Hello, I have a 2 part problem. Our customer has informed us they are seeing phase errors in the assemblies we build for them. The requirement is all channels need to have a phase delta of < 14.5 degrees. In other words, the max phase - the min phase across 48 channels. Part 1 of the problem is a phase delta in excess of 30 degrees. We have found the root cause of this problem to be PCB delamination. Part 2 of the problem is the phase delta around 15-18 degrees. This is usually brought back into tolerance by changing an SMT capacitor. Finding the root cause of part 2 is proving to be rather challenging. Originally the specification was < 8 degrees. When the customer started seeing failures, they increased the specification to < 14.5. When they saw even more failures in addition to the delam, they finally brought it to our attention. In my opinion the stripline construction "should" be rather forgiving. It's 1/2 oz, 19.4 mils wide surrounded by ~18 mil dielectrics on each side. Though one of my concerns is each trace length is around 14.5 inches and is serpentined. In addition, no two serpentine designs exhibit the exact same pattern. Another concern I have is the channels are spread across 3 different layers in the stackup (16 channels each on layers 2, 7, and 11). The PCB is 12 layers. Layers 2 and 11 have the same stackup: ==================== Ref 18 mil core -------------------- Signal 5.8 mil pp 6 mil core 5.8 mil pp ==================== Ref Layer 7 is slightly different: ==================== Ref 12 mil core 5.8 mil pp -------------------- Signal 18 mil core ==================== Ref Also to toss another variable in the mix. This board is completely round with each channel beginning at the perimeter of the PCB and equidistant from the next channel. So with that said, I am aware of the trace orientation in regard to weave/glass/resin now becomes a factor as well. So my question to the list is: What are some causes of an increased phase spread? Also, any reference material recommendations are welcomed. Thank you, Craig Sullivan Manufacturing Engineer MPL Incorporated P: 607.266.0480 F: 607.266.0482 csullivan@xxxxxxxxxx Export Control: This message is intended only for the addressee and may contain information that is company confidential or privileged. Any technical data in this message may be exported only in accordance with the U.S. International Traffic in Arms Regulations (22 CFR Parts 120-130) or the Export Administration Regulations (15 CFR Parts 730-774). Unauthorized use is strictly prohibited and may be unlawful. If you are not the intended recipient, or the person responsible for delivering to the intended recipient, you should not read, copy, disclose or otherwise use this message. If you have received this email in error, please delete it, and advise the sender immediately. ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu