JP2681188B2 - Metal surface modification method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for oxidizing a metal and a method for reducing a metal oxide or a metal sulfide.

For example, when a resin is adhered to the copper surface, the copper surface is stably oxidized and stably reduced without changing the surface shape, thereby improving the adhesion between the copper and the resin.

 The metal in the present invention includes a metal alloy.

(Prior Art) Conventionally, when bonding copper and resin, it is not possible to obtain a sufficient adhesive force by directly adhering the copper surface, so an oxide layer for improving the adhesive force is formed on the copper surface. The method was known. For example, in a copper-clad laminate used for a printed wiring board, a method of forming an oxide layer, which is a rough surface having appropriate unevenness on the copper surface, when bonding the inner layer circuit copper surface and a resin such as prepreg. Was known.
However, according to this method of forming an oxide layer, unoxidized portions may remain in an island shape, which makes the adhesive force with the resin unstable. Furthermore, this copper oxide
When it came into contact with an acidic aqueous solution, it easily dissolved as copper ions. Taking the above-mentioned printed wiring board as an example, after the copper and the resin are bonded, the oxide layer exposed in the hole wall in the through hole drilling step is removed from the bonding interface by various acid treatment steps of through hole plating. The acid permeates, and the adhesive force between the copper and the resin decreases.

In order to solve this problem, in Japanese Patent Laid-Open No. 56-153797, after forming cupric oxide on the circuit copper surface of the inner layer circuit board, by immersion treatment in an alkaline reducing agent solution,
A method of obtaining a reduced coating film of cuprous oxide having high acid resistance without damaging fine irregularities on the surface is disclosed. However, according to the results of studies conducted by the inventors, the above cuprous oxide was insufficient, and it was difficult to reduce it to metallic copper by this method under normal conditions.

For example, A-treated sodium chlorite 30g / sodium hydroxide 12g / sodium phosphate 5g / copper foil with copper oxide formed on the entire surface by treatment with a temperature of 80 ℃ is treated with B-formalin (37%) 50ml. / No reduction of the copper oxide layer to metallic copper was observed even after immersion for 30 minutes or more in an aqueous solution containing 5 g of sodium hydroxide / temperature of 75 ° C.

The surface of the copper foil exhibited a dark brown color peculiar to the oxide by the A treatment, and the same dark brown color after the B treatment. Further, after the treatment of A and B, when this was immersed in 5% hydrochloric acid, the dark brown oxide film disappeared rapidly and changed to a bright skin color peculiar to metallic copper.

These results indicate that the above-mentioned means does not metallize the oxide layer, so that the oxide layer is contacted with the acid and dissolved.

Formaldehyde is generally used as a strong reducing agent solution and thermodynamically has a standard electrode potential sufficiently low to reduce copper oxide to metallic copper. Nevertheless, the reason why the oxide layer formed on the copper surface does not reduce to metallic copper is that the reduction reaction induction period is extremely long. It was thought that activation treatment was required to eliminate this induction period.

On the other hand, it is considered that once the reduction reaction starts after the induction period, the reduction reaction rapidly proceeds in the reducing solution due to the redox potential difference between metallic copper and copper oxide.

That is, in Japanese Unexamined Patent Publication No. 61-250036, a method of partially exposing the copper base during the reduction treatment is adopted.
In Japanese Patent No. 6228, a method of dispersing a metal powder in a reduction treatment liquid is adopted. However, according to the results examined by the present inventors, in any case, the reduction reaction is unstable or incomplete. In addition, residual metal powder also occurred, resulting in poor insulation.

(Problems to be Solved by the Invention) That is, in the conventional technique, the instability and incompleteness of the method of forming the target oxide layer on the metal surface.

Instability and imperfections in the method of reducing and metallizing the oxide layer formed on the metal surface.

Instability and incompleteness of adhesiveness when adhering a resin or the like to a metal surface, which is caused by the above and.

Etc. have problems that must be solved.

(Means and Actions for Solving the Problem) The present invention has been made in view of the above circumstances, and cannot be industrially used with a method of forming a metal oxide that has been unstable or incomplete conventionally. Another object of the present invention is to improve the method for reducing a metal oxide and provide a metal surface formed by a stable redox treatment and stable adhesion between the metal surface and a resin.

The gist of the present invention is to immerse a metal in an electric field applied thermodynamically in an oxidant solution having a standard potential sufficient to oxidize the metal, and without contact with an electrode, After forming an oxide film on the surface of the metal, thermodynamically, in an electric field applied to a reducing agent solution having a standard potential sufficient to reduce the oxide film, and without an electrode. A metal surface modification method of forming a film oxidized and reduced on the metal surface by immersing in contact, wherein the electric field is
The point is that it is applied only until the formation reaction of the oxide film or the oxidation / reduction film on the metal surface is started.

As shown in FIG. 1, an anode (2) and a cathode (3) are placed in a bath (1), a printed wiring board (5) with a pattern (4) is immersed in a solution between them, and a power supply (6) is used. Is used to apply a potential between the anode (2) and the cathode (3). In the case of an oxidizing agent solution or a reducing agent solution, if an electric field is applied at the beginning of this step to start the reaction, the reaction will proceed promptly, so that the electric field may be applied for a very short time until the reaction starts. This is desirable for a minute time also in order to suppress the decomposition of the liquid due to the oxidation of the reducing agent by the anode or the reduction of the oxidizing agent by the cathode. An insoluble electrode (DSE) such as platinum having high corrosion resistance, stainless steel, or the like may be used as an electrode used when an electric field is applied.

In the adhesion between the solder mask and the metal, the surface treatment once oxidizes and reduces the metal surface as described above, thereby further improving the physical adhesion between the solder mask and the metal.

Furthermore, according to the reduction method of the present invention, it is possible to easily reduce and remove the sulfide layer formed on the surface of the Ag terminal for wire bonding of the lead frame.

As a matter of course, in the build-up method of the multilayer printed wiring board, there was an epoch-making effect also in the adhesion between the inner layer circuit surface and the interlayer insulating layer.

(Example) Hereinafter, a manufacturing process of a multilayer printed wiring board will be described as an example.

 A multilayer printed wiring board was created by the following steps.

 The pretreatment of this embodiment is as follows.

After mechanically polishing the copper foil surface of the glass cloth-epoxy resin copper clad laminate, a resist mask is formed on the circuit pattern portion using a photosensitive resist, and the copper foil other than the circuit portion is removed by etching. , A conductor circuit was formed.

The copper foil surface was immersed in an aqueous solution of H ₂ O ₂ 15 g / H ₂ SO ₄ 200 g / temperature 40 ° C. for 2 minutes, washed with water, and immersed in an aqueous solution of H ₂ SO ₄ 100 g / for 1 minute.

・ Example of oxide formation After washing with water, NaClO ₂ 40g / NaOH 17g / Na ₃ PO ₄・ 12H ₂ O 10g / oxidizing bath (1) at a temperature of 90 ° C was used, as shown in Fig. 1. Soak in the treatment layer,
The voltage of the voltmeter (8) was treated with 2 V for 4 minutes, and a copper oxide layer was stably formed on the surface.

・ Examples of oxide reduction After washing with water, formaldehyde 15g / NaOH 8g / methanol 10g / reducing bath (1) at a temperature of 70 ° C was used and immersed in a treatment tank as shown in Fig. 1,
The voltmeter (8) reading was 3 V and an electric field was applied for 10 seconds, and then immersed in the bath for 5 minutes.

 The subsequent processing is as follows.

Next, after washing with water, it was dried at 100 ° C. for 1 hour, laminated with a prepreg impregnated with epoxy resin on glass cloth, and pressure was applied at 170 ° C. and 40 Kgf / cm ² for 120 minutes.

After making holes and making a through-hole substrate, perform alkali degreasing, soft etching, acid treatment, and catalyst application treatment, which are the pretreatments for ordinary electroless copper plating, and then perform ordinary electroless copper plating and electrolytic copper plating. Through-hole plating was formed.

The outer layer circuit was formed using a photosensitive resist and etching.

When the peel strength between the inner layer copper surface and the prepreg of the multilayer printed wiring board created as described above was measured, it was 20 points for 100 sheets / 2.0 Kgf / cm or more at all measurement points of the sheet, and the electric field was applied in the process. In the method of forming the removed copper oxide layer, the non-oxidized portion remained in an island shape, so that the peel strength was unstable at 0.5 to 1.9 Kgf / cm and the adhesive strength was incomplete. Further, in the process, no acid soaked from the inner wall of the through hole was found at the same measurement point. For comparison, the same treatment was applied to the through-hole substrate excluding the steps. At all measurement points, the inner layer copper around the through-hole was 200 to 300 μm in size due to acid soaking, which is unique to metallic copper and bright. It was an imperfect one that turned into a complexion.

(Effects of the Invention) As described above, according to the present invention, when an oxide film or an oxidation / reduction film is formed on a metal surface, an electric field having a sufficient standard potential until the initiation of the formation reaction is formed. Therefore, it is possible to stably oxidize the metal surface and to stably reduce the oxide layer to a metal without changing the surface roughness, which was not industrially available in the prior art. In the through-hole part of the multilayer substrate, the acid resistance is dramatically improved, and the adhesive force equal to or higher than that of the conventional copper oxide layer can be obtained with a probability of 100%.

Further, it is possible to easily and completely reduce and remove oxides of silver, copper and the like, which cannot be easily removed by the conventional technique, so as to completely meet the purpose.

[Brief description of the drawings]

FIG. 1 is a vertical cross-sectional view showing an example of an electric field applying device for an electrolyte solution according to the present invention. Explanation of symbols 1 ... Electrolyte bath, 2 ... Anode, 3 ... Cathode, 4 ... Copper circuit pattern, 5 ... Printed wiring board, 6 ... Power supply, 7 ...
… Variable resistor, 8 …… Voltmeter, 9 …… Power switch.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 61-139437 (JP, A) JP 61-37977 (JP, A) JP 60-138099 (JP, A) JP 62- 136092 (JP, A) Japanese Patent Publication Sho 49-28815 (JP, B1)

Claims (2)

(57) [Claims] 1. A metal is immersed thermodynamically in an electric field applied to an oxidant solution having a standard potential sufficient to oxidize the metal and without contact with an electrode. After forming an oxide film on the surface of a metal, thermodynamically, in an electric field applied to a reducing agent solution having a standard potential sufficient to reduce the oxide film, and without contact with the electrode. A metal surface modification method of forming an oxidized / reduced film on the metal surface by immersion, wherein the electric field is applied only until the start of the reaction for forming an oxide film or an oxidation / reduction film on the metal surface. A method for modifying a metal surface, which is characterized by applying. 2. The metal surface modification method according to claim 1, wherein the metal is a circuit pattern formed on the surface of the printed wiring board.