It depends on exactly what you want to measure. If you want the bulk
properties of the finished PCB, then you would include the glass finer; if
all you want is the resin, then you shouldn't include it. Be sure to
eliminate any copper, as well as solder mask materials, as these will affect
the readings. It is generally best to run no less than 3 samples and use the
arbitration averaging method for determination. In addition, each sample
should be taken past the Tg while measuring once and then gradually
quenched. This has the effect of annealing and ensuring the material is
fully cured. A partially 'cured' FR4, say 95%, can have a Tg some 20C less
than the fully cured material. This method will also allow you to determine
the intrinsic stresses as opposed to the ones induced by processes.

In closing, depending on the manufacturer of the DSC equipment, you may need
as little as 1mg or as much as 20mg of material.

Best regards,
> Bill Davis, Ph.D.
>
> [log in to unmask]
>
>


-----Original Message-----
From: <Chong Chee-Leong>
[mailto:[log in to unmask]]
Sent: Monday, October 18, 1999 12:53 AM
To: [log in to unmask]
Subject: [TN] Tg Measurement for PWB
Importance: High


     Hi, ALL

     I need to measure the actual Tg of G10 & high temp FR4 by DSC method.
     My colleague was telling me that the sample need to be made into fine
     pieces. My question here is how the sample is prepare. Is it right to
     include the glass fibre that is embedded in the PWB ? I would
     appreciate all your reply.

     Thanks
     CL Chong

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