JPH0719957B2 - Copper surface treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a method for manufacturing a multilayer printed wiring board, in which the inner layer circuit board and the prepreg are laminated and integrated with each other. The present invention relates to a method for treating a copper surface, which is suitable for adhesion of copper.

(Prior Art) Conventionally, in a multilayer printed wiring board, an unnecessary portion of the copper foil of the copper clad laminate is removed by etching or the like to form an inner layer circuit, and the copper surface of the inner layer circuit is roughened with a chemical solution to roughen The oxidized surface is oxidised, and the prepreg and the copper foil to be the outer layer circuit are laminated on top of it and laminated and integrated, and holes are made at the locations where the outer layer circuit and the inner layer circuit need to be connected, and the resin that adheres to the inner surface of the hole It was manufactured by removing a piece of glass or glass with a chemical solution, forming a metal layer such as copper using electroless plating, etc., and then forming an outer layer circuit by etching or the like.
At this time, the oxidation treatment layer of the copper surface exposed on the inner surface of the hole is attacked by the acidic chemical treatment solution after that, and there is a part (called haloing) where the adhesion between the inner layer copper foil and the prepreg is not maintained around the hole, There is a problem of peeling due to thermal shock such as soldering. As a solution to this problem, there is the following method of treating the copper surface of the inner layer circuit of the multilayer printed wiring board, which is shown in the invention previously filed by the applicant.

That is, a. A step of forming copper oxide on the copper surface by contacting the copper surface with an aqueous solution containing an oxidizing agent.

b. A step of changing the potential of the oxidized copper surface within a range of −1000 mV or more to −400 mV or less with respect to the Ag-AgCl electrode by contacting the oxidized copper surface with an aqueous solution containing alkali boron hydroxide. .

c. A step of changing the potential of the oxidized copper surface to a base potential lower than −1000 mV with respect to the Ag-AgCl electrode by contacting it with an aqueous solution containing formaldehyde.

The copper surface treatment method is characterized in that the copper oxide formed on the copper surface is reduced to metallic copper by a treatment step including the above three steps in sequence.

(Problems to be Solved by the Invention) The potential of the copper surface oxidized by contacting with an alkali boron hydroxide is -1000 m with respect to the Ag-AgCl electrode.
The time required to reduce the copper oxide to metallic copper by contacting it with an aqueous solution containing formaldehyde after changing it within the range of V to −400 mV or less is longer than other steps. Is limited, which is a major obstacle in automating the process.

The present invention is capable of solving such problems and providing a method for treating an oxidized copper surface which has a high treatment rate while maintaining sufficient adhesion.

(Means for Solving the Problem) The present invention provides a method of contacting an aqueous solution containing alkali borohydride and then an aqueous solution containing formaldehyde in order to reduce copper oxide to metallic copper. It was made based on the finding that the rate of reduction can be increased by including at least one salt, and the copper oxide formed on the copper surface is reduced to metallic copper by the treatment steps including the following steps in the following order: The surface treatment method for copper is characterized by

a. A step of forming copper oxide on the copper surface by contacting the copper surface with an aqueous solution containing an oxidizing agent.

b. A step of changing the potential of the oxidized copper surface within a range of −1000 mV or more to −400 mV or less with respect to the Ag-AgCl electrode by contacting the oxidized copper surface with an aqueous solution containing alkali borohydride. .

c. A step of changing the potential of the oxidized copper surface to a base potential lower than −1000 mV with respect to the Ag—AgCl electrode by contacting with an aqueous solution containing at least one of salts and formaldehyde.

In the present invention, the method of forming copper oxide on the copper surface in the step a is performed by using a generally known alkaline aqueous solution of sodium chlorite, alkali persulfate, potassium chlorate, potassium perchlorate, or alkali peroxosulfate. It is performed by dipping in or spraying the treatment liquid containing the oxidizing agent. An example of the composition of this copper oxidation treatment solution is NaClO ₂ ; 30 to 150 g / l Na ₃ PO ₄ 12H ₂ O; 10 to 60 g / l NaOH; 5 to 30 g / l. The processing conditions are that the liquid temperature is 55 to 95 ° C. Further, as a pretreatment of the copper surface for forming copper oxide, it is preferable to perform degreasing and contact with an aqueous solution of ammonium persulfate or an aqueous solution containing cupric chloride and hydrochloric acid to roughen the copper surface.

The alkali borohydride which is the reducing agent used in the step b is sodium borohydride, potassium borohydride or the like. The concentration of the alkali borohydride affects the rate of change of the potential of the oxidized copper surface and the uniformity of the appearance after reduction. The concentration is 0.1 g / l or more, preferably 0.2 to 5 g / l.

In addition, since alkali borohydride easily decomposes spontaneously, it is preferable to add lead acetate, lead chloride, lead sulfate or thioglycolic acid in order to suppress it.
It is also possible to keep it at.

The contact time between the oxidized copper surface and alkali borohydride is extremely important. When the oxidized copper surface is brought into contact with alkali borohydride, the copper oxide begins to be reduced and the potential of the oxidized copper surface changes to the base. At this time, if the contact alicyclic ring is lengthened until the electric potential becomes less than −1000 mV, uneven appearance may occur and the adhesive strength may not increase. The range where such problems do not occur is -1000 mV or more and -400 mV or less. In practice, it is not necessary to constantly monitor the potential, and the desired contact time can be determined by the composition and temperature of the aqueous solution containing alkali borohydride. As an example, in the case of sodium hydrogen boron, the desired contact time at a concentration of 1 g / l, pH of 12.5, temperature of 40 ° is 3 to 180 seconds.

The concentration of the aqueous formaldehyde solution used in step c is 36
% When using formalin, 0.5 ml / l or more, 2-15 ml / l
Is a preferable range. The pH of the aqueous formaldehyde solution is 9 or more, preferably 10.5 or more. this
To adjust the pH, use alkali hydroxide or the like. The salts added to this formaldehyde solution are Na ₂ S
O ₄ , K ₂ SO ₄ , HCOONa, NaCl, etc. having high solubility can be used, and these can be used in combination. Also,
The amount added is 0.01 mol / l or more, preferably 0.1 mol / l or more.

When the copper surface subjected to the oxidation treatment and the treatment of step b is brought into contact with this aqueous solution containing formaldehyde and salts, the initial copper potential is in the range of -1000 mV to -400 mV, and if the contact is continued, the metallic copper It changes from -1000 mV which is the electric potential to base. The time for which this contact is continued requires at least the time until it changes to the potential of metallic copper.

The copper surface that has been subjected to the treatment of step b may be subjected to the treatment of step c as it is, or may be washed with water to perform the treatment of step c.

Further, the present invention can be used not only for the surface treatment of the inner layer circuit of the multilayer printed wiring board, but also for the surface treatment of the outer layer circuit of the printed wiring board and the bonding of the copper foil and the insulating material.

(Function) When salts are added to the alkaline aqueous solution of formaldehyde, the time required for reduction to metallic copper can be shortened as compared with the case where no salts are added.

Example 1 After preliminarily roughening an inner layer circuit board on which an inner layer circuit was formed with an aqueous solution of ammonium persulfate, it was treated with the following composition and conditions to form copper oxide on the copper surface of the inner layer circuit.

Composition Sodium hydroxide; 15g / l Trisodium phosphate; 30g / l (Na ₃ PO ₄ · 12H ₂ O) Sodium chlorite; 90g / l Water; Combined with the above composition to be 1 Condition Liquid temperature 85 ° C Treatment time; 90 seconds Next, after washing with water, treatment was performed with the following composition and conditions.

Composition Sodium borohydride; 1 g / l water; amount to be 1 together with the composition Condition pH; 12.5 Liquid temperature; 40 ° C Treatment time; 40 seconds Next, after washing with water, treatment was performed with the following composition and conditions.

Composition 36% _{formalin; 4ml / l Na 2 SO 4} ; 0.5 mol / l Conditions pH: 12.5 liquid temperature; 40 ° C. processing time; potential on the surface of copper on the inner layer circuit board and -1200mV against Ag-AgCl electrode It takes 30 minutes at 80 ℃ to wash the inner layer circuit board treated as above.
After drying for a minute, sandwich both sides with I-67 (Hitachi Chemical Co., Ltd., trade name) which is an epoxy-modified polyimide resin prepreg, and stack both sides with a copper foil of 35 μm, pressure 50 kg / cm ² , A test piece was prepared by heating and heating at a temperature of 170 ° C for 90 minutes, and by laminating and integrating.

Example 2 A test piece was prepared under the same conditions as in Example 1 except that Na ₂ SO ₄ was changed to 1 mol / l.

Example 3 A test piece was prepared under the same conditions as in Example 1, except that Na ₂ SO ₄ was changed to 2 mol / l.

Example 4 Example 4 was repeated except that Na ₂ SO ₄ was replaced with NaCl.
Test pieces were prepared under the same conditions.

Example 5 A test piece was prepared under the same conditions except that NaCl was 1 mol / l in Example 4.

Example 6 A test piece was prepared under the same conditions as in Example 4 except that NaCl was changed to 2 mol / l.

Comparative Example 1 Test pieces were prepared under the same conditions as in Example 1 except that Na ₂ SO ₄ was not added.

The time required until the copper surface after the oxidation treatment of each test piece prepared as described above was reduced to metallic copper, and the following tests were performed. The results are shown in Table 1.

(1) Inner layer copper foil peeling test test method; JIS-C6481 (2) Hydrochloric acid resistance test method; cut into a size of 130 mm × 130 mm Surface copper foil removed 19% hydrochloric acid with 30 mm 1 mm diameter holes Immersion in hydrochloric acid Measurement of time when hydrochloric acid soaks into the inner layer (3) Electroless plating solution test Test method: Cutting to a size of 130 mm x 130 mm Surface copper foil is removed 30 holes with a diameter of 1 mm are drilled Immersion in plating solution Composition CuSO ₄ , 5H ₂ O: 10g / l EDTA ・ 2Na: 30g / l 36% Formalin: 5ml / l Pure water: Amount that becomes 1 together with the composition Conditions Temperature: 70 ℃ pH: 12.5 No Measurement of time for electrolytic plating solution to soak into the inner layer (Effects of the Invention) As described above, the present invention provides a surface treatment method for copper that maintains hydrochloric acid resistance, electroless plating solution resistance, and resin adhesive strength, and that has a short processing time and is mass-produced. can do.

Claims (1)

[Claims] 1. A method for surface treatment of copper, which comprises reducing the copper oxide formed on the copper surface to metallic copper by a treatment step including the following steps in the following order: a. Forming copper oxide on the copper surface by contacting the copper surface with an aqueous solution containing an oxidizing agent. b. A step of changing the potential of the oxidized copper surface within a range of −1000 mV or more to −400 mV or less with respect to the Ag-AgCl electrode by contacting the oxidized copper surface with an aqueous solution containing alkali borohydride. . c. A step of changing the potential of the oxidized copper surface to a base potential lower than −1000 mV with respect to the Ag—AgCl electrode by contacting with an aqueous solution containing at least one of salts and formaldehyde.