IMAPS UK Technical SeminarCirciT – Thick and Thin Circuit TechnologyThe Manufacturing Technology Centre, Coventry17 October 2013

Citation

(2014), "IMAPS UK Technical SeminarCirciT – Thick and Thin Circuit TechnologyThe Manufacturing Technology Centre, Coventry17 October 2013", Soldering & Surface Mount Technology, Vol. 26 No. 1. https://doi.org/10.1108/SSMT.21926aaa.009

IMAPS UK Technical Seminar CirciT – Thick and Thin Circuit TechnologyThe Manufacturing Technology Centre, Coventry17 October 2013

Article Type: Conferences and exhibitions From: Soldering & Surface Mount Technology, Volume 26, Issue 1

Matthew Brown, Chairman of iMAPS UK, welcomed the delegates to the first conference of its kind which was held at the magnificent Manufacturing Technology Centre north of Coventry, Warwickshire. Getting anywhere nowadays is a bit of a lottery, but as an organisation who knows where they are going – iMAPS UK have a well-plotted course.

Matthew presented an overview of iMAPS UK, the who, the why and the how, and the programme of events which they are organising during the year, iPower3 in Warwick on 27 and 28 November, and Microtech 2014 on 20 March next year being held at the Rutherford Laboratories in Didcot Oxfordshire. Also next year will see the RaMP event on RF and Microwave Packaging in San Diego on 8-10 April, and the HtM “Heat of the Matter” conference at Oxford University in October. Much to look forward to.

The stalwart and invaluable supporters of such events, the exhibitors, each gave a short introduction to who they are, and what they do, and these included Inseto, API Technologies Corporation, Du Pont, Heraeus, Anglo Production Processes, CoorsTek, Mettler-Toledo and Ultra Electronics.

Peter Collier from MTC gave a short talk about the high value manufacturing project entitled "Catapult" which is in place to stimulate growth in manufacturing which is increasingly a major contributor to GDP. Some 2.5 million people in the UK work in manufacturing, of which a quarter of a million work in the electronics field. MTC opened in August 2011, and there are parallel centres in Glasgow, Sheffield, Sedgefield, Bristol, and Warwick.

MTC accelerate concepts to commercial reality, and was founded by TWI, Birmingham, Loughborough and Nottingham Universities, and they work closely with the IeMRC. Funding comes from industry. UK PLC failed to capitalise on the academic research coming out of universities, and the Catapult Centres form that essential link so that the country does not lose out commercially from the innovations of national origins. Themes include intelligent automation, electronics manufacturing, non-destructive testing, fusion welding, laser-additive manufacturing, and e-beam manufacturing, for aerospace component manufacture. They have a complete fully-automated SMT line in operation, for power and high-temperature electronics, and allowing a hands-free build of assemblies on a production-scale.

The first speaker was Vincent Barlier, Senior Research Engineer from Plastic Logic, a company involved with display technology. A spin-off from Cambridge University, his company is now based both there and in Dresden. The world is getting thinner (but not the people) and the need for more and more flexibility is increasing. As a result components are getting flexible too, as may be seen in an iPhone, and in the latest generation of cameras. The next generation will need greater flexibility, not only in circuitry but in components, such as batteries, all of which points towards plastic materials, with a functionality not seen previously.

Normal PCB manufacturing processes will be unable to produce the high resolution patterning required for sensor arrays, and here Plastic Logic has developed a solution that provides high flexibility, high resolution patterning, embedded functionality and all in a high-volume manufacturing environment.

Polyimide gives way to PET, thickness is less (down to 100 nm from 50 μm) a minimum hole size down to 15 μm from 50 μm, and resolution down to 5 μm. Only organics unlock the true flexibility of flexible substrates, he said. Manufacturing runs on a sheet-fed batch type process, using equipment normally seen in the wafer industry, which permits precision registration below 5 μm. Thin film transistors (TFTs) can be embedded, traditional ones at high temperature or organic ones at low temperature, which makes for higher yields. He showed an assembly wrapped around a pencil, with LEDs, power source, and connections all embedded and hardly noticeable!

Cambridge tends to be the place where R&D is undertaken and prototypes are produced, with the bigger facility in Dresden for normal manufacture, with a volume process, incorporating fully automated handling (some impressive robotics here) and process equipment for manufacturing large area HDI flex circuitry, making Dresden the largest such facility in the whole of Europe.

From Renishaw came Yves Lacrotte to talk about LTCC technology, a field in which his company is experienced. It is a multi-layer 50 μm technology, it is soft, flexible, and you can buy it on a roll. It is composed of aluminium, glass, and these are referred to as tapes. There is a good selection of suppliers of LTCC tape, each with their own characteristics, such as low dielectrics, and can be used for magnetic field and microfluidics application.

The process is sintering, lamination, then firing, and printing is done with a screen, for printing tracks or filling vias. Resolution is for 100 μm gaps as tracks, with 1-15 μm track thickness as a standard. Lamination at 400°C follows, then processing or adding chips, also soldering, reflow, then dicing. Cost of such a line is about £200-£300,000. The system allows for complex packaging with embedded circuits, and will withstand high operating temperatures. There is no limit to the number of layers that can be stacked, it has a CTE close to silicon, and it is perfect for use in harsh environments. It compares very favourably to against HTCC, is ideal for thin film work, with good track resolution, and any surface finish can be used. Yves described various manufacturing sequences, which include ink-jet printing.

LTCC can be used to produce passive devices, antennae, high frequency modules and wireless communication. Other applications include thermistors, mini Newton floor sensors, pressure sensors, and in optics as a support for wave guides; reliability makes it good for automotive applications, where high temperature conditions pertain.

Paul Hurtado from ESL had high temperature polymer based systems on LED lighting applications as his topic, and this is an area that is expected to achieve significant market penetration by 2020. Heat in LEDs has been the topic of many a conference paper hitherto, and we suspect there will be more of them.

ESL, established in 1962, is a thick-film company based in Reading in the UK and they are also located in Pennsylvania, USA, the latter being more into HTCC and LTCC tapes. Existing LED options include FR4, IMS/MCPCB, or TF printing on aluminium, plastic and alumina. TF LED on aluminium offers huge thermal conductivity potential, and smaller designs are possible. It is a flexible system, smaller designs are possible, and, importantly, one has full control of materials.

Their CERMET LED process involves dielectric silver conductor, and a white heat reflective coating. Their epoxy system uses the same white reflective coat but a silver-epoxy ink; the HT polymer system uses a dielectric, a silver conductor cured at 320°C, and a white reflective coating. The comparisons between the three systems shows that one is good for power, CERMET, the epoxy for consumer lighting, and the HT system for high-power circuits. CERMET is not for die-cast, by the way.

HT polymer requirements include adhesion to any surface, have to be solderable, and should have better thermal conductivity, a minimum BDV of 2 kV AC, and it has to be cheaper. Their proposed product has seven operating stages, cures at 325°C for 3 hours, and they had run some tests with the HT polymer v. aluminium, and with a five-layer board found that a BDV of less than 3 kV was obtained with just four layers each of 40 μm dielectric. Going down to 37 μm, they had 2.87 kV with just three layers. Pull tests showed very good adhesion, it soldered well, and 2 kV AC BDV was obtained with three layers of dielectric at >35 μm.

Also on the subject of LED came Vlad Stelko of Du Pont, who spoke about thermal management materials. The market in Europe will be €100 million, homes, lighting, automotive, etc. By 2020, 90 per cent of heat in LEDs is moved by conduction. The established system of IMS/MCPCB still uses interface materials, and has poor stability at temperatures above 120°C. Their new thermal management concept uses a dielectric on Al is based on additive materials and thick film printing. Their model TOM (thick film on metal) compared to MCPCB showed lower temperatures combined with lower power dissipation. Their roadmap illustrated the use of a two-layer system based on polymeric material, with less than 2 kV AC BDV. They have also evidence that a low temperature Ag sintering can be used as an alternative to solder.

IMAPS UK organised a quite excellent buffet lunch, which has raised the game for the electronics industry conference circuit. Not an onion bhaji to be seen, no carpet-endangering cheese and pickle on white, no salmonella and dill wraps, just a colourful, varied and delicious cold buffet and somewhere to sit and enjoy both the food and the company.

Peter Barnwell, the iMAPS UK Treasurer, chaired the afternoon session, and introduced Bob Hunt of API who informed the conference about the how and the why of high temperature operating electronics. API is a $250 million company, based in Gt Yarmouth, and manufacturing MCMs, mainly for defence and military applications. They define ultra high temperatures as above 200°C.

Up to 150°C is military, above that it is high, which includes harsh environments, but it is in the UHT range that applies in sensors, controls, in aerospace, and also in drilling, where UHT is in the geothermal temperatures, and when there is deep well drilling down to 10 km, temperatures can rise above 270°C. Such deep drilling, and sophisticated horizontal drilling, requires precision monitoring and controls, so drill heads contain PCBs with components mounted, these being sensors for measurement whilst drilling is taking place. Conventional silicon semiconductors do not like high temperatures, but new technologies such as SoI, GaN, and SiCN can operate at elevated temperatures. Capacitors are either ceramic or electrolytic, resistors are wire wound, and LTCC provides an excellent substrate for UHT MCMs. He illustrated a UHT MCM with an alumina substrate, chip and wire assembly, and Bob explained the thermal expansion mismatch between substrate and package, and the problems there are in that area. MCM assembly inevitably has mixed metal interfaces, polymeric breakdowns, so knowledge of polymer is an important area.

From Heraeus came Stefan Flick with news about thick film pastes for power applications. Heraeus is still a family firm, specialising precious metals, and operate under the motto of where there is life there is light, and where there is light there is Heraeus.

Thick films pastes for the automotive sector are in management systems, which proliferate in a car. Circuits for power electronics may be found in e-cars, wind power, industrial engines, and power LEDs. They need to be price competitive, have thermal resistance, and have good thermal conductivity.

Conductor pastes contain precious metal alloys, so one has to balance costly metal with performance, with silver costing $700/kg, and copper a fraction of that. There is much to consider with Ag pastes, apart from price, there is solder adhesion, solder acceptance, but then there is copper, which of necessity has to be processed in an N2 atmosphere, and can be used with a mixed bond adhesion additives such as glass frit and metal oxides; there is an oxide-bond which needs just one paste, with printing through hole to connect front and back sides. New copper pastes provide a very good and much less expensive alternative to silver nowadays. They work well with ENIG and ENEPIG plating, and provide a good bond adhesion with 300 μm Al thick wire.

Anne Vanhoestenberghe from UCl works with others on a versatile in-house HTCC substrate manufacturing process for active medical implants. Medical implants include pacemakers, for deep-brain stimulation, and for spinal cord stimulation for pain relief. But they tend to be big boxes with long tails, and they have to operate in an environment that is “active” it is aggressive, it is ionic, and is at 100 per cent RH. It also has to be well-accepted by the host. They should not leak, of course, and they should last for 50 years+.

The traditional approach is a hermetic can with a metal in glass feed-through, the can being titanium or alumina, and inside there is an LTCC (multi-level) or and ex PCB (origami). Manufacture is a tortuous process, starting with a 96 per cent alumina substrate, onto which one has to print conductive tracks, add components (reflow solder and wire bonding), then print a dielectric layer and Pt-Au pads and seal ring, creating hermetic feed-throughs. The ceramic lid has to be soldered, then the addition of a copper coil for RF telemetry, and the whole thing encapsulated in silicone rubber.

Anne suggested that with HTCC you can embed tracks within the ceramic, increasing the feed-through density and reducing the overall size. Electronic devices can work at high relative humidity as long as no condensation occurs. Or, instead of keeping the humidity low, how about preventing it? Here we have to rely on the adhesion between the silicone rubber and the substrate, and on the absence of voids. So, here is the Brindley implant, from Finetech Medical Ltd SARS, which is CE approved.

The last speaker of the day was Kelvin Williams from the Kingston University on a comparison between thin and thick film microwave filters. High frequency applications have been dominated by thin films due to edge definition, but Kingston University did some work with thick films in conjunction with Thales Defence in Chessington, Surrey and he wanted to share their findings.

Once photo-imageable thick films inks became available, they made a proposal to Thales to design a microwave filter using these photo-imageable thick film inks, and they also proposed a bandpass filter using microstrip couple line sections, designed on a Hewlett Packard Series IV CAD.

They identified two sources of photo-imageable inks available in the UK, and selected the Du Pont Fodel 5989 single step system. Here the results showed that whilst the thin film edge definition very good, it was clear that thick film technology using photo-imageable inks could be offered as a low cost alternative to the more expensive thin film version – although further work would be required to iron out any small differences.

At the end of the presentations, the delegates were taken on a tour of the MTC facility by Peter Webb, who explained the use of the myriad machines observed on the floor of the industrial applications on the floor below, and then led the party to a look at the gleaming SMT line. Incorporating both vapour-phase and reflow soldering, the line is used purely for research purposes, and does not compete with commercial SMT companies, but is very much state-of-the-art and a magnificent facility for application and testing in research projects. One would like to see it being used rather more.

IMAPS UK must be congratulated on organising yet another excellent event which will have been of great interest anyone working in the diverse sectors of the micro-electronics field, at a venue very much removed from the usual.

John Ling
Associate Editor