Patent Publication Number: US-2017359903-A1

Title: Method and System for Processing a Circuit Substrate

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with government support under Contract Number DE_EE0006260 awarded by the United States Department of Energy. The government has certain rights in the invention. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to fabricating circuitry, and more particularly to utilizing ultraviolet (UV) light emitting diodes (LEDs) for curing materials in connection with patterning or printing substrates, such as circuit boards. 
     BACKGROUND 
     Conventional approaches to manufacturing electronic circuit devices typically entail transferring a work piece along a substantial path of multiple machines and processes, each performing a discrete task. For example, a series of separate stations may be utilized to print labels and solder mask on a circuit substrate, and to cure the applied materials. The curing equipment typically operates using sources of curing energy that are large and unwieldy and that are so inefficient as to present heat dissipation issues. 
     Accordingly, improved technologies for manufacturing electronic circuit devices are needed. For example, need exists for compact and efficient sources of curing energy. Further need exists for workstations, machines, and processes that are compact, integrated, or offer other advantages. A capability addressing such a need, or some related deficiency in the art, would support improved fabrication of electronic circuit devices, including circuit substrates. 
     SUMMARY 
     In one aspect of the disclosure, an array of ultraviolet light emitting diodes can cure ultraviolet curable material, such as solder mask or ink, that has been printed, screened, or otherwise applied to a substrate in connection with fabricating circuit devices. The array of ultraviolet light emitting diodes can be compact and efficient so that inks and solder masks can be printed and cured at one fabrication station, for example in a housing or enclosure on a circuit production line. 
     The foregoing discussion of applying and curing materials on a substrate is for illustrative purposes only. Various aspects of the present disclosure may be more clearly understood and appreciated from a review of the following text and by reference to the associated drawings and the claims that follow. Other aspects, systems, methods, features, advantages, and objects of the present disclosure will become apparent to one with skill in the art upon examination of the following drawings and text. It is intended that all such aspects, systems, methods, features, advantages, and objects are to be included within this description and covered by this application and by the appended claims of the application. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a functional block diagram of a system for manufacturing electronic circuit devices in accordance with some example embodiments of the present disclosure. 
         FIG. 2  is a functional schematic of a processing station for applying materials to a substrate and curing the materials in connection with manufacturing electronic circuit devices in accordance with some example embodiments of the present disclosure. 
         FIG. 3  is flowchart of a process for applying materials to a substrate and curing the materials in connection with manufacturing electronic circuit devices in accordance with some example embodiments of the present disclosure. 
     
    
    
     Many aspects of the disclosure can be better understood with reference to the above drawings. The elements and features shown in the drawings are not necessarily to scale, emphasis being placed upon clearly illustrating the principles of exemplary embodiments of the present disclosure. Moreover, certain dimensions may be exaggerated to help visually convey such principles. 
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Some example embodiments of the present disclosure will be discussed in further detail below with reference to the figures. However, the present technology can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those having ordinary skill in the art. Furthermore, all “examples,” “embodiments,” “example embodiments,” or “exemplary embodiments” given herein are intended to be non-limiting and among others supported by representations of the present technology. 
     Some of the embodiments may comprise or involve processes that will be discussed below. Certain steps in such processes may naturally need to precede others to achieve intended functionality or results. However, the technology is not limited to the order of the steps described to the extent that reordering or re-sequencing does not render the processes useless or nonsensical. Thus, it is recognized that some steps may be performed before or after other steps or in parallel with other steps without departing from the scope and spirit of this disclosure. 
     Turning now to  FIG. 1 , this figure illustrates a functional block diagram of an example system  100  for manufacturing electronic circuit devices according to some embodiments of the present disclosure. In the illustrated embodiment, the system  100  can produce circuit boards populated with electronic components, for example. 
     As illustrated, the system  100  comprises a processing station  150  that outputs work pieces to a print solder unit  120 . The processing station  150  can comprise a housing  135  that provides an enclosure for processing the work pieces. The work pieces can comprises circuit boards or other circuit substrates, for example. The print solder unit  120  outputs work pieces to a pick-and-place unit  125 . The pick-and-place unit  125 , in turn, outputs work pieces to a solder oven  130 , for work piece completion. 
     As will be discussed in further detail below with reference to  FIGS. 2 and 3 , the processing station  150  comprises a printer label capability  105  and a printer solder mask capability  110  for applying ultraviolet curable materials to a circuit substrate. The circuit substrate can comprise a circuit board, for example. 
     The printer label capability  105  can apply labels to the circuit substrate, for example text, codes, letters, information, or indicia. Meanwhile, the printer solder mask capability  110  can apply solder masks to the circuit substrate. The labels and solder mask can comprise ultraviolet curable materials. 
     The example processing station  150  further comprises an ultraviolet cure capability  115 . In an example embodiment, the ultraviolet cure capability  115 , the printer label capability  105 , and the printer solder mask capability  110  are enclosed in the housing  135  of the processing station  150 . 
     As will be discussed in further detail below, an example embodiment of the ultraviolet cure capability  115  comprises an array of light emitting diodes (or one or more ultraviolet laser diodes) that emit ultraviolet light of sufficient intensity and appropriate wavelength to cure the applied materials. 
     Accordingly, the processing station  150  can output circuit substrates with cured labels and solder masks, for receipt by the printer solder unit  120 . The printer solder unit  120  applies solder to each circuit substrate, with the solder mask defining regions on the circuit substrate where the solder adheres to the circuit substrate. For example, the solder mask may define solder pads where electronic components are to be soldered to the circuit substrate. 
     The pick-and-place unit  125  receives the circuit substrate from the printer solder unit  120 . The pick-and-place unit  125  populates the circuit substrate with electronic components, for example capacitors, resistors, chips, light emitting diodes, transistors, and other appropriate devices. An example embodiment of the pick-and-place unit  125  can comprise a vision system and robotic arm or other appropriate technology for populating the circuit substrate. 
     The populated circuit substrate transfers from the pick-and-place unit  125  to the solder oven  130 . The solder oven  130  heats the populated circuit substrate, including the applied solder. When the heated solder cools, the electronic components are fully attached and soldered to the circuit substrate, and the system  100  outputs a completed work piece, specifically a circuit board. 
     Turning now to  FIG. 2 , this figure illustrates a functional schematic of an example processing station  150  for applying materials  260  to a circuit substrate  220  and curing the materials  260  in connection with manufacturing electronic circuit devices according to some embodiments of the present disclosure. The processing station  150  illustrated in  FIG. 2  represents an example embodiment of the processing station  150  illustrated in  FIG. 1 , and will be discussed below as such an example without limitation. As described above with reference to  FIG. 1 , the elements of the processing station  150  that are illustrated in  FIG. 2  can be sufficiently compact and energy efficient to be disposed within the housing  135  (illustrated in  FIG. 1 ). 
     The processing station  150  comprises a bed  210  that supports the circuit substrate  220 . A stencil positioner  295 , which is under control by a station controller  225 , transfers stencils  295  onto and off of the circuit substrate  220 . The stencil positioner  295  can comprise a robotic arm or other appropriate mechanized device, for example. 
     An applicator  240  applies ultraviolet curable material  260  to the stencil  230 , and thus to defined areas of the circuit substrate. The ultraviolet curable materials  260  can comprise labeling inks, solder mask materials, or other appropriate materials. In an example embodiment, the applicator  240  comprises one or more fluid reservoirs for the ultraviolet curable materials  260  and one or more squeegees for spreading the materials. In various embodiments, the applicator  240  can comprise an inkjet printer, a screen-printing system, a rotogravure system (“gravure”), or other appropriate dispenser, to mention s few representative examples without limitation. 
     A positioning system  270  moves the applicator  240  across the circuit substrate  220  to spread the ultraviolet curable materials  260 . As illustrated and discussed below, the positioning system  270  can comprise a computer-controlled positioning system. Once an ultraviolet curable material  260  is spread, an array of ultraviolet light emitting diodes  250  emits ultraviolet light to cure the material  260 . The positioning system  270  can also move the array of ultraviolet light emitting diodes  250  across the circuit substrate  220 . In various example embodiments, the positioning system  270  can provide scanning motion in one dimension, two dimensions, or three dimensions. 
     In some example embodiments, the array of ultraviolet light emitting diodes  250  is a one-dimensional array, so that the light emitting diodes  250  are arranged in a single row. In some example embodiments, the array of light emitting diodes  250  is a two-dimensional array, so that the light emitting diodes  250  extend in two perpendicular directions. 
     In some embodiments, ultraviolet light output by a one- or two-dimensional array of light emitting diodes  250  couples into one edge of a panel-shaped lightguide  231  that can be characterized as an edgelit lightguide. The panel-shaped lightguide  231  can comprise a rectangular plate of optical material that has two major faces and four edges that form a rectangular perimeter with respect to the major faces, for example. The coupled ultraviolet light propagates in the panel-shaped lightguide  231  from the input lightguide edge towards the opposing lightguide edge via total internal reflection off of the major faces of the panel-shaped lightguide  231 . The ultraviolet light then emits from the panel-shaped lightguide  231  through that opposing edge. The panel-shaped lightguide  231  can effectively blend or homogenize the ultraviolet light so that the light emits in a uniform rectangular format that corresponds to the lightguide edge, rather than as from an array of discrete sources. In such an embodiment, the panel-shaped lightguide  231  can be mounted in a fixed vertical orientation, and the circuit substrate  220  can be moved linearly (for example as if on a conveyor belt) under the light-emitting edge of the panel-shaped lightguide  231 . The ultraviolet light emitting diodes  250  can then be turned on and off in synchronization with motion of the circuit substrate  220 , to apply ultraviolet light to specified locations of the circuit substrate  220 . Thus, the station controller  225  can coordinate discrete linear movements (or continuous linear motion) of the circuit substrate  220  and firing of the light emitting diodes  250 . Alternatively, in some embodiments, the light emitting diodes  250  may remain while potentially being dimmed via pulse width modulation or other appropriate technique. Some embodiments that utilize a panel-shaped lightguide  231  for delivering curing ultraviolet light can be viewed as providing a “frame-shot” ultraviolet cure, as an alternative to a “rastering” ultraviolet cure, for example. 
     In some embodiments, one or more ultraviolet laser diodes are utilized for the light source, for example to achieve a rapid cure rate. The ultraviolet laser diode(s) may further output energy in a relatively narrow wavelength range. In some embodiments, the ultraviolet laser diode light source is mounted in a fixed position. A mirror system can receive a beam of ultraviolet light from the fixed-position, ultraviolet light source. The mirror system can then move and direct the beam of light onto the circuit substrate  220  or other part to be cured. Accordingly, in some embodiments, the positioning system  270  moves a mirror while receiving a beam of light from a light source that is mounted in a fixed position. 
     In the illustrated embodiment, the station controller  225  controls position and operation of the applicator  240  and the array of ultraviolet light emitting diodes  250 . The station controller  225  can switch the light emitting diodes  250  off and on as well as controlling intensity via dimming. 
     In some example embodiments, the station controller  255  further controls spectral content and intensity of the light emitted by the array of ultraviolet light emitting diodes  250 . Spectral content can be controlled by including light emitting diodes  250  of differing spectral outputs in the array and then activating the light emitting diodes  250  in the array that will produce a desired wavelength range of light, for example. Additionally, the light emitting diodes  250  in the array can be individually dimmed. Accordingly, the light emitting diodes  250  can be individually addressable to deliver light having precisely controlled intensity, wavelength, and position. 
     In this manner, the output intensity and spectral content of the curing illumination can be selected according to the type material being cured. Black ink typically exhibits a different absorption spectrum than white ink, and the curing illumination can be selected and delivered to match the absorption spectrum of each ink. As another example, the inks (and other curable materials) of different manufacturers may react differently to different wavelengths and intensities of curing light, and the curing light can be adjusted to match each manufacturer&#39;s ink parameters and formulation. 
     In some example embodiments, the station controller  225  comprises memory  205  or a database for storing operating parameters for the array of light emitting diodes  250 , or may access such a database from a remote server or other site. The database can comprise a lookup table  216  that associates inks and other curable materials with specified wavelengths and intensities for the curing light. An operator of the station controller  225  can make an entry that specifies the ink. The station controller  225  can then query the database and the lookup table  216  to provide the desired wavelengths and intensity for the specified ink. The station controller  225  can then control the array of light emitting diodes  250  to deliver optimized wavelength ranges and intensities of curing light according to information in the lookup table  216 . 
     In some example embodiments, the spectral content and intensity of the curing light is determined empirically, and the resulting information can then be stored in the lookup table  216 . For example, the processing station  150  can run the circuit substrate  220  (or a mockup of the circuit substrate  220 ) with different inks and different intensities and wavelengths of the curing light until desired or optimized parameters are obtained. 
     In some example embodiments, the intensity and wavelength parameters can be adjusted on the fly. That is, the processing station  150  can adjust intensity and wavelength during production operations. The real-time adjustments can refine or improve production output, yield, cure rate, or cure quality, for example. In some example embodiments, the processing station  150  can refine the curing parameters by scanning a broadband light emitting diode array while measuring the amount of absorption across a spectral range for the inks applied to the circuit substrate  220 . The intensity and wavelength output by the array of light emitting diodes  250  can then be controlled dynamically according to the absorption feedback, for example. Accordingly, some embodiments of the processing station  150  can comprise a feedback control loop in which light intensity and/or light wavelength is controlled according to cure monitoring. 
     To position the applicator  240  and the array of ultraviolet light emitting diodes  250 , the station controller  225  interfaces with a position controller  290  that in turn interfaces with a motor  280 , for example a stepper or linear motor. 
     In the illustrated embodiment, the station controller  225  comprises a processor  235 , memory  205 , and a printing engine  215  stored in the memory  205  and executed by the processor  235 . In some example embodiments, the processor  235  can comprise one or more microprocessors, microcontrollers, programmable logic controllers, personal computers, or other appropriate computing systems. 
     Example embodiments of the memory  205  can comprise volatile and nonvolatile memory, such as random access memory (RAM) and flash memory for example. In an example embodiment, the memory  205  can comprise firmware for executing management and control functions. For example, the memory  205  can comprise persistent memory that stores program code, including the printing engine  215 . An example embodiment of the printing engine  215  can comprise computer executable instructions for implementing the process  300  that is illustrated in flowchart form in  FIG. 3  and discussed below. 
     Turning now to  FIG. 3 , this figure illustrates a flowchart of an example process for applying materials  260  to the circuit substrate  220  and curing the materials  260  in connection with manufacturing electronic circuit devices according to some embodiments of the present disclosure. Process  300  can comprise an example embodiment of the printing engine  215  that is illustrated in  FIG. 2 , for example. 
     In some example embodiments, instructions for execution of process  300  (or a portion thereof) can be stored in the memory  205  and executed by the processor  235  of the station controller  225 . For example, process  300  can be practiced using instructions that are provided in the printing engine  215  or in some other appropriate location or locations. Recognizing that the process  300  can be implemented or practiced in various places and in various forms, the process  300  will be discussed below with reference to an embodiment in which instructions are stored in the memory  205  as the printing engine  215 , without limitation. 
     At block  310  of the process  300 , the processing station  225  positions the circuit substrate  220  on the bed  210 . The circuit substrate  220  may be positioned by a robotic arm or by the positioning system  270 , for example. 
     At block  320 , the stencil positioner  295  places a stencil  295  on the circuit substrate  220 . 
     At block  330 , the applicator  240  applies ultraviolet curable material  260  at the stencil  295 . 
     At block  340 , the positioning system  270  moves the applicator  240  across the stencil  295  to spread the ultraviolet curable material  260 . In an example embodiment, the positioning system  270  spreads the material  260  using a squeegee. 
     At block  350 , the stencil positioner  295  lifts and removes the stencil  230  from the circuit substrate  220 . 
     At block  360 , the array of ultraviolet light emitting diodes  250  emits ultraviolet light to cure the ultraviolet curable material  260 . 
     At decision block  370 , process  300  determines whether additional stencils  295  are to be used on the circuit substrate  220 , for example by referencing a lookup table  216  or recipe for fabricating a particular circuit board. If more stencils  295  are to be used, then execution of process  300  loops back to block  320  and iterates. For example, one iteration may dispense and cure ink for labeling, and another iteration may dispense and cure solder mask. 
     Once each of the specified ultraviolet materials have been applied and cured, the process  300  ends. Processing of the circuit substrate  220  can continue with solder printing, pick-and-place population of electronic components, and heating via units  120 ,  125 , and  130  as illustrated in  FIG. 1  and discussed above. 
     Technology for processing a circuit substrate has been described. From the description, it will be appreciated that embodiments of the present technology overcome limitations of the prior art. Those skilled in the art will appreciate that the present technology is not limited to any specifically discussed application or implementation and that the embodiments described herein are illustrative and not restrictive. From the description of the exemplary embodiments, equivalents of the elements shown therein will suggest themselves to those skilled in the art, and ways of constructing other embodiments of the present technology will appear to practitioners of the art.