Introduction
3D printing has revolutionized manufacturing and design in recent years. One area that has benefited tremendously is printed circuit board (PCB) fabrication. 3D printing enables PCB prototypes to be created quickly and cost-effectively. It is also now possible to 3D print complete electronic devices, not just the circuit boards.
This article provides an overview of how 3D printing is being used for PCB fabrication and generating 3D printing models. It covers:
- Benefits of 3D printed PCBs
- PCB design considerations for 3D printing
- Materials and processes used in 3D printed PCBs
- Creating 3D models for printing enclosures and complete devices
- Post-processing for 3D printed PCBs
- Limitations and challenges of the technology
- The future of 3D printed electronics
Benefits of 3D Printed PCBs
3D printing brings several advantages to PCB design and fabrication:
Rapid Prototyping
The ability to quickly create a tangible PCB prototype enables faster design iterations and testing. Changes can be made in the CAD design and a new iteration printed in a few hours or days rather than the weeks required with traditional PCB fabrication. This accelerates development schedules.
Design Freedom
3D printing removes many of the constraints around PCB design. Components can be placed on multiple layers, traces can cross over or under each other, and non-planar shapes are possible. This design freedom allows more compact and optimized layouts.
Customized and On-Demand Fabrication
PCBs can be 3D printed on demand in small quantities or even as a quantity of one. There is no need for large production runs or high setup costs. This makes custom designs much more accessible and economical.
Reduced Waste
Because additive 3D printing only deposits material where needed for the design, there is far less chemical waste compared with the etching processes used in traditional PCB fabrication. 3D printing is also better suited to creating complex 3D structures.
Design for Assembly
3D printing enables PCBs and components to be fabricated together into a complete electronic device assembly. This can eliminate manual assembly steps.
PCB Design Considerations
Designing PCBs for 3D printing requires some different considerations from designs for traditional fabrication:
Layer Count
Multiple layer boards are possible with some 3D printing processes, but are more complex and expensive. Single or two layer designs are recommended for most prototyping applications.
Line Width and Spacing
Traces are usually 100-200 microns wide, with 100 micron spacing as a minimum gap. This is larger than typical for PCBs.
Avoidance of Overhangs
Significant overhangs on traces or pads should be avoided to prevent drooping or failure during printing. 45 degree angles help reduce this.
Pad and Hole Sizes
Pads need to be larger to allow for registration tolerances, typically around 1-1.5mm. Holes should be greater than 400 microns for reliability.
Component Selection
Larger, surface mount components are easiest to work with. Avoid fine pitch ICs and connectors. Components can be manually placed or inserted into printed sockets.
Enclosure Design
The PCB can be printed together with a case or enclosure to create a finished device assembly. Clearances to allow for component placement need consideration.
Materials and Processes
There are several 3D printing processes suitable for PCB fabrication. The most popular include:
Stereolithography (SLA)
A liquid photopolymer resin is selectively cured layer-by-layer using an ultraviolet laser. SLA can produce detail down to 50 microns and multi-material printing.
Materials: Photopolymers, ceramic filled resins
Conductivity: Moderate, but less durable than other methods
Cost: $$$
Applications: High detail prototyping
Selective Laser Sintering (SLS)
A laser fuses powdered material to create a solid part. SLS can use plastic, metal, and ceramic powders. Conductive traces are made from silver nanoparticle inks.
Materials: Thermoplastics, metals, ceramics
Conductivity: Good conductivity with silver inks
Cost: $$$
Applications: Functional prototypes with high temp and mechanical requirements
Binder Jetting
An inkjet print head selectively deposits a binder into a powder bed to bind the powder together. Multiple print heads allow multi-material prints.
Materials: Metal, ceramic, and sand powders
Conductivity: Excellent with silver inks
Cost: $$
Applications: Metal PCB prototypes, hybrid boards with wire windings
Fused Deposition Modeling (FDM)
A thermoplastic filament is heated and extruded through a nozzle to build up a part layer by layer. Conductive tracks can be printed by extruding conductive thermoplastic composites.
Materials: ABS, PLA, PC, conductive composite filaments
Conductivity: Moderate conductivity
Cost: $
Applications: Non-critical prototypes, custom enclosures
Creating 3D Models for Printing
In addition to printing the PCB itself, 3D printing can also produce custom enclosures, mounting plates, and complete device assemblies:
Design Software
3D modeling is done in CAD software. Open source options like FreeCAD are popular for printing applications.
Model Preparation
The model needs to be exported in .STL format then processed through "slicer" software to generate the printer instructions (G-code).
Clearances and Tolerances
Designs need to account for print tolerances, such as leaving sufficient clearance for opening lids and inserting components.
Print Orientation
Orientation of the part in the printer is a key consideration to avoid overhangs, minimize supports, and ensure good strength.
Multi-Material Capabilities
Some printers can use multiple materials in one print which allows functional parts like rigid plastic combined with rubber gaskets and seals.
Post-Processing
Additional finishing may be required like sanding, polishing, painting, coating, or joining separate components.
Post-Processing for PCBs
After the PCB is 3D printed, several additional steps are required:
Cleaning
The PCB is washed to remove any uncured resin, unsintered powder, or printing supports from the surface. An ultrasonic bath can be used.
Curing
For photopolymer PCBs, additional UV curing under nitrogen is needed to fully harden the material and achieve maximum robustness.
Surface Finish
The PCB may require sanding, grinding, or chemically processing to achieve a smooth surface for soldering components.
Applying Conductors
For non-conductive base materials, conductive tracks are added using conductive ink, conductive tape, wire bonding, or other methods.
Coating
A dielectric coating can be applied to prevent shorts and protect traces. Options include conformal coatings, potting, and heat shrink.
Component Attachment
Components are manually inserted into printed sockets or soldered. Reflow or wave soldering methods are difficult, so manual soldering is typical.
Limitations and Challenges
While a promising technology, 3D printed PCBs do have some limitations currently:
- Limited Number of Layers - Only single or double layer boards are practical for most polymer printing methods. SLA is expanding this.
- Lower Conductivity - The conductivity of traces is not as high as metal boards, which can limit power transmission.
- Soldering Difficulties - Poor solder wetting and hole filling make hand soldering challenging.
- Limited Component Density - Fine pitch ICs and connectors are not feasible. Minimum component size is 0402 passives and QFN chips.
- Property Inconsistency - Mechanical and electrical properties vary across production batches with some processes.
- Moisture Absorption - Photopolymers absorb moisture which negatively affects properties.
- Part Size - Maximum part size is limited by printer build volume, typically under 20cm x 20cm.
- Vertical Resolution - Layer thickness is generally 50-200 microns, thicker than traditional PCBs.
The Future of 3D Printed Electronics
Advances in materials, processes, and design tools will help overcome current limitations and expand applications of 3D printed electronics:
- New conductive materials like graphene and carbon nanotubes will improve conductivity and printability.
- Multi-material printing with conductors, dielectrics, and encapsulants will enable more integrated devices.
- Hybrid printing combines 3D printing and dispensing of conductive pastes and tracks.
- Advancements in printed ceramic and silicon inks will allow 3D printing of semiconductors.
- Development of new substrate materials with better thermal and mechanical performance.
- Improved surface finishes will enable higher density component assembly.
- Embedded printing of actives components like sensors, chips, and batteries into device structures.
- High-speed production printers will make digital manufacturing of electronics a reality.
Conclusion
3D printing opens new possibilities in electronics design and manufacturing. As the technology continues to progress in capability and capacity, 3D printing will become a standard way of producing PCBs, prototypes, and customized electronic devices, complementing and in some applications replacing conventional PCB fabrication.
Frequently Asked Questions
Here are some common questions about 3D printing PCBs:
What materials can be 3D printed into functional circuit boards?
Most 3D printable conductive materials for PCBs are silver and copper polymer composites. There are also options using carbon allotropes, intrinsically conductive polymers, and metal-plated/sintered materials. Dielectric materials include photopolymers, thermoplastics like ABS, and ceramics.
What is the finest line width and spacing I can expect with a 3D printed PCB?
The practical minimum line width for most 3D printing processes is around 100-200 microns, with 100 micron gaps between traces being typical. This compares to trace widths below 50 microns on commercial PCBs.
Can components be directly 3D printed onto a board?
It is not yet feasible to directly print active semiconductor components or highly integrated circuits. But printing of passive components like resistors and capacitors is in development using conductive and insulating pastes. Less complex ICs like sensors could be 3D printed in the future.
How many layers can be 3D printed in a circuit board?
Most current DLP and FDM processes allow 1 or 2 conductive layers. Some SLA printers can produce 4-6 layers, but it increases cost and complexity significantly. Hybrid layered manufacturing combining printing, lamination, dispensing can provide higher layer counts.
Is heat soldering possible on 3D printed PCBs?
Reflow soldering is generally not possible with 3D printed boards due to the lower melting point of printable plastics. Special pastes and pre-treatment can improve solderability for manual soldering. Solder-free conductive adhesives are an option for component attachment.
