Please remember that we are now putting resistors inside the circuit board.
IPC is working on standards for materials, boards, and design of embedded
resistors and capacitors.  An interest group has been formed - Embedded Passives
Users Group - to promote the technology.  More information can be found at the
EPUG web site - http://www.ipc.org/EPUG.  Files are by month so the March 04
will give you the latest postings.

EPUG has a conference call every three weeks.  Last time (March 4) we had
Mike Jouppi, "Thermal Man" consultant, and he told us of the thermal models he is
developing of embedded resistors (poor conductors) within circuit boards.

Of course, resistors inside boards must be designed so the operating
temperature does not exceed the circuit board Maximum Operating Temperature certified
with Underwriters Labs.  As stated before on this thread, the proximity of
thermal planes and heat sinks will allow smaller size embedded resistors, or
improve performance by lowering resistor value change due to changes from the
"temperature coefficient of resistance" in embedded resistor material.

Denny Fritz
MacDermid, Inc.

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