JPS6337515B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing a printed wiring board that can easily obtain a fine pattern.

(Prior art) In recent years, the line width and line spacing of printed wiring boards have become thinner and thinner as LSIs become more highly integrated. Manufacturing methods for printed wiring boards include the subtract method in which a pattern is formed by etching a copper-clad laminate, the additive method in which circuits are formed by plating in the required areas, and copper-clad laminate using 5-9 μm copper foil. There is a semi-additive method in which the necessary parts are plated using a plate as a base, and then the thin copper foil on the base is quickly quenched.The semi-additive method is particularly suitable for fine patterns.

(Problems to be Solved by the Invention) In conventional manufacturing methods, for example, in the subtract method in which a pattern is formed by etching a copper-clad laminate, a line width of 100 μm is the processing limit, and a line width smaller than this may cause wire breakage or Shoots are more likely to occur. This is caused by dents, scratches, etc. on the copper foil surface that occur during the manufacturing process of copper-clad laminates.

In addition, when forming a pattern with a line width and line spacing of 50 μm or less, if there are minute irregularities or undulations on the surface of the copper-clad laminate, when forming the required etching resist, the incidence of irradiation light on the resist may be affected. The angle is not constant, and therefore, for example, where the irradiation light is obliquely incident, the line width becomes wider, making it impossible to form a pattern with a constant line width, making it impossible to form a pattern with good line width accuracy.

In addition, copper foil is usually thick at 18 to 35 μm, so 100 μm
Etching a narrow width like the one shown below is extremely difficult. Etching will be easier if a copper foil of 5 to 9 μm is used, but since through-hole plating is added to the surface layer, aside from the inner layer circuit portion,
The overall copper thickness is 30 to 40 .mu.m, and there is no difference in the fact that etching with a line width or spacing of 100 .mu.m or less is difficult.

For these reasons, the additive method, in which circuits are formed by plating in the necessary areas, rather than the etching method, is suitable for forming fine patterns, but at present, the substrate surface has a large roughness, and it is difficult to place circuits in unnecessary places. There is a copper frizz phenomenon in which mottling precipitates, and it is not possible to form finer patterns than the subtract method.

Even in the semi-dative method, it is difficult to form a fine pattern of 80 μm or less because it is dominated by the defects and characteristics of the copper-clad laminate itself.

(Means for Solving the Problems) The present invention has been made in view of the above points, and after forming a required plating resist 2 on one surface of a copper foil 1, this surface is coated with a copper etching solution that is resistant to corrosion. A certain metal 3 is plated and copper 4 is further plated to form a circuit pattern 5 made of copper and a metal that is resistant to corrosion in a copper etching solution.The plating resist 2 is removed and the circuit pattern is The insulating material 12 is superimposed on the surface on which the copper foil 1 is formed and heated and pressurized, the required holes are drilled and the inner wall of the hole is copper plated 7, and the required etching resist is formed on the other surface of the copper foil 1.
It is characterized by etching.

That is, in order to overcome the limitations based on the characteristics and defects of the copper-clad laminate itself used in the prior art, the present invention uses copper foil as the base material for forming the circuit pattern 5. The copper foil used may be a copper foil peelably plated onto a stainless steel plate or the like, a copper foil that has already been peeled off, or a rolled copper foil. As shown in Figure 1, this copper foil 1
A required plating resist 2 is formed by laminating a photoresist on one side of the substrate, and then baking and developing the photoresist. Next, a metal 3 such as gold, nickel, or solder which is resistant to corrosion by a copper etching solution is plated on this surface by electroless plating or electroplating, and then copper plating 4 is further performed. After peeling off the plating resist 2, an adhesive treatment is performed on this surface.

Next, as shown in FIG. 2, the copper foil 1 having the circuit pattern 5 formed in this way is used as the surface layer, and the circuit pattern 5 is placed on the inside for interlayer positioning together with the inner layer circuit board 6. Laminate and glue. Furthermore, drilling and through-hole plating are performed. Next, the copper foil 1 is protected by tenting or soldering so that the inner wall of the hole and a desired portion of the copper foil 1 are left with pads and other surface patterns to be formed with the copper foil, and the copper foil 1 is etched.
When the copper foil 1 serving as the base is removed by etching, the circuit pattern 5 formed in advance is exposed in the form of being embedded in the substrate.

Figure 3 shows a cross section of the printed wiring board obtained in this way, with 7 having through-hole plating;
Reference numeral 8 denotes an inner layer circuit, 5 a preformed circuit pattern, the exposed surface of which is plated with a metal 3 that is resistant to corrosion by a copper etching solution, and 1 a copper foil that remains without being etched.

(Example) After polishing the surface of stainless steel (SUS430-BA) with Scotch Bright 7448, the entire surface was plated with copper sulfate to a thickness of 30 μm. Next, a photoresist (Riston T-1215) was laminated using a roll laminator. After applying a positive mask having patterns with line widths of 40 μm and 65 μm and irradiating it with ultraviolet rays, a developer was sprayed and developed. Next, apply gold plating to 1μm.
Copper sulfate plating was further performed to a thickness of 30 μm. After immersing in a resist stripping solution to strip the resist and performing black copper oxide treatment, the patterned copper foil was peeled off from the stainless steel plate. This copper foil is placed in a multilayer mold that can be positioned using positioning pins via an adhesive prepreg between the inner layer plate prepared in advance by an etching method, and
The mixture was heated at 170° C. for 2 hours at a pressure of 60 kg/cm ² . After drilling holes in the thus laminated substrates using an NC drill, through-hole plating was performed using electroless plating.

Next, photoresist (Riston T-1215) was laminated, baked and developed to form a pad around the hole. Subsequently, the copper on the surface was etched until the built-in gold plating was exposed to produce the desired multilayer printed wiring board. The obtained circuit patterns made of gold and copper had a line width of 40 .mu.m and a line width of 65 .mu.m, both of which had extremely uniform line widths, with no wire breaks or shorts observed.

(Effects of the Invention) As explained above, according to the method for manufacturing a printed wiring board of the present invention, the following advantages are achieved.

(1) Since the pattern is formed on a copper foil surface with a smooth surface, the angle of incidence of the irradiation light on the resist can be kept constant, and a fine pattern with a line width and a line interval of 100 μm or less can be obtained with high accuracy.

(2) Since fine patterns are formed in advance and then laminated, inspection can be performed before lamination, improving yield.

(3) A conductor is formed by plating between precisely formed resist images, and this conductor is further embedded in an insulating material, and its surface is completely protected by a metal that is resistant to corrosion by copper etching solution. Because of this, there is no side etching and the line width accuracy is extremely high.

(4) As shown in FIG. 4, a circuit 9 consisting only of an embedded conductor made of a corrosion-resistant metal 3 and copper 4;
A circuit 10 consisting only of the copper foil 1 remaining without being etched, or a circuit 11 consisting of both conductors can be arbitrarily formed. Therefore, circuits with different current capacities can be configured with the same line width.

(5) Since most of the circuits can be embedded in the insulating material, unevenness caused by the circuit parts can be reduced. Therefore, the solder resist can be applied uniformly, and good soldering can be achieved.

[Brief explanation of drawings]

1 to 4 are cross-sectional views for explaining the method of the present invention. Explanation of symbols, 1: Copper foil, 2: Plating resist,
3: Corrosion-resistant metal plating with copper etching solution, 4: Copper plating, 5: Circuit pattern, 7: Through-hole plating, 12: Prepreg (insulating material).

Claims (1)

[Claims] 1 After forming the required plating resist on one side of the copper foil, plate this surface with a metal that is resistant to corrosion in a copper etching solution, and then plate copper and apply a metal that is resistant to corrosion in a copper etching solution. A circuit pattern made of copper is formed, the plating resist is removed, an insulating material is overlaid on the surface on which the circuit pattern is formed, heated and pressurized, the required holes are drilled, and the inner walls of the holes are plated with copper. A method for manufacturing a printed wiring board, which comprises etching the copper foil after forming a required etching resist on the other side of the foil.