PRINTING DEVICE AND PRINTING METHOD FOR APPLYING A VISCOUS OR PASTY MATERIAL

Abstract

The invention relates to a printing device for applying a viscous or pasty material onto a support substrate and molding a defined material geometry by means of a template. The template which is provided for application and molding purposes has at least one continuous opening, and the opening side facing the support substrate functions as an application opening surface. Furthermore, the opening, in particular the inner wall thereof, forms an outer border for the material geometry outer surface to be molded. As a whole, the template is designed such that an adhesive force of the viscous or pasty material acting on the inner wall of the opening is overcome by means of a relative movement, in particular a movement relative to the support substrate. The template is advantageously formed as a stack composite of at least two sub-templates adjoining each other in a connection region. Each of the sub-templates has at least one sub-opening, by means of which the inner wall of the opening is divided into proportional molding surfaces of the sub-template. Furthermore, sub-opening connection surfaces which correspond to one another are formed in the connection region, and each of the sub-templates can be reversibly separated in the connection region.

Claims

1. A printing device (100) for applying a viscous or pasty material (40) onto a carrier substrate (20) and shaping a defined material geometry (45) by means of a stencil, wherein the stencil has at least one continuous opening (55) with an application opening surface (50.1c) facing the carrier substrate (20) and the inner wall of the opening (55) forms an outer boundary for an outer surface (46) of the material geometry (45) to be shaped, wherein the stencil is configured to overcome an adhesive force of the viscous or pasty material (40) acting on the inner wall of the opening (55) by means of a relative movement, characterized in that the stencil is formed as a stack composite (50) of at least two sub-stencils (50.1, 50.2, 50.x) adjoining each other in a connection region (30), wherein the sub-stencils (50.1, 50.2, 50.x) each have at least one partial opening (55.1, 55.2, 55.x), by means of which the inner wall of the opening (55) is divided into proportional shaping areas (50.1a, 50.2a, 50.xa) of the sub-stencils (50.1, 50.2, 50.x), and wherein connection surfaces (50.1a, 50.1b) of the sub-openings (55.1, 55.2, 55.x) which correspond to one another are formed in the connection region (30), and the sub-stencils (50.1, 50.2, 50.x) can each be reversibly separated from one another in the connection region (30).

2. The printing device (100) as claimed in claim 1, characterized in that for the stencil (50) an overall area ratio as the ratio of the area of the inner wall to the application opening surface (50.1c) is =<0.66.

3. The printing device (100) as claimed in claim 1, characterized in that for a sub-stencil (50.1, 50.2, 50.x) a part-related area ratio as the ratio of the shaping area (55.1a, 50.2a, 55.xa) of the partial opening (55.1, 55.2, 55.x) to the connection surface area (50.1b, 50.2b) or to the application opening surface (50.1c) is >=0.66.

4. The printing device (100) as claimed in claim 1, characterized in that for the stencil (50) an overall aspect ratio as the ratio of the smallest opening width of the opening (55) to the stencil thickness (h) of the stencil (50) is <1.5.

5. The printing device (100) as claimed in claim 1, characterized in that the printing device (100) has a closed excess pressure blade (65) for applying the viscous or pasty material (40) into the at least one continuous opening (55) of the stencil, wherein the closed excess pressure blade (65) is formed by a printing head, which rests on the stencil and completely covers an entry opening surface (56) of the stencil facing away from the carrier substrate (20) and which is configured to introduce the viscous or pasty material (40) into the opening (55) under pressure.

6. The printing device (100) as claimed in claim 1, characterized in that at least two partial openings (55.1, 55.2, 55.x) of a sub-stencil (50.1, 50.2, 50.x) or the partial openings (55.1, 55.2, 55.x) of at least two sub-stencils (50.1, 50.2, 50.x) in the stack composite (50) which form the at least one opening (55) are configured differently in geometry and/or size.

7. The printing device (100) as claimed in claim 1, characterized in that the stencil (50) comprises a plurality of openings (55), wherein a center-to-center distance (pitch) of two immediately adjacent openings (55) is <=2 mm.

8. A printing method for applying a viscous or pasty material (40) onto a carrier substrate (20) and for shaping a defined material geometry (45) using a stencil, wherein the stencil has at least one continuous opening (55) with an application opening surface (50.1c) facing the carrier substrate (20) and the inner wall of the opening (55) forms an outer boundary for the outer surface (46) of the material geometry (45) to be shaped, the method comprising determining a maximum shaping area (50.1a, 50.2a, 50.xa) of the stencil for a circumferential outer surface section (46.1, 46.2, 46.x) of the material geometry (45), at which an adhesive force of the viscous or pasty material (40) acting on the shaping area (50.1a, 50.2a, 50.xa) can still be overcome under a relative movement of the stencil, and at delayed intervals, beginning the removal of at least two outer surface sections (46.1, 46.2, 46.x) of the material geometry (45) from the mold, in each case having a surface area up to the size of the specified shaping area (50.1a, 50.2a, 50xa), by means of the stencil.

9. The printing method as claimed in claim 8, characterized in that at least one of the outer surface sections (46.1, 46.2, 46.x) having an area up to the size of the specified maximum shaping area (50.1a, 50.2a, 50.xa) is completely demolded before the removal of at least one other outer surface section from the mold is begun.

10. The printing method as claimed in claim 8, characterized in that after a sub-region of at least one outer surface section (46.1, 46.2, 46.x) has already been removed from the mold, at least one other outer surface region is then removed from the mold at the same time, wherein the simultaneous demolding is executed in such a way that at any subsequent time a surface area of the remaining areas of these outer surface sections yet to be demolded is present, which is smaller than the specified maximum shaping area.

11. The printing method as claimed in claim 8, characterized in that the viscous or pasty material (40) is formed as a material deposit (26) on a bonding pad (25) on a circuit substrate (20).

12. The printing method as claimed in claim 8, characterized in that a solder paste, a thermal conducting paste, a conductive paste or a conductive adhesive is printed onto the carrier substrate (20) as the viscous or pasty material (40).

13. A circuit substrate (20) having at least one material deposit (26) applied by means of stencil printing and with a defined material geometry (45), wherein the at least one imprinted material deposit (26) has a printable surface connecting to the carrier substrate (20) and the material geometry (45) has an outer surface (46) shaped by means of an inner wall of an opening (55) of the printing stencil (50), wherein a ratio of the outer surface (46) to the printable surface is <0.66.

14. The circuit substrate (20) as claimed in claim 13, characterized in that the imprinted material deposit (26) has different cross-sectional areas and/or shapes in cutting planes parallel to the printable surface.

15. The circuit substrate (20) as claimed in claim 13, having a plurality of material deposits (26) in the form of a pattern arrangement (27).

16. The printing device (100) as claimed in claim 1, wherein the relative movement is a movement relative to the carrier substrate (20).

17. The printing device (100) as claimed in claim 1, characterized in that for the stencil (50) an overall area ratio as the ratio of the area of the inner wall to the application opening surface (50.1c) is 0.3 to 0.5.

18. The printing device (100) as claimed in claim 1, characterized in that for a sub-stencil (50.1, 50.2, 50.x) a part-related area ratio as the ratio of the shaping area (55.1a, 50.2a, 55.xa) of the partial opening (55.1, 55.2, 55.x) to the connection surface area (50.1b, 50.2b) or to the application opening surface (50.1c) is 0.66 to 2.

19. The printing device (100) as claimed in claim 1, characterized in that for the stencil (50) an overall aspect ratio as the ratio of the smallest opening width of the opening (55) to the stencil thickness (h) of the stencil (50) is 0.6 to 1.0.

20. The printing device (100) as claimed in claim 1, characterized in that the stencil (50) comprises a plurality of openings (55) in a pattern arrangement (27), wherein a center-to-center distance (pitch) of two immediately adjacent openings (55) is <=0.5 mm.

21. The method as claimed in claim 8, wherein the relative movement is a movement relative to the carrier substrate (20).

22. The printing method as claimed in claim 8, characterized in that the viscous or pasty material (40) is formed as a material deposit (26) on a bonding pad (25) on a circuit substrate (20), and in the form of a printed circuit board, a DBC, an LTCC, an IMC, a wafer or a solar cell, with the defined material geometry (45).

23. The circuit substrate (20) as claimed in claim 13, wherein the at least one imprinted material deposit (26) is a solder paste or an adhesive deposit (26)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Further advantages, features and details of the invention can be found in the following description of preferred exemplary embodiments and from the drawings. These show:

[0046] FIG. 1a) through FIG. 1e): an exemplary embodiment of a printing device for applying a viscous or pasty material to a printed circuit board with a temporal sequence during a printing process,

[0047] FIG. 2: a detail of the printing stencil in a molding region for a printable material geometry,

[0048] FIG. 3a) through 3d): different designs of a stack composite of sub-stencils,

[0049] FIG. 4: an alternative method to that of FIG. 1a)-1e) for introducing the viscous or pasty material into the opening of a stencil by means of an excess pressure blade.

DETAILED DESCRIPTION

[0050] In the figures, functionally identical components are each labeled with the same reference numeral.

[0051] FIG. 1a) shows an example of an embodiment of a printing device 100 for applying a viscous or pasty material at a time prior to the execution of a printing process. The printing device 100 comprises at least one support 10 for holding a carrier substrate 20 to be imprinted, in particular a circuit substrate. The carrier substrate 20 is, for example, a printed circuit board, a DBC, an LTCC, an IMC, a wafer or a solar cell. The carrier substrate 20 rests with its underside on the support 10. The carrier substrate 20 is preferably aligned by means of an alignment and/or fixing unit 12 within the printing device 100 with a defined orientation and/or fixed onto the bearing 10 in a stationary manner. On a top side of the carrier substrate 20, at least one bonding pad 25 is formed for electrically contacting to an electrical and/or electronic component. Using a stencil printing process, a material deposit 26 with a defined material geometry 45 will then be printed on at least one bonding pad 25. For this purpose, a novel type of printing stencil is provided in the form of a stack composite 50 composed of a plurality of sub-stencils 50.1, 50.2, 50.x. The stack composite 50 comprises at least two sub-stencils 50.1, 50.2, although more sub-stencils 50.x can be included as required. FIG. 2 shows an enlargement of a detail A of the printing stencil 50 in a molding region, for example a cylindrical material deposit 26, for a printable material geometry 45. The material geometry 45 has an outer surface 46 to be shaped in a defined way. Conventionally, the outer surface 46 would be shaped by means of a continuous opening 55 formed in a single stencil 50 (shown schematically in the right-hand side view). The inner wall of the opening 55 forms an outer boundary for the outer surface 46 of the material geometry 45 to be shaped over a printing height h. The side of the opening 55 facing the carrier substrate 20 thereby acts as an application opening surface 50.1c. This matches the subsequent printable surface on the carrier substrate 20. The left-hand side view shows a schematic representation of the design of the novel printing stencils as a stack composite 50 of at least two sub-stencils 50.1, 50.2, 50.x that adjoin each other in a connection region 30. The sub-stencils 50.1, 50.2. 50.x are each designed with a stencil thickness h1, h2, hx and each have at least one partial opening 55.1, 55.2, 55.x, through which the inner wall of the opening 55 is divided into proportional shaping areas 50.1a, 50.2a, 50.xa of the sub-stencils 50.1, 50.2, 50.x. In addition, in the connection region 30 mutually corresponding connecting surfaces 50.1b, 50.2b, 50.xb of the partial openings 50.1, 50.2, 50.x are formed, over which the print material 40 which is introduced into each of the partial openings 55.1, 55.2, 55.x is seamlessly merged. Via the proportional shaping areas 50.1a, 50.2a, 50.xa, corresponding outer surface sections 46.1, 46.2, 46.x are partially demolded at delayed intervals relative to each other. Overall, the design as a stack composite 50 allows a reduced overall area ratio.

[0052] FIGS. 1b) to 1e) show the execution of a printing process, wherein for the sake of clarity a further sub-stencil 50.x has not been shown. From FIG. 1b) it is evident that a viscous or pasty material 40, in this example a solder paste or a conductive adhesive, is provided via an application device 65 for printing onto the bonding pads 25. The application device 65 comprises, for example, a blade, by means of which the solder paste or conductive adhesive 40as shown in FIG. 1c)is spread over the surface of the outermost sub-stencil 50.2 or 50.x. In the spreading process, the solder paste or conductive adhesive 40 is mechanically pressed into the openings 55 of the stack composite 50. In the process, all partial openings 55.1, 55.2, 55.x are filled with the solder paste or conductive adhesive 40. In accordance with FIG. 1d), in a subsequent production step the outermost sub-stencil 50.2 or 50.x is separated from the stack composite 50 and lifted up until at least one shaping area 50.2a or 50.xa associated with the raised sub-stencil 50.2 or 50.x has fully removed a corresponding outer surface section 46.2 or 46.x of the material geometry 45 from the mold. Thereafter, at staggered intervals a further partial demolding of an adjacent outer surface section 46.1 is completed by separating and lifting the following sub-stencil 50.1 in the remaining stack composite 50. FIG. 1e) shows the lifting of the final sub-stencil 50.1 resting on the carrier substrate 20, which completes the entire demolding of the whole material geometry 45 and the printing process as such is then completed. Alternatively, it can be provided that after only one sub-region of at least one outer surface region has already been removed from the mold by an associated sub-stencil, at least one other adjacent outer surface region is removed from the mold by the following sub-stencil at the same time. In doing so, care must be taken to ensure that the simultaneous demolding is implemented in such a way that at any subsequent time, a surface area of the remaining areas of these outer surface sections yet to be removed from the mold is less than a maximum shaping area that is still permissible by a limiting area ratio in relation to the sub-stencils proportionally involved in the subsequent removal from the mold. In principle, the separation and lifting of the sub-stencils 50.1, 50.2, 50.x is carried out by the positioning device 60 relative to the carrier substrate 20 and the support 10. Conversely, the formation of the stack composite 50, for example, is preferably also performed by the positioning device 60. At this stage, for example, registration marks 80 applied to the sub-stencils 50.1, 50.2, 50.x can be used for their alignment within the stack composite 50. Other known alignment options may also be suitable. Guide elements 70 operatively connected to the sub-stencils 50.1, 50.2, 50.x ensure very precise partial removals of the material geometry 45 from the mold. As a result, once the printing process is completed, solder-paste deposits or adhesive deposits 26 have been printed on the outer pads 25 of the carrier substrate 20. A plurality of associated solder-paste or adhesive deposits are implemented in the form of a pattern arrangement, which corresponds in particular to the connection diagram of an electrical and/or electronic component to be electrically connected to the carrier substrate 20. By placing the electrical and/or electronic component on the solder-paste deposits or adhesive deposits in a further production step, for example, in the case of solder-paste deposits by a re-flow process, a materially bonded connection to the carrier substrate 20 can be implemented.

[0053] In FIGS. 3a) to 3d), different designs of a stack composite 50 of sub-stencils 50.1, 50.2, 50.x are shown. Common to all of them is the fact that an opening 55 in the stack composite 50 represents a particular material geometry 45 to be printed. In FIGS. 3a) to 3c), the stack composite 50 comprises in each case two sub-stencils 50.1, 50.2, while in FIG. 3d) more than two sub-stencils 50.1, 50.2, 50.x (as an example, 3 sub-stencils shown) are also used. In FIG. 3a) the sub-stencils 50.1, 50.2 are identical. This allows a material geometry 45 with a constant cross section to be printed. In FIG. 3b), the sub-stencils 50.1, 50.2 each have the same stencil thickness h1. However, the partial openings 55.1, 55.2 contained in the sub-stencils 50.1, 50.2 differ in their cross-sectional shape and/or size. This allows material geometries with varying cross-sectional area to be printed, such as stepped cylinders. The same applies to the stack composite 50 according to FIG. 3c), wherein here, however, the sub-stencils 50.1, 50.2 have different stencil thicknesses h1, h2. The definition of the stencil thicknesses h1, h2, for example, can be based on the modified cross-sectional areas or a maximum possible shaping area of the individual sub-stencils 50.1, 50.2. FIG. 3d) shows a multiplicity of sub-stencils 50.1, 50.2, 50.x within a stack composite 50. The sub-stencils 50.1, 50.2, 50.x differ in their stencil thicknesses h1, h2, hx and in the different designs of their partial openings 55.1, 55.2, 55.x. Many other designs of stack composites 50 are possible, which are produced, for example, from a partial combination of two or more sub-aspects of the designs of stack composites 50 shown in FIG. 3a) to d).

[0054] FIG. 4 shows an alternative method of introducing the viscous or pasty print material 40 into the openings 55 of the stack composite 50 by means of an excess pressure blade 65. This comprises, for example, a storage chamber 66 with the print material 40 contained therein. The storage chamber 66 is also implemented, for example, as a printing head, which rests on the stencil or the uppermost sub-stencil 50.x of the stack composite 50 during the insertion of the print material 40. The printing head covers at least one entry opening surface 56 of the stencil, facing away from the carrier substrate 20. The print head is designed to introduce the print material 40 into the at least one opening 55. The print material 40 is forced out of the storage chamber 66 using a feeder device (not shown) and introduced into the opening 55 with an excess pressure Pr. The excess pressure Pr is accordingly elevated, in particular compared to an external pressure Pa present outside the storage chamber 66, for example the atmospheric pressure. The print material 40 introduced into the opening 55 is finally leveled off by the blade 67 arranged externally on the storage chamber 66. FIG. 4 shows the excess pressure blade 65 at a time during a printing process which corresponds to that in FIG. 1c. In addition, the center-to-center distance (pitch) of two immediately adjacent openings 55 is shown. Finally, a plurality of material deposits 26 are printed on the carrier substrate 20 at a respective pitch spacing relative to each other in the form of a pattern arrangement 27.