Dave,
You are right, it is very difficult to perform a flow test on a prepreg that is supposed to be "No Flow". I assume that the weight differences you got in your test are to small to be meaningfull.

I have used less quantitative measures to test the prepreg but they served me well as for mimicing the process results:
I used to perform a lamination of two cores with one/two plies of prepreg (depends on the application) using the same temperatures and same specific pressure as in the manufacturing process. One method I used was examining the edges of the end product - expecting to see a small flesh (~2mm) of prepreg around the edges. 
Since many applications for No-Flow prepreg are with all kinds of cavity boards, you can more accurately mimic this situation by routing a large circle in the cores and prepregs prior to lamination (about 4mm diameter). After lamination check for that small flesh of prepreg INSIDE the circle (which acts as a"cavity").
If you have a stable process for the No-Flow, visual inspection of the laminated product can also suggest a clue about the state of the prepreg. If the flow properties of the prepreg are less then what you are used too, most likely that it will manifest in the form of delamination/measling between the cores.

Feel free to contact me directly for further information.

Regards,
Yehuda 

    ************************************* 
    *          Yehuda E. Weisz              
    *  e-mail: [log in to unmask]
    *  Tel: 972-3-5240362                    
    ************************************

-----Original Message-----
From:   David J Elias [SMTP:[log in to unmask]]
Sent:   Wed, September 17, 1997 12:42 PM
To:     [log in to unmask]
Subject:        [TECHNET] Prepreg test for No-flow Prepreg

We are currently using a 1" circle flow test, as our incoming inspection
method. We have started testing a new prepreg that has chemical flow
restricters, and have found that our current test is not indicative of
the preformance results that we are getting in our process.

Does anyone know of a test that I can preform in my lab that
will mimic the process results that I am getting.

Thanks
Dave

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