Note: Descriptions are shown in the official language in which they were submitted.
Z76
The present invention relates to a process ~or pro-
ducing printed circuits with high occupation density and adhe-
sive strength of the conductor paths.
Processes for producing printed circuits are known.
However, all such processes require pretreatment of the ini-
tially non-conducting surface. ThiS is usually carried out by
activating it by means of ionic, colloidal or sub-co:lloidal
noble metal comp]exes and by subsequently treating it with a
reducing agent. However, despite great advances and improve-
ments, these proc:esses do not satisfy the requirement of caus-
ing an integratecl bond of the metallic coating with the non-
conducting surface, since there inherently occurs at best an
occupation of the surface by chemical sorption.
Therefore, the present invention provides a process
which permits an integrated composite bond of the metallic
coating with the surface of the non-conductor and thus the
production of extremely adhesive and edge-sharp conductor
paths.
According to the present invention there is provided
a method of manufacture of contact switches having conductive
coatings of increased adhesive strength and resolutio~ for
producing through--contacts in boreholes of printed circuit
boards, comprising the steps of providing a base material,
drilling boreholes in said material, cleaning, activating and
reducing said base and producing a coating thereon, and heat-
ing-up said base material at temperatures within the range
from 100C to 150C immediately after said reducing step, said
heating-up step being carried out for from 5 minutes to 2
hours, said reducing step being carried out by means of reduc-
ing agent selected from t~e group consisting of alkaline
hypophosphite, sodium borohydride and dimethyl-amino-boron.
Suitably the boards are heated preferably for about 30
4Z~Ei
minutes.
In one embodiment of the present invention -the acti-
vation is carrie~ out by ionic, colloidal or sub-colloidal
noble-metal comp:Lexes or base-metal catalysts.
In another embodiment of the present invention the
activation is carried out by means of an aqueous alkaline
solution of a noble-metal complex, preferably of a palladium
salt and 2-aminopyridine.
The process according to the present invention per-
mits, in a novel way, the production of printed circuits with
great adhesive strength and edge sharpness of the conductor
paths which are intimately and composite-like bonded to the
surface of the base material.
It is particularly advantageous that according to
the process of the present invention not only can the surface
of the uncoated or coated base material be metallized in the
desired manner but that through-contacts of the boreholes of
printed circuit boards which satisfy the highest requirements
can also be produced.
The individual treatment steps in carrying out the
process according to the present invention as far as prior to
and after the heating step are conventional and, depending on
the individual case, they can be carried out substantially
unchanged by a person skilled in the art.
However, the favourable effects of the process
according to the present invention can be fully displayed only
when the heating step is carri.ed out immediately prior to or
after the activation or after the reduction.
a2~
A repetition of the heating step after -the further
trea-tment in the conventional desired manner, for example, after
the lamination, exposure and development, can be of special ad-
van-tage under certain conditions.
The heating step according -to the present invention can
be carried out with conventional means such as in corresponding
ovens or by means of infrared radiation, for example, drying by
circulating air.
The large range of application of the process according
to the present invention permits the use of any material including
glass-fibre-reinforced epoxy resin, pnenol-resin paper, epoxy-
resin paper, Plexiglas, polysulphone, polyimider polyamide, poly-
7C/6~ o r o C2r~0n
phenylene-oxide-PlYStYrene~ -flu~ydroc~rbon, polycarbollates,
polyether imide and ceramic material.
Suitably -the coated base material is a substrate whose
surface is provided with a firmly adhering layer which can be
cured by heat and con-tains at least one substance selected from
the group of modified rubber or synthetic rubber and being
oxidizable or degradable by oxidizing agents. Alterna-tively the
20 base material is a substrate whose surface is coated with an
agent, preferably copper, on one or both sides.
Therefore, the process according to the present inven-
tion is applicable to all the conventional techniques, as for
example, additive processes,subtractive processes and in selec-
tive copper plating of soldering eyes and boreholes.
The products produced according to the present inventlon
are used particuarly in electrical engineering and in electronics.
The process according to the present invention will be
illustrated by the following Example:
30 Example
A base material of glass-fibre-reinforced epoxy resin
coated with adhesive is drilled and chemically and/or mechanically
freed Erom bore dust. The board is caused -to swell in a solvent,
rinsed wi-th water and solubilized in a chromium sulphuric acid
(200 to 300 ml per li-tre oE 1-l2SO~, 10 to 100 g per li-tre oE CrO3).
This is followed by rinsing, detoxicating ancl rinsing. Activa-
tion is then carried out in an ~R~gense activa-tor based on palla-
dium, followed by rinsing, drying and reducing with a sodium boron
hydride solution.
In a fur-ther s-tep heating is carried out~for 10 minutesJ
- to 140C. This is followed by coating with a photopolymer. The
10 next step is exposure to UV light, followed by development af-ter
a reaction time in trichloroethane. The exposed circuit diagram
to be metallized and the boreholes are once more selectively
reduced. Copper is then buil-t up on conductor paths, soldering
eyes and hole walls in an aqueous chemical copper bath.
After building up the desired copper layer the photo-
polymer is stripped by treatment with methylene chloride.
After brushing the printed circuit board,it is provided
with a soldering stop print and the soldering eyes and boreholes
- are tinned while hot;
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