Polymers in electronics

Citation

Ling, J.H. (2007), "Polymers in electronics", Circuit World, Vol. 33 No. 2. https://doi.org/10.1108/cw.2007.21733bac.001

Polymers in electronics

Polymers in electronics

This first-ever conference was organised by RAPRA Technology Ltd, and held in Munich on 30-31 January 2007. The sponsors of the conference were Emerald Group Publishing, BPA Technology and EuroBrom BV

After a welcome from Miss Alix Yates, Business Manager of RAPRA, who introduced the programme to the many delegates, the first speaker was Dr Kalman Wappel, from ECEBD, Hungary. His company specialises in the Eastern European states, or the CEE; they have a massive own data base named ChemIT, which contains the data of over 6,000 firms, all of it obtained in person! It covers data on resin consumption, short- term trend indications, process technology and machinery, etc. About 7 per cent of production is used in the electrics and electronics markets, the plastics used in this sector (E&E) are (mainly) PVC, PE, and then thermosetting plastics, with some of the more specialised materials such as EVAS, PA and PP bringing up the rear. Making polymers in the CEE offers low labour costs, and proximity to markets, and access to growing markets, but there is an immature supply base, and the infrastructure is not as developed as in Western Europe. Plastic converting is of modest technical sophistication but improves daily. Injection moulding is the main sector with 20,000 firms involved, converting 6 million tonnes a year of resins. E&E applications have an important and growing share but it is still small.

Low melting alloys used to produce conductive polymers was the subject of a paper from Tobias Pfefferkorn. Conductors, connectors, sensors, RFI/EMI shielding all need intrinsically conductive polymers, but these cannot be injection moulded. However, some plastics can be loaded with low melting point metal alloys, and some plastics can be filled with solid fillers. For example, lead-frames for fuel injection systems in cars; mouldings that can be used for shielding, that offer high thermal conductivity, that can function as heat-sinks.

Low melting metal alloys are blended with the polymer during processing, plastic here being polyamides, and metal being copper flakes and fibres. High filler content affects ductility, of course, so they have carried out a series of tests to see how malleability can be improved. Successful development of highly conductive polymer blends based on low melting metal alloys has been achieved, but the injection moulding process for the production of highly conductive electrical component parts is to be further analysed and optimised.

Dr Jamshid Avioni is the President and COO of Eeonyx Corporation. His company produce conductive polymer- coated powders, textiles, foams, felts, made using in-situ polymerisation and other related methods. Any type of fabrics can be coated and the degree of electrical resistance thickness, porosity, and flame resistance can be tailor made. Continuous graduated resistances can be possible, and the coating is insoluble in water, organic solvents, detergents, and have good stability. Translucent and varied colours of conductive coatings are available, and examples illustrated included pressure and radiation sensors, camouflage netting; radar shielding coatings, resistive heating, and radar absorbing coatings with a resistivity of 10³-10⁹Ω.

Electro-static discharge coating can be applied to fabrics for static free washable surfaces, lab coats, etc. Coatings used to produce resistive heaters are more efficient than wire heaters; giving a more uniform heat. Low radar cross section antenna, ground penetrating radar, metal detectors, dynamic pressure sensors, were further illustrations of the range of interesting products available from a specialist company.

Matt Aldissi runs Fractal Systems Inc. in California, and came to talk about conductive nano-particle polymers used in EMI shielding/radar absorption applications. Multi-layer particles suit the middle range conductivity which is needed here. Fractal systems have developed novel shielding materials that encompass several materials with different electromagnetic properties at the particle level. The different materials consist of a ferromagnetic high permeability core, a nickel coating, and an intrinsically conducting polymer layer (ICP). ICPs are polythiophene, poly(3,4-ethylenedioxythiophene), polypyrrole, and polyaniline. Shielding effectiveness varies according to the combination of Ni-ICP, or ICP-ferrite, or Ni-Ferrite used, there being five combinations. The highest shielding effectiveness was achieved with 10%ICP-5%Ni-ferrite and gave 120dBs at 20,000MHz.

To make a conductive polymer coating (CPC) they form slurry by mixing the metal coated ferrite particles and the components necessary for the conductive polymer synthesis. These multifunctional particles are dispersed in the polymer binder, such as polyurethanes, or polyamides. The resulting dispersion is then used to coat a substrate by dip-coating or spraying. They have also produced transparent conductive coatings, based on zinc sulphide.

Polyanilines appeared in the paper given by the next speaker, Jukka Perento, who is the MD of Panoply Oy in Provo, Finland. His company produces conductive polymer polyaniline (Pani). Polyaniline has many virtues, including versatility and low cost, and can be modified in several ways. Application is to the ESD protection market, and for the emerging printed electronics market, currently estimated to be worth $300 million. Polyaniline EB (emeraldine base) is produced by Panipol, and is used for ESD protection – electro-static discharge damage costs industry $15 billion a year according to Frost & Sullivan. Panipol CX can be used for compounding, Panipol DX can be mixed directly with the resin, and colours can be added as well. Suitable resins are PE, PP, PS and some elastomers. Resistivity range is 10³- 10⁹V. Anti-static coatings can be printed, by flexo or gravure, or by spraying, bar coating and screen printing. Kiian, the Italian ink maker, used Panilpol to produce conductive inks. PanStat can be used on PET, PVC, PS, PC, is very resistant to colour change, solvents, etc. and may be used as ESD coatings for lamps. Panolply are now developing a next generation of water-based ink for inkjet and spray coating application, with a 200-300nm particle size, as well as a new ESD floor coating, and some highly conductive adhesives.

Troy de Soto works for the Albermarle Corporation in Belgium, and gave a paper on the relationship between flame retardants and sustainability. As there are so many interpretations of the word, Troy applied it to three sectors – societal, environmental, and economic. The societal sector is where the use of flame retardants saves lives and prevent injuries and damage to property. Here some new standards have been needed for a while, but now there is IEC 62368 for products found in the home environment. It will deal as well with candles, and parts/accessories for candles. Candles are a major cause of house fires, and plastics without flame retardants are especially vulnerable. In the economic arena, they save money. The environmental aspects include the regulations included within the WEEE Directive, and here brominated flame retardants such as Deca BDE, EBP play a major role. With RoHS – Deca BDE was exempted, and EBP is to be unaffected. Then there is REACH – pre-registration of chemicals, to be in place by 2008. VECAP is part of their product stewardship which promotes a more favourable image of the subject of flame-retardants. The addition of a flame retardant to the plastic used in a £1,000 TV set costs e3. A £1,000 TV, once alight, can destroy a home.

Dr Sebastian Hörold came from Clariant in Germany, where they have built a new plant near Cologne to make phosphinates. Phosphinates maybe a new class of FR systems, but they meet all the regulations of the world. They are stable up to 350ºC, and have no emissions. Their Exolit OP was tested up to 257ºC for lead-free soldering, checked for blistering (none) and discoloration, also none, and it showed complete stability, passing the glow wire tests. The electrical properties of PA66 GF30 looked good, and the recycling test procedure was dutifully followed, with no colour change and impact strength was not much affected. Flame retardant polyamides were OK. Phosphinates can also be used in PCBs, and Clariant's Exolit phosphinates can be used in thermoset resins, with no influence at all on electrical properties. Halogen free flame retardants will continue grow, there being a big switch globally to HF, and the new phosphinates fill a gap in the BFR market.

Rudi Borms from Eurobrom in The Netherlands took a scientific approach to the design of suitable and sustainable fire retardants for polymers in electronics. Many of the concerns raised by society about the toxicity and environmental effects of brominated flame retardants had no sound scientific basis, and detailed and rigorous assessment of Deca-BDE and TBBPA had identified no risks to either health or the environment. Eurobrom had developed and evaluated a series of polymeric brominated flame retardants, optimised for different plastic materials, and demonstrated not to generate toxic combustion products.

Bernd Hoevel from Dow Deutschland discussed new epoxy resins designed for compatibility with lead-free assembly soldering. He commented that some resin manufacturers had over- engineered their products in order to take competitive advantage of European RoHS regulations. They had pushed decomposition temperatures beyond the necessary levels without balancing other key performance properties, with the consequence that failures due to brittleness and poor adhesion were being realised in real-world processing conditions. Dr Hoevel believed that conventional FR4 laminates would continue to be the most effective base materials for applications needing only a few reflow cycles, and that bromine-free materials might show some advantages in applications where high decomposition temperature needed to be combined with high glass transition temperature.

Per Johander from IVF in Sweden expanded upon the topic of thermal degradation and failure mechanisms of printed circuit boards under lead-free soldering conditions, explaining the electrochemistry of dendrite and conductive anodic filament formation, and the influence of humidity and thermal stress. He made some interesting observations on the quality and consistency of silane bonding treatments on glass fabrics, their susceptibility to hydrolysis and their subsequent resistance to delamination and conductive anodic filament propagation.

Dr Johander collected the award for “Best Paper” from conference sponsor Emerald Group Publishing Limited (Figure 1).

Figure 1 Dr Per Johander received the Best Paper award from Circuit World Editor Professor Martin Goosey and Emerald Publisher Nancy Rolph

Florian Schluessler from University of Erlangen-Nuremberg in Germany talked in general about selection and qualification of polymers for rigid and flexible interconnect applications, and specifically about materials for moulded interconnection devices (MIDs). These three-dimensional designs presented many challenges in structuring, metallisation and assembly, and a range of different manufacturing technologies existed, selection of the appropriate technique depending on the geometry and degree of complexity of the design. Adhesion of metallisation was a significant factor in determining the reliability of MIDs, and extensive studies had been made to optimise adhesion on different substrate types. High melting point materials such as polyphenylene sulphide and polyetherimide were necessary if reflow soldering were used in assembly. Mr Schluessler described in detail how a surface mount assembly line could be adapted and configured to cope with quite complex three-dimensional MID designs.

Olaf Mundelein from Henkel in Germany described a low-pressure adhesive injection moulding technique using hot-melt polyamides for encapsulation of components and circuits, strain relief, protection against environmental impact, and in-situ formation of seals, grommets and housings. A choice of materials was available with service temperatures up to 1408C. Moulding temperatures were in the region 180-2408C and injection pressure could be as low as 5 bar, meaning that fragile components were not damaged and low-cost aluminium tooling could be employed.

Christopher Hunt from National Physical Laboratory in UK reported an extensive study of the level of protection afforded to electronic assemblies by conformal coating. A series of generic coating types, including aqueous and solvent based acrylics, silicone, polyurethane and epoxy, was exposed to a variety of harsh environments, with contaminants such as sea-water, acid rain, fluxes and surfactants. Surface insulation resistance measurement proved to be a sensitive tool in detecting coating breakdown under damp heat conditions. Although the conformal coatings tested had been applied by their individual suppliers under supposedly careful control, there appeared significant differences in coating thickness and uniformity which tended to distort some of the test results. However, the general ranking of material types was: silicone best, then polyurethane, solvent-based acrylic, aqueous-based acrylic, and epoxy worst.

Markus Grob from Ciba Speciality Chemicals in Switzerland discussed the importance of additives in changing and enhancing the properties of polymers in order to make them meet performance requirements. They fell into two main classifications: stabilisers (process stabilisers, heat stabilisers and light stabilisers) and effect-additives (antistatic, flame retardant, anti-scratch and anti- microbial). An interesting consequence of increasing environmental awareness and legislation, and the rapid growth in recycling of end-of-life plastics was the development of special additives designed to overcome some of the problems of impurities, degraded polymers and mixtures of different types and colours of plastics and non-polymeric materials, encountered in recycling.

Continuing the theme of management of end-of-life plastic materials, Gary Stevens from GnoSys in UK described a technique for the rapid identification and assessment of polymers used in electronic product enclosures. End-of- life polymer management was historically poor, and there were opportunities to retrieve more value and to reuse materials through multiple life- cycles. A wide-wavelength spectroscopic probing method had been developed to rapidly identify and qualify plastic enclosure materials used in electrical and electronic products both at the manufacturing stage and at end-of-life. The portable and robust equipment could be used for quality assurance measurements on incoming virgin materials and for evaluation of materials for end-of-life identification, classification and qualification, particularly for predicting the degree of ageing of materials at end-of-life and after multiple reprocessing operations.

Keith Freegard from Axion Recycling in UK made a convincing case for a professional European-based plastic recycling service as an alternative to exporting plastic waste in bulk to China and Asia. The marketing concept was based on the merits of the overall service: proximity to the market, traceability, auditable quality standards, with an output stream which enabled closed- loop end use of a sustainable source of raw material not linked to the oil-based chemicals market.

Mark Hutton from BPA chaired the last session, and he introduced Pete Starkey to the delegates; Pete was standing in for Dr Steve Jones, MD of Printed Electronics UK Ltd, who was unavoidably detained back in the UK.

Printed electronics, what are they? Pete explained that it is about interconnecting components but without the complexity of the PCB manufacture. Printing interconnects in the true sense of the word, and we can print components as well.

What is it not? It is not a mature manufacturing process, it is not a replacement for silicon, But it does offer the prospect to explore new opportunities. So why bother? Volumes have gone to the Far East, but we are an innovative lot, so we can design service driven business models all based on providing customer support. Talking of support, this comes from the DTI in the UK, for whom polymer electronics are rated as strategically important. The Consortia are industry led and always welcome European companies joining in.

Inkjet printing is not for high volume, nor is it high resolution. Non- Newtonian fluids are hard to handle, and functionality is inversely proportional to its jettability. An ink that jets well will be useless in performance. Resolution is critical, and Pete explained why this is so hard (presently) to achieve; we are trying to make something with 100 per cent yield with 100m gaps and tracks, and a lot more besides. The challenges facing the manufacturer were graphically described, and awesome they all were.

Mark Hutton from BPA Consulting covered market opportunities and trends with his customary positive style. One of his first rhetorical questions was – why printable electronics? Well, to-day's photolithography is a wasteful process, and might best be replaced with a one- step printing process, using lower cost substrates, allowing a move away from materials with low dimensional stability, which plague PCB producers. Inkjet was such a process; however, it may be said that with conductive inks, lower temperatures lead to higher resistivity, so with inkjet we can increase the thickness. Happily, nano-particles start to sinter at very low temperatures, (say 100ºC) have good coalescence and good conductivity. Mark looked at ink jet using very low viscosity materials (18cps) which do not clog up the works. A company called TTP have developed a system that is able to build- up quite accurate polymer layers, with tracks and gaps down to 50m, all with ink jet, using a 1-2cps low viscosity product. Another company called CTI have a process that is probably the most conductive of what is available. Copper systems that do not oxidise would be good, but do they exist?

The RFID sector offers huge volume, said Mark, as do the market for printed antennae, which will be worth $23.3 million by 2010. Another is Barcodes, which will need 611 billion units a year by 2010. PoS displays also use printing techniques – these are OLED displays, manufactured by (mostly) Taiwanese and Korean companies. The roll-to-roll photovoltaic market was also mentioned, with the demand for lifetime efficiency and cost. Improving efficiency here is needed, as by 2010 the market will have increased three or four times.

Professor Martin Goosey presented a paper discussing polymers as key enablers in electronics assembly. The plan was that he would give this paper at the beginning of the conference, but circumstances led him to be giving a recapitulation of what had gone before. He introduced the delegates to the workings of the IeMRC, who are supporting electronics research in the UK (Figure 2).

Figure 2 Representatives of the IeMRC at the Polymers in Electronic Conference

Polymers can be found in PCB laminates, in solder masks, in dielectric layers, in adhesives, in underfills, in encapsulants, and in conformal coatings. They are extant. But what are the emerging challenges? Certainly the need to meet demands for higher frequency, for greater bandwidth, for lead-free assembly, for halogen-free flame retardant systems, and high levels of integration and increased packing density, combined with extended reliability, end of life disposal and ease of recycling demands. Martin mentioned that the PCB industry was valued at $42 billion worldwide, in 2005, with Europe enjoying less than 10 per cent.

Polymers for PCBs could meet the demands for better chemical resistance and thermal stability, improved dielectric loss, new flame retardant systems.

Higher frequencies have an impact, too, with environmental considerations including higher temperatures due to lead-free soldering, with its' attendant delamination effects such as blistering and measling; barrel cracking and CAF.

Frits Feenstra from TNO Science & Industry in The Netherlands came on next to talk about flexible printing for film based FCBs by combined laser- printing and electroplating. He described the process, which was not unlike that designed and built by CIT for Productronica in 2005. They too use an inkjet applied “seed” ink (Spectra Nova AAA print head) onto the roll-to-roll printing press, using a low viscosity (water-thin) seed ink with a viscosity of 400 cps, then low melting point alloys Sn and Ag are plated onto the printed areas in a submerged plating line. They use cheap foils such as PET, and PEN, with the polymer surface modification being done with a laser, an Excimer laser, which is used to roughen the surface to improve adhesion as it increases the contact angle. They describe it as their novel laser-Inkjet Hybrid Printing Technology for additive printed high resolution mass customised conductive copper tracks. As a flexible circuit, the potential markets are huge.

Dr Gareth Hay had come over from Brunel University in the UK to discuss their work, funded by IeMRC, being carried out under the name of “The Cleaner Electronics Research Group” who are working towards the reduction of environmental impact of electronic consumer products. Dr Hay commenced by saying that in the production of traditional PCBs, the subtractive process is not environmentally friendly, so they are looking at additive circuit creativity by offset-lithography. From this they get very good resolution down to 25m, with production at high speed, with no waste, using dimensionally stable substrate materials. To produce such conductive lithographic films, inks have to be thixothropic, with drying reliant upon oxidation/absorption into the substrate. Inks have to have a particulate size of 3mm. Particulate shape will affect ink rheology and electrical characteristics, and 3mm produces a good interconnect, onto which can be added printed thermistors, printed sensors, and heating elements using resistive ink. The power source comes from photovoltaic cells, which can also be produced by lithography. They use the zinc-carbon LeClanche technology, and substrates include Teslin, PolyArt and Melinex. Gareth went on to describe how the 2nd generation cell configuration was constructed, and a demonstrator has been produced, which shows that whilst the characteristics are not perfect, they do have the potential in some applications. This was an interesting look at the use of a conventional printing process to produce an innovative process.

A timely and fascinating conference, with a wealth of excellent and informative speakers. A busy programme covered subjects of great complexity, and in a format that should be repeated, if only because of the potential, as traditional technologies contract.

J.H. LingAssociate Editor