Design Rules For 3d Printing

Flexible-non-planar-PCB-Designs-5 Now that Industry 4.0 is creeping into electronics design and manufacturing, designers and engineers need to consider how they can reconcile their electrical and mechanical PCB design requirements with these systems. Electrical design rules are critical for ensuring that a circuit functions as desired, while mechanical design rules are imposed to ensure that your board is fully manufacturable. With 3D printing, designers will have considerably more design freedom, but there are still important additive manufacturing design guidelines that should be followed.

CNC drilling machine during PCB manufacturing.

Eliminating CNC drilling with additive manufacturing significantly reduces PCB turnaround time.

Electrical Additive Manufacturing Design Guidelines

Many standard design guidelines for PCBs on rigid substrates are also applicable to 3D-printed PCBs. Issues that affect power integrity, thermal management, and component placement in rigid PCBs can be addressed by adapting the same solutions to 3D-printed PCBs. However, some design considerations in 3D-printed PCBs require their own guidelines due to the various materials used in 3D printing.

Understand Your Substrate Material Properties

The relevant material properties for FR4 (i.e., dielectric constant and magnetic permeability) and other rigid PCB substrates are well-known and even form the basis of industry standards for PCB design. Standards around PCB design for 3D-printed electronics are only now being developed, but the lack of standardized materials for these devices complicates design and analysis. With high-speed/high-frequency devices, the material properties of your substrate will affect device performance, primarily due to dispersion and dielectric losses in traces

You should not assume that traces on a 3D-printed PCB will carry signals in precisely the same way as traces on FR4. Whichever material you use for your substrate, you should have an idea of dielectric loss and dispersion when designing interconnects, especially in experimental devices that run at very high speeds or high frequencies. This helps with compensating skew and determining proper trace length matching when designing interconnects. These properties also determine trace impedance at different frequencies, which is important for ensuring proper termination along interconnects that act like transmission lines.

Consider Printing Resolution During Interconnect Design

The layer-by-layer printing process used for 3D-printed PCBs requires that the print head move laterally and vertically in discrete increments. This limits the size of the conductive elements that can be placed in a 3D-printed PCB. As devices become more complex and interconnect density increases, the size of conductive elements will eventually reach a limit where it matches the smallest feature size that can be printed.

The lateral resolution also determines the minimum spacing between conductive elements and the size of vias that can be placed in a 3D-printed PCB. A 3D printer for multilayer PCBs should be able to print conductors and substrates at sub-mm levels. This type of advanced system will be able to 3D print PCBs that are competitive with rigid PCBs in terms of interconnect density and performance.

Match Materials to the Printing Technology

Different materials can be specifically adapted to 3D printing processes, and these materials are not always interchangeable between systems. Even if a certain material is compatible with multiple systems, the feedstock may not be compatible. Therefore, you should determine which materials and print resolution you need to reach the desired level of performance before selecting your printing system.

If you already have a printing system and you want to exploit its capabilities for 3D-printed electronics, you may not be able to print the device you want. Certain materials, such as polyimide or PTFE, are not the best choice for advanced electronics, such as high-frequency RF devices. You'll likely be unable to match the best materials for your design to every 3D printer.

The Role of Your Design Software

Perhaps the most important thing to consider when designing a PCB for 3D printing is the capabilities of your design software. As PCB documents are essentially a mechanical layout of an electrical system, the CAD tools used for PCB design need to translate your design into instructions for a 3D printer.

With traditionally manufactured PCBs, the best PCB design software packages can already be used to generate a variety of deliverables for your manufacturer, including Gerber files and Excellon/NC drill files. These files are used to describe different portions of a layer in a PCB and as instructions for CNC drilling equipment, respectively.

Thankfully, the design files required for PCBs on traditional substrates and 3D-printed PCBs are the same, allowing a smooth transition to additive manufacturing for planar PCBs. With non-planar PCBs, the transition from ECAD to manufacturing is not so smooth, and your design will require some editing in MCAD software.

If you don't have access to a decent design package, you may find it difficult to implement the geometric additive manufacturing design guidelines outlined above. Working with ECAD software that includes MCAD tools helps ensure that your board satisfies the mechanical constraints imposed in 3D printing. Some new add-ons for ECAD software allow you to import your electrical model into an MCAD program so that you can design your enclosure around your PCB, allowing you to create a complete product around your 3D-printed PCB.

Engineers working with mechanical design software for additive manufacturing design guidelines.AM design guidelines 2

Satisfying additive manufacturing design guidelines requires electrical and mechanical co-design.

With 3D printing of PCBs still being something of a new process that directly competes with traditional processes, design software is still catching up to the manufacturing requirements of 3D printers. Most design tools, even those with built-in 3D design tools, still cannot generate instructions for 3D printers directly from design data. This is where you will need to use a plug-in for mechanical design software that can take your design data and generate printing instructions for an additive manufacturing system.

Choosing the right 3D printing system that interfaces with MCAD tools for generating printing instructions allows you to take advantage of all the benefits of additive manufacturing for PCBs. You can ensure that your device complies with important electrical design rules in your ECAD software, and you can quickly generate printing instructions and even implement a non-planar geometry in your MCAD software. Working with STL/STEP models in your MCAD tools also allows you to check component placement and clearances in non-planar geometries that are not compatible with traditional ECAD software.

Following additive manufacturing guidelines for 3D-printed electronics is much easier when you use the DragonFly additive manufacturing system. The SolidWorks add-in for this system will translate your Gerber files into printing instructions and allow you to modify your board to have a non-planar design. This allows you to quickly manufacture prototypes in-house with significantly reduced lead time compared to traditional processes. Read a case study or contact us today if you're interested in learning more about the DragonFly system.

Ziv Cohen

July 25, 2019

Ziv Cohen has both an MBA and a bachelor's degree in physics and engineering from Ben Gurion University, as well as more than 20 years of experience in increasingly responsible roles within R&D. In his latest position, he was part of Mantis Vision team—offering advanced 3D Content Capture and Sharing technologies for 3D platforms. The experience that he brings with him is extensive and varied in fields such as satellites, 3D, electronic engineering, and cellular communications. As our Application Manager, he'll be ensuring the objectives of our customers and creating new technology to prototype and manufacture your PCBs.