Coating processes – Electrical product produced – Integrated circuit – printed circuit – or circuit board
Patent
1998-03-13
1999-12-28
Talbot, Brian K.
Coating processes
Electrical product produced
Integrated circuit, printed circuit, or circuit board
427301, 427304, 427305, 427306, 427 98, B05D 510
Patent
active
060078669
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for producing through-connected printed circuit boards or multilayered printed circuit boards with a polymer base with conductive polymers using a combined desmearing and direct metalization process (multilayering) wherein the polymer base materials, provided with bore holes, are subjected to a number of process steps.
Multilayered circuits must be chemically cleaned after the boring process in order to remove the so-called smear (resin smears which are formed on the copper inner layers in the boring process) from the inner layers. This is necessary in order to ensure proper binding of the copper layer of the later through-connecting process to the inner layer.
The cleaning process is also called "desmearing" and is usually performed in an alkaline permanganate solution which removes the smear oxidatively after preliminary swelling of the resin with solvents.
The "desmearing" is followed by the through-connecting process in the course of which the bore hole walls are metalized with copper.
This metalization is performed either by chemical deposition of copper or by direct metalization.
A wide variety of such direct metalization processes has been decribed. Thus, there are processes in which the activation of the non-conducting bore hole wall is effected by means of Pd nucleation, or else by deposition of carbon particles.
The patent specification DE 38 06 884 describes a direct metalization process which includes a step of treatment in permanganate for producing a conductive polymer film on the bore hole wall.
Accordingly, it should be possible, in principle, to combine the bore hole cleaning and through-connecting processes by using the same permanganate bath for both steps. In addition, since the manganese dioxide formed on the resin in the permanganate attack functions as an oxidant in polymer formation in the direct metalization process, the removal of manganese dioxide in the desmearing process (generally with H.sub.2 SO.sub.4 /H.sub.2 O.sub.2), which is otherwise necessary, can even be dispensed with.
These process flows can be described by the following process steps:
a) swelling
b) rinsing
c) alkaline permanganate
d) rinsing
e) removing of manganese dioxide depositions
f) rinsing
g) drying
a) initial etching
b) rinsing
c) conditioning
d) permanganate
e) rinsing
f) catalysing with organic monomer
g) fixation (with acid) formation of the conductive polymer film
h) rinsing
i) coppering
j) rinsing
k) drying.
This idea is already contemplated in DE-A-39 31 003 and results in a simplified process flow.
However, the practical application of such simplified systems showed that considerable difficulties arise when an alkaline permanganate bath is used for desmearing with through-connecting. These are mainly due to the fact that the dwelling times in a commercially available desmearing permanganate are about 10 to 20 min, or about 1 to 2.5 min in a process with horizontal flow. The exposing times in permanganate which serves for the formation of a conductive polymer film are known from previous experience to be about 2 to 4 min or 30 to 60 s in horizontal flow. For a sufficient desmearing effect (cleaning) to be achieved, the above mentioned times cannot be further reduced.
Further, it has to be considered that the permanganate solution for the formation of the polymer film is generally employed in a pH range of from 5 to 9.
If the process is conducted as described in DE-A-39 31 003, through-connecting defects, such as defective copper covering of the resin and preferably glass, of the base material, are unavoidable, resulting in a total failure of the printed circuit board thus produced.
Being aware of these experiences, DE-A-40 40 226 proposes a process flow which contains two permanganate steps in sequence in order to solve the above mentioned problems. Indeed, it is possible to produce high quality printed circuit boards with this process flow.
Nevertheless, this process is not satisfactory either since two steps of treatment with potassium permanganate are pres
REFERENCES:
patent: 4315045 (1982-02-01), Dillard et al.
patent: 5373629 (1994-12-01), Hupe et al.
patent: 5403467 (1995-04-01), Jonas et al.
Fix Sabine
Hupe Jurgen
Blasberg Oberflachentechnik GmbH
Talbot Brian K.
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