John, I'll share with you what I know about Staggered and Spiral vias. We do some MCM-C (Multi-chip-Modules Ceramic) designs. Sometimes Staggered and Spiral vias are required. Ceramic Multi-chip-Modules are built different from pwbs. The holes are punched or laser drilled in each layer prior to printing the conductors on them. After the holes are made and gold conductors are printed, the layers are stacked. This is were the Staggered and Spiral vias come in. If holes stack up like thru hole vias, bumps appear on the outer surfaces of the ceramic MCM. This is caused by the gold fill in each hole being stacked up on top of each other. To avoid this, you can stagger the vias (blind) in different patterns. One method is to arrange them in a spiral staircase type of structure allowing you to travel to different layers. Although it appeared to solve manufacturing problems, routing the design is much harder. Auto routers don't like it either, some routers handle it better than others but setup is still complex. I believe some alternatives have been found to avoid the need for the via patterns but I'll leave it at that. Also, micro vias in PWBs may use common patterns but I haven't been there yet. TWO ################################################################ TechNet E-Mail Forum 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://jefry.ipc.org/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ################################################################