A look at the roadmap for the European printed circuit board industry

Roadmap
Digitalisation, demographic change, sustainability and globalisation are significantly driving the development of electronics and PCB technologies. This process will accelerate and intensify in the future

Multifunctional system boards are already state of the art today. Different starting materials, methods and manufacturing processes enable highly specialised circuit carriers: densely packed and/or highly integrated, RF-capable, high-current-capable, heat-optimised and three-dimensional. The current technology roadmap shows what drives and controls the development of PCB technology and where the journey is heading.

The development of PCB technology has been and continues to be driven by the development of electronic components, whose electrical and physical properties are being further perfected while the dimensions are shrinking. This process is guided by the functions to be achieved by the end products. Added to this are cost pressures, reliability and service life, as well as increasingly stringent environmental requirements, sums up Ralph Fiehler, Head of Development at KSG. The KSG Group has been actively involved in the ZVEI’s technology roadmap. Ralph Fiehler coordinated the twelve-member editorial team of the PCB chapter and presented the chapter to the professional community.

The requirements for the development of PCBs in the next few years are: miniaturisation by increasing the integration density, signal integrity and RF suitability, thermal management as well as flexible electronic systems that overcome physical and mechanical limits. The new highly specialised PCBs not only demand process management at the PCB manufacturer, but also require improved base materials and suitable system design tools for the hardware developers.

Embedding: Integrated functions in the printed circuit board

Miniaturisation has driven embedding, the process of embedding passive and active components in the PCB. Embedding enables the short and impedance-matched connections required for signal integrity. ICs, passive components and sensors are integrated on a PCB substrate as a System in Package (SiP). The SiP is later assembled on a PCB itself.

This development requires adequate, technological 3D integration solutions. At the same time, the demands on the system design are increasing, which must take into account both electrical and thermo-mechanical reliability aspects. In embedding, the following trends are emerging: use of thinner substrates, reduction of line/space, reduction of via diameters, increase of thermo-mechanical requirements as well as the increase of embedding of active components.

HDI/SBU PCBs with > 10 layers and BGA pitches equal to or less than 0.5 mm

Experts predict more layers and ultra-fine conductor structures for HDI/SBU PCBs (HDI: High Density Interconnect, SBU: Sequential Build Up). This technology accounts for about 13% of the printed circuit boards produced in Europe. Typical in Europe today are HDI multilayers with a line/space of 100 µm or less and 4 to 10 layers.

Optimised signal integrity requires an even higher integration density. For this, PCB designers are forced to combine impedance-controlled multilayers with layer structures >10 layers with complex SBU structures 3+x+3 and ultra-fine conductor patterns <75/75 µm line/space. This development will continue and gain momentum.

For the PCB, this means reducing the inner layer and PCB thickness, increasing the hole density and aspect ratio, minimising the mechanical tolerances as well as the PCB and stop varnish tolerances. In addition, the experts expect impedance-controlled structures and the use of mixed structures. The base material, the foundation of every printed circuit board, is one of the decisive factors. In concrete terms, this means an increase in the proportion of temperature-resistant, halogen-free and CAF-resistant base materials.

When unbundling fine-pitch BGA structures, the rewiring strategies with resin- or copper-filled staggered or stacked via arrangements are becoming increasingly important. If the unbundling of a 0.8 mm pitch BGA structure is still possible by means of a dog-bone connection and a through-hole, an SBU assembly with staggered micorvias is already necessary for a 0.65 mm pitch BGA structure. The BGA connection pitch of 0.5 mm or less, which will become more common in the future, requires more complex solutions. “Rewiring in the SBU structure using copper-filled stacked via or microvia on buried via solutions is unavoidable,” says Ralph Fiehler.

HF applications require optimised laminates

PCB technologies for high-frequency applications demand new PTFE material systems from base material manufacturers for requirements from 80 to 100 GHz, laminates with low loss factor/dielectric constant, limited tolerance range and lower copper treatment.

A challenge for designers and PCB manufacturers are the digital high-speed circuits with complex unbundling, e.g. of FPGAs. While current circuits process signals at around 12.5 Gb/s, in the future there will be data streams of 25Gb/s, 50Gb/s or more, estimates Helmut Schmucker, segment manager for PCB manufacturing at Rohde & Schwarz.

The unbundling in backplanes and motherboards can extend over very long, differential signal paths, over several layers and high-pole connectors. This makes the signal paths particularly critical in terms of insertion loss and differential skew.

Very high-ply structures, increasingly with HDI layers, are needed for disentanglement. While 20-layer multilayers are currently used, the trend is moving towards 30 layers. Due to the costs, the cheaper laminates are being stretched to the limit of what is electrically and technically feasible. At the same time, thinner laminate thicknesses ≤ 50 µm are needed to keep the overall thickness and via length of the structures as low as possible. Critical signal vias with connections to inner layers are increasingly back-drilled to achieve the necessary signal quality.

The RF expert points out another important aspect: Today, current processors generate power losses of 130 W and more, which at the same time requires supply currents of 140 A. 5 years ago, the power dissipation was only 30 W.

Technical solutions for thermal management

For drive electronics, lighting technology and power supplies, PCB manufacturers already offer a wide range of technical solutions to transmit high electrical power while taking thermal management into account.

In the next few years, embedded solutions for the integration of device functions will also be increasingly used here. In the majority of applications, copper-filled or unfilled thermovias are used to dissipate heat from hotspots on printed circuit boards. The heat loss from the power component is removed via these thermal paths and transferred to passive or active cooling concepts via heat spreading. Where this standard concept reaches its limits, inlay technology is usually used. Copper inlays partially embedded in the PCB and connected via thermovias can reduce the thermal resistance in the heat path by a factor of 20 and specifically avoid hotspots.

In future, according to the experts, special thermally conductive materials will increasingly be combined in a hybrid structure with integrated copper inlays. In addition, system solutions in the form of overmoulding a populated PCB with thermally conductive plastic (thermoplastic) turn the assembly into a complete system.

Flex and flex-rigid for smart textiles or wearables

If flexible or rigid-flexible standard technologies meet the requirements today, foldable or rolled circuit carriers that overcome mechanical and physical limits will also be needed in the future. Requirements for stretchability, flexibility, skin compatibility call for new materials such as polyurethane. The soft and highly flexible material adapts to different shapes and contours, making applications in medical technology directly on the human skin possible.

Lightweight, stretchable and semi-transparent circuit carriers laminated directly onto textiles offer a high level of comfort. The new technology combines the advantages of the rigid PCB, manufacturing options, assembly, robustness with the properties of stretchability, softness, biocompatibility of polyurethane films.

For flexible PCBs, the experts formulate four trends for the coming years. Firstly, an increase in the number of layers in the rigid and flexible area; secondly, an increase in embedded solutions with embedded ICs and inlays; thirdly, minimisation of mechanical tolerances and fourthly, smaller conductor pattern and stop varnish tolerances.

Additive printed circuit board production

A lot is also happening beyond conventional PCB production. Digital and additive manufacturing technologies such as laser direct exposure and soldermask inkjeting are fundamentally changing the technical basis of PCB manufacturers. In addition, the latest developments in the field of additive manufacturing technologies with 3D printing show new opportunities and possibilities for the additive fully digitalised production of a PCB outside the known standard processes. This requires printable materials that have comparable or better final properties as well as machines and systems to bring the process costs into an economic corridor.

ZVEI technology roadmap: valuable orientation for the industry

In the 330-page ZVEI Technology Roadmap “Next Generation”, experts from all sectors of the electronics industry show the technological trends and innovation fields of the future in electronics. The large-scale analysis provides decision-makers with valuable orientation to identify opportunities and risks of business fields and markets at an early stage. Ralph Fiehler, KSG, has led the editorial team of the 8th chapter PCB and explains the most important technological developments.

 

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