IE58644B1

IE58644B1 - A vacuum fixture

Info

Publication number: IE58644B1
Application number: IE172586A
Authority: IE
Original assignee: Ate Services Ltd
Priority date: 1986-06-27
Filing date: 1986-06-27
Publication date: 1993-10-20
Also published as: BE905174A; GB2195502A; IE861725L; GB8713990D0

Abstract

A vacuum fixture for testing a printed circuit board comprises a vacuum box (3) with a probe board (4) and a diaphragm board (6). Probes (5) extend from the probe board (4) through openings (14) in the diaphragm board (6) to engage the printed circuit board. To assist in identifying the probes, a schematic representation of the components to which the probes relate is provided on the surfaces of the probe board (4) and the upper surface diaphragm (6). The identity of each component is also provided. The schematic representation of the components is formed by a photographic process on a transparent film (21), which is bonded by a double sided adhesive tape to the boards (4) and (6).

Description

The present invention relates to a vacuum fixture for testing a printed circuit board and to a method for producing the fixture.

Printed circuit boards, in general are tested by using a vacuum fixture. Such fixtures, in general, comprise a vacuum box in which a vacuum is generated by a remote vacuum source. A probe location board is mounted adjacent the top of the box and a plurality of electrically conductive probes extend upwardly from the probe board. A diaphragm board extends over the probe board and a plurality of openings are provided in the diaphragm board corresponding to the probes to permit the probes to project through the diaphragm board to engage corresponding contact positions on the printed circuit board to be tested. The diaphragm board is sealably mounted in the probe board to ensure a vacuum seal. Engagement. means are provided on the diagphram board to receive the printed circuit, board, and to engage it in sealable engagement.

The problem with these vacuum fixtures is that when one looks at them, all that is visible is a plurality of electrically conductive probes projecting up through the diaphragm board. Thus, it is not possible to easily identify which probe corresponds with which electrical contact point in the printed circuit board. This presents considerable difficulty if there is a problem with one of the pins. Considerable time can be spent in attempting to identify the faulty pin. Thus, there is a need for a vacuum fixture which overcomes the problems of existing vacuum fixtures. There is also a need for a method for producing such a vacuum fixture.

The present invention is directed towards providing such a vacuum fixture and a method for manufacturing the f i xture.

According to the invention there is provided a vacuum fixture for testing a printed circuit board, the vacuum fixture comprising a vacuum box, a probe location board mounted towards the top of the box, a plurality of electrically conductive probes extending upwardly from the probe location board, a diaphragm board sealably mounted to and above the probe location board, and movable towards and away from the probe location board, the diaphragm board having a plurality of openings to permit the probes to extend therethrough for electrical engagement with contact points on the printed circuit board, engagement means on the diaphragm board to receive and engage the printed circuit board in sealable engagement therewith, wherein a schematic diagram of at least some of the components on the printed circuit board and their appropriate positions relative to the probes is provided on the upwardly directed face of the diaphragm board.

Preferably, the identity of at least some of the components is provided adjacent the respective component of the schematic diagram on the diaphragm board.

Advantageously, all the components on the printed circuit board are schematically represented on the diaphragm board.

In one embodiment of the invention, a schematic diagram of at least some of the components of the printed circuit board and their appropriate positions relative to the probes is provided on the upwardly directed face of the probe location board. Preferably, a schematic diagram of at least some of the components of the printed circuit board and their appropriate positions relative to the probe is provided on the downwardly directed face of the probe board.

In another embodiment of the invention, the schematic diagram of the components is provided on a transparent film. Preferably, the transparent film is bonded to either the diaphragm board or the probe location board by double-sided bonding tape.

In a further embodiment of the invention a templet is prov i ded. - 5 Additionally, the invention provides a method for forming a schematic diagram of the components on the diaphragm board or the probe location board, comprising the steps of forming the schematic diagram on a sheet of material, and bonding the sheet of material to the appropriate face of the board. Preferably, the method includes the step of forming the diagram on the sheet of material by a photographic process. Advantageously, the schematic diagram of the components is developed onto a transparent film.

In another embodiment of the invention, the photograph is obtained by photographing the printed circuit board.

In a further embodiment of the includes the step of attaching the board after the appropriate have been drilled. Preferably, bonded to the board by a double invention, the method the sheet of material holes for the probes the sheet of material sided adhesive tape. to The invention will be more clearly understood from the following description of a preferred embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which; Fig. 1 is a perspective view of a vacuum fixture according to the invention, Fig. 2 is an exploded perspective view of the fixture ol Fig. 1, Fig. 3 is a perspective view of the fixture of Fig. 1 in a different position, Fig. 4 is apparatus a partly cut-away perspective view of the of Fig. 1, Fig. 5 i s a apparatus of that of Fig. partly cut-away perspective view of the Fig. 1 shown in a different position to , and Fig. 6 is a plan view of a templet according to the invention .

Referring to the drawings, there is provided a vacuum fixture according to the invention, indicated generally by the reference numeral 1 for testing a printed circuit board 2. Such vacuum fixtures in general will be well known to those skilled in the art, and it is not intended to describe the fixture in particular detail, however, briefly, the fixture comprises a box 3. A probe board 4 is mounted on a lid 11 pivotally mounted on the box 3 at 12 and comprises a plurality of electrically conductive probes 5 for engaging electrical contact points on the printed circuit board 2. A diaphragm board 6 is mounted on top of the probe board 4 and a sealing member 7 extends around the periphery of the probe board 4 between the board 4 and the diaphragm board 6. A clamping frame 13 and screws (not shown) secures the probe board 4 and the diaphragm board 6 together, to ensure a vacuum tight chamber 8 is formed between the two boards 4 and 6. A vacuum port 9 is provided in the box 3 and a duct 10 connects the port 9 to the vacuum chamber 8. A seating frame 28 is provided on the board 6 to form a seat and an airtight seal between the printed circuit board 2 and the bond 6.

Sockets 23 in the box 3 are provided for connecting the probes into suitable analysing apparatus.

A plurality of openings 14 are provided in the diaphragm board 6 to align with the probes 5 and to permit the probes 5 to project therethrough to engage the electrical contact points on the printed circuit board 2. Locating pins 15 extend upwardly from the probe board 4 through holes 16 the diaphragm board 6 to engage the corresponding locating holes 17 in the printed circuit board 2.

So that each probe 5 can be readily easily identified, a schematic diagram 22 of each of the components with its identification number is provided on the upwardly directed surface 18 of the diaphragm board. The schematic representation of the components are provided in locations corresponding to their position on the printed circuit board and corresponding to the location ol' the probes. Additionally, similar· schematic representations are provided on the upper and lower surfaces 19 and 20 of the diaphragm board 6. Thus, a user can readily easily identify which probe is provided to engage a particular contact point on the printed circuit hoard 2 by locating the position of the particular component by its schematic representation on either the diaphragm board or the probe board.

In this particular embodiment of the invention, the schematic representation of the components is first formed on transparent film 21 by a photographic process. Initially, the printed circuit board having a schematic representation of the components in their appropriate positions is photographed and the photograph is developed onto transparent film. The film is reproduced in the exact size of the printed circuit board. The film is then bonded to the appropriate surfaces of the probe board 4 and the diaphragm board 6 by double-sided adhesive tape (not shown). Initially, the adhesive tape is bonded to the transparent film. It is then after alignment, bonded to the surface of the two boards. A small portion of the protective tape of the double-sided tape is removed and the film 21 is aligned with the appropriate board by aligning the schematic representation of the components with their appropriate position on the boards using the holes for location. The exposed strip of the adhesive tape is bonded to the board and any final finer alignment adjustments are made. After that, the remaining protective covering on the double-sided adhesive is removed and the film is securely bonded to the appropriate surfaces of the boards 4 and 6.

In use, the vacuum fixture is used in a conventional manner, however, should a faulty reading of any component be discovered and it is necessary to check the probes which are connected to the particular component, the probes can readily easily be identified by merely identifying the schematic representation of the component on either the probe board or the diaphragm board and then checking the probes alignment, conductivity or the like.

While the vacuum fixture according to the present invention has many advantages over and above those used heretofore, its main advantage is the fact that, by virtue of the fact that the components to which the probes relate are schematically represented on both the probe board and the diaphragm board, the probe relating to any particular contact point on the printed circuit board can readily easily be identified without the need for counting probes in various directions or using other electrical techniques.

Referring now to Fig. 6 there is illustrated a template 25 also according to the invention for use with the vacuum fixture. In this case, the template 25 is of 1.6 mm fibreglass material, and comprises a plurality of holes 26, which correspond to the probes 5. Holes 27 correspond to the two locating pins 15. In fact, as can be seen, more holes 26 than probes 5 are provided. This is to accommodate additional probes, should the printed circuit board being tested be expanded with additional components or connections.

The advantage of this template is that it can be supplied with the vacuum fixture and accordingly, a user prior to testing a board, can check the alignment of the probes 5 by merely placing the template 25 in position in place of the printed circuit board. Should there be a mal-aligned pin, it will immediately be detected by use of the template. It is envisaged in general use that the template would be used periodically throughout the day to check the alignment of the probes 5. It will also be appreciated that while the template board has been described as being of fibreglass material any other suitable material could be used. It will also, of course, be appreciated that while it has been described as having more holes than the number of probes, this is not necessary, in certain cases, it may be provided with the exact number of holes to correspond with the probes.

It will be appreciated that while a particular construction of vacuum fixture has been described, any other suitable construction could be used without departing from the scope of the invention. Further, it will be appreciated that while the fixture has been described as having a schematic representation of all the components provided on both the probe and diaphragm board, this is not necessary. Firstly, it will be appreciated that the schematic representation of the components need only be provided on one of the boards, and needless to say, in the case of the probe board, while it is advantageous to have a schematic representation of the components on both sides of the probe board, this is not always necessary, it need only be provided on one side. Additionally, it is not necessary to have a schematic representation of all the components, in certain cases, it is envisaged that it will be necessary only to have a schematic representation of some of the components, and furthermore, it will be appreciated that while the description of each component has been provided on the boards, this is not necessary .

It will also be appreciated that while a particular method of applying the schematic representation of the components to the boards has been described, any other suitable method of applying the schematic representation could be used, for example, in certain cases it is envisaged that it may be printed directly onto the boards, or in another case, it is envisaged that it may be applied directly onto the boards using a photographic process. Further, in certain cases, it is envisaged that it may be drawn, printed or any other technique may be used. Additionally, it is envisaged that, in certain cases, instead of reproducing the schematic representation onto clear film, it could be reproduced onto any sheet of material.

It is also envisaged in certain cases that instead of providing the schematic representation of the components on a film and then bonding it to the boards 4 and 6, the schematic representation could be printed directly onto the boards.

Further, in certain cases, it is envisaged that where a large number of holes have to be drilled side by side on the diaphragm board to accommodate the probes, portion of the board surrounded by the holes may perforate from the board. In which case, part of the schematic representation of the relevant component may be lost on the diaphragm board, however, in such cases it is envisaged that the identifying number of the component will be provided on a portion of the film adjacent the probes, which will not part from the board.

Claims

1. A vacuum fixture for testing a printed circuit board, the vacuum fixture comprising a vacuum box, a probe location board mounted towards the top of the box, a plurality of electrically conductive probes extending upwardly from the probe location board, a diaphragm board sealably mounted to and above the probe location board, and movable towards and away from the probe location board, the diaphragm board having a plurality of openings to permit the probes to extend therethrough for electrical engagement with contact points on the printed circuit board, engagement means on the diaphragm board to receive and engage the printed circuit board in sealable engagement therewith, wherein a schematic diagram of at least some of the components on the printed circuit board and their appropriate positions relative to the probes is provided on the upwardly directed face of the diaphragm board.

2. A vacuum fixture as claimed in claim 1 in which the identity of at least some of the components is provided adjacent the respective component of the schematic diagram on the diaphragm board.

3. A vacuum fixture as claimed in claim 1 or 2 in which all the components on the printed circuit board are schematically represented on the diaphragm board.

4. A vacuum fixture as claimed in any preceding claim in which a schematic diagram of at least some of the components of the printed circuit board and their appropriate positions relative to the probes is provided on the upwardly directed face of the probe location board .

5. A vacuum fixture as claimed in any preceding claim in which a schematic diagram of at least some of the components of the printed circuit board and their appropriate positions relative to the probe is provided on the downwardly directed face of the probe board.

6. A vacuum fixture as claimed in any preceding claim in which the schematic diagram of the components is provided on a transparent film.

7. A vacuum fixture as claimed in any preceding claim in which the transparent film is bonded to either the diaphragm board or the probe location board by double-sided bonding tape.

8. A vacuum fixture as claimed in any preceding claim in which a templet is provided, the templet comprising at least a hole corresponding to each probe for testing the alignment of the holes periodically.

9. Λ vacuum fixture as claimed in claim 8 in which additional holes are provided in the templet board.

10. A method for forming a schematic diagram of the components on the diaphragm board or the probe location board, comprising the steps of forming the schematic diagram on a sheet of material, and bonding the sheet of material to the appropriate face of the board.

11. A method as claimed in claim 10 in which the method includes the step of forming the diagram on the sheet of material by a photographic process.

12. A method as claimed in claim 11 in which the schematic diagram of the components is developed onto a transparent film.

13. A method as claimed in claim 11 or 12 in which the photograph is obtained by photographing the printed circuit board.

14. A method as claimed in any of claims 10 to 13 in which the method includes the step of attaching the sheet of material to the board after the appropriate holes for the probes have been drilled.

15. A method as claimed in any of claims 10 to 14 in which the sheet of material is bonded to the board by a double sided adhesive tape.

16. A method as claimed in claim 15 in which the method includes the additional step of bonding one side of the double sided adhesive tape to the film, removing a small 5 portion of the protective covering of the other side of the double sided tape to expose portion of the double sided tape, placing the film and tape over the board, aligning if with the board, bonding the exposed portion o 1' 1 he double sided tape to the board, removing the 10 remaining protective coverings of the double sided tape, and bonding the entire combination of double sided tape and film to the board.

17. A vacuum fixture substantially as described herein with reference to and as illustrated in the accompanying 15 drawings.

18. A method for forming a vacuum fixture substantially as described herein with reference to and as illustrated in the accompanying drawings.