In the early thick film days, resistors were designed using one mil squares
and often ended up in a variety of shapes as serpentine, or? In those days,
we used air abraiding techniques (sand blasting) to "trim" the resistors to
the correct value after the resistor ink was screened and cured on the
substrate. Much depended on the thermal coefficient of expansion of the ink
after cure and after being subjected to many tests.

Not much has changed in the process, from design through acceptance, but for
markedly improved inks that are much more stable, and the laser trimming
process. Where this applies in some PCB designs is when using resistive
inner layers as "Omega" ply types. In some instances the same concept is
used to trim the resistors to their intended value and required tolerances.

MoonMan

---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------