JPH0739574B2 - Treatment liquid to improve acid resistance of copper oxide surface - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a treatment liquid for making copper used for adhesion with a resin have both adhesive strength and acid resistance.

[0002]

2. Description of the Related Art Conventionally, when bonding a metal and a resin, it is not possible to obtain a sufficient bonding force by directly bonding a smooth metal surface. Therefore, Plating and Surfac
e Finishing, vol. 69, No. 6 pp
As described in 96-99 (June 1982), a method of forming an oxide layer for improving the adhesive force on a metal surface has been known. However, in general, many metal oxides have a problem that they are easily hydrolyzed and dissolved as metal ions when they are brought into contact with an acidic aqueous solution.

Conventionally, various methods have been studied as a surface treatment method of copper for adhering copper and resin. However, it is difficult to obtain a sufficient adhesive force even if the resin is directly adhered to the copper surface. Therefore, as a surface treatment method for copper for the purpose of improving the adhesive force, various methods of forming an oxide layer of cuprous oxide, cupric oxide or the like on the copper surface have been studied. For example, an alkaline aqueous solution containing potassium persulfate or an alkaline aqueous solution containing sodium chlorite is used to treat the copper surface to be bonded,
Methods of forming oxide layers have been known. like this,
The method of forming the copper oxide layer has been extremely effective in improving the adhesive strength. However, in general, the copper oxide is easily dissolved by hydrolysis when it comes into contact with an acid, so it is necessary to avoid contact with the acid after the treatment and before the adhesion. When acid treatment is performed even after adhesion, the oxide layer at the adhesive interface exposed at the inner surface of the hole penetrating the adhesive surface or at the end of the cut surface dissolves and the acid soaks into the interface, and the oxide at the adhesive interface It has been pointed out that an unfavorable phenomenon of adhesion occurs that layers are lost. This phenomenon has a through hole drilling step for penetrating the bonding interface and various acid treatment steps for through hole plating, especially after bonding. There has been a big problem in bonding the copper circuit and the prepreg resin in the lamination bonding process of the multilayer printed wiring board.

JP-A-56-153797 describes that the problem of acid resistance is solved by a method of reducing cupric oxide to cuprous oxide. It is generally said that cuprous oxide is less soluble in acid than cupric oxide.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to bond copper with a resin having good acid resistance and sufficiently high adhesive strength, and particularly to laminate a multilayer printed wiring board required to have high reliability. It is an object of the present invention to provide a treatment liquid suitable for adhesion, which is used in adhesion between copper and resin and improves the acid resistance of the copper oxide surface.

[0006]

[Means for Solving the Problems] Generally, the improvement of the adhesive strength by forming an oxide layer is attributed to the fact that the chemical affinity between copper oxide and resin is higher than the chemical affinity between metallic copper and resin. it seems to do. For example, in a copper-clad laminate used for a printed wiring board, the adhesive surface (so-called mat side) is a rough surface having large unevenness,
A sufficient adhesive force can be given due to this throwing effect. On the other hand, on a polished copper surface, a normal plating surface, a copper surface having a flat surface such as an etching surface, it was difficult to obtain sufficient adhesive force even if the resin was directly adhered. By the way, the oxide layer formed by the above-mentioned treatment has a surface having fine irregularities. If the mechanical projection effect due to the fine irregularities is the main cause of the improvement of the adhesive force, it should be possible to obtain a sufficient adhesive force without necessarily forming the oxide layer. For example, such fine irregularities are realized by metallic copper that does not dissolve in acid,
It is considered that the above-mentioned problem of acid resistance can be avoided if a sufficient adhesive force can be obtained. As a result of various studies from such a viewpoint, the inventors have found that once the oxide layer is formed on the copper surface, the oxide layer is reduced and metallized to obtain good acid resistance and oxidation. It was found that an adhesive force equivalent to that obtained by adhering through a physical layer can be realized. This supports the above inference that the main cause of the improvement in the adhesive strength due to the formation of the oxide layer is the mechanical entrainment effect due to the fine irregularities on the surface that accompany the formation of the oxide layer. In this case, as a method of first forming the copper oxide layer, it is preferable to apply a neutral or alkaline aqueous solution containing an oxidizing agent. For example, a method of treating with an alkaline aqueous solution containing an oxidizing agent such as sodium chlorite and potassium persulfate gives good results in terms of adhesive strength.
The oxide layer formed may be either cuprous oxide or cupric oxide.

On the other hand, as a method of reducing the formed oxide layer, a method of electrochemically reducing it by applying a 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 reduction-treated parts are electrically connected, and this is not applicable when there are electrically independent parts. For example, in the case of a printed wiring board as an example, after forming a wiring pattern, in many cases, island-shaped portions that are not electrically connected to the outer peripheral portion are present. Is difficult to apply over. In these cases, it is desirable to reduce the oxide layer to metallic copper by chemical treatment. Formaldehyde, hypophosphite, hydrazine, and the like are used as the reducing agent used in the aqueous solution, and formaldehyde is effective as the reducing agent for electroless copper plating. However, according to the results examined by the present inventors, it was difficult to reduce the oxide layer to metallic copper with these reducing agents under normal conditions. For example, the surface of the copper foil treated with formalin was dark brown due to the formation of the oxide layer, but remained the same dark brown after the treatment with formalin. But this:
When it was immersed in 1 hydrochloric acid, the dark brown color easily disappeared and changed to a bright skin color peculiar to metallic copper. This is because the oxide layer was not metallized but contacted with the acid and dissolved. Similar results were obtained with hypophosphite or hydrazine.
With respect to these reducing agents, metalization of the oxide layer was not achieved even when the concentration, pH, and treatment temperature were changed.

As far as the inventors have studied, the number of reducing agents capable of reducing the oxide layer formed on the copper surface to metallic copper is extremely limited, and the general formula, BH ₃ .NHRR ′ (in the formula,
R, R 'represents any of _{H, CH 3, CH 2 CH} 3. ) Limited amineboranes represented by
Only dimethylamine borane, ammonia borane and the like were used. When a copper surface on which an oxide layer was formed in advance was treated with an aqueous solution containing at least one of these amineboranes, no discoloration or dissolution was observed even when directly immersed in 1: 1 hydrochloric acid. This is because the oxide layer was reduced to acid-insoluble metallic copper by the reduction treatment using the solution containing dimethylamine borane. As a result of X-ray diffraction analysis of the copper foil after the copper oxide layer formation treatment, a diffraction line peculiar to CuO was observed, and it was confirmed that a cupric oxide film was formed on the copper surface. On the other hand, the diffraction line corresponding to CuO was not detected from the copper foil surface after the reduction treatment with the dimethylamine borane solution.

Further, no diffraction line corresponding to Cu ₂ O was observed, and it was confirmed that the oxide layer was completely reduced to metallic copper. The copper surface after the reduction treatment did not have the bright skin color peculiar to the flat metallic copper surface, but rather had a dark brown color close to the color tone of the oxide film as described above. This is because the dark brown color tone generated by the formation of the oxide layer comes from the shape having fine irregularities on the surface, and the shape is retained even in the metallized surface layer after the reduction treatment. It indicates that Such a difference in catalytic activity on the surface can be clearly shown by an electrochemical method. When the anodic polarization curves of copper electrodes such as formaldehyde, sodium borohydride, and hydrazine are measured, in the region where the electrode surface is metallic copper, the higher the potential, the higher the current value observed. It is known that when the surface of a copper electrode having a different potential is oxidized and enters a region covered with a copper oxide layer, the current value sharply decreases. This indicates the low activity of these reducing agents on copper oxide. On the other hand, according to the results examined by the inventors, in the case of the specific amine boranes, the current value does not decrease even in the potential region where copper oxide is formed on the copper surface, and the potential is noble. Was found to increase. This is an indication that the specific amine boranes have sufficiently good reducing power even on copper oxide.

As described above, it is presumed that the reason why only the specific amine boranes are effective for the reduction of the formed oxide layer is mainly due to the difference in the activity of the reaction of various reducing agents on the copper oxide. As you know, formaldehyde is
It is widely used as a reducing agent for electroless copper plating, and the oxidation reaction of formaldehyde occurring on the copper surface has a standard electrode potential sufficient to reduce copper oxide to metallic copper thermodynamically. However, as already mentioned, copper oxide cannot be reduced to metallic copper by formaldehyde. The oxidation reaction of formaldehyde on the copper surface largely depends on the catalytic ability of the metallic copper surface, and on the copper oxide, the copper oxide surface does not have a good catalytic action like the metallic copper surface. It is presumed that copper oxide cannot be reduced. The same applies to sodium borohydride, hydrazine and the like. On the other hand, in the case of the specific amine boranes, since the oxidation reaction does not depend so much on the catalytic ability of the surface, it is thought that the reaction occurs promptly even on the copper oxide and it can be reduced to metallic copper. Be done.

For reference, polarization characteristic diagrams of various reducing agents on a copper electrode are shown in FIG. Curve i is 0.5 M NaOH, 0.
1M HCHO, curve ii is N ₂ H ₄ , curve iii
Is NaBH ₄ and the curve iv is BH ₃ · NH (CH ₃ ) ₂
This is the case of a reducing solution to which is added respectively. According to this, in the case of i, ii, and iii, the current flows well as the potential of the electrode is increased up to -1.0 to -0.6V, but when the potential exceeds -0.6V, a sudden current drop occurs. Will end up.
However, in the case of iv, the current increases even when it exceeds -0.6V. It is considered that this is because when the reducing agent of iv is added, the copper oxide on the electrode surface is converted into metallic copper at around -0.5V.

When the oxide layer is subjected to a reduction treatment using the above-mentioned specific amine borane solution, the adhesion between the copper and the resin after the reduction treatment is achieved by providing the oxide layer on the copper surface. It was confirmed that the above-mentioned level was maintained and that good adhesive strength and acid resistance were simultaneously realized. Using these specific amine boranes, regardless of whether the copper oxide layer is cuprous oxide or cupric oxide, can be reduced to metallic copper, and insolubilization with respect to acid can be achieved. it can.

On the other hand, among the amineboranes, compounds such as trimethylamineborane and triethylamineborane in which all hydrogen atoms of the amine moiety are substituted with alkyl groups have low solubility in water and are difficult to use as an aqueous solution. Further, the reducing power was not sufficient, and good results were not obtained (the amine borane according to the present invention showed a tendency that the more hydrogen atoms directly bonded to the nitrogen atom, the stronger the reducing power). Also, good results were not obtained with borohydrides known as reducing agents for the same boron compounds, such as sodium borohydride. Further, when the immersion time in the sodium borohydride solution became longer, the dark brown surface layer formed by the oxide layer forming treatment gradually became mottled brown. It is considered that this is because the surface shape gradually changed during the immersion and the fine irregularities were lost. Such a phenomenon is not desirable in terms of ensuring uniform adhesive force.
In addition, borohydrides gradually react with water in an aqueous solution and decompose, so that it is difficult to use the borohydride stably for a long period of time. In order to keep the liquid stable, it is necessary to keep it highly alkaline, which causes a problem in handling. Further, since the decomposition reaction is promoted by raising the temperature, it is difficult to raise the temperature to strengthen the reducing power.

The present invention provides a method for bonding copper and resin by thermocompression bonding, in which a copper oxide layer is provided on the copper surface in advance and then a treatment for improving the acid resistance of the copper oxide surface of the present invention. By applying a liquid and reducing it to form metallic copper, it was possible to achieve both adhesive strength and acid resistance. As a treatment liquid for improving the acid resistance of the copper oxide surface, a general formula, BH ₃ · N HRR ′ (R, R ′: H, CH ₃ , C
A group of the specified amineboranes represented by H ₂ CH ₃ ) gives good results. At this time, it is preferable that the treatment liquid does not substantially contain copper ions. This is because when copper ions are contained, copper metal is plated on the surface and the unevenness due to the formation of the oxide layer is lost. In addition, it is desirable to apply a neutral or alkaline aqueous solution containing an oxidizing agent to the formation of the copper oxide layer.

The reducing solution used in the present invention may be a weakly acidic, neutral or alkaline solution.
When the pH is low, the oxide layer is dissolved in competition with the reduction reaction, which is not preferable. The reduction reaction rate depends on the reducing agent concentration, liquid temperature, and pH. By increasing these, the reducing power can be strengthened and the reduction time can be shortened. However, it is desirable to select the temperature within a range in which decomposition of amine borane does not occur. For example, in the case of dimethylamine borane, it is desirable to use it at 70 ° C. or lower, and sufficient reduction can be performed at a temperature lower than this. The pH can be adjusted by adding sodium hydroxide, sodium carbonate, sodium phosphate or the like. As described above, the copper oxide can be promptly reduced without adding an alkali, but the addition of the alkali can further shorten the treatment time.

As the copper to which the treatment liquid of the present invention is applied,
Electroplated copper, chemically plated copper, rolled copper, etc. can be used regardless of the processing method. A small amount of different metals may be added to improve the properties of copper. In addition, polishing or etching the surface prior to the formation of the oxide layer has no problem in the practice of the present invention, and it is preferable to perform these treatments in terms of surface cleaning. In addition to copper, copper alloys or other metals such as nickel, cobalt or nickel alloys, cobalt alloys, etc. may be applicable to the present invention.

As a resin to which the present invention is applied, an epoxy resin, a polyamide resin, a polyimide resin, a polyester resin, a phenol resin or the like can be used. Further, a thermoplastic resin such as polyethylene or polyphenylene sulfide may be used. When the present invention is applied to a multilayer printed wiring board, a copper foil such as electroplated copper, chemically plated copper or rolled copper is provided on both or one side of these resin plates containing a reinforcing material such as glass cloth, It is also possible to use those having a pattern formed therein, and further to laminate them through a prepreg impregnated with these resins on a reinforcing material such as glass cloth, and press and heat to bond them. With such a process, it has excellent adhesive strength and acid resistance,
A highly reliable multilayer printed wiring board can be obtained.

As described above, by applying the treatment liquid of the present invention, it is possible to perform the adhesion having excellent adhesive strength and acid resistance. Also, do not pressurize or heat when bonding,
The method described in the present invention can also be applied to bonding at room temperature and pressure. Also, the adhesion of copper and resin is
No problem occurs even if it is carried out in air at room temperature. Normal,
It is said that a copper oxide layer of about a monomolecular layer or a few molecular layers is formed on the metallic copper surface when contacted with air. Even when the previously formed thick oxide layer is reduced to metallic copper by the reduction treatment, a very thin copper oxide film is again formed on the surface by contact with air after the reduction and before the lamination adhesion. It is possible that However, the presence of such an oxide layer does not cause any particular problem in terms of acid resistance or adhesive strength of the surface treatment layer. From the viewpoint of the affinity between copper and resin, it is considered that the presence of an oxide layer of about several molecular layers is rather preferable.

An example of using the treatment liquid for improving the acid resistance of the copper oxide surface of the present invention will be described below by taking the lamination adhesion of a multilayer printed wiring board as an example.

Example of use 1. 1) The copper foil surface of the glass cloth-filled polyimide resin copper-clad layer board was immersed in an aqueous solution of CuCl ₂ · H ₂ O 50 g / l HCl (36%) 500 g / l at a temperature of 40 ° C for 1 minute for etching. 2) Then after washing, were treated for 2 minutes with _{NaClO 4 30g / l NaOH 10g /} l Na 3 PO 4 · 2H 2 O 5g / l temperature 75 ° C. of an aqueous solution to form a copper oxide layer on the surface . 3) Next, after washing with water, the treatment liquid of Example 1 was used for 25
The oxide layer was reduced by treatment at 2 ° C. for 2 minutes. 4) The copper clad laminate treated as described above was washed with water, dried, and then laminated via a prepreg impregnated with a polyimide resin on a glass cloth, and at 170 ° C., a pressure of 20 kgf / cm ² was applied for 80 minutes. Glued

Adhesion between the copper foil laminated and adhered in this manner and the polyimide resin of the prepreg layer was good, and the peel strength was 1.2 kgf / cm. Further, even if the copper clad laminate after the reduction treatment was dipped in 1: 1 hydrochloric acid prior to lamination adhesion, discoloration or dissolution of the surface treatment layer was not observed.
Further, after the multi-layered adhesion, through-holes are opened, and 1:
The sample was immersed in 1 hydrochloric acid, but even after immersion for 3 hours or more, no acid soaking from the through-hole wall or discoloration of the adhesive interface layer was observed.

The steps up to (2) of Use Example 1 were carried out to form a copper oxide film on the copper surface, and then immersed in a solution containing various reducing agents shown in Table 1 for 20 minutes to examine the reducing property. Copper oxide dissolves rapidly in 17.5% HCl, but metallic copper does not dissolve easily, so it is possible to determine whether it has been reduced to metallic copper by the change in the color of the surface. The reduction treatment conditions are shown in Table 2.

[0023]

[Table 1]

[0024]

[Table 2]

Example of use 2. In place of the glass cloth-containing polyimide resin copper-clad laminate of Use Example 1, a glass cloth-containing epoxy resin copper-clad laminate is used,
Instead of a prepreg in which a glass cloth was impregnated with a polyimide resin, a prepreg in which a glass cloth was impregnated with an epoxy resin was used, and except that the prepreg was laminated and bonded using the same steps as in Use Example 1. The adhesion between the copper foil and the epoxy resin of the prepreg layer was good, and the peel strength was 2.2 kgf / cm. Also, the hydrochloric acid resistance was good, and even after immersion of the through-holes in 1: 1 hydrochloric acid for 3 hours or more, acid penetration from the through-hole walls and discoloration of the adhesive interface were not observed.

Example of use 3. In use example 1, a reduction treatment was performed at 50 ° C. using the treatment liquid of Example 2 instead of the treatment liquid described in step 3). In this case, the reduction reaction was completed within 30 seconds. Similar to Example 1, good results were obtained for both adhesive strength and acid resistance.

Example of Use 4. In Use Example 1, the treatment liquid of Example 3 was used instead of the treatment liquid described in Step 3) to reduce the oxide layer at 25 ° C., and lamination adhesion was performed in the same manner as in Use Example 1. The reduction of the oxide layer occurred promptly, and the adhesive strength after adhesion and the acid resistance were as good as in Use Example 1.

Use example 5. Prior to Step 1) of Use Example 1, using a commercially available photoresist as a mask, the copper foil on the surface of the copper-clad laminate is etched to form a circuit pattern, and Steps 1) to 4) of Example 1 are performed. Lamination adhesion was performed. After that, necessary through-holes were opened with a drill, the inner surface of the holes was activated with a commercially available hydrochloric acid-type palladium-tin catalyst aqueous solution, and through-hole plating was performed by electroless plating to manufacture a multilayer printed wiring board. After drilling the through-holes, an acid resistance test was conducted by immersing in 1: 1 hydrochloric acid in the same manner as in Example 1. However, even after 3 hours or more, discoloration of the adhesive interface and acid penetration were not observed. It was The adhesion between the copper foil and the prepreg resin was also good as in Example 1. In addition, even after immersion in a hydrochloric acid type catalyst solution, which was carried out as a pretreatment for through-hole plating, no permeation or discoloration of acid from the wall surface of the through-hole to the adhesive interface was observed.

Example of use 6. In Use Example 5, prior to patterning by etching with a photoresist mask, through-hole drilling was performed on the copper-clad laminate, followed by activation with a commercially available hydrochloric acid-type palladium-tin catalyst aqueous solution, and then in the holes and on the surface of the copper foil. And ethylene diamine tetraacetic acid 35 g / l copper sulfate 6 g / l formalin (37%) 5 ml / l polyethylene glycol 10 g / l 2-2, dipyridyl 50 mg / l pH 12.5 temperature 75 ° C using a chemical copper plating solution Then, plating with a thickness of 15 μm was performed. After that, a pattern was formed by etching using a commercially available photoresist as a mask in the same manner as in Use Example 5, etching of the surface, formation of an oxide layer and reduction treatment thereof were performed, and then lamination adhesion was performed. Good adhesion and acid resistance were obtained for the chemically plated copper, as in Example 5.

Comparative Example 1. In Use Example 1, the lamination bonding of step 4) was performed without performing the reduction treatment step described in step 3). The peel strength between the copper foil and the prepreg layer was as good as 1.2 kgf / cm, but as a result of immersing in 1: 1 hydrochloric acid after drilling through holes, discoloration and dissolution of the adhesive interface occurred after about 10 minutes. ,
There was a problem with acid resistance. Further, when the copper foil having the oxide layer formed in the step 2) is directly immersed in 1: 1 hydrochloric acid, the oxide layer is dissolved and lost within 1 second.

Comparative Example 2. In Use Example 2, as in Comparative Example 1, lamination adhesion was performed without performing reduction treatment. The peel strength between the copper foil and the prepreg layer was 2.2 kgf / cm, which was the same value as in Use Example 2, but like Comparative Example 1, there was a problem of acid resistance.

Comparative Example 3. In use example 1, instead of the reduction treatment in step 3), the mixture was immersed in a solution of sodium borohydride 2 g / l sodium hydroxide 15 g / l temperature 50 ° C. for 20 minutes. When washed with water and then immersed in 1: 1 hydrochloric acid, the surface-treated layer was easily dissolved and discoloration was observed. Also,
With longer soaking time in sodium borohydride solution,
The dark brown surface layer formed by the oxide layer forming treatment gradually became mottled brown.

Comparative Example 4. In use example 1, instead of the reduction treatment in step 3), the solution was immersed in a solution of formalin (37 ° C.) 50 ml / l sodium hydroxide 4 g / l temperature 70 ° C. for 20 minutes. When washed with water and immersed in 1: 1 hydrochloric acid, the surface-treated layer was easily dissolved and discoloration was observed. Compared to Use Example 1, the surface-treated layer was more easily dissolved in acid.

Comparative Example 5. In Use Example 1, lamination adhesion was performed without performing the oxide layer forming treatment of step 2) and the reduction treatment step of step 4).
Peel strength between copper foil and prepreg layer is 0.2kgf / c
Since it was less than m, sufficient adhesive strength could not be obtained.

[0035]

Example 1 10 g of dimethylamine borane was dissolved in 1 liter of water to prepare a treatment solution for improving the acid resistance of the copper oxide surface.

Example 2 5 g of dimethylamine borane and 5 g of sodium hydroxide were dissolved in 1 liter of water to prepare a treatment solution for improving the acid resistance of the copper oxide surface.

Example 3 3 g of ammonia borane and 4 g of sodium hydroxide were added to 1 part of water.
A treatment liquid was prepared which was dissolved in a liter to improve the acid resistance of the copper oxide surface.

Example 4 3 g of ammonia borane and 4 g of sodium hydroxide were added to 1 part of water.
A treatment liquid was prepared which was dissolved in a liter to improve the acid resistance of the copper oxide surface.

[0039]

As described above, when the treatment liquid for improving the acid resistance of the copper oxide surface of the present invention is used, a high adhesive force can be obtained without depending on the copper oxide which is easily dissolved in acid. Therefore, good adhesion can be achieved while avoiding the problem of acid resistance before and after adhesion of copper and resin.

[Brief description of drawings]

FIG. 1 is a polarization characteristic diagram of various reducing agents on a copper electrode.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Kiyonori Furukawa 1 Horiyamashita, Hadano City, Kanagawa Hitachi Ltd. Kanagawa Plant (72) Inventor Ritsuji Toba 1 Horiyamashita, Hadano City, Kanagawa Hitachi, Ltd. Kanagawa Inside the factory (72) Inventor Takeshi Shimazaki 1 Horiyamashita, Hadano City, Kanagawa Prefecture Hitachi, Ltd. Kanagawa Factory

Claims (1)

[Claims] 1. A compound selected from the group represented by the following general formula: BH ₃ .NHRR ′ (in the formula, R and R ′ represent any of H, CH ₃ and CH ₂ CH ₃ ). A treatment liquid for improving the acid resistance of a copper oxide surface, which contains at least one compound and is substantially free of copper ions.