METHOD OF ETCHING APERTURES IN A THIN METAL FOIL

METHODE D'ATTAQUE PAR L'ACIDE DES OUVERTURES DANS UNE MINCE FEUILLE DE METAL

English Abstract

ABSTRACT:
A method of etching apertures in a thin
metal foil. The foil is first covered on both sides
with etchant-resistant layers which have the desir-
ed pattern of apertures. One of the said layers is
covered with a continuous protective layer. First,
the side not covered with a protective layer is
etched. The protective layer is then removed by
means of a solvent, and then the other side is
etched. According to the invention, the protective
layer consists of a waxy hydrocarbon and the solvent
consists of perchloroethylene.
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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of etching apertures in a thin metal
foil, in which method each side of the foil is covered
with an etchant-resistant layer of fish glue having a
desired pattern of apertures, a first of the two sides
of the foil is then covered with a continuous covering
layer which is also etchant-resistant, then the foil is
treated with an etchant to form cavities on the second
side of the foil which is not covered with the said
covering layer, the covering layer is then removed by
means of a solvent, after which the foil is treated
with an etchant to form cavities on the first side of
the foil in such a manner that the cavities on both
sides form continuous apertures in the foil, character-
ized in that the covering layer consists of a waxy
hydrocarbon and the solvent consists of perchloro-
ethylene.
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Description

P~IN 7
BKS/R~1
2~.3.75
~6~5~
"Method o:f etching apertures in a thin metal foil'i.
.
The invention relates to a method of etch-
ing aper-tures in a thin me-tal foil, ~l~ich.l~e-th~:ithQi.foil is
.~ covered on both sides with an etchan-t-resistant
layer having a desired pattern of apertures, a
; 5 first of the two sides of the foil is then covered
with a continuous covering layer~which is also
s-tchant-resistant, then the foil is treated with
an etchant to form cavities on the second side of
the foil which is not covered w:ith ths said cover-
ing layer, the covering layer is then removed with ~-
a solvelLt after which the foil is treated with an
etchant to forrn cavities on the first side of the
foil irl such a manner that the caviti~s on both
: .sides form contlnuous apertures in the foil.
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Such a method is known from United States
Patent Speclfication 2,750,524 and is used, for
~ample,: for etching apertures in a metal foil
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used in the manufacture of a shad~pw mask for a dis- .
play tube for colour tele~vision. In order to snsure
that the apertures have -the desired profils, in the
kno~n method ons of the two ~ldes is first subjeot-
cd to an init:ial etching trsa-tment - a covering
layer beil1~ present on the other side - succeeded
by etching the aper-tur.es through frorll said other
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PIIN. 7874.
1-10-1975
sicle.
In the known method it i5 difficult both
`. to ~ind a suitable composition for the covering layer
O which is provided on the first side o~ the foil~and to
'~ 5 find a suitable solvent for the said covering layer.
~, The apertured etchant-resis-tant layer rnust not be
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attached either by the covering layer or by the solYent
for the said covering layer. The aperture~ etchant-
7, resistant generally consists of photosensitive fish
glu0 which prior to 0xposure to light is water~soluble
and after exposure to light and ba~ing can be removed
by sodium hydroxide solution.
It is the object o~ the invention to pro-
~` vide a covering layer and a solv0nt ~or the covering
'~ 15 layer which can be used in partiGular in combination
with a layer of ~ish glueO
: ~ For tha-t purpose~ according to the invention
;the covering layor ~hould consist of a waxy hydrooarbon
j~ ~ and the solvent should consist of p0rchloroethylene.
Experiments with a.large number of~ substances
j for the covering lay0r hav0 demonstrated that a wa~y
hydrocarbon and perchloroethylene ls the best combina-
tion of covering lay0r and solvent for the covering layer.
. It was o:~ particular importance that the covering layer
j 25 could be remov0d withou-t leaving any r0sidues, since
otherwise on0 or more o~ the apertures in the pattern
of a.pertures rnay get clogged,
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PHN. 7874.
10-1975.
The invcntion wlll now be de.scribed in
greater detail with reference to the accompanying
dra~ing, in which each Figure shows a part of a
I metal foil in successive stages of a meth~d of e-tch-
c 5 ing apertures in it.
In Figure 1~ the metal foil 1 bears two
la-yers 2 and 3 which are etchant-resistant and in
:~ each of which a pattern of apertures 3 for example 7
i 4, 5, 6 and 7 respectively have been produced. The
apertures 4 and 6 make a pair, as do the aper-tures
1 5 and 7. The layers 2 and 3 consi.st of fish glue in
j which the apertures 4, 5, 6 and 7 have been produced
by mQans of a kno~n pho-togra.phic method.
i ~ In Figure 2, the layer 2 is covered with
a layer 8.which also covers the apertures 4 and 5.
The layer 8 consists of a waxy hydrocarbon which does
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not attack the fisll glue layer 2 and is provided by
~ mearls o~ a ~solution of 16 kg "Apiezon" wax in 100 l
j ~ .of perchloroethylene "Apiezonl' is -the trademark of
.: 20 . Apiezon Products Ltd.~in England for l~axy hydrocarbons.
The wax used ma~ be) for example, of -the type Apiezon 1~.
: ~ An etchan-t is then sprayed against the
- foil 1 with the layers 2, 3 and 8, and7 as is shown
in Fieure 3, the cavities 9 and 10 are etched in
: 25 the foiJ 1 v:La the apertures 6 and 7 in the layer 3.
The depth of the cavities g and lO is approxima-tely
2/3 of the thicklless ~approxlmately 0 150 mm th:ick)
. . . .

PMN. 787~.
1--10 19750
,~ . .
of the fo~l 1.
As is shown in Figure 4, the layer 8 is then
removed f`rom the layer 2 and from the apertures 4 and
5 by means of a solvent. The said solvent is again
perchloroethylene whic'h dissolves the waxy hydrocarbon
without leaving a residue but which does not attack
3 the fish glue of the layers, 2 and 3.
¦ Etchant is -then spra~ed against the foil
so that the cavities 11 and 12 are etched in the foil
via the apertures 4 and 5 as is shown in Fi~re 5. ..
The cavities 9 and 10 are also slightl~ enlarged
. by this etching treatment. The cavities 11 and 12 ''
i
: ~ debouch :into -the cavlties 9 and 10, respectivelyO
After remo~ing the layers 2 and 3 b~ means
of sodium hydroxide solu-tion, the ~oil then comprises
: the apertures 13 and 14 shown in Figure 6 which have
the requlred shape, ~or example~ narrow on the side
on which the electron impinge in an operating shadow,
~ mask tube, a.nd wide on the screen side o~ the tubeO
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