Patent Publication Number: US-2022235481-A1

Title: Selective screen electroplating

Description:
BACKGROUND 
     Electroplating (also referred to as electrodeposition) encompasses a variety of processes that create a metal coating on a solid substrate through the reduction of cations of that metal using a direct electric current. Three-dimensional (3D) printing (also referred to herein as additive manufacturing (AM)) refers to the construction of a 3D object from a computer-aided design (CAD) generated or otherwise obtained digital 3D model. 
     Selective electroplating utilizes a mask to selectively apply a layer of metal on specific areas of the solid substrate. A successive series of selective electroplating processes, each using the same or different masks may be used to iteratively build a metallic three-dimensional object, which may be considered an example of a 3D printing process. Another example 3D printing process is localized pulsed electrodeposition (L-PED), which is a technique for directly printing metallic structures at the tip of an electrolyte containing nozzle. L-PED conceptually utilizes traditional electroplating; however, the area of deposition is defined by the size of a liquid bridge (or meniscus) formed between the nozzle tip and a substrate onto which the metallic structures are printed. 
     While selective electroplating is capable of creating complex three-dimensional objects, application of each electroplating layer is relatively slow, particularly when a new mask is needed for the next electroplating layer (e.g., selective electroplating requires many iterations of multiple complex steps (mask, electroplate, polish, and remove mask) to generate a single part). L-PED is also capable of creating complex three-dimensional objects; however, L-PED is also relatively slow as the nozzle is moved and selectively actuated to produce individual micro-scale or nano-scale metallic structures one layer at a time. 
     The slow speed of conventional selective electroplating and L-PED (and further requirement of a series of masks in the case of selective electroplating) necessary to generate a metallic three-dimensional object makes conventional selective electroplating and L-PED not viable for mass manufacturing metallic three-dimensional objects. A faster and cost competitive option for mass manufacturing metallic three-dimensional objects without expensive tooling required by conventional metal manufacturing processes (e.g., molding, forcing, extrusion, etc.) would be generally advantageous. 
     SUMMARY 
     Implementations of the presently disclosed technology provide a selective screen electroplating process comprising orienting a switched array of regularly spaced electrodes occupying pores within a screen parallel to and in close proximity to a substrate within an electrolyte bath, and selectively activating a subset of the electrodes to print a pattern of metal through the electrolyte bath on the substrate. 
     Implementations of the presently disclosed technology further provide a selective screen electroplating system comprising a bath containing an electrolyte, a substrate, a screen, and a switched array of regularly spaced electrodes occupying the pores within the screen. The screen is oriented parallel to and in close proximity to the substrate within the bath. The selective screen electroplating system further comprises an electroplating power controller to selectively activate a subset of the electrodes to print a pattern of metal through the electrolyte bath on the substrate. 
     Implementations of the presently disclosed technology still further provide one or more computer-readable storage media encoding computer-executable instructions for executing on a computer system a selective screen electroplating process. 
     Other implementations are also described and recited herein. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         FIG. 1  illustrates an example selective screen electroplating system. 
         FIG. 2A  illustrates an example pair of electrodes within a screen, each in an OFF state. 
         FIG. 2B  illustrates the example pair of electrodes of  FIG. 2A , with one of the electrodes in an OFF state and the other of the electrodes in an ON state. 
         FIG. 2C  illustrates the example pair of electrodes of  FIG. 2A , with both of the electrodes in an ON state. 
         FIG. 3  illustrates an example pair of electrodes within a porous screen, the electrodes each having a venting through-hole. 
         FIG. 4  illustrates example operations for manufacturing a metallic 3D structure using a selective screen electroplating process. 
     
    
    
     DETAILED DESCRIPTIONS 
     The presently disclosed technology generally utilizes electroplating and L-PED technologies, but further utilizes a porous electroplating screen to accelerate manufacturing as described in further detail below. As a result, the presently disclosed selective screen electroplating processes are able to achieve much faster results in printing a complex metallic 3D structure using electroplating. 
     3D printing encompasses a variety of processes in which material is deposited and joined or solidified under computer control to create a 3D object, with material being added together (traditionally, liquid molecules or powder grains being fused together) iteratively, typically layer by layer. 3D printing generally provides a capability to produce complex shapes or geometries that would be otherwise difficult or impossible to construct using conventional manufacturing techniques (e.g., molding, forcing, extrusion, etc.). Traditionally, 3D printing utilizes polymers for printing, due to the ease of manufacturing and handling polymeric materials. However, traditional 3D printing has evolved to not only print various polymers but also metals. 
     Selective laser melting (SLM), also referred to herein as direct metal laser melting (DMLM) or laser powder bed fusion (LPBF), is a 3D printing technique that utilizes a high power-density laser to melt and fuse metallic powders together. Generally, thin layers of atomized fine metal powder, each representing a 2D slice of a part geometry, are evenly distributed using a coating mechanism onto a substrate. Once each layer has been distributed, each 2D slice of the part geometry is fused by selectively melting the powder together. 
     Traditional 3D printing processes, including SLM, have several drawbacks when compared to conventional manufacturing processes. For example, traditional 3D printing processes generally operate at a slow speed (e.g., SLM requires many iterations of multiple complex steps (print, bake, and wash) to generate a single part). Further, when used to print a metal object, traditional 3D printing processes generally operate at a high temperature (e.g., a temperature sufficient to melt layers of the metal three-dimensional object together), which can cause warping of heat-sensitive parts. As noted above, electroplating, including the screen electroplating processes disclosed herein, may be considered 3D metal printing processes as well, but the selective screen electroplating processes disclosed herein are capable of achieving a faster throughput and a lower workpiece temperature than traditional 3D printing processes can provide, particularly traditional metal 3D printing processes. 
       FIG. 1  illustrates an example selective screen electroplating system  100 . The system includes a porous screen  102  that includes an array of regularly spaced electrodes (e.g., electrodes  104 ,  106 ,  108 ,  110 ) oriented in the pores. The screen  102  is arranged parallel and in close proximity to a solid substrate  112  onto which a metallic 3D structure is to be created. At least one side of the screen  102 , as well as the substrate  112  are submerged in a bath  114  containing an electrolyte  116 , which includes a salt of a metal to be coated on the substrate  112  (referred to herein as a printing metal). In operation, the substrate  112  acts as a cathode (or negative electrode) and the individual electrodes selectively act as anodes (or positive electrodes), which when combined with current provided by an electroplating power supply  134 , forms an electrolytic cell for printing metal on the substrate  112 . 
     In some implementations, the polarity of the system  100  may be selectively reversed to remove metal, rather than add metal to the substrate  112 . More specifically, the substrate  112  acts as an anode and the individual electrodes selectively act as cathodes when the polarity is reversed, which when combined with current provided by the electroplating power supply  134 , ionizes a pattern of metal from the substrate  112  through the electrolyte  116 . 
     In one example, the electrodes may be formed from the printing metal. For example, the electrolyte  116  for forming a copper 3D structure can be a solution of copper(II) sulphate, which dissociates into Cu 2+  cations and SO 2−   4  anions. At the substrate  112  (cathode), the Cu 2+  is reduced to metallic copper by gaining two electrons. When the electrodes (anodes) are made of the coating metal and active, the opposite reaction may occur, turning the electrodes into dissolved cations within the electrolyte  116 . The copper oxidizes at active electrodes (anodes) to Cu 2+  by losing two electrons. The rate at which the active electrodes (anodes) are dissolved will be approximately equal to the rate at which the substrate  112  (cathode) is plated and thus the ions in the electrolyte  116  are continuously replenished by the active electrodes (anodes). The net result is the effective transfer of metal from the active electrodes (anodes) to the substrate  112  (cathode). 
     In another example, the electrodes may be formed from another relatively inert conductive material. For example, the electrodes may be made of a material that resists electrochemical oxidation to prolong the life of the screen  102 , such as lead or carbon. If the electrodes are made of a conductive material other than the printing metal, ions of the printing metal may be periodically replenished in the bath  114  as they are drawn out of the electrolyte  116 . In sum, the pattern of metal is printed from material obtained from one or both of the electrolyte  116  and the electrodes, one or both of which is referred to herein as printing the pattern of metal through the electrolyte  116 . In some implementations, the electrodes may be made of different metals across the screen  102 . In an implementation where the pattern of metal is printed from material obtained from the electrodes, electrodes made of different metals may enable the system  100  to print the metallic 3D structure with different metals in different regions of the metallic 3D structure. 
     In some implementations, the electrodes may be charged (or coated) with the printing metal before performing the disclosed screen electroplating process. For example, the electrodes may be charged by reversing the aforementioned process and making the electrodes the cathode and a source material the anode for charging. This charging process may be performed at regular intervals to replenish the printing metal coated on the electrodes. Further, a subset of the electrodes may be connected as cathodes to selectively charge the subset of electrodes to the exclusion of the remaining electrodes. Selective charging of a subset of electrodes may also allow for using different printing metals on different electrodes, which can later yield the printed metallic 3D structure made of different printing metals depending on which electrodes were used and their respective X-Y coordinates when performing the disclosed screen electroplating process. 
     Further, the electrolyte  116  may be replenished with printing metal using a 2-chamber process, where one chamber contains the porous screen  102  and the substrate  112  and a second chamber contains a charging material including the printing metal. The electrolyte  116  is then cycled through both of the chambers to continuously both deplete and recharge the printing metal within the electrolyte  116 . 
     The screen  102  may be made of any electrically insulating material effective at physically and electrically isolating the electrodes from one another. The substrate  112  is generally made of another inert conductive material suitable for receiving the printing metal and in some implementations, facilitating a later separation of the metallic 3D structure from the substrate  112  (e.g., lead or carbon). As mentioned above, the electrolyte  116  contains positive ions (or cations) of the printing metal. The cations are selectively reduced at the substrate  112  cathode to the metal in a zero-valence state depending on which of the electrodes are active. The printing metal may be a single metallic element or an alloy. While some alloys can be electrodeposited, (e.g., brass and solder), electrodeposited alloys are not true alloys (i.e., solid solutions), but rather discrete tiny crystals of the constituent metallic elements being deposited on the substrate  112 . In some implementations, it is desirable to have a true alloy rather than an as-deposited alloy if the true alloy has superior qualities (e.g., a true alloy of solder is more corrosion resistant than its as-plated alloy). To form a true alloy, the as-plated alloy may be melted together in a processing step subsequent to forming the metallic 3D structure using the system  100 . 
     As an example, electrodes  104 ,  106 ,  108 ,  110  are illustrated as active in  FIG. 1 . Arrows  118 ,  120 ,  122 ,  124  illustrate localized reductions of the cations through the electrolyte  116  on the substrate  112 , which results in localized deposits  126 ,  128 ,  130 ,  132  of the metal on the substrate  112 , respectively. Each of the localized deposits  126 ,  128 ,  130 ,  132  are caused by corresponding active electrodes  104 ,  106 ,  108 ,  110 , respectively. In sum and over time, the illustrated localized deposits  126 ,  128 ,  130 ,  132 , as well as additional localized deposits make up the metallic 3D structure. 
     As discussed above, the substrate  112  acts as a cathode and the individual electrodes selectively act as anodes, which when combined with current provided by the electroplating power supply  134 , forms an electrolytic cell. In the example depicted in  FIG. 1 , the substrate  112  and a negative lead from the electroplating power supply  134  are connected to a common ground  136 . A positive lead from the electroplating power supply  134  is connected to an electroplating power controller  138 . The electroplating power controller  138  is connected to each of the electrodes within the screen  102  and is capable of selecting which of the electrodes are active (or connected to the electroplating power supply  134 ) at any given moment in time. In the example of  FIG. 1 , the electrodes  104 ,  106 ,  108 ,  110  are made active by the electroplating power controller  138  by connecting the electrodes  104 ,  106 ,  108 ,  110  to the electroplating power supply  134  to the exclusion of the remaining electrodes in the screen  102 . In this manner of operation, the regularly spaced electrodes within the screen  102  may be considered a switched array. 
     The electroplating power controller  138  is controlled by a computing system  101 . The computing system  101  includes major subsystems such as a processor  105 , system storage  107  (such as random-access memory (RAM) and read-only memory (ROM)), an input/output (I/O) controller  109 , removable storage  123  (such as a memory card), a power supply  129 , and external devices such as a display screen  103  and an image projector  111 , and various input peripherals  113  (e.g., a mouse, trackpad, keyboard, stylus, and a touchscreen). Communication interfaces  125  (wireless and/or wired) may be used to interface the computing system  101  with the electroplating power controller  138 , a data storage network and/or a local or wide area network (such as the Internet) using any network interface system known to those skilled in the art. 
     Other devices or subsystems (not shown) may be connected in a similar manner to the electroplating power controller  138  (e.g., servers, personal computers, tablet computers, smart phones, mobile devices, etc.). It is also not necessary for all of the components of the computing system  101  depicted in  FIG. 1  to be present to practice the presently disclosed technology. Furthermore, devices and components thereof may be interconnected in different ways from that shown in  FIG. 1 . Code (e.g., computer software, including an operating system (e.g., operating system  140 ) and various applications (e.g., computer-aided design (CAD) application  142  and electroplating application  144 ) implement the presently disclosed technology and may be operably disposed in the system storage  107  and/or the removable storage  123 . 
     The operating system  140  controls numerous applications, including for example, the CAD application  142  (e.g., SolidWorks). The CAD application  142  may be used to generate a digital 3D model of the metallic 3D structure to be created. In some cases, the CAD application  142  is omitted from the operating system  140  and a file containing the digital 3D model is generated from a 3D scan of an object to be reproduced. The digital 3D model may also be otherwise obtained from an outside source. The digital 3D model is stored in a format usable for a 3D printing process, such as stereolithography file format (STL) or additive manufacturing file format (AMF). 
     The operating system  140  may further include an electroplating application  144 , which is used to instruct the electroplating power controller  138  which of the electrodes to activate (or be connected to the electroplating power supply  134 ) at any given moment in time. In an example implementation, the CAD application  142  and/or the electroplating application  144  operates as a “slicer” in dividing the digital 3D model of the metallic 3D structure to be into a series of 2D layers and may output a G-code file specific to the system  100 . The G-code file maps each of the 2D layers to the electrodes in the screen  102  and each of the electrodes are assigned an ON (active) or OFF (inactive) state for printing each 2D layer. The electroplating application  144  then instructs the electroplating power controller  138  via the communication interfaces  125  of the computing system  101  to set the appropriate electrodes assigned an ON state for a current 2D layer to be printed. 
     The electroplating application  144  may further define the duration that each of the electrodes assigned the ON state are to be active based on a desired height of the current 2D layer. The electroplating application  144  further loads subsequent 2D layers and outputs their assigned electrodes with an ON state to the electroplating power controller  138  to iteratively build the metallic 3D structure layer-by-layer. 
     In some implementations, the electroplating application  144  is capable of a non-binary use of the electrodes (e.g., the electroplating application  144  is capable of additional partially ON states between a completely OFF state and a completely ON state). For further example, the electroplating application  144  may be capable of applying different power levels to the electrodes, pulsing the electrodes at different frequencies at a given power level, and/or using a combination of power levels and frequencies to achieve the non-binary use of the electrodes. Non-binary use of the electrodes gives the electroplating application  144  additional control over rate of printing metal deposition, resolution, and accuracy as well as the structure and density of the printing metal deposited. In other words, non-binary use of the electrodes yields effects on printing rate and resolution as well as physical properties of the deposited printing metal. 
     In another example implementation, the electroplating application  144  utilizes the image projector  111  to project an image of a current to-be-printed 2D layer onto the screen  102 , as illustrated by arrow  146 . Here, each of the electrodes (or commonly controlled groupings of electrodes) are equipped with a photosensor that defines their ON/OFF state. The projected image then controls the ON/OFF state of the electrodes in place of the electroplating power controller  138 . 
     The computing system  101  may include a variety of tangible computer-readable storage media (e.g., the system storage  107  and/or the removable storage  123 ) and intangible computer-readable communication signals. Tangible computer-readable storage can be embodied by any available media that can be accessed by the computing system  101  and includes both volatile and non-volatile storage media, as well as removable and non-removable storage media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules, and/or other data. Tangible computer-readable storage media includes, but is not limited to, firmware, RAM, ROM, electrically erasable programmable read-only memory (EEPROM), flash or other memory technology, optical disc storage, magnetic cassettes, magnetic tape, magnetic disc storage or other magnetic storage devices, and any other tangible medium which can be used to store information, and which can be accessed by the computing system  101 . 
     Intangible computer-readable communication signals may embody computer readable instructions, data structures, program modules, or other data resident in a modulated data signal, such as a carrier wave or other signal transport mechanism. A “modulated data signal” is a signal that has one or more of its characteristics set or changed in such a manner as to encode information within the signal. By way of example, and not limitation, intangible communication signals include signals traveling through wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, radio frequency (RF), infrared (IR), and other wireless media. Computer-readable storage media as defined herein specifically excludes intangible computer-readable communications signals. 
     Some implementations may comprise an article of manufacture which may comprise a tangible storage medium to store logic. Examples of a storage medium may include one or more types of computer-readable storage media capable of storing electronic data, including volatile memory or non-volatile memory, removable or non-removable memory, erasable or non-erasable memory, writeable or re-writeable memory, and so forth. Examples of the logic may include various software elements, such as software components, programs, applications, computer programs, application programs, system programs, machine programs, operating system software, middleware, firmware, software modules, routines, subroutines, operation segments, methods, procedures, software interfaces, application program interfaces (APIs), instruction sets, computing code, computer code, code segments, computer code segments, words, values, symbols, or any combination thereof. In one implementation, for example, an article of manufacture may store executable computer program instructions that, when executed by a computer, cause the computer to perform methods and/or operations in accordance with the described implementations. The executable computer program instructions may include any suitable type of code, such as source code, compiled code, interpreted code, executable code, static code, dynamic code, and the like. The executable computer program instructions may be implemented according to a predefined computer language, manner or syntax, for instructing a computer to perform a certain operation segment. The instructions may be implemented using any suitable high-level, low-level, object-oriented, visual, compiled and/or interpreted programming language. 
     The metallic 3D structure to be created may be of any shape, size, and purpose. For example, the metallic 3D structure may be printed on a circuit board substrate to create a printed circuit board (PCB) (e.g., a nickel 3D structure printed on a copper circuit board substrate). The PCB also may be of phenolic paper, fiberglass, aluminum, or a flexible foil substrate, for example. In some implementations, an adhesion and/or conduction promoter is applied on the substrate prior to printing metallic 3D structure on the substrate  112 . For example, a conductive paint may be coated on the substrate  112  and then the metallic 3D structure is applied over the painted substrate  112 . More specifically, the substrate  112  could be first printed with an adhesion and/or conduction promoting ink and then the metallic 3D structure is printed above the adhesion and/or conduction promoting ink. 
     The metallic 3D structure may further be a flexible cable, a component of a micro-electromechanical system (MEMS), or a micro-structural component (e.g., honeycomb, webbing, etc.), for example. The metallic 3D structure may further be a solid structure printed with air gaps to reduce density (a printed foam, e.g., with 70-80% solid content). Still further, the metallic 3D structure may be intended to be separated from the substrate  112  once the metallic 3D structure is complete, or conversely may be intended to remain a permanent fixture on the substrate  112 . 
     A lower limit on overall size (and discrete feature reproduction) of the metallic 3D structure is defined in part by the screen  102  resolution. Akin to pixel resolution in digital imaging, the number of electrodes within the screen, spacing between the individual electrodes, and their associated printing area in part defines the electrode resolution of the system  100 . Layer thickness further defines the electrode resolution of the system  100 . X-Y (planar) resolution may be expressed in dots per inch (DPI) or micrometers (μm) and layer thickness (Z-direction) may be expressed in micrometers (μm). In an example implementation, a minimum Z-direction layer thickness is approximately (+/−10%) 2 μm (1,600 DPI). Further, X-Y resolution of the screen  102  may be 50 to 100 μm (510 to 250 DPI). In one example implementation, the system  100  may be capable of printing variable thicknesses (e.g., 2 μm-10 μm layers) of metal on the substrate  102  as the metallic 3D structure is printed, as defined by the electroplating application  144 . 
     In a further example implementation, the electrodes within the screen  102  may be nanopores (i.e., pores having a diameter less than 20 nm) in scale. Nanopore electrodes theoretically have an extremely high X-Y (planar) resolution, however, the nanopore electrodes may not be individually switched between ON (active) or OFF (inactive) states for printing. In this case, groupings of nanopore electrodes within an area are switched, thus the switched area defines the X-Y (planar) resolution of the nanopore electrode screen  102 . Further, electrodes of a larger scale than the nanopore electrodes may also be arranged in groupings. In both cases, selectively activating a subset of the electrodes includes activating one or more of the switched electrode groupings rather than the individual electrodes. 
     In a still further implementation, the screen  102  is substantially smaller than the substrate  112  and the metallic 3D structure to be printed thereon. As a result, the screen  102  is moved laterally (within the X-Y plane) to an area of the substrate  112  to be printed using a movement controller  148  while the substrate  112  remains in a fixed position. In an example implementation, the screen  102  is repeatedly reoriented in the X-Y plane to fully cover an area to be occupied by the metallic 3D structure to be printed. In another implementation, the screen  102  is sufficiently large in one of the X-direction and the Y-direction and the screen  102  is only reoriented in the other of the X-direction and the Y-direction to fully cover an area to be occupied by the metallic 3D structure to be printed. For example, the screen  102  may cover several full rows (X-direction) of printing capacity and the movement controller  148  moves the screen  102  up/down columns (Y-direction) only to fully cover an area to be occupied by the metallic 3D structure to be printed. In various implementations, the substrate  112  is instead moved while the screen  102  remains in a fixed position or both the substrate  112  and the screen  102  are moveable to achieve the foregoing. 
     In various implementations, one or both of the screen  102  and the substrate  112  may be moved in the Z-direction to achieve and maintain a desired screen  102 /substrate  112  spacing for electrodeposition (e.g., 5-15 millimeters), which is referred to herein as close proximity. Movement of one or both of the substrate  112  and the screen  102  in one or more of the X-direction, Y-direction, and/or Z-direction using the movement controller  148  is referred to herein as re-orienting the screen above an area of the substrate  112  to the printed. Movement exclusively in the X-Y plane is referred to herein as laterally re-orienting the screen  102 . 
       FIG. 2A  illustrates an example pair of electrodes  204 ,  206  within a screen  202 , each in an OFF (or inactive) state. The electrodes  204 ,  206  are an example two of an array of two or more regularly spaced electrodes oriented in and filling respective pores within the screen  202 . The screen  202  is arranged parallel and in close proximity to a solid substrate  212  onto which a metallic 3D structure is to be created. At least a side of the screen  202  facing the substrate  212 , as well as a side of the substrate  212  facing the screen  202  are submerged in a bath containing an electrolyte  216 , which includes a salt of a metal to be coated on the substrate  212  (referred to herein as a printing metal). 
     In operation, the substrate  212  acts as a cathode (or negative electrode) and the electrodes  204 ,  206  selectively act as anodes (or positive electrodes), which when combined with current provided by an electroplating power supply (not shown, see e.g., electroplating power supply  134  of  FIG. 1 ), forms an electrolytic cell for printing metal and/or ionic compounds on the substrate  212 . More specifically, the substrate  212  and a negative lead from the electroplating power supply are connected to a common ground  236 . A positive lead from the electroplating power supply is connected to an electroplating power controller (illustrated in  FIG. 2A-C  as circuits  250 ,  252 ). The electroplating power controller is connected to each of the electrodes  204 ,  206  and is capable of selecting which of the electrodes  204 ,  206  are active (illustrated as circuits  250 ,  252  moved from an OPEN state to a CLOSED state) at any given moment in time. As both circuits  250 ,  252  are illustrated in an OPEN state in  FIG. 2A , each corresponding one of the electrodes  204 ,  206  is in an OFF (or inactive) state. 
       FIG. 2B  illustrates the example pair of electrodes  204 ,  206  of  FIG. 2A , with electrode  206  in an OFF (or inactive) state and electrode  204  in an ON (or active) state. As circuit  250  is illustrated in a CLOSED state in  FIG. 2B , the corresponding ON electrode  204  is illustrated as actively printing metal on the substrate  212 .  FIG. 2C  illustrates the example pair of electrodes  204 ,  206  of  FIG. 2A , with both of the electrodes  204 ,  206  in an ON (or active) state. As both circuits  250 ,  252  are illustrated in a CLOSED state in  FIG. 2C , both ON electrodes  204 ,  206  are illustrated as actively printing metal on the substrate  212 . 
     The substrate  212  is generally made of an inert conductive material suitable for receiving the printing metal. The electrolyte  216  contains cations  256  (illustrate as “+”s) of the printing metal. The cations  256  are selectively reduced at the substrate  212  cathode to the metal in a zero-valence state below the ON electrode(s). A pattern of metal  254  is printed from material obtained from one or both of the electrolyte  216  and the ON electrode(s), one or both of which is referred to herein as printing the pattern of metal  254  through the electrolyte  216 . In sum and over time, multiple layers of the printed pattern of metal  254  on top of one another becomes the metallic 3D structure. 
     The electrode  204  is illustrated in  FIGS. 2A-2C  as a solid pin shaped electrode that fills a pore in the screen  202 . In various implementations, to increase the surface area of electrode  204  in contact with the electrolyte  216 , the electrode  204  may include a dimple  266  or other projection that extends below the screen  202 , as an example. The electrode  206  is illustrated in  FIGS. 2A-2C  as a closed cylindrical liner of a pore in the screen  202 . The electrolyte  216  fills an interior of the electrode  206  and the closed cylindrical liner shape provides more surface area of the electrode  206  in contact with the electrolyte  216  as compared to a similarly sized and shaped solid pin shaped electrode, such as the electrode  204 . 
     In various implementations, to further increase the surface area of electrode  206  in contact with the electrolyte  216 , a central pin  264  may extend through the middle of the electrode  206 , as an example. In various implementations, the central pin  264  may also provide recharge metal for the electrolyte  216 . Any combination of features to increase surface area of the electrodes in contact with the electrolyte  216  may be used as the increased surface area generally lowers current density applied at each electrode, which in turn reduces power demand on the electroplating power supply. 
       FIG. 3  illustrates an example pair of electrodes  304 ,  306  within a porous screen  302 , the electrodes  304 , each having venting through-holes  358 ,  360 , respectively. The electrodes  304 ,  306  are an example two of an array of two or more regularly spaced electrodes oriented in and filling respective pores within the screen  302 . The screen  302  is arranged parallel and in close proximity to a solid substrate  312  onto which a metallic 3D structure is to be created. At least a side of the screen  302  facing the substrate  312 , as well as a side of the substrate  312  facing the screen  302  are submerged in a bath containing an electrolyte  316 , which includes a salt of a metal to be coated on the substrate  312  (referred to herein as a printing metal). 
     In operation, the substrate  312  acts as a cathode (or negative electrode) and the electrodes  304 ,  206  selectively act as anodes (or positive electrodes), which when combined with current provided by an electroplating power supply (not shown, see e.g., electroplating power supply  134  of  FIG. 1 ), forms an electrolytic cell for printing metal on the substrate  312 . More specifically, the substrate  312  and a negative lead from the electroplating power supply are connected to a common ground  336 . A positive lead from the electroplating power supply is connected to an electroplating power controller (illustrated as circuits  350 ,  352 ). The electroplating power controller is connected to each of the electrodes  304 ,  306  and is capable of selecting which of the electrodes  304 ,  306  are active at any given moment in time. As both circuits  350 ,  352  are illustrated in a CLOSED state in  FIG. 3 , both ON electrodes  304 ,  306  are illustrated as actively printing metal on the substrate  312 . 
     The substrate  312  is generally made of an inert conductive material, with or without an adhesion and/or conduction promoting coating, suitable for receiving the printing metal. The electrolyte  316  contains cations  356  (illustrate as “+”s) of the printing metal. The cations  356  are selectively reduced at the substrate  312  cathode to the metal in a zero-valence state below the ON electrodes  304 ,  306 . A pattern of metal  354  is printed from material obtained from one or both of the electrolyte  316  and the electrode  304 , one or both of which is referred to herein as printing the pattern of metal  354  through the electrolyte  316 . In sum and over time, multiple layers of the printed pattern of metal  354  on top of one another becomes the metallic 3D structure. 
     The electrodes  304 ,  306  are illustrated in  FIG. 3  as open cylindrical liners of pores in the screen  302 . Accordingly, gasses generated within the electrolyte  316  may be vented through the screen  302  by venting through the through-holes  358 ,  360 , as illustrated by the depicted bubbles (e.g., bubble  362 ). The cylindrical liner shaped electrodes  304 ,  306  further provide more surface area of the electrodes  304 ,  306  in contact with the electrolyte  316  as compared to a similarly sized and shaped solid pin shaped electrode. 
     In some implementations, the electrolyte bath is individually applied at each of the active electrodes rather than existing between all electrodes and the substrate  312  at all times. When an electrode is activated, the electrolyte  316  may be pumped through a through-hole in the electrode while the electrode is active. The electrolyte  316  may then be shut off from the electrode when the electrode is de-activated. In some implementations, selectively permitting flow of the electrolyte  316  (e.g., via valves connected to the electrodes) may be used to selectively activate the electrodes instead of or in additional to using selective application of power to the electrodes to selectively activate the electrodes. 
       FIG. 4  illustrates example operations  400  for manufacturing a metallic 3D structure using a selective screen electroplating process. A dividing operation  405  divides a digital 3D model of a metallic structure into a series of 2D layers of the digital 3D model. The 3D model of a metallic structure may be obtained from a CAD drawing or a 3D scan of an object to be reproduced, for example. An outputting operation  410  outputs the series of 2D layers to an electroplating power controller sequentially. The electroplating power controller controls which electrodes within a switched array are selectively activated to print each of the series of 2D layers. 
     An orienting operation  415  orients a switched array of regularly spaced electrodes occupying pores within a screen parallel to and in close proximity to a substrate within an electrolyte bath. The orienting operation  415  may be achieved by moving one or both of the screen and the substrate in X, Y, and/or Z coordinate directions until the placement of the screen with respect to the substrate is correct for accurately applying a 2D layer of electroplating to the substrate. A selectively activating operation  420  selectively activates a subset of the electrodes to print a pattern of metal through the electrolyte bath on the substrate. The selectively activating operation  420  is a selective electroplating operation. The selectively activating operation  420  continues until a desired thickness of the 2D layer is achieved. As discussed above, the selectively activating operation  420  may apply printing metal to the entire substrate at once, or one or more lines of pixels of material at a time depending on the X-Y size of the selective screen as compared to the X-Y size of the metallic structure to be printed. 
     A decision operation  425  determines if additional 2D layers are required to complete the metallic 3D structure. If so, the orienting operation  415  repeats to re-orient the screen with respect to the substrate in X, Y, and/or Z coordinate directions until the placement of the screen with respect to the substrate is correct for accurately applying the next 2D layer of electroplating to the substrate. The selectively activating operation  420  repeats as well to selectively activate a potentially different subset of the electrodes to print a potentially different pattern of metal on the substrate. The decision operation  425  then repeats to determine if additional 2D layers are required to complete the metallic 3D structure. This process is iterated until all 2D layers making up the 3D model of the metallic structure have been electroplated on the substrate. Once no additional 2D layers are required, the metallic 3D structure is complete  430 . 
     The presently disclosed technology may be implemented as logical steps in one or more computer systems (e.g., as a sequence of processor-implemented steps executing in one or more computer systems and as interconnected machine or circuit modules within one or more computer systems). The implementation is a matter of choice, dependent on the performance requirements of the computer system implementing the presently disclosed technology. Accordingly, the logical operations making up implementations of the presently disclosed technology are referred to variously as operations, steps, objects, or modules. Furthermore, it should be understood that logical operations may be performed in any order, adding or replacing operations as desired, unless explicitly claimed otherwise or a specific order is inherently necessitated by the claim language. 
     The above specification, examples, and data provide a complete description of the structure and use of exemplary embodiments of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended. Furthermore, structural features of the different embodiments may be combined in yet another embodiment without departing from the recited claims.