Does anyone know the CTE above Tg?

My supplier told me that CTEs (in plane)  of HL-832 are as following:

14-16 ppm @ 60-120C
9.5 ppm @ 120-240C
5 ppm @ 240-280C

I am very supprised that CTE2 is lower than CTE1. Their explanations are
as follows:

1)  Regarding alpha2
As for the Z-direction of CTE, alpha2 is higher than alpha1,
but XY direction of CTE is different.

Of course alpha2 of resin is higher than alpha1.  On the other
hand, glass fabric has no Tg and no alpha2.  It's CTE is constant
--  5ppm/k --- under 800 degC.

Under Tg, resin is hard and solid, so resin's thermal expansion
(60-80 ppm/k) is stronger than glass fabric's resistance (5ppm/k)
against resin expansion.

Over Tg, resin is soft, so glass fabric's resistance is stronger than
resin's expansion.  Therefore, alpha2 of XY is nearly glass fabric's
CTE  --- around 5ppm/k.

What are your comments? I still think CTE2 (above Tg) should be much
higher than CTE1 (below Tg), that's what is claimed in many literatures.

Thanks,


Yuan Li

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