JPS6174791A - Method of forming through holes in base plate - Google Patents

Abstract

PURPOSE:To pierce many minute through-holes of good form in a short time and to improve its efficiency by removing copper layers on both sides of a part where holes are to be pierced by etching and then piercing by irradiating laser light. CONSTITUTION:Desired hole diameter 3a, 4b in copper foils 2a, 2b at positions to be pierced is removed by etching. An oxide film of copper is removed by immersing the surface of copper foils 2a, 2b in aqueous solution of hydrochloric acid. Laser light is irradiated using a CO2 gas laser light equipment on the part from where copper is removed by etching deviating the position of focus of the laser light from the base plate. By this way, through-holes can be pierced in the base plate surely in a short time.

Description

[Detailed description of the invention] [Field of application of the invention] The present F! A-C relates to a method for forming through holes in a copper-clad laminate used in a multilayer wiring board.

[Background of the invention]

Currently, through-holes in printed circuit boards are generally formed using a mechanical drilling method using a drill. With this method, it is difficult to make the through hole diameter less than φ[L2w1. On the other hand, as computers have recently become more sophisticated, higher wiring density has been required. To meet this requirement, it is essential to miniaturize the through holes of printed circuit boards.

For this reason, many attempts have been made to form fine holes.

In particular, micro-hole drilling using laser light is attracting attention. However, in the conventional method using laser light, the energy absorption efficiency is poor because the laser light is particularly reflected on the copper, and the through holes cannot be made unless a high-output device is used. In addition, even if a hole is formed, the shape is extremely rough, and the inside of the insulating layer of the board is hollow and large compared to the hole diameter of the copper foil, which is a disadvantage.
It was not intended for practical use.

Further, the pore diameter is limited to about φα15 m, and the pore diameter is not necessarily a constant size. Furthermore, the percentage of holes was not necessarily 100%, and there were often cases where no holes were formed.

Furthermore, in the case of ultra-high density multilayer substrates, 1100X10
It was necessary to drill tens of thousands of holes of φ [11 m+ or less] in the 0, which required an extremely long time with a drilling knife.

Note that, as a document related to drilling using laser light, for example, IBM Journal Op Research and Development (IBM, J.

Res, Develop, Vol. 26, No. 3, (1
, May 9132, pp. 306-317.

[Purpose of the invention]

The object of the present invention is to overcome the above-mentioned drawbacks and to provide a method for efficiently forming small holes of good shape.

[Summary of the invention]

To summarize the present invention, the present invention relates to a method for forming a through hole in a substrate, and the present invention relates to a method for forming a through hole in a substrate, in which a hole is formed by irradiating a laser beam on a double-sided steel-clad 9 substrate, in which copper layers are formed on both sides of the portion where the hole is to be formed. The method is characterized in that the copper layer is removed by etching in advance, and then a laser beam is irradiated to the portion where the copper layer has been removed to form a hole in the substrate.

In the present invention, in order to achieve the above object, the copper layers above and below the place where the through hole is to be drilled are etched in advance to the desired hole diameter, and if necessary, the copper surface on the side that is hit by the laser beam is removed. In order to give the surface a glossy surface that reflects most of the laser light that hits it, the team used a process to remove the oxide film on the copper surface, and then emitted a laser beam with enough energy to penetrate the substrate.

In addition, in the case of the example described later, the focal position of the laser beam was set at the bottom of the perforated substrate, but it does not necessarily have to be in this way, and the laser beam can be used as long as it has a spot with a large hole diameter. . Furthermore, since the laser light output varies depending on the type, thickness, etc. of the base material to be drilled, conditions suitable for this may be selected, and the conditions are not necessarily limited to those shown in the examples described later.

Furthermore, when a large number of holes are to be drilled, the holes may be drilled by scanning the etched copper holes with continuous laser light output.

For example, it would take 10 to 20 hours to drill a relatively good hole using the conventional method of directly irradiating a laser beam onto steel, but the method of the present invention only takes 20 to 30 minutes and is extremely efficient.

Note that the scope of the present invention includes irradiating one side with laser light and then irradiating laser light from the opposite side.

Furthermore, various types of laser beam irradiation devices are known, and are not necessarily limited to the CO and gas laser beam devices described in the embodiments below.

And, by using the method of the present invention, it became possible to make a through hole of φ(L 05 wn).

[Embodiments of the invention]

Hereinafter, the present invention will be explained in more detail with reference to Examples.
The invention is not limited to these examples.

In addition, FIG. 1 is a sectional view showing an embodiment of the method of the present invention, FIG. 2 is a sectional view of a through hole after being processed by the method of the present invention, and FIG. 5 is a sectional view of a through hole after being processed by the conventional method. It is a diagram. In each figure, 1 is an insulating layer, 2a and 2b are steel foil,
5a and 3b are etched portions of the copper foil, 4 is a laser beam, and 5 is a through hole.

Example 1 1 is an insulating layer made of glass cloth and idioide resin. The insulation layer thickness is approximately 100 μm. 2a.

Reference numeral 2b is a copper foil having a thickness of 35 μm, and holes 5a and 3b with desired diameters are etched in advance at the desired positions. In addition, the copper surfaces of 2a and 2b were immersed in a 10% aqueous hydrochloric acid solution to remove the copper oxide film, resulting in a glossy appearance.

Next, using a CO or gas laser beam device, the laser beam 4 was applied to the portion where the F copper was removed during etching, with the focal position of the laser beam being shifted by 9 points on the substrate. Laser light output rz1
oow was irradiated with 11 m8 of pulsed laser light five times.

Figure 2 shows the results of laser beam irradiation on the parts where the steel was etched away, and 5 is the page through hole.

Comparative Example 1 FIG. 5 shows the results of drilling in the case of direct laser beam irradiation using the conventional method. The base material is the same as that shown in Example 1 of the present invention, and the output 1-j of the CO, gas laser source device is
The pulsed light of loQ(lW′″c(LlrnB) was irradiated five times. Note that it was not possible to make a through hole in the substrate under the conditions below.

From the results shown in FIG. 3, it can be seen that in the conventional method, the diameter of the hole on the entrance side of the laser beam is larger than that on the exit side, and the inside of the insulating layer is uneven and has an extremely rough shape. Also, the copper foil around the holes is peeled up and uneven. On the other hand, as can be seen from the results shown in Figure 2 when holes were drilled using the method of the present invention, the through-holes in the insulating layer are almost straight, and the copper foil frames on the laser beam entrance and exit sides are turned over. First, it is possible to have holes of the same diameter.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to form a fine mz through hole with an extremely better shape than in the conventional method, which contributes to improved performance. Also,
It is possible to reliably drill many holes in a short time, and
Since a low-output laser beam device can be used, the efficiency is improved and the extremely remarkable effect of being economical can be achieved.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the method of the present invention, and FIG.
The figure shows a cross-sectional view of the through hole after processing by the method of the present invention, and a third
The figure is a sectional view of a through hole after processing using a conventional method. 1: Insulating layer, 2a and 2b: Copper foil, 3a and 5b: Etched portion of copper foil, 4: Laser light, 5: Through hole

Claims (2)

[Claims] 1. In the method of making holes by irradiating a double-sided copper-clad board with laser light, the copper layers on both sides of the part where the hole is to be made are removed by etching in advance, and then the part from which the copper layer has been removed is irradiated with laser light to make the hole in the board. 1. A method for forming a through-hole in a substrate, the method comprising: forming a through-hole in a substrate. 2. 2. The method of forming a through hole in a substrate according to claim 1, wherein before irradiating the copper surface with laser light, a process is performed to remove an oxide film on the copper surface so as to increase the reflectance of the laser light.