JPS61250036A - Bonding of copper and resin - Google Patents

Abstract

PURPOSE:To enable bonding to be accomplished between copper and resin and allow to be applied for production of multi-layered printed wiring board, by forming oxide layer on copper surface followed by reducing said layer to convert into metallic copper to effect both increased bond strength and acid resistance. CONSTITUTION:Copper surface is treated with an aqueous alkaline solution containing such an oxidizing agent as sodium chlorite to form an oxide layer followed by partly eliminating said layer to allow metallic copper to be exposed, which is then treated with a reducing agent (e.g., formaldelyde, boron sodium hydride) -contg. solution, thus enabling the objective bonding to be accomplished.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method of adhering copper and resin that achieves both adhesive strength and acid resistance, and particularly relates to a method of adhering copper and resin by laminating and adhering a copper circuit layer and a resin layer. The present invention relates to a method for adhering copper and resin, which is suitable for manufacturing multilayer printed wiring boards.

[Background of the invention]

Conventionally, when adhering copper and resin, it was necessary to directly bond the copper surface & 6
P p 96-99 (June 1982), a method of forming an oxide layer on a copper surface to improve adhesion was known. However, these steel oxides have a problem in that when they come into contact with an oxidizing aqueous solution, they are easily hydrolyzed and dissolved as copper ions.

[Purpose of the invention]

An object of the present invention is to provide a method for bonding copper and resin that has good acid resistance and provides sufficiently high adhesive strength.
In particular, it is an object of the present invention to provide a method for bonding copper and resin, which is suitable for laminating bonding of multilayer printed wiring boards that require high reliability.

[Summary of the invention]

Conventionally, various methods have been studied as surface treatment methods for copper for bonding copper and resin. For example, in copper-clad laminates used for printed wiring boards, the adhesive surface (so-called Matt cider) has a rough surface with large irregularities, and is known to provide sufficient adhesive strength due to its anchoring effect. On the other hand, with flat copper surfaces such as polished copper surfaces, ordinary plated surfaces, etched surfaces, etc., it is difficult to obtain sufficient adhesion force even if the copper surfaces are directly bonded to a resin. For this reason, various methods are used to treat the surface of copper to improve its adhesion.
Methods of forming copper oxide layers such as cuprous oxide and cupric oxide have been studied. For example, an alkaline aqueous solution containing potassium persulfate.

Alternatively, a method has been known in which an oxide layer is formed by treating the copper surface to be bonded using an alkaline aqueous solution containing sodium chlorite. This method of forming a copper oxide layer was an extremely effective method for improving adhesive strength. However, since copper oxides generally easily dissolve due to hydrolysis when they come into contact with acids, it has been necessary to avoid contact with acids after treatment and before adhesion. In addition, even after bonding, the acid treatment process dissolves the oxide layer at the bonding interface exposed on the inner surface of the hole penetrating the bonding surface and the edge of the cut surface, and the acid soaks into the interface, causing the oxide layer at the bonding interface to dissolve. It has been pointed out that an undesirable phenomenon in terms of adhesion occurs, in which the adhesive is lost. This phenomenon involves, in particular, after bonding, a through-hole drilling step that penetrates the bonding interface, and various acid treatment steps for through-hole plating. This was a major problem in the adhesion of copper circuits and prepreg resin in the lamination adhesion process of multilayer printed wiring boards.

The present invention provides an adhesive method that essentially solves the problem of acid resistance as described above and provides sufficient adhesive strength.

It was thought that the improvement in adhesive strength due to the formation of an oxide layer was due to the fact that the chemical affinity between copper oxide and resin was higher than the chemical affinity between copper metal and resin. On the other hand, the oxide layer formed by the above-described treatment has a surface with fine irregularities. If the mechanical anchoring effect of these fine irregularities is the main reason for the improvement in adhesive strength, it should be possible to obtain sufficient adhesive strength without necessarily forming an oxide layer. For example, if such fine irregularities can be realized using copper metal, which does not dissolve in acids, and sufficient adhesive strength can be obtained, it is thought that the above-mentioned problem of acid resistance can be avoided. As a result of various studies from this point of view, the inventors found that by forming a temporary oxide layer on the steel surface and then reducing this oxide layer to metallize it.

It has been found that it is possible to achieve good acid resistance and adhesive strength equivalent to that achieved by bonding through an oxide layer. This supports the above-mentioned speculation that the main reason for the improvement in adhesive strength due to the formation of the oxide layer is the mechanical anchoring effect due to the fine irregularities on the surface caused by the formation of the oxide layer. In this case, the method of first forming the copper oxide layer has already been described.

This method is used as a conventional adhesive pretreatment method.

For example, a method of treating with an alkaline aqueous solution containing an oxidizing agent such as sodium chlorite or potassium persulfate gave good results in terms of adhesive strength. Further, the oxide layer to be formed may be either the oxidized first #f or the second oxidized #f.

On the other hand, as a method of reducing the formed oxide layer, a method of electrochemical reduction by passing an electric current from the outside in an electrolyte solution can be considered. However, in order to apply the electrochemical reduction method, it is necessary that all the processing parts are electrically connected, and it cannot be applied when there are electrically independent parts.For example, it cannot be applied when there are electrically independent parts. For example, after forming a wiring pattern, it is difficult to apply an electrochemical reduction method to the entire surface because in many cases there are island-shaped parts that are not electrically connected to the outer periphery. Have difficulty. In these cases, it is desirable to reduce the oxide layer to metallic copper by chemical treatment.Formaldehyde, hypophosphite, hydrazine, etc. are well-known reducing agents used in aqueous solutions. , formaldehyde is widely used as a reducing agent in electroless steel plating. However, according to the results of studies conducted by the inventors, it is difficult to reduce the oxide layer to metallic copper using these reducing agents under normal conditions. For example, even if a copper foil treated with a solution of to form a copper oxide layer on the entire surface is immersed in an aqueous solution of at a temperature of 70°C for 20 minutes or more, the copper oxide layer will not be reduced to metallic copper. Not observed. The surface of the copper foil had a dark brown color due to the formation of the oxide layer, and the same dark brown color remained even after formalin treatment. However, when this was immersed in 1:1 hydrochloric acid, the dark brown color easily disappeared and changed to a bright skin color characteristic of metallic copper. This is because the oxide layer came into contact with the acid and dissolved without being metallized.

As can be seen from the fact that formaldehyde is widely used as a reducing agent in electroless steel plating.

The surface of metallic copper has sufficient reducing power to reduce divalent copper ions to metallic copper, and thermodynamically, it has a sufficiently circular standard electrode potential to reduce copper oxide to metallic copper. ing. Despite this, the copper oxide layer formed on the copper surface is not reduced to metallic copper because the copper oxide surface does not have sufficient catalytic ability for the formaldehyde oxidation reaction like the metallic copper surface. It is thought that. This is considered to be the same for reducing agents other than formaldehyde, such as sodium borohydride and hydrazide. On the other hand, once the reduction reaction begins to proceed, it is expected that the subsequent reduction reaction will proceed quickly even if a reducing agent such as formaldehyde is used, since metallic copper with catalytic ability is the main constituent.
The present invention has been made from this viewpoint, and relates to a reaction initiation method for autocatalytically proceeding a reduction reaction.

The key point of the present invention is to partially expose metallic copper when reducing the steel oxide layer formed on the copper base.

When using the conventional method of forming a copper oxide layer by immersing it in an alkaline solution containing an oxidizing agent, the entire copper surface that came into contact with the solution is covered with copper oxide.
It was difficult to reduce with reducing agents such as formaldehyde.

However, if metallic copper is exposed in at least one portion of a continuous copper circuit, a local battery will be formed between the exposed metallic copper and the copper oxide-covered region, and the reducing agent will form on the metallic copper. As the oxidation reaction progresses, the copper oxide layer is successively reduced, making it possible to reduce all of the copper oxide layer to metallic copper.

Examples of methods for exposing metallic copper on a continuous copper circuit after oxide layer forming treatment will be shown below, but these methods are not intended to limit the embodiments of the present invention.For example,
Such a state can be achieved by covering a portion of the surface of the copper base with a chemically resistant resist during the oxide layer forming process. Another method is to first form a copper oxide layer over the entire surface, then cover the areas where metallic copper is exposed with an acid-resistant resist, and then treat with acid to remove the oxide layer. can. In addition to the chemical methods described above, it is also possible to mechanically peel off and remove the oxide layer. In this way, it is naturally more difficult to obtain sufficient adhesion in areas where metallic copper is exposed prior to reduction treatment than in areas where an oxide layer is formed and then reduced. . Therefore, it is desirable to expose the copper metal in areas that do not require particularly high adhesion. Taking a multilayer printed wiring board as an example,
It can be provided in the part that is removed by drilling one through hole after adhesion. On the other hand, the exposed portion of metallic copper is necessary only for the initiation of the reduction reaction, and once the reduction reaction occurs, the area of the metallic copper portion increases as the reaction progresses. Therefore, it is sufficient that the area of the exposed metal copper part is extremely small compared to the area of the copper surface to be bonded, and by keeping this area to the minimum necessary, in effect, the overall adhesive strength can be sufficiently increased. It is possible to maintain high standards.

The reducing agent used in the present invention may include formaldehyde, sodium borohydride, hydrazine, etc. Other reducing agents are also sufficient to reduce copper oxide to metallic copper on the copper surface. Reducing agents that cannot directly reduce steel oxides can also be used as long as they have sufficient reducing power.

In this way, by once forming a copper oxide layer on the copper base and reducing it to metallic copper, it is possible to bond copper and resin with excellent adhesive strength and acid resistance. It becomes possible.

[Embodiments of the invention]

The present invention will be explained below with reference to Examples.

Example 1 Bonding between steel and resin was performed through the following steps.

1) After polishing the surface of the #l tension calendar board with an abrasive,
uCf12・H, Osog,”n HCffi (36%) 500g/R temperature
The copper surface was etched by immersing it in a solution at 40° C. for 1 minute, followed by washing with water.

2) Then N a CQ Oz 30 g/fl
It was immersed for 2 minutes in an aqueous solution of NaOH 10g/Q Na, PO4"2H, 05gzl at a temperature of 75°C to form a copper oxide layer on the surface.

3) A portion of the formed copper oxide layer was mechanically removed to expose metallic copper.

4) Next Formaldehyde 0.5M N　a　OHO, 2M Temperature 70℃ After being immersed in the reducing solution for S minutes, it was washed with water and dried.

5) Next, a glass cloth was laminated via a prepreg impregnated with polyimide resin, and 170T:, 20kgf/cm
'' for 80 minutes to bond.

After adhesion, a through hole was made and immersed in 1:1 hydrochloric acid for 180 minutes, but no acid seepage from the inner wall of the hole to the adhesive interface was observed. In addition, after completing step 4), the copper-clad laminate was directly immersed in 1:1 hydrochloric acid, but no discoloration or dissolution of the surface was observed. For those bonded using the adhesive method, acid seepage from the inner wall of the hole to the adhesive interface and discoloration were observed.

As a result of analyzing the surface of the copper-clad laminate after completing step 4) by X-ray diffraction, no copper oxide was found.

In step 4), it was confirmed that the copper oxide layer was reduced to metallic copper. The peak strength of the bonded cocoon and polyimide resin is 1.1 Jf/am, and the adhesive force equivalent to the conventional bonding method that does not include step 3) and t4) is obtained, and it has excellent acid resistance and adhesive strength. It was shown that this is an adhesion method that achieves both.

Example 2 Copper and resin were bonded together in the same manner as in Example 1) except that the polyimide resin in Step 5) was replaced with an epoxy resin. The beer strength was 2.2 kg/cm, and the acid resistance was the same as in Example 1.

Comparative Example Copper and resin were bonded together in the same manner as in Example 1 except for step 3) in Example 1). Although the adhesive strength was equivalent to that of Example 1, the acid resistance was not sufficient. When the copper surface that had undergone step 4) was brought into contact with 1=1 hydrochloric acid, the surface instantly dissolved and changed color.

Analysis of the surface layer confirmed that copper oxide remained unreduced.

〔Effect of the invention〕

Claims (1)

[Claims] 1. Prior to adhesion, the method includes the steps of forming a copper oxide layer on the copper surface and treating the oxide layer with a reducing agent solution.
In the bonding method of copper and resin by heat and pressure bonding, the method of bonding copper and resin is characterized by exposing metallic copper to a part of the copper surface covered with a copper oxide layer when treated with a reducing agent solution. Adhesion method. 2. The method for bonding copper and resin according to claim 1, wherein the reducing agent solution contains at least one selected from formaldehyde, sodium borohydride, and hydrazine.