EIPC 50th Anniversary Conference Day 2: The Past, the Present and the Future, Pt. 1

Estimated reading time: 9 minutes

It had been observed that both all-polyimide and LCP flexible laminates exhibited degraded performance after environmental ageing, and further work was necessary to explain this effect. For the future, a new flexible laminate was required with low relative permittivity and loss tangent, together with a smooth high-conductivity conductor.

“The future belongs to those who create it” is the tag-line of the Holst Centre, an independent R&D centre based in Netherlands that develops technologies for wireless autonomous sensor technologies and flexible electronics. Jaap Lombaers and Corné Rentrop took a new approach to hybrid integration of electronics and delivered an inspirational presentation on large-area printed electronics becoming curved, flexible, stretchable and three-dimensional.

When they referred to the shape of things to come, the emphasis was definitely on shape and they demonstrated that wherever there was a surface, whether flat or three-dimensional, and whether it was in a car, a house, a hand-held device, a health-care device or an item of sports apparel, it was potentially a smart functional surface with electronics unobtrusively integrated into it.

Lombaers likened himself to a chef in a kitchen, asking “What kind of cooking is needed?” and “What can we serve today?” in the context of being able to prepare a whole range of dishes from a few basic ingredients.

He explained that hybrid integration of printed electronics offered savings in weight and space, as well as flexibility, bendability, stretchability and wearability. Devices could be easily integrated into anything and any product surface could become a user interface. Devices would be more robust and with a longer lifetime, contain less material, be less expensive and easily manufactured using new manufacturing concepts. Hybrid printed electronics could be combined with traditional electronics and were available in various form factors. They were applicable in various market sectors: for example, packaging, wearables, medical, Smart building—the possibilities were infinite.

Rentrop compared rigid and flexible PCBs, produced through conventional process routes on relatively expensive substrates using photoimaging, plating and etching processes, with printed electronics circuitry, and discussed printing techniques and materials. Various well-established printing techniques were available: inkjet, flat-bed screen, rotary screen and flexo-gravure for example, and a wide range of plastic foil substrates: polyethylene terephthalate, polyethylene naphthenate, thermoplastic polyurethane foils or even paper. These could be processed roll-to-roll if necessary, at speeds up to 60 metres per minute, and it was possible to print multiple layers. Metal inks were used, typically nano-particle silver, sintered by photonics or near-infrared. An example of industry-proven capability was a dry thickness of 5−8 microns with conductivity 10−20% of that of bulk silver and 150-micron feature size and pitch. On a laboratory scale, conductivity 20−40% of that of bulk silver and feature size and pitch as fine as 20 microns had been achieved at 5−8 microns dry thickness. Thin-film transistors had been produced, as well as stretchable circuits using either stretchable inks or meander patterns. The largest circuit they had made was 300 metres long, roll-to-roll assembled with 2000 LEDs.

Lombaers showed many practical examples of printed sensors and integrated displays in apparel, fashion and sportswear, some of which could be self-powered by energy harvesting. Rentrop demonstrated how 3D electronics, including discrete components, could be created by printing and thermoforming, and discussed in-mould electronics: “There’s no PCB any more, the component becomes the PCB.” And the opportunities for combining printed electronics with 3D printing techniques were endless.

Back to normality—the optimisation of SMT component land dimensions to achieve the most effective and reliable solder joint geometry—as Rainer Taube of Taube Electronic discussed “The Proportional Land Dimensioning Concept” and reported the results of the Proportional Verification Project carried out by FED, the Fachverband Elektronik-Design.

Taube explained that since the introduction of surface mount technology, the development of component packages has progressed rapidly, but IPC and IEC calculation standards for component land dimensions were still largely based on the component packaging conventions of the 1980s and 1990s. This led to problems in design and assembly and could also affect the reliability of the solder joints. As component terminations became progressively smaller, a new method was required for calculating the dimensions of surface-mount pads on PCBs, and this was reflected in the FED’s approach to a proportional land dimensioning concept.

The concept recognised two classes of terminations: those with facing wettable areas and those  with a combination of facing and vertical wettable areas. Land dimensions were defined by solder joint requirements, terminal type, terminal size and terminal height in the case of those with vertical wettable areas. Advantages were that land dimensions were defined and easily scalable for future components, leading to smoother assembly and higher reliability. In many cases additional design space was created. The only disadvantage was that there were no longer any generic footprints. The concept had been extensively tested and proven over a wide range of component package types and dimensions through the FED’s Proportional Verification Project.

The continuation of this article will be published tomorrow.

EIPC 50th Anniversary Conference Day 1: The Past, the Present and the Future, Pt. 1

1EIPC 50th Anniversary Conference Day 1: The Past, the Present and the Future, Pt. 2

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