value of several ohms, resulting in an inspection result that appears as if the printed circuit board to be inspected is a defective product, even though it is a good product. There was a problem in that the reliability of the test was lacking because of the large amount of data obtained. In addition, as the current repeatedly flows from the plunger to the coil spring through the metal sphere as described above, the surface of the metal sphere becomes oxidized and becomes rough, further impeding the smoothness of rotation and further reducing the reliability of the test. Getting worse.

The purpose of the present invention was to solve the above-mentioned problems of conventional contact probes. It is an object of the present invention to provide a contact probe with high inspection reliability without forming any path other than a conductive path.

(Means for Solving the Problem) In order to achieve the above object, the contact probe of the present invention includes a holding tube whose inner layer is conductive at least, and a holding tube that can freely slide into the opening of the holding tube so as not to fall out. A plunger having a bias cut surface whose rear end is oblique with respect to the sliding direction, a coil spring that elastically biases the plunger in a direction to project from the holding cylinder, and the coil spring and the bias cut surface of the plunger. and a pressing member interposed between the contact probe and the pressing member, the pressing member being an insulator.

(Function) Since the pressing member interposed between the bias cut surface at the rear end of the plunger and the coil spring is made of an insulator, current does not flow from the plunger to the coil spring via the pressing member, and temporarily If the normal conductive path with the contact probe is interrupted, it can be immediately determined that the contact probe is malfunctioning.
The inspection results do not indicate that a good printed circuit board or the like is a defective product, and the reliability of the inspection can be improved.

(Description of Embodiments) Hereinafter, embodiments of the present invention will be described with reference to FIG. FIG. 1 is a sectional view of the contact probe of the present invention.

In FIG. 1, a contact probe 1 is arranged such that a plunger 3 is slidably inserted into an opening 2b at the other end of a protective tube 2, which has a constricted portion 2a formed at one end and a highly conductive layer such as gold plating formed on the inner layer. It is set up.
The plunger 3 is made of a good conductor and has a narrow diameter portion 3a in the middle, a sharply pointed needle portion 3b at the tip, and a bias cut surface 3c oblique to the sliding direction at the rear end. And protection tube 2
A projection 2c is formed facing the narrow diameter portion 3a of the plunger 3 to prevent the plunger 3 from coming off. Furthermore, a coil spring 4 is attached to the protective tube 2.
is enclosed, a sphere 5 is interposed between the rear part of the protective cylinder 2 and the coil spring 4, and a pressing member 5 is interposed between the bias cut surface 3c and the coil spring 4. This pressing member 5 is made of a spherical body made of an insulating material such as Teflon or plastic having a small coefficient of friction (μ=0.02). A cable 6 is connected to the constricted portion 2a at one end of the protection tube 2 by crimping or soldering.

The contact probe 1 having such a configuration has the following features:
The probe holder 7 is press-fitted into a socket 9 inserted into a hole 8 formed in the probe holder 7.

Here, the feature of the present invention is that the pressing member 5 interposed between the bias cut surface 3c and the coil spring 4 is composed of a spherical body made of an insulating material with a small coefficient of friction. By making this pressing member 5 an insulator, if the plunger 3 cannot come into contact with the protective tube 2 and the normal conductive path is interrupted, the pressing member 5 is an insulator and the plunger 3 A path from the contact probe 1 to the coil spring 4 is not formed, and it can be immediately determined that the contact probe 1 is malfunctioning. Therefore, unlike conventional contact probes, there is no possibility that a path other than the normal conductive path is formed and a test result that makes a good product appear as if it is a defective product is obtained, and the reliability of the test is improved. In addition, by reducing the friction coefficient of the pressing member 5, the bias cut surface 3c and the coil spring 4
Bias cut surface 3
A sufficient component force F perpendicular to the sliding direction due to c can be applied to the plunger 3, and the plunger 3
can be brought into contact with the protection tube 2 reliably. Therefore, the contact force of the plunger 3 to the protective tube 2 can be strengthened, so that dust, flux, etc. that have entered the protective tube 2 can be removed from the contact surface, and a normal conductive path can be ensured. .

The entire pressing member 5 may be formed of an insulating material with a small coefficient of friction such as Teflon, or it may be formed by covering the surface of a metal sphere with an insulating material.
A structure in which the surface is covered with an insulating material is easier and cheaper to manufacture than a structure in which the entire surface is made of an insulating material.

FIG. 2 is a sectional view of a main part of another embodiment of the contact probe of the present invention. In FIG. 2, the pressing member 15 has a shaft 15a on the coil spring 4 side and a conical portion 1 on the bias cut surface 3c side.
5b is formed into a top shape, and the whole is made of an insulating material such as Teflon or plastic, which has a small coefficient of friction. The shaft 15a is inserted into the coil spring 4 to regulate the posture of the pressing member 15, and the conical portion 15b
Press the bias cut surface 3c with the tip of the. Since the friction coefficient of the pressing member 15 is small, there is no need for rotation by a sphere as in conventional contact probes, and a component force F perpendicular to the sliding direction is applied to the plunger 3.
can be made to work.

FIG. 3 is a sectional view of a main part of still another embodiment of the contact probe of the present invention. In FIG. 3, the pressing member 25 has conical portions 25a at both ends.
25a, one conical part 25a
The coil spring 4 regulates the posture, and the other conical portion 25a presses the cut bias surface 3c.

Note that the contact probe of the present invention is not limited to the above-mentioned embodiments, and may have any structure as long as the pressing member is made of an insulator so that the path from the plunger 3 to the coil spring 4 is electrically interrupted. It may be formed of an insulating material such as ceramics other than plastic. Furthermore, if the part of the pressing member that comes into contact with the bias cut surface 3c is made of a material with a small coefficient of friction, the component force F perpendicular to the sliding direction can be applied to the plunger 3 sufficiently, compared to conventional contact probes. can be made to work,
The plunger 3 can be reliably brought into contact with the protection tube 2. Furthermore, it goes without saying that the cable 6 may be connected to other parts of the protection tube 2 or to the socket 9 electrically connected to the protection tube 2.

(Effects of the invention) As explained above, in the contact probe of the invention, the pressing member interposed between the bias cut surface at the rear end of the plunger and the coil spring is made of an insulator, so that the pressing member can be removed from the plunger. If no current flows through the coil spring and the normal conductive path between the plunger and the protective tube is interrupted, it can be immediately determined that the contact probe is faulty, and the printed circuit board, etc., is a good product, but it is treated as a defective product. However, the test result is not as bad as the above, and the test has an excellent effect of improving the reliability of the test.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the contact probe of the present invention, FIG. 2 is a cross-sectional view of main parts of another embodiment of the contact probe of the present invention, and FIG.
FIG. 7 is a sectional view of a main part of still another embodiment of the contact probe of the present invention. 1...Contact probe, 2...Protection tube, 3
...Plunger, 3c...Bias cut surface,
4... Coil spring, 5, 15, 25... Pressing member.

Claims (1)

[Claims for Utility Model Registration] (1) A holding cylinder whose inner layer is conductive at least, and a bias cut whose rear end is slidable at an angle with respect to the sliding direction so as not to fall through the opening of the holding cylinder. A plunger formed on a surface, a coil spring that elastically urges the plunger in a direction to project from the holding cylinder, and a pressing member interposed between the coil spring and the bias cut surface of the plunger. A contact probe, characterized in that the pressing member is made of an insulator. (2) The contact probe according to claim 1, wherein at least the member of the pressing member that contacts the bias cut surface is made of an insulating material with a small coefficient of friction. (3) The contact probe according to claim 1 or 2, wherein the pressing member is formed into a sphere by covering the surface of a metal sphere with an insulating material.