Exposure system and method of exposing printing plate

Abstract

This invention discloses a photochemical radiation source for curing printed circuit boards. The source includes a base having a heat sink and a length greater than its width. A plurality of light-emitting diodes (LEDs) are provided along the length of the base via one or more circuit boards mounted on the base. A transparent or translucent cover, together with the base, defines an enclosure for the plurality of LEDs. The source provides radiation at an emission angle greater than the emission angle of a single LED in a plane perpendicular to the axis of the base, in the axis containing the base, or in a plane parallel to the axis of the base and perpendicular to a target illumination plane, or a combination thereof. The source can be configured to replace a fluorescent lamp. Methods and systems for using such sources for exposure of printed circuit boards are also described.

Description

[Previous Technology]

[0001] Fluorescent tubes have been used in the field of photopolymer curing for decades. In most embodiments, approximately 10 to 30 of these tubes are arranged close together in a plane adjacent to and parallel to the photopolymer plate to create a light source covering the entire photopolymer plate. Such systems are commonly referred to as "bank light systems" or "flood" systems. For example, a common standard system is the DuPont ECDFL 1000 system. For example, a common fluorescent tube used for this purpose is the Philips TL 80W / 10-R SLV / 25. An exemplary diagram of this prior art fluorescent tube is depicted in FIG. 8. As is known in the art, the exemplary fluorescent tube has opposing end caps 810 (which are typically metal), two pin connectors 812 extending from each end cap, and a light-emitting portion 814 between the end caps. These tubes may be characterized by having a uniform diameter D, a length A between opposing end caps 810, and a length C between the ends of the prongs 812 extending from the end caps, wherein each prong has a length (C to B). The exemplary published dimensions of the TL 80W / 10-R SLV / 25 type tube are shown in Table 1 below: Table 1 D (maximum) A (maximum) B (largest) B (smallest) C (maximum) 40.5 mm 1500 mm 1507.1 mm 1504.7 mm 1514.2 mm

[0002] The aforementioned dimensions are merely one example, and various tube manufacturers and lighting systems may use tubes of different sizes. The spacing between the pins and the geometry of the pins may also have a predetermined dimension (not shown).

[0003] Lighting systems with fluorescent tubes have the following disadvantages: ● Higher power consumption compared to LEDs; ● Frequent short-term output drift after the lights are turned on; ● To avoid output drift, the tubes are usually operated in standby mode, which consumes additional energy; ● Inconsistent light output throughout the bulb's lifespan; ● UV output may decrease after 500 and 1000 hours, making the curing results unacceptable; Frequent tube replacements increase costs; Mercury content in the tubes poses environmental concerns.

[0004] LEDs offer advantages over fluorescent tubes, including (but not limited to) lower power consumption, slower aging, more stable UV output across the entire temperature range, and no warm-up phase. While the UV output of an LED also decays over its entire lifespan, the lifespan of an LED is approximately an order of magnitude longer than that of a fluorescent tube. Once turned on, LED output is more stable. Therefore, to reap these benefits, almost all system manufacturers in the flexible printing industry have introduced their own commercial UV LED exposure systems using LEDs. These commercial systems are typically based on the relative movement between the photopolymer plate and the light source. Typically, LEDs are configured in a row extending along one dimension of the plate, while other dimensions are exposed by the relative movement between the light source and the plate. A large portion of the cost of these systems is related to the mechanics required to generate the relative movement between the plate and the UV source. Further costs arise from the need to cool LEDs concentrated in a relatively small area. The complex driving electronics required to balance and control the UV output of the LEDs introduce even more costs.

[0005] As UV LEDs become increasingly cheaper, it is now more economical to use UV LEDs in an array having a length and width that are at least as large as the size of the printed circuit board to be exposed, for example, as described in PCT Patent Application No. WO2017072588A1 filed by a co-applicant on May 4, 2017.

[0006] Although this art (e.g., as described in U.S. Patent No. 7,507,001, which is incorporated herein by reference) has described the direct replacement of fluorescent tubes with tubes containing LEDs in the visible light range for lighting purposes, there is now increasing interest in incorporating UV LEDs into photopolymer curing applications, given the advantages of LEDs and their cost reduction. [Summary of the Invention]

[0007] One embodiment of the present invention includes a radiation source for curing a photopolymer printed circuit board using photochemical radiation. The source includes a base comprising a heat sink and having a width and a length along an axis, wherein the length is greater than the width. One or more circuit boards are mounted on the base, the circuit boards collectively having a plurality of light-emitting diodes (LEDs) distributed above the length of the base, each LED configured to emit photochemical radiation at an emission angle in a direction toward a target illumination plane. A cover, transparent or translucent to the photochemical radiation and mounted on the base, together with the base, defines an enclosure for the plurality of LEDs. The source can be configured to provide the photochemical radiation at an emission angle greater than that of a single LED in a first plane perpendicular to the axis of the base, in a second plane containing the axis of the base or parallel to the axis of the base and perpendicular to the target illumination plane, or a combination thereof. In one embodiment, the cover may include one or more prisms and / or refractive structures (such as in the form of Fresnel lenses). The source may be configured to replace a fluorescent bulb having a specified length and a set of electrical connectors configured to be mounted in their respective sockets at opposite ends. The source may include control electronics for controlling the output of the plurality of LEDs disposed in the source, such as (but not limited to) a remote control receiver connected to and configured to receive signals for operating the control electronics.

[0008] In one embodiment, the base may include a plurality of surfaces arranged at an angle relative to each other and parallel to the axis of the base, wherein a subgroup of the plurality of LEDs and corresponding portions of one or more circuit boards or the like are mounted on each of the plurality of surfaces. At least one of the plurality of surfaces is arranged parallel to the target illumination plane. In one embodiment, three of these surfaces may be angled relative to each other at a reflection angle (e.g., such as 210 to 240 degrees).

[0009] The base may have a planar cover mounting area parallel to the target lighting plane for receiving a corresponding surface of the cover. The base and the cover may have an interface including one or more positive or negative features of the cover configured to engage with one or more engaging features in the base. One or more clamps may hold the cover and the base in a compression relationship.

[0010] The base may include at least one rectangular LED mounting surface facing the printed circuit board for receiving one or more circuit boards including the plurality of LEDs. The heat sink may include a lower portion connected to a lower side of one of the rectangular mounting surfaces, wherein the rectangular mounting surface has a width greater than the width of the lower portion, and the LEDs are distributed in an array of one plurality of LEDs (such as an array of five LEDs wide) comprising a distribution across the width of the rectangular mounting surface. Wherein the radiation source is configured to replace an embodiment including a fluorescent bulb with a tube having a diameter, the width of the rectangular mounting surface may be greater than the diameter of the tube.

[0011] The base may include a front portion facing the target illumination plane and a lower portion facing away from the target illumination plane, wherein the lower portion has a geometry defining a semi-cylindrical shape. In one embodiment, the heat sink may define a plurality of fins spaced apart from each other by radial edges defining the semi-cylindrical geometry.

[0012] Another aspect of the invention includes an exposure system comprising a plurality of radiation sources as described herein. The exposure system may include a substrate for receiving a printed circuit board in a target illumination plane corresponding to the plurality of radiation sources. The exposure system may include a housing configured for use with fluorescent tubes, wherein the sources replace the fluorescent tubes. A remote control transmitter may be configured to transmit signals to a plurality of remote control receivers among the plurality of radiation sources and may have one or more inputs for receiving information to be transmitted to the remote control receivers. The one or more inputs may include a control panel for setting a desired illumination intensity of one of the radiation sources. One or more photodetectors can be configured to detect the intensity of radiation emitted by one or more of the plurality of radiation sources. Each photodetector is configured to provide a feedback signal to one or more inputs of the remote control transmitter, wherein the control electronics are configured to use the feedback signal to control the intensity emitted by one or more of the plurality of radiation sources.

[0013] The exposure system may include: a first set of sources spaced above a first surface of the substrate, and the substrate may be transparent or translucent to photochemical radiation as needed; and a second set of sources spaced below a second surface of the substrate opposite to the first surface.

[0014] In the system in which the sources replace fluorescent tubes, the sources have a predetermined spacing between the axes of adjacent sources, the predetermined spacing defining a gap between adjacent edges of adjacent sources, wherein the gap between the sources is smaller than a corresponding gap between the fluorescent tubes replaced by the sources.

[0015] Another aspect of the present invention is a method for exposing a printed circuit board, the method comprising: placing a printed circuit board on a target illumination plane of an exposure system as described herein; and activating a radiation source to provide photochemical radiation directed at the board. The method may include: measuring irradiance at the target illumination plane; and controlling the intensity of a plurality of LEDs from one or more of the radiation sources based on the measured irradiance. Controlling the intensity of the plurality of LEDs may include compensating for output power attenuation caused by aging of the plurality of LEDs. Controlling the intensity of the plurality of LEDs in a first source may also, or alternatively, include compensating for differences in the performance characteristics of the LEDs in the first source relative to the performance characteristics of each plurality of LEDs in a second source. Controlling the intensity of the plurality of LEDs may also, or alternatively, include adjusting the radiation output according to application requirements, such as providing a first exposure characteristic for producing a rounded top point in the printed circuit board and a second exposure characteristic for producing a flat top point in the printed circuit board.

Implementation Method

[0017] This application claims priority to U.S. Provisional Application No. 62 / 893,395, filed on August 29, 2019, entitled "UV LED RADIATION SOURCES FOR USE IN PHOTOPOLYMER EXPOSURE," the entire contents of which are incorporated herein by reference.

[0018] This application relates to an apparatus and method for exposing a photopolymer printed circuit board to photochemical UV radiation using LEDs to replace fluorescent tubes in a lamp holder. In its simplest form, this can be achieved by providing a housing containing semiconductor LEDs that is electrically and mechanically compatible with existing fluorescent tubes, the housing comprising an LED-based photochemical radiation source suitable for use as a replacement for existing fluorescent tubes in a lamp holder. The LED light source array covering the entire surface of the printed circuit board does not require relative movement to irradiate the entire front or rear board surface. Cooling requirements are reduced when the heat generated by the LED light source is distributed over a broad area approximately the size of the board, rather than concentrated in a small, relatively linear area to minimize the travel time for achieving full exposure.

[0019] One embodiment of the present invention includes: a UV LED light source that covers the entire surface of a photopolymer printed circuit board with a fluorescent tube replacement equipped with a UV LED; and a method for modifying a panel lamp exposure unit by replacing all fluorescent tubes in a panel lamp exposure unit with replacement tubes as described herein. While LED replacements for fluorescent tubes are known for use in lighting applications, photopolymer board exposure may present different requirements and offer opportunities to use different structures.

[0020] Figure 1 illustrates a simplified embodiment, showing a cross-section of an exemplary LED radiation exposure source embodiment according to one aspect of the present invention. An LED chip 101 is positioned on a circuit board 102 extending along the length of the source. The circuit board is preferably mounted on a base 103, such as that made of metal (preferably aluminum), including a heat sink. The LEDs are preferably connected in series, and opposite ends of the sources have connectors configured to allow each source to be mounted in a socket configured to receive a fluorescent tube. Thus, an array of sources constructed in this way can be mounted inside a row of lamp holders and powered. The emitting side of the source is covered by a UV transmission cover 104, which keeps dust and solvents away from the sensitive output window of the UV LED. Suitable materials for constructing the cover 104 include plastics such as polymethyl methacrylate (PMMA) (also known as acrylic, acrylic glass, or plastic glass), such as (but not limited to) Plexiglas® acrylic manufactured by Arkema France and PMMA manufactured by Evonik of Essen, Germany, or their successors. As shown in Figure 1, the cover has a semi-cylindrical shape on the upper surface of a plane facing the lighting plane and connected to the base. The cover can be attached to the base in any manner known in the art, including (but not limited to) using an adhesive, such as a UV-curable adhesive.

[0021] Although Figure 1 schematically depicts the heat sink of base 103, it should be understood that the heat sink can have any geometry suitable for providing the desired level of heat transfer in use. Figure 2 depicts an exemplary aluminum base 203 including one of a plurality of cooling fins 206a to 206i. Most lamp stands are equipped with fans that remove waste heat from the rear side of the fluorescent tube, meaning that the convective airflow supplied by such fans may be particularly suitable for cooling a source having one of a plurality of fins. Although shown in a design including a semi-cylindrical distribution of fins originating from a horizontal surface 207 of base 208 (where each fin extends along a radius), the heat sink is not limited to any particular geometry. However, in one exemplary geometry, some or all of the radii may originate from a common center point 210 at the intersection of the centerlines of the fins (such as the respective centerlines 216c, 216e of the depicted fins 206c, 206e), spaced above a horizontal surface. One or more of the fins (such as the central fin 206e) may be relatively thicker than the other fins 206b to 206d, 206f to 206h, and the end fins 206a, 206i may be attached to the horizontal surface 207 of the base on one side and have a gap that separates them from the adjacent fins 206b, 206h on the opposite side. Although it is shown that the base 208 has a polygonal upper surface 209 (as further described with reference to the embodiment discussed in FIG. 3), the upper surface may be flat (as schematically depicted with respect to the base 103 in FIG. 1). The upper surface of the base may include connection areas 220 on opposite sides for receiving the cover, each connection area defining a plane parallel to the target lighting plane.

[0022] One advantage of fluorescent tubes over LEDs is their wide range of light emission angles. The fluorescent coating on the walls of a fluorescent tube emits photons in all directions, making it a nearly ideal surface source, which is desirable when exposing a photopolymer printed circuit board through a mask. LEDs are point source properties and are therefore less ideal from this perspective, as each LED emits radiation toward the target illumination plane X (e.g., the top surface of a printed circuit board 110) at a relatively narrow emission angle β, as depicted in Figure 1.

[0023] Specific measures may be adopted to fully overcome this defect and expand the angular distribution of radiation, including (but not limited to): ● Using a relatively large number of uniformly distributed, relatively low-power LEDs instead of a relatively small number of relatively high-power LEDs; ● Configuring LEDs into groups with different tilt angles; ● Using reflective optics (including but not limited to a kaleidoscope) to convert a point source into a surface source; ● Using transmissive optics (such as but not limited to Fresnel lenses or diffusers).

[0024] The number of LEDs per tube length is a parameter that can be used to characterize the distribution of light along the length axis of the source. A source rated to deliver 20 watts of UV power may (for example) include 20 LEDs, each with an output of 1 watt, arranged along the length of the source, or more preferably 40 LEDs, each with an output of 0.5 watts, or even more preferably 60 LEDs, each with an output of 0.33 watts.

[0025] Figure 3 depicts an embodiment in which LEDs 301a to 301c are configured on corresponding circuit boards 302a to 302c, which are angled relative to each other on one of the upper surfaces of a base 303. This configuration improves the angular distribution in the illumination plane Y perpendicular to the tube's length axis Z, while having little or no effect on the angular distribution in planes parallel to or containing the tube's length axis (these planes are perpendicular to both the plane Y and the plane X where the board is located). Therefore, although each source 301a to 301c still has only one emission angle β, the three sources together produce a total emission angle θ greater than β. As depicted in Figure 3, the upper surface of the heat sink is semi-hexagonal in shape, wherein the three angled surfaces are each offset relative to each other by a reflection angle (e.g., preferably an angle where Ф = 210-240 degrees, as depicted in Figure 3). More than three surfaces angled relative to each other can be provided. However, preferably, regardless of the number of surfaces, at least one of the surfaces is parallel to the target illumination plane. The connection area 320 for receiving the opposite edge of the cover 304 is preferably a planar surface parallel to the target illumination plane X and configured to receive the corresponding planar surface of the cover 304. However, the interface between the cover and the base is not limited to any particular configuration. Therefore, an odd number of angled surfaces is preferred. The base is preferably configured such that all circuit boards lie flat on the corresponding surfaces of the base for maximum heat conduction through the heat sink. While the base 303 is preferably configured such that circuit boards 302a and 302c intersect circuit board 302b at equal angles, in other embodiments, Φ may be greater than or less than 120 to 150 degrees. Θ may be a multiple of the number of surfaces β, or a fraction of β. Θ is preferably less than 180 degrees to increase the percentage of total radiation emitted by the LED toward the printed circuit board.

[0026] Figure 4 depicts an embodiment in which the base 403 and circuit board 402 have widths W1 and W2, respectively, on the front side of the base, larger than the original diameter of the source fluorescent tube designed to replace it. The cover 404 may be generally rectangular, but is not limited to any particular geometry. This configuration also includes a plurality of LEDs 401a to 401e arranged in an array over a width, the array comprising at least some LEDs (e.g., 401a, 401e) in positions within the gaps between the source fluorescent tubes being replaced. For comparative purposes, the dimension D of the semicircular lower portion 403s of the base, which connects to the rectangular portion 403r, is depicted as approximately the same size as the original diameter of the fluorescent tube it replaces. Dimension D may be smaller than a chord of the actual diameter of the semicircular portion and / or the original diameter of the fluorescent tube. The heat sink may have a semicircular portion having a diameter smaller than or larger than that of the original fluorescent tube. However, the geometry of the lower portion is not limited, and some embodiments may not have a semi-circular geometry at all. The expanded width of the source can be designed such that adjacent sources replace adjacent tubes in a one-to-one ratio with almost no gap between adjacent lateral edges of adjacent sources, or each source can be designed to replace multiple fluorescent tubes (e.g., 1 LED source for 2 fluorescent tubes, 1 for 3, etc.). This configuration also has the effect of providing an emission angle θ from the source that is greater than the individual emission angle β of each LED.

[0027] To improve the angular distribution in a plane parallel to or containing the tube length axis, the cover 104 shown in FIG1 may include prisms or other refractive structures (such as a plurality of cylindrical Fresnel lenses) above the LED positioning locations. FIG5A and FIG5B depict an exemplary portion of this cover 500 having five cylindrical Fresnel lenses aligned above the five linear LED positions indicated by arrows 510a to 510e. As used herein, the term "cylindrical Fresnel lens" refers to a lens geometry having a refractive power to focus or diffuse light along a line (e.g., the axis along which the LED source distribution is located) or from that line, as opposed to a spherical Fresnel lens that focuses or diffuses light to or from a point. Each linear LED position may represent more than one LED, such as in the angular distribution of three LEDs depicted in FIG2. The structure in the lens cover 500 may include a prism structure that does not perfectly conform to the mathematical precision of a Fresnel lens but still refracts UV radiation in a manner that results in a wider angular distribution than in the absence of such a structure. Therefore, the prism and refractive structure in the lens cover is not limited to any particular geometry.

[0028] Notably, as depicted in FIG5B, the cover 500 has planar surfaces 502 at opposite ends configured to interface with the planar mounting regions 220, 320 depicted in FIG2 and FIG3. Therefore, when assembled to a corresponding base, the planar surfaces 502 are parallel to the target illumination plane. The planar surfaces at the ends of the cover can exist in any cover structure, such as any of the cover structures depicted in any of the other embodiments discussed herein. In alternative configurations, the cover may have one or more protrusions intersecting with fitting recesses or holes in the base. For example, in one alternative configuration depicted in FIG5C, the base 550 may have a recess 551 configured to receive a lip 552 extending radially inward from the end of the cover 540. This recess and the corresponding lip may extend the entire length of the source or may exist only in a selected fitting position. The strength of the solid connection between the groove and the lip can be enhanced by using an adhesive on the mating surfaces of the lip and the groove. The geometry of the groove and the lip can have any geometry known in this art and is not limited to those depicted. The interface between the cover and the base is not limited to any particular structure. As a non-limiting example, additional interfaces (such as those depicted in Figures 5D to 5H) may be provided.

[0029] As depicted in FIG. 5D, the base 560 may have one or more recesses or holes 561 into which pins or tabs 562 protruding from the cover 564 are inserted. These interfaces may be reinforced with adhesive. Although the widths of the base and the cover are depicted as substantially the same at the interface in FIG. 5D, the base 590 may have a width greater than that of the cover 594 at the interface (as shown in FIG. 5G), wherein the pins or tabs 592 include protrusions extending from the cover 594 with the same width or diameter as the cover, and the base has corresponding recesses or holes 591 in a relatively large platform area of ​​the base configured to receive the corresponding pins or tabs.

[0030] In another embodiment, clamps 576 (such as those made of spring steel) may be disposed around a portion of the cover 574 and extend below the base 570, as depicted in FIG5E. Such clamps may be preferably positioned at the location of the end cap 810 on the prior art bulb shown in FIG8, so that curing exposure does not require any radiation blocked by the clamps.

[0031] In other configurations, such as those depicted in FIG. 5F, the cover 584 may include a portion of a plastic glass extending more than 180 degrees in cross-section, wherein a subsequent opening in the tube 587 is provided for cooling. The tube may have a first thickness in the front portion of the tube and a smaller thickness in peripheral contact with the base 580, such as to provide a lip 588 interfacing with the front surface 585 as depicted on the right side of FIG. 5F, or the tube may have a protrusion 589 contacting the front surface of the base. Although different structures are depicted on the right and left sides of FIG. 5F, it should be understood that the figures are for illustrative purposes only, and the opposite sides of the cover and base generally have the same structural features, although the structures may include a combination of variations in wall thickness and protrusions, and some embodiments may have different structures on one side relative to the other to facilitate assembly.

[0032] Although depicted as a protrusion or other positive feature on the cover intersecting with a hole, recess, or other negative feature in the base, embodiments in which the cover intersectes with a positive feature on the base (such as depicted in FIG. 5H) may also be provided, wherein a protrusion 597 from the base 595 receives an edge of the cover 596. The protrusion may extend the entire length of the cover and the base, or may include a series of discrete protrusions. The cover may have a continuous edge of the same thickness at all times, or may have a notch or region with relatively thin and thicker walls to engage with a corresponding protrusion from the base. An adhesive layer may be provided between the mating surfaces of the base and the cover.

[0033] The clamps and / or adhesives may be combined with any of the interfaces described herein, and may be combined with combinations of negative, positive, or neutral features that interface with corresponding mating features of the cover and the base, including (but not limited to) any of or all of the following described herein. As used herein, the term "positive" is intended to mean a feature that protrudes from an edge or surface, the term "negative" is intended to mean a feature that is recessed relative to an edge or surface, and "neutral" is intended to mean a feature that is neither positive nor negative, such as a feature that contacts a corresponding feature plane. For example, a "matting" feature may include a positive feature (such as a pin 562) adapted to a negative feature (such as a hole 561), or a positive feature 589 or a negative feature 588 (e.g., a region that reduces wall thickness), or a combination of the like that that creates a lip that receives a neutral surface (e.g., the front surface 585 of the base). Although the semi-cylindrical cover shown in Figures 5C to 5H is depicted, it should be understood that any of the interfaces between the cover and the base may also be applied to embodiments having other shapes, such as (but not limited to) the rectangular cover geometry depicted in Figure 4.

[0034] Preferably, LEDs from each individual source are selected from the same production batch such that the light output properties (and any other material properties) of these LEDs are sufficiently identical to obtain a constant UV output over the entire length of the source. Not all LEDs in all sources of a single exposure unit can be produced from the same LED batch; therefore, control electronics are desired to maintain a desired current through the LEDs to compensate for the different output intensities emitted per unit current from different LED batches. Using such control electronics, the total UV output of all tubes can be adjusted to a common intensity level within a predetermined tolerance, such that all locations on the board are exposed to UV radiation at the same intensity level within the desired tolerance.

[0035] Suitable control electronics for controlling LEDs and LED intensity are well known in the field of lighting technology, such as using pulse width modulation to obtain acceptable linearity of UV output relative to control signals. Remote control signals can be used to set the output of LED sources, such as to compensate for output power attenuation caused by aging. Control signals can be transmitted to individual power controllers located in each source, such as by means of infrared (IR) or radio frequency (RF) signals. Remote control of radiation intensity can also allow adjustment of radiation output according to application requirements, such as exposing highly sensitive polymer boards (e.g., DuPont® EFX boards) in a round-top to flat-top mode, as known in the art. Adjusting radiation output according to application requirements can also involve providing a first exposure with a low intensity followed by a second exposure with a higher intensity to fully cure the printed circuit board. The first exposure provides a first fraction of the required total cure, while the second exposure provides the remaining fraction of the required total cure, such that the first and second exposures together provide the total energy required to cure the board.

[0036] To compensate for nonlinearity in the electronics or to control the dimming of the LED source, one or more photodetectors integrated into or placed on the support plane of the photopolymer plate during exposure can provide feedback to the UV output controller, thereby providing a precise amount of UV intensity within a predetermined tolerance. Figure 6 schematically illustrates an exemplary feedback loop and an overall schematic diagram for controlling an exemplary LED source as described herein. A power supply 601 supplies power to control electronics 602 that control the LEDs in each LED source 603. Individual LEDs in each source may be individually controllable, or more preferably, controlled as a whole. A photodetector 606 measures the radiation received at a calibrated location representing the radiation received by the printed circuit board. A signal from the photodetector is then provided to a remote control transmitter 605, which sends a signal to a remote control receiver 604 connected to control electronics. The control electronics use this feedback signal as an input to determine whether to increase, decrease, or maintain the current. A control panel 607 can provide a desired intensity level command to the remote control transmitter, which can use this information as a feedforward signal to set an appropriate current level to be adjusted using the feedback.

[0037] Figure 9 depicts an exemplary radiation system 900 incorporating a plurality of sources 902, which may be any of the configurations described herein for replacing a fluorescent tube. For example, the system may be a pre-existing system designed for use with a fluorescent bulb and modified with the sources of the present invention, and the sources may also include, as needed, any of the additional controllers and sensors described herein. The system may also be a state-of-the-art system designed for use with sources described herein. The exemplary system includes a cover 912 typically attached to a base 914 by a hinge 913 or other component, the hinge 913 or other component allowing the cover to move relative to the base to insert a printed circuit board (not shown) onto a support surface 916 for receiving the board. The support surface 916 is typically sized to have a width and length that are at least the same size as (and preferably larger than) the largest printed circuit board to which the unit is rated for exposure. The radiation source array is accordingly configured to provide light over the entire length and width of the plate to which the unit is rated for exposure, and is therefore preferably sized to provide exhaust or floodlight across an area slightly larger than the maximum plate size by a predetermined margin.

[0038] In the illustrated configuration shown, a cover depicted in an open configuration has a first plurality of upper radiation sources 902 having a central spacing S relative to the axis of the source mounted therein. The number of upper radiation sources 902 shown is not intended to represent an actual number of sources or the relative size of the sources in a typical system, but is only schematically shown for reference. Furthermore, as depicted, the width / diameter of the source is depicted to leave a gap G between adjacent sources. As discussed herein with reference to the embodiment depicted in FIG4, in an embodiment where the source replaces a fluorescent bulb having a diameter D, the size of the gap G has a first value, and the width of the source may be greater than D such that the size of the gap G has a second value, smaller than the first value.

[0039] As depicted, each source is electrically connected and physically received in mounting unit 910ul on the left and mounting unit 910ur on the right. Each mounting unit is attached to a power supply and other controls, collectively represented by block 918, mounted in base 914. As shown in the enlarged portion of FIG9, each source 902 has an end connector 958 configured to be compatible with electrical sockets 954, which may initially be configured to receive pins 812 of prior art tube 800. Each socket is connected to electrical wiring connected to opposite poles 956, 957 of a power supply. Each source 902 may have a local controller 952 for regulating power to LED 950. Although depicted as a block 952 located on one end of the tube, components of the controller may be located at both ends, or the controller may include components housed on a circuit board to which the LED is mounted and may not be a discrete component as depicted. However, as is known in this art, the end cap 810 of a fluorescent bulb is typically metal and therefore does not emit light, so the replacement tube does not necessarily need to provide illumination in this area to replicate the performance of the fluorescent tube. This makes this portion of the tube an ideal location for one of the electronic components that may be needed to control power or operate the LED in a desired manner. Controls for operating an LED source modified within a system configured to receive a fluorescent tube, and any other modifications to systems typically used to power such LED sources, are generally known in this art, such as those described in U.S. Patent No. 7,507,001. Although the source 902 depicted in the enlarged section has a configuration consistent with the embodiment depicted in FIG3, the source may have a design conforming to any of the sources described herein.

[0040] An exemplary control system may include one or more controllers commonly programmed with some or all of the features depicted in FIG. 6 and described herein. The location of the power supply and controls is not limited to placement in the base and may be located elsewhere, including a distributed configuration in which some parts of the control system are mounted in the base, some in the cover, and some in the source, as described herein. The lines shown in connection block 918 represent electrical connections (such as wired connections) and control signal connections (such as wired or wireless connections). As depicted, the source 902 in the cover is preferably used for front-side exposure of a plate mounted on support surface 916.

[0041] The support surface 916 in the base may be transparent or translucent to photochemical radiation as needed, and an additional set of optional sources 902 may be installed between the lower left socket 910ll and the lower right socket 910lr below the support surface for providing back-side exposure. The control system may have a controller programmed to provide a combination of back-side and front-side exposures to the board, wherein there is a predetermined delay between the front and back exposures, included in a plurality of fractional exposure cycles and / or including one or more back-side-only exposure steps, generally as described herein in U.S. Patent Application Publication No. 20180210345A1 entitled PROCESS AND APPARATUS FOR CONTROLLED EXPOSURE OF FLEXOGRAPHIC PRINTING PLATES AND ADJUSTING THE FLOOR THEREO, as cited by a co-applicant herein by reference.

[0042] Therefore, a user can use an exemplary exposure system to expose a printed circuit board by placing the board on a support surface, closing the cover, and activating the upper source and selecting the lower source for a desired duration (including a desired exposure pattern further described below). This exposure method may involve controlling the intensity of the LED emission using a control system depicted in Figure 6 for any of the reasons discussed herein.

[0043] In other embodiments, the UV LED 701 may be configured as a planar array as depicted in FIG. 7, the array being the same size as or preferably at least slightly larger than the photopolymer printed circuit board to be irradiated. To maintain irradiance at the edges of the LED array, a mirror wall 702 may be used to surround the array, such as that generally disclosed in U.S. Patent No. 8,578,854, which is incorporated herein by reference. As depicted, the mirror wall is adapted to the size of a planar array. A kaleidoscope method is also disclosed in U.S. Patent No. 8,578,854, owned by a co-applicant of this application and incorporated herein by reference. U.S. Patent No. 8,578,854 and FIG. 3 through 6 corresponding to the present invention illustrate the advantages of using a surface source for curing printed dots in a photopolymer board. The surface source cures a wider support socket under the printed details at the top surface of the board. The wider support sockets allow smaller printing details to remain on the board during solvent cleaning processes and also provide a longer run time for the board under pressure before point cracking.

[0044] Although this document is primarily discussed in the context of LEDs in the ultraviolet (UV) emission range (e.g., having a central emission wavelength in the UV spectrum, preferably in the range of 320 nm to 420 nm, more preferably in the range of 360 nm to 420 nm), the radiative output of an LED is not limited to any particular wavelength, as long as it is photochemical radiation relative to the photopolymer plate to be cured. It should also be understood that although the rectangular array is depicted as a regular array of columns and rows in Figure 7, the LED array may have an alternating configuration from column to column or row to row. Furthermore, each source may contain more than one species of LED, each species having a different common central emission wavelength, wherein the respective species are arranged adjacent to each other in a repeating sequence. For example, LEDs can be patterned and / or have wavelength characteristics, as described in PCT application serial number PCT / EP20 / 061556, filed April 26, 2020, which claims priority from U.S. Provisional Patent Application Serial No. 62 / 839,171, filed April 26, 2019, both entitled APPARAUS AND METHOD FOR EXPOSING PRINTING PLATES USING LIGHT EMITTING DIODES, filed by a co-applicant of this invention, and is incorporated herein by reference. Therefore, according to the foregoing incorporated reference, a source may include a plurality of light-emitting diodes (LEDs) arranged in an array of rows and columns, the plurality of LEDs comprising a plurality of species (e.g., 2, 3, 4, etc.) of LEDs, each species having a common central emission wavelength distinct from any other species. Each species of the LED preferably has a central emission wavelength in the UV spectrum, more preferably in the range of 320 nm to 420 nm, and most preferably in the range of 360 nm to 420 nm (e.g., 365 nm, 395 nm, and 415 nm in a 3-species configuration). The array can be configured such that each species is arranged close to each other in a repeating sequence (such as a pattern in which alternating columns consist of individual species in the column, an interleaved configuration as needed, or a pattern in which alternating species in each column are distributed such that adjacent members of the same species in adjacent columns are diagonally aligned). The array controller can be configured to independently control each species and cause multiple species to emit simultaneously such that the emission patterns of adjacent members of each species of the LED overlap each other on the board. Different species can be tuned to provide different mixtures of common emission intensities or relative emission intensities different from those of individual species. Members of each species of the LED can be electrically connected to a common driver configured to cause each electrically connected member of the species to emit at a common intensity. Each source in this array may have one or more user-adjustable emission characteristics (such as user-adjustable emission intensity).In some implementations, the plurality of sources can be configured to allow one source to emit emission characteristics different from another source simultaneously and / or allow the same source to emit different emission characteristics during different portions of an exposure duration. The relative intensities of the individual species of LEDs can also be tuned to compensate for differences in exposure sensitivity in different batches of boards or to compensate for differences between individual exposure systems. The use of different species or distribution patterns as described above can be used in any of the embodiments depicted herein. Thus, for example, although only cross-sectional views are provided for the embodiments depicted in Figures 1, 3, and 4, it should be understood that the LEDs are distributed along the length of each source, and this distribution can be a regular rectangular array or any other spacing pattern found to have operational advantages, including (but not limited to) patterns of single or multiple species of any of the patterns disclosed in the preceding application 62 / 839,171.

[0045] Although references are made herein to the use of sources as replacements for fluorescent bulbs and to the modification of pre-existing array lamp systems with sources as disclosed herein for the purpose of exposing photopolymer panels, it should be understood that sources and systems using them may include original equipment designed for any purpose (but not limited to retrofit applications).

[0046] Although the invention has been illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. In fact, various modifications to the details may be made within the scope and within the equivalents of the claims and without departing from the invention. [Simplified Explanation of the Diagram]

[0016] Figure 1 is a cross-sectional schematic diagram showing an exemplary source of the present invention, which is juxtaposed with a portion of an exemplary plate positioned on an illumination plane for exposure radiation from the source. Figure 2 is a perspective schematic diagram showing an exemplary finned heat sink design for an angled mounting surface of an LED. Figure 3 is a cross-sectional schematic diagram showing an exemplary source of an LED mounted on an angled mounting surface, which is juxtaposed with a portion of an exemplary plate positioned on an illumination plane for exposure radiation from the source. Figure 4 is a cross-sectional schematic diagram showing an exemplary source of a relatively wide rectangular LED array, which is juxtaposed with a portion of an exemplary plate positioned on an illumination plane for exposure radiation from the source. Figure 5A is a schematic plan view showing an exemplary cover of a plurality of cylindrical Fresnel lenses. Figure 5B is a perspective view of the cover of Figure 5A. Figures 5C to 5H show schematic plan views of an exemplary interface between the cover and the base structure. Figure 6 is a schematic diagram of an exemplary control system for controlling an exemplary system incorporating sources as described herein. Figure 7 is a schematic perspective view of a rectangular LED array having reflective sidewalls surrounding the array. Figure 8 is a schematic plan view of an exemplary fluorescent lamp of the prior art. Figure 9 is a schematic front view of an exemplary array exposure system in which a plurality of exemplary sources are mounted, including an enlarged portion showing an exemplary interface between the sources and system components.

Claims

1. A modified exposure system for modifying a row of lamp exposure units configured for use with fluorescent tubes configured to emit photochemical radiation, each of the fluorescent tubes having a specific length and a first set of electrical connectors in a first configuration, the first set of electrical connectors in the first configuration being configured to engage with a second set of electrical connectors in the row of lamp exposure units having a second configuration and connected to a power supply, the row of lamp exposure units including a substrate having a first surface for receiving a photopolymer printed circuit board, the modified exposure system comprising: A photopolymer printed circuit board is disposed on a first surface of the substrate and defines a target illumination plane on a top side of the photopolymer printed circuit board; a plurality of radiation sources are spaced apart from the first surface of the substrate, each radiation source is configured to emit photochemical radiation guided only toward the target illumination plane, the photochemical radiation being operated to cure the photopolymer printed circuit board, each radiation source comprising: a base having a width and a length along an axis, wherein the length is greater than the width, the base including a front portion facing the target illumination plane and a lower portion facing away from the target illumination plane, the front portion including a single rectangular planar mounting surface, the single rectangular planar mounting surface being disposed parallel to the target illumination plane and having a length and a width facing the target illumination plane, the lower portion including a metal heat sink; One or more circuit boards are mounted on the mounting surface of the base. The circuit boards collectively include a plurality of light-emitting diodes (LEDs), each having a central ultraviolet emission wavelength. The plurality of LEDs are arranged in an array above the length of the base. The array defines the plurality of LEDs across the length of the LED mounting surface and across the width of the LED mounting surface. All LEDs face the target illumination plane. The plurality of LEDs across the width of the LED mounting surface are configured to provide photochemical radiation at an emission angle greater than that of a single LED in a first plane perpendicular to the axis of the base, an emission angle greater than that of a single LED in a second plane containing the axis of the base or parallel to the axis of the base and perpendicular to the target illumination plane, or a combination thereof. One or more first controllers are disposed in the radiation source for regulating the power delivered to the plurality of LEDs. Each first controller is configured to maintain a desired current through one of the plurality of LEDs. A plurality of radiation source electrical connectors configured to interface with the second set of electrical connectors; and a cover, which is transparent or translucent to the photochemical radiation and mounted on the base, the cover together with the base defining an enclosure for one of the plurality of LEDs.

2. The exposure system of claim 1, wherein the base includes a planar cover mounting area for receiving a corresponding surface of the cover, wherein the planar cover mounting area is parallel to the target illumination plane.

3. The exposure system of claim 1, wherein the base and the cover have an interface, the interface including one or more positive or negative features of the cover configured to engage with one or more engagement features in the base.

4. The exposure system of claim 3, wherein the base has a groove configured to receive a radially inwardly extending lip of the cover.

5. The exposure system of claim 4, wherein the cover has a semi-cylindrical shape.

6. The exposure system of claim 5, wherein the plurality of LEDs are distributed in a regular rectangular array over the length of the base.

7. The exposure system of claim 1 further includes one or more clamps configured to hold the cover and the base in a compression relationship.

8. The exposure system of claim 1, wherein the cover includes one or more prisms and / or refractive structures.

9. The exposure system of claim 8, wherein the cover includes one or more cylindrical Fresnel lenses.

10. The exposure system of claim 1, wherein the heat sink includes a lower portion connected to a lower side of a single rectangular planar mounting surface, wherein the single rectangular planar mounting surface has a width greater than the width of the lower portion.

11. The exposure system of claim 10, wherein the array is five LEDs wide.

12. The exposure system of claim 10, wherein the radiation source is configured to replace a fluorescent bulb including a tube having a diameter, and the width of the single rectangular planar mounting surface is greater than the diameter of the tube.

13. The exposure system of claim 1, wherein the heat sink defines a plurality of fins spaced apart from each other by radial edges that define a semi-cylindrical geometry having a semi-circular cross-section.

14. The exposure system of claim 1 further includes a second controller configured to send control signals to each of the first controllers, the second controller being configured to send control signals operated to adjust the plurality of radiation sources to a common intensity level within a predetermined tolerance.

15. The exposure system of claim 14, wherein the second controller includes a remote control transmitter for transmitting wireless signals to one of the one or more wireless remote control receivers, the remote control receiver having one or more inputs for receiving information to be transmitted by the remote control transmitter.

16. The exposure system of claim 15, wherein the one or more inputs include a control panel for setting a desired illumination intensity of one of the plurality of radiation sources.

17. The exposure system of claim 15 further includes one or more photodetectors for detecting the intensity of radiation emitted by one or more of the plurality of radiation sources, each photodetector being configured to provide a feedback signal to the one or more inputs of the second controller for controlling the intensity emitted by the one or more of the plurality of radiation sources.

18. The exposure system of claim 15 further includes a sensor configured to measure irradiance emitted by each of the plurality of radiation sources, wherein the first controller and the second controller are co-configured to control the intensity of each of the plurality of radiation sources based on the measured irradiance.

19. The exposure system as claimed in claim 18, wherein the first controller and the second controller are configured to: control the intensity of a first of the plurality of radiation sources to compensate for the difference in performance characteristics of the first of the plurality of radiation sources relative to the performance characteristics of a second of the plurality of radiation sources.

20. The exposure system as claimed in claim 18, wherein the first controller and the second controller are configured to control the intensity of one of the plurality of radiation sources to compensate for a change in the performance characteristics of the first of the plurality of radiation sources over time.

21. The exposure system of claim 1, wherein the exposure system includes a housing, and a plurality of radiation sources configured to be mounted in the housing have a predetermined spacing between the axes of adjacent radiation sources, the predetermined spacing defining a gap between adjacent edges of adjacent radiation sources, wherein the gap between the radiation sources is smaller than a corresponding gap between fluorescent tubes replaced by the radiation sources within the housing.

22. The exposure system of claim 1, wherein the substrate is transparent or translucent to photochemical radiation, and wherein a second set of radiation sources is spaced below a second surface of the substrate, the second surface being opposite to the first surface and facing a bottom side of the printed circuit board opposite to the top side of the printed circuit board.

23. The exposure system of claim 1, wherein all of the plurality of LEDs in each radiation source are operable to emit a common central emission wavelength.

24. The exposure system of claim 1, wherein the heat sink comprises aluminum.

25. The exposure system of claim 1, wherein the heat sink defines a heat transfer surface region having a plurality of first portions disposed at a first radial distance from a defined longitudinal axis and a plurality of second portions disposed at a second radial distance from the defined longitudinal axis.

26. The exposure system of claim 25, wherein the first portion and the second portion of the metal heat sink increase the total heat transfer area of ​​the heat transfer surface of the metal heat sink.

27. The exposure system of claim 26, wherein the metal heat sink includes a plurality of longitudinally extending fins that originate from one surface of the base and extend along their respective radii originating from a common center point above the base.

28. The exposure system of claim 1, wherein each of the tubular radiation sources has at least one non-luminescent longitudinal region at at least one adjacent end.

29. The exposure system of claim 28, wherein at least one of the one or more first controllers is disposed within the enclosure in the non-luminescent longitudinal region.

30. The exposure system of claim 1, wherein the radiation source electrical connector comprises two sets of radiation source electrical connectors, one set disposed at each end of the radiation source and spaced apart from each other by the specified length, each set having the first configuration and configured to engage with the second set of electrical connectors having the second configuration.

31. The exposure system of claim 30, wherein the first configuration of the first set of electrical connectors includes a pair of fins having a predetermined geometry and being spaced apart from each other.

32. The exposure system of claim 1, wherein each of the one or more first controllers is configured to compensate for the different output intensities of the current emitted by the LEDs per unit.

33. The exposure system of claim 1, wherein the cover has a semi-cylindrical geometry.

34. An exposure system configured to expose a photopolymer printed circuit board to photochemical radiation operated to cure the photopolymer printed circuit board, the photopolymer printed circuit board having a top side and a bottom side opposite the top side, the exposure system comprising: A substrate that is photochemically transparent or translucent has a first surface for receiving a photopolymer printed circuit board and a second surface opposite to the first surface; a photopolymer printed circuit board disposed on the first surface of the substrate; a plurality of radiation sources, including at least one first set of radiation sources, the at least one first set of radiation sources being spaced apart from one of the first surface or the second surface of the substrate and facing the photopolymer printed circuit board disposed on the substrate; each of the plurality of radiation sources is configured to emit photochemical radiation guided only toward the photopolymer printed circuit board disposed on the substrate, each radiation source including: a base having a width and a length along an axis, wherein the length is greater than the width, the base including a front portion facing the substrate and a lower portion facing away from the substrate, the front portion including a single rectangular planar mounting surface, the single rectangular planar mounting surface being disposed parallel to the substrate and having a length and a width facing the substrate, the lower portion including a metal heat sink; One or more circuit boards are mounted on the mounting surface of the base. The one or more circuit boards collectively include a plurality of light-emitting diodes (LEDs), each having a central ultraviolet emission wavelength. The plurality of LEDs are distributed in an array above the length of the base. The array defines the plurality of LEDs across the length of the LED mounting surface and across the width of the LED mounting surface. All of them face the substrate. The plurality of LEDs across the width of the LED mounting surface are configured to provide photochemical radiation at an emission angle greater than that of a single LED in a first plane perpendicular to the axis of the base, at an emission angle greater than that of a single LED in a second plane containing the axis of the base or parallel to the axis of the base and perpendicular to the substrate, or a combination thereof. One or more first controllers disposed in the radiation source for regulating the power delivered to the plurality of LEDs, each first controller being configured to maintain a desired current through one of the plurality of LEDs; and a cover that is transparent or translucent to the photochemical radiation and is mounted on the base, the cover together with the base defining an enclosure for one of the plurality of LEDs.

35. The exposure system of claim 34, wherein the first set of radiation sources is spaced above the first surface of the substrate and faces a top side of the photopolymer printed circuit board disposed on the substrate, and the plurality of radiation sources further includes a second set of radiation sources, which is spaced below the second surface of the substrate and faces a bottom side of the photopolymer printed circuit board disposed on the substrate.

36. The exposure system of claim 34, further comprising an exposure system controller programmed to cause the plurality of radiation sources to: perform a front-side exposure operation on the top side of the photopolymer printed circuit board, perform a back-side exposure operation on the bottom side of the photopolymer printed circuit board, or a combination thereof.

37. The exposure system of claim 36, wherein the photopolymer printing plate is a flexible-printed photopolymer printing plate.

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