JPH03175695A - Manufacture of through hole printed wiring board - Google Patents

Abstract

PURPOSE:To realize the advancement of wiring density and the improvement of performance by etching the copper foil of a printed wiring board so as to form a circuit pattern, and then performing electroless nickel plating and electroless gold plating, and then electrolessly plating its whole face, and electrically plating only the through hole and the land part selectively. CONSTITUTION:A copper foil 2 is stuck to a base material 1, and a through hole 3 is bored, and an etching resist 6 is made at the part required as a circuit, and the copper foil 2 and the etching resist 6 at the unnecessary part are removed by etching, and electroless platings of nickel and gold are applied onto the parts to become circuits so as to form electroless nickel and electroless gold plating layers 8, and then electroless copper plating is applied to the whole face of the board so as to form an electroless plating layer 5. Next, plating resists 10 are made at the parts excluding the through hole 3, requiring through hole plating, and the land part 30, and then electric copper plating is applied to form an electric copper plating layer 9. Lastly, after the plating resist 10 is separated, the electroless copper plating layer 5 is removed.

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to a method for manufacturing a through-hole printed wiring board.

<Prior Art> FIGS. 2(a) to 2(d) show schematic cross-sectional views over time of a panel plating method that has been conventionally used.

As shown in (a), a copper foil 2 is bonded to a base material 1, and then through holes 3 are bored.

The thickness of this copper foil 2 is usually 18 μm, and a thinner copper foil of 9 μm or 5 μm is used, or a copper foil made thinner by etching the entire copper-clad base material is used. The through hole 3 is formed by drilling or punching.

Then, as shown in (b), throughhole 3 and copper M2
Electroless copper plating and electrolytic copper plating are performed to form electroless steel plating and electrolytic copper plating layer 4, and as shown in FIG. When unnecessary copper is removed by (
As shown in d), a circuit 7 is formed.

<Problems to be Solved by the Invention> With the development of the tC chip mounting method, the circuit pitch has already exceeded the 100 μm line, which is said to be capable of stable industrial production.

In conventional manufacturing methods, the thickness of the through-hole copper plating layer of 15 to 25 μm is added to the thickness of the copper foil bonded to the base material, so if the etching process is excessive during pattern formation, fine etching may occur. If the circuit becomes thin and breaks, or if the etching process described above is insufficient, copper will not be sufficiently etched away in areas where the distance between the circuits 5 is narrow, resulting in a touch.

In order to prevent the occurrence of touching, which is a problem in pattern formation, the circuit spacing needs to be approximately twice or more the total thickness of the copper foil and its plating layer. However, if the thickness of the copper plating layer is reduced, it is not possible to ensure conduction reliability of the through-holes due to the thermal stress during soldering.

As a means of solving such problems, conventionally, a base material has been used in which a copper foil of 9 μm or 5 μm, which is thinner than usual, is bonded to the base material.

This copper foil is laminated with aluminum foil to prevent wrinkles. However, this copper foil is expensive and requires a step to remove the aluminum foil, which increases the number of manufacturing steps. Another method is to etch a generally used base material to which a copper foil of 18 μm thick is attached to a thickness of about 9 μm before forming the pattern, but in this case, the substrate It is difficult to etch the entire surface uniformly and to control it to a predetermined thickness. The present invention solves these problems.

<Means for solving the problem> A method for manufacturing a through-hole printed wiring board is a printed wiring board in which copper foil is bonded to a base material to form through-holes. rl F
After shaping the circuit pattern by etching fi and electroless nickel plating and electroless gold plating on the circuit pattern, electroless plating is applied to the entire surface of the printed wiring board, and then only the through holes and their lands are plated. It is characterized by selectively electroplating and removing the electroless plating layer.

<Function> In the manufacturing method of the present invention, since only the copper foil is etched, it is easy to form a fine circuit. Furthermore, by performing electroless nickel plating and electroless gold plating on the fine circuit, the plating layer becomes a protective film. Furthermore, by selectively plating only the through-holes and their lands, the plating layer can have a desired thickness that allows sufficient conduction in the through-holes.

<Example> FIGS. 1(a) to 1(h) are examples of the present invention, and show schematic cross-sectional views of the manufacturing process thereof.

As shown in (a), a copper foil 2 is bonded to a base material 1, and then through holes 3 are bored.

The thickness of this copper foil 2 is 18 μm, which is commonly used.

Next, as shown in FIG. 3B, an etching resist 6 is formed in the areas necessary for the circuit.

Next, as shown in (C), unnecessary portions of the copper foil 2 and etching resist 6 are removed by etching to form a portion that will become a circuit.

Next, as shown in (d), after performing pretreatment such as catalyst treatment required for the next step, electroless plating of nickel and gold is performed on the part that will become the circuit, and electroless nickel and gold are plated. A gold plating layer 8 is formed.

Next, as shown in (e), after pre-treatment such as catalyst treatment required for the next step, electroless copper plating is performed on the entire surface of the substrate to form an electroless plating layer 5.

Next, as shown in (f), the electroless copper plating layer 5
At the top, a coating resist 10 is formed on the portions excluding the through-holes 3 that require through-hole plating and their land portions 30.

Next, as shown in (g), electrolytic copper plating is performed to form an electrolytic copper plating layer 9 within the through hole 3 and its land portion 30 to a predetermined thickness. In this case, solder plating may be performed if necessary.

Finally, as shown in (h), the plating resist 10
After peeling off, the entire surface is further subjected to quick etching to remove the electroless copper plating layer 5 adhering to areas other than the circuit pattern 11, thereby obtaining the circuit pattern 11.

In circuit formation, if it is necessary to provide a partially thick circuit, such as a bump, for direct bonding of an IC, by not applying the plating resist 10 to a predetermined portion in the above embodiment, the through hole 3 and its land portion 30 can be formed. The circuit can be formed at the same time as plating.

The above embodiments are used for through-hole boards with a circuit pitch of 1100II or less, but especially with a circuit pitch of 25 to 40
Even in the case of μm, the circuit pattern can be formed by using copper foil with a thickness of 5 μm or 9 μm and following the same steps as in the example. Furthermore, the above embodiments can be applied not only to single-sided and double-sided substrates but also to multilayer substrates.

<Effects of the Invention> As explained above, according to the manufacturing method of the present invention,
It becomes easy to form fine circuits with a circuit pitch of 100 μm or less. In addition, since a protective film for the microcircuit is formed in that process, there is no influence on the microcircuit in subsequent steps. Furthermore, since the electrolytic copper plating on the through-hole portion can ensure a predetermined thickness, its conduction reliability is increased.

Therefore, the wiring density and its performance are further improved.

[Brief explanation of drawings]

FIGS. 1(a) to (h) are schematic cross-sectional views of an embodiment of the method of the present invention, and FIGS. 2(a) to (d) are schematic cross-sectional views of a conventional example shown over time. 1... Base substrate 2... Copper foil 3... Through hole 5... Electroless copper plating layer 6... Etching resist 8... Electroless nickel and electroless gold plating layer 9... Electricity Copper plating layer 10...Plating resist 11...Circuit pattern 30...Through hole land portion Fig. 1 Fig. 1

Claims (1)

[Claims] In a printed wiring board formed by bonding copper foil to a base material and forming through holes, a circuit pattern is formed by etching the copper foil of the printed wiring board, and the circuit pattern is coated with electroless nickel plating and non-electrolytic nickel plating. A through-hole printed wiring board characterized in that after performing electrolytic gold plating, the entire surface of the printed wiring board is electrolessly plated, and further, only the through holes and their lands are selectively electroplated, and the electroless plating layer is removed. manufacturing method.