Todd Zorn asked (about using buried resistors) :

> What is the cost attributed to this type of process for a typical 4-layer FR-4 PCB?


The answer, sorry to say, is not as easy as the question.
After consulting with my price guys, I got the following answer,
 although somewhat of a runaround. 

1. The cost of raw material is ROUGHLY double that of standard laminates.

2. The cost is affected by the same yield issues as the rest of the board.

     - Density and size of resistors. 
        The more there are and their smallness may cause yield
        problems to drive up the board cost.

     - Basic 4-layer boards are not usually a candidate for buried resistors.
        Because there is not a density crunch on the surface.
   
     - However, if a buried resistor is desired, you can expect the following benifits:
        elimination of discrete resistors
        rework reduction
        board density and size reduction
        elimination of solder joints
        excellent reliability
        elimination of shock/vibration effects on resistors
        elimination of moisture/dirt around resistors
        shorter signal path (tyically right at pin)
        termination of ALL signals possible
        reduced surface EMI
        can place UNDER components
        weight savings

3. They were also quick to remind me that the overall yield and quantities
   would impact final prices. 
   For example, 
        If you had a board that had many surface resistors and was a high yield 
        board to construct, then you could save on the fabrication as well as the 
        assembly of a board by eliminating the discretes from the surface.

I hope this helps, 
For a more exact rundown of price I would need much more job specific data.

I typically do this type of design sparingly since most designs are able to
accomdate the old guard of surface discretes. 

--
Robert Blomstrom, DWB Design            
Advanced Interconnection Technology, Inc. - Atlanta
3289 Montreal Industrial Way, Tucker, Ga. 30084
Phone: 404-938-9387 x226    
fax:   404-934-9885         
e-mail address: [log in to unmask]     


PS. DWB stand for Discrete Wiring Board... but that's another topic.
    See us at http://www.ait-atl.com soon !!!