I missed that article, David, although I subscribe on SMART, interesting article, really. We have a PWB of the kind with nervous caps also. After a few tempcycles, the nervous components ( just a few in stressed positions) are removed and superseded with new ones, most solder joints seem to have relaxed, no more problem. Clumsy method, but works. In fact, we can sometimes hear (!) what happens when running up and down in temperature. A tiny, crispy 'krzt' tells that a 'tension' release happened, same reason as for earthquakes, but at a smaller scale. Talking about this, one can wonder how some boards survive and work without these problems, I mean boards in movable equipments, toys, vehicles, weapon etc. jumping up and down mechanically, vibrating, slammering and running up and down in quite unpredictable manners, many of these just leave the line, are packed and sent to the market on the other side of the globe, are unwrapped and put immediately into work. A contradictory world, isn't it. Thanks again Regards // Ingemar Kühl R.W. "Mechanical stress and deformation of SMT components during temperature cycling and PCB bending" Soldering & Surface Mount Technology, 22 April 1999, vol. 11, no. 2, pp. 35-41(7) Abstract: A very common method to predict the reliability of components soldered on printed circuit board (PCB) or substrates is by bending tests and temperature cycle tests, for instance between -55°C and 125°C (up to 2,000 cycles at 1h cycle period). Sensitive SMD constructions such as chips with ball grid array mounting or multilayer chip capacitors (MLCC) are often a major issue due to their "flex cracking" problems. This paper describes the real behaviour of deformation at temperature cycling and PCB bending of chip components (body size 0603). By using the piezoresistive effect in thick film resistors the effects of stress on the alumina body can be determined and described for the whole temperature range of interest. The complete system of component, PCB/substrate and solder joint will be discussed and different influences will be isolated. It will be shown that CTE-matching of the component and substrate does not lead to an optimum situation. The influence of the solder joint plays an important part. Optimization potentials and design rules for the whole system will be given. The basis of this paper is a quite unusual "measurement tool" the effect of piezoresistivity. The investigation into that phenomenon will be described very thoroughly first. ############################################################## 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 Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ############################################################## ############################################################## 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 Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ##############################################################