Hi,
The thermal expansion of FR-4 will greatly depend on the resin content as well
as on how much copper (P/G planes) is in the MLB. Also, there is an
independent  volume expansion with the absorption of water. Measurements
typically are in the following ranges:
Resin ONLY:
  CTE(below Tg)~30 to 40 ppm/°C, CTE(above Tg)~90 to 130 ppm/°C;
CTE-constraint by glass cloths:
  CTE(x,y, below Tg) ~18±2 ppm/°C, typically there is a 2 ppm/°C difference
between x and y;
  CTE(z) @ 3a => CTE(z,below Tg)~50 to 85 ppm/°C, CTE(z,above Tg)~240 to 390
ppm/°C;
CTE(electrolytic Cu) ~17 to 18 ppm/°C.

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]

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