GB2178604A

GB2178604A - Apparatus for use in testing a printed circuit board

Info

Publication number: GB2178604A
Application number: GB08612929A
Authority: GB
Inventors: Brian Diggle
Original assignee: Fujitsu Services Ltd
Current assignee: Fujitsu Services Ltd
Priority date: 1985-07-25
Filing date: 1986-05-28
Publication date: 1987-02-11
Also published as: GB8612929D0; GB8518861D0; GB2178604B

Abstract

An interposer device, which converts the pattern of a bed-of-nails tester to the pattern required by a printed circuit board to be tested, comprises a pair of spaced apart plates (8,9) of insulting material, one of which (9) has conductive elements (11) extending therethrough corresponding in position with the test probes of the bed-of-nails tester and the other one (8) containing apertures (19) corresponding to the test locations of the circuit board to be tested. Conductive pins (18) are retained at one end by the conductive elements (11) and extend through the apertures (19) provide test probes at the locations required by the circuit board under test. Each conductive element (11) is formed with spring contacts (16) which resiliently grip a pin (18). <IMAGE>

Description

SPECIFICATION Apparatus for use in testing a printed circuit board The present invention relates to apparatus for use in testing a printed circuit board.

One device used for printed circuit board testing is commonly known as a bed-of-nails tester and comprises rows and columns of test probes arranged in a regular pattern and projecting from a flat surface. The test probes may be spring-loaded and when a circuit board is brought into engagement with the device, the probes contact test locations at various parts of the circuitry on the board.

A disadvantage with this arrangement, however, is that, due to the regular pattern and fixed pitch of the test probes, a test probe is not always aligned with every required test location.

It has previously been proposed to utilise an interposer device which effectively converts the regular pattern and fixed pitch of the bedof-nails tester to the patterns and locations required by a circuit board to be tested. Such a device consists essentially of a pair of spaced apart plates of insulating material, a lower one of which contains conductive elements extending therethrough and corresponding in position with the test probes of the bed-of-nails tester and an upper one containing apertures corresponding to the test locations of the circuit board to be tested. Flexible pins rest on the conductive elements of the lower plate and extend upwards through the apertures of the upper plate to provide test probes in the positions required by the circuit board under test.

One disadvantage with this arrangement is, that as the pins rely on gravity to retain them in position, they are easily dislodged and can fall out of the device.

According to one aspect of the present invention apparatus for testing a printed circuit board having a plurality of test locations thereon includes: a bed-of-nails tester comprising a plurality of probes arranged in positions different from said test locations; and an interposer device including a plurality of conductive pins, one end of each of the pins being retained in a conductive member located so as to correspond with one of the test probes and opposite ends of the pins projecting from the device at locations corresponding with said test locations.

According to a further aspect of the invention an interposer device for use in testing a printed circuit board includes: a pair of spaced apart planar insulating members, one of the members having a plurality of conductive retaining elements extending therethrough and being arranged in a first pattern and the other member having a plurality of apertures extending therethrough, the apertures being arranged in a second pattern different to said first pattern; and conductive pins retained at one end by the retaining elements, the other ends of the pins projecting through the apertures of said other member.

Apparatus for testing a printed circuit board will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a schematic diagram of a printed circuit board under test using an interposer device, Figure 2 shows part of the interposer device in more detail, and Figure 3 shows a test pin retaining element.

Referring to Figs. 1 and 2 of the drawing, a printed circuit board 1 which is to be tested carries conductive test locations such as, for example, conductive pads 2 which may be connected to conductive tracks (not shown).

In order to test the circuit board 1 conductive probes are required to be applied to the conductive pads 2. The pads 2 may be distributed over the circuit board 1 in a random fashion or may, for example, be arranged in groups or patterns.

A conventional bed-of-nails tester 4 comprises a flat base 5 from which test probes 6 extend. The test probes 6 are spring-loaded to ensure good electrical contact with conductive locations on a circuit board under test. In a typical bed-of-nails tester the probes 6 may be arranged in a regular pattern of rows and columns spaced at 2.5mm. It will be realised that although such a device is useful in applications where the test locations correspond with at least a considerable proportion of the test probes it is not suitable for testing a circuit board where this is not the case, as with the circuit board 1.

In order to utilise the conventional bed-ofnails tester 4 to test the circuit board 1 an interposer device 7 is provided. The interposer device 7 consists of a pair of flat plates 8 and 9 formed from insulating material. Spacers 10 secure the plates 8 and 9 together in spaced relationship. Conductive bushes 11 extend through holes 12 in the plate 9 and are arranged in rows and columns, their positions corresponding to the positions of the test probes of the bed-of-nails tester 4. The bushes 11, shown more clearly in Fig. 3, are a loose fit in the holes 12 and include a central aperture 13, which does not extend all the way through the bush, and a flange 14. The flanges 14 are accommodated in counter bores 15 in the plate 9.A cylindrical spring member 16 (shown in broken lines) and formed from a suitable material such as, for example, phosphor bronze, is secured within the apertures 13. The spring member 16 has inwardly projecting portions 1 7 and is arranged to receive and grip conductive pins 18.

The pins 18 extend through holes 19 in the plate 8, the holes 19 being positioned so as to correspond with the conductive pads 2 on the circuit board 1. Enlarged rounded portions 20 are provided on the ends of the pins 16. It will be noted that, due to the different spacings of the bushes 11 and the holes 17, the pins assume leaning attitudes. This lean is accommodated by the resilience of the inwardly projecting portions 17 of the spring members 16.

In operation the interposer device 7 is placed upon the bed-of-nails tester 4 so that the test probes 6 of the bed-of-nails tester engage the flanges 14 of the bushes 11. In order to accomplish this, spacers 21 support the device in such a way that the test probes 6 are depressed against their spring loadings to provide good electrical contact with the flanges 14. It will be noted that the flanges 14, in addition to determining the extent of axial movement of the bushes 11 in the plate 9, also provide flat surfaces of increased area to facilitate contact with the test probes 6.

The circuit board 1 under test is placed over the plate 8 of the interposer device 7 so that the conductive pads 2 are aligned with the end portions 20 of the flexible pins 18. Spacers 22 support the circuit board 1 and space it from the plate 8. The spacing is such that a downward pressure is applied to the pins 18 which is transmitted through the pins to cause the bushes 11 to move in the holes 12 thereby depressing the test probes 6 of the bed-of-nails tester. Thus, the rounded ends 20 of the pins 18 are urged into contact with the conductive pads 2, the contact pressure being determined by the spring loading of the test probes 6.

It will be realised that the interposer device of the present application provides a more effective and easier to handle device than prior art arrangements in that the pins are held captive within the device and therefore cannot be dislodged. The rounded portions 18 at the ends of the pins 16 are larger than the holes 16 thereby preventing the ends of the pins from passing through the plate 8. Although the enlarged ends of the pins 18 which contact the conductive pads 2 have been described as being rounded, it will be realised that other shapes may be more suitable for some applications. For example, although rounded ends have been found suitable for contacting gold plated pads, it has been found more satisfactory to use pointed ends for sol der coated pads.

Claims

1. Apparatus for testing a printed circuit board having a plurality of test locations ther eon including: a bed-of-nails tester comprising a plurality of probes arranged in positions different from said test locations; and an interposer device including a plurality of conductive pins, one end of each of the pins being retained in a conductive member located so as to correspond with one of the test probes and opposite ends of the pins projecting from the device at locations corresponding with said test locations.

2. An interposer device for use in testing a printed circuit board including: a pair of spaced apart planar insulating members, one of the members having a plurality of conductive retaining elements extending therethrough and being arranged in a first pattern and the other member having a plurality of apertures extending therethrough, the apertures being arranged in a second pattern different to said first pattern; and conductive pins retained at one end by the retaining elements, the other ends of the pins projecting through the apertures of said other member.

3. An interposer device as claimed in claim 2, in which the conductive retaining elements are in the form of bushes containing spring elements arranged to grip the conductive pins.

4. An interposer device as claimed in claim 3, in which each bush includes a flange which is accommodated in a corresponding counterbore in said one planar insulating member.

5. An interposer device as claimed in claim 3 or 4, in which said spring elements allow the conductive pins to assume leaning attitudes.

6. An interposer device as claimed in any of claims 2 to 5, including an enlarged portion provided on said other end of each conductive pin.

7. Apparatus for testing a printed circuit board having a plurality of test locations thereon constructed and arranged to operate substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawing.

8. An interposer device for use in testing a printed circuit board constructed and arranged to operate substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawing.