Dual-camera prism assembly for template printing machine

Abstract

A vision system for use in a stencil printer configured to print an assembly material on an electronic substrate. The vision system includes 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 viewed vertically upward at the bottom of the stencil and a second optical path viewed vertically downward on the electronic substrate.

Description

[0001] BACKGROUND OF THE DISCLOSURE 1. Field of the Invention The present application relates generally to electronic automation equipment used in the production and assembly of electronic circuit boards, and more particularly to stencil printers for depositing patterns of solder paste or other pasty materials onto electronic substrates.

[0002] 2. Discussion of Related Technologies When manufacturing surface mount printed circuit boards, a stencil printer can be used to print solder paste onto the board. Typically, a circuit board, having a pattern of pads or some other conductive surface onto which the solder paste is to be deposited, is automatically fed into the stencil printer. One or more small holes or markings (called "fiducials") on the board are used to properly align the board with the stencil or screen of the stencil printer before the solder paste is printed on the board. In some systems, an optical alignment system, embodying a vision system, is used to align the board with the stencil.

[0003] Once the circuit board has been properly aligned with the stencil in the printer, the board is raised onto the stencil, solder paste is dispensed onto the stencil, and a scraper blade (or squeegee) is moved across the stencil to force the solder paste through the holes in the stencil and onto the circuit board. As the squeegee moves across the stencil, the solder paste tends to roll in front of the blade, which advantageously causes mixing and shearing of the solder paste to achieve the desired viscosity for filling the holes in the screen or stencil. Solder paste is typically dispensed onto the stencil from a standard cartridge. The stencil is then separated from the circuit board, and the adhesion between the circuit board and the solder paste causes most of the material to remain on the circuit board. Before printing additional circuit boards, the remaining material on the stencil surface is removed in a cleaning process.

[0004] Another process in printed circuit boards involves inspecting the board after solder paste has been deposited on its surface. Inspecting the board is important to ensure that a clean electrical connection can be made. Excess solder paste can cause a short circuit, while too little solder paste in the appropriate locations can prevent electrical contact. Often, vision inspection systems are also employed to provide two-dimensional or three-dimensional inspection of the solder paste on the board.

[0005] One challenge facing the design of such stencil printers and dispensing systems is the ability to quickly and comprehensively inspect large substrate areas after applying solder paste in a single pass.

[0006] As is well known in the industry, vision systems (e.g., machine vision cameras) can be used to capture images of both the stencil and the substrate 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 utilized to selectively capture images of either the underside of the stencil or the top surface of the substrate. In such systems, the single camera can be configured to selectively view either of these objects. The selection of which image to capture can be influenced, for example, by energizing one of two illumination sources.

[0007] In other prior art vision systems, a single camera can use optics to image both the stencil and the substrate within a single, split field of view. This solution has the advantage of imaging both scenes simultaneously, but has the disadvantage of a reduced field of view.

[0008] Abstract One aspect of the present disclosure relates to a stencil printer for printing assembly material on an electronic substrate. In one embodiment, the stencil printer includes a frame, a stencil coupled to the frame, the stencil having an aperture formed therein, a support assembly coupled to the frame, the support assembly configured to support the electronic substrate in a printing position beneath the stencil, a printhead gantry coupled to the frame, a printhead assembly supported by the printhead gantry such that the printhead assembly is configured to traverse the stencil during a printing stroke, the printhead assembly including a printhead having a squeegee blade assembly configured to roll solder paste along the stencil, and a vision system configured to obtain an image of the stencil and the electronic substrate. The vision system includes 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 looking vertically upward at the bottom of the stencil and a second optical path looking vertically downward at the electronic substrate.

[0009] Embodiments of the stencil printer may further include configuring a dual-camera assembly to include a bracket and a first lens and a second lens secured to the bracket, wherein the first lens and the second lens are spaced apart from each other and extend perpendicularly from the bracket. The dual-camera assembly may further include a first programming camera and a second programming camera, the first programming camera being configured to obtain an image of the stencil via a first optical path passing through the first lens, and the second programming camera being configured to obtain an image of the electronic substrate via a second optical path passing through the second lens. The dual-camera assembly may further include two heat sinks, wherein the first heat sink is secured to the first programming camera via a first thermal pad, and the second heat sink is secured to the second programming camera via a second thermal pad. The prism assembly may include: a support having a base and a holder; and a prism structure positioned on the base and fixed in position relative to the base when the holder is fixed to the base, wherein the prism structure is configured to direct light along the first optical path to the template and to direct light along the second optical path to the electronic substrate, and to direct an image from the template along the first optical path to the first programming camera via the first lens, and to direct an image from the electronic substrate along the second optical path to the second programming camera via the second lens. The prism assembly also includes an optical window including a quarter wave plate fixed in position relative to the holder by a cover, wherein the optical window is placed above an opening formed in the cover through which the first optical path reaches the template. The base of the prism assembly may include an opening, The second optical path reaches the electronic substrate through the opening. The prism assembly may further include a double-sided LED board configured to generate light from one side of the LED board and from an opposite side of the LED board. The LED board may include a first illuminator having a matrix of LED lights disposed on one side of the LED board and a second illuminator having a matrix of lights disposed on an opposite side of the LED board. The prism assembly may further include a third illuminator comprising an LED ring light to provide off-axis illumination of the electronic substrate along the second optical path. The prism structure may include a first arm segment, a second arm segment, and a connecting segment. The first arm segment may include three prisms arranged to form a generally rectangular block structure, the second arm segment may include three prisms arranged to form a generally rectangular block structure, and the connecting segment may include two prisms arranged to form a cube disposed between the first and second arm structures to create a generally U-shaped prismatic structure. The stencil printer may further include 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. The stencil printer may further include a third printed circuit board configured to control the illumination of an LED associated with the prism assembly. The first and second printed circuit boards may be separated from each other by a spacer, and when assembled within and secured to the housing, the first and second printed circuit boards are coplanar relative to each other. The stencil printer may further include a fan module disposed at one end of the housing to cool 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 for use in a stencil printer configured to print assembly material on an electronic substrate. In one embodiment, the vision system includes 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 having a bracket and first and second lenses secured to the bracket, wherein the first and second lenses are spaced apart from each other and extend perpendicularly from the bracket. The dual-camera assembly may further include a first programming camera and a second programming camera, the first programming camera configured to obtain an image of the stencil via a first optical path through the first lens, and the second programming camera configured to obtain an image of the electronic substrate via a second optical path through the second lens. The dual-camera assembly may further include two heat sinks, wherein the first heat sink is secured to the first programming camera via a first thermal pad, and the second heat sink is secured to the second programming camera via a second thermal pad. The prism assembly may include a support having a base and a holder, and a prism structure positioned on the base and fixed in position relative to the base when the holder is secured to the base, wherein the prism structure is configured to direct light along the first optical path to the stencil and along the second optical path to the electronic substrate, and to direct an image from the stencil along the first optical path to the first programming camera via the first lens, and to direct an image from the electronic substrate along the second optical path to the second programming camera via the second lens. The prism assembly also includes an optical window comprising a quarter-wave plate secured in position relative to the holder by a cover, wherein the optical window is disposed above an opening formed in the cover, through which a first optical path passes to the stencil. The base of the prism assembly may include an opening, through which a second optical path passes to the electronic substrate. The prism assembly may also include a double-sided LED board configured to generate light from one side of the LED board and from an opposite side of the LED board. The LED board may include a first illuminator having a matrix of LED lights disposed on one side of the LED board and a second illuminator having a matrix of lights disposed on an opposite side of the LED board. The prism assembly may also include a third illuminator comprising an LED ring light to provide off-axis illumination to the electronic substrate along the second optical path. The prism structure may include a first arm segment, a second arm segment, and a connecting segment. The first arm segment may include three prisms arranged to form a block structure having a generally rectangular shape, wherein the second arm segment includes three prisms arranged to form a block structure having a generally rectangular shape, and the connecting segment includes two prisms arranged to form a cube disposed between the first arm structure and the second arm structure to produce a generally U-shaped prism structure. The vision system may further include 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. The vision system may further include a third printed circuit board configured to control illumination of an LED associated with the prism assembly. The first printed circuit board and the second printed circuit board may be separated from each other by a spacer, and when assembled within and secured to the housing, the first printed circuit board and the second printed circuit board are coplanar with respect to each other.The vision system may further include a fan module disposed at one end of the housing to cool components of the vision system, including the dual camera assembly, the prism assembly, the printed circuit board, and the second printed circuit board. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component shown in various figures is represented by a like numeral. For clarity, not every component may be labeled in every figure. In the drawings: Figure 1 It is a front view of the stencil printing press; Figure 2 It is a front perspective view of a stencil printing press; Figure 3 yes Figure 2 A plan view of the stencil printing press shown in , with some parts removed; Figure 4 is a top perspective view of a vision system of a stencil printer according to an embodiment of the present disclosure; Figure 5 It is a bottom stereogram of the visual system; Figure 6 is a top perspective view of a vision system with a cover removed to reveal components of the vision system; Figure 7 It is a side view of the visual system; Figure 8 It is an exploded stereogram of the visual system; Figure 9 is an exploded perspective view of the dual-camera assembly of the vision system; Figure 10 It is an exploded perspective view of the prism assembly of the vision system; Figure 11A and 11B This is a three-dimensional diagram of the LED board assembly; Figures 12A-12C is a perspective view showing the installation of an LED board assembly in a prism assembly; Figures 13A-13F is a view of the prism assembly with the enclosing structure removed; Figure 14A is a perspective view of a dual camera assembly of a vision system illustrating the optical path of illumination generated by the vision system and directed to a stencil and an electronic substrate; and Figure 14B is a perspective view of the dual camera assembly of the vision system, showing the optical paths for images from the stencil and electronic substrate. DETAILED DESCRIPTION

[0013] The present disclosure generally relates to material application machines (referred to herein as stencil printers, "screen printers," printers, or "printers") and other equipment used in surface mount technology (SMT) process lines and configured to apply assembly materials (e.g., solder paste, conductive ink, or encapsulation material) to substrates (e.g., printed circuit boards, referred to herein as electronic substrates, "circuit boards," "boards," "PCBs," PCB substrates, "substrates," or "PCB boards") or perform other operations, such as inspection, rework, or placement of electronic components on the substrates. Specifically, embodiments of the present disclosure are described below with reference to stencil printers used to produce printed circuit boards.

[0014] For purposes of illustration only, and not limitation, the present disclosure will now be described in detail with reference to the accompanying drawings. The present disclosure is not limited in its application to the details of construction and arrangement of components set forth in the following description or illustrated in the accompanying drawings. The principles set forth in the present disclosure are capable of other embodiments and can be practiced or carried out in various ways. Likewise, the phraseology and terminology used herein are for descriptive purposes and should not be construed as limiting. Any reference herein to examples, embodiments, components, elements, or actions of systems and methods in the singular may also encompass embodiments that include the plural, and any reference herein to multiple embodiments, components, elements, or actions may also encompass embodiments that include only the singular. References in the singular or plural are not intended to limit the presently disclosed systems or methods, their components, actions, or elements. As used herein, the words "include," "comprising," "having," "containing," "involving," and variations thereof are intended to encompass the items listed thereafter and equivalents thereof, as well as additional items. References to "or" should be interpreted as inclusive, such that any term described using "or" may refer to one, more than one, or all of the described terms. In addition, in the event of inconsistencies in the usage of terms between this document and documents incorporated herein by reference, the usage of the terms in the incorporated reference documents supplements the usage of the terms in this document; for irreconcilable inconsistencies, the usage of the terms in this document controls.

[0015] The present disclosure utilizes a specially configured prism assembly and two complete camera systems to facilitate simultaneous capture of the full field of view of both the stencil and the electronic substrate.The structure and function of the prism assembly will now be described in further detail.

[0016] For purposes of illustration, embodiments of the present disclosure will now be described with reference to a stencil printer for printing assembly materials, such as solder paste, onto circuit boards. 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 may be used in other applications where it is necessary to dispense other viscous assembly materials, such as glues and sealants. For example, the apparatus may be used to print epoxy for use as an underfill for chip scale packages. Furthermore, stencil printers according to embodiments of the present disclosure are not limited to those that print assembly materials onto circuit boards, but include those that are used to print other materials onto various substrates, such as semiconductor wafers. Furthermore, the terms "screen" and "stencil" are used interchangeably herein to describe a device in a printer that defines a pattern to be printed onto a substrate. In certain embodiments, the stencil printer may include a Momentum® or Edison™ series stencil printer platform offered by ITW Electronic Assembly Equipment of Hopeton, Massachusetts. Exemplary stencil printers are available in the Figure 1 Indicated generally at 5, in this embodiment, the stencil printer 5 is a Momentum® series stencil printer platform provided by ITW Electronics Assembly Equipment, Inc. of Hopeton, Massachusetts.

[0017] refer to Figure 2 , a stencil printer according to an embodiment of the present disclosure is shown generally at 10. As shown, the stencil printer 10 includes a frame 12 that supports 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, generally indicated at 20, that is configured to apply solder paste in a manner described in more detail below.

[0018] like Figure 2 As shown and described below, the stencil and printhead assembly can be suitably coupled or otherwise connected to the frame 12. In one embodiment, the printhead assembly 20 can be mounted on a printhead assembly mount 22, which can be mounted on the frame 12. The printhead assembly mount 22 enables the printhead assembly 20 to move in the y-axis direction under the control of the controller 14 and to apply pressure on the printhead assembly as it engages the stencil 18. In some embodiments, the printhead assembly 20 can be placed over the stencil 18 and can be lowered in the z-axis direction to contact and sealingly engage the stencil.

[0019] The stencil printer 10 may also include a conveyor system having a guide rail (not shown) for conveying printed circuit boards to a printing position in the stencil printer. The guide rail, which may sometimes be referred to herein as a "tractor feed mechanism," is configured to feed, load, or otherwise convey circuit boards to a working area of ​​the stencil printer, which may be referred to herein as a "printing nest," and unload circuit boards from the printing nest.

[0020] Additional references Figure 3 The stencil printer 10 includes a support assembly 28 for supporting a circuit board 29 (shown in phantom). The support assembly 28 elevates and secures the circuit board to stabilize it during the printing operation. In certain embodiments, the substrate support assembly 28 may also include a specific substrate support system, such as a solid support member, a plurality of pins, or a flexible tool that is positioned beneath the circuit board when the circuit board is in the printing position. The substrate support system may be used, in part, to support an interior region of the circuit board to prevent bending or warping of the circuit board during the printing operation.

[0021] In one embodiment, the print head assembly 20 can be configured to receive solder paste from a source such as a dispenser (e.g., a solder paste cartridge) that provides solder paste to the print head assembly during the printing operation. Other methods of supplying solder paste can be used in place of the solder paste cartridge. For example, solder paste can be manually deposited between the blades or from an external source. Additionally, in one embodiment, the controller 14 can be configured to use a personal computer with a suitable operating system, such as the Microsoft Windows® operating system provided by Microsoft Corporation, and specialized software for controlling the operation of the stencil printer 10. The controller 14 can be networked with a main controller for controlling a production line for manufacturing circuit boards.

[0022] In one configuration, the stencil printer 10 operates as follows. A circuit board 29 is loaded into the stencil printer 10 using a conveyor track. A support assembly 28 raises and secures the circuit board 29 into the printing position. The print head assembly 20 is then lowered in the z-axis direction until the print head assembly blades contact the stencil 18 with the desired pressure. The print head assembly 20 is then moved across the stencil 18 in the y-axis direction by the print head assembly stage 22. The print head assembly 20 deposits solder paste onto the circuit board 29 through the apertures in the stencil 18. Once the print head assembly has completely traversed the stencil 18 past the apertures, the print head assembly is raised off the stencil and the circuit board 29 is lowered back onto the conveyor track. The circuit board 29 is released from the stencil printer 10 and conveyed away, allowing a second circuit board to be loaded into the stencil printer. To print on the second circuit board 29, the print head assembly is lowered in the z-axis direction into contact with the stencil and moved across the stencil 18 in the opposite direction to that used for the first circuit board.

[0023] A vision system 30 may be provided for aligning the stencil 18 with the circuit board 29 before printing and inspecting the circuit board after printing. In one embodiment, the vision system 30 may be positioned between the stencil 18 and the support assembly 28 on which the circuit board is supported. The vision system 30 is coupled to a vision system gantry 32 for movement. In one embodiment, the vision system gantry 32 may be coupled to the frame 12 and include a beam extending between the side rails of the frame 12 to provide for traversal of the imaging system 30 in the y-axis direction over the circuit board 29. The vision system gantry 32 may also include a carriage device that houses the vision system 30 and is configured to move along the length of the beam in the x-axis direction. The configuration of the imaging gantry 32 for moving the vision system 30 is well known in the solder paste printing art. This arrangement allows the vision system 30 to be positioned anywhere below the stencil 18 and above the circuit board 29 to capture images of predefined areas of the circuit board or stencil, respectively. In other embodiments, when the imaging system is positioned outside of the printing position, the imaging system may be positioned above or below the stencil and circuit board.

[0024] This arrangement allows the vision system 30 to be positioned anywhere along the scan axis below the stencil 18 and above the circuit board 29 to determine the topology of a predefined area of ​​the circuit board or stencil, respectively. In other embodiments, the vision system 30 can be positioned above or below the stencil 18 and circuit board 29 when the vision system 30 is positioned outside the print nest.

[0025] After one or more applications of solder paste to a circuit board, excess solder paste may accumulate at the bottom of stencil 18, and a stencil wiper assembly (generally indicated at 34) may be moved under the stencil to remove the excess solder paste. In other embodiments, stencil 18 may be moved over the stencil wiper assembly.

[0026] Embodiments of the present disclosure relate to an improved vision system capable of providing two full fields of view for two cameras, respectively. In one embodiment, one camera is provided to look upward at a template, and another camera is provided to look downward at an electronic substrate. The vision system includes a prism assembly that provides two collinear optical paths at the look-up / look-down viewpoints. Specifically, the prism assembly refracts the two optical paths so that they are parallel at the lens / camera exit surface. In certain embodiments, the prism assembly provides a path for on-axis illumination, as many metal surfaces to be imaged are mirror-like in nature.

[0027] refer to Figures 4 to 8 , and more specifically with reference to Figure 6 and Figure 8, a vision system of a preferred embodiment of the present disclosure is generally indicated at 40. Vision system 40 includes several major components, including a dual camera assembly, generally indicated at 42, and a prism assembly, generally indicated at 44. Vision system 40 includes a housing 46 configured to support the components of the vision system, including dual camera assembly 42 and prism assembly 44. A housing cover 48 is provided to surround the top of housing 46 and protect the components of vision system 40 supported by the housing, including dual camera assembly 42 and prism assembly 44. Dual camera assembly 42 and prism assembly 44 are configured to operate relative to each other to provide a first optical path looking vertically upward at the bottom of the reticle (e.g., reticle 18), and a second optical path looking vertically downward at the electronic substrate (e.g., circuit board 29).

[0028] The vision system 40 also includes a first printed circuit board 50, which is configured to provide control for the dual-camera assembly 42, and a second printed circuit board 52, which is configured to provide control for the remaining components of the vision system. A third printed circuit board, described in greater detail below, controls the illumination of LEDs associated with the prism assembly 44. The first and second printed circuit boards 50, 52 are separated from each other by a plurality of spacers, each indicated at 54, and are coplanar relative to each other when assembled within and secured to the housing 46 of the vision system 40. The vision system 40 also includes a fan module 56, which is disposed at one end of the housing 46 to cool the components of the vision system. The fan module 56 is configured to move air within the housing 46 to cool the components supported by the housing, including, but not limited to, the dual-camera assembly 42, the prism assembly 44, and the first and second printed circuit boards 50, 52.

[0029] The housing 46 of the vision system 40 further supports components of the hard stop assembly. For example, the housing 46 can be configured to support an actuator 58, a clamp 60, a sensor 62, and a flag 64. The hard stop assembly is configured to stop the movement of the electronic substrate when the electronic substrate is loaded into the stencil printer. As shown, the housing 46 is configured to support the actuator 58 on one side of the housing with a pair of screw fasteners. The sensor 62 is supported by the housing 46 in a position next to the actuator 58 and the prism assembly 44. The sensor 60 and the prism assembly 44 are also secured to the housing 46 by screw fasteners. The sensor 62 mentioned above is part of the hard stop assembly and can be actuated to a lower position to engage the edge of the electronic substrate, or actuated to a retracted upper position. The sensor 62 ensures that the pneumatically actuated hard stop is positioned as commanded.

[0030] The dual camera assembly 42 is secured to the housing 46 adjacent to the prism assembly 44, with the first camera being directed to one side of the prism assembly 44 and the second camera being directed to the opposite side of the prism assembly. The third circuit board mentioned above is disposed between the gaps provided in the prism assembly 44 and provides LED illumination for the prism assembly. The first and second printed circuit boards 50, 52 are secured to the housing 46 adjacent to the dual camera assembly 42 via screw fasteners secured to the spacers 54. As described above, the fan module 56 of the vision system 40 is disposed at the end of the housing 46 and is configured to move air through the housing, specifically the first and second circuit boards 50, 52, the dual camera assembly 42, and the prism assembly 44, respectively.

[0031] The vision system 40 also includes a focus adjustment screw 66 ( Figure 7 ) and two springs, each with 68 ( Figure 5 ) instructions to maintain light force on the focus adjustment screw to keep the dual camera assembly 42 as linear as possible when adjusting the focus during calibration and setup.

[0032] refer to Figure 9 The dual-camera assembly 42 includes a bracket 70 configured to support the components of the dual-camera assembly. Bracket 70 is a rectangular structure configured to hold a first lens 72 and a second lens 74 spaced apart from each other and extending perpendicularly from the bracket. In the illustrated embodiment, the first lens 72 is configured to look upward at the stencil, and the second lens is configured to look downward at the electronic substrate. One of the lenses (e.g., the first lens 72) includes a lens hood 76 secured to the second lens via a clamp 78. The purpose of lens hood 76 is to prevent stray light from entering the camera, thereby preserving the integrity of the image from the stencil. Although not shown, the second lens 74 can be configured to include a lens hood similar to lens hood 76, which can be secured to the second lens via another clamp similar to clamp 78. In a preferred embodiment, both the first lens 72 and the second lens 74 include lens hoods, such as lens hood 76, to prevent stray light from entering their respective cameras.

[0033] In some embodiments, two identical lenses 72, 74 are used. In one embodiment, each of the first lens 72 and the second lens 74 is manufactured by VST under model # MC075-50. Each of the first lens 72 and the second lens 74 has a magnification of 0.75.

[0034] The dual camera assembly 42 also includes a first programming camera 80 and a second programming camera 82, the first programming camera 80 being configured to obtain an image of the stencil via a first optical path through the first lens, and the second programming camera 82 being configured to obtain an image of the electronic substrate via a second optical path through the second lens 74. This arrangement enables the dual camera assembly 42 to obtain simultaneous images of the stencil via the first programming camera 80 and the first lens 72, and images of the electronic substrate via the second programming camera 82 and the second lens 74. The dual camera assembly 42 also includes two heat sinks 84 and 86, wherein the first heat sink 84 is secured to the first programming camera 80 via a first thermal pad 88, and the second heat sink 86 is secured to the second programming camera 82 via a second thermal pad 90. The first heat sink 88 and the second heat sink 90 are provided to cool the first programming camera 80 and the second programming camera 82, respectively.

[0035] In some embodiments, two identical programming cameras 80 , 82 are used. In one embodiment, programming cameras 80 , 82 are manufactured by Teledyne FLIR under model # BFS-GE-50S5M-BD2, and each includes a monochrome sensor manufactured by Sony under model # IMX264. In certain embodiments, each programming camera 80 , 82 has a resolution of 2464 (H) x 2056 (V), approximately 5.07 M pixels. The pixel size at the image sensor is 3.45 μm x 3.45 μm. In certain embodiments, programming cameras 80 , 82 are connected via Gigabit Ethernet, and a three-port broadband communication GbE-Net switch may be provided as part of vision system 40 .

[0036] refer to Figure 10 The prism assembly 44 includes a support member having a base 92 and a retainer 94 configured to be secured together to hold the components of the prism assembly. The components of the prism assembly 44 are supported on the base 92 and protected by the retainer 94 once assembled. The prism assembly 44 also includes a prism structure, generally indicated at 96, which is positioned on the base 92 and is fixed in position relative to the base when the retainer 94 is secured to the base. The prism structure 96 is configured to direct light along a first optical path to the stencil and along a second optical path to the electronic substrate, sometimes referred to as the object. The prism structure 96 is also configured to direct an image from the stencil along the first optical path to the first programming camera 80 via the first lens 72, and to direct an image from the electronic substrate along the second optical path to the second programming camera 82 via the second lens 74. As described above, the first lens 72 includes a lens shield 76 to prevent stray light from impairing the imaging of the stencil and being directed to the image of the first programming camera 80. As described above, the second lens 74 may also be configured with a lens cover.

[0037] Prism assembly 44 also includes two self-adhesive foam pads, each indicated at 98, configured to engage prism structure 96 when holder 94 is secured to base 92. Holder 94 of prism assembly 44 also includes an optical window 100, within which a quarter-wave plate is embedded. The quarter-wave plate is secured in position relative to holder 94 by a cover 102, with the optical window positioned over an opening 104 formed in the holder. In one embodiment, the quarter-wave plate is a thin film. Therefore, for installation and handling purposes, the quarter-wave plate is laminated between two thin glass layers to form a window assembly that can be handled and installed as a single, integral piece. Window 100 may be referred to as a quarter-wave plate assembly. The orientation of the quarter-wave plate is critical to its function to a certain extent. Alignment between the quarter-wave plate and the edge of the glass window ensures proper positioning of the quarter-wave plate. Furthermore, while this embodiment describes one such window within the stencil-side optical path, the same window with a *4 waveplate can be utilized on the substrate-side optical path to enhance the contrast of any specular features that may be present on the electronic substrate (e.g., exposed copper pads on the electronic substrate).

[0038] The cover 102 includes an opening 106 that aligns with the opening 104 of the holder 94 to allow light to pass from the prism assembly 44 to the stencil. An optical window 100 is provided for a first optical path to the stencil. The cover 102 is secured to the holder 94 by screw fasteners and may include a gasket 108 to position and seal the optical window 100 in place.

[0039] The base 92 of the prism assembly 44 includes an opening 110 through which the second optical path passes to the electronic substrate. The opening 110 of the base 92 does not require an optical filter; however, if an optical filter is required, the base can support an optical window similar to the optical window 100, the cover 102, and the gasket 108 used on the holder 94.

[0040] Prism assembly 44 also includes two stacked polarizers, indicated at 112A, 112B, on a diffuser structure, which is mounted with the polarizers facing the prism structure 96. The purpose of diffuser structures 112A, 112B is to help ensure that the light generated by the illuminator LED matrices 116, 118 is spatially uniform. By scattering the light as it passes through the diffusers, the structure of the light, particularly the brighter areas where the LEDs are located and the thin dark bands between individual LEDs, is averaged out to ensure more uniform illumination across the entrance face of the prism (e.g., surfaces 152, 154 described below). The polarizers stacked onto diffusers 112A, 112B ensure that only S-plane polarized light enters the prism, as only S-plane polarized light will be directed onto the optical axis by polarizing surfaces within the prism (e.g., surfaces 136, 150 described below). Consequently, any P-plane polarized light from the illuminator is undesirable and is therefore blocked by the polarizers.

[0041] refer to Figure 11A and Figure 11B The prism assembly 44 also includes a double-sided LED board 114 that is configured 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 an opposite side of the LED board. Specifically, a first matrix of LED lights 116 is disposed on one side of the LED board 114, and a second matrix of lights 118 is disposed on an opposite side of the LED board. In one embodiment, the LED board 114 can be configured to generate light from one side of the LED board and from an opposite side of the LED board. Figure 12A The double-sided LED board 114 is assembled by placing two separate LED boards back to back with each other in the manner shown.

[0042] In some embodiments, each matrix of LED lights 116, 118 is composed of 81 Cree XD 16 LEDs arranged in a 9x9 array. Each set of 81 LEDs is electrically connected as three parallel strings of 27 LEDs. The matrix of LED lights 116, 118 that provides coaxial illumination for the stencil and electronic substrate includes 3000K white LEDs.

[0043] In one embodiment, the prism assembly 44 further includes a third illuminator comprising an LED ring light 120 to provide off-axis illumination LEDs to the electronic substrate along the second optical path. Figure 5 As shown in FIG, LED ring light 120 (sometimes called an off-axis light source) consists of 32 LEDs arranged in a ring, with eight LEDs along each side of a square. Electrically, the LEDs of LED ring light 120 are connected as a single string of 32 LEDs. The LED ring light that provides the off-axis light includes red LEDs.

[0044] In some embodiments, the driver circuitry for the LED lights can be located on the LED board 114. The driver circuitry for the LED ring light 120 can be located on the interconnect board. In one embodiment, the first programming camera 80 and the second programming camera 82 each provide three general-purpose input / output (GPIO) signals. The first programming camera 80, used to view the stencil, provides one output signal as a gate select (on-axis) and a second output signal as TRIGGER_ENABLE. The second programming camera 82, used to view the electronic substrate, provides two output signals as gate selects (on-axis and off-axis, respectively). The actual TRIGGER signal is created by ANDing TRIGGER_ENABLE with a motion control output called XY_IN_POS. If no immediate triggering is performed, the XY_IN_POS signal should be asserted to allow TRIGGER_ENABLE to reach the TRIGGER. The TRIGGER signal is fed back to both the first programming camera 80 and the second programming camera 82 via a third GPIO signal configured as an input to the programming cameras. This configuration allows for simultaneous triggering of both the first programming camera 80 and the second programming camera 82.

[0045] In some embodiments, the gating of three different illuminators, ie, the two matrices of LED lights 116, 118 of LED board 114 and one LED ring light 120, are independent of each other, and the active lighting can be controlled by varying the duration of the respective gating.

[0046] In some embodiments, the LEDs in LED board 114 and LED ring light 120 are controlled to operate at 1 ampere (A). This current level is significantly higher than the continuous current rating. Therefore, the gating duration should be limited to prevent overheating of the LEDs. In one embodiment, the gating duration can be less than 100 microseconds (ps), typically 30-50 μs.

[0047] like 12A to 12C As shown, the LED board 114 is mounted within the prismatic structure 96 of the prism assembly 44 by inserting the LED board into the gap or space provided in the prismatic structure. Figure 12A As shown, two separate LED boards are positioned back-to-back with a first matrix of LED lights 116 pointing in one direction and a second matrix of LED lights 118 pointing in the opposite direction. Figure 12B The LED board 114 is shown prior to being inserted into the gap formed in the prismatic structure 96 of the prism assembly 44 . Figure 12C The LED board 114 is shown mounted within the prismatic structure 96 of the prism assembly 44 .

[0048] refer to 13A to 13FThe prism structure 96 of the prism assembly 44 in the illustrated embodiment is generally U-shaped in construction and comprises several conjugate prisms affixed to one another to achieve the desired U-shaped prism structure shown. As is known in optics, a prism is a transparent optical element having a flat, polished surface designed to refract light. In the illustrated embodiment, several triangular prisms are used. The prisms can be made of optical glass or some other suitable material that is transparent to the wavelength for which the prisms are designed. Other materials can include acrylic and fluorite.

[0049] Prism structure 96 can be broken down into three sections: a first arm section 122, a second arm section 124, and a connecting section 12. The first arm section 122 includes three prisms 128, 130, and 132 arranged to form a generally rectangular block structure. Reinforced aluminum is provided on inner surface 134. A polarizing, S-plane reflecting, P-plane transmitting material is provided on inner surface 136. A broadband visible antireflection (AR) coating is applied to surfaces 138 and 140. Similarly, the second arm section 124 includes three prisms 142, 144, and 146 arranged to form a generally rectangular block structure. Second arm section 124 is a mirror image of first arm section 122, with reinforced aluminum provided on inner surface 148. A polarizing, S-plane reflecting, P-plane transmitting material is provided on inner surface 150. A broadband visible AR coating is applied to surfaces 152 and 154. The connector or middle section 126 includes two prisms 156, 158 arranged to form a cube. Reinforced aluminum is provided on the inner surface 160. A broadband visible AR coating is used on surfaces 162, 164. In addition, a broadband visible AR coating can be used on the inward facing surfaces 166, 168 of the first arm section 122 and the second arm section 124, respectively. And finally, black paint is used on surface 170 and many other non-optical surfaces. It should be noted that Figure 13A The small triangular prisms 132, 146 in the embodiment may not be light activated. If these small prisms were not present, the prismatic structure 44 would be difficult to assemble and fix. Therefore, some smaller triangular prisms are added for mechanical reasons rather than optical reasons.

[0050] The presence of polarizers mounted to the output face of the diffuser and the polarizing surface within the prism structure 44 work in conjunction with each other to redirect light from the illuminator onto the primary optical centerline path. Without the use of a quarter-wave plate, light reflected back from the stencil would still be largely S-plane polarized and, therefore, upon encountering the polarizing surface with the prism, would be reflected back toward the illuminator rather than passing toward the camera. Therefore, the quarter-wave plate is provided as part of the beam-steering function of the prism assembly. On the substrate side, since non-specular surfaces do not preserve the polarization structure of light, the quarter-wave plate is less critical. Light returning from the substrate-side image is a combination of S- and P-plane polarized light. The P-plane portion passes through the polarizing surface toward the camera and lens. The S-plane portion of light is reflected back toward the illuminator and lost. As mentioned above, a quarter-wave plate window can also be incorporated into the stencil-side optical path to help increase the contrast of any specular features that may be present in the substrate scene.

[0051] Embodiments of the prismatic structure 96 of the prism assembly 44 may include providing a 1 / 4 wave flatness on all optical surfaces of the prismatic structure, with all optical surfaces finished to 40-20 scratches / pits (S / D), all linear dimensions ±0.10 mm, and all angles of arc ±3 minutes of arc (0°03').

[0052] In some embodiments, the effective pixel size at 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).

[0053] The illumination is slightly reduced 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.

[0054] As described above, the first optical path provided to the reticle has only on-axis illumination, as the surface of the reticle is substantially specular in nature.However, the second optical path for the electronic substrate includes both on-axis and off-axis illumination.

[0055] refer to Figure 14A As described above, the prism structure 96 of the prism assembly 44 allows simultaneous illumination from the LED board 114 along the first optical path (at Figure 14A A) and a second optical path (designated as A in Figure 14A Designated as B) is directed to the stencil and electronic substrate. Figure 14B , the images are to be taken along the first optical path (in Figure 14B C in the figure) and a second optical path (in the Figure 14B The light (designated D in FIG) is reflected back to the first programming camera 80 and the second programming camera 82. The configuration of the prismatic structure 96 may vary depending on its intended use.

[0056] The first and second optical pathways are substantially collinear. Each optical pathway is refracted 90° at a common internal aluminized surface 160, which is oriented at a 45° angle relative to the optical pathways and emerges as two horizontally opposed pathways. The two horizontal pathways are each refracted 90° at aluminized surfaces 134, 148 and emerge along parallel paths. In a preferred embodiment, the two optical pathways are separated by 32 millimeters (mm).

[0057] As described above, the vision system 40 includes a double-sided LED board 114 positioned within a U-shaped gap in the prism structure 96 of the prism assembly 44 to provide illumination for the vision system. A first matrix of LED lights 116 of the LED board 114 and a second matrix of LED lights 118 of the LED board direct light into a first optical path and a second optical path, respectively. The prism structure 96 of the prism assembly 44 includes a polarizer film bonded to the exit faces of the diffusers 112A, 112B to limit light entering the prism assembly to S-plane polarization. The interior surface within each arm portion 122, 124 of the prism structure 96 is coated with a dielectric layer that is fabricated to preferentially reflect S-plane polarized light. Because these internal facets are oriented at 45° to the optical axis, S-plane polarized light is directed on-axis along each of the two optical paths.

[0058] After each optical path passes through two refractive mirrors, the illumination light passes through a 1 / 4 retardation film embedded in the window and installed adjacent to the prism structure 96, and emerges as circularly polarized light directed to the object surface. Although not shown, a substrate-side 1 / 4 wave plate may be provided.

[0059] Light reflected from the illuminated object surface is reflected back into prismatic structure 96. Light reflected from the mirror surface retains circular polarization. After passing through the quarter-wave retarder film a second time, the light enters prismatic structure 96 as P-plane polarized light. In this embodiment, the substrate-side optical path is not equipped with a quarter-wave plate window, as most electronic substrates are not particularly mirror-like. However, since some substrate features (such as bond pads) can themselves be mirror-like, a substrate-side quarter-wave plate window can also be included, and its presence can enhance the contrast of such mirror-like features.

[0060] As light passes through the internal polarizing surface, the P plane is transmitted through the prismatic structure 96 and exits the prismatic structure 96 toward the imaging lenses 72, 74. Any light that is not P plane polarized (ie, S plane polarized) will be reflected away from the optical axis at the internal surface.

[0061] 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.

[0062] In some embodiments, the illumination produced by LED board 114 is managed to maximize the signal-to-noise ratio between the valuable structured light and any unwanted or non-image light.

[0063] In some embodiments, prism structure 96 of assembly 44 is designed to manage the illumination and image paths for a dual-camera system in an automated stencil printer. The two optical paths are collinear and 180° opposite on the object side and parallel on the image side. In one embodiment, prism structure 96 of prism assembly 44 has a width of 48 mm, a length of 35 mm, and a height of 16 mm.

[0064] As described above, the purpose of the prism assembly 44 of the vision system 40 is multifaceted. The prism assembly 44 provides two full fields of view for two cameras, namely, the first programming camera 80 and the second programming camera 82, one looking upward at the stencil and the other looking downward at the electronic substrate. In addition, the prism assembly 44 provides two optical paths that are collinear at the look-up / look-down points.

[0065] In some embodiments, the two optical paths are refracted to be parallel at the lens / camera exit surface.

[0066] In some embodiments, prism assembly 44 of vision system 40 is configured to provide an illumination path for on-axis illumination, as many metal surfaces to be imaged are specular in nature.

[0067] 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 the structured light and any unwanted or non-image light.

[0068] In operation, vision system 40 is configured to look vertically "up" along a first optical path at the bottom of the stencil, and simultaneously look vertically "down" along a second optical path at the electronic substrate. In some embodiments, illumination is generated by a double-sided LED board 114 positioned within a U-shaped gap in prism structure 96 of prism assembly 44. A first facet of LED board 114, such as matrix 116, directs light through diffuser polarizer 112A into the first optical path, while a second facet of LED board 114, such as matrix 118, directs light through diffuser / polarizer 112B into the second optical path. A polarizing film is bonded to the diffuser output facet, thereby confining the light to S-plane polarization. The interior surface within each arm portion 122, 124 of prism structure 96 is coated with a dielectric layer fabricated to preferentially reflect S-plane polarized light. Because these interior facets are oriented at 45° to the optical axis, S-plane polarized light is directed on-axis along each of the two optical paths. After passing through two fold mirrors, the illumination light passes through a quarter-wave retarder film stacked within the window and mounted adjacent to the prism, emerging as circularly polarized light directed toward the object surface. Light reflected from the illuminated object surface is reflected back by the quarter-wave plate and returned to the prismatic structure 96. Light reflected from the mirror surface retains its circular polarization. After a second pass through the quarter-wave retarder film, the light enters the prismatic structure 96 as P-plane polarized light. As the light passes through the internal polarizing surface, it is transmitted through the P plane and exits the prismatic structure 96 toward the imaging lenses 72, 74. Any light that is not P-plane polarized (i.e., S-plane polarized) will be reflected away from the optical axis by the internal surface.

[0069] Various controllers, such as controller 14, can perform the various operations discussed above. Using data stored in associated memory and / or storage devices, controller 14 also executes one or more instructions stored on one or more non-transitory computer-readable media, which the controller may include and / or be coupled to, and which may generate manipulation data. In some examples, controller 14 may include one or more processors or other types of controllers. In one example, controller 14 is or includes at least one processor. In another example, in addition to or in place of a general-purpose processor, controller 14 uses an application-specific integrated circuit (ASIC) to perform at least a portion of the operations discussed above, the ASIC being customized to perform the specific operations. As these examples illustrate, many specific combinations of hardware and software may be used to perform the operations described herein according to examples of the present disclosure, and the present disclosure is not limited to any specific combination of hardware and software components. Examples of the present disclosure may include a computer program product configured to perform the methods, processes, and / or operations discussed above. A computer program product may be or include one or more controllers and / or processors configured to execute instructions to perform the methods, processes, and / or operations discussed above.

[0070] The disclosed systems and methods relate to capturing images of topographical features of stencils and electronic substrates.The description of the systems and methods provided herein refers to an exemplary electronic substrate (eg, a printed circuit board) supported on a support assembly of a stencil printer.

[0071] Having thus described several aspects of at least one embodiment, it should be understood that various changes, modifications, and improvements will readily occur to those skilled in the art. Such changes, modifications, and improvements are intended to be part of this disclosure and are intended to fall within the scope of this disclosure. Therefore, the foregoing description and accompanying drawings are intended to be examples only.

[0072] What is claimed is.

Claims

1. A stencil printer for printing assembly materials on an electronic substrate, the stencil printer comprising: frame; a stencil coupled to the frame, the stencil having an aperture formed therein; a support assembly coupled to the frame, the support assembly being configured to support the electronic substrate in a printing position beneath the stencil; a print head gantry coupled to the frame; a printhead assembly supported by the printhead gantry such that the printhead assembly is configured to traverse the stencil during a printing stroke, the printhead assembly comprising a printhead having a squeegee assembly configured to roll solder paste along the stencil; as well as A vision system configured to obtain images of the stencil and the electronic substrate, the vision system comprising: case, a dual camera assembly supported by the housing, and A prism assembly is supported by the housing and configured with the dual camera assembly to provide a first optical path looking vertically upward at the bottom of the stencil and a second optical path looking vertically downward at the electronic substrate.

2. The stencil printing machine according to claim 1, wherein The dual-camera assembly includes: brackets, and A first lens and a second lens are fixed to the bracket, the first lens and the second lens are spaced apart from each other and extend perpendicularly from the bracket.

3. The stencil printing machine according to claim 2, wherein: The dual-camera assembly further includes: a first programming camera configured to obtain an image of the stencil through the first lens via the first optical path, and A second programming camera is configured to obtain an image of the electronic substrate through the second lens via the second optical path.

4. The stencil printing machine according to claim 3, wherein: The dual camera assembly further includes two heat sinks, a first heat sink secured to the first programming camera via a first thermal pad, and a second heat sink secured to the second programming camera via a second thermal pad.

5. The stencil printing machine according to claim 3, wherein: The prism assembly comprises: a support having a base and a retainer, and a prismatic structure positioned on the base and fixed in position relative to the base when the holder is secured to the base, the prismatic structure configured to direct light along the first optical path to the stencil and along the second optical path to the electronic substrate, and to direct an image from the stencil along the first optical path to the first programming camera via the first lens, and to direct an image from the electronic substrate along the second optical path to the second programming camera via the second lens.

6. The stencil printing machine according to claim 5, wherein: The prism assembly also includes an optical window comprising a quarter wave plate secured in position relative to the holder by a cover, wherein the optical window is positioned over an opening formed in the cover through which the first optical path passes to the stencil.

7. The stencil printing machine according to claim 6, wherein: The base of the prism assembly includes an opening through which the second optical path travels to the electronic substrate.

8. The stencil printing machine according to claim 5, wherein: The prism assembly also includes a double-sided LED board configured to generate light from one side of the LED board and from an opposite side of the LED board.

9. The stencil printing machine according to claim 8, wherein: The LED board includes a first luminaire having a matrix of LED lights disposed on one side of the LED board and a second luminaire having a matrix of lights disposed on an opposite side of the LED board.

10. The stencil printing machine according to claim 9, wherein: The prism assembly further includes a third illuminator comprising an LED ring light to provide off-axis illumination to the electronic substrate along the second optical path.

11. The stencil printing machine according to claim 5, wherein: The prism structure includes a first arm segment, a second arm segment and a connecting segment.

12. The stencil printing machine according to claim 11, wherein The prismatic structure further comprises two stacked polarizers on a diffuser structure, the diffuser structure being mounted with the polarizers facing the prismatic structure.

13. The stencil printing machine according to claim 11, wherein The first arm segment includes three prisms arranged to form a block structure having a generally rectangular shape, the second arm segment includes three prisms arranged to form a block structure having a generally rectangular shape, and the connecting segment includes two prisms arranged to form a cube, the cube being disposed between the first arm structure and the second arm structure to form a generally U-shaped prismatic structure.

14. The stencil printer of 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 remaining components of the vision system.

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

16. The stencil printing machine according to claim 14, wherein The first and second printed circuit boards are separated from each other by a spacer and are coplanar with respect to each other when assembled within and secured to the housing.

17. The stencil printer of claim 14, further comprising a fan module disposed at one end of the housing to cool the components of the vision system, including the dual-camera assembly, the prism assembly, the printed circuit board, and the second printed circuit board.

18. A vision system for use in a stencil printer configured to print assembly material on an electronic substrate, the vision system comprising: case; a dual-camera assembly, the dual-camera assembly being supported by the housing; as well as A prism assembly is supported by the housing and configured with the dual camera assembly to provide a first optical path looking vertically upward at the bottom of the stencil and a second optical path looking vertically downward at the electronic substrate.

19. The visual system according to claim 18, wherein: The dual-camera assembly includes: brackets, and A first lens and a second lens are fixed to the bracket, the first lens and the second lens are spaced apart from each other and extend perpendicularly from the bracket.

20. The visual system of claim 19, wherein: The dual-camera assembly further includes: a first programming camera configured to obtain an image of the stencil through the first lens via the first optical path, and A second programming camera is configured to obtain an image of the electronic substrate through the second lens via the second optical path.

Images