Issue link: https://iconnect007.uberflip.com/i/271756
20 The PCB Magazine • March 2014 If you really need a thinner dielectric with a heavy copper, you can consider the use of RTF foil…but peel strength will be reduced. Beware of Data Sheet Values and Manufacturers Claims There is still a tendency for some manufac- turers to quote figures based on in-house test methods, even thermal conductivity data is significantly overstated against recognised test methods by some producers. Until the IMS market matures and a uni- versally accepted set of test methods emerges, inconsistent test methods will result in some anomalies making direct correlation of data sheet values difficult. Dielectric breakdown and dielectric with- stand values—results depend on the design of the test coupon for some commonly used test methods—as a manufacturer we tend to use the well-recognised methods of IPC-TM-650. Only use data sheet values as a guide, which means: • Don't rely on the accuracy of figures where the exact test method is not stated. • don't take the results too literally, even when a recognised test method is stated • To quote from ASTM D149, Standard Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials at Commercial Power Frequencies: Results obtained by this test method can seldom be used directly to determine the dielectric behaviour of a material in an actual application. In most cas- es it is necessary that these results be evaluated by comparison with results obtained from other func- tional tests or from tests on other materials, or both, in order to estimate their significance for a particu- lar material. International standards for production of IMS, and metal backed circuits; part of the prob- lem is that there are no concrete standards at the moment. Committees are in place to devel- op standard for IMS and conductive substrates, we along with a number of manufacturers and LEADING end users are involved. Until this is resolved, buyer beware! Over the last few years, there has been a pro- table 4: dielectric comparison. THERMALLY CONDUCTIVE SUBSTRATES & THERMAL MANAGEMENT continues