System and method for manufacture of circuit boards

Methods, systems, and apparatus for fabricating a circuit board. The method includes fabricating, using an additive manufacturing device, a trace layer, a sacrificial layer, a rail layer and a lid. The method includes placing the sacrificial layer on the trace layer such that the raised traces protrude through corresponding openings of the sacrificial layer. The method includes depositing a conductive material on top of the sacrificial layer and the plurality of traces. The method includes removing the sacrificial layer from the trace layer and placing the rail layer on the trace layer such that the raised traces align with the corresponding openings of the rail layer. The method includes connecting one or more electrical components and melting a sealing sheet on top of the rail layer and the electrical components to reinforce connections and to provide protection. The method includes placing the lid on top of the sealing sheet.

BACKGROUND

This specification relates to systems and methods for manufacturing circuit boards.

2. Description of the Related Art

The current state of the art for fabricating printed circuit boards (PCBs) includes the mechanical milling of copper circuit boards and the soldering of electronic components into place. The copper board consists of a copper sheet laminated onto an electrically insulating fiber resin or glass requiring powerful presses, rolling equipment, and potentially toxic substances such as epoxies. A milling machine employing a selection of drill bits isolates the wire traces by removing copper on the surface. Oftentimes, during this milling process, expensive drill bits are broken or worn down, or the traces do not have the proper width or other parameters. Alternatively, laser etching may be used; however, there is a high cost to obtain a laser cutter that is capable of cutting through the metal layers. Laser cutting creates concerns about eye safety and generated vapors. Wet and dry chemical etching also poses a safety threat. Working with hazardous chemicals such as ferric chloride, ferric nitrate, and hydrochloric acids can be detrimental to human health if handled incorrectly. Afterwards, final processing steps include placing solder-paste through a stencil with the pads cut out, placing components on the solder-pasted pads, and then using a reflow oven or another direct application of heat to melt the feet of the components onto the traces. Labeling and isolation is further achieved by adding additional polymer layers onto the surface.

For using the PCB in underwater sensing, the PCB is potted in an epoxy, resin, or thermo/photo-setting polymer. Adhesive problems lead to breakage of such seals over time resulting in water intrusion and destruction of the sensing circuitry. Furthermore, there are concerns about the toxicity that PCBs pose on the environment. The length and expense of the milling process makes iterating circuit designs a time-consuming process and unsatisfactory for rapid prototyping.

Fabricating multilayer circuits is a complex process involving many steps. First, the circuit design is transferred to the board, possibly using ultraviolet (UV) light polymerization. Next, the inner layers need to be etched using chemicals such as copper chloride and ferric chloride. The lamination process involves applying an oxide layer to each layer and then stacking the layers together at a certain temperature and pressure. Holes are then drilled and copper plated to form connections between the layers. This is followed by preparing the via holes using solder mask ink or epoxy resin and a stencil. Finally solder mask ink is applied to the board and exposed areas are cured with UV light. The covered parts have the ink removed in a chemical process. Finally, the board surface is finished with materials such as electroless nickel immersion gold and tested for performance. This method for fabricating multilayer PCBs requires expensive specialized equipment and toxic materials.

SUMMARY

What is described is a method for fabricating a circuit board. The method includes fabricating, using an additive manufacturing device, a trace layer, a sacrificial layer, a rail layer and a lid. The trace layer has a plurality of raised traces, the sacrificial layer has a plurality of openings corresponding to the plurality of raised traces of the trace layer, and the rail layer has a plurality of openings corresponding to the plurality of raised traces of the trace layer and one or more recesses for receiving electrical components. The method also includes placing the sacrificial layer on top of the trace layer such that the plurality of raised traces of the trace layer align with the corresponding plurality of openings of the sacrificial layer and protrude through the corresponding plurality of openings of the sacrificial layer. The method also includes depositing a conductive material on top of the sacrificial layer and the plurality of traces of the trace layer. The method also includes removing the sacrificial layer from the trace layer. The method also includes placing the rail layer on top of the trace layer such that the plurality of raised traces of the trace layer align with the corresponding plurality of openings of the rail layer. The method also includes connecting one or more electrical components to be in electrical communication with the conductive material by placing the electrical components in the respective one or more recesses of the rail layer. The method also includes melting a sealing sheet on top of the rail layer and the electrical components to reinforce connections between the electrical components and the conductive material and to provide elemental protection. The method also includes placing the lid on top of the sealing sheet while the sealing sheet is warm, the lid configured to reinforce connections between the electrical components and the conductive material and to provide elemental protection.

Also described is a method for fabricating a multilayer circuit board. The method includes fabricating, using an additive manufacturing device, a first trace layer, a second trace layer, a sacrificial layer, a rail layer, and a lid. The first trace layer has a plurality of vias, the second trace layer has a plurality of raised traces and a plurality of openings corresponding to the plurality of vias, the sacrificial layer has a plurality of openings corresponding to the plurality of raised traces of the second trace layer, and the rail layer has a plurality of openings corresponding to the plurality of raised traces of the second trace layer and one or more recesses for receiving electrical components. The method also includes depositing a conductive material onto at least a portion of the first trace layer, including the plurality of vias. The method also includes placing the sacrificial layer on top of the second trace layer such that the plurality of raised traces of the second trace layer align with the corresponding plurality of openings of the sacrificial layer and protrude through the corresponding plurality of openings of the sacrificial layer. The method also includes depositing the conductive material onto the sacrificial layer and the plurality of traces of the second trace layer. The method also includes removing the sacrificial layer from the second trace layer. The method also includes placing the second trace layer on top of the first trace layer such that the plurality of vias of the first trace layer align with and protrude from the corresponding plurality of openings of the second trace layer. The method also includes placing the rail layer on top of the second trace layer such that the plurality of raised traces of the second trace layer align with the corresponding plurality of openings of the rail layer. The method also includes connecting one or more electrical components to be in electrical communication with the conductive material by placing the electrical components in the respective one or more recesses of the rail layer. The method also includes melting a sealing sheet on top of the rail layer and the electrical components to reinforce connections between the electrical components and the conductive material and to provide elemental protection. The method also includes placing the lid on top of the sealing sheet while the sealing sheet is warm, the lid configured to reinforce connections between the electrical components and the conductive material and to provide elemental protection.

Also described is a method for fabricating a circuit board. The method includes fabricating, using an additive manufacturing device, a trace layer, a gap layer onto the trace layer, and a sacrificial layer onto the gap layer, the gap layer being printed above the trace layer and not directly onto the trace layer such that extruded filament from the additive manufacturing device cools before touching the trace layer and creating a non-permanent bond to the trace layer. The method also includes fabricating, using the additive manufacturing device, a rail layer. The method also includes depositing a conductive material on top of the sacrificial layer and a plurality of traces of the trace layer. The method also includes breaking the non-permanent bond established by the gap layer to remove the sacrificial layer from the trace layer. The method also includes placing the rail layer on top of the trace layer such that the plurality of raised traces of the trace layer align with a corresponding plurality of openings of the rail layer.

DETAILED DESCRIPTION

The novelty of the systems and methods described herein is a completely different additive approach to creating printed circuit boards (PCBs) than conventional methods. The materials are not wasted, as the plastic and liquid metal can be re-melted and used again. Furthermore, the sacrificial layer can be reused given that it is not damaged in the removal process. The materials used, plastic and liquid metal, are completely non-toxic, unlike traditional PCB fabrication methods. This increases the applications that PCBs can be used. For example, PCBs made through the systems and methods described herein can be used in water that people and animals drink.

The systems and methods described herein have significantly lower costs associated with manufacture of circuit boards and can be done in-house and by amateurs. To make a PCB through the systems and methods described herein, a 3D printer, filaments, and liquid metal (e.g., tin and gallium) are required. 3D printers can be purchased for under $1,000 and the plastic filaments arrive in large spools for typically less than $25. The driving cost for this method is the liquid metal (e.g., gallium). However, as will be described herein. the traces that are printed are thin, and this allows for a small amount of liquid metal to create many traces. The biggest potential waste for the liquid metal is the liquid metal that is disposed on the sacrificial layer during fabrication. However, the liquid metal may be removed from the sacrificial layer and used again. In some embodiments, the sacrificial layer covered in liquid metal may be submerged in a solution (e.g., NaOH), and the liquid metal may be rinsed off of the sacrificial layer.

As the systems and methods described herein use additive manufacturing, which may be referred to as “printing,” the resulting circuit boards are true “printed circuit boards.”

The systems and methods described herein design and fabricate at least three parts for each printed circuit board—the trace, the sacrificial layer, and the rail layer. In addition, a lid may be fabricated, which may be used to create a more robust package and a higher yield of functioning. A computer aided design (CAD) software such as SketchUp™ by Trimble, Inc. is used to design the traces, sacrificial layers, and rail layers.

FIGS. 1A-1Lillustrate the various components and assemblies of components that result in a circuit board using the systems and methods described herein.

FIG. 1Aillustrates a trace layer102. The trace layer102has a plurality of raised traces104. Between the raised traces104are valleys105. Any of the trace layers, sacrificial layers, rail layers, lids, or any other circuit board component described herein may be manufactured using additive manufacturing. In some embodiments, a 3D printer, such as a MakerGear™ M2 3D printer, is used. The 3D printer may include a nozzle and a reservoir of material. For example, a 0.25 mm nozzle and 1.75 mm polyethylene terephthalate glycol (PETG) may be dispensed by the 3D printer at a 0.1 mm height increment. The printer filament type and nozzle head size may be varied to achieve greater detail and robustness of a design. PETG is not conductive, inexpensive, and capable of being extruded to the level of detail needed to print the board pieces. While 3D printing is described herein, any additive manufacturing process may be used, including vat polymerization, powder bed fusion, binder jetting, material jetting, sheet lamination, material extrusion, directed energy deposition, or a combination of laser material deposition and CNC machining. The additive manufacturing process may use materials that are non-toxic and/or materials that may be reused.

FIG. 1Billustrates a sacrificial layer106. The sacrificial layer106has a plurality of openings108that correspond to the shape of the traces104of the trace layer102. The sacrificial layer106is configured to be placed on top of the trace layer102such that the traces104of the trace layer102protrude from the openings108of the sacrificial layer106. In this way, the sacrificial layer106is a stencil for the trace layer102. The sacrificial layer106may be manufactured using additive manufacturing, similar to the trace layer102.

FIG. 1Cillustrates a rail layer110. The rail layer110also includes a plurality of openings112that correspond to the shape of the traces104of the trace layer102. The rail layer110is also configured to be placed on top of the trace layer102such that the traces104of the trace layer102protrude from the openings112of the rail layer110. The rail layer110may be manufactured using additive manufacturing, similar to the trace layer102and the sacrificial layer106.

FIG. 1Dillustrates a bottom side of a lid114, which may be placed on top of the circuit board to protect the circuit board. The bottom side of the lid114may include recesses115configured to receive electrical components placed on the circuit board. The bottom side of the lid114may also include protrusions117configured to contact electrical components that are located deeper within the circuit board.

FIG. 1Eillustrates the sacrificial layer106placed on top of the trace layer102. The traces104of the trace layer102protrude from the openings108of the sacrificial layer106. Thus, the traces104of the trace layer102are exposed, while the valleys105of the trace layer102are covered by the sacrificial layer106. In some embodiments, the sacrificial layer106and the trace layer102have corresponding features that allow the sacrificial layer106to securely fasten (or snap) to the trace layer102such that vertical and/or horizontal movement of the sacrificial layer106relative to the trace layer102is limited.

FIG. 1Fillustrates a conductive material116brushed onto the sacrificial layer106that is on top of the trace layer102. Thus, the conductive material116is disposed on top of the sacrificial layer106and the traces104of the trace layer102. The conductive material116may be a liquid metal, such as liquid tin or gallium. In some embodiments, the ratio of gallium to tin is 2:1.

FIG. 1Gillustrates the trace layer102after the sacrificial layer106has been removed. The trace layer102has conductive material116covering the traces104, but not the valleys105. The sacrificial layer106ensures that the conductive material116covers only the traces104. The conductive material116remains on the traces104due to surface tension. As the sacrificial layer106is rigid, the removal of the sacrificial layer106from the top of the trace layer102is simple and clean. The sacrificial layer106may be reused in subsequent fabrications of subsequent circuit boards. In some embodiments, the conductive material is removed from the sacrificial layer106and the sacrificial layer106is melted and then placed into a reservoir of additive manufacturing material for later use. In this way, the systems and methods described herein are more sustainable than conventional fabrication methods, as components may be reused.

FIG. 1Hillustrates the rail layer110placed on top of the trace layer102. The openings112of the rail layer110allow the traces104covered with the conductive material116to be exposed. Thus, the rail layer110serves as a filler for the valleys105of the trace layer102. As will be shown inFIGS. 2A-2L, the rail layer110is configured to support insertion of pin headers. In some embodiments, the rail layer110and the trace layer102have corresponding features that allow the rail layer110to securely fasten (or snap) to the trace layer102such that vertical and/or horizontal movement of the rail layer110relative to the trace layer102is limited. The rail layer110also has recessed cavities111for electronic surface mount components to be placed on the traces, as well as pin holders that align with the pin holders of the trace layer.

FIG. 1Iillustrates pin headers118and electrical components120, such as transistors, inserted and connected to the circuit board100. The dimensions of the pin holders are designed so that the pin headers fit tightly. The pin headers have the added benefit of keeping the trace and rail layers together. Surface mounted elements can be easily placed in the recessed cavities111of the rail layer110to form a complete circuit. While pin headers are shown herein, in some embodiments, a female header or header connector configured to receive a male pin may be attached to the circuit board100instead. In these embodiments, one end of a male pin is connected to the conductive material covered traces and the other end of the male pin protrudes out of the circuit board100and may be received by a female header.

FIG. 1Jillustrates placement of a sealing sheet122on top of the circuit board100. The sealing sheet122may be made of the same material that the trace layer102, the sacrificial layer106and/or the rail layer110is made of. In other embodiments, the sealing sheet122is made of a material that is different from the trace layer102, the sacrificial layer106and/or the rail layer110. In some embodiments, the sealing sheet122is made of polycaprolactone (PCL).

FIG. 1Killustrates the resulting circuit board100after the sealing sheet122is heated. When the sealing sheet122is heated, the sealing sheet122covers and molds to the features of the circuit board100. The sealing sheet122also provides downward force on the components to ensure they are secured. In some embodiments, the sealing sheet122is larger than the dimensions of the circuit board100, such that an overhang of the sealing sheet122molds with the pin headers118, further keeping the pin headers118in place.

If a waterproof design is required, a second sealing sheet can be applied to the back of the board, covering all crevices. A thermoplastic with a higher melting point can be used in place of PCL to accommodate circuits that generate more heat.

FIG. 1Lillustrates the placement of the lid114on top of the circuit board100and covering the circuit board100. When the lid114is placed on top of the circuit board100and pressed down while the sealing sheet122remains warm, the lid114may form an additional seal over the circuit board100, protecting the components of the circuit board100from debris and/or liquid. The lid114may bond with the sealing sheet122. The lid114may also provide a downward force on the electrical components120to maintain reliable and consistent contacts with the conductive material116. The lid114may account for the electrical components120by including corresponding recesses on a bottom surface of the lid114to receive the electrical components120and/or protrusions on the bottom surface of the lid114to contact electrical components located deeper (or lower) in the circuit board.

FIGS. 2A-2Lillustrate side cross-sectional views of the circuit board100corresponding to the views shown inFIGS. 1A-1L. The number measurements illustrated inFIGS. 2A-2Lare illustrative of a particular embodiment created using the systems and methods described herein and are not limiting.

FIG. 2Aillustrates a side cross-sectional view of the trace layer102with a plurality of raised traces104. The traces104are elevated paths on which the liquid metal rests. Between the raised traces104are valleys105. Also shown are pin header holders202which are located on the sides of the circuit board. The pin header holders202are hollow channels that align with the metal traces. They guide the pin headers to the metal traces to form a secure contact during the final assembly.

FIG. 2Billustrates a side cross-sectional view of the sacrificial layer106. The sacrificial layer106has a plurality of openings108that correspond to the shape of the traces104of the trace layer102. The sacrificial layer106is configured to be placed on top of the trace layer102such that the traces104of the trace layer102protrude from the openings108of the sacrificial layer106. The sacrificial layer106may be manufactured using additive manufacturing, similar to the trace layer102.

FIG. 2Cillustrates a side cross-sectional view of the rail layer110. The rail layer110also includes a plurality of openings112that correspond to the shape of the traces104of the trace layer102. The rail layer110is also configured to be placed on top of the trace layer102such that the traces104of the trace layer102protrude from the openings112of the rail layer110. The rail layer110may be manufactured using additive manufacturing, similar to the trace layer102and the sacrificial layer106. While the sacrificial layer106and the rail layer110appear similar from the perspective views ofFIGS. 1B and 1C, the side cross-sectional views show that the rail layer110is thicker than the sacrificial layer106and also include pin header openings203for receiving pin headers.

FIG. 2Dillustrates a side cross-sectional view of the lid114, which may be placed on top of the circuit board to protect the circuit board. As described herein, the lid114may include recesses115and protrusions117.

FIG. 2Eillustrates a side cross-sectional view of the sacrificial layer106placed on top of the trace layer102. The traces104of the trace layer102protrude from the openings108of the sacrificial layer106. Thus, the traces104of the trace layer102are exposed, while the valleys105of the trace layer102are covered by the sacrificial layer106.

FIG. 2Fillustrates a side cross-sectional view of the conductive material116brushed onto the sacrificial layer106that is on top of the trace layer102. Thus, the conductive material116is disposed on top of the sacrificial layer106and the traces104of the trace layer102.

FIG. 2Gillustrates a side cross-sectional view of the trace layer102after the sacrificial layer106has been removed. The trace layer102has conductive material116covering the traces104, but not the valleys105.

FIG. 2Hillustrates a side cross-sectional view of the rail layer110placed on top of the trace layer102. The openings112of the rail layer110allow the traces104covered with the conductive material116to be exposed. Thus, the rail layer110serves as a filler for the valleys105of the trace layer102. The openings203of the rail layer110line up with the openings202of the trace layer102, forming pin header openings204.

FIG. 2Iillustrates a side cross-sectional view of pin headers118and electrical components120, such as transistors, inserted and connected to the circuit board100. The electrical components120are in electrical communication with the conductive material116covering the traces104. The conductive material116covering the traces104are also in electrical communication with the pins206of the pin headers118. The pins206of the pin headers118are received by the pin header openings204.

FIG. 2Jillustrates a side cross-sectional view of the placement of a sealing sheet122on top of the circuit board100.

FIG. 2Killustrates a side cross-sectional view of the resulting circuit board100after the sealing sheet122is heated. When the sealing sheet122is heated, the sealing sheet122covers and molds to the features of the circuit board100.

FIG. 2Lillustrates a side cross-sectional view of the placement of the lid114on top of the circuit board100and covering the circuit board100. The lid114and the sealing sheet122protect the circuit board100and provide additional pressure and stability to maintain the connections in the circuit board100.

In addition to the single-layer circuit board illustrated inFIGS. 1A-1L and 2A-2L, multilayer circuit boards may also be fabricated using the systems and methods described herein. The multiple layers of the multilayer circuit boards are connected using vias. The vias used in the systems and methods described herein are equivalent to traditional PCB vias.

FIGS. 3A-3OandFIGS. 4A-4Lillustrate a process of fabricating a multilayer circuit board using the systems and methods described herein. In a similar manner as described herein with respect to the trace layer102, the sacrificial layer106, the rail layer110, and the lid114, a first trace layer302(shown inFIG. 3A), a second trace layer306(shown inFIG. 3B), a sacrificial layer310(shown inFIG. 3C), a rail layer314(shown inFIG. 3D), and a lid318(shown inFIG. 3E) are fabricated using additive manufacturing.

As illustrated inFIG. 3A, the first trace layer302has a plurality of vias304and valleys305. As illustrated inFIG. 3B, the second trace layer306also has a plurality of traces308and a plurality of valleys309, similar to trace layer102. The second trace layer306also includes openings307to receive the vias304of the first trace layer302. The vias304will connect the first trace layer302with the second trace layer306.

As illustrated inFIG. 3C, the sacrificial layer310has a plurality of openings312that correspond to the shape of the traces308of the second trace layer306. In some embodiments, an additional sacrificial layer may be fabricated and used that has openings that correspond to the vias304of first trace layer302. This will be shown inFIGS. 4B-4C.

As illustrated inFIG. 3D, the rail layer314has a plurality of openings316. The rail layer314will be placed on top of the second trace layer306, which will be placed on top of the first trace layer302. Accordingly, the openings316of the rail layer314correspond to the shape of the traces formed when the second trace layer306and the first trace layer302are combined. The rail layer314includes cavities315configured to receive electrical components.

FIG. 3Eillustrates the lid318. If the electrical components form recessed cavities with the rail layer314, the lid portion above the components will need to protrude out to fill the empty space and securely press the components onto the traces.

FIG. 3Fillustrates a conductive material320brushed onto the first trace layer302. In the example shown inFIGS. 3A-3O, the design is such that the first trace layer302serves as a ground plane and may have the conductive material320covering both the vias304and the valleys305of the first trace layer302, but in other situations, a separate sacrificial layer may be used for the first trace layer302. As described herein, the conductive material320may be a liquid metal, such as liquid tin or gallium. In some embodiments, the ratio of gallium to tin is 2:1.

FIG. 3Gillustrates the sacrificial layer310placed on top of the second trace layer306. The traces308of the second trace layer306protrude from the openings312of the sacrificial layer310. Thus, the traces308of the second trace layer306are exposed, while the valleys309of the second trace layer306are covered by the sacrificial layer310. In some embodiments, the sacrificial layer310and the second trace layer306have corresponding features that allow the sacrificial layer310to securely fasten (or snap) to the second trace layer306such that vertical and/or horizontal movement of the sacrificial layer310relative to the second trace layer306is limited.

FIG. 3Hillustrates the conductive material320brushed onto the sacrificial layer310that is on top of the second trace layer306. Thus, the conductive material320is disposed on top of the sacrificial layer310and the traces308of the second trace layer306.

FIG. 3Iillustrates the second trace layer306after the sacrificial layer310has been removed. The second trace layer306has conductive material320covering the traces308, but not the valleys309. The sacrificial layer310ensures that the conductive material320covers only the traces308. The conductive material320remains on the traces308due to surface tension. As the sacrificial layer310is rigid, the removal of the sacrificial layer310from the top of the second trace layer306is simple and clean. The sacrificial layer310may be reused in subsequent fabrications of subsequent circuit boards. In some embodiments, the conductive material is removed from the sacrificial layer310and the sacrificial layer310is melted and then placed into a reservoir of additive manufacturing material for later use. In this way, the systems and methods described herein are more sustainable than conventional fabrication methods, as components may be reused.

FIG. 3Jillustrates the second trace layer306placed on the first trace layer302. In some embodiments, the first trace layer302and the second trace layer306have corresponding features that allow the first trace layer302to securely fasten (or snap) to the second trace layer306such that vertical and/or horizontal movement of the first trace layer302relative to the second trace layer306is limited. As will be better shown inFIGS. 4A-4L, the vias304of the first trace layer302connect to traces308of the second trace layer306, allowing for the multilayer design.

FIG. 3Killustrates the rail layer314placed on top of the second trace layer306on top of the first trace layer302. The openings316of the rail layer314allow the traces308covered with the conductive material320to be exposed. Thus, the rail layer314serves as a filler for the valleys309of the second trace layer306. As will be shown inFIGS. 4A-4L, the rail layer314is configured to support insertion of pin headers. In some embodiments, the rail layer314and the second trace layer306on top of the first trace layer302have corresponding features that allow the rail layer314to securely fasten (or snap) to the second trace layer306on top of the first trace layer302such that vertical and/or horizontal movement of the rail layer314relative to the second trace layer306on top of the first trace layer302is limited. The rail layer314also has recessed cavities315for electronic surface mount components to be placed on the traces, as well as pin holders that align with the pin holders of the trace layer.

FIG. 3Lillustrates pin headers322and electrical components324, such as transistors, inserted and connected to the circuit board300. The dimensions of the pin holders are designed so that the pin headers fit tightly. The pin headers have the added benefit of keeping the trace and rail layers together. Surface mounted elements can be easily placed in the recessed cavities315of the rail layer314to form a complete circuit.

FIG. 3Millustrates placement of a sealing sheet326on top of the circuit board300. The sealing sheet326may be made of the same material that the first trace layer302, the second trace layer306, the sacrificial layer310and/or the rail layer314is made of. In other embodiments, the sealing sheet326is made of a material that is different from the first trace layer302, the second trace layer306, the sacrificial layer310and/or the rail layer314. In some embodiments, the sealing sheet326is made of polycaprolactone (PCL).

FIG. 3Nillustrates the circuit board300after the sealing sheet326is heated. When the sealing sheet326is heated, the sealing sheet326covers and molds to the features of the circuit board300. The sealing sheet326also provides downward force on the components to ensure they are secured. In some embodiments, the sealing sheet326is larger than the dimensions of the circuit board300, such that an overhang of the sealing sheet326molds with the pin headers322, further keeping the pin headers322in place.

If a waterproof design is required, a second sealing sheet can be applied to the back of the board, covering all crevices. A thermoplastic with a higher melting point can be used in place of PCL to accommodate circuits that generate more heat.

FIG. 3Oillustrates the placement of the lid318on top of the circuit board300and covering the circuit board300. When the lid318is placed on top of the circuit board300and pressed down while the sealing sheet326remains warm, the lid318may form an additional seal over the circuit board300, protecting the components of the circuit board300from debris and/or liquid. The lid318may bond with the sealing sheet326. The lid318may also provide a downward force on the electrical components324to maintain reliable and consistent contacts with the conductive material320. The lid318may account for the electrical components324by including corresponding recesses on a bottom surface of the lid318to receive the electrical components324and/or protrusions on the bottom surface of the lid318to contact electrical components located deeper (or lower) in the circuit board.

FIGS. 4A-4Lillustrate side cross-sectional views of the circuit board300shown inFIGS. 3A-3O. The number measurements illustrated inFIGS. 4A-4Lare illustrative of a particular embodiment created using the systems and methods described herein and are not limiting.

FIG. 4Aillustrates a side cross-sectional view of the first trace layer302with a plurality of raised vias304. The vias304are elevated paths on which the liquid metal rests. Between the raised vias304are valleys305. Also shown are pin header holders402which are located on the sides of the circuit board. The pin header holders402are hollow channels that align with the metal traces. They guide the pin headers to the metal traces to form a secure contact during the final assembly.

FIG. 4Billustrates a side cross-sectional view of an initial sacrificial layer410. The initial sacrificial layer410has a plurality of openings that correspond to the shape of the vias304of the first trace layer302. The initial sacrificial layer410is configured to be placed on top of the first trace layer302such that the vias304of the first trace layer302protrude from the openings of the initial sacrificial layer410, and some of the valleys305are exposed. The initial sacrificial layer410may be manufactured using additive manufacturing, similar to the first trace layer302. As described herein, in some situations, depending on the design of the multilayer circuit board, use of the initial sacrificial layer410may be optional.

FIG. 4Cillustrates a side cross-sectional view of the conductive material320brushed onto the initial sacrificial layer410that is on top of the first trace layer302. Thus, the conductive material320is disposed on top of the initial sacrificial layer410, on top of the vias304, on some of the sides of the vias304, and on some of the valleys305. These conductive material320portions disposed on the sides of the vias304will connect the multiple layers of the multilayer circuit board.

FIG. 4Dillustrates a side cross-sectional view of the first trace layer302after the initial sacrificial layer410has been removed. The first trace layer302has conductive material320covering the tops and some sides of vias304, as well as some of the valleys305.

FIG. 4Eillustrates a side cross-sectional view of the second trace layer306placed on top of the first trace layer302. The vias304of the first trace layer302protrude from openings307in the second trace layer306.

FIG. 4Fillustrates a side cross-sectional view of the sacrificial layer310placed on top of the second trace layer306. The vias304of the first trace layer302and the traces308of the second trace layer306both protrude from the openings312of the sacrificial layer310. Thus, the vias304of the first trace layer302and the traces308of the second trace layer306(along with the conductive material320on top of the vias304of the first trace layer302) are exposed, while the valleys305of the first trace layer302and the valleys309of the second trace layer306are covered by the sacrificial layer310.

The height of the vias304is dependent on the thickness of the second trace layer306. The first trace layer302and the second trace layer306must be designed such that the vias304and the traces308on the second trace layer306are the same height when combined. As shown inFIG. 4E, the second trace layer306is secured in place only when the vias304are snapped together with the second trace layer306. Although for certain applications, electrical vias alone will suffice, additional supporting vias could be made for the purpose of improving board structure.

FIG. 4Gillustrates a side cross-sectional view of the conductive material320brushed onto the sacrificial layer310that is on top of the first trace layer302and the second trace layer306. Thus, the conductive material320is disposed on top of the sacrificial layer310and the vias304of the first trace layer302and the traces308of the second trace layer306.

FIG. 4Hillustrates a side cross-sectional view of the first trace layer302and the second trace layer306after the sacrificial layer310has been removed. The second trace layer306has conductive material320covering the traces308, but not the valleys309. The conductive material320on top of the second trace layer306is connected to the vias304and the conductive material320covering the valleys305of the first trace layer302.

FIG. 4Iillustrates a side cross-sectional view of the rail layer314placed on top of the first trace layer302and the second trace layer306.FIG. 4Icorresponds withFIG. 3K. The openings316of the rail layer314allow the vias304and traces308covered with the conductive material320to be exposed. The pin header openings of the rail layer314line up with the pin header holders402of the first trace layer302, forming pin header openings404.

FIG. 4Jillustrates a side cross-sectional view of pin headers322and electrical components324, such as transistors, inserted and connected to the circuit board300.FIG. 4Jcorresponds toFIG. 3L. The electrical components324are in electrical communication with the conductive material320covering the vias304of the first trace layer302and/or traces308of the second trace layer306. The conductive material320covering the vias304of the first trace layer302and/or traces308of the second trace layer306are also in electrical communication with the pins406of the pin headers322. The pins406of the pin headers322are received by the pin header openings404. The top layer414of conductive material320on top of the vias304of the first trace layer302and the traces308of the second trace layer306are connected to the bottom layer412of conductive material320at the valleys305of the first trace layer302via the vias304, resulting in the multilayer circuit board.

FIG. 4Killustrates a side cross-sectional view of the placement of a sealing sheet326on top of the circuit board300.FIG. 4Kcorresponds toFIG. 3M.

FIG. 4Lillustrates a side cross-sectional view of the resulting circuit board300after the sealing sheet326is heated. When the sealing sheet326is heated, the sealing sheet326covers and molds to the features of the circuit board300.FIG. 4Lcorresponds toFIG. 3N.

As shown inFIG. 3O, a lid318may be placed on top of the circuit board300and covering the circuit board300. The lid318and the sealing sheet326protect the circuit board300and provide additional pressure and stability to maintain the connections in the circuit board300.

FIGS. 3A-3Oillustrate the second trace layer306having the conductive material320brushed onto its traces308and then placed on top of the first trace layer302.FIGS. 4A-4Lillustrate the second trace layer306placed on top of the first trace layer302and then having the conductive material320brushed onto its traces308. Either order may be used with the systems and methods described herein.

WhileFIGS. 3A-3O and 4A-4Lillustrate the electrical components324being located on top of the rail layer314, the electrical components324may additionally be placed between the first trace layer302and the second trace layer306, enabling a more compact and protective design.

In some embodiments, the channels that are designed for liquid metal traces can be hollow. These hollow channels can be used for microfluidics.

Applications of the multilayer circuit board include heat dissipation, reconfigurable antennas, lab on a chip, and embedded biomedical devices.

With more precise devices for additive manufacturing, such as more precise 3D printers, more detailed circuit boards can be produced. For example, with a 0.25 mm nozzle, electronic traces can only be as small as 0.25 mm, but with a 0.1 mm nozzle, the systems and methods described herein will be able to produce 0.1 mm traces. However, the systems and methods described herein are capable of more than just fabricating circuit boards as the scale becomes smaller. With a printer or other device that is capable of producing micron precision traces, MEMS (Micoelectronicmechanical Systems) devices can be fabricated with the systems and methods described herein. In addition, with more tightly patched traces and wires produced by the system, electromagnets and transformers may also be produced.

If the printer filament is replaced with a flexible material such as polyurethane, flexible electronics can be produced. Similarly, a clear filament can produce transparent electronics. High temperature or high strength filaments will also change the characteristics of the electronic circuit. Optical fibers can be incorporated in the circuit through the hollow channels to create optoelectronics. Optical transmission and optoelectronic circuits can then be readily integrated.

The thinner each layer is, the easier and more likely it is to deform while being printed. Once the trace layers are snapped together, they must be as flat as possible without any defects such as curled up edges or corners. The conductive material will add some height between the layers. Multilayer circuit boards require a much higher tolerance than single layer circuit boards; therefore, the iteration process for multilayer circuit boards is longer

FIGS. 5A-5Cillustrate use of a pin stopper proximal to the pin header openings204,404to provide a more robust contact between the circuit board100,300and the pin headers118,322.

FIG. 5Aillustrates a trace layer502and a rail layer510receiving a pin header518. The trace layer502has a conductive material516disposed on top of a trace. When the circuit board is initially fabricated and connected to the pin header518, the pin header518and the conductive material516are in electrical communication. However, as shown inFIG. 5A, a force or impact may be made at an exterior location530of the pin header518. The force or impact may cause the pin header518to angle in a manner whereby the pin header518and the conductive material516are no longer in electrical communication.

FIG. 5Billustrates use of a pin stopper550. The pin stopper550may be located adjacent to the pin header opening504and on the trace layer502. The conductive material516may be disposed on the trace layer502, including on top of the pin stopper550. The pin header518may be inserted into the pin header opening504, causing the pin header518to be in electrical communication with the conductive material516at the pin stopper550. The pin stopper550ensures the pin header518is not inserted too far into the pin header opening504.

FIG. 5Cillustrates the pin stopper550maintaining electrical communication despite a force or impact made to the exterior location530of the pin header518. The height of the pin stopper550allows the electrical communication between the pin header518and the conductive material516to be maintained despite the force or impact.

While the systems and methods described herein describe additively manufacturing the trace layer (e.g., trace layer102) and the sacrificial layer (e.g., sacrificial layer106) separately and placing the sacrificial layer on the trace layer before applying the conductive material to the traces of the trace layer, in some embodiments, the sacrificial layer and the trace layer may be additively manufactured together. The combined additive manufacture may obviate the steps of snapping components together and separating them, which may cause undesirable and non-negligible defects in smaller circuits.

FIGS. 6A-6Dillustrate the combined additive manufacturing of the trace layer and the sacrificial layer.

FIG. 6Aillustrates a side cross-sectional view of the combined trace-sacrificial layer600.

The trace layer602is printed normally, but the sacrificial layer606is printed slightly above the trace layer602. Because the sacrificial layer606is printed slightly above the trace layer602and not directly onto the trace layer602, the extruded filament will cool slightly before touching the trace layer602, creating a weaker and less permanent bond to the trace layer602. In effect, a gap layer603that serves as a printed support structure is created that connects the trace layer602to the sacrificial layer606. The gap layer603is weakly connected to both the sacrificial layer606and the trace layer602. As shown inFIG. 6A, the traces604of the trace layer602still protrude from the sacrificial layer606, and the gap layer603and the sacrificial layer606are printed around the traces604.

In some embodiments, the trace layer602, the gap layer603, and the sacrificial layer606are made of the same material. In some embodiments, the trace layer602is made of a first material, and the gap layer603and the sacrificial layer606are made of a second material. In some embodiments, the trace layer602and the sacrificial layer606are made of a first material and the gap layer603is made of a second material. In some embodiments, each of the trace layer602, the gap layer603, and the sacrificial layer606are made of a different material.

As shown inFIG. 6B, once the trace-sacrificial layer600is printed, a conductive material616(e.g., conductive material116) can be applied to the trace-sacrificial layer600. As shown inFIG. 6C, the sacrificial layer606is removed. The gap layer603may be brittle and separate from the trace layer602when the sacrificial layer606is removed. Any remaining remnants of the gap layer603may be wiped or blown away.

Not only does this integrated method produce a circuit with fewer defects, but also, the height of all layers can be significantly reduced. The sacrificial layer606no longer needs the extra thickness for structural integrity, as compared with the sacrificial layer106; therefore, the sacrificial layer606and trace layer602can be much thinner. Although, the rail layer can be fabricated normally and snapped onto the trace layer at this step without concern, the rail layer can also be printed onto the trace layer by resuming the printing process. Unlike the sacrificial layer606, the rail layer can be printed directly onto the surface of the trace layer602, and this creates a stronger bond than the systems and methods described herein where the trace layer, the sacrificial layer, and the rail layer are fabricated separately.

The thickness of each layer may be reduced using this integrated process. For example, with the integrated method ofFIGS. 6A-6D, and using a 0.25 mm nozzle and a 0.1 mm height increment printer, the sacrificial layer thickness can be reduced to 0.2 mm from 0.7 mm, the trace layer thickness can be reduced to 0.7 mm from 1.8 mm, possibly 0.5 mm or 0.3 mm, and the second trace layer thickness can be reduced to 0.7 mm from 1.425 mm. With a more precise printer, these heights can be easily controlled and reduced. The image of the CAD design with dimensions is shown inFIG. 6D. If the liquid metal can be precisely deposited onto the elevated trace paths, the sacrificial layer can be eliminated, reducing the minimum height of the trace layer to 0.4 mm.

When designing and fabricating integrated circuit boards as described herein, it is important to consider that the larger the gap between the trace and sacrificial layer is, the weaker the bond between the trace and sacrificial layer will be, resulting in easier removal. However, a larger gap also means that the printer may have a more difficult time printing the sacrificial layer accurately. This issue can be somewhat countered by printing a thicker and more structurally sound sacrificial layer, but will also result in a thicker trace layer altogether. For the setup described herein, the minimum thickness of the gap is 0.2 mm and the maximum thickness is 0.4 mm. This allows the sacrificial layer to be removed without damaging the trace layer. Using a filament with different properties to print the sacrificial layer will allow for an even easier removal. For example, in an experiment, a sacrificial layer using acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) filament was tested on a PETG trace layer. The ABS sacrificial layer allowed removal of a 0.1 mm gap whereas the PLA sacrificial layer allowed removal with no gap at all between the trace and sacrificial layer.

FIG. 7illustrates the circuit board manufacturing system according to various embodiments. The system700includes a circuit board control device702connected to an additive manufacturing device704.

The circuit board control device702is configured to design circuit boards and communicate instructions to the additive manufacturing device704regarding how to manufacture the designed circuit boards. The circuit board control device702may include a processor, an input unit, a non-transitory memory, and a display. The processor may be one or more computer processing devices capable of performing instructions stored on the non-transitory memory. The input unit is configured to receive input from a user. For example, the input unit may be a keyboard, a mouse, a microphone, or a touchscreen. The non-transitory memory is configured to store data, such as circuit board design data. The display is configured to display the circuit board design.

The additive manufacturing device704includes an actuator706, a reservoir708, and a nozzle710. The actuator706may be one or more actuators configured to adjust a location of the nozzle710relative to a platform or surface where the components of the circuit board (e.g., trace layer, sacrificial layer, rail layer, or lid) may be manufactured.

The actuator706may also control an amount (or flow) of material stored in the reservoir708that is emitted from the nozzle710.

In some embodiments, the actuator706is also configured to cause a grabbing device712configured to grasp and move manufactured components, to move a first component on top of a second component. For example, the grabbing device712may grasp the sacrificial layer and place it on top of the trace layer, as described herein.

In some embodiments, the actuator706is also configured to cause a painting device714configured to apply or brush the conductive material to a surface, to brush the conductive material on top of manufactured components. For example, the painting device714may brush the conductive material on the sacrificial layer that is located on top of the trace layer.

Experiments using the systems and methods described herein with respect to single-layer circuit boards (e.g.,FIGS. 1A-1L;FIGS. 2A-2L) were performed.

The commonly used instrumentation amplifier circuit was fabricated using the systems and methods described herein. The circuit design is shown inFIG. 8. A JFET quad operational amplifier (TL084) was used in this case. All four parts were printed using a MakerGear™ M2 3D printer with a 0.25 mm nozzle and 1.75 mm polyethylene terephthalate glycol (PETG) at a 0.1 mm height increment. PETG was chosen because it is not conductive, inexpensive, and capable of being extruded to the level of detail needed to print the board pieces.

The traces stand at 1 mm tall and 0.5 mm wide. The sacrificial layer was snapped on top of the trace layer.

Liquid metal comprised of a 2:1 ratio of gallium (Ga) and tin (Sn) is heated to between 99° C. and 110° C. on a hotplate and painted on using a warm synthetic makeup brush. It is important to note that the Ga—Sn alloy should have a slush-like consistency at room temperature. The trace-sacrificial layer was uniformly coated and then the sacrificial layer was removed. The sacrificial layer was removed vertically such that the liquid metal traces remain intact and separated. This layer may be reused to produce more boards if it is not damaged during the removal step.

The rail layer was snapped into the trace layer. The rail layer is 0.7 mm taller than the sacrificial layer standing at 1.7 mm. Pin headers were inserted into the holders. The pin headers must be secure and resist movement if fiddled with. The components were placed using tweezers and slight pressure was applied to establish a strong contact with the liquid metal traces.

For additional downward force on the components and to ensure that the components are secured, a thin polycaprolactone (PCL) sheet is used to seal the components on the traces. A thin PCL sheet is created on a heated surface by melting PCL filaments on a non-stick material such as a teflon cloth on a hotplate at 110° C. A straightedge was used to spread the melted PCL until a uniform sheet about 0.1-0.2 mm thick was created. After the PCL sheet cooled, a piece slightly larger than the circuit board was cut. Excess around the borders is desired to coat the edges of the circuit board. The PCL sheet was placed on the board and heated to 140° C. with a heat gun until the PCL molded to the board. If desired, a lid piece that accounts for protruding components can be designed in a CAD software, printed, and molded onto the circuit with the PCL sheet and heat gun.

The resultant circuit board depends highly on the quality of the print job. If the trace or rail layer is deformed during the print process or while being taken off the print bed, the pieces were not used, as they would not snap into place as designed. These imperfections are consequences of the quality of printer used. The printing process of all layers (including the lid) takes 55 minutes with 50% infill and 3-layer outlines sliced in simplify 3D.

Printer settings were as follows:

Assembling the circuit as seen inFIGS. 1A-1Ltook an additional 10 minutes, bringing the total fabrication time to slightly over an hour. Once the final iteration of the design was determined, six instrumentation amplifiers were assembled using the systems and methods described herein. All six circuit boards were tested and yielded the expected output as seen inFIG. 9. This indicates reliability in the method. An input voltage of 10 mV with no offset voltage at 1 kHz yielded an output voltage of 1.06 V with an experimental gain of 106 compared to the theoretical gain of 110V/V.

Resistivity tests were performed for various trace widths. Table I contains the results. When the liquid metal is brushed on, the height of the liquid metal is not uniform and has a certain thickness to it. The thickness is an advantage to the circuit board fabrication as it increases the cross-sectional area of the metal trace. Metal contacts from the surface mount elements form better contacts as they sink into the Ga—Sn alloy. To ensure that the thickness of the traces is as uniform as possible for resistivity testing, the traces were scraped with a straight edge, reducing the thickness of the traces significantly. Thus, the experimental values in Table I are the worst-case scenarios.

TABLE IResistance of the Liquid Metal Traces at 23 Degrees CelsiusTrace Width (mm)Resistance per 10 mm (Ω/mm)0.250.2080.500.1970.600.1780.700.1660.800.1640.900.1521.000.145

It was not possible to print widths between 0.25 mm and 0.50 mm because the nozzle size is 0.25 mm. For example, to print a width of 0.3 mm, the printer produces a single trace of 0.25 mm, and then it must extrude a trace that is 0.05 mm, which was not possible due to the nozzle diameter. It was possible for the printer to perform zig zag motions to create a 0.3 mm trace; however, the MakerGear™ printer did not produce consistent trace widths without first printing the borders of straight traces. The inconsistency leads to uneven heights and deformations.

Experiments using the systems and methods described herein with respect to multilayer circuit boards (e.g.,FIGS. 3A-3O;FIGS. 4A-4L) were also performed.

As a proof of concept for multilayer, a dual port voltage regulator circuit as seen inFIG. 10was fabricated using the systems and methods described herein. A low-dropout regulator chip (MIC5211 LFLX) was used in this example. A multilayer design was implemented using a ground plane to connect the three grounds together.

All parts were designed on the computer aided design (CAD) program, SketchUp™ and fabricated using a MakerGear™ M2 3D printer with a 0.25 mm nozzle and 1.75 mm polyethylene terephthalate glycol (PETG) at 0.1 mm height increment. Other printer filaments and nozzle head sizes may be used to achieve different degrees of details and rigidity.

The process illustrated inFIGS. 3A-3Owere performed. The liquid metal was made by melting a ratio of 2:1 Ga—Sn at 232° C. Once alloyed, it was applied to the trace layer at 110° C. The alloy is a liquid when brushed onto the traces. At room temperature, the alloy has a slush-like consistency, meaning the alloy is in a more solid state. Oxidation causes the outer shell to be more solid, but the inside is like an extremely viscous liquid resembling wet sand.

The circuit was tested with an input of 12V DC, and the EnableA and EnableB pins were connected to the 12V supply. Pins 2, 4, and 6 were connected through the ground plane, and the expected 3.3V and 5V outputs were achieved.

The sealing sheet was made by melting PCL pellets on Teflon at 110° C. A straight edge was used to form a thin sheet about 0.1 to 0.2 mm thick. The PCL sealing sheet was heated with a heat gun at 140° C. until the PCL molded to the circuit board. The lid was quickly adhered to the board while the PCL is still warm and malleable.

The MakerGear™ M2 printer used did not maintain consistency with each print job. The vias were often slightly contorted instead of standing perfectly straight, and the via holes tended to be irregular in shape. Additionally, the heights of the traces were not continuously uniform. The ends of the traces were taller because when the nozzle moved away, a small amount of the filament would be pulled out of the nozzle due to surface tension. The print speed was reduced to increase the accuracy of the print job at the expense of an increased print time. Furthermore, the legs and spacing of the MIC5211 chip are much smaller (2.8 mm×2.9 mm×1.0 mm) than the amplifier chip shown inFIG. 8that was previously fabricated in a previous experiment. This design pushed the printer to its limits by printing 0.25 mm traces. With the thinner traces, the inconsistency of the printer was further exacerbated. These factors resulted in a success rate of 90% after the final iteration of the design. The dimensions of the board, not including the pin headers, were 17.7 mm×9.6 mm×4.4 mm.

Common contact metals such as anodic coloring 6063 aluminum-alloy and 1Cr18Ni9 stainless steel showed no reaction with gallium. The reaction between the Ga—Sn alloy and a gold-plated nickel strip (40 mm×1.3 mm×0.2 mm) was tested. The gallium and tin alloyed with the gold immediately. The initial end to end resistance of the metal strip was 0.138Ω and increased to 0.145Ω after corrosion. The alloying did not diminish the conductivity of the metal significantly because the metal underneath the gold plating does not react with the Ga—Sn alloy. An alloy of different metals for the liquid metal traces such as bismuth, indium and/or, tin would also combat the alloying issue.

The MIC5211 chip used in this example has an operating temperature range of −40° C. to 125° C. whereas the melting point (MP) of PETG and PCL is 210° C. and 60° C. respectively. Using a filament with a higher MP or incorporating heat sinks would eliminate this issue. Plastics such as polycarbonate (PC) and polyetherimide (PEI) have a glass transition point (GTP) above 148° C. and 215° C. respectively. Both PC and PEI are available in filament form. For even higher GTP thermoplastics, it is possible to use polyetherketones (PEEKs) which continue to maintain mechanical properties at 248° C.

The systems and methods described herein have the potential to become an alternative for PCB production. As Electronic Design Automation (EDA) software is developed for the systems and methods described herein, the process will become more efficient. The boards can be fabricated with a $2,000 3D printer instead of an expensive milling machine that can cost tens of thousands of dollars. The MakerGear™ M2 3D printer was purchased for $1,800 in 2014. One pound of white 1.75 mm PETG filament was purchased for $38.00 from MatterHackers, and 32 ounces of PCL pellets were bought from IC3D for $29.99 in 2018. Operation of a 3D printer is much easier than a milling machine, making PCB fabrication a more accessible process. Soldering is a procedure that can be completely eliminated since all the circuit elements are placed on the traces and secured with plastic. PCBs fabricated with the systems and methods described herein can also be completely recycled, which is a challenge for traditional PCBs. The board is made of a recyclable thermoplastic. The Ga—Sn alloy can be removed as Galinstan (Ga—In—Sn) would with sodium hydroxide. This was tested on the circuit described herein. The plastic can be melted down and repurposed. Although both gallium and tin are more expensive than copper, because the traces are produced with additive manufacturing and not subtractive manufacturing, the actual amount of gallium and tin required and wasted is minimal. The instrumentation amplifier circuit board fabricated used 0.1039 g of the Ga—Sn alloy, which translates to approximately $0.0242. Additionally, the PETG, PCL, and metals are non-toxic. This broadens the range that these circuit boards can be used. For example, they can be used in water that humans and animals consume. There is a much lower risk of contaminating the environment compared to traditional PCBs. The assembly of a circuit board as described herein emphasizes simplicity and accessibility. No special technique is required to create functioning circuit traces. While there have been numerous successes with screen printing techniques, simply brushing the liquid metal onto the trace-sacrificial layers completely coated the traces. Using a mesh screen may lead to discontinuities in the liquid metal as it is more solid than other liquid conductive inks. Spray brushing the liquid metal on via an aerosol is another cheap method to deposit the Ga—Sn alloy onto the substrate. However, the brushing method leaves a thick coat on the traces, so the electrical components can sink in without the use of any epoxies.

The Ga—Sn alloy was a more favorable conductive material to use because it becomes more solid as it cools off. When the surface mounted elements are placed on the warm liquid metal, the liquid metal conforms around the element and cools off in that shape. It is also less expensive than inks on the market such as silver, gold, and carbon nanotube inks. The significance of the systems and methods described herein is not just in its ability to create functioning circuit traces, but the fact that recyclable, robust, fully packaged circuitry can be achieved quickly and inexpensively.

A circuit board control device (e.g., circuit board control device702) creates a design for the circuit board. The circuit board control device communicates instructions to an additive manufacturing device (e.g., additive manufacturing device704) to fabricate components of the circuit board. The additive manufacturing device fabricates a trace layer (e.g., trace layer102), a sacrificial layer (e.g., sacrificial layer106), a rail layer (e.g., rail layer110), and a lid (e.g., lid114) (step1102).

The additive manufacturing device fabricates the trace layer to include a plurality of raised traces (e.g., traces104). The additive manufacturing device fabricates the sacrificial layer to include a plurality of openings (e.g., openings108) corresponding to the raised traces of the trace layer. The additive manufacturing device fabricates the rail layer to include a plurality of openings (e.g., openings112) corresponding to the raised traces of the trace layer. The additive manufacturing device fabricates the lid to include a plurality of recesses (e.g., recesses115) configured to receive electrical components and/or protrusions (e.g., protrusions117) configured to contact electrical components.

The sacrificial layer is placed on top of the trace layer such that the plurality of raised traces of the trace layer align with the corresponding plurality of openings of the sacrificial layer and protrude through the corresponding plurality of openings of the sacrificial layer (step1104). In some embodiments, this is done by hand. In some embodiments, a machine (e.g., grabbing device712) automatically performs this step according to instructions received from the circuit board control device.

A conductive material (e.g., conductive material116) is deposited onto the sacrificial layer and the plurality of traces of the trace layer (step1106). In some embodiments, this is done by hand. In some embodiments, a machine (e.g., painting device714) automatically performs this step according to instructions received from the circuit board control device.

The sacrificial layer is removed from the trace layer (step1108). In some embodiments, this is done by hand. In some embodiments, a machine (e.g., grabbing device712) automatically performs this step according to instructions received from the circuit board control device.

The rail layer is placed on top of the trace layer such that the plurality of raised traces of the trace layer align with the corresponding plurality of openings of the rail layer (step1110). In some embodiments, this is done by hand. In some embodiments, a machine (e.g., grabbing device712) automatically performs this step according to instructions received from the circuit board control device.

One or more electrical components (e.g., electrical components120) and a plurality of pin headers (e.g., pin headers118) to be in electrical communication with the conductive material are connected (step1112). In some embodiments, this is done by hand. In some embodiments, a machine (e.g., grabbing device712) automatically performs this step according to instructions received from the circuit board control device.

A sealing sheet is placed on top of the rail layer and the electrical components and melted in order to reinforce connections and to provide elemental protection (step1114). In some embodiments, this is done by hand. In some embodiments, a machine (e.g., grabbing device712) automatically performs this step according to instructions received from the circuit board control device.

The lid is placed on top of the sealing sheet while the sealing sheet is warm to reinforce connections and to provide elemental protection (step1116). In some embodiments, this is done by hand. In some embodiments, a machine (e.g., grabbing device712) automatically performs this step according to instructions received from the circuit board control device.

A circuit board control device (e.g., circuit board control device702) creates a design for the multilayer circuit board. The circuit board control device communicates instructions to an additive manufacturing device (e.g., additive manufacturing device704) to fabricate components of the multilayer circuit board. The additive manufacturing device fabricates a first trace layer (e.g., first trace layer302), a second trace layer (e.g., second trace layer306), a first sacrificial layer (e.g., sacrificial layer410), a second sacrificial layer (e.g., sacrificial layer310), a rail layer (e.g., rail layer314), and a lid (e.g., lid318) (step1202).

The first sacrificial layer is placed on top of the first trace layer such that the plurality of vias (e.g., vias304) of the first trace layer align with the corresponding plurality of openings of the first sacrificial layer and protrude through the corresponding plurality of openings of the first sacrificial layer (step1204). In some embodiments, this is done by hand. In some embodiments, a machine (e.g., grabbing device712) automatically performs this step according to instructions received from the circuit board control device.

A conductive material (e.g., conductive material320) is deposited onto the first sacrificial layer and onto the plurality of vias of the first trace layer (step1206). In some embodiments, this is done by hand. In some embodiments, a machine (e.g., painting device714) automatically performs this step according to instructions received from the circuit board control device.

The first sacrificial layer is removed from the first trace layer (step1208). In some embodiments, this is done by hand. In some embodiments, a machine (e.g., grabbing device712) automatically performs this step according to instructions received from the circuit board control device.

The second sacrificial layer is placed on top of the second trace layer such that the plurality of raised traces (e.g., traces308) of the second trace layer align with the corresponding plurality of openings (e.g., openings312) of the second sacrificial layer and protrude through the corresponding plurality of openings of the second sacrificial layer (step1210). In some embodiments, this is done by hand. In some embodiments, a machine (e.g., grabbing device712) automatically performs this step according to instructions received from the circuit board control device.

The conductive material is deposited onto the second sacrificial layer and onto the plurality of traces of the second trace layer (step1212). In some embodiments, this is done by hand. In some embodiments, a machine (e.g., painting device714) automatically performs this step according to instructions received from the circuit board control device.

The second sacrificial layer is removed from the second trace layer (step1214). In some embodiments, this is done by hand. In some embodiments, a machine (e.g., grabbing device712) automatically performs this step according to instructions received from the circuit board control device.

The second trace layer is placed on top of the first trace layer such that the plurality of vias of the first trace layer align with and protrude from the plurality of openings (e.g., openings307) of the second trace layer (step1216). In some embodiments, this is done by hand. In some embodiments, a machine (e.g., grabbing device712) automatically performs this step according to instructions received from the circuit board control device.

The rail layer is placed on top of the second trace layer such that the plurality of raised traces of the second trace layer align with the corresponding plurality of openings (e.g., openings316) of the rail layer (step1218). In some embodiments, this is done by hand. In some embodiments, a machine (e.g., grabbing device712) automatically performs this step according to instructions received from the circuit board control device.

One or more electrical components (e.g., electrical components324) and a plurality of pin headers (e.g., pin headers322) to be in electrical communication with the conductive material are connected (step1220). In some embodiments, this is done by hand. In some embodiments, a machine (e.g., grabbing device712) automatically performs this step according to instructions received from the circuit board control device.

A sealing sheet is placed on top of the rail layer and the electrical components and melted in order to reinforce connections and to provide elemental protection (step1222). In some embodiments, this is done by hand. In some embodiments, a machine (e.g., grabbing device712) automatically performs this step according to instructions received from the circuit board control device.

The lid is placed on top of the sealing sheet while the sealing sheet is warm to reinforce connections and to provide elemental protection (step1224). In some embodiments, this is done by hand. In some embodiments, a machine (e.g., grabbing device712) automatically performs this step according to instructions received from the circuit board control device.