T. Gaylor:
     
     As you already know the main area of consideration in flex 
     manufacturing is the material.  The flex layers are an integral part 
     of the construction and being a different material than the rigid 
     layers, they change differently.  Flex material is a film which by 
     itself will shrink or grow depending on ambient conditions.  Typically 
     polyimide film, (Kapton) can change a mil per inch during processing. 
     Some of this change can be compensated by scaling artwork, lamination 
     cycles and lam materials and a big one, handling.
     
     Flex lamination requires a minimum of two lam cycles.  The first is a 
     coverlayer which is the insulating film in the flex area.  This 
     requires a conformal pad top and bottom in order to wrap the film 
     around the conductor.  This pad structure can consist of teflon glass 
     cloth, tedlar, combination materials such a trade name product, 
     "pacothane" or silicone rubber.  The second lam cycle is the 
     multilayer lamination which usually utilizes no-flow prepreg but could 
     be constructed using an unsupported adhesive film such as Dupont's 
     Pyralux.  Again there can be different pad make ups.  As with rigid 
     boards there can be blind or buried via processing.
     
     The basic processing steps are the same for a rigid-flex as for a 
     rigid board except that there are more of them, and it requires more 
     tooling and front end engineering.
     
     Obviously equipment must be capable of handling thin cores.  A typical 
     double clad core will 1 oz cu/2 mil dielectric/1 oz cu which is less 
     than 5 mils thick.  The copper is usually dead soft, rolled and 
     annealed which is where the handling problem comes in to play.
     
     Another area of concern is hole quality.  There are different drill 
     parameters required for rigid-flex and you would not typically stack 
     more than one high on the drill.  Desmearing in most cases requires 
     plasma etch capabilities.  
     
     These are a few of my rambling thoughts.  If you would like to discuss 
     off line give me a call.
     
     Regards,
     
     Ron Yanuszewski
     
     603-337-1691


______________________________ Reply Separator _________________________________
Subject: Flex
Author:  [log in to unmask] at !INTERNET
Date:    1/3/97 12:18 AM


I am curious, about the manufacturing of rigid/flex circuits. 
     
At our shop, we currently are not looking into any type of technology 
similar to this.  I would like to know the considerations of working 
with a process such as this. 
     
I have heard that the lamination  technique is somewhat different than 
conventional rigid multilayer processing. Also, another difference I 
have heard is the registrationing of the flex to rigid.
     
I would appreciate if someone could give me some insight on rigid/flex 
processing.
     
Thanks in advance
     
T. Gaylor 
     
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