Hi Sam,
according to UL746 (?) the temperature limit for FR4 is 130 ºC.
Kind regards,
Dieter

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From:   Sam Mollet[SMTP:[log in to unmask]]
Sent:   Monday, 11 May, 1998 14:25
To:     [log in to unmask]
Subject:        [TN] Maximum FR4 operating temperature


I have an application with a maximum ambient temperature of 70 °C.  I am using copper planes on FR4 to help cool some power resistor leads.  The copper planes can hit 115 °C.  Is this a problem?  Is there a rule of thumb on how hot FR4 can continuously be operated at?