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
################################################################