Title of Invention

PROCESS AND DEVICE FOR ALIGNING THE SUBSTRATE AND A PRINTING STENCIL IN SOLDER PASTE PRINTING

Abstract

The invention relates to a process and a device for aligning a substrate and a printing stencil to one another in the printing of the substrate with solder paste, said process comprising the following steps: Bringing the first substrate into a position opposite to and at a distance from the printing stencil, introducing a first optical sensing device between the printing side of the first substrate and the printing stencil, sensing the position-determining first structures of the first substrate and of the printing stencil by means of the first optical sensing device, aligning the first substrate and the printing stencil with one another on the basis of information gained from the structure sensing, by means of a second optical sensing device acquiring reference data of position-determining second structures on the side of the first, aligned substrate facing away from the printing side, removing the first optical sensing device, removing the first substrate and bringing a second substrate into a position opposite the printing stencil, acquiring the actual data of position-determining second structures on the side of the second substrate facing away from the printing side by means of the second optical sensing device and aligning the second substrate and the printing stencil with one another based on a comparison of the reference data with the actual data. (Figure 4)

Full Text

FORM 2 THE PATENT ACT 1970 (39 of 1970) & The Patents Rules, 2003 COMPLETE SPECIFICATION (See Section 10, and rule 13) 1. TITLE OF INVENTION PROCESS AND DEVICE FOR ALIGNING THE SUBSTRATE AND A PRINTING STENCIL IN SOLDER PASTE PRINTING APPLICANT(S) a) Name : b) Nationality : c) Address : EKRA EDUARD KRAFT GMBH GERMAN Company ZEPPELINSTRASSE 16 74357 BONNIGHEIM GERMANY 3. PREAMBLE TO THE DESCRIPTION The following specification particularly describes the invention and the manner in which it is to be performed : - Process and Device for Aligning the Substrate and the Printing Stencil in Solder Paste Printing Description The invention relates to a process for aligning the substrate and the printing stencil with one another in the printing of the substrate with solder paste and to a device for aligning the substrate and the printing stencil with one another in the printing of the substrate with solder paste. In the printing of substrates, particularly printed wiring boards, with solder paste, it is known to introduce a printed wiring board into the printing recess of the printing apparatus. This is done while maintaining a distance from the printing stencil of the printing apparatus. Subsequently, an optical sensing device is introduced into the region between the substrate and the printing stencil to make it possible, by means of structures of substrate and printing stencil, to achieve an alignment of these two parts relative to one another. The optical sensing device in the form of a camera preferably has two lenses and, hence, can simultaneously inspect the printing side of the substrate and the side of the printing stencil facing the printing side of the substrate. The said structures consist, for example, of conductor structures and/or edges of the substrate or delivery parts or of edges of the printing stencil. In cases where during the printing process solder paste is to be applied to a conductor, particularly to a pad, an appropriate scannable conductor structure is present on the substrate and a corresponding opening in the printing stencil. For flawless printing, it is necessary that the substrate and the printing stencil be accurately aligned with one another before the printing is carried out to ensure that the solder paste is accurately positioned on the conductor. In highly integrated electronic circuits, the distances between the individual conductors are very small so that high accuracy is needed in printing. The said aligning procedure with the aid of the optical sensing device must be repeated for the printing of each individual substrate of a printing lot, meaning that after the optical sensing device is introduced between the substrate and the printing stencil an alignment takes place between the substrate and printing stencil and only then can printing take place. For the execution of the printing process, it is necessary that the camera again be removed from the space between the substrate and the printing stencil. Only then can the printing stencil and the substrate approach each other and the printing process be carried out. Obviously, because of this kind of printing procedure involving an introduction and removal of the camera, the time required for the printing process is relatively long, which means that in a printing lot the number of substrates to be printed per unit time is relatively small. The object of the invention is therefore to provide a process and a device whereby the cycle time needed for the application of solder paste to each substrate is reduced so that a large number of substrates in a printing lot can be printed per unit time. High accuracy in achieving this must be ensured, meaning that the solder paste deposits must be applied with high accuracy to the involved conductor structures or the like. This objective is reached by means of the following process. A first substrate is disposed at a 2 distance from and opposite to the printing stencil. The "first" substrate is the first substrate of a lot to be printed which, for example, consists of a few hundred substrates. Then, a first optical sensing device, particularly a camera, is introduced between the printing side of the first substrate and the printing stencil. With the aid of this first optical sensing device, the position-determining first structures of the first substrate and of the printing stencil are sensed. In other words, structures to be brought into coincidence on the first substrate and the printing stencil are sensed. This must take place on at least two sites located at a distance from one another so as to prevent torsional alignment errors. An alignment of the first substrate with the printing stencil takes place on the basis of the information obtained during structure sensing. To this end, the substrate receptacle and/or the printing stencil holder can be moved in both the X- and the Y-direction and are also rotatable in this plane. After the alignment has been accomplished, by means of a second optical sensing device disposed below the printing recess, namely the substrate receptacle, the acquisition of reference data of position-determining second structures on the first, aligned substrate facing away from the printing side takes place. Consequently, second structures of the first substrate are determined by means of the second optical sensing device (second camera) on the side of the substrate that is not to be printed. Because previously an alignment between the first substrate and the printing stencil had taken place, the substrate is in the correct printing position so that the second structures sensed by means of the second optical sensing device can be located with regard to their position, size and/or shape, and the result obtained can be stored in the form of reference data. Because each substrate of a printing lot, for example the identical printed wiring boards of a lot, contain on their top and bottom side highly accurately placed structures, the aligned position of the substrate is "noted" in the printing recess because of the sensed structures facing away from the printing side. Once the reference data have been acquired, the first optical sensing device is removed and the first substrate can be printed on the printing side. The printed first substrate is then removed and the second substrate of the printing lot is introduced into the printing recess so that it is disposed opposite the printing stencil. It is now no longer necessary to introduce the first optical sensing device between the substrate and the printing stencil in order to undertake the aligning between the printing stencil and the substrate; rather, it suffices if the second optical sensing device is made to sense the structures present on the side of the second substrate facing away from the printing side and in this manner determine the actual data. If no accurate alignment exists between the substrate and the printing stencil, the acquired actual data will deviate from the reference data previously determined for the first substrate. Hence, an alignment of the second substrate and the printing stencil is to be carried out on the basis of the information obtained from the comparison between the actual data and the reference data. Because - as previously stated - the first optical sensing device need not move between the substrate and the printing stencil for each substrate, but from the second substrate onward, by means of the second optical sensing device, only the side of the substrate facing away from the printing side must be inspected to acquire the actual data, the printing cycle can be much faster so that per unit time a large number of substrates of a printing lot can be printed with solder paste with high accuracy. 3 As an alternative to the foregoing process, it is also possible, after the sensing of the position-determining first structures of the first substrate and of the printing stencil with the aid of the first optical sensing device, not to undertake an alignment of the first substrate with the printing stencil. It is sufficient to sense position deviations between these two components with the aid of the first optical sensing device and record them "virtually" in the form of correction data. In this case, the procedure for the second substrate is then the same as previously described, the alignment of the second substrate with the printing stencil being undertaken by comparing the reference data with the actual data and by taking into account the correction data. In other words, the correction data undertake a quasi "virtual" alignment of the first substrate with the printing stencil, which must be taken into account during the sensing of the second structures on the side of the first substrate facing away from the printing side, namely during the acquisition of the reference data. The invention also refers to a device for alignining a substrate with a printing stencil during the printing of the substrate with solder paste, it being possible to use said device particularly for the execution of the aforesaid process. Between the printing side of the substrate and the printing stencil, the device is provided with an insertable and removable first optical sensing device. It is also provided with a second optical sensing device for the inspection of the side of the substrate opposite the printing side. Moreover, there is provided a correction device for the processing of the data acquired by the first optical sensing device and of the inspection data of the second optical sensing device and which serves to provide a positional correction for the substrate and the printing stencil relative to one another. Other advantageous features of the invention are described in the claims. The drawings represent the invention in the form of flow diagrams shown in Figs. 1 to 4. Figure 1 shows a printing stencil 1 of a printing machine, not shown, for applying solder paste to substrate 2 of a printing lot. The printing machine that is not shown is configured as a screen-printing machine. By means of a supply system, substrates 2 are fed from the printing lot, first substrate 2' being introduced into printing recess 4 of the printing machine at the beginning of the printing process as indicated by arrow 3. In Figure 1, this position occupied by the inserted first substrate 2' is represented by a broken line. According to Figure 2, after the introduction of the first substrate 2' at a distance from and opposite to printing stencil 1, the introduction (arrow 5) of a first optical sensing device 6 takes place between a first substrate 2' and the printing stencil 1. The first optical sensing device 6 is configured as a camera 7 with two lenses 8 and 9 so that the printing side 10 of the first substrate 2 and side 11 of printing stencil 1 facing printing side 10 can be inspected at the same time. During this inspection, first structures 12 and 12' on side 11 of printing stencil 1 and on printing 4 side 10 of first substrate 2' are sensed, namely position information (coordinates) and/or geometric information (shape, size) are acquired. The structures can consist of openings in and/or edges of printing stencil 1 and/or of other kinds of characteristic features on printing stencil 1 as well as of edges and/or conductor configurations or other characteristic features on first substrate 2'. The foregoing enumeration of structures is not conclusive, but it is evident that the elements involved must permit unequivocal positioning of a particular element by means of optical sensing device 6. After the optical sensing of the structures of printing stencil 1 and first substrate 2' has taken place according to Figure 2, the positions of these two components are accurately aligned with each other based on the information gained so that it is ensured that during the subsequent application of pressure the openings in printing stencil 1 will assume with high accuracy a position opposite the corresponding structures on first substrate 2' and, hence, under pressure, the solder paste will be applied in the form of solder deposits accurately and to an exact height. Before this printing step is carried out, however, second structures 17 on side 18 of first substrate 2' opposite the printing side 10 are sensed with a second optical sensing device 14 configured as a camera with a lens 16. This step is shown in Figure 3. As an alternative, this step can also be carried out after the printing. Because a firm correspondence exists between first structures 12' on printing side 10 of first substrate 2' and second structures 17 on side 18 of first substrate 2, and this also applies to every subsequent substrate, by sensing second structures 17 with second optical sensing device 14, the position of first substrate 2' can be accurately maintained so that for subsequent substrates of the same kind a similarly accurate alignment of these subsequent substrates is possible when by means of the second optical sensing device 14 their second structures are sensed and compared with the reference data obtained with first substrate 2'. Hence, the subseqent substrates are aligned until appropriate matching with the obtained reference data has taken place and the desired position, already determined for first substrate 2', is accurately assumed. Because in this practical example, in particular, the X-Y position of printing stencil 1 does not change, for all substrates 2 of the printing lot, the openings in printing stencil 1 are accurately aligned with the regions to be printed on printing side 10 of substrate 2. The remainder of the course of the process before the subsequent substrates can be printed is shown in Figure 3. After second structures 17 of the first, aligned substrate 2' have been sensed, first optical sensing device 6 is removed from the space between printing stencil 1 and first substrate 2', as indicated by arrow 13. As indicated by arrows 19, 20, printing stencil 1 and first substrate 2' then approach each other, preferably so that printing stencil 1 remains in position and the printing recess together with first substrate 2' is moved in the direction of printing stencil 1. The printing process is then carried out. Printing screeen 1 and first printed substrate 2' then come apart as indicated by arrow 21. This also occurs preferably in that printing stencil 1 remains in its position and only first substrate 2' moves. Then - as indicated by arrow 22 in Figure 4 - first 5 substrate 2' is removed from printing recess 4. A second substrate 2" is introduced into printing recess 4 as indicated by arrow 23 and by means of second optical sensing device 14 is inspected on its side 18. On this side, second structures 17 are sensed and compared with the reference data of first substrate 2'. If there are any deviations, a position correction for second substrate 2" is performed resulting in a correct alignement of second substrate 2" with printing stencil 1. The printing process can then be carried out. This shortened procedure for substrate 2" compared to first substrate 2' can also be carried out for all subsequent substrates 2, namely from second substrate 2" onward, it is no longer necessary to introduce the first optical sensing device between substrate 2 and printing stencil 1 and - before the printing process - remove said device from this region. Rather, from second substrate 2" onward, the first optical sensing device 6 is no longer used, because only the second optical sensing device 14 is needed to perform the alignment. Figure 4 shows a correction device 24 whereby the aforesaid processing steps, namely the evaluation of the data of the first optical sensing device 6 and the second optical sensing device 14 as well as the position corrections, can be carried out. In this manner, a very large number of substrates 2 of a printing lot can be accurately printed with solder paste per unit time. From the foregoing, it is clear that by a comparison of the actual with the desired data the position (coordinates) and/or the geometry (shape, size) of structures of the substrate underside and/or substrate edges can be performed with the aid of the previously sensed position (coordinates) and/or geometry (shape, size) of structures and/or structure edges of the top side of the substrate and used for the alignment of the substrate relative to the printing stencil or printing screen, the exact positioning of the printing stencil or printing screen also having been attained by a corresponding sensing of the position (coordinates) and/or geometry (shape, size) of structures and/or stencil edges. From the second substrate onward, the invention obviates the need for a camera unit disposed for purposes of alignment between the substrate and the printing stencil. This reduces markedly the overall cycle time required for the traversing operation of the camera. The exact determination of the structure positions is preferably carried out by means of the so-called glass scale. Moreover, on the basis of the invention, it is possible, with the aid of an optical sensing device or even several optical sensing devices, to determine an unequivocal reference point or unequivocal reference points of a substrate (for example an edge) so that even substrates without special characteristics, for example fiducials on the substrate underside, can be even multiply printed with appropriate accuracy and repeatability. In place of a second optical sensing device 14 in the region of the bottom side (side 18) of substrate 2, there can also be provided two second optical sensing devices so that these devices need not be used for an accurate position sensing of substrate 2. With two optical sensing devices, a rotation error is immediately recognizable. 6 We Claims 1. Process for aligning a substrate and a printing stencil with one another in the printing of the substrate with solder paste, comprising the following steps: a) bringing the first substrate into a position opposite to and at a distance from the printing stencil; b) introducing a first optical sensing device between the printing side of a first substrate and the printing stencil; c) sensing the position-determining first structures of the first substrate and of the printing stencil by means of a first optical sensing device; d) aligning the first substrate and the printing stencil with one another on the basis of information gained from structure-sensing; e) by means of a second optical sensing device, acquiring the reference data of position-determining second structures on the side of the first, aligned substrate facing away from the printing side; f) removing the first optical sensing device. Removing the first substrate and bringing a second substrate into a position opposite the printing stencil; g) by means of the second optical sensing device, acquiring the actual data of position-determining second structures on the side of the second substrate facing away from the printing side; h) aligning the second substrate and the printing stencil with one another by comparing the reference data with the actual data; 2. Process for aligning a substrate and a printing stencil with one another in the printing of the substrate with solder paste, comprising the following steps: a) bringing the first substrate in a position opposite to and at a distance from the printing stencil; b) introducing a first optical sensing device between the printing side of a first substrate and the printing stencil; c) sensing the position-determining first structures of the first substrate and of the printing stencil by means of a first optical sensing device; d) obtaining the characterizing correction data for the relative position of of the first substrate and the printing stencil based on structure sensing; e) by means of a second optical sensing device, sensing the reference data of position-determining second structures on the side of the first substrate facing away from the printing side; f) removing the first optical sensing device, removing the first substrate and bringing a second substrate into a position opposite the printing stencil; g) by means of a second optical sensing device, sensing the actual data of position-determining second structures on the side of the second substrate 7 facing away from the printing side; h) aligning the second substrate and the printing stencil with one another by comparing the reference data with the actual data while taking into account the correction data; 3. Device for aligning a substrate (2) and a printing stencil (1) with one another in the printing of the substrate (2) with solder paste, particularly for the purpose of carrying out the process as defined in one or more of the preceding claims, with a first optical sensing device (6) capable of being inserted between and removed from between the printing side (10) of the substrate (2) and printing stencil (1), with a second optical sensing device (14) inspecting the side (18) disposed opposite the printing side (10) of the substrate (2) and with a correction system (24) for processing the inspection data of the second optical sensing device (14) for the purpose of correcting the position of the substrate (2) and the printing stencil (1) relative to one another. 4. Device as claimed in claim 3, wherein the printing is done with a screen-printing machine. 5. Device as claimed in one of the preceding claims, wherein the first optical sensing device is a camera (7) with two diametrically opposed lenses (8,9). 6. Device as claimed in one of the preceding claims, wherein the first optical sensing device (6) is disposed insertably and removably between the printing stencil (1) and the substrate (2). 7. Device as claimed in one of the preceding claims, wherein the first optical sensing device (6) is configured so as to be movable in the X- and Y-direction. 8. Device as claimed in one of the preceding claims, wherein the second optical sensing device (14) is configured so as to be movable in the X- and Y-direction. 9. Device as claimed in one of the preceding claims, wherein there are provided two second optical sensing devices (14) inspecting different regions of the side (18) of the substrate (2). 8 Abstract The invention relates to a process and a device for aligning a substrate and a printing stencil to one another in the printing of the substrate with solder paste, said process comprising the following steps: Bringing the first substrate into a position opposite to and at a distance from the printing stencil, introducing a first optical sensing device between the printing side of the first substrate and the printing stencil, sensing the position-determining first structures of the first substrate and of the printing stencil by means of the first optical sensing device, aligning the first substrate and the printing stencil with one another on the basis of information gained from the structure sensing, by means of a second optical sensing device acquiring reference data of position-determining second structures on the side of the first, aligned substrate facing away from the printing side, removing the first optical sensing device, removing the first substrate and bringing a second substrate into a position opposite the printing stencil, acquiring the actual data of position-determining second structures on the side of the second substrate facing away from the printing side by means of the second optical sensing device and aligning the second substrate and the printing stencil with one another based on a comparison of the reference data with the actual data. (Figure 4) To The Controller of Patent The Patent Office Mumbai

Documents:

00981-mumnp-2005-abstract(15-12-2006).doc

00981-mumnp-2005-abstract(15-12-2006).pdf

00981-mumnp-2005-assignment(15-12-2006).pdf

00981-mumnp-2005-cancelled pages(15-12-2006).pdf

00981-mumnp-2005-claims(granted)-(15-12-2006).doc

00981-mumnp-2005-claims(granted)-(15-12-2006).pdf

00981-mumnp-2005-correspondence(12-12-2006).pdf

00981-mumnp-2005-correspondence(ipo)-(08-02-2007).pdf

00981-mumnp-2005-drawings(15-12-2006).pdf

00981-mumnp-2005-form 1(07-11-2006).pdf

00981-mumnp-2005-form 1(15-12-2006).pdf

00981-mumnp-2005-form 18(17-02-2006).pdf

00981-mumnp-2005-form 2(granted)-(15-12-2006).doc

00981-mumnp-2005-form 2(granted)-(15-12-2006).pdf

00981-mumnp-2005-form 3(06-09-2005).pdf

00981-mumnp-2005-form 3(15-12-2006).pdf

00981-mumnp-2005-form 5(06-09-2005).pdf

00981-mumnp-2005-form 5(15-12-2006).pdf

00981-mumnp-2005-form 6(15-12-2006).pdf

00981-mumnp-2005-power of attorney(15-12-2006).pdf

981-mumnp-2005-abstract.doc

981-mumnp-2005-abstract.pdf

981-mumnp-2005-claims.doc

981-mumnp-2005-claims.pdf

981-mumnp-2005-correspondence-others.pdf

981-mumnp-2005-correspondence-received-071105.pdf

981-mumnp-2005-correspondence-received-080905.pdf

981-mumnp-2005-correspondence-received-091106.pdf

981-mumnp-2005-correspondence-received-101105.pdf

981-mumnp-2005-correspondence-received-120905.pdf

981-mumnp-2005-correspondence-received-150206.pdf

981-mumnp-2005-correspondence-received-240306.pdf

981-mumnp-2005-correspondence-received-270306.pdf

981-mumnp-2005-correspondence-received.pdf

981-mumnp-2005-descripiton (complete).pdf

981-mumnp-2005-form-1.pdf

981-mumnp-2005-form-18.pdf

981-mumnp-2005-form-2.doc

981-mumnp-2005-form-2.pdf

981-mumnp-2005-form-3-080905.pdf

981-mumnp-2005-form-3.pdf

981-mumnp-2005-form-5-060905.pdf

981-mumnp-2005-form-5.pdf

981-mumnp-2005-form-pct-ipea-409.pdf

981-mumnp-2005-form-pct-ro-101.pdf

981-mumnp-2005-granted.pdf

981-mumnp-2005-pct-search report.pdf

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