These flex circuits included trace encapsulation with polyimide coverfilm. Examination of x-sections showed that the dendritic growth was following the field lines between traces in the coverfilm adhesive. For the materials that were failing, the adhesive itself was acting like a solid state electrolyte. The incubation period was related to the time it took for the ionic level of the adhesive to attack the traces and get copper in solution, creating something like a plating cell. By the way, all of the Rogers R/flex adhesives have been tested and are immune to this effect. Andy Magee [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: FW: Re[2]: Humidity Testing Author: Dill, Norm J::(DILLNJ) at ~FABRIK Date: 7/11/96 5:46 AM From: Dill, Norm J Date: Thu, Jul 11, 1996 5:46 AM Subject: FW: Re[2]: Humidity Testing To: "'IPC - Technet Input'" Andy, Considering your test was run at 100 v with a .006" spacing, is there any chance that airborne contaminants contributed to your 300/500 hour failures? Norm Dill [log in to unmask] ------------------------ Subject: Re[2]: Humidity Testing Date: Wednesday, July 10, 1996 4:18PM We've done some testing on flex circuits and found that there was about a 300 hour incubation period before visible defects were evident on the failing circuits. Actual electrical failures (shorting) took up to 500 hours. The insulation resistance falls off early in the test as the moisture reaches equilibrium in the polyimide, and then falls further at about the time of the incubation period. The continuous bias voltage was 100V. 85C, 85%RH 100 mA current limited, 0.006" spaces between traces. Measurements were taken at 24, 48, 72, 144, 200, 300, 400, 500, 550 and 1500 hours. Andy Magee - Applications Engineer Rogers Corp - Circuit Materials Unit Tel: (602) 917-5237 Fax: (602) 917-5256 E-Mail: [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: Re: Humidity Testing Author: SIRGuru::(SIRGUR) at ~FABRIK Date: 7/10/96 1:12 PM From: [log in to unmask] Date: Wed, Jul 10, 1996 1:12 PM Subject: Re: Humidity Testing To: TechNet I'll give you my favorite engineering answer - It depends. If you are trying to determine if a fabrication or assembly process is Bellcore-compliant, the answer is no. Bellcore compliancy is only obtained through the SIR and Electromigration testing in Chapter 13 of TR-78. If you are trying to determine if a vendor has acceptable product, and you don't really care about Bellcore compliance, then I would say the answer is yes. The seven day SIR test, IPC-TM-650, method 2.6.3.3 rev A, is an alternative. The Bellcore electromigration test is 85C/85% RH, so is the SIR method. The Bellcore test goes 96 hours before the first measurement in an unbiased state, then a bias of 10 volts is applied. The SIR test is biased from the start with a 50 volt bias. The Bellcore test is not tied to an absolute resistance value. The SIR test has a minimum of 100 megohms. I'm not really trying to bash the Bellcore electromigration test, but I understand the time constraint. In my opinion (that and 50 cents gets you a Diet Coke), you are best to do both methods concurrently. The SIR test should be able to allow you to make the decision in 7 days vs. 25 days. Alternatively, you could interrupt the electromigration test after 7-10 days and see if you have any signs of corrosion or metal migration. It has been my experience that if you have not seen electromigration and corrosion after 7 days at 85/85 and a 50 volt bias, you would not see it in 500 hours. Again, my opinion. Hope this was helpful. If you want to discuss it in greater depth, give me a call at (317) 457-8095. Doug Pauls CSL, Inc. [log in to unmask] *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ***************************************************************************