Dual camera prism assembly for stencil printers

Abstract

A vision system is used within a stencil printer configured to print assembly material onto an electronic circuit board. The vision system comprises a housing, a dual camera assembly supported by the housing, and a prism assembly supported by the housing and configured with the dual camera assembly to provide a first optical path that looks vertically upward at the bottom of the stencil and a second optical path that looks vertically downward at the electronic circuit board.

Description

Technical Field

[0001] This application generally relates to automated electronic equipment used for manufacturing and assembling electronic circuit boards, and more specifically to a stencil printer used to deposit patterns of solder paste or other paste-like materials onto an electronic substrate.

Background Art

[0002] When manufacturing a surface mount printed circuit board, a stencil printer can be used to print solder paste onto the circuit board. Typically, a circuit board having a pattern of pads or some other conductive surface, onto which the solder paste will be deposited, is automatically fed into the stencil printer, and one or more small holes or marks (known as "fiducials") on the circuit board are used to properly align the circuit board with the stencil or screen of the stencil printer before printing the solder paste onto the circuit board. In some systems, an optical alignment system embodying a vision system is used to align the circuit board with the stencil.

[0003] In the above printer, when the circuit board is properly aligned with the stencil, the circuit board is raised up to the stencil and solder paste is supplied to the stencil. A wiper blade (i.e., squeegee) traverses the stencil and extrudes the solder paste through the holes of the stencil onto the circuit board. As the squeegee moves across the stencil, the solder paste tends to spread out in front of the blade. This causes desirable mixing and shearing of the solder paste and results in the desired viscosity to easily fill the holes of the screen, i.e., the stencil. The solder paste is typically supplied to the stencil from a standard cartridge. Thereafter, the stencil is separated from the circuit board, and most of the material remains on the circuit board due to the adhesion between the circuit board and the solder paste. The material remaining on the surface of the stencil is removed in a cleaning process before further circuit boards are printed.

[0004] Another process in printing circuit boards involves inspecting the circuit board after the solder paste has been deposited on its surface. Inspecting the circuit board is crucial for determining whether clean electrical connections can be formed. Too much solder paste can cause short circuits, while too little solder paste in the correct locations can impede electrical contact. Generally, visual inspection systems are further utilized to provide two-dimensional or three-dimensional inspection of the solder paste on the circuit board.

[0005] One of the challenges facing the design of such stencil printers and supply systems is the ability to perform rapid and comprehensive inspection over a large area of ​​the substrate after depositing solder paste in a single pass.

[0006] As is well known in the industry, vision systems, such as machine vision cameras, can be used to capture images of stencils and substrates for the purpose of performing alignment operations. In some prior art systems, such as U.S. Patent No. 5,943,089, a single camera can be used to selectively capture an image of either the underside of the stencil or the top surface of the substrate. In such systems, a single camera can be configured to selectively observe either of these objects being imaged. The choice of which image is captured may depend, for example, on energizing one of two illumination sources. [Prior art document] [Patent] [Patent Document 1] U.S. Patent No. 5,943,089 [Overview of the Initiative]

[0007] In other conventional vision systems, a single camera can use an optical system to image both the stencil and the substrate within a single divided field of view. Such a solution has the advantage of capturing both scenes simultaneously, but it has the limitation of a narrow field of view.

[0008] One aspect of the present disclosure relates to a stencil printer for printing assembly material onto an electronic substrate. In one embodiment, the stencil printer comprises a frame; a stencil coupled to the frame, having a hole formed therein; a support assembly coupled to the frame and configured to support an electronic substrate at a printing position below the stencil; a printhead gantry coupled to the frame; a printhead assembly comprising a printhead supported by the printhead gantry so as to be configured to traverse the stencil during a printing stroke, and having a squeegee blade assembly configured to spread solder paste along the stencil; and a vision system configured to acquire images of the stencil and the electronic substrate. The vision system comprises a housing; a dual camera assembly supported by the housing; and a prism assembly supported by the housing and configured with the dual camera assembly to provide a first optical path that looks vertically upward at the bottom of the stencil and a second optical path that looks vertically downward at the electronic substrate.

[0009] Embodiments of a stencil printer may further include configuring a dual camera assembly to include a bracket and a first lens and a second lens fixed to the bracket, spaced apart from each other and extending perpendicularly from the bracket. The dual camera assembly may further include a first programmed camera configured to acquire an image of a stencil through the first lens via a first optical path, and a second programmed camera configured to acquire an image of an electronic substrate through the second lens via a second optical path. The dual camera assembly may further include two heatsinks, the first heatsink being fixed to the first programmed camera by a first thermal pad, and the second heatsink being fixed to the second programmed camera by a second thermal pad. A prism assembly may comprise a support having a base and a retainer, and a prism structure positioned on the base and fixed in place to the base when the retainer is fixed to the base, the prism structure being configured to guide light along a first optical path to a stencil, guide light along a second optical path to an electronic substrate, guide an image from the stencil along the first optical path via a first lens to a first programmed camera, and guide an image from the electronic substrate along the second optical path via a second lens to a second programmed camera. The prism assembly further comprises an optical window including a quarter-wave plate fixed in place to the retainer by a cover, the optical window positioned over an opening formed in the cover through which light passes when traveling along the first optical path to the stencil. The base of the prism assembly may have an opening through which light passes when traveling along the second optical path to the electronic substrate. The prism assembly may further comprise a double-sided LED board, which is configured to generate light from one side (face) of the LED board and from the opposite side (face) of the LED board. The LED board may comprise a first illuminator with an LED light matrix on one side of the LED board and a second illuminator with a light matrix on the opposite side of the LED board.The prism assembly may further comprise a third illuminator comprising an LED ring light that provides off-axis illumination to an electronic substrate along a second optical path. The prism structure may comprise a first arm section, a second arm section, and a connector section. The first arm section may comprise three prisms arranged to form a generally rectangular block structure, the second arm section may comprise three prisms arranged to form a generally rectangular block structure, and the connector section may comprise two prisms arranged to form a cube, the cube positioned between the first and second arm structures to form a generally U-shaped prism structure. The stencil printer may further comprise a first printed circuit board configured to control a dual camera assembly and a second printed circuit board configured to control the remaining components of the vision system. The stencil printer may further comprise a third printed circuit board configured to control the illumination of LEDs associated with the prism assembly. The first printed circuit board and the second printed circuit board can be separated from each other by a partition, and the first and second printed circuit boards are on the same plane when assembled and fixed within the housing. The stencil printer may further include a fan module provided at one end of the housing for cooling the components of the vision system, including the dual camera assembly, the prism assembly, the printed circuit board and the second printed circuit board.

[0010] Another aspect of the present disclosure relates to a vision system used in a stencil printer configured to print assembly material onto an electronic substrate. In one embodiment, the vision system comprises a housing, a dual camera assembly supported by the housing, and a prism assembly supported by the housing and configured with the dual camera assembly to provide a first optical path that looks vertically upward at the bottom of the stencil and a second optical path that looks vertically downward at the electronic substrate.

[0011] Embodiments of the vision system may include configuring a dual camera assembly to include a bracket and a first lens and a second lens fixed to the bracket, spaced apart from each other and extending perpendicularly from the bracket. The dual camera assembly may further include a first programmed camera configured to acquire an image of a stencil through the first lens via a first optical path, and a second programmed camera configured to acquire an image of an electronic substrate through the second lens via a second optical path. The dual camera assembly may further include two heatsinks, the first heatsink being fixed to the first programmed camera by a first thermal pad, and the second heatsink being fixed to the second programmed camera by a second thermal pad. A prism assembly may comprise a support having a base and a retainer, and a prism structure positioned on the base and fixed in place to the base when the retainer is fixed to the base, the prism structure being configured to guide light along a first optical path to a stencil, guide light along a second optical path to an electronic substrate, guide an image from the stencil along the first optical path via a first lens to a first programmed camera, and guide an image from the electronic substrate along the second optical path via a second lens to a second programmed camera. The prism assembly may further comprise an optical window including a quarter-wave plate fixed in place to the retainer by a cover, the optical window positioned over an opening formed in the cover through which light passes when traveling along the first optical path to the stencil. The base of the prism assembly may comprise an opening through which light passes when traveling along the second optical path to the electronic substrate. The prism assembly may further comprise a double-sided LED board, the double-sided LED board being configured to generate light from one side of the LED board and from the opposite side of the LED board. The LED board may include a first illuminator with an LED light matrix on one side of the LED board, and a second illuminator with a light matrix on the opposite side of the LED board.The prism assembly may further comprise a third illuminator comprising an LED ring light that provides off-axis illumination to an electronic substrate along a second optical path. The prism structure may comprise a first arm section, a second arm section, and a connector section. The first arm section may comprise three prisms arranged to form a generally rectangular block structure, the second arm section may comprise three prisms arranged to form a generally rectangular block structure, and the connector section may comprise two prisms arranged to form a cube, the cube positioned between the first and second arm structures to form a generally U-shaped prism structure. The vision system may further comprise a first printed circuit board configured to control a dual camera assembly, and a second printed circuit board configured to control the remaining components of the vision system. The vision system may further comprise a third printed circuit board configured to control the illumination of LEDs associated with the prism assembly. The first printed circuit board and the second printed circuit board can be separated from each other by a partition, and the first and second printed circuit boards are on the same plane when assembled and fixed within the housing. The vision system may further include a fan module provided at one end of the housing for cooling the components of the vision system, including the dual camera assembly, the prism assembly, the printed circuit board and the second printed circuit board.

[0012] The attached drawings are not intended to be drawn to scale. In the drawings, identical or nearly identical components shown in various figures are represented by the same reference numerals. For clarity, not all components may be referenced in all drawings. [Brief explanation of the drawing]

[0013] [Figure 1] This is a front view of the stencil printer. [Figure 2]This is a front perspective view of a stencil printer. [Figure 3] Figure 2 is a top view of the stencil printer with some parts removed. [Figure 4] This is a top perspective view of a vision system for a stencil printer according to one embodiment of the present disclosure. [Figure 5] This is a bottom perspective view of the vision system. [Figure 6] This is a top perspective view of the vision system with the cover removed to clearly show the components of the vision system. [Figure 7] A side view of the vision system. [Figure 8] This is a disassembled perspective view of the vision system. [Figure 9] This is an exploded perspective view of the dual camera assembly of the vision system. [Figure 10] This is an exploded perspective view of the prism assembly of a vision system. [Figure 11A] This is a perspective view of the LED board assembly. [Figure 11B] This is a perspective view of the LED board assembly. [Figure 12A] This is a perspective view showing the installation of the LED board assembly within the prism assembly. [Figure 12B] This is a perspective view showing the installation of the LED board assembly within the prism assembly. [Figure 12C] This is a perspective view showing the installation of the LED board assembly within the prism assembly. [Figure 13A] This is a diagram of the prism assembly with the outer casing removed. [Figure 13B] This is a diagram of the prism assembly with the outer casing removed. [Figure 13C] This is a diagram of the prism assembly with the outer casing removed. [Figure 13D] This is a diagram of the prism assembly with the outer casing removed. [Figures 13E-13F]It is a diagram of a prism assembly with the exterior removed. [Figure 14A] It is a perspective view of a dual - camera assembly of a vision system showing the optical path of illumination generated by the vision system and guided to the stencil and the electronic substrate. [Figure 14B] It is a perspective view of a dual - camera assembly of a vision system showing the optical path of an image from the stencil and the electronic substrate.

Mode for Carrying Out the Invention

[0014] The present disclosure comprehensively relates to a material - coating machine (referred to herein as a "stencil printer", "screen printer", "printer", or "coater") and other equipment that is utilized in a surface - mount technology (SMT) process line and is configured to apply an assembly material (such as solder paste, conductive ink, or encapsulation material) onto a substrate (such as a printed circuit board referred to herein as an "electronic substrate", "circuit board", "board", "PCB", "PCB substrate", "substrate", or "PCB board") or perform other operations such as inspection, re - work, or placement of electronic components onto the substrate. Specifically, embodiments of the present disclosure are described below with reference to a stencil printer used to fabricate a printed circuit board.

[0015] For illustrative purposes only and not to limit its universality, the present disclosure is described in detail here with reference to the accompanying drawings. The present disclosure is not limited to the details of configurations and arrangements of components described below or shown in the drawings in terms of its applications. The principles described in the present disclosure are also applicable to other embodiments and can be practiced or implemented in various ways. Furthermore, the expressions and terminology used in this application are for illustrative purposes only and should not be considered limiting. Any reference in this application to an example, embodiment, component, element or operation of a system or method referred to singularly may also encompass embodiments containing multiple components, and any reference in this application to any embodiment, component, element or operation as plural may also encompass embodiments containing only singular components. References in singular or plural form are not intended to limit the systems or methods, their components, operations or elements disclosed in this application. The use of the terms “including,” “equipped with,” “having,” “containing,” “accompanying,” and variations thereof in this application means that the articles listed before them, their equivalents and additional articles, are included. A reference to “or / or” can be interpreted as comprehensive, such that any term described using “or / or” can refer to any single, two or more, or all of the terms described. In addition, if there is inconsistency in the use of terminology between this document and any document that, by reference, forms part of this application, the use of terminology in the document forming part of this application is supplementary to the use in this document, and the use of terminology in this document shall prevail if the inconsistency results in a contradiction.

[0016] This disclosure utilizes a specially configured prism assembly and two complete camera systems to facilitate simultaneous imaging of the entire field of view of both the stencil and the electronic substrate. The structure and function of the prism assembly are described in further detail below.

[0017] For illustrative purposes, embodiments of the present disclosure will be described below with reference to a stencil printer used to print assembly materials, such as solder paste, onto a circuit board. However, those skilled in the art will understand that embodiments of the present disclosure are not limited to stencil printers for printing solder paste onto circuit boards, but can be used in other applications requiring the supply of other viscous assembly materials, such as adhesives and encapsulants. For example, the apparatus can be used to print epoxy used as underfill for chip-scale packages. Furthermore, the stencil printers of embodiments of the present disclosure are not limited to those for printing assembly materials onto circuit boards, but include those used for printing other materials onto various substrates, such as semiconductor wafers. Also, the terms screen and stencil can be used interchangeably in this application to describe devices within a printer that define the pattern printed on the substrate. In certain embodiments, the stencil printer may include the Momentum® or Edison® series stencil printer platforms provided by ITW Electronic Assembly Equipment in Hopkinton, Massachusetts. An exemplary stencil printer is generally shown as 5 in Figure 1. In this embodiment, the stencil printer 5 is a Momentum® series stencil printer platform provided by ITW Electronic Assembly Equipment in Hopkinton, Massachusetts.

[0018] Referring to Figure 2, the stencil printer of an embodiment of the present disclosure is generally shown as 10. As shown, the stencil printer 10 has a frame 12 that supports the components of the stencil printer. The components of the stencil printer may include, in part, a controller 14, a display 16, a stencil 18, and a print head or print head assembly. The print head or print head assembly is generally shown as 20 and is configured to apply solder paste in the manner described in more detail below.

[0019] As shown in Figure 2 and described below, the stencil and printhead assembly can be connected to the frame 12 as appropriate, or otherwise connected. In one embodiment, the printhead assembly 20 can be mounted on a printhead assembly gantry 22, which can be mounted on the frame 12. The printhead assembly gantry 22 allows the printhead assembly 20 to move in the y-axis direction under the control of the controller 14 and to apply pressure to the printhead assembly by engaging with the stencil 18. In a particular embodiment, the printhead assembly 20 can be placed above the stencil 18 and descend in the z-axis direction to contact the stencil and engage with it.

[0020] The stencil printer 10 may also have a conveyor system having rails (not shown) for transporting printed circuit boards to the printing position within the stencil printer. The rails may be referred to in this application as a "tractor feed mechanism." The tractor feed mechanism is configured to feed, deliver, or otherwise deliver circuit boards into the work area of ​​the stencil printer, which may be referred to in this application as a "print nest," and to discharge the circuit boards from the print nest.

[0021] Referring further to Figure 3, the stencil printer 10 has a support assembly 28 that supports the circuit board 29 (shown by a dashed line). The support assembly 28 raises and secures the circuit board so that it is stable during printing. In certain embodiments, the board support assembly 28 may further have a specific board support system, such as a rigid support, multiple pins, or a flexible tool, which is positioned below the circuit board when the circuit board is in the printing position. Part of the board support system can be used to support the internal region of the circuit board to prevent bending or warping of the circuit board during printing.

[0022] In one embodiment, the printhead assembly 20 may be configured to receive solder paste from a supply source, such as a dispenser or solder paste cartridge, which provides solder paste to the printhead assembly during printing operations. Other methods of supplying solder paste may be used instead of a cartridge. For example, solder paste can be manually deposited between blades or from an external supply source. In addition, in certain embodiments, the controller 14 may be configured to use a personal computer with a suitable operating system, such as the Microsoft Windows® operating system provided by Microsoft Corporation, and to control the operation of the stencil printer 10 using application-specific software. The controller 14 may be networked with a master controller used to control a production line for manufacturing circuit boards.

[0023] In one configuration, the stencil printer 10 operates as follows: The circuit board 29 is transported into the stencil printer 10 using a conveyor rail. A support assembly 28 raises and secures the circuit board 29 to the printing position. The print head assembly 20 is then lowered in the z-axis direction until the blades of the print head assembly contact the stencil 18 with the desired pressure. The print head assembly 20 is then moved in the y-axis direction across the stencil 18 by the print head assembly gantry 22. The print head assembly 20 deposits solder paste onto the circuit board 29 through the holes in the stencil 18. Once the print head assembly has completely traversed the stencil 18 across the holes, the print head assembly is lifted from the stencil, and the circuit board 29 is lowered back onto the conveyor rail. The circuit board 29 is released and transported from the stencil printer 10, thereby allowing a second circuit board to be transported into the stencil printer. To print on the second circuit board 29, the print head assembly is lowered in the z-axis direction to contact the stencil and moved across the stencil 18 in the opposite direction to that used for the first circuit board.

[0024] A vision system 30 may be provided for the purpose of aligning the stencil 18 with respect to the circuit board 29 before printing and for inspecting the circuit board after printing. In one embodiment, the vision system 30 may be positioned between the stencil 18 and a support assembly 28 on which the circuit board is supported. The vision system 30 is connected to a vision system gantry 32 for moving the vision system. In one embodiment, the vision system gantry 32 may be connected to a frame 12 and has beams extending between the lateral rails of the frame 12, providing for the imaging system 30 to move back and forth above the circuit board 29 in the y-axis direction. The vision system gantry 32 may further have a carriage device housing the vision system 30, configured to move along the length of the beams in the x-axis direction. The structure of the vision system gantry 32 used to move the vision system 30 is known in solder paste printing technology. The arrangement allows the vision system 30 to be positioned at any position below the stencil 18 and above the circuit board 29 to capture images of predetermined areas of the circuit board or stencil, respectively. In other embodiments, when the imaging system is positioned outside the printing position, the imaging system can be placed below the stencil or above the circuit board.

[0025] This configuration allows the vision system 30 to be positioned at any position along the scanning axis below the stencil 18 and above the circuit board 29 to determine the surface shape of a predetermined area of ​​the circuit board or stencil, respectively. In other embodiments, when the vision system 30 is positioned outside the print nest, the vision system 30 can be positioned below the stencil 18 or above the circuit board 29.

[0026] After applying solder paste to the circuit board one or more times, excess solder paste may accumulate at the bottom of the stencil 18, and the stencil wiper assembly, generally shown as 34, can move below the stencil to remove the excess solder paste. In other embodiments, the stencil 18 may move above the stencil wiper assembly.

[0027] Embodiments of the present disclosure relate to an improved vision system capable of providing two full fields of view to two cameras, respectively. In one embodiment, one camera is positioned to look up at a stencil, and the other camera is positioned to look down at an electronic substrate. The vision system comprises a prism assembly that provides two optical paths to be collinear in the upward / downward viewing angles. Specifically, the prism assembly bends the two optical paths to be parallel at the exit surfaces of the lens / camera. In a particular embodiment, the prism assembly provides a path for on-axial illumination, since many of the metal surfaces to be imaged are specular.

[0028] Referring to Figures 4 to 8, and more specifically Figures 6 and 8, a vision system of a preferred embodiment of the present disclosure is generally shown as 40. The vision system 40 comprises several main components, including a dual camera assembly generally shown as 42 and a prism assembly generally shown as 44. The vision system 40 includes a housing 46 configured to support the components of the vision system, including the dual camera assembly 42 and the prism assembly 44. A housing cover 48 is provided to cover the top of the housing 46 and to protect the components of the vision system 40 supported by the housing, including the dual camera assembly 42 and the prism assembly 44. The dual camera assembly 42 and the prism assembly 44 are configured to operate relative to each other to provide a first optical path that looks vertically upward at the bottom of a stencil, for example, a stencil 18, and a second optical path that looks vertically downward at an electronic substrate, for example, a circuit board 29.

[0029] The vision system 40 further comprises a first printed circuit board 50 configured to provide control to a dual camera assembly 42, and a second printed circuit board 52 configured to provide control to the remaining components of the vision system. A third printed circuit board, described in more detail below, is provided to control the illumination of LEDs associated with a prism assembly 44. The first printed circuit board 50 and the second printed circuit board 52 are separated from each other by a separation portion indicated by 54, and are coplanar with respect to each other when assembled and fixed within the housing 46 of the vision system 40. The vision system 40 further comprises a fan module 56 provided at one end of the housing 46 for cooling the components of the vision system. The fan module 56 is provided to move air within the housing 46 to cool the dual camera assembly 42, the prism assembly 44, and the components supported by the housing, including but not limited to the first printed circuit board 50 and the second printed circuit board 52.

[0030] The housing 46 of the vision system 40 further supports components of the hard stop assembly. For example, the housing 46 may be configured to support an actuator 58, a clamp 60, a sensor 62, and a flag 64. The hard stop assembly is provided to stop the movement of the electronic circuit board when it is loaded into the stencil printer. As shown in the figure, the housing 46 is configured to support the actuator 58 on the side of the housing by a pair of screw fasteners. The sensor 62 is supported by the housing 46 in a position adjacent to the actuator 58 and the prism assembly 44. The sensor 60 and the prism assembly 44 are also fixed to the housing 46 by screw fasteners. The aforementioned sensor 62 is part of the hard stop assembly and can be actuated to a downward position to engage with the edge of the electronic circuit board, or to an upward retracted position. The sensor 62 ensures that the pneumatically actuated hard stop is positioned as commanded.

[0031] The dual camera assembly 42 is fixed to the housing 46 adjacent to the prism assembly 44, with the first camera facing one side of the prism assembly 44 and the second camera facing the opposite side of the prism assembly. The aforementioned third circuit board is positioned in the gap provided in the prism assembly 44 and provides LED illumination to the prism assembly. The first printed circuit board 50 and the second printed circuit board 52 are fixed to the housing 46 adjacent to the dual camera assembly 42 via screw fasteners fixed to the separation portion 54. As described above, the fan module 56 of the vision system 40 is provided at the end of the housing 46 and is configured to move air through the housing, specifically through the first circuit board 50 and the second circuit board 52, the dual camera assembly 42, and the prism assembly 44, respectively.

[0032] The vision system 40 further comprises a focus adjustment screw 66 (Figure 7) and two springs, indicated 68 (Figure 5), which maintain a light force on the focus adjustment screw to keep the dual camera assembly 42 as straight as possible when adjusting the focus during calibration and setup.

[0033] Referring to Figure 9, the dual camera assembly 42 includes a bracket 70 configured to support the components of the dual camera assembly. The bracket 70 is a rectangular structure configured to secure a first lens 72 and a second lens 74 that are spaced apart from each other and extend perpendicularly from the bracket. In the illustrated embodiment, the first lens 72 is configured to look up at the stencil, and the second lens is configured to look down at the electronic substrate. One of the lenses, for example, the first lens 72, includes a lens hood 76 that is secured to the second lens by a clamp 78. The purpose of the lens hood 76 is to prevent stray light from entering the camera, thereby preserving the image from the stencil. Although not shown, the second lens 74 may be configured to include a lens hood similar to the lens hood 76, which can be secured to the second lens by another clamp similar to the clamp 78. In a preferred embodiment, both the first lens 72 and the second lens 74 are equipped with lens hoods, such as the lens hood 76, to prevent stray light from entering their respective cameras.

[0034] In some embodiments, two identical lenses 72 and 74 are used. In one embodiment, each of the first lens 72 and the second lens 74 is manufactured by VST under the model number MC075-50. The magnification of each of the first lens 72 and the second lens 74 is 0.75.

[0035] The dual camera assembly 42 further comprises a first programmed camera 80 configured to acquire an image of a stencil through a first lens 72 via a first optical path, and a second programmed camera 82 configured to acquire an image of an electronic substrate through a second lens 74 via a second optical path. This configuration allows the dual camera assembly 42 to simultaneously acquire an image of the stencil by the first programmed camera 80 and the first lens 72, and an image of the electronic substrate by the second programmed camera 82 and the second lens 74. The dual camera assembly 42 further comprises two heatsinks 84 and 86, the first heatsink 84 being fixed to the first programmed camera 80 by a first thermal pad 88, and the second heatsink 86 being fixed to the second programmed camera 82 by a second thermal pad 90. The first heatsink 88 and the second heatsink 90 are provided to cool the first programmed camera 80 and the second programmed camera 82, respectively.

[0036] In some embodiments, two identical pre-programmed cameras 80 and 82 are used. In one embodiment, the pre-programmed cameras 80 and 82 are manufactured by Teledyne FLIR under the model number BFS-GE-50S5M-BD2 and each incorporates a monochrome sensor manufactured by Sony Corporation under the model number IMX264. In a particular embodiment, the resolution of each pre-programmed camera 80 and 82 is 2464(H) × 2056(V) for approximately 5.07 megapixels. The pixel size of the image sensor is 3.45 μm × 3.45 μm. In a particular embodiment, the pre-programmed cameras 80 and 82 are connected by Gigabit Ethernet, and a 3-port Broadcom GbE-Net switch can be provided as part of the vision system 40.

[0037] Referring to Figure 10, the prism assembly 44 comprises a support having a base 92 and a retainer 94, the base 92 and the retainer 94 being configured to be fixed together to secure the components of the prism assembly. The components of the prism assembly 44, when assembled, are supported on the base 92 and protected by the retainer 94. The prism assembly 44 further comprises a prism structure generally shown as 96, the prism structure being positioned on the base 92 and fixed in place to the base when the retainer 94 is fixed to the base. The prism structure 96 is configured to guide light along a first optical path to a stencil and along a second optical path to an electronic substrate, the stencil and electronic substrate may be referred to as objects. The prism structure 96 is further configured to guide an image from the stencil along the first optical path through a first lens 72 to a first programmed camera 80 and an image from the electronic substrate along a second optical path through a second lens 74 to a second programmed camera 82. As described above, the first lens 72 is equipped with a lens hood 76 to capture the stencil and prevent stray light from damaging the image guided to the first programmed camera 80. As described above, the second lens 74 can also be configured with a lens hood.

[0038] The prism assembly 44 further comprises two auto-adhesive foam pads, each indicated by 98, which are provided to engage with the prism structure 96 when the holder 94 is fixed to the base 92. The holder 94 of the prism assembly 44 further comprises an optical window 100 into which a quarter-wave plate is embedded. The quarter-wave plate is secured in place to the holder 94 by a cover 102, and the optical window is positioned over an opening 104 formed in the holder. In one embodiment, the quarter-wave plate is a thin film. Thus, for mounting and handling purposes, the quarter-wave plate is laminated between two thin glass layers to form a window assembly that can be handled and mounted as a single piece. The window 100 may be referred to as the quarter-wave plate assembly. The orientation of the quarter-wave plate is somewhat important for its function. Alignment between the quarter-wave plate and the edge of the glass window ensures the proper positioning of the quarter-wave plate. Furthermore, although this embodiment describes having one such window in the stencil-side optical path, utilizing the same window with a quarter-wave plate in the substrate-side optical path can improve the contrast of any specular features that may exist on the electronic substrate, such as exposed copper pads on the electronic substrate.

[0039] The cover 102 has an opening 106 that aligns with the opening 104 of the retainer 94 to allow light to move from the prism assembly 44 to the stencil. The optical window 100 is provided for the first optical path to the stencil. The cover 102 may be secured to the retainer 94 by screw fasteners and may include a gasket 108 that positions and seals the optical window 100 in place.

[0040] The base 92 of the prism assembly 44 has an opening 110 through which the second optical path to the electronic substrate passes. The opening 110 of the base 92 does not require a filter, but if a filter is required, the base can support an optical window similar to the optical window 100, as well as a cover 102 and gasket 108 used on the holder 94.

[0041] The prism assembly 44 further comprises two structures, indicated by 112A and 112B, in which polarizers are stacked on a diffuser (plate), with the polarizers of these structures 112A and 112B positioned facing the prism structure 96. The purpose of the diffuser structures 112A and 112B is to help ensure that the light generated by the illuminator LED matrices 116 and 118 is spatially uniform. By diffusing the light as it passes through the diffusers, the structure of the light, specifically the relatively bright areas where the LEDs are located and the thin dark bands between individual LEDs, is averaged out, ensuring more uniform illumination across the incident surface of the prism, for example, surfaces 152 and 154 described later. The polarizer-stacked diffusers 112A and 112B ensure that only S-polarized light enters the prism, as it is guided along the optical axis by the polarization surfaces within the prism, for example, surfaces 136 and 150 described later. Therefore, P-polarized light from the illuminator is undesirable and is blocked by the polarizers.

[0042] Referring to Figures 11A and 11B, the prism assembly 44 further comprises a double-sided LED board 114 provided to provide light to the vision system 40. As shown, the LED board 114 is configured to generate light from one side of the LED board and from the opposite side of the LED board. Specifically, a first LED light matrix 116 is provided on one side of the LED board 114, and a second light matrix 118 is provided on the opposite side of the LED board. In one embodiment, the double-sided LED board 114 can be assembled by placing two separate LED boards back to back, as shown in Figure 12A.

[0043] In some embodiments, each LED light matrix 116, 118 consists of 81 CreeXD16 LEDs physically arranged as a 9x9 array. Each set of 81 LEDs is electrically connected as three parallel strings of 27 LEDs each. The LED light matrices 116, 118, which provide on-axial illumination for both the stencil and the electronic substrate, include 3000K white LEDs.

[0044] In one embodiment, the prism assembly 44 further comprises a third illuminator, including an LED ring light 120, to provide off-axis illumination to an electronic substrate along a second optical path. The LED ring light 120 is shown in Figure 5. The LED ring light 120, sometimes referred to as an off-axis light source, consists of 32 LEDs arranged as a ring, with 8 LEDs along each side of the square. Electrically, the LEDs of the LED ring light 120 are connected as a single string of 32 LEDs. The LED ring light providing off-axis light includes red LEDs.

[0045] In some embodiments, the drive circuit for the LED light may reside on the LED board 114. The drive circuit for the LED ring light 120 may reside on the interconnect board. In one embodiment, the first programmed camera 80 and the second programmed camera 82 each provide three general-purpose input / output (GPIO) signals. The first programmed camera 80, used to observe the stencil, provides one output signal as a strobe (on-axis) and a second output signal as TRIGGER_ENABLE. The second programmed camera 82, used to observe the electronic circuit board, provides two output signals as strobes (on-axis and off-axis, respectively). The actual TRIGGER signal is generated by ANDing TRIGGER_ENABLE with a motion control output called XY_IN_POS. If on-the-fly triggering is not performed, the XY_IN_POS signal should be asserted to allow TRIGGER_ENABLE to pass to TRIGGER. The TRIGGER signal is fed back to both the first programmed camera 80 and the second programmed camera 82 on a third GPIO signal configured as an input. This configuration makes it possible to trigger both the first programmed camera 80 and the second programmed camera 82 simultaneously.

[0046] In some embodiments, the strobes for three different illuminators, namely two LED light matrices 116, 118 and one LED ring light 120 on an LED board 114, are independent of each other, and the effective illumination can be controlled by changing the duration of each strobe.

[0047] In some embodiments, the LEDs in the LED board 114 and the LED ring light 120 are controlled to operate at 1 ampere (A). This current level is substantially higher than the continuous rated current. Therefore, the strobe duration should be limited to prevent the LEDs from overheating. In one embodiment, the strobe duration can be less than 100 microseconds (μs), typically 30 μs to 50 μs.

[0048] As shown in Figures 12A to 12C, the LED board 114 is installed within the prism structure 96 of the prism assembly 44 by inserting the LED board into a gap or space provided in the prism structure. As shown in Figure 12A, the two separate LED boards are positioned back-to-back with the first LED light matrix 116 facing in one direction and the second LED light matrix 118 facing in the opposite direction. Figure 12B shows the LED board 114 before insertion into the gap formed in the prism structure 96 of the prism assembly 44. Figure 12C shows the LED board 114 installed within the prism structure 96 of the prism assembly 44.

[0049] Referring to Figures 13A to 13F, the prism structure 96 of the prism assembly 44 in the illustrated embodiment is generally U-shaped, and embodies several conjugate prisms fixed to one another to realize the desired, illustrated U-shaped prism structure. As is known in optics, a prism is a transmissive optical element having a flat, polished surface designed to refract light. In the illustrated embodiment, several triangular prisms are used. Prisms can be manufactured from optical glass or several other suitable materials that are transmissive to the wavelength for which the prism is designed. Other materials include acrylic and fluorite.

[0050] The prism structure 96 can be divided into three sections: a first arm section 122, a second arm section 124, and a connector section 126. The first arm section 122 comprises three prisms 128, 130, and 132 arranged to form a roughly rectangular block structure. Reinforced aluminum is provided on the inner surface 134. A polarizing material that reflects S-polarized light and transmits P-polarized light is provided on the inner surface 136. A broadband visible anti-reflective (AR) coating is used on surfaces 138 and 140. Similarly, the second arm section 124 comprises three prisms 142, 144, and 146 arranged to form a roughly rectangular block structure. The second arm section 124 is a mirror image of the first arm section 122. Reinforced aluminum is provided on the inner surface 148. A polarizing material that reflects S-polarized light and transmits P-polarized light is provided on the inner surface 150. A broadband visible AR coating is used on surfaces 152 and 154. The connector section or intermediate section 126 comprises two prisms 156 and 158 arranged to form a cube. Reinforced aluminum is provided on the internal surface 160. A broadband visible AR coating is used on surfaces 162 and 164. Furthermore, a broadband visible AR coating can be used on the inward surface 166 of the first arm section 122 and the inward surface 168 of the second arm section 124, respectively. Finally, black paint is used on surface 170 and many other non-optical surfaces. It should be noted that the small triangular prisms 132 and 146 in Figure 13A may not be optically active. Without these small prisms, assembly and fixing of the prism structure 44 would be difficult. Therefore, some of the smaller triangular prisms are added for mechanical reasons rather than optical reasons.

[0051] The presence of a polarizer mounted on the output surface of the diffuser and the polarization surface inside the prism structure 44 work together to steer the light from the illuminator onto the main optical centerline path. Without the quarter-wave plate, the light reflected from the stencil would still be mostly S-polarized, and upon encountering the polarization surface with the prism, it would be reflected back towards the illuminator rather than passing towards the camera. Therefore, the quarter-wave plate is provided as part of the beam steering function of the prism assembly. On the substrate side, the quarter-wave plate is less important because the non-mirrored surface does not maintain the polarization structure of the light. The light returning from the substrate image is a combination of S-polarized and P-polarized light. The P-polarized portion passes through the polarization surface towards the camera and lens. The S-polarized portion of the light is reflected back towards the illuminator and lost. As described above, the quarter-wave plate window can also be incorporated into the optical path on the stencil side, which can help enhance the contrast of any specular features that may be present in the substrate scene.

[0052] Embodiments of the prism structure 96 of the prism assembly 44 may include providing all optical surfaces of the prism structure with a flatness of within 1 / 4 wavelength, all optical surfaces being finished to 40-20 scratches / dig (S / D), all linear dimensions being ±0.10 mm, and all angles being ±3 minutes (0 degrees 3 minutes).

[0053] In some embodiments, the effective pixel size in the stencil (object) is 3.45 μm / 0.75 = 4.60 μm. The field of view of the stencil and electronic substrate is 11.33 mm (H) × 9.46 mm (V).

[0054] Illumination is slightly attenuated at the edges of the field of view. Therefore, a region of interest (ROI) slightly smaller than the entire field of view can be guaranteed.

[0055] As described above, since the surface of the stencil is substantially mirror-like, the first optical path provided to the stencil has only on-axis illumination. On the other hand, the second optical path for the electronic substrate incorporates both on-axis and off-axis illumination.

[0056] Referring to Figure 14A, as described above, the prism structure 96 of the prism assembly 44 can simultaneously guide the illumination from the LED board 114 to the electronic circuit board and the electronic circuit board along the first optical path (indicated as A in Figure 14A) and the second optical path (indicated as B in Figure 14A), respectively. Referring to Figure 14B, the images reflected back along the first optical path (indicated as C in Figure 14B) and the second optical path (indicated as D in Figure 14B) are guided to the first programmed camera 80 and the second programmed camera 82, respectively. The configuration of the prism structure 96 can be changed depending on its intended application.

[0057] The first and second optical paths are substantially collinear. The two optical paths are each bent by 90 degrees at a common internal aluminum-treated surface 160 oriented at 45 degrees to the optical paths, so that the two paths appear horizontally opposite each other. The two horizontal paths are each bent by 90 degrees at aluminum-treated surfaces 134 and 148, so that they appear along parallel paths. In a preferred embodiment, these two optical paths are separated by only 32 millimeters (mm).

[0058] As described above, the vision system 40 includes a double-sided LED board 114 located in a U-shaped gap within the prism structure 96 of the prism assembly 44 to provide illumination to the vision system. The first LED light matrix 116 of the LED board 114 and the second LED light matrix 118 of the LED board guide light into the first and second optical paths, respectively. The prism structure 96 of the prism assembly 44 includes polarizer films bonded to the exit surfaces of diffusers 112A and 112B, which restrict the light entering the prism assembly to S-polarization. The internal surfaces within each arm portion 122 and 124 of the prism structure 96 are coated with dielectric layers fabricated to preferentially reflect S-polarization. Since these internal surfaces are oriented at a 45-degree angle to the optical axis, the S-polarization is guided axially along each of the two optical paths.

[0059] After passing through two folding mirrors in each optical path, the illumination light passes through a quarter-wavelength retarder film embedded in the window and mounted adjacent to the prism structure 96, appearing as circularly polarized light guided to the object surface. Although not shown, a quarter-wavelength plate may be provided on the substrate side.

[0060] Light reflected from the illuminated surface of an object is reflected back by the prism structure 96. The light reflected from the mirror surface maintains circular polarization. After passing through the quarter-wavelength retarder film a second time, the light enters the prism structure 96 as P-polarized light. In this embodiment, since most electronic substrates are not particularly mirrored, a quarter-wavelength plate window is not installed in the optical path on the substrate side. However, since some features of the substrate, such as bonding pads, may themselves be mirrored, a quarter-wavelength plate window on the substrate side may be included, which, if present, can enhance the contrast of such mirrored features.

[0061] When light passes through the internal polarization surface, P-polarized light is transmitted and exits the prism structure 96 towards the imaging lenses 72 and 74. If there is light that is not P-polarized (i.e., S-polarized light), it is reflected away from the optical axis at the internal surface.

[0062] In some embodiments, the vision system 40 utilizes a single double-sided LED board 114. In other embodiments, the vision system utilizes two separate single-sided LED boards mounted back-to-back.

[0063] In some embodiments, the illumination generated by the LED board 114 is controlled to maximize the signal-to-noise ratio between significant structured light and unwanted or non-image light.

[0064] In some embodiments, the prism structure 96 of assembly 44 is intended to manage the illumination and image paths for a dual-camera system in an automated stencil printer. The two optical paths are collinear, 180 degrees opposite on the object side, and parallel on the image side. In one embodiment, the prism structure 96 of prism assembly 44 has dimensions of 48 mm in width, 35 mm in length, and 16 mm in height.

[0065] As described above, the prism assembly 44 of the vision system 40 serves multiple purposes. The prism assembly 44 provides two full fields of view to the two cameras, namely the first programmed camera 80 and the second programmed camera 82, one field of view looking up at the stencil and the other field of view looking down at the electronic circuit board. Furthermore, the prism assembly 44 provides two optical paths that are collinear in the upward and downward viewing angles.

[0066] In some embodiments, the two optical paths are bent so that they are parallel at the exit surface of the lens / camera.

[0067] In some embodiments, the prism assembly 44 of the vision system 40 is configured to provide an illumination path for on-axial illumination, since many of the metal surfaces to be imaged are specular.

[0068] In some embodiments, the prism assembly 44 of the vision system 40 is configured to manage illumination to maximize the signal-to-noise ratio between significant structured light and unwanted or non-image light.

[0069] During operation, the vision system 40 is configured to "look up" vertically at the bottom of the stencil along the first optical path and simultaneously "look down" vertically at the electronic substrate along the second optical path. In some embodiments, illumination is generated by a double-sided LED board 114 located in a U-shaped gap in the prism assembly 44 of the prism structure 96. The first surface of the LED board 114, e.g., matrix 116, directs light into the first optical path through a diffuser polarizer 112A, and the second surface of the LED board, e.g., matrix 118, directs light into the second optical path through a diffuser / polarizer 112B. A polarizing film is bonded to the output surface of the diffuser to restrict the light to S-polarization. The internal surfaces within each arm portion 122, 124 of the prism structure 96 are coated with a dielectric layer fabricated to preferentially reflect S-polarization. These internal surfaces are oriented at a 45-degree angle to the optical axis so that S-polarization is directed axially along each of the two optical paths. After passing through two folding mirrors, the illumination light passes through a quarter-wavelength retarder film stacked within the window and mounted adjacent to the prism, emerging as circularly polarized light directed to the object surface. Light reflected from the illuminated object surface is reflected again through the quarter-wave plate and returns to the prism structure 96. Light reflected from the mirror surface maintains its circular polarization. After passing through the quarter-wavelength retarder film a second time, the light enters the prism structure 96 as P-polarized light. As the light passes through the internal polarization surface, the P-polarized light is transmitted and exits the prism structure 96 toward the imaging lenses 72 and 74. Any light that is not P-polarized (i.e., S-polarized light) is reflected away from the optical axis at the internal surface.

[0070] Various controllers, such as controller 14, can perform the various operations described above. Using data stored in associated memory and / or storage devices, controller 14 can also execute one or more instructions stored in one or more non-temporary computer-readable media, which controller 14 may include and / or combine, thereby producing manipulated data. In some examples, controller 14 may include one or more processors or other types of controllers. In one example, controller 14 is at least one processor or includes at least one processor. In other examples, controller 14 performs at least some of the operations described above using application-specific integrated circuits, which are tuned to perform specific operations, in addition to or instead of general-purpose processors. As illustrated by these examples, examples relating to the present disclosure can perform the operations described herein using many specific combinations of hardware and software, and the present disclosure is not limited to any specific combination of hardware and software components. Examples of the present disclosure may include computer program products configured to perform the methods, processes, and / or operations described above. A computer program product may be one or more controllers and / or processors configured to execute instructions for performing the methods, processes, and / or operations described above, or may include such controllers and / or processors.

[0071] The systems and methods of this disclosure relate to capturing images of surface morphological features of stencils and electronic substrates. The description of the systems and methods provided herein refers to an exemplary electronic substrate (e.g., a printed circuit board) supported on a support assembly of a stencil printer.

[0072] Thus, while several aspects of at least one embodiment have been described, it will be understood that various variations, modifications, and improvements will be readily conceivable to those skilled in the art. Such variations, modifications, and improvements are intended to be part of and within the scope of this disclosure. Accordingly, the foregoing description and drawings are merely illustrative.

Claims

1. A stencil printer for printing assembly materials onto an electronic circuit board, Frame and, A stencil coupled to the frame, wherein a hole is formed in the stencil, A support assembly coupled to the frame, configured to support the electronic circuit board at the printing position below the stencil, A print head gantry coupled to the aforementioned frame, A printhead assembly supported by the printhead gantry so as to be configured to traverse the stencil during a printing stroke, comprising a printhead having a squeegee blade assembly, wherein the squeegee blade assembly is configured to spread solder paste along the stencil, A vision system configured to acquire images of the stencil and the electronic circuit board, Housing and A dual camera assembly supported by the aforementioned housing, A prism assembly supported by the housing, configured to provide, together with the dual camera assembly, a first optical path that looks vertically upward at the bottom of the stencil and a second optical path that looks vertically downward at the electronic substrate, A vision system equipped with, A stencil printer equipped with this feature.

2. The aforementioned dual camera assembly is Bracket and A first lens and a second lens fixed to the bracket, the first lens and the second lens being spaced apart from each other and extending perpendicularly from the bracket, A stencil printer according to claim 1, comprising:

3. The aforementioned dual camera assembly is A first programmed camera configured to acquire an image of the stencil through the first optical path and the first lens, A second programmed camera configured to acquire an image of the electronic circuit board through the second optical path and the second lens, The stencil printer according to claim 2, further comprising the following:

4. The stencil printer according to claim 3, wherein the dual camera assembly further comprises two heatsinks, the first heatsink being fixed to the first programmed camera by a first thermal pad, and the second heatsink being fixed to the second programmed camera by a second thermal pad.

5. The prism assembly is A support having a base and a holder, A prism structure positioned on the base and fixed to the base in an appropriate place when the holder is fixed to the base, the prism structure is configured to guide light along the first optical path to the stencil, guide light along the second optical path to the electronic substrate, guide the image from the stencil along the first optical path through the first lens to the first programmed camera, and guide the image from the electronic substrate along the second optical path through the second lens to the second programmed camera, A stencil printer according to claim 3, comprising:

6. The stencil printer according to claim 5, wherein the prism assembly further comprises an optical window including a quarter-wave plate, which is fixed in place to the holder by a cover, and the optical window is positioned above an opening formed in the cover through which the first optical path to the stencil passes.

7. The stencil printer according to claim 6, wherein the base of the prism assembly has an opening through which the second optical path to the electronic substrate passes.

8. The stencil printer according to claim 5, wherein the prism assembly further comprises a double-sided LED board, the LED board being configured to generate light from one side of the LED board and from the opposite side of the LED board.

9. The stencil printer according to claim 8, wherein the LED board comprises a first illuminator having an LED light matrix provided on one side of the LED board, and a second illuminator having a light matrix provided on the opposite side of the LED board.

10. The stencil printer according to claim 9, further comprising a third illuminator having an LED ring light that provides off-axis illumination to the electronic substrate along the second optical path, the prism assembly.

11. The stencil printer according to claim 5, wherein the prism structure comprises a first arm section, a second arm section, and a connector section.

12. The stencil printer according to claim 11, wherein the prism structure further comprises two structures in which polarizers are stacked on a diffuser, and the polarizers of the structure are installed facing the prism structure.

13. The stencil printer according to claim 11, wherein the first arm section comprises three prisms arranged to form a generally rectangular block structure, the second arm section comprises three prisms arranged to form a generally rectangular block structure, the connector section comprises two prisms arranged to form a cube, the cube being positioned between the first arm structure and the second arm structure to form a generally U-shaped prism structure.

14. The stencil printer according to claim 1, further comprising: a first printed circuit board configured to control the dual camera assembly; and a second printed circuit board configured to control the remaining components of the vision system.

15. The stencil printer according to claim 14, further comprising a third printed circuit board configured to control the illumination of the LEDs associated with the prism assembly.

16. The stencil printer according to claim 14, wherein the first printed circuit board and the second printed circuit board are separated from each other by a separation portion, and the first printed circuit board and the second printed circuit board are on the same plane when assembled and fixed within the housing.

17. The stencil printer according to claim 14, further comprising a fan module provided at one end of the housing for cooling the components of the vision system, wherein the components include the dual camera assembly, the prism assembly, the printed circuit board, and the second printed circuit board.

18. A vision system used in a stencil printer configured to print assembly materials onto an electronic circuit board, Housing and A dual camera assembly supported by the aforementioned housing, A prism assembly supported by the housing, configured together with the dual camera assembly to provide a first optical path that looks vertically upward at the bottom of the stencil and a second optical path that looks vertically downward at the electronic substrate, A vision system equipped with these features.

19. The aforementioned dual camera assembly is Bracket and A first lens and a second lens fixed to the bracket, the first lens and the second lens being spaced apart from each other and extending perpendicularly from the bracket, The vision system according to claim 18, comprising:

20. The aforementioned dual camera assembly is A first programmed camera configured to acquire an image of the stencil through the first optical path and the first lens, A second programmed camera configured to acquire an image of the electronic circuit board through the second optical path and the second lens, The vision system according to claim 19, further comprising the following:

Images