JPH0646672B2 - Circuit board manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a circuit board which is required to have a high density circuit and has high quality and excellent work efficiency.

[Conventional technology]

In general, there is known a method of obtaining a desired circuit pattern by performing resist printing / etching on a cladding plate obtained by bonding a Cu foil to a substrate when obtaining a printed circuit board, and laminating these in multiple layers as necessary. However, this so-called subtractive method requires many steps and a large amount of C
This is not suitable for forming a fine circuit having a width of 0.1 to 0.25 mm, as well as increasing the cost due to etching u.

On the other hand, a so-called additive method is becoming popular in which a Pd-catalyzed special substrate is used to chemically form Cu after resist treatment to form a desired pattern at once. This method has a simple process, and at the same time, has no problems such as side etching, which are observed in the conventional method, and is particularly advantageous for forming a fine circuit pattern.

[Problems to be solved by the invention]

In recent years, the demand for higher density and finer patterning of circuit boards has become stronger as electronic components become smaller and more dense and equipment and circuits have higher density and higher performance.

Although the additive method meets these requirements, it is pointed out that not only the cost increases due to the use of a special substrate, but also the electrical characteristics (insulating property). That is, in this method, a soldering process is required for mounting components, connecting to an external circuit, and the like, and manual soldering work is indispensable for repairing circuits, mounting special components, and the like. As a result, the solder erosion phenomenon of the Cu circuit occurs,
Cu dissolves and disappears in the solder, and in the extreme case, the substrate is exposed. In order to prevent such a phenomenon, it is apparently thick Cu (eg, 35 μ) that is excessive from the electrical characteristics.
Is chemically damaged. 20 to 30 for such a mating process
Not only does it take a long time and the cost is high, but as a result of the substrate being exposed to the plating solution for a long period of time, elution, absorption, swelling, etc. occur at the same time and the substrate is likely to deteriorate. Further, Cu which is abnormally deposited in a narrow circuit gap during the plating process easily causes a short defect, which is against the demand for circuit miniaturization.

Therefore, it is desired to directly form an efficient and high-density circuit on a cheaper ordinary substrate without requiring a special substrate that has been catalyzed in advance. Further, it is necessary that the circuit board is free from solder erosion, which is inevitably a problem, and that the circuit board has a strong adhesive force to withstand a long-term thermal mechanical stress. In particular, solder erosion is an important issue to be solved in surface mounting, which is ideal for high-density mounting of electronic components.

[Means for solving problems]

The present invention has been made in view of the above situation. That is, after printing a Cu resin paste on an arbitrary insulating substrate to form a desired circuit, NiB chemical plating, Cu
It is characterized in that a conductive circuit is formed by sequentially performing chemical plating.

In the present invention, the NiB chemical plating uses a borane-based reducing agent such as dimethylamine borane and sodium borohydride, and Ni ²⁺ such as NiSO ₄ , a complexing agent, a pH adjusting agent,
It is a plating bath containing a stabilizer and the like and is usually applied to a thickness of 1 to 5 μm. Cu plating is a plating bath usually containing formalin or the like as a reducing agent and a Cu ²⁺ salt such as CuSO ₄ or the like, a chelating agent such as EDTA, a pH adjusting agent, a CN ^- compound or a stabilizer such as an S compound, and the like. It is applied to a thickness of 5 to 15 μ. The Cu resin paste contains Cu or Cu alloy powder and a resin such as phenol, epoxy, polyimide, modified phenoxy, etc., as well as a solvent such as butyl carbinol, a viscosity modifier, a stabilizer, etc. The compounding ratio of the resin is 60 to 95% by weight of Cu or Cu alloy powder. After the paste is screen printed, 100
Cured at a temperature of ~ 250 ° C.

[Work]

In the present invention, the Cu resin paste has a sheet resistance of about 5 to 100 mΩ / □ and has a Ni content of about 5 to 100 mΩ / □.
It also exerts a catalytic action for B chemical plating. But Cu
When the ratio of Cu or Cu alloy powder in the resin paste is less than 60%, the above effect is poor, and when it exceeds 95%, the strength of the paste portion decreases, and neither is practical.

NiB is usually alloyed with B content of 0.1-10%,
It can be directly plated on Cu paste without the need for Pd catalyst.
Therefore, the NiB plating prevents the abnormal deposition of Cu induced by Pd which is easily adsorbed to the insulating portion when the substrate is catalyzed by a PdCl ₂ bath or the like. Further, NiB has excellent adhesion and mechanical strength, and is resistant to corrosion because it is resistant to oxidation, has excellent solderability described below, and does not cause solder erosion. But Ni
If the thickness of B plating is less than 1 μ, the above effect is poor.
It is desirable that the thickness be equal to or larger than μ, and practically 1 to 5 μ.

Since the NiB plating is used in combination, the thickness of the Cu plating can be determined mainly on the basis of the conductivity, and in practical use, it is preferably about 5 to 15 μm. In the method of the present invention, even if the thickness of the Cu plating is reduced, the insulating layer is not exposed due to solder erosion. The reason for this is that Ni, which has high heat resistance, has a dissolution rate of 1/10 in solder compared to Cu.
This is because it is low as below. Also, the plating work time can be shortened to less than half of the conventional one, but this is due to the difference in the plating speed, that is, 1 to 5 μ / hr for Cu and 5 to 1 for NiB.
This is due to the high speed of 5 μ / hr. Further, since the thickness of Cu plating is thin, the risk of abnormal Cu precipitation is reduced at an accelerating rate, and it becomes possible to form a highly reliable fine circuit.

One feature of the circuit board obtained by the method of the present invention is a component,
In particular, it is extremely excellent in wire bondability when directly mounting a semiconductor element. That is, in the substrate manufactured by the conventional additive method, since the rubber-like adhesive layer is placed under the Cu layer, the energy of the ultrasonic bond is absorbed and it is not effectively used for bonding. Therefore, it was necessary to make the Cu layer as thick as possible. On the other hand, what is obtained by the method of the present invention is
Since it has a hard Cu paste and NiB layer, even if the Cu layer is thin, ultrasonic energy applied through the bonding capillary is concentrated between the circuit surface and the bonding wire and is used efficiently, facilitating reliable bonding at high speed. Will be realized.

Although the present invention has been described with reference to the single-layer circuit board, it can be applied to the production of a double-sided circuit board or a multilayer circuit board in which these are laminated. In this case, C instead of through hole
Conductivity can be efficiently formed by filling the drill holes with u resin paste. Further, the second layer circuit can be formed in exactly the same manner after forming a through-stud with a Cu resin paste on the one-layer circuit and printing an insulating layer. Further, the method of the present invention can be applied to form a multi-layer on a circuit board manufactured by a conventional subtractive method.

〔Example〕

1) Example 1, Comparative Examples 1 to 5 One side of an Al plate (thickness: 1.5 mm) was insulated with a polyimide coating film (thickness: about 50 μm) to obtain a substrate. A circuit was screen-printed using a Cu resin paste prepared by mixing 80% by weight of spherical Cu powder having an average particle diameter of 9μ and 20% by weight of phenol resin with a small amount of butylcarbinol acetate. The minimum circuit width is 0.15 mm, the circuit interval is 0.2 mm, 210 ° C,
It was cured by heating for 15 minutes. This circuit board is 10% HC
After immersing in l for 10 minutes and washing the surface, it was immersed in a bath of Niclad 741 (Okuno Pharmaceutical Co., Ltd.) (65 ° C., pH 7.1).
Immerse for 5 minutes, and about 3.5μ thick NiB (B content about 0.9
%) I made a woodpecker. Next, it was immersed in an ELC-HS bath (manufactured by Uemura Kogyo Co., Ltd.) (65 ° C.) for 2 hours to make Cu plating having a thickness of about 8 μm. This is Example 1.

Comparative Example 1 In Example 1, Cu plating was performed without NiB plating.

Comparative Example 2 In Comparative Example 1, Cu plating was performed for 8 hours to obtain a Cu plating thickness of about 30 μ.

Comparative Example 3 In Example 1, a NiP plating bath was used instead of the NiB plating bath, but no Ni was deposited. Therefore,
It was dipped in 0.1 g of PdCl ₂ / water solution for 30 seconds, washed with water, and then dipped in a NiP plating bath and a Cu plating bath, and plated as in Example 1.

Comparative Example 4 In order to perform the following characteristic comparison, a commercially available subtractive method circuit board was used. The minimum circuit width of the board is 0.35 mm,
The circuit spacing was 0.40 mm and the Cu foil thickness was 35 μ.

Comparative Example 5 Similarly, a commercially available additive circuit board was used. The minimum circuit width of the substrate was 0.2 mm, the circuit interval was 0.25 mm, and the Cu plating thickness was 35 μ.

For each of the circuit boards thus obtained, (A) a stereoscopic microscope with a magnification of 100 was used to examine the presence or absence of abnormal precipitation of Cu on the inter-circuit insulating portion. (B) 23 to try to eat solder
The operation of immersing in a eutectic bath at 0 ° C. for 10 seconds was repeated 4 times, and then the wetted areas of the soldering surfaces were compared. (C) Al-1%
Wet bonding was performed using a Si wire (35 μφ), both free ends were further bonded to form a loop, and the tensile strength was measured. 20 loops were measured and the average strength was calculated. The results are summarized in Table-1.

From Table 1 above, it is clear that the product of Example 1 according to the present invention is a fine circuit without solder erosion and having a high bond strength. Comparative Examples 4 to 5 by the conventional method have a thick Cu of 35 μm.
Since the layer had a layer, the same results as in Example 1 were shown in solder erosion, but the bond strength was poor and the circuit remained coarse. Comparative Examples 1 to 3 are common to the example of the present invention in that a Cu resin paste is used, but since they lack the conditions of the present invention, they all have disadvantages.

2) Example 2 and Comparative Examples 6 to 7 As described above, the present invention utilizes the characteristics of NiB plating to produce C
High performance of u resin paste application circuit is realized.
In order to make this point clearer, in Example 1, N
Samples having iB plating thicknesses of 1.5 μ (Example 2), 0.5 μ (Comparative Example 6) and 0 μ (Comparative Example 7) (B) and (C)
Was measured. The results are shown in Table-2.

[Advantages of the Invention] The present invention is a novel method for producing a high-density fine printed circuit board of good performance, which will be required more and more industrially in the future in accordance with the development of electronics. It enables more efficient and economical manufacturing without requiring multi-stage and various processes such as. In addition, the obtained circuit board is a fine circuit board without solder erosion and is suitable for surface mounting, which is becoming the mainstream of electronic component mounting in the future, and the industrial significance of the present invention is extremely great.

Claims (3)

[Claims] 1. A Cu resin paste on an insulating substrate,
A method for manufacturing a circuit board, which comprises forming a desired circuit pattern, performing NiB chemical plating, and then performing Cu chemical plating to form a conductive circuit. 2. The method for producing a circuit board according to claim 1, wherein a Cu resin paste containing 60 to 95% by weight of Cu or Cu alloy powder is used as the Cu resin paste. 3. NiB chemical plating of at least 1 μm thick, Cu
The method for manufacturing a circuit board according to claim 1, wherein the chemical plating is applied to a thickness of at least 5 μm.