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columns | June 27, 2005

evertiq at the EIPC Summer Conference - Day 2

Paul Waldner maintains that conferences are about meeting people as much as they are about learning from people, so he got everyone on their feet to say hello to one another.
Day 2 - June 10th
Markus Willie of Ruwel AG told us that his company has been making flex-rigid boards for 30 years now, and whereas before the application was for the military and avionic industries, now it is more for the automotive and communication sectors as well. It was Schoeller Elektronik started it all in 1974, now they are part of Ruwel. Flex-rigid boards can eliminate many connector or solder joints that are potential sources of failure, and a single flex-rigid board can replace a complete wiring system. They weigh less and occupy less space, have uniform properties, and also allow for a decreasing amount of space being used to best effect.

Ruwel have 'Multiflex' which are hybrid constructions consisting of flexible and rigid substrates laminated together in layer counts to choice. Interconnect is through plated via holes, but you do however have to have a symmetrical build-up to minimise bow and twist. Some panels are best constructed during manufacture with a rigid layer that contains a snap-out section that can be removed after assembly. Multiflex boards can be made in sequential build-up and high-density interconnect techniques, so an 18-layer flex board is possible, 'Semiflex' is another possibility, where the flex element is only required for installation, rework or maintenance. Only 10 bend cycles are allowed, but this is usually enough. Finally, he came to 'Yellowflex', which is something new - a halfway house between the two former concepts. Instead of using a flexible copper clad polyimide foil ( or similar) they use a copper sheet selectively coated with a flexible polymer material, which is laminated onto the rigid board material. This build-up can then be processed as a normal PCB.

Daniel Kush of Pacothane Technologies was another American who came across the Atlantic, he is from New York. Daniel brought us up to speed with the problems encountered with the use of coverlay films in flexible circuitry. It is the squeeze-out of adhesive that takes place during lamination that causes the problems, and with increasing circuit density the mount of surface area lost to accommodate adhesive squeeze-out is pushing current materials and processes to the point of failure. His company had embarked upon a test programme incorporating all known materials, through set test conditions, but with a number of material combinations, and had concluded that the best of these was to use 1.5mm reinforced red rubber with optimised conformal-release film 125µ thick.

Giacomo Angeloni is the R&D Director at Somacis in Italy. In what might arguably be rated as the most inconclusive paper of the conference he went into some detail about the complexity of obtaining accuracy and reference for laser hole drilling in SBU boards. Not his fault, of course, it's the nature of the beast, there are so many different factors that can influence the accuracy that the mind boggles, and the enormity of the problem is not confined to any one phenomenon. The warp and the weft of the material used in the substrate, during both C-stage and B-stage, the Z registration, the X-Y registration, all contribute, in varying percentages, and of course the larger the panel the more the problems are magnified. How best to deal with these problems? Pray for more stable materials, or, if all else fails, go and play football.

Marc Hüske of LPKF Laser & Electronics AG brought the question of laser cutting flex and rigid PCB materials to the conference, and when one considers the diversity of shapes manifest in hand-held electronic devices, you can see why such a method is gaining increasing popularity. However, it is not without its problems. Laser cutting offers great advantages, you can cut assembled boards, you don't need tools to cut coverlays, and you can cut any shape you wish, out of any material. However, you do tend to get carbonisation during cutting, which gives conductivity problems, and you will get loss of definition.

Wolfgang Alberth of Isola GmbH reminded us that we need to find niche markets, and here it is the flex and semi-flexible markets. Flex has a growth rate of 12% per annum. Really something to be looked at in Europe. Main sector is computers, then display, then communication, etc A $6bn market in 2004. By region Asia produces 56%, Europe only 3%, Japan 32%. One interesting market sector is automotive, and maybe European companies should now be putting more R&D effort into this sector. 90% of the materials used in flex is polyimide, which might a little bit 'over the top' for some applications. Using an alternative film would be more cost effective. Perhaps what we want is a semi-dynamic film. After all, polyimide was not exactly easy to buy last year, was it? This new material has to be double-sided, based on epoxy, and would allow freedom of design. The good news is that this product exists; it is called Duraflex and is produced in some volume at the Isola plant at Bottegone in Italy. Good news all round. It has a Tg of 150oC, cu peel strength of 1.3, and can be used for reel-to-reel production. Thank you, Isola.
Halogen-free laminates - worldwide trends, driving forces, and the state of play was presented by Dr.

Adrian Beard of Clariant GmbH. OEM strategies, environmental concerns, flame retardants, all play a part, FR plastics are used in 30% of all plastic production, but less than half is halogenated, and BFR is the main plastic used in electronics. There is balance between safety, (flame retardants) and the environment; traces of PBDE in breast milk, for example, have been alarming, and flame retardants have been banned in certain applications. Brominated flame retardants (BFRs) have been found in farmed salmon, but where does it come from? Whilst risk assessment on TBBPA is expected by the end of 2005. End of life, scrap, waste etc., what are the options? Recycling is something of a cottage industry in China, but the impact on the environment is of somewhat larger significance. Environmental discussions have resulted in legislation which has been brought into effect in Europe (WEEE/RoHS) but the situation re Deca-BDE is blurred. WEEE Directive 2002/96/EC demands separation of plastics containing brominated flame retardants.

However, discussions which are driven by a mixture of scientific and emotional behaviour are rarely conclusive (the use of nuclear energy in the UK for the generation of electricity as a case in point) so the industry has had to take the initiative and has moved towards halogen free options. However a study on these for the PCB industry was inconclusive, with the inference being that no-one wanted to take a decision. Companies do tend to abide by legislation, however, not only from motives of social responsibility but also to preserve their good name. As a result, many of the world's leading OEMs have now committed to going down the halogen-free route, and there are developments in new halogen-free raw materials, Clariant have Exolit OP, as do Chemtura, Supresta, and new halogen free resins are available from Huntsman, Dow, Bakelite etc. Park, Matsushita have halogen-free laminates for PCBs available, and 20% of Chinese PCB exports are now halogen-free. The USA is now beginning to consider halogen-free products, but in Europe there is little activity. Halogen-free is a market, so halogen-free PCBs should account for 3-4% of the market. Perhaps we should be getting on with it.

Erik Bergum is VP Sales for Polyclad in Europe and was on next. How to chose laminates for lead-free was the subject of his paper. Not all laminates are suitable for lead-free, with the higher temperatures that pertain, thermal stress is a factor. Whilst a higher Tg is generally better for lead-free assembly, that is not in itself sufficient. It is the Td, the decomposition temperature that is getting increasing attention. Polyclad put together a team of nine people from all over the world to look at what laminate would 'do the trick' and simplify the process. They have colour coded, so that an immediate 'go-no-go' guide is available. Within that guide lies a range of variables, such as surface finish, lamination cycles, layer count, blind & buried vias etc. There are 5 different materials, with a Tg ranging from 140 - 180oC, and a Td ranging from 320 - 350. Erik showed how each laminate fitted into the possible specification on the colour chart, and it all made perfect sense.

Young Gao is a market development manager at the Advanced Circuit Materials Division of the Rogers Corporation. His paper was based upon the impact of PCB material dielectric properties on high-speed digital systems, from a designer's perspective. He drew our attention to the laminate material possibilities, and which ones might suit the designer. High-speed digital transmission is rated at 2.5 Gb/S, and most now run at 5 Gb/S, but systems operating at 10 Gb/S and higher are on the horizon. Whatever the transmission medium, signal distortion exists. This can be due to amplitude reduction and dispersion. The former is measured in dB, and the rise time is measured in picoseconds (pS). So, for better transmission, you need better signal integrity. The 'eye' diagram shows both time and amplitude, from which you can see that the wider the eye, the better the signal. Signals have formerly been in analogue format, up to 2GHz, and microwave >2GHz, but now digital transmission gives better band width, and is more tolerant of distortion. In the selection of a laminate you have to bear in mind that signal loss can be traced to dielectric and the conductor. So, low loss material is important. Thus a laminate with 59pS and 472 mV is superior to one with 112pS and 208 mV, it has a wider 'eye' but with the same input. As an example, Rogers RO4350 without a connector has this wide eye, the same laminate without a connector is has a narrow eye. Rogers have vision.

John LingCarter-Lane Consulting,
The Reddings, Old Colwall,
Worcestershire, England WR13 6HH
Telephone & Fax: +44 (0) 1684 540901 Mobile: 07968 190649
Email: johnling@onetel.com

EIPC chose the gleaming tower of the Scandic Infra City Hotel at Upplands Väsby, where inside all was light, air and open space. The facilities were excellent, and the Dinner and Tour of Stockholm gave the delegates a welcome break for an evening of relaxation and an excellent dinner at the Wärdshuset Godthem restaurant, followed by a look at the city by night, all memorable experiences. Another high-quality EIPC event, and maybe, just maybe, the word is getting out - a 30% increase in the number of delegates is not happenchance.

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