What you've described has all the characteristics of dendritic growth. More specific detail about the operating conditions and board construction would be required to know definitively. For flex circuits the traditional model attributes the dendrite growth to ionic contaminants at the adhesive interface of the coverfilm and base laminate. These contaminates arise from exposure to process chemicals prior to encapsulation of the traces with coverfilm. During use the contaminants respond to moisture exposure by creating conductive pathways between oppositely charged circuit traces. In the past few years failures attributable to the adhesive composition have been encountered. In these cases examination revealed that the positively biased traces (anodes) had tarnished and the negatively biased traces (cathodes) had grown dendrites visible at 100X. These developed in <300 hours at 100V, 85C, 85%RH. Cross-sections of the dendrite structures revealed that the coverfilm adhesive itself was acting as an electrolyte, providing the path for growth, rather than arising from any contaminants at the interface. We worked with Seagate Technology, Bloomington, MN a couple of years ago to develop qualification tests to insure that our adhesive systems are immune to this phenomenon. Various types of adhesive from several other suppliers were tested and several constituents were identified that commonly lead to this effect. Chief among them are excessive levels of BF3 catalyst or various sulfur compounds. Andrew P. Magee - Applications Engineer Rogers - Circuit Materials Unit Tel: (602) 917-5237 Fax: (602) 917-5256 E-Mail: [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: Dendritic Growth? Author: mmlettan (mmlettang) {NAME:mmlettang|EMS:INTERNET|MBX:[log in to unmask] at MCIMAIL Date: 10/6/95 4:05 PM Background: We had a PWA fail in the field after approximately 6-7 months. The unit was powered on approximately 1000-2000 hours. Analysis of the PWA revealed a short had developed between two parallel traces underneath an IC. The traces are .006" wide and .010" apart. The short was not visible (even under a microscope). The short was approximately 2 1/2 ohms in value. Once a razor was run between the traces the short was eliminated and the PWA was functional once again. Someone I spoke to at a PWB Fabricator suggested it might have been dendritic growth. Questions: What is dendritic growth? Does causes it on a PWA? Where can I get more information about it? Can it be attributed to the PWB fabrication? Any and all assistance is GREATLY APPRECIATED! Best Regards, Mark Lettang 3M [log in to unmask] (507)359-0418