JPH0146590B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel copper colloid for activating non-conductive materials, particularly plastics, to prepare them for metallization processes by conventional electroless plating and electroplating. be.

Today, many applications of this type of metal plating can be found in the commercial field, where the metal plating is applied to plastic, glass, or similar non-conductive substrates, either as a continuous coating or as a patterned plating. Processes such as discontinuous plating are desired. Among the applications of such metal-plated articles are automobile parts, various building supplies or tools, toys, buttons, wiring boards, etc., where the coating is generally (with some exceptions) applied to one or more surfaces. It is formed substantially continuously over the above surface.

In all cases, the non-conductive substrate must be activated during the process, otherwise electroless plating or electroplating cannot be applied to such substrates. After this activation, electroless plating is performed, which serves as the current supply for later electroplating.

Prior art activation methods practiced in the commercial world generally utilize precious metals, particularly palladium. For example, one of the earliest methods of activating such substrates was a two-step operation. That is, the substrate is first immersed in a stannous chloride solution and then immersed in an acidic palladium chloride solution. Later, single-step methods were also commercially adopted. Specifically, there is a method using a colloidal dispersion of palladium and tin chlorides as disclosed in US Pat. Nos. 3,011,920 and 3,672,923.

The noble metal, such as palladium, in the activating solution acts as an activator, catalyst or seed for the subsequent electroless plating bath step on the non-conductive substrate. After soaking in the electroless plating bath for several minutes,
The treated articles are covered with a very thin film of the metal in the bath.
This is then cleaned and plated with the same metal or another metal using a known electroplating process.

The above-mentioned U.S. Pat. No. 3,011,920 to Shipley discloses:
By combining colloidal dispersions of various metals with reducing agents,
Activation for subsequent electroplating of the insulating substrate is achieved. As an example, a noble metal or a hydrous oxide of a noble metal is used as the colloidal particles, and tin chloride or tannic acid is used as the reducing agent. No. 2 of the above US patent specification
The column cites the fact that other precious metals can also be used for similar purposes.

U.S. Patent No. Granted to Kenny
Nos. 3,657,002, 3,783,005 and 3,950,570 disclose hydrous oxides of many different metals, including precious and non-precious metals, for treating or coating insulating substrates for subsequent electroplating. A method is described for colloids.

U.S. Pat. Nos. 3,993,799 and 4,136,216 to Feldstein also treat non-conductive plastics with hydrous oxide colloids or metal colloids of non-precious metals,
A method is disclosed in which the hydrous oxides on the plastic are subsequently reduced to provide at least some activation for subsequent electroless plating.

U.S. Pat. No. 3,958,048 to Donovan describes a method of surface activation of non-conductive substrates for electroless plating by treating the substrate surface with an aqueous composition containing catalytically active insoluble particles. This aqueous composition is obtained by reacting a non-noble metal with a water-soluble hydride in the presence of a water-soluble organic suspending agent. For effective operation, the suspension must have a pH of less than 5 or in the range of 7.7 to 9.5. An example of a non-precious metal is copper salt.
The hydride includes dimethylamine borane (DMAB) and gelatin is one example of many possible organic suspending agents. In order to maintain catalytic activity, Donovian's composition requires a pH
In addition to the inherent drawback of having to maintain the above range of values, Donovan's compositions suffer from insufficient stability for practical commercial use. For example, the compositions of the above examples have been found to degrade over a period of several hours to several days, rendering suspension commercially impractical.

The present invention relates to a novel stable copper colloid for activating a non-conductive substrate to enable electroless plating.The particle size of the colloid is approximately
10 to 100 millimicrons (mμ), a zeator potential of approximately +3 to +13 millivolts (mV), and a sufficient number of particles for activation. The colloids of the present invention are stable and have the ability to activate non-conductive substrates over virtually all PH ranges, particularly effectively over a PH range of approximately 2 to 8. The ability of this colloid to be used over a wide range of PHs gives it further characteristics and allows continuous operation even under commercial conditions where PH changes occur during operation.

The content of the invention will be described in more detail below.

The colloids of the invention are obtained by using stabilizers or suspending agents which give the metallic copper particles and/or copper oxide particles a zeta potential of between approximately +3 and +13 mV, preferably between approximately +4 and +10 mV. . The suspending agent should have a zeta potential such that when combined with colloidal copper particles, it produces a zeta potential on the particles of approximately +3 to +13 mV. If the copper particles have a negative zeta potential, it may be necessary to use a suspending agent with a strong positive zeta potential, eg +18 mV, to impart the desired zeta potential to the colloidal particles.

An example of a suspending agent that produces the desired zeta potential is certain gelatins. As a typical example, gelatin with sufficient purity can be used, but
In particular, acid-washed type A gelatin, which has been acid-washed during production to remove impurities, can be used more preferably.

The type of gelatin, its preparation, its purification method and its purity also play an important role in imparting the desired zeta potential to the colloidal copper particles. The suspending agent or gelatin must be free of interfering ions such as excess sodium ions. These ions act as a hindrance to imparting the desired zeta potential to the particles of the colloid. It has the desired zeta potential, and the colloidal particles have approximately +3 to +
Other suspending agents can be used in place of gelatin, as long as they provide a zeta potential of 13 mV and do not strongly dissociate or liberate from the copper particles. Those skilled in the art can measure the zeta potential and, using the teachings of this application, can select the correct suspension to produce the desired zeta potential in the particles.

According to the prior art, non-noble metal colloids can be made in a number of ways, all of which have various drawbacks that preclude their commercial use. For the use of colloids in practical applications, especially for copper-coated wiring boards, stability, particle size and zeta potential are essential properties. The colloidal particles must be deposited on the non-conductive surface in sufficient quantity and with sufficient uniformity. This allows for a sufficiently uniform precipitation to permit subsequent electroless plating and further step electroplating. The colloidal particles must also be strongly adhered after electroless plating and electroplating so that delamination does not occur during processing and use of the final product. In other words, it should not be deposited in spots on the colloid substrate. Uneven, patchy deposits are caused by a variety of factors. For example, there is an insufficient number of particles in a colloid, an excessively stable colloid, agglomerated colloid particles, etc. This occurs when the colloid is unstable, or when the number of particles is excessive and the particle size is excessively small. There are various other factors as well. For example, the zeator potential is approximately +2mV
Colloids containing the following particles are not stable and do not adhere properly to or activate non-conductive surfaces such as glass.

The colloids of the present invention not only have a low positive zeta potential, but also have a small particle size suitable for activation, especially in plastics and plastic parts of circuit boards, and especially in the case of glass-filled plastics.

The closest prior art to this application appears to be Donovan US Pat. No. 3,958,048. Although Donovan mentions gelatin, he does not recognize its importance in creating a stable colloid that can activate non-conductive substrates at pH values above 5 and above 7.7. In fact, he also states that the colloids created by Donovian's invention do not work in this pH range. Gelatin in the broader sense of the term does not teach anything about the special stabilizers of the present application, ie, the special zeta potential stabilizers that can impart the desired zeta potential to the colloidal particles.

An example of the present invention will be given below and will be explained in more detail.

Before explaining the embodiments of the present invention, for the purpose of comparing the differences in effects with the present invention, the prior art shown in Examples 1 and 2 of Donovan U.S. Pat. No. 3,958,048 will be described. A copper colloidal suspension for activation was prepared and the pH value was varied to measure the zeta potential of the colloidal particles.

Comparative Example 1 Composition of Copper Colloidal Suspension for Activation Cupric glutarate...0.80g/ DAXAD11 (product name of Grace Co., Ltd.)...6.67g/ Sodium salt of alkylene naphthalene sulfonic acid polymer Sodium borohydride... 0.62g/Temperature...98〓 The zeta potential of the colloidal particles in the above suspension is
Although approximately -20 mV at PH6, the velocity of the colloidal particles varied during the experiment, ie, the velocity of some colloidal particles of some species was significantly slower than the average. At PH4, the zeator potential was approximately -25 mV. Using this suspension,
Surface activation treatment of non-conductive substrate (soaking time approx. 4
As a result, the copper colloid was sparsely deposited on the surface and not sufficiently deposited.

Comparative Example 2 Composition of copper colloidal suspension for activation Cupric acetate...0.7g/ DAXAD11...6.67g/ Dextrin...3.3g/ Sodium borohydride...0.1g/ Temperature...130〓 Above The zeta potential of colloidal particles in suspension is
Approximately +1mV at PH2, approximately -1mV at PH4,
It was about -2 mV at PH6. When a non-conductive substrate was surface activated using this suspension (dipping time: about 4 minutes), the adhesion of copper colloid to the surface became sparse and a uniform copper colloid film could not be formed. Ta.

Example 1 Composition of copper colloidal suspension for activation Cupric glutarate......0.80g/Acid-washed type A gelatin...6.67g/ (gelatin subjected to acid-washing treatment during production) Sodium borohydride... 0.62g/Temperature...98〓 As a result of measuring the zeta potential of the colloidal particles while changing the pH value of the suspension, it was found to be about +9 mV at PH4 and about +13 mV at PH2.
A non-conductive substrate was immersed in this suspension for about 4 minutes to activate its surface, resulting in an activated copper colloid film that adhered uniformly and firmly to the surface of the non-conductive substrate. I was able to form it.

Example 2 Composition of copper colloidal suspension for activation Cupric acetate...0.7g/Acid-washed type A gelatin...6.67g/Sodium borohydride...0.1g/Temperature...130〓 Above suspension As a result of measuring the zeta potential of colloidal particles while changing the pH value of the liquid, it was approximately +3 mV at PH6 and approximately +4 mV at PH2.
And at PH5, the zeator potential is approximately +
However, when dextrin was removed and only pickled type A gelatin was used, the zeta potential was about +13 mV. When a non-conductive substrate was immersed in this suspension for about 4 minutes to activate its surface, an activated copper colloid film was formed uniformly and firmly on the surface of the non-conductive substrate. I was able to form it.

The stability of the copper colloid for activation of the present invention can be maintained over the entire pH range of 2 to 8, but the stability of the copper colloid for activation and the corrosiveness of plating equipment and equipment may be affected. Considering these factors, the PH value is preferably in the range of 4 to 8, more preferably 5.5 to 7.5, and the most preferable range is neutral, that is, the PH value is in the vicinity of 7, for example, in the range of 6.5 to 7.5. It is desirable to adjust to In addition, the activation copper colloid for electroless plating of the present invention can be added with a suspending agent etc. to raise the zeta potential to +3 to +
In order to adjust the voltage to a range of 13 mV and uniformly and firmly adhere a sufficient amount of activating copper colloid to the surface of a non-conductive substrate for electroless plating, it is necessary to use colloidal particles of metallic copper or copper oxide. the size of 10~
It needs to be in the 100 millimicron range. When the size of the colloidal particles is outside the above range,
The adhesion layer of the activating copper colloid that is attached to the surface of the non-conductive base material becomes uneven and its adhesion strength becomes weak, resulting in peeling of the electroless plating and electroplating formed on it. This is not preferable because it tends to occur.

The copper colloid of the present invention is unique and novel;
It is particularly suitable for activating copper-coated wiring boards employing glass-filled plastics. The objects to be treated in this case are at least three different materials: copper coatings, plastics and glass fillings. The activated colloid must adhere well to all three of these or it will delaminate during subsequent processing and use in subsequent electroless plating and electroplating. Regarding the copper part,
It is desirable to remove excess colloidal particles using an aqueous stripper, such as a neutral hydrated hydrazine. Activation of such a wiring board uses a novel colloid of the present application, that is, a colloid whose particle size is approximately 10 to 100 mμ and whose particle zeta potential is approximately +3 to +13 mV, preferably between 4 and 10 mV. This is achieved by doing. One of the novelties of the colloids of the invention lies in the fact that the particles are not only small but also have a low positive zeta potential. In addition, the colloid is stable, i.e., the particle size will grow and precipitate, and effective activation may occur with a small amount of residual particles, or the zeta potential may change and it may not be sufficiently deposited on the substrate. Never. This stability of the colloids of the present application is
Advantageously maintained over a wide range of pH. Stability over only a narrow PH range is impractical in commercial production since the PH inevitably changes during operation.

Claims (1)

[Claims] 1. A stable aqueous colloid for activating the surface of a non-conductive substrate to which electroless plating is applied, the colloid having a colloid particle size in the range of 10 to 100 millimicrons. containing at least one of metallic copper and copper oxide and a suspending agent, and adjusting the zeta potential of the colloid to a range of +3 to +13 millivolts;
The colloid has a pH value ranging from 5.5 to 7.5, and a sufficient amount of the colloid particles is attached to activate the surface of the base material and perform electroless plating. Activating colloidal copper solution for metal plating insulating surfaces. 2 Claim 1 in which the suspending agent is gelatin
Copper colloid solution for activation as described in Section 1. 3. The copper colloidal solution for activation according to claim 1 or 2, wherein the suspending agent is gelatin produced by acid washing. 4. The copper colloidal solution for activation according to any one of claims 1 to 3, wherein the zeator potential is adjusted to a range of +4 to +10 millivolts. 5. The copper colloidal solution for activation according to any one of claims 1 to 4, which has a pH value of 6.5 to 7.5.