GB1602392A - Apparatus for applying a layer of pasty material to a carr - Google Patents

Description

(54) APPARATUS FOR APPLYING A LAYER OF PASTY MATERIAL TO A CARRIER THROUGH A SCREEN (71) We, COMPAGNIE INTERNATIONALE POUR L'INFORMATIQUE CII-HONEYWELL BULL, a French Body Corporate, of 94 Avenue Gambetta, Paris (20), France, 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: The present invention relates to an apparatus for applying a layer of pasty material to a carrier through a screen, this apparatus being intended particularly, but not exclusively, for obtaining, by screen printing, circuits containing multiple thicklayer connections such as are generally referred to as substrates.

Our copending British Patent Applications Nos. 9267/78 (Serial No. 1602391) and 8019635 (Serial No. 1602393) have claims which are directed to similar apparatus and contain subject matter which is common to the present application.

Accordingly from a first aspect the present invention consists an apparatus for printing onto a carrier by applying material to the carrier through a screen comprising a screen having a plurality of substantially parallel lines, a blade, blade supporting and actuating means for displacing the blade relative to said screen, said blade supporting and actuating means including means for adjusting the direction of displacement of the blade to any desired angle, whereby the blade can slide parallel to said lines in the screen irrespentive of the angular position thereof.

From a second aspect the invention consists in apparatus for printing onto a carrier by applying material to the carrier through a planar screen, the screen having a pattern including a number of substantially parallel lines, means for mounting the screen and the carrier so material forced through the lines of the screen are deposited on the carrier in the same pattern as the pattern of the screen, a blade having an elongated, straight edge positioned for forcing the material through the screen onto the carrier, blade supporting and actuating means for displacing the blade edge in a plane parallel to the plane of the screen and in a straight line, said blade supporting and actuating means including means for adjusting the direction of displacement of the blade to any angle, whereby the blade can slide parallel to soid lines in the screen irrespective of the angular position of the screen.

In order that the present invention may be more readily understood, an embodiment thereof will now be described by way of non-limiting example, and with reference to the accompanying drawings, in which: Fig. 1 is an elevational view of one embodiment of a screen-printing apparatus formed in accordance with the invention, Fig. 2 is a partial cross-sectional view of the apparatus shown in Fig. 1, taken on the chain line and looking in the direction of arrows 2-2, Fig. 3 is a plan view, partly cut-away, of the apparatus shown in Fig. 1, Fig. 4 is a plan view showing a screenprinting screen fitted to its frame, Fig. 5 is a sectional view of the apparatus on the line 5-5 in Fig. 2, Fig. 6 is a partial circuit diagram of the electrical circuits for controlling and monitoring the screen-printing apparatus, and Fig. 7 is another partial circuit diagram of the circuits for controlling and monitoring the screen-printing apparatus.

Figs. 1, 2 and 3 show the main parts of a screen-printing apparatus which enables multilayer substrates with a high circuit density to be produced. As can be seen in these Figures, this apparatus has a frame formed by two vertical side-plates 10 and 11 which are attached to a bed 12 which rests on two cross-pieces 13 and 14 supported by legs 15, the two plates being connected at their upper ends by a horizontal support plate 16. This support plate 16 is provided with a circular opening 17 under which a screen-printing screen 18 fitted to a frame 19 may be positioned so as to cover the opening, as shown in Figs. 1 and 2. The assembly formed by the screen 18 and the frame 19, which can be withdrawn from the screen-printing apparatus, is shown schematically in Fig. 4.

Thus, referring to this figure, it can be seen that the frame 19 is provided with two bores 20 into which two corresponding pins in the screen-printing apparatus may be inserted, thus enabling the screen and frame assembly to be positioned in the apparatus with extreme accuracy. For reasons of simplicity only one of the two pins, indicated by reference 21, is shown in Fig. 1. Fig. 4 also shows that the frame 19 is additionally fitted with two screws 22 which, when screwed into the screen-printing apparatus, hold the screen and frame assembly in position against the lower face of the support plate 16, as can be seen in Fig. 2. It should be mentioned that the manufacturing tolerances on the bores 20 which co-operate with the pins 21 are of the order of a few microns and it is therefore virtually inpossible for the frame 19 to be removed manually from the pins 21 after it has been engaged on them. It is for this reason that the frame 19 incorporates two screws 23 (Fig. 4) which, when screwed in, bear against the lower face of the support plate 16 and thus enable the frame 19 to be released from the pins 21 of the apparatus without the risk of damaging them.

In Fig. 4, the pattern of openings in the screen 18 is shown at 24. This pattern of openings 24, which lies substantially at the centre of the screen, is enclosed by two marks of which one, 25, is formed by a cross and of which the other, 26, is formed by a line. These two marks are used to position the pattern 24 very accurately relative to the two bores 20. This setting-up operation, which is performed before the assembly formed by the screen 18 and the frame 19 is inserted in the screen printing apparatus, may for example be carried out by means of the pattern setting-up device which is illustrated and described in French patent No.

2,182,298.

Referring now to Fig. 2, it can be seen that the screen printing apparatus includes a platen 38 on which a carrier 28 of an insulating material such as alumina, which may or may not be covered with one or more insulating or conductive layers, may be placed in order to be brought into contact with a screen 18 which has previously been inserted in the apparatus. This platen 38 is attached to a setting-up unit 27 which is itself arranged on a horizontal plate 29 which is fitted with two bushes 30 and 31 which are able to slide on two vertical rods 32 and 33 secured to the frame of the apparatus, these two rods 32 and 33 extending upwardly alongside vertical plates 10 and 11 respectively. The setting-up unit 27 includes a slide member 34 which is attached to the plate 29 and which carries a swivelling ring 35. On the ring are in turn mounted two superimposed plates 36 and 37 which form two mutually orthogonal horizontal sliders.

A threaded spindle 39 which is arranged in a vertical position underneath plate 29 is attached at its upper end to a bearer block 40 secured to plate 29. The threaded spindle 39, which passes freely through an opening 41 in the bed 12, is engaged in an internally threaded sleeve 42. The sleeve 42 is housed in a socket 43 and is able to turn in the latter without being able to escape from it, this socket 43 being attached to a horizontal carrier plate 44 arranged below the bed 12 which is attached to the latter by fixing straps 45. The internally threaded sleeve 42 is attached to a gear wheel 46 which meshes with a pinion 47 mounted on the drive shaft of an electric motor 49 attached to the carrier plate 44. It should be mentioned that the components 34, 35, 36, 37, 38, 39, 40, 42 and 43 which have just been described, and also the assembly of the screen 18 and the frame 19 which is inserted in the apparatus, are centred on the vertical axis Z Z1 which passes through the centre of the opening 17 in the support plate 16. This being the case, if the motor 49 is energised to turn in a direction such that the sleeve 42, when turned by pinion 47 and gear 46, raises the threaded spindle 39 and the plate 29 attached to this spindle, the setting-up unit 27 which is attached to the plate 29 rises towards the screen 18. This movement continues until such time as the carrier 28 in position on the plate 38 mounted on the setting-up unit 27 comes into contact with the screen 18. To enable the carrier 28 to be exactly positioned relative to the screen, the screen-printing apparatus is fitted with locating means which will now be described. For this purpose, two studs 52 and 53 (Figs. 1 and 5) are attached to plate 29 next to the vertical plate 11 and on either side of the vertical plate PP1 which passes through the axes of rods 32 and 33. The upward movement of the plate 29 and the unit 27 which it carries is halted by two stops 54 and 55, against which the studs 52 and 53 respectively come to bear when carrier 28 comes into contact with screen 18, these stops 54 and 55 being attached to plate 11 as can be seen in Figs. 2, 3 and 5. Also, the plate 29 is fitted with a locating dowel 56 (Figs. 2 and 5) of conical shape which is arranged in a vertical position near bush 30 and which, at the end of the upward movement of the assembly 27, engages in a conical cavity in a locating socket 57 (Fig. 2) attached to upright 10. This cavity is machined in such a way that its conical surface exactly mates with the male conical surface of the dowel 56 when the studs 52 and 53 are in contact with their respective stops 54 and 55. The result is than when, at the end of the upward movement of the assembly 27. this male conical surface is in contact with the conical surface of the cavity in the socket 57, and when in addition the studs 52 and 53 are pressed against their respective stops 54 and 55, plate 29 is in a precisely defined and absolutely unvarying position relative to the frame of the apparatus and to the screen printing screen 18 inserted in the apparatus.

It is important that, at the end of the upward movement, the carrier 28 in position on the platen 38 mounted on the plate 29 should also occupy an exactly defined position relative to the screen 18 with which it has been brought into contact. To achieve this result, there are provided, on the upper face of the platen 38, three rollers 60, 61 and 62 (Fig. 5) against which one of the longitudinal edges and one of the transverse edges of the carrier 28 are applied by the pressure exerted by three pressure roller 63, 64 and 65 on the other edges of the carrier. The carrier 28, of which one longitudinal edge is pressed against the rollers 60 and 61 and of which one transverse edge is pressed against roller 62, is thus exactly positioned relative to platen 38. The plates 36 and 37 (Fig. 2) on which the platen 38 is mounted form mutually orthogonal sliders which allow the platen 38 to be shifted horizontally in two mutually perpendicular directions which are shown as X and Y respectively in Fig. 5, so that the centre of the carrier 28 which has been positioned on the platen can be moved onto the vertical axis ZZ1. The displacement of platen 38 in direction X are controlled by a knuried headed screw 66 (Fig. 2) arranged in plate 37. Similarly, the displacement of plate 38 in direction Y are controlled by a knurled-headed screw 67 (Fig. 2) arranged in plate 36. Two screws 68 and 69 associated with plates 37 and 36 respectively enable the operator to lock each of the two plates once these shifts have been completed. Furthermore, it may also be necessary to rotate the carrier 28 in its plane to bring the straight line joining the centres of rollers 60 and 61 parallel to a straight line connecting the two marks 25 and 26 on the screen 18 inserted in the machine. This rotary movement, which is of the order of a few degrees, for example 5 , at the maximum, may be achieved by operating a knurled headed screw 70 the effect of which is to turn the swivelling ring 35. When all these adiustments have been made, the carrier 28 which is in position on the platen 38 is in an exactly defined position relative to the screen 18 which has previously been inserted in the apparatus. It may also be mentioned that, when the plate 29 has been raised to its highest position, the contact between the carrier 28 and the screen 18 may be accurately adjusted by operating a knurled-head screw 71 which is mounted in slide member 34 and allows the assembly formed by the ring 35, the plates 36 and 37 and the platen 38 to be raised or lowered, the size of this movement being relatively small however, being less than a centimeter for example.

If reference is again made to Fig. 5, it can be seen that the platen 38 has passing through it a passage 72 which is connected by a nozzle 73 to a vacuum device (not shown) and which opens onto the platen through an opening 74. In this way a carrier 28 positioned on the platen may be held in position by suction. It should also be pointed out that the pressure rollers 63, 64 and 65 are under the control of an actuating rod 75, which, when operated by the operator, withdraws the three rollers from the carrier 28 to enable the operator to remove the carrier from platen 38 once the suction is shut off.

As can be seen from reference to Figs. 1 and 2, the circular opening 17 with which the horizontal support plate 16 is provided is intended to enable a blade 76 to come into contact with the screen-printing screen 18 inserted in the apparatus in order to apply a layer of a pasty material deposited on the pattern of openings in the screen through the screen and onto a carrier 28 which has previously been brought against the screen. The blade 76 is mounted on a blade carrier 77 which is in turn attached to the lower end of a vertical spindle 78 which is arranged, in a manner which will be described below, on a movable carriage 79 which is mounted to slide on two horizontal guide rods 80 and 81 (Figs. 2 and 3). The two rods are attached, parallel to one another, to a frame 82 mounted on a movable part 83. The movable part 83, which is formed in the embodiment being described by a circular plate provided with a central opening 84, rests on the horizontal support plate 16 and is able to pivot about the vertical axis ZZ1. In the embodiment illustrated in Figs. 2 and 3, this circular plate is provided, on its lower face, with a circular ridge 85 which engages in a corresponding circular channel formed in the upper face of the support plate 16 and which allows the operator to turn the circular plate 83 and the various parts mounted on it about axis ZZ1. Clips 86 attached to the upper face of the support plate 16 prevent the circular ridge 85 from escaping from its channel. Figs. 1 and 3 show that the movable carriage 79 is engaged with a threaded spindle 87 which is arranged parallel to guide rods 80 and 81 and is able to turn in frame 82, which threaded spindle 87 may be rotated by an electric motor 88 attached to the frame 82 in order to cause the carriage 79 to slide on rods 80 and 81.

As can be seen in Fig. 2, the vertical spindle 78, which is mounted to slide on carriage 79, is threaded in its upper part to enable it to be retained by a nut 100 which, being screwed onto the threaded part, comes to rest against the carriage when the blade 76 is in contact with the screen-printing screen 18. A second nut 90, which is also screwed onto the threaded part, enables the spindle 78 to be operated by an actuating lever 92 which is articulated at one of its ends to a shaft 93 secured to carriage 79, support for the spindle 78 from the lever being provided by a washer 91 which incorporates a knife edge and is inserted between nut 90 and lever 92, as shown in Fig.

2. The other end of the lever 92 is pressed against a cam 94 which is fixed on a shaft 95 (Figs. 2 and 3) driven by a motor 96 mounted on carriage 79. In Fig. 2, this cam 94 is shown in the raised position, that is to say the position which it normally occupies when the screen-printing apparatus is at rest. In this position, the blade 76 is spaced away from the screen-printing screen 18, as shown in Fig. 2. If motor 96 is then energised to turn shaft 95 for half a revolution, the cam 94 comes to the lowered position and lever 92, pivoting about its shaft 93, allows the assembly formed by spindle 78, blade 76, blade carrier 77 nut 90 and washer 91 to descend. By means of nut 90 and ring nut 100 the assembly is so adjusted that when cam 94 is in the lowered position, blade 76 rests against the screen-printing screen 18. Two detectors D1 and D2, which are formed in the embodiment being described by two photo-electric cells, are mounted on carriage 79 to detect, respectively, the moment when the cam 94 reaches its raised position and the moment when it reaches its lowered position. These two detectors form part of an electrical control and monitoring circuit which will be described below.

The movable carriage 79, which slides on rods 80 and 81, can be moved between two extreme positions, namely a first extreme position which is that normally occupied by the carriage 79 when the screen-printing apparatus is at rest, the presence of the carriage 79 at this first extreme position being detected by a detector D3 (Fig. 3), and a second extreme position in which the carriage 79 lies in line with a detector D4 (Fig. 3).

This being the case, it can be seen that if, after the appropriate pasty material has been deposited on the screen-printing screen 18 and after the motor 96 has been energised to bring the blade 76 into contact with the screen, motor 88 is operated to tum in a direction such that blade 79 moves from its first extreme position towards its second extreme position, the blade 76, propelled by the carriage, will spread this pasty material across the screen 18 and will apply it, through the pattern of openings 24 in the screen, to the wafer 28 which has previously been brought into contact with the screen.

In cases where, as can be seen in Fig. 4, the pattern of openings 24 is made up in essence of lines extending substantially in the same direction, the circular plate 83 may be pivoted until the guide rods 80 and 81 of the carriage are parallel to this direction before motors 96 and 88 are energised. This being the case, when the blade 76 is then driven forward by the carriage, the pasty material will be spread across the screen 18 in this direction, which enables a deposit of pasty material to be obtained on the carrier 28 pressed against the screen whose configuration exactly matches the outline of the pattern of openings 24 in the screen.

As shown in Figs. 1 and 3, the frame 82 is hinged to movable part 83 by means of a horizontal shaft 97 arranged transversely to the guide rods 80 and 81. This being the case, by tilting the frame 82 about its shaft 97, the operator can easily gain access to the blade 76, to clean it for example, without it being necessary to remove the screenprinting screen 18 for this purpose. When the apparatus is operating, the frame 82 is held fixed on part 83 by means of a screw 98.

Returning to Fig. 2, there can also be seen a detector D5 which is mounted on the bed 12 and which is used to detect whether the plate 29 is or is not in its rest position, this rest position being that normally occupied by the plate 29 when the screen-printing apparatus is at rest and the plate is in its lowest position as shown in Fig. 2. Another detector D6, which is attached to vertical plate 11 is used to detect whether or not the plate 29 is in its highest position, this position being that occupied by plate 29 when the carrier 28 in position on platen 38 is in contact with screen 18. As can be seen in Fig. 1, plate 29 is fitted with a vertical bar 99 which moves past a detector D7 when plate 29 is set in motion by motor 49, this bar being adjusted to excite detector D7 for as long as the distance between screen 18 and the carrier 28 in position on platen 38 is less than a predetermined value which, in the example being described, has been taken as equal to 5 mm and which represents the distance between the screen 18 and the carrier 28 at which the upward movement of the plate 29 should be slowed down to enable the carrier 28 to come to bear against the screen 18 without injury.

It should be mentioned that, in the embodiment being described, each of the detectors D1 to D7 is formed by a photoelectric cell which normally receives a light beam emitted by a light source (not shown in the drawings) and which, in response to receiving this beam, generates a voltage at its output. This voltage ceases whenever a movable part passes between the cell and the light source and interrupts the beam.

There will now be described, with refer ence to Figs. 6 and 7, the electrical control circuit which is used to control the upward and downward movements of the plate 29 and the movements of the blade 76. The circuit diagram which is shown in Figs. 6 and 7 is a general diagram which iricludes manually operated contacts and relay contacs intended for use under the conditions which are about to be described. The relay contacts are designated by the same references as the coils which control them but with the letter C prefixed. A contact which is normally closed when the coil of the relay which controls it is not energised is represented in the diagram by a black triangle. The motors 49, 88 and 96, and the relays shown in Figs. 6 and 7, are normally fed by DC current between two terminals (+) and (-).

When the apparatus is not operating, the movable plate 29 is in its rest position close to the bed 12. The plate 29 then interrupts the light beam which is transmitted towards detector D5 and a positive voltage therefore fails to appear at the output of detector D5.

This being the case, two relays B1 1 and B28 (Fig. 6) which are connected to the output of D5 are not energised. The contacts CB11 and CB28 (Fig. 7) which are controlled by these relays are thus open. Since the light beams which are transmitted towards detectors D6 and D7 are not interrupted, positive voltages appear at the outputs of both of these detectors. Two relays B04 and B03 (Fig. 6), which are connected to the outputs of detectors D6 and D7 respectively, are thus energised. Because of this contact CB03 of relay B03 is closed whilst contact CB04 (Fig. 7) of relay B04 is open. Also, since cam 94 is in the raised position, the light beams transmitted towards detectors D1 and D2 are not interrupted. Positive voltages thus appear at the outputs of these detectors and energise two relays B09 and B05 (Fig. 6) which are connected to the outputs of detectors D1 and D2 respectively. Being energised, relays B09 and B05 thus hold their re spective contacts CB09 and CB05 (Fig. 7) in the working position. In addition, carriage 79, being in its first extreme position, interrupts the light beam transmitted towards detector D3 and as a result, three relays B10, B31 and B32 (Fig. 6), which are connected to the output of D3, are not energised. Relay B10, being unenergised, holds its contact CB10 (Fig. 7) open, while relay B32, being un-energised, holds its contact CB32 closed.

Because relay B31 is not energised, contact CB31 1 is held in the rest position. Given that carriage 79 is not interrupting the light beam transmitted towards detector D4, a positive voltage appears at the output of this detector and energises three relays B08, B30 and B40 (Fig. 6) connected to this output. Being energised, relays B30 and 1340 hold their con tacts CB30 and CB40 (Fig. 7) open, whilst relay B8, being energised, holds its contact C1308 in the working position.

By using adjusting means which will not be described here, the operator is able, by using screws 66, 67, 68, 69, 70 and 71, to shift the platen 38 in such a way that the rollers 60, 61 and 62 occupy an accurately established position relative to the pattern in the screen 18 inserted in the apparatus.

When this operation has been completed, a carrier 28 may be placed on the platen and held against it by suction, the wafer being pressed against rollers 60, 61 and 62 in the manner indicated above. When this placing in position has been completed, the operator places a little pasty material on the screen 18. If the operator then presses a manual push-switch K (Fig. 7) and holds it closed until, as will be seen below, contacts C1311 closes, a DC current flows from terminal (+) through the closed switch K and energises two relays B01 and B02. Being energised, relay B01 closes its contact CB01. Similarly, being energised, relay B02 closes its contact CB02. Under these conditions an electrical circuit is closed, this circuit comprising, as can be seen in Fig. 6, the (+) terminal, closed contact CB02, changeover contact BP1 in the rest position, closed contact CB03, motor 49, changeover contact BP2 in the rest position and the (-) terminal.

Motor 49, which thus has a supply, turns in a direction such that the threaded spindle 39 moves upwards, thus driving the plate 29, the setting-up unit 27, the platen 38 and the carrier 28. In the course of this upward movement, plate 29 ceases to interrupt the light beam transmitted towards detector D5 and a positive voltage thus appears at the output of this detector and energises relays B11 and B28. Being energised, relay B28 closes its contact CB28 (Fig. 7). Similarly, being energised, relay B11 closes its contact CB1 1 and thus establishes a circuit to hold in relays B01 and B02, even if the operator should cease to press the manual switch K at this moment. The ascent of the plate 29, at a relatively high speed of the order of 10 cm per second, continues until such time as the plate 29 ceases to interrupt the light beam transmitted towards detector D7. At this moment a positive voltage appears at the output of D7. Relay B03, which is thus energised, opens its contact CB03 and motor 49 is thus fed by a current which flows through a resistor R connected in parallel with the terminals of contact Cub03, as shown in Fig. 6. Because of this, the ascent of the plate 29 now takes place at reduced speed of the order of 5 mm per second. This ascent continues until such time as the plate 29 is brought to a halt by the stops 54 and 55 and by the locating dowel 56 which has engaged in the cavity in socket 57. in this position the carrier 28 is pressed against the screen-printing screen 18, it being ensured that it is held against the screen by the fact that the energisation of motor 49 continues, known means (not described) being provided to enable the motor to slip, which avoids any danger of parts being damaged. It should be mentioned that plate 29, having arrived at its highest position and being sustained there in the above-mentioned manner, interrupts the light beam which is transmitted towards detector D5. The positive voltage which was present up to that point at the output of this detector then ceases, causing relay B04 to be energised. Being de-energised, relay B04 thus closes its contact CB04. A DC current then flows from the (+) terminal, through the closed contact CB04, the changeover contact CB05 in the working position, the closed contact CB32 and a closed contact CBl9 which will be referred to below, and energises a relay B18.

Being energised, relay B18 closes its contact CB18 (Fig. 6). The effect of contact CB18 closing is to energise motor 96 and thus to turn the cam 94. Cam 94 then moves away from its raised position, thus allowing the assembly formed by spindle 78, blade-carrier 77 and blade 76 to descend. In the course of this movement cam 94 interrupts the light beam which is transmitted towards detector Dl. Because of this, the relay B09 which is connected to the output of D1 is de-energised and changes its contact CB09 over to the rest position. The blade 76 comes into contact with the screen-printing screen 18 slightly before the cam 94 reaches its lowest position. Cam 94 interrupts the light beam transmitted towards detector D2 at the moment when it reaches its lowest position.

At this moment the relay B05 connected to the output of D2 is de-energised and changes its contact CB05 over to the rest position. As a result of this change-over, relay B18 is de-energised and opens its contact CB18, the effect of which is to cut off the supply to motor 96 and thus to stop cam 94 in the lowered position. Also, because of the changeover of contact CB05, a DC current now flows from the (+) terminal, through the closed contact CB04, the changeover contact CB05 in the rest position, and the changeover contact CB08 in the working position, and energises a relay B07. Being energised, relay B07 closes its contact CB07.

(Fig. 6). An electrica changes its contact CB05 over to the working position. This changeover has no effect on the supply to motor 88 however, due to the fact that relay B20 continues to be energised by the current which flows from the (+) terminal through the closed contact C1304, the contact CB09 in the rest position, and the closed contact Cub21. Under these conditions, contact CB20 remaills closed and cam 94, being driven by motor 96, continues its movement towards its raised position. At the moment when it reaches the raised position, cam 94 ceases to interrupt the light beam which is transmitted towards detector D1. The positive voltage which then appears at the output of this detector is applied to relay B09 which, being energised, changes its contact CB09 over to the working position. As a result of this changeover, relays B20 and B21 are de-energised and open their contacts CB20 and Cub21, the effect of which is to stop motor 96 and thus to halt cam 94 in its raised position. In addition, owing to the fact that contact CB09 is now in the working position, a DC current flows from the (+) terminal, through the closed contact CB04, the contact C1309 in the working position, and the closed contact CBl0, and energises relay B07. Relay B07, being energised, closes its contact CB07. Motor 88 is then energised but, since changeover contacts BC1 and BC2 are now in the working position, it turns in a direction such that carriage 79, leaving its second extreme position, is brought back towards its first extreme position. Carriage 79 thus ceases to interrupt the light beam which is transmitted towards the detector D4 and the positive voltage which appears at the output of this detector is applied to relays B08, B30 and B40, Relays B30 and B40, being energised, open their contacts CB30 and CB40, although this has no effect on the energisation of relays B41, B42, B25, B19 and BC, since contacts CB25, CB41 remain closed. Relay B08, being energised, changes its contact Cub08 over to the working position. It should be mentioned that, during the return movement of the carriage towards its first extreme position, the blade 76 remains spaced away from screen 18 owing to the fact that the cam 94 is now stopped in its raised position. At the moment when it reaches its first extreme position, carriage 79 interrupts the light beam which is transmitted towards detector D3. This interruption causes relays B10, B31 and B32 to be de-energised. Relay B10, being de-energised, opens its contact CB10. Because of this, relay B07 is de-energised and opens its contact CB07, the effect of which is to stop motor 88 and thus to half carriage 79 in its first extreme position. Also, relay B32, being de-energised, closes its contact CB32.

Finally, relay B31, being de-energised, changes its contact CB31 1 over to the rest position. A DC current then flows from the (+) terminal, through the contact CB31 in the rest position and the closed contact CB42, and energises a relay BP. Relay BP, being energised, then changes over its contacts BP1 and BP2 (Fig. 6) to the working position. Because of this the current which up to that point was supplying motor 49 to enable the carrier 28 to be held in contact with screen 18 is then reversed, and as a result motor 49 now drives the assembly formed by threaded spindle 39, plate 29, unit 27, platen 38 and carrier 28 downwards. In the course of this movement plate 29 ceases to interrupt the light beam which is transmitted towards detector D6 and the voltage which appears at the output of this detector is applied to relay B04. Relay B04, being energised, opens its contact CB04.

When, in the course of the downward movement of plate 29, bar 99 then again interrupts the light beam which is transmitted towards detector D7, the positive voltage which was present at the output of this detection ceases and relay B03, being de-energised, closes its contact CB03. When plate 29, as it arrives at its rest position, finally interrupts the light beam which is transmitted towards detector D5, the positive voltage which was present at the output of this detector ceases and, because of this, relays B11 and B28 are de-energised. Relay B11, being de-energised, then opens its contact CB11 and this de-energises relay B01 and B02. Consequently, contacts CBO1 and CB02 of the de-energised relays B01 and B02 open, the effect of the opening of contact CB02 being to cut-off the supply to motor 49 and thus to immobilise plate 29 in its rest position. Also, relay B28, being deenergised, opens its contact CB28 and thus causes relays B41, B42, B25, B19 and BC to be de-energised. Relays B25, B41 and B42, being de-energised, open their respective contacts CB25, CB41 and CB42. Relay B19, being de-energised, closes its contact CB19. Relay BC, being de-energised, changes its contacts BC1 and BC2 over to the rest position. Finally, the effect of contact CB42 opening is to de-energise relay BP, which then changes its contacts BP1 and BP2 over to the rest position. As soon as plate 29 has returned to its rest position, carrier 28, to which a layer of pasty material has been applied, can be removed by the operator to be placed in an oven to enable the layer to solidify. The screenprinting apparatus is then ready to make a fresh application of pasty material, which application may be made either to a carrier already coated with one or more solidified layers of insulating or conductive materials, or to a carrier to which no pasty material has as yet been applied.

Although the description and the accompanying drawings relate to a preferred embodiment of the invention, it is understood that various modifications, additions, and substitutions which do not exceed the scope of the said invention may be made to suit particular cases and applications, without affecting the principle of the invention. In particular, the relay circuitry of the control circuit which is shown in Figs. 6 and 7 could be wholly or partly replaced by any electronic circuitry which performs an equivalent function.

WHAT WE CLAIM IS:- 1. Apparatus for printing onto a carrier by applying material to the carrier through a screen comprising a screen having a plurality of substantially parallel lines, a blade, blade supporting and actuating means for displacing the blade relative to said screen, said blade supporting and actuating means including means for adjusting the direction of displacement of the blade to any desired angle, whereby the blade can slide parallel to said lines in the screen irrespective of the angular position thereof.

2. Apparatus according to claim 1, wherein said blade supporting and actuating means includes a frame supported by screen supporting means, and wherein said means for adjusting the direction of movement of the blade comprises means for rotating said frame about itself on said screen supporting means.

3. Apparatus according to claim 2, wherein said frame rotating means comprises a substantially annular plate mounted on said frame and having a ridge slidably mounted in a corresponding annular channel provided in said screen supporting means.

4. Apparatus for printing onto a carrier by applying material to the carrier through a planar screen, the screen having a pattern including a number of substantially parallel lines, means for mounting the screen and the carrier so material forced through the lines of the screen are deposited on the carrier in the same pattern as the pattern of the screen, a blade having an elongated, straight edge positioned for forcing the material through the screen onto the carrier, blade supporting and actuating means for displacing the blade edge in a plan parallel to the plane of the screen and in a straight line, said blade supporting and actuating means including means for adjusting the direction of displacement of the blade to any angle whereby the blade can slide parallel to said lines in the screen irrespective of the angular position of the screen.

5. Apparatus according to any one of the preceding claims and wherein said blade supporting and actuating means include means for controlling lowering of the blade towards the screen and for controlling the attitude of the blade on the screen.

6. Apparatus according to claim 5, wherein said blade supporting and actuating means further includes a carriage for displacing the blade on the screen along said predetermined direction and a blade carrier, and wherein said means for controlling lowering of the blade includes an actuating lever coupled to said blade carrier and having a first end pivotable on a shaft secured to said carriage and another end pressing against a motor driven cam.

7. Apparatus according to either claim 5 or claim 6, wherein said means for controlling lowering of the blade further includes means for adjusting the length of travel of said blade.

8. Apparatus according to claim 7, wherein said blade carrier is coupled to said actuating lever through a spindle connected to the blade carrier, and wherein said means for controlling lowering of the blade further comprises a nut mounted on said spindle and adjusted for a rest position of the blade on said carriage when the blade is in said lowered position.

9. Apparatus for printing on a carrier as claimed in claim 1 or claim 4, substantially as hereinbefore described with reference to the accompanying drawings.

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

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. Although the description and the accompanying drawings relate to a preferred embodiment of the invention, it is understood that various modifications, additions, and substitutions which do not exceed the scope of the said invention may be made to suit particular cases and applications, without affecting the principle of the invention. In particular, the relay circuitry of the control circuit which is shown in Figs. 6 and 7 could be wholly or partly replaced by any electronic circuitry which performs an equivalent function. WHAT WE CLAIM IS:-

1. Apparatus for printing onto a carrier by applying material to the carrier through a screen comprising a screen having a plurality of substantially parallel lines, a blade, blade supporting and actuating means for displacing the blade relative to said screen, said blade supporting and actuating means including means for adjusting the direction of displacement of the blade to any desired angle, whereby the blade can slide parallel to said lines in the screen irrespective of the angular position thereof.

2. Apparatus according to claim 1, wherein said blade supporting and actuating means includes a frame supported by screen supporting means, and wherein said means for adjusting the direction of movement of the blade comprises means for rotating said frame about itself on said screen supporting means.

3. Apparatus according to claim 2, wherein said frame rotating means comprises a substantially annular plate mounted on said frame and having a ridge slidably mounted in a corresponding annular channel provided in said screen supporting means.

4. Apparatus for printing onto a carrier by applying material to the carrier through a planar screen, the screen having a pattern including a number of substantially parallel lines, means for mounting the screen and the carrier so material forced through the lines of the screen are deposited on the carrier in the same pattern as the pattern of the screen, a blade having an elongated, straight edge positioned for forcing the material through the screen onto the carrier, blade supporting and actuating means for displacing the blade edge in a plan parallel to the plane of the screen and in a straight line, said blade supporting and actuating means including means for adjusting the direction of displacement of the blade to any angle whereby the blade can slide parallel to said lines in the screen irrespective of the angular position of the screen.

5. Apparatus according to any one of the preceding claims and wherein said blade supporting and actuating means include means for controlling lowering of the blade towards the screen and for controlling the attitude of the blade on the screen.

6. Apparatus according to claim 5, wherein said blade supporting and actuating means further includes a carriage for displacing the blade on the screen along said predetermined direction and a blade carrier, and wherein said means for controlling lowering of the blade includes an actuating lever coupled to said blade carrier and having a first end pivotable on a shaft secured to said carriage and another end pressing against a motor driven cam.

7. Apparatus according to either claim 5 or claim 6, wherein said means for controlling lowering of the blade further includes means for adjusting the length of travel of said blade.

8. Apparatus according to claim 7, wherein said blade carrier is coupled to said actuating lever through a spindle connected to the blade carrier, and wherein said means for controlling lowering of the blade further comprises a nut mounted on said spindle and adjusted for a rest position of the blade on said carriage when the blade is in said lowered position.

9. Apparatus for printing on a carrier as claimed in claim 1 or claim 4, substantially as hereinbefore described with reference to the accompanying drawings.