GB2511724A

GB2511724A - Print head and print head assembly

Info

Publication number: GB2511724A
Application number: GB1223005.8A
Authority: GB
Inventors: George Harold Bertram Foot; Jeffrey Richard Willshere
Original assignee: DTG International GmbH
Current assignee: ASM Assembly Systems Switzerland GmbH
Priority date: 2012-12-20
Filing date: 2012-12-20
Publication date: 2014-09-17
Also published as: GB201223005D0

Abstract

There is provided a print head 1 with multiple printing blades 5 in spaced relation in order to reduce the length of a print stroke and hence the time of a print cycle. The print head 1 and print head assembly incorporating the same for use in printing a pattern 7 of deposits of a print medium onto a workpiece 11 through a pattern of apertures in a printing screen 9. The print head 1 acts to bias print medium onto a surface of the printing screen 9. The printing blades 5 have a pitch d which is less than a length l of the pattern 7. The print head 1 may contain as many as ten printing blades 5. The printing blades 5 may be squeegee elements (105, Fig.5) which form enclosed chambers (117, Fig.5)

Description

PRINT HEAD AND PRINT HEAD ASSEMBLY

The present invention relates to a print head for use in printing a pattern of deposits of a print medium, typically a paste, such as a solder or silver paste, or an adhesive, through a printing screen, often alternatively referred to as a stencil, onto a workpiece, typically a circuit board or a wafer, such as for a fuel or solar cell, and print head assembly which incorporates such a print head.

Various print heads exist for printing onto substrates, both in the form of squeegees and enclosed print heads. These print heads operate by traversing in a single stroke across the image to be deposited.

The present inventors have recognized that it would be possible to reduce the length of the print stroke, and hence the time of the print cycle, by providing the print head with multiple printing blades in spaced relation.

For example, by arranging the printing blades at a pitch which is half of the length of the print stroke for the image to be printed, the print head needs correspondingly only to traverse half of the usual, full-length print stroke of a conventional print head 201, having a single print medium applicator 205 in the form of a squeegee, as illustrated in Figures 8(a) and (b), and so on for greater numbers of printing blades.

The skilled person would not hitherto have contemplated this arrangement, as separation of the printing screen and the workpiece, known as "snap off", with a printing blade and the associated print medium roll located on the image to be printed, would have been understood to cause a line defect, corresponding to the edge of the printing blade, in the printed deposit.

The present inventors have developed a multi-bladed print head which provides for the printing of a uniform pattern on a workpiece when using a printing stroke which is shorter than the image to be printed.

The present inventors have also devised a print head which can be operated with either a reciprocating motion or an oscillating motion.

In one aspect the present invention provides a print head for use in printing a pattern of deposits of a print medium onto a workpiece through an image pattern of apertures in a printing screen, the print head including a plurality of print medium applicators which are arranged in spaced relation and act to bias print medium onto a surface of the printing screen.

In one embodiment the print medium applicators comprise elongate elements which are arranged substantially in parallel relation.

In one embodiment the print medium applicators comprise elements arranged in a two-dimensional array.

In one embodiment the print medium applicators have a pitch which is less than an extent of the image pattern.

In one embodiment the print head includes at least two print medium applicators within a dimension corresponding to the extent of the image pattern.

In one embodiment the print head includes at least three print medium applicators within a dimension corresponding to the extent of the image pattern.

In one embodiment the print head includes at least five print medium applicators within a dimension corresponding to the extent of the image pattern.

In one embodiment the print head includes at least ten print medium applicators within a dimension corresponding to the extent of the image pattern.

In one embodiment the print medium applicators have a pitch of less than about 20 mm.

In one embodiment the print medium applicators have a pitch of less than about 10 mm.

In one embodiment the print medium applicators have a pitch of from about 2 mm to about 10 mm.

In one embodiment the print medium applicators have a pitch of from about 2 mm to about 5 mm.

In one embodiment the print medium applicators comprise squeegee elements.

In one embodiment the squeegee elements each comprise a squeegee blade which presents an applicator surface which is downwardly facing relative to a surface of the printing screen.

In another embodiment the squeegee elements each comprise a body which presents oppositely-directed applicator surfaces, each presenting an applicator surface which is downwardly facing relative to a surface of the printing screen.

In another embodiment the applicator surfaces extend in multiple directions or can have components which extend in multiple directions.

In one embodiment the applicator surfaces define a rectangular or square ape rt u re.

In one embodiment the squeegee elements, together with the printing screen, define enclosed chambers which contain the print medium.

In one embodiment the print head includes flow passages which provide fluid communication to the chambers, to which can be connected a print medium supply, which is operative to supply print medium to the chambers.

In one embodiment the print head allows for reciprocating operation.

In one embodiment the print head is operative to print a pattern of deposits onto a first workpiece in a single stroke in a first direction and onto a second, subsequent workpiece in a single stroke in a second, opposite direction.

In another embodiment the print head is operative to print a pattern of deposits onto a workpiece with multiple, reciprocating strokes in first and second directions.

In one embodiment the print head is operative to print a pattern of deposits onto a workpiece with two strokes, being a first stroke in a first direction and a second stroke in a second direction.

In another embodiment the print head is operative to print a pattern of deposits onto a workpiece by performing multiple strokes in first and second directions.

In one embodiment the print head is employed in the printing of elongate patterns.

In one embodiment the print head is employed in the printing of metallization lines of solar cell wafers.

In one embodiment the print heads are supported by a support element.

In another aspect the present invention relates to a print head assembly, comprising: the above-described print head; and an oscillator which couples the print head to a print head transport mechanism which displaces the print head over a print stroke.

In one embodiment the oscillator provides for oscillation in a single axis.

In another embodiment the oscillator provides for oscillation in a dimensional plane over a surface of the printing screen during a print stroke.

In one embodiment the print head follows a predetermined path during the print stroke, optionally an annular, figure of eight or zig-zag path.

Preferred embodiments of the present invention will now be described hereinbelow by way of example only with reference to the accompanying drawings, in which: Figure 1 illustrates a print head in accordance with a first embodiment of the present invention; Figures 2(a) and (b) illustrate the start and finish positions of the print stroke of the print head of Figure 1; Figure 3 illustrates an image of a line as printed using the print head of Figure 1 corresponding to the point of contact of one print medium applicator on the printing screen during separation of the printing screen and the workpiece; Figures 4(a) to (c) illustrate a print head as a modification of the first embodiment of the present invention; Figure 5 illustrates a print head in accordance with a second embodiment of the present invention; Figure 6 illustrates a print head as a modification of the second embodiment of the present invention; and Figure 7 illustrates a print head in accordance with a third embodiment of the present invention; and Figures 8(a) and (b) illustrate a conventional print head, in the form of a squeegee, in the start and finish positions of a conventional print stroke.

Figures 1 and 2 illustrate a print head 1 in accordance with a first embodiment of the present invention.

The print head 1 comprises a body element 3, and a plurality of print medium applicators 5 which are mounted to the body element 3 in spaced relation, in this embodiment in parallel relation.

In this embodiment the print medium applicators 5 have a pitch d, which is less than a length I of a pattern 7 in a printing screen 9 to be printed onto a workpiece 11 therebelow, and represents half of the length of the stroke as would be required to traverse the length I of the pattern 7 using a conventional print head.

Figures 2(a) and (b) respectively illustrate the start and finish positions of one print stroke of the print head 1, in this embodiment over a wafer 11 having three bus bars.

With this arrangement, the print head 1 reduces the print cycle by approximately one half as compared to a conventional print head.

In this embodiment the print medium applicators 5 comprise blades, here flat blades, in the form of a typical squeegee, which are inclined forwardly relative to the surface of the printing screen 9.

In this embodiment the print medium applicators 5 each present a downwardly-facing applicator surface 15, which encloses an angle of inclination of about 60 degrees relative to the surface of the printing screen 9 and is operative to maintain the print medium ahead of the contact edge of the respective print medium applicators 5. In alternative embodiments the applicator surface 15 could have an angle of inclination of between about 30 degrees and about 60 degrees, such as 45 degrees.

In this embodiment the print medium applicators 5 comprise plastic or elastomeric blades. In an alternative embodiment the print medium applicators 5 could comprise metal blades.

In this embodiment the printing screen 9 is arranged in off-contact relation to the workpiece 11. In an alternative embodiment the printing screen 9 could be arranged in on-contact relation to the workpiece 11.

Figure 3 illustrates an image of a line as printed using the print head 1 corresponding to the point of contact of one print medium applicator S on the printing screen 9 during separation of the printing screen 9 and the As can be seen, contrary to that which would have been expected by the skilled person prior to the present invention, there is no visible change in the height or width of the print line at the point of contact of the print medium applicator 5 on the printing screen 9.

In an alternative embodiment the print medium applicators 5 could comprise a body which presents first and second, oppositely-directed applicator surfaces 15, in the form a "diamond" shaped blade, which allows for reciprocating operation of the print head 1, either with a single reciprocation per workpiece 11 or multiple reciprocations per workpiece 11.

In one modification, as illustrated in Figures 4(a) to (c), the print head 1 could comprise four print medium applicators 5 which have a pitch d which is half that of the embodiment having two print medium applicators 5, and requires a print stroke of half of the length.

Figure 5 illustrates a print head 101 in accordance with a second embodiment of the present invention.

The print head 101 comprises a body element 103, and a plurality of print medium applicators 105 which are arranged to the body element 103 in spaced relation, in this embodiment in parallel relation.

In this embodiment the print medium applicators 105 have a pitch d, which is less than an extent or length / of the pattern 107 in a printing screen 109 to be printed onto a workpiece 111 therebelow, and, here having six print medium applicators 105, represents one-sixth of the length of the stroke as would be required to traverse the length I of the pattern 107 if printed using a conventional print head.

With this arrangement, the print head 101 reduces the print cycle to that of approximately one sixth as compared to a conventional print head. With a greater or fewer number n of print medium applicators 105, the print stroke would be reduced or increased in correspondence to the number of print medium applicators 105.

In this embodiment the print medium applicators 105 comprise a body 114, which includes first and second applicator surfaces 115, which are oppositely directed and inclined downwardly relative to the surface of the printing screen 109, in the form a "diamond" shape.

In this embodiment, adjacent print medium applicators 105, as defined by the opposing applicator surfaces 115 thereof, together with the printing screen 109, define an enclosed chamber 117 which contains the print medium. This arrangement is particularly advantageous, in allowing the chamber 117 to be of small size, thus requiring only a small amount of print medium to be retained.

With this arrangement, the print head 101 allows for reciprocating operation by operation of a print head transport mechanism 119, either with a single reciprocation per workpiece 111 or multiple reciprocations per workpiece 111. The print head 101 of this embodiment has particular application in the printing of a plurality of elongate patterns, such as the metallization lines of solar cell wafers. In such an application the pitch d of the print medium applicators 105 can be configured so as to correspond to the pitch of the patterns to be printed.

In this embodiment each downwardly-facing applicator surface 115 encloses an angle of inclination of about 45 degrees relative to the surface of the printing screen 109 and is operative to maintain the print medium ahead of the contact edge of the respective print medium applicator 105. In alternative embodiments the applicator surface 115 could have an angle of inclination of between about 30 degrees and about 60 degrees, such as 60 degrees.

In this embodiment the printing screen 109 is arranged in off-contact relation to the workpiece 111. In an alternative embodiment the printing screen 109 could be arranged in on-contact relation to the workpiece 111.

In this embodiment the print head 101 includes flow passages 121 which provide fluid communication to the chambers 117, to which is fluidly connected a print medium supply 123, which is operative to supply print medium to the chambers 117.

-10 -With this arrangement, a predetermined amount of print medium can be maintained in the chambers 117 without user intervention.

In a first mode of operation, the print head 101 is operative to print a pattern of deposits onto the workpiece 111 in a single stroke in a first direction A of a displacement corresponding to the pitch d of the print medium applicators 105, with the subsequent workpiece 111 being printed in a single stroke of a corresponding displacement in a second, opposite direction B. In a second mode of operation, the print head 101 is operative to print a pattern of deposits onto the workpiece 111 with multiple, reciprocating strokes in first and second directions A, B of displacement corresponding to the pitch d of the print medium applicators 105.

In one embodiment the print head 101 performs a printing operation with two strokes, being a first stroke in a first direction A of a displacement corresponding to the pitch d of the print medium applicators 105 and a second stroke of corresponding displacement in a second direction B. In another embodiment the print head 101 performs a printing operation by performing multiple strokes in first and second directions A, B of displacement corresponding to the pitch d of the print medium applicators 105.

In one modification, as illustrated in Figure 6, the print medium applicators can be arranged such as to be in a two-dimensional array.

With this arrangement the applicator surfaces 115 extend in multiple directions or can have components which extend in multiple directions.

-11 -In this embodiment the applicator surfaces 115 define a rectangular aperture, here a square aperture, but could have other aperture shapes, including arcuate shapes, such as circular or ovoid.

Figure 7 illustrates a print head 101 in accordance with a third embodiment of present invention.

The print head 101 of this embodiment is similar to the print head 101 of the above-described second embodiment, and thus, in order to avoid unnecessary duplication of description, only the differences will be described in detail, with like parts being identified by like reference signs.

The print head 101 of this embodiment differs from the second-described embodiment only in further comprising an oscillator 131 which couples the print head 101 to the print head transport mechanism 119 which displaces the print head 101 over the print stroke.

In this embodiment the oscillator 131 provides for oscillation in a single dimension, such as along the axis of displacement or at an angle thereto, such as orthogonally thereto or at an angle intermediate the axis of displacement and its orthogonal.

In another mode of operation, the print head 101 can be operated to oscillate in a two-dimensional plane, and in embodiments can follow annular, figure-of-eight or zig-zag paths.

Finally, it will be understood that the present invention has been described in its preferred embodiment and can be modified in many different ways without departing from the scope of the invention as defined by the appended claims.

Claims

-12 -CLAIMS1. A print head for use in printing a pattern of deposits of a print medium onto a workpiece through an image pattern of apertures in a printing screen, the print head including a plurality of print medium applicators which are arranged in spaced relation and act to bias print medium onto a surface of the printing screen.
2. The print head of claim 1, wherein the print medium applicators comprise elongate elements which are arranged substantially in parallel relation.
3. The print head of claim 1, wherein the print medium applicators comprise elements arranged in a two-dimensional array.
4. The print head of any of claims 1 to 3, wherein the print medium applicators have a pitch which is less than an extent of the image pattern.
5. The print head of claim 4, wherein the print head includes at least two print medium applicators within a dimension corresponding to the extent of the image pattern.
6. The print head of claim 5, wherein the print head includes at least three print medium applicators within a dimension corresponding to the extent of the image pattern.
7. The print head of claim 6, wherein the print head includes at least five print medium applicators within a dimension corresponding to the extent of the image pattern.

-13 -
8. The print head of claim 7, wherein the print head includes at least ten print medium applicators within a dimension corresponding to the extent of the image pattern.
9. The print head of any of claims 1 to 8, wherein the print medium applicators have a pitch of less than about 20 mm.
10. The print head of claim 9, wherein the print medium applicators have a pitch of less than about 10 mm.
11. The print head of claim 10, wherein the print medium applicators have a pitch of from about 2 mm to about 10 mm.
12. The print head of claim 11, wherein the print medium applicators have a pitch of from about 2 mm to about 5 mm.
13. The print head of any of claims 1 to 12, wherein the print medium applicators comprise sq ueegee elements.
14. The print head of claim 13, wherein the squeegee elements each comprise a squeegee blade which presents an applicator surface which is downwardly facing relative to a surface of the printing screen.
15. The print head of claim 13, wherein the squeegee elements each comprise a body which presents oppositely-directed applicator surfaces, each presenting an applicator surface which is downwardly facing relative to a surface of the printing screen.
16. The print head of claim 15, wherein the applicator surfaces extend in multiple directions or can have components which extend in multiple directions.

-14 -
17. The print head of claim 16, wherein the applicator surfaces define a rectangular or square aperture.
18. The print head of any of claims 15 to 17, wherein the squeegee elements, together with the printing screen, define enclosed chambers which contain the print medium.
19. The print head of claim 18, wherein the print head includes flow passages which provide fluid communication to the chambers, to which can be connected a print medium supply, which is operative to supply print medium to the chambers.
20. The print head of any of claims 1 to 19, wherein the print head allows for reciprocating operation.
21. The print head of any of claim 1 to 20, wherein the print head is operative to print a pattern of deposits onto a first workpiece in a single stroke in a first direction and onto a second, subsequent workpiece in a single stroke in a second, opposite direction.
22. The print head of any of claims 1 to 20, wherein the print head is operative to print a pattern of deposits onto a workpiece with multiple, reciprocating strokes in first and second directions.
23. The print head of claim 22, wherein the print head is operative to print a pattern of deposits onto a workpiece with two strokes, being a first stroke in a first direction and a second stroke in a second direction.
24. The print head of claim 22, wherein the print head is operative to print a pattern of deposits onto a workpiece by performing multiple strokes in first and second directions.

-15 -
25. The print head of any of claims 1 to 24, where employed in the printing of elongate patterns.
26. The print head of claim 25, where employed in the printing of metallization lines of solar cell wafers.
27. The print head of any of claims 1 to 26, wherein the print heads are supported by a support element.
28. A print head assembly, comprising: the print head of any of claims 1 to 27; and an oscillator which couples the print head to a print head transport mechanism which displaces the print head over a print stroke.
29. The print head assembly of claim 28, wherein the oscillator provides for oscillation in a single axis.
30. The print head assembly of claim 28, wherein the oscillator provides for oscillation in a dimensional plane over a surface of the printing screen during a print stroke.
31. The print head assembly of claim 30, wherein the print head follows a predetermined path during the print stroke, optionally an annular, figure of eight or zig-zag path.
32. A print head substantially as hereinbefore described with reference to the accompanying drawings.
33. A print head assembly substantially as hereinbefore described with reference to the accompanying drawings.