Note: Descriptions are shown in the official language in which they were submitted.
7~973
The invention relates to printed circuit boards and
methods of making the same.
A known printed circuit board has a printed circuit of
electrically conductive material which is adhesively secured to
a non-conductive substrate. The printed circuit is chemically
deposited on the substrate in a thickness sufficient to carry
the current which is supplied to the circuit board.
Printed circuit boards are manufactured in various
ways. In the additive technique, an aluminum foil is coated
with an adhesive, e.g. acrylonitrile, butadiene or a
phenolic-based adhesive. After pressing, this carrier material
constitutes a core catalyst on which copper may be chemically
deposited. The core catalyst may also be cast or may be coated
by immersion. This coating is dried at a temperature of 140C.
After cutting and drilling, etching is performed in a mixture
of chronic and sulfuric acids. This is followed by the screen
printing process and the further copper plating by chemical
means.
Another method uses a base material which is laminated
with a copper foil. Pressure is applied via the screen printing
process. The areas which remain exposed are etched.
The methods used heretofore for the production of
printed circuit boards require relatively complicated and
expensive procedures. The production of a base core catalyst,
in particular, is a very costly step.
The known methods for the production of printed
circuit boards also have disadvantages aside from their high
cost. Thus, they contribute strongly to environmental polution
and require large amounts and material and labor.
According to the invention, a printed circuit board
3 ~77973
having a printed circuit of a predetermined pattern includes a
substrate and an adhesive layer on the substrate conforming to
the pattern. A base layer is provided on the adhesive layer and
an electrically conductive layer is chemically deposited on and
bonded to the base layer. In accordance with one feature of
the invention, the adhesive layer is substantially free of
solvent when the base layer is applied thereto.
me electrically conductive layer is deposited in a
t~ickness sufficient to carry the current which is supplied to
the printed circuit board.
The substrate which receives the adhesive layer is
preferably non-conductive.
The invention further provides a method of ~aking a
printed circuit bcard having a printed circuit of a predetermined
pattern. m e method involves applying an adhesive layer to a
substrate in conformance with the pattern and coating the adhesive
layer with an electrically conductive layer.
According to a preferred em~odiment of the method, the
adhesive layer is pressed onto a non-conductive substrate in
accordance with the predetermined pattern of the printed circuit
and the solvent present in the adhesive layer is removed there-
from. A foil oomposed of a material which is capable of bonding
to a chemically deposited, electrically conductive substance is
pressed onto the adhesive layer after removal of the solvent
but before the adhesive layer has set or hardened. After the
adhesive layer has set, the foil is peeled away in such a
manner that the portions of the foil corresponding to the pattern
of the printed circuit and the adhesive layer remain on the latter.
The portions of the foil which remain bound to the adhesive
layer constitute a base or base layer for the electrically
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~77973
conductive layer. The electrically conductive layer, which is
advantageously metallic, is subsequently chemically desposited
on the base layer in a predetermined thickness sufficient to
carry the current which is supplied to the circuit board.
m e only pretreatment which the substrate requires is
a degreasing, m e ninin~m di:stance of separation between the
conducting strips of the printe circuit to be produced, as well
as the fineness of the conducting strips, are deternuned by the
particular manner in which pressure is applied.
m e base layer, which is capable of being chemically
metallized and via which chemical metallization of the adhesive
layer is effected, may be desposited in very precise thicknesses.
The base layer may be very thin (100-400 Angstroms) so that only
small amounts of chemically metallizable material are required
to produce the sante. m is makes it possible to form the b~se
layer from expensive materials such as, for example, noble rltetals
and valuable rare ear~ls t~;~ich ena~le good deposits of tile chem-
ically deposited, electrically conductive layer to be achieved.
me invention does not require the substrate to be
provided with a core catalyst or to be etched. Rather, only
those areas corresponding to the electrically conductive layer,
i.e. the conducting strips of the printed circuit, are coated
with a layer which is capable of being chemically metallized
and which forms the base for the metallic, electrically conduc-
tive layer to be deposited by chemical means. me electrically
conductive layer may be made of any metal which can be deposited
via chemical metallization. Accordingly, the base layer may be
deposited on the adhesive layer independently of the particular
~tetal which is selected fDr the electrically conductive layer or
strips. A printed circuit board ~anufactured in accordance with
~ ~'77973
the invention is inexpensive as regards both the manufacturing
operations and the basic materials to be used.
The novel features which are considered as
characteristic of the invention are set forth in particular in
the appended claims. The improved printed circuit board itself,
however, both as to its construction and its mode of operation,
together with additional features and advantages thereof, will be
best understood upon perusal of the following detailed
description of certain specific embodiments with reference to the
accompanying drawing.
Figure 1 is a cross-section through a degreased
substrate;
Figure 2 is a cross-section through the substrate of
Figure 1 illustrating the application of an adhesive layer to
the substrate;
Figure 3 is a cross-section through the substrate of
Figure 2 showing the application of a foil of a base metal to
the adhesive layer of the substrate;
Figure 4 is a cross-section through the substrate of
Figure 3 illustrating the removal of those portions of the foil
which do not adhere to the adhesive layer of the substrate; and
Figure 5 schematically illustrates an apparatus for
manufacturing printed circuit boards in accordance with the
invention.
Figure 1 illustrates a substrate 1 which is to be
provided with electrically conductive strips or paths forming
the printed circuit of a printed circuit board. The substrate 1
has been degreased in a known and non-illustrated manner.
As seen in Figure 5, which schematically illustrates
an apparaius advantageously used for carrying out the method of
973
the invention, the substrate l is placed in a non-illustrated
supply vessel together with other similar substrates. In the
illustrated embodiment, the substrate l and the other substrates
are assumed to be in the form of individual sheets or wafers
and are arranged in a stack. However, it is also possible for
the substrate l and the other substrates to be supplied from a
roll.
Referring to Figures 2 and 5, the substrate l is
conveyed from the stack to a printing station 3 where a layer
4 of adhesive is applied to or imprinted upon the substrate l.
The adhesive layer 4 is applied to the substrate l in a
pattern which corresponds to that of the printed circuit to be
formed on the substrate l. In other words, the adhesive layer
4 is not applied to the substrate l uniformly but only in
those areas where the conducting strips of the printed circuit
are to be located. The adhesive layer 4 may be applied to the
substrate l by means of the screen printing process or the
intaglio process.
The adhesive used for the adhesive layer 4 will
generally be a dry lamination adhesive which should be free of
solvent at the time of lamination. As seen in Figure 5, a
drying station 9 for careful drying of the adhesive layer 4 is
located downstream of the printing station 3. All of the
solvent contained in the adhesive layer 4 is driven out of the
same in the drying station 9. Instead of using a solvent-
containing adhesive for the adhesive layer 4, it is possible to
use an adhesive which contains no solvent.
After leaving the drying station 9, the adhesive layer
4, which is now free of solvent, is brought into contact with a
strip 18 consisting of a carrier 12 and a metallic foil lO.
~;"7~73
This is shown in Figures 3 and 5. As best seen in Figure 5,
the strip 18 is produced by passing the carrier 12 through a
vapor deposition station 13 in which the metallic foil 10 is
vapor-deposited on the carrier 12~ The vapor deposition station
13 accommodates a metallic bath 15 and a heating unit 14. Both
an electrical field and a vacuum are maintained in the vapor
deposition station 13. The heating unit 14 heats the metallic
bath 15 to such a high temperature that metal ions 16 are
released from the bath 15 and, under the influence of the
electrical field and the vacuum, travel upwards towards the
carrier 12 and are deposited on the latter.
Referring again to Figure 3 in conjunction with Figure
5, the metallic foil 10 of the strip 18 is pressed against the
adhesive layer 4 by a pair of rolls 11. The rolls 11 press the
metallic foil 10 against the adhesive layer 4 in such a manner
that the metallic foil 10 adheres to the adhesive layer 4 at all
locations where the metallic foil 10 and adhesive layer 4 come
into contact. The rolls 11 may be heated in order to achieve
adhesion between the metallic foil 10 and the adhesive layer 4.
After being compressed by the rolls 11, the adhesive
layer 4 sets or hardens while in engagement with the strip 18.
Once the adhesive layer 4 has set, the metallic foil 10 firmly
adheres to the adhesive layer 4. The adhesion between the
metallic foil 10 and the adhesive layer 4 is so great that, when
the carrier 12 is peeled away, the portions of the metallic foil
10 which adhere to the adhesive layer 4 remain bound to the
latter. The adhesion between the metallic foil 10 and the
adhesive layer 4 is much greater than the cohesion between the
metallic foil 10 and the carrier 12. It is only along the
adhesive layer 4 that portions of the metallic foil 10 continue
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l~t77973
to adhere to the substrate 1 upon rem~val of the carrier 12.
me edges of those portions of the metallic foil 10 which remain
on the adhesive layer 4 are well-defined.
Subsequent to setting of the adhesive layer 4, the
carrier 12 may be readily removed from the substrate 1. As
illustrated in Figure 4, those portions of the metallic foil 10
which do not contact the adhesive layer 4 continue to adhere to
the carrier 12 when this is peeled away from the substrate 1.
After removal of the carrier 12, a pretreated, printed
circuit board 19 is obtained as shown in Figure 5. The adhesive
layer 4 of the pretreated board 19 has a metallic coating which
is constituted by the portions of the metallic foil 10 left
behind upon removal of the carrier 12 and which forms a base
layer capa~le of bonding to a chemically deposited, electrically
conductive metal. As illustrated in Figure 5, the pretreated
board 19 is conveyed through a bath 17 in which a layer of an
electri~lly conductive metal is chemically deposited on the
base layer and is konded thereto. The chemical metallization
which occurs in the bath 17 takes place in a known mEnner. The
electrically conductive layer of the finished printed circuit
board 20 emerging from the bath 17 has a thickness which is
adjusted to the magnitude of the electrical current to be
supplied to the printed circuit board 20.
As already mentioned, the substrate 1 may be in the
form of a sheet or wafer. Such a sheet may be composed of a
phenolic resin. It is also possible for the substrate 1 to be
composed of paper, and epoxy web or woven epoxy sheet, epoxy
paper or a non-woven epoxy sheet and phenolic resin paper or a
sheet of non-woven phenolic resin. In addition, melanine resins
have been found suitable for the substrate 1. Other materials
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1~t77973
which can be used for the substrate 1 are polyesters, polyimides,
polycarbonates and polysulfanes. It is further p~ssible to use
inexpensive papers which are coated or laminated with a poly-
ester, a polyimide, a polycarbonate or a polysulfane.
me adhesive layer 4 may be composed of a reactive
resin system. Fbr instance, a polyurethane may be used as an
adhesive. m e adhesive may be hardenable by contact with
atmospheric moisture or when exposed to electron beam radiation.
It is likewise possible to use an adhesive which sets or hardens
under the influence of ultravîolet light. me adhesive may also
be in the form of a multicomponent system. Thus, an isocyanate-
containing resin may be used. It is further possible to utilize
a hardenable ep~xy resin. In addition, an acrylic resin system
may be used as an adhesive.
As mentioned earlier, the adhesive layer 4 may be
applied to the substrate 1 of a printed circuit board, for
example, by means of the screen printing process or the intagli~o
process. me screen printing process has the advantage that the
adhesive layer 4 may be produced more readily and cheaply.
The base layer which i5 capable of being chemically
metallized may be composed of a non-ferrous metal. Thus, oopper
or nickel may be used for producing the base layer. The base
layer may also be composed of a noble meta] and, in particular,
gold or silver. In addition, elements of the rare earths group
which are capable of being chemically metallized may be used for
the base layer. It is to be understood that the base layer need
not be constituted by a metal but may be composed on any
substance which is capable o~ banding to a chemically deposited
metal~
The carrier 12 may be provided with a parting layer
-~ ~77973
prior to vapor deposition of the material which is to form the
base layer. The purpose of the parting layer is to facilitate
disengagement of the material whichis to form the base layer
from the carrier 12. m e parting layer must be such that it
does not adhere to the material of the base layer under any
circumstances. mus, the base layer must be absolutely clean so
that the metallization in the chemical metallizing bath 17 takes
place without difficulty. The parting layer may consist of wax
which is firmly secured to the carrier 12. It is further
possible for the parting layer to be composed of a silicone
which firmly adheres to the carrier 12. A parting lacquer
or varnish which releases more readily from the material of the
base layer than from the carrier 12 may likewise be utilized for
the parting layer.
Appropriate selection of the material of the carrier
12 is advantageous. Materials which may be used for the carrier
1~ include polypropylenes, polyesters and polycarb~nates.
m e coating of the adhesive layer 4 with a base layer
which is capable of bonding to a chemically deposited metal
may also be achieved by means of the known sputtering process.
Without further analysis, the foregoing will so fully
reveal the gist of the present invention that others can, by
~; applying current knowledge, readily adapt it for various
applications without omitting features that, from the standpoint
of prior art, fairly constitute essential characteristics of the
generic and specific aspects of my contribution to the art and,
therefore, such adaptions should and are intended to be
comprehended within the meaning and range of equivalents of the
appended claims.
.
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