GB1564003A - Screen printing apparatus - Google Patents

Description

(54) SCREEN PRINTING APPARATUS (71) We, LUCAS INDUSTRIES LIMITED, of Great King Street, Birmingham B19 2XF, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a screen printing apparatus.

Apparatus, according to the invention, includes a table adapted to support and retain a substrate to which a screen printed pattern is to be applied, a printing assembly operable to print the required pattern on said substrate through a screen, means for indicating the required position of said substrate relative to the pattern to be applied to the substrate by the printing assembly, a carrier which supports said table and which is movable relative to the indicating means and the printing assembly so that, in use, said substrate can be located in turn adiacent said indicating means and said printing assembly, and means for adjusting the position of the table relative to the carrier so that in use, when the substrate is located adjacent said indicating means, the substrate can be moved with the aid of said indicating means into the correct position for subsequent application of the required pattern by the printing assembly.

Preferably. said carrier is movable in a horizontal plane into proximity with said printing assembly and said indicating means while the latter components remain stationary and the apparatus includes means for raising and lowering the table when the substrate is located adjacent each of said printing assembly and said indicating means.

Conveniently, the carrier is also movable to a loading station where said substrate is, in use, supplied to the table and is subsequently removed thereform after the printing operation.

Conveniently. said carrier is movable linearly along an elongated bar and said loading station is positioned intermediate the indicating means and the printing assembly.

Preferably, a fixed part of the apparatus defines adjacent the printing assembly, a device for accurately locating a frame which, in use, releasably supports a holder for carrying said screen, the holder being movable relative to said frame and clamping means being provided to retain the holder in position relative to the frame during a printing operation.

Preferably, said printing assembly includes a device which, in use, is moved across the screen to apply printing ink to the substrate through the screen, a bellows unit connected to said device so that deformation of the bellows unit urges the device in a direction towards the screen, and means for providing an adjustable controlled pressure difference between the interior and exterior of the bellows unit so that the device can be urged against the screen with a predetermined force.

Preferably, said device includes a resilient pad which presents an inclined surface to the screen and the apparatus includes means for supplying printing ink to the wedgeshaped space defined between the screen and said surface.

Preferably, said indicating means includes a viewing window and an illuminatable transparent or translucent member which is provided with indicia for defining the required location of the substrate and which is located beneath the window, so that when the carrier is in use adjacent the indicating means, the substrate can be viewed through the window by way of said illuminatable member whereby the position of said indicia relative to the substrate will indicate any misalignment of the substrate, said member being carried by a fixed part of the apparatus but, to allow said member to be aligned with said screen, means being provided for adjusting the position of said member relative to the substrate in a plane parallel with the substrate.

In the accompanying drawings, which illustrate one example of the invention: Figure 1 is a plan view of the overall apparatus, Figure 2 is a part sectional side view of Figure 1, and Figure 3 is a sectional view of the printing station.

Referring to the drawings, the apparatus includes a fixed support frame 11 which stands on feet 12 and across which extends a pair of horizontal bars 13 (only one shown).

Slidably mounted on the bars 13 is a carrier 14 which is connected to opposite ends of a drive cable 15 which extends parallel with the bars 13 over a pair of pulleys 16 located adjacent opposite ends respectively of the bars 13. Coupled to the cable 15 is the piston of a double-acting piston and cylinder arrangement 17 so that, in use, the cable 15 can be driven over the pulleys 16 to move the carrier 14 between opposite ends of the bars 13. In this way, the carrier 14 is movable from a central, loading station indicated at 18 in opposite directions respectively to a printing station indicated at 19 and an alignment station indicated at 21.

The carrier 14 is formed in two parts, namely a first part 14a which extends around the bars 13 and a second part 14b which is mounted vertically above the part 14a and supports a table 22. Located between the carrier parts 14a, 14b is a rotatable member carrying 3 pairs of ball races 23 (only one shown) located at 1200C to one another.

One race of each pair of races 23 bears on a flat plate 24a on the part 14a, while the other race of each pair engages a ramp surface 24b on the part 14b. The rotatable member is connected via a linkage to the piston of a piston and cylinder unit 25, so that operation of the unit 25 moves the races 23 over the ramp surface 24b. In this way the assembly of the carrier part 14b and table 22 can be either raised or lowered relative to the carrier part 14a, the part 14b being constrained to move in the vertical direction only by means of 3 pillars (not shown) fixed to the part 14b and engaging 3 ball bushings (not shown) fixed to the part 14o The table 22 is supported by the carrier part 14b so as to be capable of three independent horizontal movements respectively relative to the part 14b, that is angular movement about a central axis of the table, linear movement parallel with the bars 13 and linear movement perpendicular to the bars.

Journalled in the carrier part 14b are three manually operable adjusting knobs 26 which are coupled to the table 22 and which serve to control said three independent movements respectively of the table. In use, when a substrate is to be subiected to a screen printine operation, it is initially mounted on the table 22 and during subsequent processing is retained in position relative to the table by means of suction applied by a vacuum source (not shown). Then, as will be described in detail below, by rotating the knobs 26, the position of the table 22 can be adjusted until the substrate is accurately in alignment with the pattern which to be applied to the substrate.

Turning now to the various operating stations of the apparatus, at the loading station 18 there is provided a cover 27 which is hingedly connected to the frame 11 so as to be movable between a raised, open position and a lowered, closed position. Thus, when the carrier 14 is in use at the loading station 18, the cover 27 can be raised to its open position to enable a substrate to be either mounted on the table 22 or be removed therefrom after a printing operation.

A reed switch 27a is used to detect the attitude of the cover 27, the arrangement of the apparatus being such that when the switch 27a detects that the cover 27 is open, the carrier 14 cannot be moved.

At the printing station 19, the frame 11 defines a location device which is shown partly at 58 and which serves to accurately locate a removable carrier 59. Adjustably supported by the carrier is a removable screen holder 61, in use, is held relative to the carrier 59 by a series of clamps 62 (Figure 3). Mounted in the holder 61 is a screen 28 provided with the required pattern to be screen printed, the screen being replaceable by further screens carrying different patterns so as to allow over-printing of a series of patterns. Slidably mounted above the screen 28 on rods 31 is a carrier assembly 29 which supports a printing ink applicator in the form of a resilient pad 32.

A fluid pressure actuated hydraulic cylinder 56 acts upon the carrier assembly 29 and is operable to slide the carrier assembly along the rods 31 in a direction parallel with the screen whereby. in use, the member 32 can be moved across the screen to effect a printing operation. As shown in Figure 3 the pad 32 is arranged so as to present an inclined surface to the screen 28, the ink required to effect screen printing then being fed to the wedge-shaped space defined between the screen 28 and said inclined surface.

Referring now particularly to Figure 3, the carrier assembly 29 includes a pair of spaced, vertical pillars 33 having a support plate 34 rigidly secured to their upper ends.

Depending from the plate 34 is an elongated pressure chamber 35 which is connected by way of a conduit 36 and a pressure regulator 37 to a source of compressed air. At its end 35a remote from the plate 34 the chamber 35 supports one end of a cylindrical bellows unit 38, which is urged by a low rated spring 39 towards an extended condition. At the other end of the bellows unit 38 is secured a vertically extending rod 41 which is slidably received, and extends through, the end 35a of the chamber 35 to be connected at its free end to a generally U-shaped support bracket 43. The limbs of the bracket 43 are slidably mounted around the pillars 33 respectively and one of the limbs is also provided with a pair of projections 44 which are locked by nuts 45 in respective key-way grooves 46 (Figure 2) formed in a carrier plate 47 which supports the pad 32. It will therefore be appreciated that if the regulator 37 is adjusted so that compressed air is supplied to the chamber 35 at a pressure sufficient to overcome the action of the spring 39, the bellows unit 38 will be compressibly deformed so causing the rod 41 to slide the bracket 43 down the pillars 33, whereby the pad 32 will be moved towards the screen 28.

Thus, by operating the regulator 37 to control the air pressure supplied to the unit 38, the pad 32 can be urged against the screen 28 with an adjustable controlled force. Moreover, by virtue of the spring 39, this force will remain substantially constant over a substantial degree of movement of the member 32.

Secured to the frame 11 at the alignment station 21 is a cover plate 48 having a centrally disposed viewing window 49 which is conveniently fitted with a magnifying lens (not shown). Mounted on the underside of the plate 48 around the window 49 are a plurality of bulbs (only one shown) for illuminating a translucent or transparent, position indicating member 52 which is supported by the frame 11 so as to be directly below, and visible through, the window 49.

The purpose of the member 52 is to enable each substrate which is to be provided with a screen printed pattern to be accurately aligned at the station 21 with the pattern on the screen 28 before the substrate is transferred to the printing station 19. This is achieved by arranging that the member 52 carries indicia which correspond with indicia on each substrate to be screen printed and which could, for example, include a pattern already printed on each substrate. Then, when a given substrate is at the alignment station, the indicia on the substrate are viewed through the member 52 by way of the window 49, so that, if necessary, the knobs 26 can be rotated to adjust the position of the table 22 sufficiently to bring the indicia on the substrate into alignment with those carried by the member 52. It will, however, be readily appreciated that alignment of the substrate with the member 52 will only allow the required pattern to be subsequently applied to the substrate if the member 52 is itself correctly aligned with the pattern on the screen 28. The necessary alignment between the pattern 28 and the member 52 is achieved in the manner described below and, of course, requires that the member 52 is movable relative to the frame 11. Thus the member 52 is provided with adjustment means which is shown in part at 53 and which is similar to the adjustment provided for the table 22 in that it allows the member 52 to undergo angular movement in a horizontal plane together with horizontal linear movement both parallel with the perpendicular to the bar 13. It will, however, be appreciated that when the member 52 is correctly aligned with the screen 28, it is important that no further adjustment of the member should occur until the screen 28 is replaced. Thus the adjusting mechanism 53 is conveniently operated by keys which can be removed when the member 52 is correctly aligned so as to prevent further accidental adjustment of the member 52.

When the apparatus described above is used to screen print a pattern on each of a plurality of substrates, the apparatus is operated as follows: With the carrier 14 at the loading station 18, the cover 27 is raised and a first substrate is located on the table 22 is approximately the required position for subsequent screen printing, the table 22 conveniently being marked to assist in initial location of the substrate. The vacuum source connected to the table 22 is then energised to retain the substrate in position whereafter, assuming the member 52 has not been aligned with the screen 28 during an earlier printing run the piston and cylinder arrangement 17 is operated to move the carrier 14 to the printing station 19. On reaching the printing station 19, the carrier 14 engages a mechanical stop (not shown) on the frame 11 and operates a swithch 54 to energise the unit 25 so that the races 23 are moved over the ramp surface 24b. At the same time part of the linkage connecting the piston of the unit 25 to the rotatable member 20 is moved so as to impinge upon the anvil of a micrometer screw adiuster 25a (Figure 1) which serves to control the extension of the piston of the unit 25 and hence the amount of separation of the parts 14a, 14b. Thus, by appropriate setting of the adjuster 25a the table 22 can be raised by an amount sufficient to bring the first substrate into an accurately defined position adjacent to, or into contact with, the lower surface of the screen 28. With the substrate in this position, printing ink is supplied to the space between the screen 28 and pad 32 and the fluid pressure actuated means acting on the carrier assembly 29 is energised. The assembly 29 is thereby caused to slide along the rods 31 so that the pad 32 is moved across the screen 28 to urge the printing ink to flow through the screen and produce a pattern on the first substrate.

When the first printing operation is complete, the unit 25 is energised to lower the table 22, whereupon the carrier 14 is moved along the bars 13 by the arrangement 17 to the alignment station 21. At the alignment station, a further switch 54 is operated to re-energise the unit 25 so that the table 22 together with the first substrate are raised towards the member 52. As before, movement of the piston of the unit 25 is controlled by a further micrometer screw adjuster 25b (Figure 1) and hence, by appropriate setting of the adjuster 25b, the table 14 can be raised by an amount to bring the substrate to an accurately defined position iust below the member 52. When. the table 14 has been raised, the operator of the apparatus views the member 52 and the first substrate through the window 49 and without moving the knobs 26, operates the adjustment mechanism 53 to bring the indicia on the member 52 into accurate alignment with corresponding indicia forming part of the pattern which has been printed on the substrate. When this operation is complete, the member 52 is accurately aligned with the pattern on the screen 28 and hence no further adjustment of the member 52 is carried out until the screen 28 is replaced.

After setting of the member 52, the unit 25 is again operated to lower the table 22, whereupon the carrier 14 is moved by the arrangement 17 back to the loading position 18. The first substrate is then removed from the table 22 and can be retained for further processing if the screen printing operation just completed is the first such operation to which the substrate has been subjected. If, however, earlier screen printing operations have been performed on the substrate, it will be appreciated that the final pattern will probably be misaligned with respect to the earlier patterns and thus the first substrate will have to be rejected. Where this may prove expensive of course a cheap dummy substrate may be employed for the setting operation.

After the first substrate has been removed, a further substrate is located on the table 22 and, as before, the vacuum source is then operated to retain the further substrate in position. However, when the piston and cylinder arrangement 17 is subsequently energised to move the carrier 14, the arrangement is such that the carrier then slides to the alignment station 21. At this point, the table 22 is again raised by the unit 25 so as to bring the further substrate adjacent the member 52, which is of course now correctly aligned with respect to the screen 28. The operator of the aparatus then looks through the window 49 once again and now, without touching the mechanism 53, rotates the knobs 26 to adjust the table 22 such that the indicia on the further substrate are moved into alignment with the corresponding indicia on the member 52. As will be seen from Figures 1 and 2, this operation is facilitated by the provision of apertures 55 in the frame 11 from which the knobs 26 respectively extend when the carrier 14 is at the alignment station 21.

When the further substrate has been aligned with the member 52, the table 22 is lowered and the carrier 14 is transferred to the printing station 19 whereupon a printing operation is performed on the further substrate to produce a pattern which is correctly aligned with the substrate. Thereafter the carrier 14 is returned to the loading station 18 so that the further substrate can be removed and the cycle repeated.

It is to be appreciated that, when the screen 28 is initially employed or is to be replaced by a further screen, the arrangement of the carrier 59 and holder 61 enables the further screen to be approximately aligned with the substrate location marking on the table 14 before being mounted in the apparatus. Thus, with the carrier 59 removed from the device 58, the holder 61 can be moved relative to the carrier 59 until approximate alignment of the further screen with the marking on the table is achieved.

The clamps 62 are then tightened to secure the holder 61 in position relative to the carrier 59, whereafter the assembly is reinserted in the device 58 which then serves to accurately locate the carrier 59 with the further screen being clamped in approximately the required printing position.

Further, it is to be appreciated that, apart from adjustment of the table 22 and the member 52, and initial alignment of the screen 28, the various operations performed by the machine would in use be effected automatically in response to the operator depressing various control buttons.

Further, it is to be understood that the accuracy in the positioning of the printed pattern which is produced by the apparatus described above makes the apparatus particularly suitable for printing diffusion mask patterns on semi-conductor devices or for printing complex, multi-layer thick film circuits.

WHAT WE CLAIM IS:- 1. Screen printing apparatus including a table adapted to support and retain a substrate to which a screen printed pattern is to be applied; a printing assembly operable to print the required pattern on said substrate through a screen. means for indicating the required position of said substrate relative to the pattern to be applied to the substrate by the printing assembly, a carrier which supports said table and which is movable relative to the indicating means and the printing assembly so that,

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

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. When the first printing operation is complete, the unit 25 is energised to lower the table 22, whereupon the carrier 14 is moved along the bars 13 by the arrangement 17 to the alignment station 21. At the alignment station, a further switch 54 is operated to re-energise the unit 25 so that the table 22 together with the first substrate are raised towards the member 52. As before, movement of the piston of the unit 25 is controlled by a further micrometer screw adjuster 25b (Figure 1) and hence, by appropriate setting of the adjuster 25b, the table 14 can be raised by an amount to bring the substrate to an accurately defined position iust below the member 52. When. the table 14 has been raised, the operator of the apparatus views the member 52 and the first substrate through the window 49 and without moving the knobs 26, operates the adjustment mechanism 53 to bring the indicia on the member 52 into accurate alignment with corresponding indicia forming part of the pattern which has been printed on the substrate. When this operation is complete, the member 52 is accurately aligned with the pattern on the screen 28 and hence no further adjustment of the member 52 is carried out until the screen 28 is replaced. After setting of the member 52, the unit 25 is again operated to lower the table 22, whereupon the carrier 14 is moved by the arrangement 17 back to the loading position 18. The first substrate is then removed from the table 22 and can be retained for further processing if the screen printing operation just completed is the first such operation to which the substrate has been subjected. If, however, earlier screen printing operations have been performed on the substrate, it will be appreciated that the final pattern will probably be misaligned with respect to the earlier patterns and thus the first substrate will have to be rejected. Where this may prove expensive of course a cheap dummy substrate may be employed for the setting operation. After the first substrate has been removed, a further substrate is located on the table 22 and, as before, the vacuum source is then operated to retain the further substrate in position. However, when the piston and cylinder arrangement 17 is subsequently energised to move the carrier 14, the arrangement is such that the carrier then slides to the alignment station 21. At this point, the table 22 is again raised by the unit 25 so as to bring the further substrate adjacent the member 52, which is of course now correctly aligned with respect to the screen 28. The operator of the aparatus then looks through the window 49 once again and now, without touching the mechanism 53, rotates the knobs 26 to adjust the table 22 such that the indicia on the further substrate are moved into alignment with the corresponding indicia on the member 52. As will be seen from Figures 1 and 2, this operation is facilitated by the provision of apertures 55 in the frame 11 from which the knobs 26 respectively extend when the carrier 14 is at the alignment station 21. When the further substrate has been aligned with the member 52, the table 22 is lowered and the carrier 14 is transferred to the printing station 19 whereupon a printing operation is performed on the further substrate to produce a pattern which is correctly aligned with the substrate. Thereafter the carrier 14 is returned to the loading station 18 so that the further substrate can be removed and the cycle repeated. It is to be appreciated that, when the screen 28 is initially employed or is to be replaced by a further screen, the arrangement of the carrier 59 and holder 61 enables the further screen to be approximately aligned with the substrate location marking on the table 14 before being mounted in the apparatus. Thus, with the carrier 59 removed from the device 58, the holder 61 can be moved relative to the carrier 59 until approximate alignment of the further screen with the marking on the table is achieved. The clamps 62 are then tightened to secure the holder 61 in position relative to the carrier 59, whereafter the assembly is reinserted in the device 58 which then serves to accurately locate the carrier 59 with the further screen being clamped in approximately the required printing position. Further, it is to be appreciated that, apart from adjustment of the table 22 and the member 52, and initial alignment of the screen 28, the various operations performed by the machine would in use be effected automatically in response to the operator depressing various control buttons. Further, it is to be understood that the accuracy in the positioning of the printed pattern which is produced by the apparatus described above makes the apparatus particularly suitable for printing diffusion mask patterns on semi-conductor devices or for printing complex, multi-layer thick film circuits. WHAT WE CLAIM IS:-

1. Screen printing apparatus including a table adapted to support and retain a substrate to which a screen printed pattern is to be applied; a printing assembly operable to print the required pattern on said substrate through a screen. means for indicating the required position of said substrate relative to the pattern to be applied to the substrate by the printing assembly, a carrier which supports said table and which is movable relative to the indicating means and the printing assembly so that,

in use, said substrate can be located in turn adjacent said indicating means and said printing assembly, and means for adjusting the position of the table relative to the carrier so that in use, when the substrate is located adjacent said indicating means, the substrate can be moved with the aid of said indicating means into the correct position for subsequent application of the required pattern by the printing assembly.

2. Apparatus as claimed in Claim 1, wherein said carrier is movable in a horizontal plane into proximity with said printing assembly and said indicating means while the latter components remain stationary and the apparatus includes means for raising and lowering the table when the substrate is located adjacent each of said printing assembly and said indicating means.

3. Apparatus as claimed in Claim 2, wherein the carrier is also movable to a loading station where said substrate is, in use supplied to the table and is subsequently removed therefrom after the printing operation.

4. Apparatus as claimed in Claim 3, wherein said carrier is movable linearly along an elongated bar and said loading station is positioned intermediate the indicating means and the printing assembly.

5. Apparatus as claimed in any one of the preceding claims, wherein a fixed part of the apparatus defines adjacent the printing assembly, a device for accurately locating a frame which, in use, releasably supports a holder for carrying said screen, the holder being movable relative to said frame and clamping means being provided to retain the holder in position relative to the frame during a printing operation.

6. Apparatus as claimed in any one of the preceding claims, wherein said printing assembly includes a device which, in use, is moved across the screen to apply printing ink to the substrate through the screen, a bellow unit connected to said device so that deformation of the bellows unit urges the device in a direction towards the screen, and means for providing an adjustable controlled pressure difference between the interior and exterior of the bellows unit so that the device can be urged against the screen with a predetermined force.

7. Apparatus as claimed in Claim 6, wherein said device includes a resilient pad which presents an inclined surface to the screen and the apparatus includes means for supplying printing ink to the wedgeshaped space defined between the screen and said surface.

8. Apparatus as claimed in any one of the preceding claims, wherein said indicating means includes a viewing window and an illuminatable transparent or translucent member which is provided with indicia for defining the required location of the substrate and which is located beneath the window, so that when the carrier is in use adjacent the indicating means, the substrate can be viewed through the window by way of said illuminatable member whereby the position of said indicia relative to the substrate will indicate any misalignment of the substrate, said member being carried by a fixed part of the apparatus but, to allow said member to be aligned with said screen, means being provided for adjusting the position of said member relative to the substrate in a plane parallel with the substrate.

9. Screen printing apparatus comprising the combination and arrangement of parts substantially as hereinbefore described with reference to and as shown in the accompanying drawings.