Just one note of caution when evaluating CEM3 material.  This material 
     is seen to differ considerably in its mechanical characteristics from 
     vendor to vendor.  Some vendors in the U.S. like GE and Allied signal 
     have CEM3 which is much different from for instance, Nanya which is an 
     Asian supplier.  CEM3 is typically used in double sided applications.  
     It is much better for punching than FR-4, it is weaker mechanically, 
     will warp more through the reflow or wave solder.  Price is typically  
     8% to 10% raw material cost savings than FR-4.  Is largely used in 
     Japan.
     
     Regards:
     
     Steve O'Hara
     [log in to unmask]


______________________________ Reply Separator _________________________________
Subject: [Fwd: Re: CEM-3 vs. FR-4]
Author:  Non-HP-pcbdsn ([log in to unmask]) at HP-Vancouver,mimegw2
Date:    12/16/96 7:53 AM


RwF - ext. 355 - Pat Bailey wrote:
> 
> Are there any significant differences/concerns in fabrication, assembly, or 
> long term reliability when comparing CEM-3 to FR-4 for double sided PTH
> boards?  Is it compatible with carbon direct metallization?  In what
> product applications is CEM-3 typically used for double sided PTH boards?
>  From what I've been able to gather, it is used quite a bit in Asia but not 
> in North America.  Why (availability, end product application/reliability
> reqiuirements, no significant cost advantage...)? 
> 
> Regards,
> 
> Pat Bailey
> Zytec Corporation
     
Pat while in another life we used CEM-3 quite extensivly. The main 
problem we has was with Bow & Twist. The material moved around so much 
that we ended up switching to FR-4. The movement was around .001 per 
linear inch. What our vendors ended up doing was trying to predict the 
movement and adjust the drill, Rout & A/W to compensate. An after 
thought I have had recently was if we were to have been able to use an 
OSP on our boards in our production environment would that have made the 
material more stable. We did try an OSP but not for this reason and it 
failed in our application using "no clean" assembly techniques.
     
Steve Collins
PCB Design Supervisor
TSX Corporation
El Paso, TX
Ph: (800) 351-2345
Fax: (915) 543-4898
email: [log in to unmask]
     
     
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