GB2106838A

GB2106838A - Method and apparatus for producing slides for use in the assembly of printed circuit boards

Info

Publication number: GB2106838A
Application number: GB08129638A
Authority: GB
Inventors: Leslie John Honey Barnacle
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-10-01
Filing date: 1981-10-01
Publication date: 1983-04-20
Also published as: DE3235213A1

Abstract

Apparatus for producing slides for use in the assembly of components on a printed circuit board comprises a support consisting of a base plate (1), a strut (2) and a platform (3) and an elongate member (4) mounted in a bearing located in a bore in the platform (3). A first pointed member (16) is mounted at one end of the elongate member (4) for tracing details of a printed circuit board to be produced and a second pointed member (31) is mounted at the other end of the elongate member (4). Holding means in the form of an apertured plate (32), locating pegs (35, 36) and clamps (37) are provided for holding a glass slide (42) in a position to be contacted by the second pointed member (31) which projects through the aperture in the plate (32). The arrangement is such that movement of the first pointed member (16) to trace circuit components on a specimen circuit board (41) located on the base plate (1) is effective to cause the second pointed member (31) to mark the slide (42) to indicate the desired positions of the said circuit components. <IMAGE>

Description

SPECIFICATION Method and apparatus for producing slides for use in the assembly of printed circuit boards This invention relates to a method and apparatus for producing slides for use in the assembly of printed circuit boards.

It is known to use a projector by means of which the positions of circuit components indicated on a slide or other image carrier can be projected onto a printed circuit board to indicate the correct positions at which the circuit components should be placed on the board.

Various methods have previously been proposed for the manufacture of such slides or other image carriers. One such method has been to produce a slide using 35mm film. The disadvantage with this photographic method is that it requires a specialpurpose camera and there is a delay in preparation of the slide owing to the time needed for film development. A further disadvantage is that this system is inflexible, any design change made on the circuit board requires the preparation of a new slide on a new film.

Photographically-prepared slides which are located in a surrounding frame have also been proposed and an advantage of this system is that a design change on the circuit board entails the preparation of only one slide as opposed to a whole film in the system above-described. However, this system suffers not only the disadvantages of requiring a special-purpose camera and of delay while the film is being developed but also the additional problem of correctly aligning the slide transparency in the surrounding frame. The distances involved are fractions of a millimetre on the slide and correct alignment of the transparency in the frame is virtually impossible.Suggestions have been made for achieving the required accuracy of alignment, including frames with adjustment pins engageable in adjustment holes in the film transparency but the method has proved to be awkward, time-consuming and expensive.

It has also been proposed to utilise an electronic method in which a point light source is directed at a circuit board and movement of the light source is controlled by a computer. The disadvantage with this system is the expense of the equipment which is highly complex and involves high initial capital expenditure and high maintenance costs.

Another method, using a slide, has been prepared in British Patent Specification No. 1517039. In this method, an opaque laminer image carrier is perforated in a pre-determined manner to indicate the positions of circuit components on a printed circuit board and is then positioned in a pre-determined relation to the board. Light is beamed through the image carrier so that a series of illuminated dots or points are projected onto the circuit board. The opaque image carrier in fact comprises a punched metal slide and the equipment required to perforate the slide is a highly technical piece of equipment which is expensive to buy and maintain. The slides suffer from the disadvantage that dirt and dust can block or partially block the perforations which results either in no illumination or in only blurred indistinct illumination of the circuit board.Further, it is only possible to project points through the slide so that the illuminated information projected onto the circuit board is strictly limited.

The present invention aims to provide a method and apparatus for making slides which can be produced cheaply and yet extremely accurately.

According to one aspect of the invention, there is provided apparatus for producing slides for use in the assembly of components on a printed circuit board, said apparatus comprising a support, an elongate member mounted for movement in the support, a first pointed member at one end of said elongate member for tracing details of a printed circuit board to be produced, a second pointed member at the other end of said elongate member, and means for holding a glass slide in a position to be contacted by said second pointed member, whereby movement of the first pointed member to trace circuit components on a specimen circuit board is effective to cause the second pointed member to mark the slide to indicate the desired positions of the said circuit components.

The glass slide is preferably coated on one side with an opaque material such as paint which can be cut or scraped through by the second pointed member to produce a miniature version of the specimen printed circuit board. This slide can then be inserted in conventional projection apparatus to indicate on a circuit board the locations of the various circuit components which are to be assembled on the board.

Preferably, at least the second pointed member is retractably mounted in the elongate member but desirably both pointed members are retractably mounted in or on said elongate member.

According to a preferred embodiment of the invention,the second pointed member is suitably mounted in an end of the elongate member and is urged by resilient means away from the associated end of said elongate member and means are provided for allowing the pointed member to move further into the associated end of the elongate member against the action of said resilient means.

The resilient means desirably comprise a coil spring.

The first pointed member is preferably provided with a sleeve which is mounted over the other end of the elongate member and is free to slide in an axial direction with respect thereto, means being provided to prevent the said first pointed member from slipping off the end of said elongate member.

The elongate member is preferably mounted in the support by means of a self-aligning bearing which permits rotation and/or movement of said member about an axis located at the centre of the bearing. Means are preferably provided for preventing the elongate member from rotating about its own longitudinal axis. These means may comprise a bar, rod or like member extending substantially parallel to the elongate member and secured at one end to said member and located at the other end in a bearing in the support. Said bearing is preferably a self-centring bearing.

The invention also extends to a method of producing slides for use in the assembly of components on a printed circuit board, said method utilising the apparatus above described and comprising the steps of locating a specimen circuit board below the support of the apparatus, position- a glass slide in the holding means and tracing the circuit components on the specimen circuit board with the first pointed member whereby the positions of said components are marked on the slide by the second pointed member The invention further provides a glass slide when produced by the apparatus and/or by the method above described.

The invention will now be further described, by way of example, with reference to the drawings, in which Figure lisa side elevation of one embodiment of an apparatus for producing slides according to the invention; Figure2 is a vertical section through the upper part of the apparatus shown in Figure 1 to an enlarged scale; Figure 3 is a section taken on the line Ill-Ill in Figure 1 in the direction of the arrows; Figure 4 is a plan view of the upper part of the apparatus shown in Figure 1; and Figure 5 is a section taken on the line V-V in Figure 4 in the direction of the arrows.

Referring to the drawings, the apparatus comprises a plate 1 to which the lower end of a strut is secured e.g. by welding. A platform 3 is secured, e.g.

by welding, to the upper end of the strut 2, said platform and strut constituting a support for an elongate member 4. The member 4 comprises a rod or shaft of circular cross-section which is mounted, adjacent its upper end, in a self-aligning bearing 5 which is fixed in a bore 6 in the platform 3 by means of a set screw 7. The shaft 4 is a force-fit in the bearing 5 so that it is secured against axial movement with respect to the bearing. The shaft is, however, capable of rotational movement about an axis located at the centre of the bearing 5 but is prevented from rotating about its own longitudinal axis by means of an auxiliary rod 8. One end of the rod 8 is pivotally connected by a pivot pin 9 to a collar 11, which is mounted on the shaft 4 intermediate its ends, and the other end of the rod 8 extends through a bore 12 in the platform 3.The bore 12 may be double-conical as shown in the drawings but, as an alternative, a self-centring bearing may be provided in said bore.

Mounted on the lower end of the shaft 4 is a sleeve 13 with a ball bushing 14 being located between the shaft 4 and sleeve 13 as shown in Figure 3. The sleeve 13 is provided at one end with a circlip 15 to prevent the sleeve from falling off the end of the shaft 4 and a pointed member 16 is mounted in the other end of the sleeve 13. The ball bushing 14 is an interference fit on the shaft 4 whereas the sleeve 13 is free to move axially with respect to the shaft within the limits defined by the circlip 15 and pointed member 16.

A lever 17 is pivotally mounted on a lug 18 secured, e.g. by welding, to the sleeve 13 and the outer sheath 19 of a Bowden cable extends between the lug 18 and the collar 11 as shown in Figure 1.The inner core 21 of the Bowden cable is fitted at one end to the lever 17 and, at the other end, to a small pin or bar 22. The pin or bar 22 extends through a transverse slot 23 in the shaft 4 as well as through a bore in the lower end of a rod 24. The rod 24 is slidably mounted in an axial bore in the upper end of the shaft 4 and a coil spring 25 is mounted on the shaft 4 between the collar 11 and the pin or bar 22.

The spring 25 thus serves to force the pin or bar 22 towards the upper end of the slot 23 in the shaft 4, the length of travel being determined by conventional adjustment means (not shown) on the Bowden cable.

Mounted on the upper end of the shaft 4 which projects above the platform 3 is a second ball bushing 26 over which a sleeve 27 is fitted. The ball bushing 26 is an interference fit on the shaft 4 whereas the sleeve is free to move axially with respect to the shaft within limits defined by circlips 28 fitted in the sleeve adjacent to the ends thereof. A frusto-conical member 29 is fitted over the outer end of the sleeve 27 and is arranged to be normally engaged by the upper end of the rod 24. The member 29 may, if desired, be secured to said rod 24 but this is not essential. A pointed member or scriber 31 is fitted in the member 29 and is axially aligned with the longitudinal axis of the shaft 4.

A slide holder is mounted on the platform 3, said slide holder comprising a plate 32 which is located above the platform 3 and extends substantially parallel thereto. The plate 32 is supported by pillars 33 at each of its corners, which pillars are secured at their ends respectively to the plate and the the platform. The plate 32 has a central, substantiallysquare, aperture 34 and a pair of upstanding pegs 35 are provided adjacent to one edge of the aperture. A further upstanding peg 36 is provided adjacent to an adjacent edge of the aperture and a pair of releasable clamps or holders 37 are provided on the plate 32 on two opposite sides of the aperture 34. As shown in Figure 5, each clamp or holder 37 is substantially L-shaped in cross-section and is mounted on a setting screw 38 mounted on the plate 32.A knurled adjuster 39 is engageable with the screw 38 to hold the associated clamp or holder 37 in position on the plate 32.

When it is desired to produce a slide of a specimen printed circuit board using the above-described apparatus, the circuit board 41 is first carefully located on the base plate 1. A slide 42 is then carefully located on the plate 32 over the aperture 34 so that one edge of the slide bears against the two pegs 35 and an adjacent edge of the slide bears against the peg 36. The clamps or holders 37 are then positioned over two opposite edges of the slide as shown in Figures 4 and 5 and the adjusters 39 are tightened so that the clamps or holders 37 are effective to hold the slide 42 firmly in position.

The apparatus is so adjusted that, under normal conditions, the scriber 31 projects through the aperture 34 in the plate 32 to make contact with the underneath surface of the slide 42. The scriber may, however, be retracted from this position by operat ing the lever 17. This has the effect of drawing the pin or bar 22 down towards the collar 11 under the action of the cable 21 and against the force of the spring 25. The pin or bar 22 entrains the rod 24 and draws this rod downwards which in turn causes the member 29 and sleve 26 to move downwards. Since the scriber 31 is fitted in the member 29, this too will move downwards out of contact with the slide 42.

Thus, as long as the lever 17 is held, no mark will be made on the slide 42.

An operator of the apparatus will normally hold the sleeve 13 and lever 17 in one hand and trace the circuit on the circuit board 41 with the point at the end of the pointed member 16. The scriber 31 will follow the movements of the pointed member 16 in inverted mirror image since it is mounted at the other end of the same shaft 4. The extent of the movements of the scriber 31 will, however, be much less than those of the pointed member 16 because the scriber is much closer to the axis of pivoting. A ratio which has been found to be particularly useful is 10:1 Since the pointed member 16 is axially slidably mounted on the shaft 4 it can be lifted from the circuit board 41 as desired and is capable of free movement in all directions over the board.It will normaly be positioned at one end of the position which a desired component is to occupy on the board and the lever 17 is then released. This has the effect of causing the scriber 31 to contact the underneath surface of the slide 42 under the action of the spring 25. The pointed member 16 is then moved over the circuit board 41 to the other end of the said desired component and the scriber makes a corresponding mark in the correct position but to a reduced scale on the slide 42. The lever 17 can then again be gripped to retract the scriber 31 and the pointed member 16 moved to the position of a second component whereupon the operation is repeated.When all of the components have been marked on the slide 42 in this way, the slide can simply be removed from the apparatus by releasing the clamps or holders 37 and the slide is then ready for immediate use in conventional projection apparatus.

The slide will normally be provided on one surface with an opaque coating and this coating will be scratched through by the point of the scriber 31. As mentioned above, the scriber will make an inverted mirror image of the circuit board on the coated surface of the slide so that if the slide is inserted in projection apparatus with its coated surface remote from the light source, the image projected by the projection apparatus will be the same as the original specimen circuit board.

In addition to inserting the positions of various components to be assembled on a circuit board, it is also possible to insert the values and kinds or types of components by writing appropriate figures and letters by the sides of the positional marks. It is also possible to write onto the slide, information and instructions for assembling circuit boards. This represents a considerable advantage over the prior systems which were not able to do this. Further, since the slides are always accurately positioned in the apparatus according to the invention, it is possible to produce a slide which is correctly and accurately marked on every occasion. A further advantage is that additions to the circuit can be made simply by positioning a marked slide on the plate 32 and marking in the additional components.

Other changes to the circuit will, however, require the appliation of coating material to the regions of the slide at which changes are to be made and then re-marking these regions.

The opaque coating will normaly consist of matt black paint although other materials and colours may be used if desired.

The auxiliary rod 8 is provided to prevent the shaft 4from turning which could cause inaccuracies in the production of slides if the axis of the shaft is not true.

If the shaft 4 is manufactured with very great precision, it might be possible to dispense with the auxiliary rod 8 but a further advantage of having means for preventing the shaft from turning is that the Bowden cable is then kept neatly in line and the lever 17 is always positioned for easy operation.

The plate 32 and pillars 33 may if desired be replaced by a solid block of, for example, aluminium or aluminium alloy. THis would provide a more precise construction but it would also increase the cost of the apparatus.

Although reference has been made in this specification to the slide being made of glass, it should be noted that this is not essential and the slide could be made of other transparent materials having like properties to those of glass References to glass in this specification therefore intended to extend to such other materials.

It should be noted that the present invention is not restricted to the above described embodiment but that modifications and variations may be made without departing from the scope of the invention.

For example, instead of being welded to the sleeve 13, the lug 18 may, if desired be secured to said sleeve by means of a clamp or strap.

CLAIMS (filed 16 Feb 82) 1. Apparatus for producing slides for use in the assembly of components on a printed circuit board, said apparatus comprising a support, an elongate member mounted for movement in the support, a first pointed member at one end of said elongate member for tracing details of a printed circuit board to be produced, a second pointed member at the other end of said elongate member, and means for holding a glass slide in a position to be contacted by said second pointed member, whereby movement of the first pointed member to trace circuit components on a specimen circuit board is effective to cause the second pointed member to mark the slide to indicate the desired positions of the said circuit components.

2. Apparatus according to claim 1, wherein the slide is coated on one side with an opaque material which can be cut or scraped through by the said second pointed member to produce a replica of the specimen printed circuit board.

3. Apparatus according to claim 2, wherein the

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. ing the lever 17. This has the effect of drawing the pin or bar 22 down towards the collar 11 under the action of the cable 21 and against the force of the spring 25. The pin or bar 22 entrains the rod 24 and draws this rod downwards which in turn causes the member 29 and sleve 26 to move downwards. Since the scriber 31 is fitted in the member 29, this too will move downwards out of contact with the slide 42. Thus, as long as the lever 17 is held, no mark will be made on the slide 42. An operator of the apparatus will normally hold the sleeve 13 and lever 17 in one hand and trace the circuit on the circuit board 41 with the point at the end of the pointed member 16. The scriber 31 will follow the movements of the pointed member 16 in inverted mirror image since it is mounted at the other end of the same shaft 4. The extent of the movements of the scriber 31 will, however, be much less than those of the pointed member 16 because the scriber is much closer to the axis of pivoting. A ratio which has been found to be particularly useful is 10:1 Since the pointed member 16 is axially slidably mounted on the shaft 4 it can be lifted from the circuit board 41 as desired and is capable of free movement in all directions over the board.It will normaly be positioned at one end of the position which a desired component is to occupy on the board and the lever 17 is then released. This has the effect of causing the scriber 31 to contact the underneath surface of the slide 42 under the action of the spring 25. The pointed member 16 is then moved over the circuit board 41 to the other end of the said desired component and the scriber makes a corresponding mark in the correct position but to a reduced scale on the slide 42. The lever 17 can then again be gripped to retract the scriber 31 and the pointed member 16 moved to the position of a second component whereupon the operation is repeated.When all of the components have been marked on the slide 42 in this way, the slide can simply be removed from the apparatus by releasing the clamps or holders 37 and the slide is then ready for immediate use in conventional projection apparatus. The slide will normally be provided on one surface with an opaque coating and this coating will be scratched through by the point of the scriber 31. As mentioned above, the scriber will make an inverted mirror image of the circuit board on the coated surface of the slide so that if the slide is inserted in projection apparatus with its coated surface remote from the light source, the image projected by the projection apparatus will be the same as the original specimen circuit board. In addition to inserting the positions of various components to be assembled on a circuit board, it is also possible to insert the values and kinds or types of components by writing appropriate figures and letters by the sides of the positional marks. It is also possible to write onto the slide, information and instructions for assembling circuit boards. This represents a considerable advantage over the prior systems which were not able to do this. Further, since the slides are always accurately positioned in the apparatus according to the invention, it is possible to produce a slide which is correctly and accurately marked on every occasion. A further advantage is that additions to the circuit can be made simply by positioning a marked slide on the plate 32 and marking in the additional components. Other changes to the circuit will, however, require the appliation of coating material to the regions of the slide at which changes are to be made and then re-marking these regions. The opaque coating will normaly consist of matt black paint although other materials and colours may be used if desired. The auxiliary rod 8 is provided to prevent the shaft 4from turning which could cause inaccuracies in the production of slides if the axis of the shaft is not true. If the shaft 4 is manufactured with very great precision, it might be possible to dispense with the auxiliary rod 8 but a further advantage of having means for preventing the shaft from turning is that the Bowden cable is then kept neatly in line and the lever 17 is always positioned for easy operation. The plate 32 and pillars 33 may if desired be replaced by a solid block of, for example, aluminium or aluminium alloy. THis would provide a more precise construction but it would also increase the cost of the apparatus. Although reference has been made in this specification to the slide being made of glass, it should be noted that this is not essential and the slide could be made of other transparent materials having like properties to those of glass References to glass in this specification therefore intended to extend to such other materials. It should be noted that the present invention is not restricted to the above described embodiment but that modifications and variations may be made without departing from the scope of the invention. For example, instead of being welded to the sleeve 13, the lug 18 may, if desired be secured to said sleeve by means of a clamp or strap. CLAIMS (filed 16 Feb 82)

1. Apparatus for producing slides for use in the assembly of components on a printed circuit board, said apparatus comprising a support, an elongate member mounted for movement in the support, a first pointed member at one end of said elongate member for tracing details of a printed circuit board to be produced, a second pointed member at the other end of said elongate member, and means for holding a glass slide in a position to be contacted by said second pointed member, whereby movement of the first pointed member to trace circuit components on a specimen circuit board is effective to cause the second pointed member to mark the slide to indicate the desired positions of the said circuit components.

3. Apparatus according to claim 2, wherein the

opaque material coating is paint.

4. Apparatus according to any preceding claim, wherein the second pointed member is retractably mounted in or on the elongate member.

5. Apparatus according to claim 4, wherein the second pointed member is slidably mounted on the said other end of the elongate member and is urged by resilient means away from the said other end of the elongate member.

6. Apparatus according to claim 5, wherein the resilient means comprise a coil spring.

7. Apparatus according to claim 5 or claim 6, wherein the second pointed member comprises a scriberwhich is mounted in a block member secured to or integral with a sleeve slidably mounted on the said other end of the elongate member.

8. Apparatus according to claim 7, wherein the said other end of the elongate member is provided with an axially extending bore containing a rod or shaft which is secured to or arranged to engage with the block member.

9. Apparatus according to claim 8, wherein the resilient means is arranged to act on a pin extending transversely though said rod or shaft and located in a slot provided in the said elongate member.

10. Apparatus according to claim 9, wherein one end of a cable is connected to the pin and the other end of the cable is arranged to be acted on by a lever against the action of the said resilient means.

11. Apparatus according to claim 10, wherein the lever is pivotally mounted on the first pointed member.

12. Apparatus according to any preceding claim, wherein the first pointed member is retractably mounted in or on the elongate member.

13. Apparatus according to claim 12, wherein the first pointed member is provided with a sleeve which is mounted over the said one end of the elongate member and which is free to slide in an axial direction with respect thereto.

14. Apparatus according to claim 13, wherein means are provided to prevent said first pointed member from slipping off the end of said elongate member.

15. Apparatus according to claim 14, wherein said means comprise a ball bushing mounted adjacent said one end of the elongate member and a circlip engageable with said ball bushing and fitted in the sleeve at the end remote from the said first pointed member.

16. Apparatus according to any preceding claim, wherein the elongate member is mounted in the support by means of a self-aligning bearing which permits rotation and/or movement of said member about an axis located at the centre of the bearing.

17. Apparatus according to any preceding claim, wherein means are provided for preventing the elongate member from rotating about its own longitudinal axis.

18. Apparatus according to claim 17, wherein said rotation preventing means comprise a bar, rod or like member extending substantially parallel to the elongate member and secured at one end to said member and located at the other end in a bearing in the support.

19. Apparatus according to claim 18, wherein the bearing in the support for the member extending substantially parallel to the elongate member comprises a self-centring bearing.

20. Apparatus according to any preceding claim, wherein the elongate member is mounted in the support in such a manner that the end of the first pointed member is further away from the support than the end of the second pointed member.

21. Apparatus according to claim 20, wherein the ratio of the distance of the end of the first pointed member from the support to the distance of the end of the second pointed member from the support is approximately 10:1.

22. Apparatus according to any preceding claim, wherein the slide holding means comprise a plate mounted on the support, an aperture in the plate through which the second pointed member is arranged to project, locating pins adjacent at least two edges of the aperture against which a slide is designed to abut and clamping means for clamping a slide to the plate, said slide being located over the aperture, for engagement by the second pointed member.

23. Apparatus for producing slides substantially as described herein with reference to the drawings.

24. A method of producing slides for use in the assembly of components on a printed circuit board, said method utilising the apparatus claimed in any one of the preceding claims and comprising the steps of locating a specimen circuit board below the support of the apparatus, positioning a glass slide in the holding means and tracing the circuit components on the specimen circuit board with the first pointed member whereby the positions of said circuit components are marked on the slide by the second pointed member.

25. A slide when produced by the apparatus claimed in any one of claims 1 to 23 and/or by the method claimed in claim 24.