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Hacker, Robert W. (ed.) / The Wisconsin engineer
Volume 53, Number 4 (January 1949)

W. M. H.; R. R. J.
The way we see it,   pp. 17-32 ff.

Page 24

Science . . 0
        (conlli-tedS frn Page 12)
would not permit high quality pic-
tures. Motivated by the possible
military use of the image orthicon,
intensive work was begun to find a
way to make high transmission, uni-
form screen of 500 mesh or more.
  In  the  process that resulted,
screens are plated on a specially
prepared glass "master" that con-
tains grooves etched into the glass
surface corresponding to the net-
work of screen wires. The master is
prepared for plating by sputtering
the surface in air with a thin layer
of palladium and then rubbing the
metal from the glass surface while
leaving the metal in the grooves
untouched. Copper is then electro-
plated on the palladium remaining
in the grooves to form the finished
screen. After removal of the screen,
the glass master is cleaned for reuse.
  Techniques similar to those prac-
ticed in making half-tone screens
on glass are used in making the
    The "world's finest screen" is shown being manufactured at
the RCA plant,
Lancaster, Pa.                                         (Photo cotu-tesy RCA)
glass masters. In general, a piece
of plate glass is covered with a
layer of acid-resistant material. Lines
are ruled through this layer with a
ruling engine of the type used for
optical gratings. Then the glass is
etched for a short time in hydro-
partners in creating
For 81 years, leaders of the engineering profession
have made K & E products their partners in creating
the technical achievements of our age. K & E instru-
ments, drafting equipment and materials-such as the
LEROYt Lettering equipment in the picture-have thus
played a part in virtually every great engineering
                                        TKeg. U. . rat. Ott.
            EST. -18
   Chicago * St. Louis * Detroit
San Francisco * Los Angeles * Montreal
fluoric acid to form grooves where
the lines have been ruled. In mak-
ing masters for screens of 500 or
more mesh, one problem is to keep
the etched grooves very narrow in
order to produce screens with more
open area than metal area. Another
is to obtain grooves with sharp
edges and, at the same time, suf-
ficient depth to withstand the abra-
sions of the rub-off process for a
reasonable number of operations.
The 500 line masters have a line
width between 0.0003 and 0.0004 of
an inch.
  The unwanted palladium layer is
removed by placing the master in
a shallow dish of water and rubbing
the surface with a small piece of
rubber. A small strip of palladium
is allowed to remain on one edge of
the master to serve as an electrical
contact during the electroplating.
Since scratches show up in the final
screen as extra wires, the utmost
care and cleanliness is essential dur-
ing the rub-off. Although a continu-
ous layer of palladium is left on the
grooves after the rub-off, its con-
ductivity is too low to permit direct,
uniform plating over the surface.
Therefore it is necessary to place
the plating contact under the solu-
tion and depend on a plating growth
phenomenon. Deposition takes place
        (please torn to page 28)

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