If I was a betting man, I would bet that your opens are due to plated through hole failures. Most rigid flex stackups heavily depend on special adhesive materials that enable the polyimide material to bond to the FR-4 laminate. One unfortunate side effect of this is the fact that these adhesives have an extremely high Z-Axis expansion of the PTH during thermal excursions such as assembly, particularly IR for SMT assembly. Conventional Rigid flex materials and technology does not mix well with SMT assembly processes. This problem is much worse if you are using small vias (i.e. much less than 30 mils diameter). If you have an SMT design I'd bet you are using small vias. You can solve this problem by using larger vias or using less adhesive in your stackup. If this is not possible you might go to some of the more advanced rigid flex technologies that are out there such as Regal Flex which has a clever way of avoiding this problem. Contact someone at Zycon or Automata and they can help you with Regal Flex. [log in to unmask] ------------------------------------------------------------ Problem: We experience an unacceptable failure rate with open in rigid flex boards AFTER assemby and thermal cycling. Question: I feel there is a good chance the problem is in the assembly process. What kind of things should I look for? The boards are mixed surface mount and thru-hole, with much hand soldering and rework. Thanks George Franck