Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a process for the
removal of contaminats from boreholes of printed circuit
boards (pcs) using oxidants such as permanganates in aqueous
~ oa~,~)
solutions and/or swelling~agents, and employing an ultrasonic
treatment.
In the production of multilayer structures it is
necessary to carry cut a pretreatment procedure in order to
remove resinous smearings caused by drilling ~called "smear"
in the common technical usage). The removal of the "drill
smear" is effected to ensure a proper electrical contact of
the conducting inner layers with the through-contacts in the
boreholes. Moreover, the removal of "smear" eliminates the
residues of PCB materials, either loosely attached or stuck to
the boreholes, which facilitates the adhesion of the metal
layer which is deposited during the through-contacting. This
is important, above all, after the thermal treatment that
printed circuit boards undergo in the soldering operation.
It is known to remove smear using potassium or
sodium permanganate solutions. In many cases, this oxidlzing
treatment is preceded by soaking (swelling) in aqueous solu-
tions containing various solvents and/or surfactants. The
duration of the treatment is very long, and therefore it has
also been known to accelerate such procedures by employing
ultrasonic treatment. There is, however, a problem associated
with the above prior art process in that a uniform ultrasonic
field cannot be set up with the conventional arrangement of
the printed circuit boards in the processing basket. As a
result, cleaning action of varying force takes place depending
on the positioning of the board in the basket and thus, a uni-
form and complete remova~ of the drilling residue is not guar-
anteed.
The present invention provides a process that
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1 307353
enables a complete removal of contaminants from the boreholes.
According to the present invention there is provided in
a process for the removal of boring smear contaminations from the
bore holes of conductor plates, of the type wherein said
conductor plates are treated by applying oxidation agents and/or
soaking agents, a well as an ul-trasonic treatment, the
improvement comprising transporting said conductor plates
horizontally during said treatment~ Suitably the oxidants and
the soaking (swelling) agents are splashed onto the horizontally
passed boards by means of a nozzle which is disposed below the
board feed path and at right angles to the direction of feed.
The oxidants are suitably aqueous solutions of
permanganate.
. .,
The aqueous permanganate solution suitably contains 30
- 65 gJl sodium permanganate or 30 - 60 g/l potassium
permanganate.
2~
The particularly suitable soaking ~swelling) agents are
methoxyethanol, ethoxyethanol, l-methyl-2-pyrrolidinone, butyl-
carbitol, dimethylformamide alone or in a mixture with or without
ethylene glycol and surfactants in neutral to strongly alkaline
agents.
2~
3U
3~
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Conventional ultrasonic vibrators can be employed
for the ultrasonic treatment.
The circuit boards can be led horizontally in a
known manner using apparatus such as described for instance
in DE~ - 3~ 36 545.
The process of the present invention makes it
possible to achievel in a known way, a uniform cleaning,
or removal, of drilling residues in all the treatment
steps in order to ensure a positive electrical contact of
the multilayered inner laminations.
Another advantage of the invention is a substantial
imnrovem~n-t ~f the qllality ~f the boreholes, since a
partial "~ver-etching" is avoicled.
Further unexpected benefits of the invention include
a markedl,v improved purification of even very small
boreholes due to the directed flow (of the solution~ through
the holes and a significantly shortened treatment time
(0.2 to 2 min) and hence improved operational efficiency of
the treatment facilities.
The process of the present invention is carried out
for instance in a following manner. The drilled multilayer
boards are passed horizontally through a flushing device
with an,-ultrasonic (attachment). In this connection, it is
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possible to pretreat the coating (sticky) surface, in the
first stage, with a "swelling~ solution, then rinse it, like-
wise during a continuous horizontal pass, and subject the
board to the oxldizing treatment with potassium or sodium per-
manganate. Subsequently, the residual permanganate from the
treatment is removed by passing the rinsed board again trough
a flushing treatment zone where the build-up of manganese
dioxide is reduced. Finally, the board is rinsed again and
can be passed on to the through-metallization step.
The invention will be further illustrated by the
following Examples.
Example 1
Soaking (swelling) with 120 ml/l ethoxyethanol,
80 ml/l methoxyethanol 60-90C
and 90 g/l NaOH
Rinsing
Etching with 60 g/l XMnO4
c. 30 g/l NaOH 60-90 C
Rinsing
Decontamination with hydroxylammonium
chloride in a hydro-
chloric acid or sul-
f.uric acid solution 60-90C
Rinsing
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,. . .
o O /' ~ ~ ~ o r~ e
Soakillg with 120 ml/l 1-met.hy~-2-p~rolid;nc,
80 ml/l methoxyethanol and RT ~40 C
90 g/l NaOH
R;ns;ng
~tching wi-~h 60 g/l KMnO4 and 3n g/l NaOH 60-90 C
Rinsing
Decontamination with hydroxylammonium chloride
in a hydrochloric acid or 25-90C
sulfllric acid solut.ion
Rinsing
Exam~le 3
Soakin~ with 120 ml/l dimethylformamide,
80 ml/1 methoxyethanol and RT -40C
90 g/l NaOH
Rinsing
Etching with - 60 g/l KMnO4 and 30 g/l NaOH 60-90 C
Rinsing
Decontamination
with hydroxylammonium chloride 25-90C
in a hydrochloric acid or
sulfuric acid solution
, Rinsing
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--6--
~xample 4
Soaking with 120 ml/l butyl~ ~ ,
80 ml/l methoxyethanol RT -90 C
90 g/l NaOH
Rinsing
Etching with 60 g/l KMnO4 and 30 g/l NaOH 60-90C
Rinsing
Decontamination with hydroxylammonium chloride 25-90C
in a hydrochloric acid or
sulfuric acid solution
Rinsina
Example 5
Soakina with 120 ml/l ethYlene glycol, 60-90C
80 ml/l methoxyet.hanol and
90 g/l NaOH
R;.ns;ng
~tching witll 60 g/l KMnO~ and 30 g/l NaO~I 60-90 C
Rinsing
Decontamination with hydroxylammonium chloride 25-90C
in a hydrochloric acid or
sulfuric ac;d solution
Rinsinq
.
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Example 6
Soaking as in examples 1 to 5 but with the addition of
ca-tionic, anionic or nonionic surfactants.
ExamPle 7
.
Soaking with 120 ml/l ethylene ~lycol, 60-90C
80 ml/l methoxyethanol and
90 g/l NaOH
Rinsing
Etching with 60 g/l KMnO4 and pH ea. 12-14
X g/l NaOH
Rinsinq
Decontamination with hvdroxylammonium chloride 25-90C
in a hydroehlorie or
sulfurie aeid solution
Rinsing
Exam~le 8
-
Soaking with 120 ml/l ethylene glyeol 60-90C
80 ml/l ~Qethoxyethanol ~nd
90 g/l NaOH
R;nsing
Deeontamination with hydroxylammonium ehloride in 25-90C
hydrochloric acid or
sulfuric aeid solution
Rinsing
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Exaln~le 9
Soakin~ with 120 ml/l ethylene glycol, 60-90C
80 ml/l me~thoxyethanol and
g n g/l NaOH
R;nsin~
Etching with 60 g/l KMnO4 and
30-100 g/l K~H
R;nsing
10 Decnnt~minat;on with hy~.xoxylammnni~lm chloride 25-90C
i.n a hydrochloric acid
Rinsing
~3xampl~ 1 0
Soaking with 120 ml/l ethylene glycol, 60-90C
80 ml/l methoxyethanol
and 90 g/l NaOH
Rinsinq
Etching with 60 g/l KMnO4,
X g/l NaOH or KOH and
0.1 g/l fluorinated wetting agent
Rinsing
Decontamination with hydroxylammonium chloride in a
hydrochloric acid or sulfuric
acid solution 25-90C
Rinsing
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_9_
Example 11
-
Soaking with 120 ml/l ethylene glycol, 60-90C
80 ml/l methoxyethanol and
90 g/l NaOEI
Rinsing
Etching with 200 g/l NaMnO4 and
70 g/l NaOH
Rinsing
10Decontamination with hydroxylammonium chloride 25-90C
in a hydrochloric acid or
. sulfuric acid solution
Rinsing
Rxam~le 12
Soakinq with 120 ml/l ethylene glycol, 60-90C
80 ml/l methoxyethanol and
90 g/l NaOH
Rinsinq
Etching with 200 q/l NaMnO4 and
70 g/l NaOlI
Rinsinq
Decontamination with stannous chloridè solution in
hydrochloric acid
Rinsing
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Example 13
-
Soakinq with 120 ml/l ethylene glycol, 60-90C
80 ml/l methoxyethanol and
90 g/l NaOII
Rinsing
Etching with 200 g/l NaMnO4 and
70 g/l NaO~
Rinsing
Decontamination with an acidic solution of formaldehyde
Rinsing
Example 14
Soaking with 120 ml/l ethylene glycol, 60-90C
80 ml/l methoxyethanol and
90 g/l NaOH
Rinsing
Etching with ~00 g/l NaMnO4 and
70 g/l NaOM
Rinsing
Decontamination with an acidic solution of hydrazine
hydrate
Rinsing
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Example 15
Soa]ci.ny wi.th 120 ml/1 e-thylene glyco], 60-90C
80 ml/l methoxyethanol and
90 g/l NaOH
Rinsing
Etching with 200 g/l NaMnO4 and
70 g/l NaOH
Rinsing
Decontamination with an acidic glyoxal solution
Exam~le 16
Soaking with 120 ml/l ethylene glycol, 60-90C
80 ml/l methoxyethanol and
90 g/l NaOH
Rinsing
Etehing with 200 g/l NaMnO4 and
70 g/l NaOH
Rinsing
Deeontamination with redueiny diearboxylic acids,
alone or in a mixture with
inorganic acid supplement
Rinsing
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~anlp]e 17
Soaking with 120 ml/l ethylene glycol, 60-90C
80 ml/l methoxyethanol and
90 g/l NaO~
Rinsing
Etching with 60 g/l KmnO4 and 30 g/l NaOII 60-90C
Rinsing `
Decontamination with sodium bisulfite solution
Rinsing
Example 18
Soa]cing with 120 ml/l ethylene glycol 60-90C
80 ml/l methoxye-thanol
90 g/l NaOII
Rinsing
Etching with 200 g/l NaMnO4 and 70 g/l NaOH
Rinsing \~
Decontamination with simultaneous glass etclling back
adding ammonium bifluoride or
another fluoride-containing additive
Rinsing
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