GB2439533A

GB2439533A - A wiper blade for a screen printing machine and a method of fabricating the same

Info

Publication number: GB2439533A
Application number: GB0612702A
Authority: GB
Inventors: Neil Short
Original assignee: DEK International GmbH
Current assignee: ASM Assembly Systems Switzerland GmbH
Priority date: 2006-06-27
Filing date: 2006-06-27
Publication date: 2008-01-02
Anticipated expiration: 2026-06-27
Also published as: GB0612702D0; GB2439533B; WO2008001075A2; WO2008001075A3

Abstract

A rigid wiper blade for a screen printing machine and a method of fabricating the same, the wiper blade comprising an elongate body member which may include a recess in a surface thereof, and an elongate contact member, having an arcuate screen contact surface, which is mounted on the body or in the recess by an adhesive.

Description

1 2439533

A WIPER BLADE FOR A SCREEN PRINTING MACHINE AND A METHOD

OF FABRICATING THE SAME

The present invention relates to a wiper blade for a screen printing head, and a method of fabricating the same, in particular for the application of a layer of encapsulant material to a semiconductor wafer.

In the manufacture of semiconductor devices, a protective coating is commonly applied to the surface of the semiconductor wafer prior to cutting to form the semiconductor dies. It is important that this protective coating has a uniform thickness and a very smooth surface finish in order to provide..

good protection.

Currently, such protective coatings are applied using a printing screen with a single large printing aperture which has the same diameter as the diameter of the semiconductor wafer and a squeegee which is driven over the printing screen to fill the printing aperture with encapsulant material.

A traditional squeegee is illustrated in Figure 7. This squeegee 1 comprises an elongate body member 5, generally in the form of a rectangular bar, which includes a recess 6, here of V-section, in the lower edge thereof, and an elongate contact member 7, here a square-sectioned member of a synthetic material, typically a semi-hard polyurethane, which is bonded in the recess 6 in the body member 5, such as to present a pointed contact surface 9 which has sufficient flexibility as to conform to unevenness in the object being printed.

For the printing of encapsulant materials, squeegees have been developed which include a stiffening member at the lower edge thereof. One such squeegee is disclosed in US-A-6730170.

Although such stiffened squeegees represent an improvement as compared to the traditional squeegee, a particular problem associated with such squeegees is a lack of flatness along the length thereof, which can be caused by small imperfections which can arise as a result of ridges being ground into the contact surface of the squeegee, and flexing of the squeegee when being moved across the surface of the printing screen.

This lack of flatness in such squeegees provides for an uneven coating, where ridges in the contact surface cause surface defects in the coating which present an unsmooth surface, and flexing causes material to be scooped from a central region of the printing aperture, which undesirably results in the coating being thinner in the central region. S.. * S

In one aspect the present invention provides a rigid wiper blade for a screen printing machine, comprising an elongate body member which includes a recess in a surface thereof, and an elongate contact member, having a screen contact surface, which is mounted in the recess by an adhesive.

In one embodiment the contact surface is an arcuate surface. S... * S S 5

In one embodiment the contact surface is a part-circular surface.

In one embodiment the contact member comprises a cylindrical rod.

In one embodiment the cylindrical rod has a diameter of about 6 mm.

In another embodiment the cylindrical rod has a diameter of less than about 6mm.

In a further embodiment the cylindrical rod has a diameter of greater than about 6 mm.

In one embodiment the contact member is formed of stainless steel.

In one embodiment the contact surface is ground and burnished.

In one embodiment the contact surface has an average surface roughness of less than about 0.2 pm.

In one embodiment the contact surface has a flatness of less than about 10 pm over the length thereof.

In one embodiment the contact surface has a flatness of less than about 5 pm over the length thereof.

In one embodiment the contact surface has a flatness of less than about 1..

pm over the length thereof. .:: In one embodiment the recess has an arcuate surface. *.. S * *

In one embodiment the recess has a part-circular surface. S... *55*

In one embodiment the wiper blade further comprises a deformable element ** disposed between the contact member and a surface of the recess.

In one embodiment the recess and the deformable element are configured such as to define one or more cavities adjacent the deformable element which contain the adhesive.

In one embodiment the deformable element comprises a resilient element.

In one embodiment the resilient element comprises a foam rubber element.

In one embodiment the resilient element comprises a high-density foam rubber element.

In one embodiment the adhesive provides a rigid connection between the contact member and the body member.

In one embodiment the adhesive comprises an epoxy resin.

In another aspect the present invention provides a wiper blade for a screen printing machine, comprising an elongate body member, and an elongate contact member, having a screen contact surface, which is mounted to the body member by an adhesive.

In one embodiment the contact surface is an arcuate surface.

In one embodiment the contact surface is a part-circular surface. * *** * * *

In one embodiment the contact member comprises a cylindrical rod. ***

S

In one embodiment the cylindrical rod has a diameter of about 6 mm. S...

In another embodiment the cylindrical rod has a diameter of less than about * S S 6mm.

In one embodiment the contact member is formed of stainless steel.

In one embodiment the contact surface is ground and burnished.

In one embodiment the contact surface has a flatness of less than about 1 pm over the length thereof.

In one embodiment the body member includes a recess in a surface thereof, and the contact member is mounted in the recess.

In one embodiment the recess has an arcuate surface. * * **..

In one embodiment the recess has a part-circular surface.

In one embodiment the wiper blade further comprises a deformable element disposed between the contact member and the body member. ****

In one embodiment the body member and the deformable element are ***.

configured such as to define one or more cavities adjacent the deformabte element which contain the adhesive.

In one embodiment the deformable element comprises a resilient element.

In one embodiment the resilient element comprises a foam rubber element.

In one embodiment the adhesive comprises an epoxy resin.

In one embodiment the wiper blade is a rigid blade.

In a further aspect the present invention provides a method of fabricating a wiper blade for a screen printing machine, comprising the steps of: providing a body member; disposing a deformable element to the body member; disposing an adhesive to the body member; disposing a contact member, having a screen contact surface, to the deformable element; and pressing a levelling member, having a flat levelling surface, against the contact member, such that the deformable element is at least in part deformed and the contact member is rendered flat along the length thereof.

In one embodiment the body member includes a recess and the deformable *.

element, adhesive and contact member are disposed in the recess.

In one embodiment the recess has an arcuate surface.

In one embodiment the recess has a part-circular surface.

SS

In one embodiment the contact surface is an arcuate surface.

In one embodiment the contact surface is a part-circular surface.

In one embodiment the contact member comprises a cylindrical rod.

In one embodiment the cylindrical rod has a diameter of about 6 mm.

In another embodiment the cylindrical rod has a diameter of less than about 6 mm.

In one embodiment the contact member is formed of stainless steel.

In one embodiment the contact surface is ground and burnished.

In one embodiment the contact surface has a flatness of less than about 1.

pm over the length thereof.

In one embodiment the deformable element is disposed to the body member such as to define one or more cavities adjacent the deformable element which act to contain the adhesive. :;:; In one embodiment the deformable element is disposed to the body member prior to disposing the adhesive to the body member.

In one embodiment the deformable element comprises a resilient element.

In one embodiment the resilient element comprises a foam rubber element.

In one embodiment the resilient element acts to maintain the contact surface in engagement with the levelling member.

In one embodiment the adhesive comprises an epoxy resin.

In one embodiment the method further comprises the step of: setting the adhesive, such that the adhesive provides a rigid connection between the contact member and the body member.

In one embodiment the wiper blade is a rigid blade.

In a still further aspect the present invention provides a levelling jig for levelling a contact member of a wiper assembly, the levelling jig comprising: first and second levelling bars which are disposed in opposed relation and each have a flat levelling surface between which a wiper assembly is in use S...

disposed; and a clamping yoke assembly to which the levelling bars are.**.

fitted to allow for clamping of the same and the wiper assembly where.

disposed therebetween, such as to level the contact member of the wiper assembly.

In one embodiment the levelling surface of each of the levelling bars comprises a precision-ground surface. :;:; In one embodiment the clamping yoke assembly comprises at least two clamping yokes which are disposed at spaced locations along a length of the levelling bars.

In one embodiment the clamping yokes each comprise a pressure screw, by means of which screws one of the levelling bars is driven against the contact member of the wiper assembly, such as to level the same.

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 perspective view of a wiper blade in accordance with a preferred embodiment of the present invention; Figure 2 illustrates a vertical sectional view (along section I-I in Figure 1) of the wiper blade of Figure 1; Figures 3(a) to (d) illustrate fragmentary vertical sectional views (along section I-I in Figure 1) of the fabrication steps in fabricating the wiper blade of Figure 1; Figure 4 illustrates a perspective view of a levelling jig in accordance with a preferred embodiment of the present invention; Figure 5 illustrates a side view of the levelling jig of Figure 4, where *.

including a wiper assembly disposed between the levelling bars thereof; . Figure 6 illustrates a vertical sectional view (along section 11-lI in Figure 5) of the levelling jig of Figure 4, where including a wiper assembly disposed between the levelling bars; and Figure 7 illustrates a perspective view of a traditional squeegee.

The wiper blade 11 comprises a rigid, elongate body member 15, in this embodiment generally in the form of a rectangular bar, which includes a recess 16, in this embodiment of arcuate section, in the lower edge thereof, and a rigid, elongate contact member 17 which has an arcuate contact surface 19, in this embodiment a part-circular surface, and is mounted in the recess 16 in the body member 15 by an adhesive 21, in this embodiment an epoxy resin.

In this embodiment the adhesive 21 is of a kind which, when set, is rigid under the pressures as experienced by the wiper blade 11, such as to avoid deflection of the contact member 15 during a printing operation.

In this embodiment, as will be described in more detail hereinbelow, the wiper blade 11 includes a resilient element 23 which acts as a spacer in -10 -spacing the contact member 17 from a surface of the recess 16 in the fabrication of the wiper blade 11.

In this embodiment the contact member 17 is formed of a cylindrical rod, here having a diameter of about 6 mm.

In this embodiment the contact member 17 is formed of stainless steel.

In this embodiment the contact member 17 is ground and roller burnished, which provides the contact surface 19 thereof with an average surface roughness of less than about 0.2 pm and also work hardens the contact surface 19, such as to provide an increased resistance to wear and corrosion.

The fabrication of the wiper blade 11 will now be described with reference to Figures 3(a) to (d) of the accompanying drawings. I..'

In a first step, as illustrated in Figure 3(a), a resilient element 25, in this embodiment a foam rubber element, preferably a high-density rubber element, is located in the recess 16 in the body member 15.

In this embodiment the resilient element 25 comprises an elongate element which extends along a length, here substantially the entire length of the recess 16 in the body member 15.

In an alternative embodiment the resilient element 25 could comprise a plurality of elements which are disposed at spaced locations along a length, here substantially the entire length of the recess 16 in the body member 15.

In one embodiment the resilient element 25 is adhered in the base of the recess 16 in the body member 15.

-11 -In this embodiment the resilient element 25 is one or both of sized and shaped such as to define one or more cavities 27 adjacent the resilient element 25 and along the length of the body member 15.

In a second step, as illustrated in Figure 3(b), the adhesive 21, in this embodiment delivered as a liquid epoxy resin, is disposed in the one or more cavities 27 adjacent the resilient element 25 in the recess 16 in the body member 15.

In a third step, as illustrated in Figure 3(c), the contact member 15 is disposed in the recess 16 in the body member 15. (-.s * . .

In a fourth step, as illustrated in Figure 3(d), this wiper assembly is levelled in a levelling jig 41, as will be described in more detail hereinbelow, and the adhesive 21 allowed to set, such as to provide a rigid connection between the contact member 17 and the body member 15. **.* S... * . S

Figure 4 illustrates a perspective view of the levelling jig 41.

The levelling jig 41 comprises first and second levelling bars 43a, 43b which each have a flat levelling surface 45, in this embodiment a precision-ground surface, which are disposed in opposed vertical relation, and first and second clamping yokes 45a, 45b to which the levelling bars 43a, 43b are fitted to allow for clamping of the same.

In this embodiment each of the clamping yokes 45a, 45b comprises a stand 47, a first, clamping screw 49 for clamping the upper levelling bar 43b in position, and a second, pressure screw 51 for applying a pressure, in this embodiment a downward pressure, to the upper levelling bar 43b.

In disposing the wiper assembly in the clamping jig 41, the operation is as follows.

-12 -The upper levelling bar 43b is first raised to an elevated position and clamped in position by the clamping screws 49 of the clamping yokes 45a, 45b.

The wiper assembly is then inserted between the levelling surfaces 45 of the levelling bars 43a, 43b.

The clamping screws 49 of the clamping yokes 45a, 45b are then released, allowing the upper levelling bar 43b to rest on the contact member 17 of the wiper blade 11. * S..

The pressure screws 51 of the clamping yokes 45a, 45b are then wound first * * to contact the upper clamping bar 43b and then press the upper clamping..

bar 43b against the contact member 17 of the wiper blade 11, as illustrated *.: in Figures 5 and 6. S... * S **** **

In tightening the pressure screws 51 of the clamping yokes 45a, 45b, the.. : contact member 17 of the wiper blade 11 is biased against the resilient element 25 which is disposed in the recess 16 in the body member 15 of the wiper blade 11, thereby resiliently compressing the resilient element 25.

The pressure screws 51 are tightened to the point where the contact member 17 of the wiper blade 11 is in perfect, continuous contact with the levelling surface 45 of the upper levelling member 43b, with the resilient element 25 acting to maintain this contact whilst the adhesive 21 is subsequently allowed to set.

In this embodiment the establishment of the continuous contact between the contact member 17 of the wiper blade 11 and the levelling surface 45 of the upper levelling member 43b is determined, through visual inspection, of the absence any light passing between the contact member 17 of the wiper blade 11 and the levelling surface 45 of the upper levelling member 43b. In an alternative embodiment a vision system could be utilized to determine -13 -the perfect contact between the contact member 17 of the wiper blade 11 and the levelling surface 45 of the upper levelling member 43b.

Following this levelling of the contact member 17 of the wiper blade 11, the adhesive 21 is allowed to set, in this embodiment by curing of the epoxy resin, to yield a wiper blade 11 which has a perfectly flat and rigid contact member 17, as illustrated in Figure 3(d). In one embodiment the contact member 17 has a flatness, that is, a deviation in height, of less than about pm over the length thereof, preferably less than about 5 pm over the length thereof, and more preferably less than about 1 pm over the length thereof.

Finally, it will be understood that the present invention has been described..

in its preferred embodiments and can be modified in many different ways.: without departing from the scope of the invention as defined by the S...

appended claims. *S.. S * * *S S

Claims

-14 -

CLAIMS

1. A rigid wiper blade for a screen printing machine, comprising an elongate body member which includes a recess in a surface thereof, and an elongate contact member, having a screen contact surface, which is mounted in the recess by an adhesive.

2. The wiper blade of claim 1, wherein the contact surface is an arcuate surface. S...

3. The wiper blade of claim 2, wherein the contact surface is a part-circular surface.

4. The wiper blade of claim 3, wherein the contact member comprises a cylindrical rod. S... S...

5. The wiper blade of claim 4, wherein the cylindrical rod has a.. : diameter of about 6 mm.

6. The wiper blade of claim 4, wherein the cylindrical rod has a diameter of less than about 6 mm.

7. The wiper blade of claim 4, wherein the cylindrical rod has a diameter of greater than about 6 mm.

8. The wiper blade of any of claims 1 to 7, wherein the contact member is formed of stainless steel.

9. The wiper blade of any of claims 1 to 8, wherein the contact surface is ground and burnished.

10. The wiper blade of claim 9, wherein the contact surface has an average surface roughness of less than about 0.2 pm.

-15 - 11. The wiper blade of any of claims 1 to 10, wherein the contact surface has a flatness of less than about 10 pm over the length thereof.

12. The wiper blade of claim 11, wherein the contact surface has a flatness of less than about 5 pm over the length thereof.

13. The wiper blade of claim 12, wherein the contact surface has a flatness of less than about 1 pm over the length thereof. S...

14. The wiper blade of any of claims 1 to 13, wherein the recess has an arcuate surface.

S

15. The wiper blade of claim 14, wherein the recess has a part-circular surface. *5S S * *...

16. The wiper blade of any of claims 1 to 15, further comprising a.. : deformable element disposed between the contact member and a surface of the recess.

17. The wiper blade of claim 16, wherein the recess and the deformable element are configured such as to define one or more cavities adjacent the deformable element which contain the adhesive.

18. The wiper blade of claim 16 or 17, wherein the deformable element comprises a resilient element.

19. The wiper blade of claim 18, wherein the resilient element comprises a foam rubber element.

20. The wiper blade of claim 19, wherein the resilient element comprises a high-density foam rubber element.

-16 - 21. The wiper blade of any of claims 1 to 20, wherein the adhesive provides a rigid connection between the contact member and the body member.

22. The wiper blade of claim 21, wherein the adhesive comprises an epoxy resin.

23. A wiper blade for a screen printing machine, comprising an elongate body member, and an elongate contact member, having a screen contact surface, which is mounted to the body member by an S...

adhesive. * *.. * . . S *

24. The wiper blade of claim 23, wherein the contact surface is an arcuate surface. *.*.

25. The wiper blade of claim 24, wherein the contact surface is a part-***.

circular surface. ** 26. The wiper blade of claim 25, wherein the contact member comprises a cylindrical rod.

27. The wiper blade of claim 26, wherein the cylindrical rod has a diameter of about 6 mm.

28. The wiper blade of claim 26, wherein the cylindrical rod has a diameter of less than about 6 mm.

29. The wiper blade of claim 26, wherein the cylindrical rod has a diameter of greater than about 6 mm.

30. The wiper blade of any of claims 23 to 29, wherein the contact member is formed of stainless steel.

-17 - 31. The wiper blade of any of claims 23 to 30, wherein the contact surface is ground and burnished.

32. The wiper blade of claim 31, wherein the contact surface has an average surface roughness of less than about 0.2 pm.

33. The wiper blade of any of claims 23 to 32, wherein the contact surface has a flatness of less than about 10 pm over the length thereof.

34. The wiper blade of claim 33, wherein the contact surface has a:; flatness of less than about 5 pm over the length thereof.

35. The wiper blade of claim 34, wherein the contact surface has a flatness of less than about 1 pm over the length thereof.

36. The wiper blade of any of claims 23 to 35, wherein the body member.. : includes a recess in a surface thereof, and the contact member is mounted in the recess.

37. The wiper blade of claim 36, wherein the recess has an arcuate surface.

38. The wiper blade of claim 37, wherein the recess has a part-circular surface.

39. The wiper blade of any of claims 23 to 38, further comprising a deformable element disposed between the contact member and the body member.

40. The wiper blade of claim 39, wherein the body member and the deformable element are configured such as to define one or more cavities adjacent the deformable element which contain the adhesive.

-18 - 41. The wiper blade of claim 39 or 40, wherein the deformable element comprises a resilient element.

42. The wiper blade of claim 41, wherein the resilient element comprises a foam rubber element.

43. The wiper blade of claim 42, wherein the resilient element comprises a high-density foam rubber element. S...

44. The wiper blade of any of claims 23 to 43, wherein the adhesive provides a rigid connection between the contact member and the body member. *.. . * S S.

45. The wiper blade of claim 44, wherein the adhesive comprises an S...

epoxy resin. * . . ** *

46. The wiper blade of any of claims 23 to 45, wherein the wiper blade is a rigid blade.

47. A method of fabricating a wiper blade for a screen printing machine, comprising the steps of: providing a body member; disposing a deformable element to the body member; disposing an adhesive to the body member; disposing a contact member, having a screen contact surface, to the deformable element; and pressing a levelling member, having a flat levelling surface, against the contact member, such that the deformable element is at least in part deformed and the contact member is rendered flat along the length thereof.

-19 - 48. The method of claim 47, wherein the body member includes a recess and the deformable element, adhesive and contact member are disposed in the recess.

49. The method of claim 48, wherein the recess has an arcuate surface.

50. The method of claim 49, wherein the recess has a part-circular surface.

51. The method of any of claims 47 to 50, wherein the contact surface is * an arcuate surface. * **I * ** * *

52. The method of claim 51, wherein the contact surface is a part-circular surface.

53. The method of claim 52, wherein the contact member comprises a cylindrical rod. *:::: 54. The method of claim 53, wherein the cylindrical rod has a diameter of about 6 mm.

55. The method of claim 53, wherein the cylindrical rod has a diameter of less than about 6 mm.

56. The method of claim 53, wherein the cylindrical rod has a diameter of greater than about 6 mm.

57. The method of any of claims 47 to 56, wherein the contact member is formed of stainless steel.

58. The method of any of claims 47 to 57, wherein the contact surface is ground and burnished.

-20 - 59. The method of claim 58, wherein the contact surface has an average surface roughness of less than about 0.2 pm.

60. The method of any of claims 47 to 59, wherein the contact surface has a flatness of less than about 10 pm over the length thereof.

61. The method of claim 60, wherein the contact surface has a flatness of less than about 5 pm over the length thereof.

62. The method of claim 61, wherein the contact surface has a flatness of less than about 1 pm over the length thereof. :::;:; 63. The method of any of claims 47 to 62, wherein the deformable element is disposed to the body member such as to define one or more cavities adjacent the deformable element which act to contain the adhesive. *0 *

64. The method of any of claims 47 to 63, wherein the deformable element is disposed to the body member prior to disposing the adhesive to the body member.

65. The method of any of claims 47 to 64, wherein the deformable element comprises a resilient element.

66. The method of claim 65, wherein the resilient element comprises a foam rubber element.

67. The method of claim 66, wherein the resilient element comprises a high-density foam rubber element.

68. The method of any of claims 65 to 67, wherein the resilient element acts to maintain the contact surface in engagement with the levelling member.

-21 - 69. The method of any of claims 47 to 68, wherein the adhesive comprises an epoxy resin.

70. The method of any of claims 47 to 69, further comprising the step of: setting the adhesive, such that the adhesive provides a rigid connection between the contact member and the body member.

71. The method of any of claims 47 to 70, wherein the wiper blade is a rigid blade. **.. * ..*

72. A levelling jig for levelling a contact member of a wiper assembly, the levelling jig comprising: .:.

first and second levelling bars which are disposed in opposed relation **.:: and each have a flat levelling surface between which a wiper **** assembly is in use disposed; and *..

a clamping yoke assembly to which the levelling bars are fitted to.. : allow for clamping of the same and the wiper assembly where disposed therebetween, such as to level the contact member of the wiper assembly.

73. The levelling jig of claim 72, wherein the levelling surface of each of the levelling bars comprises a precision-ground surface.

74. The levelling jig of claim 72 or 73, wherein the clamping yoke assembly comprises at least two clamping yokes which are disposed at spaced locations along a length of the levelling bars.

75. The levelling jig of claim 74, wherein the clamping yokes each comprise a pressure screw, by means of which screws one of the levelling bars is driven against the contact member of the wiper assembly, such as to level the same.

-22 - 76. A wiper blade substantially as hereinbefore described with reference to Figures 1 to 3, optionally in conjunction with Figures 4 to 6, of the accompanying drawings.

77. A method of fabricating a wiper blade substantially as hereinbefore described with reference to Figures 1 to 6 of the accompanying drawings.

78. A levelling jig substantially as hereinbefore described with reference to Figures 4 to 6 of the accompanying drawings. **.. * .** * *. * I

I S.. * * S *.*. * .

* S. -**. * ..

S