iNEMI Roadmap
Can PCB FABRICATION PROCESSES Keep Up with Design Demands?
New hole formation technologies and low-cost low-loss materials are needed.
by STEVE PAYNE
Ed.: This is the fourth of an occasional series by the authors of the 2019 iNEMI Roadmap. This information is excerpted from the roadmap, available from iNEMI (inemi.org/2019-roadmap-overview).
iNEMI’s Organic PCB Roadmap summarizes the technology needs for rigid PCB, flexible circuits and optical circuits, and it includes the gaps and challenges that need to be addressed to meet the expectations of the key product groups that are driving industry demands. Successfully meeting these challenges will provide significant business opportunities for PCB fabricators.

Technology needs are divided into two major segments: research needs and development needs. Each has their challenges and opportunities.

A summary of the development needs in PCB technology include:

  • Microvia technology improvement.
  • Improved or new via hole formation (drilling or ablation or additive).
  • Improved plating for additive fabrication and high aspect ratio blind vias.
  • Continuing development of design and modeling tools for embedded actives, passives and optoelectronic PCBs.
  • Improved layer alignment accuracy (improved registration).
  • Finer line and space development in imaging and fabrication techniques.
  • High-speed alternatives to back-drilling (e.g., additive buildup techniques).
  • Continuous cycle-time reduction for rigid and flexible circuits.
  • Adoption of Industry 4.0/smart manufacturing for improving traceability and enabling continuous processing lines.

Rigid circuits. Multiple challenges face PCB fabricators and those in the supply chain. For example, new or previously rare failure modes, such as pad cratering, are becoming more common and surface treatment of coppers to aid innerlayer adhesion in multilayer circuits can affect high-speed signal properties. These and many other challenges need to be investigated and understood to eliminate or at least mitigate the issues. Often, collaborative research will be the most expedient way forward for the successful adoption of future technology requirements.

Use of embedded technology is predicted to increase in the next 10 years. Standard process methodology, testing methods and acceptance standards must be developed for embedding discrete and active components.

Solder mask is now used as a structural material with the adoption of underfill under the BGA. Its adhesion to the board and the need for reduced moisture absorption and permeability are critical factors, as electrical characteristics are affected. There is also a need for sub 25µm solder mask registration of features and tolerances. Ink-jetting solutions may be developed to respond to these challenges.

Measurement capability, terminology and associated specifications are needed for finer/smoother copper foils below today’s low-profile copper. Copper-foil tooth reduction with increased adhesion of foil to resin is a definite need, as this will improve signal integrity. The trend for lower-loss laminates is growing, driven by high-frequency applications (e.g., 5G) and is a concern in the cost-sensitive consumer category.

Flexible circuits. Growing demand for “portability” fuels demand in notebook PCs, cellphones, wearables, etc. Technology considerations for flexible circuits include the following:

  • Narrower spacing between conductors and thinner dielectric layers require dielectrics with higher breakdown voltage.
  • High-frequency, controlled-impedance circuits, utilizing low-cost, low-Dk, process-friendly dielectric.
  • Wearable and medical technologies will continue to drive adoption of stretchable flexible circuits.
  • A lower-cost polyimide flex substrate or equivalent may be necessary to expand into the domain of lower-cost rigid boards.

Optical circuits. Laminated and embedded polymer waveguides are likely to be enablers for high-speed optical backplane applications. Laminated optical technologies are critical to enable next-generation high-speed architectures, solving issues for high-speed and high-bandwidth signals, while preserving the cost and enabling full system integration. Optical electronics technologies are emerging continually, and we need to watch for important developments and keep an open mind.

Research needs. Long-term research is being undertaken by academia, research institutes and several companies in the PCB supply chain. A major challenge affecting the interconnect industry is the decline in PCB/substrate R&D investment, which does not bode well for meeting the ambitious density and cost targets defined in the roadmap chapter. Collaborative R&D must be considered as a way forward to successfully meet the challenges.

Some of these challenges include:

  • Electrical test (higher throughput and more complex, physically inaccessible circuit elements).
  • Dimensional consistency/stability of materials at higher assembly and use temperatures.
  • Understanding the true cost/performance relationship and its effect on design and material choices.
  • Reconciling the price inelasticity of the major product applications with sharply increasing electrical and thermal performance expectations.

The chapter concludes by describing how advanced technologies used for organic semiconductor packaging substrates are now being adapted for advanced high-density interconnect (HDI) PCBs (e.g., SLPCB). PCB fabricators must prepare for these demands driven by miniaturization and increased product functionality. Specific future product demands will drive and accelerate the development of new materials and manufacturing methods. In 10 years, we will likely be at 6G, or whatever it will be called, and artificial intelligence (AI) may be the next boundary to cross.

Steve Payne is a project manager at iNEMI and past chairman and fellow of the Institute of Circuit Technology (ICT); steve.payne@inemi.org. This excerpt from the 2019 iNEMI Roadmap is based on the Printed Circuit Board (PCB) chapter.