Jan 7, 2020

High-Speed PCB Material: The Advantages of 3D-Printed Substrates

high speed pcb materialPCB designers that pay attention to the laminate market know there are plenty of high-speed PCB material options. The wealth of high-speed substrates are optimized for different applications, including high-speed/frequency operation, high-temperature environments, and high mechanical strength. These materials have enabled many advanced applications and have been instrumental in bringing circuit board technology to the place of prominence it occupies today.

In high-speed and high-frequency products, IC designers are continuously pushing the limits of technology. With switching speeds reaching 10s of ps and researchers in Europe already working towards 6G at 100s of GHz, materials companies are already working toward substrate materials that can accommodate such high frequencies. Devices that run at such high frequencies will continue carrying small form factor requirements, and designers will need access to a high-speed PCB material that can provide low losses for these advanced applications. This is where specialized 3D-printed materials can solve a major innovation bottleneck by providing low losses in high-speed devices with customizable interconnect geometry.

Pluggable SSD on a high-speed PCB material

This SSD and other devices can benefit from an adaptable high PCB speed material.

Common Signal Integrity Problems in High-Speed PCBs

The weave pattern and the intrinsic dielectric properties of common PCB substrates are responsible for a number of signal distortion and attenuation problems in extremely high-speed and high-frequency PCBs. Although there is a broad range of planar materials available from companies like Isola and Rogers, it can be difficult to choose the best material for your particular application.

In high-speed/high-frequency designs, one of the limiting factors that determines its usefulness in different applications is the bandwidth of digital signals it can accommodate. This is related to the level of attenuation (i.e., loss tangent) as a function of frequency, optical dispersion, and homogeneity and isotropy of the substrate material. FR4 and other glass weave materials are inherently inhomogeneous and anisotropic, meaning the dielectric properties vary in space and along different directions in the material. 

At low speeds/low frequencies (i.e., sub-GHz frequencies), the prominent signal integrity problems were primarily related to inconsistent or mismatched impedance along an interconnect, ringing due to poorly considered parasitic inductance/capacitance, and crosstalk.

With the highest speed digital signals, bandwidths can reach up to ~50 GHz, and newer applications in the analog/RF domain are already operating at similar or higher frequencies. New signal integrity problems result in devices built from an inhomogeneous anisotropic substrate material like FR4. The fiber weave effect leads to periodic loading of the substrate, which creates EMI problems, as well as small impedance inconsistencies along an interconnect.

This leads to higher insertion losses and creates the potential for standing waves to form on a trace, leading to an EMC problem where traces radiate EMI just like antennas. The inconsistent dielectric properties also lead to signal distortion along an interconnect. Dispersion in the substrate stretches and distorts a digital signal, which can cause skew to accumulate in parallel interconnects, leading to inconsistent triggering of downstream components.

The high-frequency signal integrity problems outlined here continue motivating the search for alternative substrate materials. Many big players in the electronics materials industry have spent significant time and effort optimizing FR4 substrates to overcome these and other problems, as well as develop new materials that are not prone to such signal integrity problems. 

With additive manufacturing systems reaching the point that they can 3D print fully functional PCBs with less time and lower costs, designers should seriously consider using these systems for ultrafast digital systems and high-frequency boards at 10s or 100s of GHz.

The Advantage of a 3D-Printed High-Speed PCB Material

Working with a 3D-printable high-speed PCB material is ideal for compensating signal integrity problems that dominate GHz-level devices and for extending the usable bandwidth of a device to high GHz levels. This extension of bandwidth to high GHz levels and beyond is achieved by using unique insulating polymer materials as PCB substrates. The range of polymers that can be synthesized very broad, and many of these materials can be easily used in low-temperature 3D printing deposition processes, such as aerosol jetting and inkjet printing.

In inkjet printing, a dielectric substrate and conductive traces can be deposited directly from nanoparticle inks, forming a continuous thin film of material that is slowly built up into a multilayer PCB. These materials provide the following benefits over other high-speed PCB material options:

  • No copper etch. The smooth interface between printed conductors and the insulating substrate material eliminates DC losses at the rough copper interface that is normally found in PCBs on conventional laminates. This compensates for losses at high frequency that arise due to the skin effect.
  • Homogeneous and isotropic material properties. This compensates for fiber weave effects. In particular, cavities resonances in the material do not occur as there are no cavities in the substrate material, in contrast to glass weave PCB substrates. In addition, skew and directional effects are eliminated as the dielectric constant is consistent in all directions.
  • Tunable bandwidth. Polymers can be easily modified with various functional groups or doped with other materials, allowing their optical properties to be optimized for specific frequency ranges. This allows losses to be minimized within relevant frequency bands that extend to the high GHz region.

high speed pcb material 23D printer for high-speed PCB material deposition

Newer additive manufacturing systems will be able to accommodate a broader high-speed PCB material range.

Additive manufacturing systems for PCB production provide broader benefits beyond the use of an optimized high-speed PCB material. The layer-by-layer deposition process allows designers to print boards with unique shapes, including non-planar geometry and customized compact solutions with many functionalities. The same characteristic allows designers to create a non-orthogonal interconnect architecture and RF components that are optimized for specific frequency bands. The cost drivers in additive manufacturing are unique in that costs and fabrication time only depend on the weight of deposited materials, rather than depending on the complexity of the device. This reduces lead times to a matter of hours and allows new devices to be immediately tested in-house.

As more materials become commercialized and adapted to low-temperature additive manufacturing processes, engineers can expect to access a broad range of high-speed PCB materials for their specific applications. Examples include semiconducting organic polymers for direct printing of semiconductor devices and biopolymers for use in 3D-printed medical device electronics. 

These advanced devices can be co-deposited alongside customized interconnects and standard components, allowing innovative design teams to experiment with unique electronics for advanced applications.

If you’re developing advanced electronics with a unique form factor, you need access to a high-speed PCB material that can be printed directly from advanced nanoparticle inks. The DragonFly LDM system from Nano Dimension can be used to 3D print fully functional parts, producing complex electronics in-house from advanced materials as part of rapid prototyping or at scale. You can produce high-mix, low-volume PCBs with a planar or non-planar geometry, complex interconnect architecture, and embedded components. Read a case study or contact us today to learn more about the DragonFly LDM system.

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