Institute of Circuit Technology AGM and Evening Seminar
Arundel, UK, 3rd February 2010
The AGM of the institute was held prior to the evening technical session. Martin Goosey was deputising for the retiring chairman, Steve Payne. Martin Goosey was elected our new Chairman and Andy Colby was elected Vice Chairman. The treasurer’s report confirmed that the Institute was financially sound and is now a limited company to enable us to partake in European funding and dissemination initiatives. We continue to offer training and development courses and technical seminars for our members.
Bill Wilkie welcomed a large audience of 55 delegates to the evening technical session themed on “High Performance Laminates”. Special thanks were acknowledged to the four sponsor companies of the evening: Taconic, Isola, Ventec Europe and CCI Eurolam.
The first presentation “Material for Flexible Printed Circuits” was from Dominique Garmy, Senior Accounts Manager, High Performance Laminates, Dupont.
Dominique has over 30 years experience with flexible materials and outlined the history and development of flexible laminates. He explained the choice of materials today and the development of new materials for the future. He explained how to choose dielectrics, adhesives and copper styles to suit the technology demands of the application. Water absorption is still the key cause of delamination and baking cycles up to 24 hours may be required in some instances. Future materials will give the designer the choice of very thin or thick copper as well as alternative metals such as aluminium, constantan and other resistive foils. A polyimide product is now available with a copper or aluminium heat sink incorporated which is mainly intended for LED applications. High speed controlled impedance flex material. Black Kapton and very thin dielectrics down to 12 microns are now available.
Material for Flexible Printed Circuits
The second presentation was by Jim Francey of Taconic. Jim is Technical Service Manager, Advanced Dielectric Division.
The development of point to point high speed wireless applications enabling gigabyte transmission rates requires that signal degradation in conductors must be reduced as far as possible. PCB constructs are preferred to ceramic due to the very much lower tooling costs. The engineering aspects are demanding for the PCB manufacturer. The use of Rolled and Annealed copper is preferred with a resulting trade off of lower peel strengths. Surface finishes have to be considered to minimise conductor loss. Silver is a preferred finish due to the excellent conductivity properties. Depth milling is used to mount “Monolithic Microwave Integrated Circuits” into cavities on the surface of the PCB to enabling shorter wire bond lengths. Printed filters require best in class imaging and etching capabilities. Very precise milling of the PCB material is also required to enable advanced connectors to be mounted. Dimensional stability of materials must be optimised to ensure layer to layer registration is near perfect. Passive inter-modulation from adjacent signals on the PCB must be minimised. Contaminants on the edge of pcb tracks can cause increased inter-modulation. High frequency PCB’s will require the use of laser cutting for complex features and connect interfaces.
Trends in RF and High Speed Digital and their effect on PCB Technology Requirements.pdf
The next two presentations were from Alun Morgan, Director of OEM Marketing, Europe for the Isola Group and MD of Isola UK .
Alun explained the driving forces for the development of PCB base materials. Key factors are thermal stability, signal integrity and cost performance. With the advent of Lead free soldering the thermal reliability of the base material is now of prime importance. The ability to withstand the increased temperatures, the enhanced demands of thermal cycling and the elimination of conductive anodic filamentation (CAF) are all critical for today’s laminates. Delamination and decomposition properties have been improved by the use of phenolic and novel curing agents. Increased Tg values and inorganic fillers have reduced z-axis expansion during the thermal cycling phases of assembly, rework and during the PCB life cycle. CAF failures are typically propagated at the glass to resin interface. Modification of the glass fabric to incorporate a more evenly distributed glass weave has improved the ability of the resin to wet and impregnate the glass bundles. Circuit design has also to be considered where CAF may develop. For example critical gaps may be staggered off the x and y axes in order to improve performance. Signal integrity was then discussed. Signal frequencies are continually increasing. The increased data rates, higher computing power and the need to reduce energy loss in the PCB are all key factors. The choice of dielectric properties and the influence of different styles of copper foil need to be fully understood by designers.
Base Materials for High End PCB's.pdf
Alun then gave a brief overview of Halogen Free Laminates. Halogen free means “free of halogenated flame retardants”. Asia is primarily the driving force for the use of these materials. Bromine compounds are still by far the most widely used flame retardants worldwide. As there is no legislation in place to limit the use of the reactive bromine based fire retardant, TBBA, the adoption of bromine free laminates is largely marketing driven.
In 2010 Europe will follow the lead from the USA and Japan in enhancing the requirement of television casings to once again have a degree of flame retardancy. Despite the lack of supporting scientific evidence there are still lobbyists who continue to put pressure on the use of halogen fire retardants so the research and development of alternative materials is important.
Comparing Halogen and Halogen Free Base Materials.pdf
Bill Wilkie closed the meeting by reminding delegates of the forthcoming ICT Foundation Course to be held at Loughborough University from the 12th to 18th April, and the ICT Annual Symposium to be held at the National Motorcycle Museum on 8th June.