CA2023846A1

CA2023846A1 - Process for the direct metallization of a non-conducting substrate

Info

Publication number: CA2023846A1
Application number: CA002023846A
Authority: CA
Inventors: Klaus Majentny; Hermann-Josef Middeke; Habil Meyer
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-08-24
Filing date: 1990-08-23
Publication date: 1991-02-25
Also published as: KR910004840A; DD297194A5; JPH03170680A; EP0414097A2; DE3928435A1; EP0414097A3

Abstract

ABSTRACT OF THE DISCLOSURE

The present invention relates to a process for the direct metallization of a non-conducting substrate, particularly for the production of printed circuits, which is characterized by the following process steps: pre-cleaning, when required, pre-corroding, pre-swelling the surface to be metallized coating the surface with an adhesive adsorption of a metal compound reaction of the metal compound to the metal galvanic metallization.

Description

2023~46 The present invention relates to a process for the direct metallization of a means for non-conductive substrate, particularly the electrolytlc metallization of non-metallic substrates for the purpose of producing prlnted circuits. The present invention provides a simplification to the production process and an increase in the final quality of the circuit.

The throughplating of these printed circuit boards is usually attained in that the supporting material is drilled and that the residues caused by the drilling action are removed by means of a cleanser. These cleansers usually contain additives which condition the surface of the substrate in order to facilitate the later activation in this manner. ~;

In the next process step cleansing with a caustlc cleans the copper surfaces. This is followed by the activation in a solution based on a mixture of tin, chloride, palladium chloride and hydrochloric acid or by ionogenic activators. In a subsequent step the excess tin usually is complexed and removed from the surface, which then is substantially covered only by metal nuclei reduced to metallic palladium in the meantime.

These nuclei then serve in a copper bath as crystallization and starting point of a homogeneous copper layer applied without current. This copper layer can in turn be reinforced electrolytically. After the coating procedure and the removal of the film (drying resist, soluble in solvents or in an agueous alkali) the circult diagram is obtained and its constructure is then completed in a sulfuric electrolytic copper bath.

On attaining the desired layer thickness the final treatment for facilitating the soldering process can be carried out by means of various methods.

~ ... . . ~ ~ , - 2023~6 However, it is already known to carry out these electrolytic processes while avoiding the currentless metalliz~tion (US-PS 3 099 608, DE-OS 3 304 004, DE-OS 3 323 476).

Nevertheless there exists in practice an ever increasing substantial need of having available further processs of the kind with simpler and more reliable process control ln order to satisfy particularly the more demanding re~uirements of industry.

Therefore, it is an ob~ect of the present invention to make available a process which alleviates the disadvantages of the conventional processes and improves the process control by omitting process stages.
.
Accordingly the present invention provides a process for the direct metalllzation of a non-conductive, substrate, -~
comprising: a) pre-cleaning, pre-corroding, and~or pre-swelling a surface of the substrate; b) coating said surface with an adhesive material c) absorbing a metal compound on said adhesive material d) reducing said metal compound to metal; and e) ~ -carrying out the galvanic metallization of said metal(compound~

The direct galvanization described in the present invention avoids all the above-defined disadvantages. The process is short and can be carried out without e~treme temperatures and high concentrations of complexing agents. The present invention lies in the fact that a sufficiently hlgh concentration of metal is produced on the surface to be galvanized so that there is first produced a water-insolùble adhesive layer that can bind a metal compound in an amount such that an electrically conductive layer can be produced therefrom.
The following sequence of process steps is suitable for this purpose.

:`::

. ~

-- ~02~

When suitably selecting the process steps the electric conductivity of the metal thus coated on the sur~ace is so high that a direct ~alvanic deposition of metal can be carried out subsequently.

The surface of an insulating material, preferably printed circuit board material s~ch as FR3, FR4, consisting of polymers such as epoxide or phenol resins or polyamide or other ~-polymers or a composite material filled with ceramics partlcles or glass fibres is first presoaked in solvents and/or cleansed by ~ d~
surfactants and made wettable or broken up by oxidizing agents or acids or similar media. Thi~ procedure has been described in~
detail in another publication and is not the sub~ect matter of ;-the present invention. -The sur~ace is subsequently coated with a processing aid so that an adequate amount of a metal compound can be adsorbed thereafter. This can be an aqueous and ~ater-lnsoluble oxide or hydroxide or carbonate or the llke, which is developed on the surface to be coated from the hydrolysis or other reactions of substances such as aluminum chloride, sodium aluminate, tin or silicon halides or corresponding titanium compounds generally based on metals of group II to IV or on the elements of the subgroups, or it is formed by reduction of corresponding substances, as for example, permanganates, or it can be another compound that is correspondingly difficult to dissolve, as for example, calcium oxalate. The substance thus deposited should have a certain bond strength with regard to the base material, it should be hydrophilic and should have a large surface for the subsequent adsorption of the metal compound. It has been found that it is favorable for the subsequent steps when 3~ the adhesive or adsorption layer applied in the present step is Ndoped" with metal compounds of cobalt, iron, nickel or a palladium or of other similar metal compounds. The coating parameters depend on the system applied: when selecting manganese oxide from the reduction of a permanganate solution as primer, ,.. .. .

2~2~

then the permanganate concentration is between 1 g/litre and 150 g/litre but preferably between 10 g/litre and 100 g/litre. The solution is rendered alkaline with a hydroxide, preferably an alkali hydroxlde, the hydroxide concentration being from l.Og/litre to 100 g/litre, preferably 5 g/litre to 60 g/litre of hydroxide. The doping metal is added to the permanganate solution as salt. Halogen compounds, particularly chlorldes are preferably used in concentrations of between 0.1 g/litre and 50 g/litre, but preferably between 0.5 g/litre and 10 g/litre. The reaction time is from 1 minute up to 60 minutes, preferably 2 minutes to 15 minutes at temperatures of 0C to 120C, preferably at temperatures of 20C to 80C. This can be followed by a -~
corrosive cleaning step with a solution of conventional composition.

In the next step the surface is coated with a metal compound in a suitable manner, but primarily by immersing, spraying or an exposure to splashing. This metal compound can be in the form of complexes of the metals silver, gold, palladium, platinum, osmium, iridium or rhodium having the general formula MC(Lx)-A, wherein Lx represents a nitrogen-containing organic or inorganic radical, x represents an integer of at least 1, preferably 2 to 4 and A represents an inorganic or organic acld radical like that described in DE-PS 2 116 389 for other purposes. All the substances and compounds described in said patent are also sub~ect matter of the present invention; they have the advantages that metal is not deposited on other metal layers, particularly not on the copper-clad printed circuit boards. The metal content of the solutions applied is between 0.1 g/litre and 20 g/litre, preferably between 0.5 g/litre and 12 g/litre. The application temperature sultably is between the melting point and the boiling point of the solution used, but preferably between 20C and 60C. The reaction time of the solutions can be between one second and 60 minutes a reaction time of one minute up to 10 minutes is preferred.

.. .......... . . . . ..... . . . .

r, ~J .
~`,': . . :

2n23846 In the last process step according to the present invention the free, electrically conductlve metal is then produced from the absorbed metal compound by reduction with a suitable reducing agent. This can be performed for example, by aminoboranes or boron hydrides or aluminium hydrides or related similar reducing agents such as sodium boron hydride or lithium aluminium hydride, sodium hypophosphite, hydrazinet hydroxyl ammonium chloride in suitable solutions and concentrations. The ~ -~
concentrations are not critical; they are between 0.2 g/litre and 50 g/litre, preferably between 0.5 g/litre and 10 g/litre of the reducing agent. The temperatures are between 0C and 120C
preferably between 20C and 60C. The reaction time or reducing time should be between 5 seconds and 60 minutes, preferably between one minute and 10 minutes.
::
Following the reduction of the metal compound to the metal the metallization can be carried out directly in a commercial galvanic bath. ~-:;
By non-conducting substrates are meant, for example, glass fibre-reinforced epoxide resin, ceramics, polyimide, polytetrafluoroethylene (PTFE), phenol resin, bis-maleimide-triazine ~BT) ~teflo~ polysulphone, etc.
._ _ ... .
Therefore, the process according to the present invention allows the enhancement of the quality of the flnal product in a technologically simple manner since the construction of a first, chemically deposited copper layer that has necessarily a different structure can be dispensed with prior to the construction of the electrolytically deposited copper layer.

All the above-mentioned process steps can be carried out by immersion, spraying or splashing.

The following examples will illustrate the present invention.

" ~ ' 2~23~4~

Example 1 After cleaning a piece of FR4 material in a suitable -~
surfactant solution and subsequent rinsing for five minutes the material was put into a solution of 60 g/litre of KMnO4 30 g/litre of NaOH, 10 g/litre of NaH2PO4, 500 p.p.m of palladium and 2 ml/lltre of wetting agent 613 at 65C. the board was subsequently rinsed with water and was then also placed for five minutes at room temperature in a solution of a palladlum complex with an aromatic amine, dissolved in diluted sulphuric acid(Pd content 5 g/litre, P~ value approximately 1.5). After subsequent rinsing the coating on the board surface lt was reduced to metallic palladium by immersion in a solution of 5 g/litre of NaOH and 2 g/litre of NABH4. The board could then be copper-plated holohedrally in a commercial acid copper electrolyte (current density 2-5~/cm2).

Example 2 The procedure was like that in Example 1, but drilled copper-backed multilayer material was used in this case. After only 15 seconds the borehole walls were tightly copper-plated.
Therefore, no flaws could be detected in the metal coatlng. The multilayer inner layers were flawlessly bonded. Nelther manganese nor palladium could be detected per EDX on thP copper back.

Example 3 The same procedure was used as in Example 2, but using FR3 (epoxide/paper) as base material.

Exam~le 4 The same procedure was used as in Example 3, but a solution of the palladium complex with a palladium content of 2 ~

only 2.5 g/litre was used. As compared with Example 1 the result showed no differences.

ExamPle 5 The same procedure as in Example 1 was followed, but printed circuit board material having a high aspect ratio was used for the metallization. The board of 5mm thickness had holes having diameters of 0.3 mm. After maximally 15 seconds the holes and the edge of the board were completely copper-plated.

Example 6 The procedure was li~e that in Example 4 but with a palladium content of Pd-complex solution of only 1.0 gJlitre.
The treatment temperature in this solution was increased to 35C.

Claims

1. A process for the direct metallization of a non-conductive substrate, comprising:
a) pre-cleaning, pre-corroding, and/ or pre-swelling a surface of the substrate;
b) coating said surface with an adhesive material;
c) absorbing a metal compound on said adhesive material d) reducing said metal compound to metal: and e) carrying out the galvanic metallization of said metal (compound.)

2. A process as claimed in claim 1, wherein the adhesive material is an aqueous and/or water insoluble metal oxide, metal hydroxide or metal carbonate.

3. 2. A process as claimed in claim 2, wherein the aqueous and/or water insoluble metal oxide, metal hydroxide or metal carbonate is a hydrolysis or reaction product of aluminum chloride, sodium aluminate, tin or silicon halides, titanium compounds or compounds based on metals of groups II to IV or on the elements of the subgroups.

4. A process as claimed in claim 2, wherein the adhesive material consists of reduction products of reducible substances.

5. A process as claimed in claim 2, wherein the adhesive material consists of permanganates such as potassium permanganate and/or sodium permanganate.

6. A process as claimed in claim 4, wherein the reduction product is manganese dioxide.

7. A process as claimed in claim 2, wherein the adhesive material is calcium oxalate.

8. A process as claimed in claim 1, wherein the adhesive material is applied to said surface either jointly or in a subsequent step with metal compounds selected from the group consisting of cobalt, nickel, iron and/or palladium.

9. A process as claimed in claim 1, wherein the absorbed metal compounds contain complexes of metal M such as silver, gold, palladium, platinum, osmium, iridium or chromium having the general formula Mc-(Lx)-A, wherein Lx represents a nitrogen-containing organic or inorganic radical, X
represents an integer of at least 1, and A represents an organic or inorganic acid radical.

10. A process as claimed in claim 9, wherein said integer is from 2 to 4.

11. A process as claimed in claim 1, wherein the reduction of the metal is carried out with the aid of aminobenzenes, boron hydrides or aluminum hydrides, dimethyl aminoborane or lithium aluminum hydride, sodium hydrophosphite, hyrazine, hydroxyl ammonium chloride, in suitable solutions or concentrations.

12. A process as claimed in claim 1, wherein the reduction of the metal is carried out with the aid of sodium boron hydride.

13. A process as claimed in claim 1, wherein galvanic metallization baths, such as copper or nickel baths, are used for the galvanic deposition step.

14. A process as claimed in claim 1, without the use of currentless metallization baths.