TABLE OF CONTENTS Dr. Hayao Nakahara
N.T. Information Ltd., Huntington, New York
For 40 years the PTH process of choice has been palladium followed by electroless copper, but there have been at least 12 DMT processes challenging that established process, with several hundred installations, a significant percentage of the total number of PCB shops. The basic idea for the palladium systems dates back to the Radovsky patent of 1963,1 which claimed a method of using an electrically nonconductive film of palladium in a semicolloidal form to directly metallize through holes in printed circuit boards. Radovsky s invention was never commercialized. The basic idea for the carbon/graphite systems dates back to the very early days of eyelet boards when Photocircuits was experimenting with graphite, silver, and other media to turn their single-sided PCBs into reliable double-sided boards.
From the many media and technical variations, some common elements have evolved.
There are two elements common to all DMT:
Holes must be conditioned more specifically and thoroughly than for electroless copper.
Conductive media must be removed from the copper foil in a majority of the techniques (an exception is DMS-E).
It is understood that additional desmear steps are necessary or advisable when processing multilayer PCBs. Common elements to all horizontal conveyorized DMT systems are:
Throughput is typically 6 to 15 min for a panel, with the next panel following 1 in behind
Tremendous economies in rinse water use
Lower...
