Hi K.K.,
While your idea to "specify in my PCB drawing such that a fab. house always
orientates my PCB in a particular axis...as a means to match with the CTE of
certain components on that PCB", is a good one theoretically, in practical
terms it is not very practical. The CTEs between X-axis and Y-axis vary
typically by 2 to 3 ppm/C, but the CTEs for these directions themselves have a
varibility of about +/-2 ppm/C. If you are that desperate to tailor the PCB
CTE to the coponent CTE, you will have to measure and select from a population
of PCBs.
But I can not believe to achieve adequate reliability requires such drastic
measures.

Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL  32174  USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask]

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