I have a comprehensive chart which I can fax you, if you want to provide the phone #. Generally, Z-axis is 60 to 80 ppm (or microinches/inch/C), X is 17-20 ppm, and Y is 15 to 18 ppm. Lots of variables however: a. These values are for a temp ramp up to the Tg, which is 135C typically for FR4. b. Remember that FR4 today can be a material with a Tg as high as 180C. Higher Tg FR4's tend to exhibit a slightly lower Z-expansion below the Tg than 135C types. c. Z-axis is particularly affected by resin:glass ratio. Higher Resin content means greater expansion, which has to be considered in high layer count designs. d. Above the Tg, the X and Y movements get squirrelly because the softened resin allows the glass fabric to pull back against the expanding matrix, resulting in much lower values. jimpaulus ################################################################ 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's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################