EP0515605A1 - Process for producing through hole plated or multilayer printed circuit boards - Google Patents

Abstract

A method of manufacturing printed circuit boards with metallized or multilayer holes combines two methods known per se. According to the first, the contact holes are cleaned by immersion (1), by rinsing (2) and by an oxidizing treatment with a permanganate solution (3). The known method also comprises, after an additional rinsing, a so-called decontamination process followed again by rinsing; according to the invention, however, these latter steps are superfluous. The second known method makes it possible to deposit an electrically conductive layer without current on the external surface of the contact holes, by stages of conditioning or immersion, rinsing, of oxidizing treatment with a permanganate solution (9), by a second rinsing. (10) and by precipitation of monomers contained in a solution (11), which are then polymerized (12) so as to form an electrically conductive layer. After a subsequent rinsing or pickling (13), the printed circuit boards or the multilayer boards are subjected to other manufacturing processes which are not within the scope of the invention. The method described makes it possible to eliminate the initial conditioning or immersion, as well as the rinsing which follows, of the second method described above, by virtue of the combination with the first method. In this way, at least two manufacturing steps are eliminated, during which the printed circuit boards or the multilayer boards are exposed to a treatment liquid, as well as the corresponding rinsing operations.

Description

 Process for producing printed circuit boards or multilayers

The invention relates to a method for producing plated-through circuit boards or multilayers, in which the boreholes produced for contacting the different layers are cleaned with the following method steps:

a) swelling with a treatment liquid;

b) rinsing;

c) oxidative treatment with a permanganate solution.

Electronic printed circuit boards, in particular so-called "multilayers", have several layers of electrically conductive structures. So that they can be contacted, the entire printed circuit boards or multilayer must be drilled through and the lateral surfaces of the bores then covered with an electrically conductive layer. Since high demands are placed on the reliability of such printed circuit boards and multilayers, it goes without saying that the contacting of the various electrically conductive structures in the different layers is of great importance. This presupposes that the lateral surfaces of the boreholes, which become soiled when the boreholes are drilled, in particular have resin smearings, are carefully cleaned.

Such a cleaning method for the lateral surfaces of the boreholes, also called "desmearing" method, is described in DE-OS 36 38 630, from which the present invention is based. Cleaning begins here with swelling, treatment of the printed circuit boards or multilayer with a treatment liquid which generally contains various organic solvents. The swelling liquid is then removed in a rinsing process. The actual cleaning is then carried out by an oxidative treatment with a permanganate solution, after which excess oxidizing liquid is washed away again. This is followed by a so-called "detoxification", in which brown stone, which has formed in the oxidative treatment, is reduced and removed. A new rinse follows. The printed circuit boards pretreated in this way can then be metallized on the lateral surfaces of the boreholes in methods known per se and not described further in DE-OS 36 38 630.

By simply joining the known processes for cleaning the boreholes and the metallization of the lateral surfaces, a large number of process steps are created which require many treatment fluids and many individual device modules in terms of implementation.

The object of the present invention is to supplement a method of the type mentioned at the outset as cost-effectively as possible with method steps which serve to produce electrically conductive layers on the lateral surfaces of the boreholes.

This object is achieved according to the invention in that, immediately after process step c, a process for the currentless production of electrically conductive layers follows without the interposition of a neutralization process or a further conditioning or swelling process is carried out on the lateral surfaces of the boreholes with the following process steps:

d) oxidative treatment with a permanganate solution;

e) rinsing;

f) depositing a layer of organic monomers from a solution of these monomers;

g) polymerization of the deposited monomers to form an electrically conductive layer.

The invention is based on the knowledge that the "desmearing" process is particularly favorable with a special currentless one

Process for producing the electrically conductive layers on the lateral surfaces of the boreholes can be combined: This process is also known per se (DE-PS 38 06 884). However, it is possible with the combination of the two proposed according to the invention

Process "to skip" some of their individual steps, ie the number of process steps in which the circuit boards or multilayers have to be treated with a treatment liquid, as well as the associated rinsing processes, to be saved. In particular, in the procedure according to the invention, it is no longer necessary to carry out a "detoxification", ie a removal of the manganese dioxide which forms, after the oxidative treatment using the "desmearing" method, since this manganese dioxide in the oxidative pretreatment prior to the separation of the monomers has a beneficial effect. In addition, there is no additional conditioning or swelling process, which was still necessary in the process described in DE-PS 38 06 884 for the currentless deposition of conductive layers on the lateral surfaces of the boreholes. Since the chemical processes occurring in the oxidative treatmen ^¬ development of the "desmearing" process, are not identical with those of the electrically conductive in the oxidative treatment prior to the electroless deposition

Layers take place, it may be advisable to carry out both oxidative processes in different baths, which then e.g. be able to differentiate in terms of the pH value but also in terms of the content of manganese dioxide. In general, however, it is not necessary in any case to separate the two baths in which permanganate solution is used by rinsing.

According to a special feature of the invention, it is also conceivable in certain cases that can be determined by tests, the above. Process steps c and d, that is to say the process steps in which an oxidative treatment with permanganate solution is carried out, are combined into a single process step.

An embodiment of the invention is explained below with reference to the drawing; show it

Figure 1: schematically the "Desmearing" process known from DE-OS 36 38 630;

Figure 2: schematically the method known from DE-PS 38 06 884 for the currentless deposition of electrically conductive layers on the lateral surfaces of the boreholes;

FIG. 3: the method according to the invention, partially using method steps of the sub-methods shown in FIGS. 1 and 2. For a better understanding of the measures proposed according to the invention, it is first briefly repeated with reference to FIG. 1, as in the known method described in DE-OS 36 38 630, the boreholes are cleaned of plated-through circuit boards or multilayers. For details of the method, reference is made to the publication mentioned.

Before the process section shown in FIG. 1, the printed circuit boards or multilayers have already been provided with boreholes which are intended to contact the electrically conductive structures arranged in different layers. When drilling these holes, the drill walls were contaminated; in particular, resin smearings or loose contaminants have accumulated. To remove them, the printed circuit boards are passed through a first treatment liquid (method step 1), in which the lateral surfaces of the bores are swollen. This is done with a mixture of different organic solvents in sodium hydroxide. After rinsing (process step 2), the printed circuit boards are placed in an oxidative treatment bath, preferably a potassium permanganate bath (process step 3). This is where the impurities are actually removed from the boreholes. In the course of the chemical reactions that take place, the reduction of the potassium permanganate also produces manganese dioxide, which until now has generally been assumed that it must be removed again in order to successfully metallize the surface of the borehole. Therefore, in the method known from DE-OS 36 38 630 (FIG. 1), after a further rinsing (method step 4), a so-called "detoxification process" (method step 5) is provided. For "detoxification" (also called "neutralization"), treatment with a hydroxylammnium chloride solution is carried out. After rinsing again (process step 6) the printed circuit boards arrive at a station in which the cleaned lateral surfaces of the boreholes are covered with a metallic layer in a manner not specified in any more detail.

Of the various known methods with which electrically conductive coatings are produced on the lateral surfaces of boreholes, the invention has selected a very specific one for combination with the method shown in FIG. 1, which is described in DE-PS

38 06 884 is described and is briefly explained below with reference to FIG. 2. For details, reference is again made to the last-mentioned publication.

The pretreated circuit boards are first swollen in an organic solution (it would be more correct to speak of a general "conditioning" since the relevant processes are not known in detail). This is process step 7 in FIG. 2. After rinsing (process step 8), the printed circuit boards enter a permanganate solution (process step 9), in which an oxidative pretreatment of the lateral surfaces of the boreholes to be coated takes place. It has been found that it is not desirable to have a complete absence of foreign substances after going through this step, but rather to have a certain amount of manganese dioxide which remains when the permanganate solution is reduced.

The printed circuit boards pretreated in this way are rinsed (process step 10) and then introduced into a solution of organic monomers (process step 11). A layer of these organic monomers is deposited on the lateral surfaces of the boreholes. In the next process step 12, which is carried out without the interposition of a rinse these monomers are then polymerized out, forming an electrically conductive layer. Excess polymerization products and residues of the treatment liquids are removed from process steps 11 and 12 in a decap and rinsing module, after which the printed circuit boards are fed to the further construction of the electrically conductive layers, for example in an electrolysis process.

The two methods described are now combined with one another according to the invention, as shown in FIG. 3. In FIG. 3, those method steps which have been adopted from the known methods according to FIGS. 1 and 2 are identified with the same reference symbols. The comparison of FIG. 3 with FIGS. 1 and 2 makes it clear that not all process steps of the known processes are adopted in the process according to the invention. Rather, the detoxification process 5 and the subsequent rinsing process 6 are omitted from FIG. 1. The conditioning or swelling process 7 and the subsequent rinsing process 8 are eliminated from the process shown in FIG. The printed circuit boards thus go from the oxidation bath 3 of FIG. 1 directly into the oxidation bath 9 of FIG. 2. The saving of four process steps means not only the saving of two treatment liquids which may have to be disposed of; in terms of apparatus, this means the saving of four device modules, which means a considerable reduction in costs.

Under favorable conditions, which can be determined in individual cases by a few tests, process steps 3 and 9 in FIG. 3 can also be combined into a single process step, as indicated by dashed lines. Of course, this is associated with a further reduction in costs.

Claims

Claims

1. Process for the production of plated-through circuit boards or multilayers, in which the boreholes produced for contacting the various layers are cleaned with the following process steps:

a) swelling with a treatment liquid;

) Do the washing up;

c) oxidative treatment with a permanganate solution,

characterized in that

immediately after process step c, a process for the currentless production of electrically conductive layers on the lateral surfaces of the boreholes is carried out with the following process steps, without the interposition of a neutralization process or a further conditioning or swelling process:

d) oxidative treatment with a permanganate solution;

e) rinsing;

f) depositing a layer of organic monomers from a solution of these monomers;

g) polymerization of the deposited monomers to form an electrically conductive layer.

2. The method according to claim 1, characterized in that the process steps c and d are combined in a procedural step.