GB2066590A - Test pin - Google Patents

Abstract

A test pin (10) has a spring- loaded plunger (24) which is offset to one side to ensure electrical contact between it and a conductive housing (18). The means for providing the offset may comprise an upper portion (30) of a spring (28) bent to one side. <IMAGE>

Description

SPECIFICATION Test pin This invention relates to test pins useful, for example, in testing the electrical characteristics of printed circuit boards (PCB's).

Spring-loaded test pins are known in the art.

U.S. Patent 4,105,970 discloses a test pin assembly having a cylindrical plunger with a PCBcontacting crown, the plunger being slidably mounted within a tubular housing and spring biased. A problem that has been noted with such a construction is that occasionally there will be insufficient contact force between the lower portion of the plunger and the housing, resulting in lack of electrical contact between the PCB and the analyzing instrument.

It has been discovered that improved electrical contact can be provided for a test pin assembly by including means to bias the plunger, thereby improving electrical contact between the plunger and housing. In a preferred embodiment the upper portion of the spring that engages the plunger is tilted at an angie prior to its connection to the plunger in the assembly of the test pin and is offcenter.

Presently preferred embodiments of the invention will now be more particularly described by way of example and with reference to the accompanying drawings in which: Fig. 1 is a vertical sectional view, partially broken away, of a portion of a test pin assembly of the invention; and Fig. 2 is a side elevation view of the spring of one of the preferred embodiment.

There is shown in Fig. 1 portion 10 of an upper assembly of a test pin similar to that disclosed in U.S. Patent 4105970. Tubular housing 12 has dimple 14 for frictionally engaging insert 1 6, which has edge 1 8 of narrow diameter. Plunger 20 has pointed crown 22 on its upper end, iarge diameter portion 24 and tapered portion 26, which is biased against upper edge 1 8 by spring 28. Housing 12, insert 16, and plunger 20 are all made of hardened beryllium copper, plated with nickel and then gold. Spring 28 is made of stainless steel 5/1000 of an inch in diameter with a total of 31 turns. Spring 28 has two windings 30 at its upper end which are of a smaller diameter and frictionally engage stud 32 of plunger 20. Fig.

1 is diagrammatic in that the left-hand side of insert 1 6 is not shown forced against the inner surface of the left-hand wall of housing 12, but in reality it is so forced by dimple 14. Although not evident in Fig. 1, the upper end windings 30 are offset 450 to the right with respect to the rest of the spring (Fig. 2), thereby forcing portion 24 of plunger 20 against the inner surface of the righthand wall of insert 18.

Operation of test pins is well known in the art.

With the test pin of the present invention, accidental, occasional undesired open circuits to the test pin crown are prevented.

Improved contact results not only from the forcing of plunger portion 24 against insert 18, but as well because of an electrical path through stud 32, the spring turns gripping it, and the top largerdiameter spring turn diagrammatically shown touching insert 1 6.

In another embodiment, the spring is symmetrical about a single straight line axis, but the stud axis is not coaxial therewith.

1. A test pin comprising: a tubular shaped housing, a plunger with a contacting end that is slidably mounted within said housing, a spring carried in said housing for resiliently biasing said plunger away from said spring, and means to offset said plunger to one side, whereby electrical contact between said plunger and said housing is improved.

2. The test pin of claim 1 in which said offset means is an upper smaller diameter portion of said spring bent to one side, said upper portion engaging said plunger.

3. A test pin substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Test pin This invention relates to test pins useful, for example, in testing the electrical characteristics of printed circuit boards (PCB's). Spring-loaded test pins are known in the art. U.S. Patent 4,105,970 discloses a test pin assembly having a cylindrical plunger with a PCBcontacting crown, the plunger being slidably mounted within a tubular housing and spring biased. A problem that has been noted with such a construction is that occasionally there will be insufficient contact force between the lower portion of the plunger and the housing, resulting in lack of electrical contact between the PCB and the analyzing instrument. It has been discovered that improved electrical contact can be provided for a test pin assembly by including means to bias the plunger, thereby improving electrical contact between the plunger and housing. In a preferred embodiment the upper portion of the spring that engages the plunger is tilted at an angie prior to its connection to the plunger in the assembly of the test pin and is offcenter. Presently preferred embodiments of the invention will now be more particularly described by way of example and with reference to the accompanying drawings in which: Fig. 1 is a vertical sectional view, partially broken away, of a portion of a test pin assembly of the invention; and Fig. 2 is a side elevation view of the spring of one of the preferred embodiment. There is shown in Fig. 1 portion 10 of an upper assembly of a test pin similar to that disclosed in U.S. Patent 4105970. Tubular housing 12 has dimple 14 for frictionally engaging insert 1 6, which has edge 1 8 of narrow diameter. Plunger 20 has pointed crown 22 on its upper end, iarge diameter portion 24 and tapered portion 26, which is biased against upper edge 1 8 by spring 28. Housing 12, insert 16, and plunger 20 are all made of hardened beryllium copper, plated with nickel and then gold. Spring 28 is made of stainless steel 5/1000 of an inch in diameter with a total of 31 turns. Spring 28 has two windings 30 at its upper end which are of a smaller diameter and frictionally engage stud 32 of plunger 20. Fig. 1 is diagrammatic in that the left-hand side of insert 1 6 is not shown forced against the inner surface of the left-hand wall of housing 12, but in reality it is so forced by dimple 14. Although not evident in Fig. 1, the upper end windings 30 are offset 450 to the right with respect to the rest of the spring (Fig. 2), thereby forcing portion 24 of plunger 20 against the inner surface of the righthand wall of insert 18. Operation of test pins is well known in the art. With the test pin of the present invention, accidental, occasional undesired open circuits to the test pin crown are prevented. Improved contact results not only from the forcing of plunger portion 24 against insert 18, but as well because of an electrical path through stud 32, the spring turns gripping it, and the top largerdiameter spring turn diagrammatically shown touching insert 1 6. In another embodiment, the spring is symmetrical about a single straight line axis, but the stud axis is not coaxial therewith. CLAIMS

1. A test pin comprising: a tubular shaped housing, a plunger with a contacting end that is slidably mounted within said housing, a spring carried in said housing for resiliently biasing said plunger away from said spring, and means to offset said plunger to one side, whereby electrical contact between said plunger and said housing is improved.

2. The test pin of claim 1 in which said offset means is an upper smaller diameter portion of said spring bent to one side, said upper portion engaging said plunger.

3. A test pin substantially as hereinbefore described with reference to the accompanying drawings.