US-12623450-B2 - Angled printing

US12623450B2US 12623450 B2US12623450 B2US 12623450B2US-12623450-B2

Abstract

The print quality of elongate deposits is improved by introducing an inclination offset between the squeegee blade and the elongate aperture of a stencil during a printing operation.

Inventors

Neil SHORT
Tom Falcon

Assignees

ASMPT SMT SINGAPORE PTE. LTD.

Dates

Publication Date: 20260512
Application Date: 20220907
Priority Date: 20210914

Claims (11)

1 . A method of printing an elongate deposit of print medium onto an elongate deposit target of a workpiece, using a printing machine comprising a print carriage, which, during a printing operation, travels in a printing direction across a stencil provided in the printing machine to force print medium on the stencil into at least one aperture provided in the stencil, the print carriage comprising an elongate squeegee blade with a major axis disposed along the length of the squeegee blade, the method comprising the steps of: i) transporting the workpiece into the printing machine in an orientation in which the elongate deposit target of the workpiece is orthogonal to the printing direction, ii) aligning the workpiece with a stencil within the printing machine so that an elongate aperture, having a major axis disposed along the length of the elongate aperture, provided in the stencil overlies the elongate deposit target, the stencil being disposed in the printing machine with the major axis of the elongate aperture disposed inclined to the printing direction, by rotating the workpiece so that the elongate deposit target is rotated to underlie the elongate aperture and lifting the workpiece into an opening formed in a surround plate such that upper surfaces of the workpiece and the surround plate are co-planar, the opening having a major axis inclined to the printing direction, and iii) performing a printing operation by driving the print carriage across the stencil in the printing direction, to force print medium on the stencil into the elongate aperture, wherein in step iii) the major axis of the squeegee blade and the major axis of the elongate aperture of the stencil are inclined so as to subtend an angle θ during the printing operation, where 0°<θ<90°, wherein step i) comprises transporting the workpiece to overlie tooling in the printing machine, and step ii) comprises bringing the tooling into engagement with the workpiece, and rotating it with the workpiece, wherein step ii) comprises lifting the tooling, with the workpiece supported thereon, toward the stencil, and rotating at least part of the tooling during the lifting, and wherein the tooling and the printing machine comprise a respective key and keyway which mutually engage to convert vertical movement of the tooling into rotation of a tooling rotor, such that lifting of the tooling produces a predetermined rotation of the tooling rotor about the vertical axis.
2 . A method of printing an elongate deposit of print medium onto an elongate deposit target of a workpiece, using a printing machine comprising a print carriage, which, during a printing operation, travels in a printing direction across a stencil provided in the printing machine to force print medium on the stencil into at least one aperture provided in the stencil, the print carriage comprising an elongate squeegee blade with a major axis disposed along the length of the squeegee blade, the method comprising the steps of: i) transporting the workpiece into the printing machine in an orientation in which the elongate deposit target of the workpiece is orthogonal to the printing direction, ii) aligning the workpiece with a stencil within the printing machine so that an elongate aperture, having a major axis disposed along the length of the elongate aperture, provided in the stencil overlies the elongate deposit target, iii) performing a printing operation by driving the print carriage across the stencil in the printing direction with the major axis of the squeegee blade inclined to the printing direction so as to subtend an angle α during the printing operation, where 0°<α<90°, to force print medium on the stencil into the elongate aperture, the major axis of the squeegee blade and the major axis of the elongate aperture of the stencil being inclined so as to subtend an angle θ during the printing operation, where 0°<θ<90°; and iv) moving the squeegee blade in a horizontal direction orthogonal to the printing direction during the printing operation.
3 . The method of claim 2 , comprising the step of rotating the squeegee blade relative to the printing machine about a vertical axis prior to performing step iii).
4 . A printing machine operative to print a print medium onto a workpiece in a printing operation by driving a print carriage in a printing direction across a stencil provided in the printing machine to force print medium on the stencil into at least one aperture provided in the stencil, the printing machine comprising: a movable gantry, a drive configured to move the gantry in the printing direction, and a print carriage comprising: a head unit mounted to the gantry for movement therewith, and an elongate squeegee blade, the squeegee blade having a major axis disposed along the length of the squeegee blade, the squeegee blade being mounted to the head unit, wherein the squeegee blade may be disposed in an inclined configuration in which the major axis of the squeegee blade is inclined to the printing direction so as to subtend an angle α during the printing operation, where 0°<α<90°, and wherein the squeegee is horizontally movable relative to the gantry with at least a component of horizontal movement in a direction orthogonal to the printing direction.
5 . The printing machine of claim 4 , wherein the squeegee blade is rotatable relative to the head unit into the inclined configuration.
6 . The printing machine of claim 5 , wherein the head unit is rotatable relative to the gantry into the inclined configuration.
7 . The printing machine of claim 4 , comprising a rotary actuator operative to rotate the squeegee blade into the inclined configuration.
8 . The printing machine of claim 4 , wherein the squeegee blade may be disposed at a plurality of inclined configurations, such that at each respective inclined configuration the major axis of the squeegee blade is inclined to the printing direction so as to subtend a different respective angle α during the printing operation.
9 . The printing machine of claim 4 , wherein the head unit is horizontally movable relative to the gantry with at least a component of horizontal movement in a direction orthogonal to the printing direction.
10 . The printing machine of claim 4 , comprising a linear actuator operative to move the squeegee horizontally relative to the gantry in a direction orthogonal to the printing direction.
11 . A printing machine operative to print conductive medium onto a workpiece located in a printing position of the printing machine by driving a print carriage in a printing direction across a stencil provided in the printing machine to force print medium on the stencil into at least one aperture provided in the stencil, the printing machine comprising: an input region for receiving workpieces to be printed, an output region for outputting printed workpieces, a lifting table which is movable along a vertical axis, the lifting table being disposed directly below the printing position, a print carriage drivable in the printing direction over the printing position, transport means for successively transporting a plurality of workpieces from the input region to a position directly above the lifting table, and subsequently transporting the plurality of workpieces away from the lifting table to an output region of the printing machine, tooling mounted on the lifting table, the tooling comprising a tooling support surface for supporting a workpiece thereon, configured so that moving the lifting table vertically upwards causes a workpiece supported on the tooling support surface to be moved to the printing position, and a surround plate having an opening to receive a workpiece in the printing position, wherein the opening has a major axis inclined to the printing direction, wherein the tooling support surface is rotatable with respect to the table about the vertical axis and operative to successively rotate each of the plurality of workpieces supported thereon a predetermined angle of rotation about the vertical axis, so that a workpiece located in the printing position is rotated about the vertical axis relative to a workpiece located in the input region of the printing machine, wherein the tooling and the printing machine comprise respective members which mutually engage to convert vertical movement of the tooling into rotation of the tooling support surface, and wherein the members comprise respective ones of a key and a keyway.

Description

This invention relates to a method of printing an elongate deposit of print medium onto an elongate deposit target of a workpiece and printing machines. BACKGROUND AND PRIOR ART Industrial screen-printing machines typically apply a print medium, which may be a conductive print medium such as solder paste, silver paste or conductive ink, onto a planar workpiece, such as a circuit board, by applying the conductive print medium through a pattern of apertures in a thin planar layer or mask, such as a stencil (which is a patterned solid material such as stainless steel) or a screen which is a mesh material coated with emulsion. The present invention is equally applicable to both screen and stencil printing, and for convenience the term “stencil” will be used to refer to any such patterned mask throughout the remainder of this document. The print medium is applied using a print carriage which includes a squeegee. The same machines may also be used to print certain non-conductive media, such as glue or other adhesive, onto workpieces. The present invention is equally applicable to both conductive and non-conductive print media. To ensure high quality printing, it is necessary to support the workpiece so that the surface to be printed is parallel to the stencil, generally horizontal, with the workpiece support being capable of withstanding the pressure placed upon it during the printing operation, especially by the downward pressure applied by the squeegee as the print carriage travels across the stencil, while maintaining the correct alignment of the workpiece. The simplest type of support is to use a flat surface or platen on which a workpiece may be placed. However, there are many circumstances where this type of arrangement is not possible, in particular where the underside of a workpiece has previously been printed and equipped with components (for example during a so-called “placement” operation), and this underside needs to be supported during a printing operation applied to the topside of the workpiece. The presence of components on the underside of the workpiece means that the workpiece will not be flat, and also the components are liable to damage if they are “squashed” during a printing operation. It will be appreciated that workpieces also need support during other processes, for example during a placement operation. To this end, specialist support solutions, known as “tooling”, are used. There are currently two common tooling options for providing support for a printed circuit board (PCB) during printing and placement operations: 1) Dedicated tooling blocks—these are blocks whose upper surface is caused, for example by machining, to have a three-dimensional profile designed to accommodate a specific PCB placed thereon. They are relatively expensive, product-specific, and can easily become obsolete when a PCB design changes.2) Tooling pins—these are thin columns which are positioned to contact the board in use, avoiding contact with any components (or other delicate or critical regions) on the underside. The pins are usually magnetic, i.e. they include either a permanent or an electro-permanent magnet within them, to non-permanently attach the pins to a flat, underlying support plate or “tooling table”, which may conveniently be made from a magnetically permeable material such as steel. By way of example, ASM currently uses simple, low-cost, moulded plastics tooling pins with a single Neodymium permanent magnet in the base of each pin. In this document, the term “tooling” will be used to encompass all such supports, including simple flat platens, tooling blocks and pin supports. Typically, a workpiece supported by the tooling will be raised into a printing position in which it is pushed upwards into the overlying stencil, and in which a printing operation may be performed. This lifting is achieved by locating the tooling on top of a lifting table (also known as a “tooling table”), which is disposed directly below the printing position and drivable along a vertical axis. At the upper end of the lifting table's range of vertical movement, a workpiece supported on the associated tooling is placed in the printing position, while at the lower end of its range of vertical movement, the workpiece engages with transport means, such as rails or conveyors, which act to transport workpieces to be printed from an input region of the printing machine to a position above the lifting table, and to transport printed workpieces away from the lifting table to an output region of the printing machine at which the printed workpieces may be outputted, for example transferred to another machine in the production line. FIG. 1 schematically shows, from above, part of an exemplary printing machine 1 for performing the above-described process. It should be understood that throughout the entirety of this document, the X axis and orthogonal Y axis are considered to lie in the horizontal plane, with a mutually orthogonal Z-axis ext