>Hi technos, we have some problems with 1812 (and also with 1210) capacitors >on FR4 because cracks at the corner. Is there any size limit for SMT cap's >on FR4 (may be different classed for different application temperatures)? >Thanks, Bernhard, Zürich Bernhard, I ran some tests over 10 years ago where we did -55 to +125 cycling tests of (mostly) 1206 and 1812 chip components wave-soldered onto FR4. The 1206s survived 2000 cycles with little evidence of degredation, but the 1812s had severe cracks in the solder fillets after only 1000 cycles. The test regime may or may not have much to do with your own product use environment, but the results do show that things rapidly get worse for larger components. I also had some TCE measurements performed at the UK National Physical Laboratory on 4 different types of capacitor dielectric material, which although all supplied by the same manufacturer, covered most of their commonly used range of dielectrics. The variation in TCE was surprisingly small - only 8.1 to 9.1 ppm/C (20-100C), so the results are likely to be similar for different capacitor types. The fact that narrower pads are often favoured for the larger capacitors suggests that their ability to survive the stresses of life on a PCB is pretty marginal and in the 60's it was shown that without yielding in the solder that chip capacitors on alumina wouldn't stand a chance - one of my worries about the prospect of a switch to lead free is that "harder" solders might result in a dramatic rise in the incidence of component failures and force the abandonment of the larger chip sizes, even in less severe operating environments. Do any other technetters have a view on this? David Whalley ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ##############################################################