JPH02266592A - How to form through holes - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for forming through-holes in a printed wiring board using both the formation of through-holes using an energy beam and finishing processing using plasma treatment.

[Prior Art] Conventionally, through-holes in printed wiring boards are formed by forming the through-holes in the substrate for forming the printed wiring board by machining using a drill or the like, and then coating the inner walls of the formed through-holes with a conductive material. It has been done by doing.

[Problems to be Solved by the Invention] However, in the conventional method of forming a through hole by machining, the following problems arose when forming a through hole with a smaller diameter.

1) Small diameter drills generally do not have sufficient blade durability, their strength decreases as the number of drills increases, their lifespan is short, and they are expensive.

2) In order to extend the life of the drill, reducing the feed speed of the drill will increase the machining time.

3) It is difficult to achieve perpendicularity and positional accuracy of the through hole.

4) As shown in FIGS. 2(a) and (b), the unevenness of the inner wall of the through hole formed by the drill is large compared to the hole diameter, making it difficult to uniformly coat the inner wall of the through hole with the conductor material. In many cases, sufficient adhesion of the conductive material to the inner wall of the through-hole cannot be obtained, and the reliability of the through-hole against various stresses is often compromised.

An object of the present invention is to provide a through-hole forming method that can efficiently form highly reliable through-holes even when forming through-holes with minute diameters.

[Means for Solving Problem B] The through-hole forming method of the present invention includes a process of forming a through-hole in a substrate made of a composite material using an energy beam, and finishing the inside of the formed through-hole by plasma treatment. and a step of forming a through hole by coating the finished inner wall of the through hole with a conductive material.

Since the method of the present invention utilizes the formation of through holes by thermal processing using an energy beam, it is possible to form through holes with good straightness and positional accuracy even when forming through holes with minute diameters. Finishing using a chemical reaction called treatment can easily provide the conditions necessary for uniform and good coating of the conductive material on the inner wall of the through hole, so if the method of the present invention is used, it can be achieved with excellent positional accuracy and shape accuracy. , it is possible to form highly reliable through holes.

Moreover, since the through holes are not formed by machining using a drill or the like, the various problems described above when using machining can be avoided.

An example of the method of the present invention will be described below with reference to the drawings.

In the method of the present invention, thermal processing using an energy beam is used to create holes in the substrate.

The energy beam used for drilling may be appropriately selected depending on the material of the substrate made of composite material. For example,
Laser beams, electron beams, ion beams, etc. can be used.

The energy beam irradiation conditions may be set to such a value that the desired hole drilling can be performed.

The inner wall of the through hole formed by the energy beam has
Normally, unevenness is easily formed.

This is thought to be because the substrate is made of a composite material made of different materials, and the states of these materials change differently when irradiated with the energy beam.

For example, when a hole is drilled using the energy beam 3 in a substrate having a layer 2 made of a composite material formed by impregnating and curing glass fiber with resin as shown in FIG. 1(a), the hole shown in FIG. 1(b) is formed. As shown, a convex portion mainly containing glass is formed.

Therefore, plasma processing is next performed to smooth out such irregularities.

The plasma treatment for smoothing the unevenness is performed by selecting operating conditions that can selectively remove the unevenness. For example, when removing a protrusion mainly containing glass as shown in Fig. 1(b), fluorine ion plasma etching is used to select the protrusion as shown in Fig. 1(c). Target removal can be performed.

The plasma treatment conditions for selectively removing the convex portions are as follows:
It may be selected as appropriate depending on the material forming the convex portion.

In the present invention, plasma treatment for cleaning the inside of the through hole may be added to the plasma treatment for smoothing the unevenness described above.

Specifically, for example, when a hole is made using an energy beam in a layer containing resin as shown in FIG. 1(a), the 17th
As shown in J4 (b), black carbide 4 is generated from the resin, and by removing this black carbide by the 02 ashes treatment using 02 plasma, the inside of the through hole can be purified.

This 0□ Ashing purification treatment is performed before the above-mentioned plasma treatment for smoothing unevenness.

That is, unless the carbide is first removed by the 02 plasma ashing process, the smoothing reaction by the plasma will be hindered by the coated carbide and will not be carried out effectively.

This purification process may be performed additionally depending on the state inside the through hole formed by the energy beam, and the operating conditions may also be set depending on the type of black carbide scum etc. to be removed.

By performing the following two plasma treatments, a through hole with a smooth inner wall can be obtained.

Next, as shown in FIG. 1(d), for example, the inner wall of the through hole is coated with a conductive material by electroless plating, electroplating, or the like to form a coating layer 7 to obtain a through hole. can.

When coating with the conductive material, the inner wall of the through hole is a smooth surface that has been purified by the plasma treatment, so that the conductive material can be coated uniformly and the formed coating layer has good adhesion. .

[Example] Example 1 A double-sided copper-clad glass epoxy substrate (manufactured by Toshiba Chemical Corporation, TLG-W-551, 0, 66m) having the configuration shown in FIG.
+r+t), a carbon dioxide laser beam with a wavelength of 10.8 μm, an average output of 30 W, a pulse oscillation frequency of 10 Hz, a spot diameter of 0.1 mo+φ, and an irradiation time of 1.2 seconds are applied to the desired position, and a diameter of 0. ．． A through hole of Imm was obtained.

Next, the formed through-hole was subjected to O2 ashing treatment by a conventional method (at a low temperature of 150° C. for 70 minutes) to remove black carbide remaining on the inner wall of the through-hole.

Furthermore, treatment with F-plasma using NF and gas (pressure 10-'' Torr, 400 W, 150° C., 60 minutes) was performed.

After the F-plasma treatment, the inside of the through hole was cut along a plane passing through the center of the hole, cleaned, and the cross section was observed using an optical microscope. It was confirmed that the inside wall of the through hole was sufficiently purified and smoothed. Ta.

Next, a copper coating layer (layer thickness 20
gmt) was formed on the inner wall of the through hole to obtain a through hole.

Table 1 shows the results of evaluating the obtained through-holes by conducting a current check, a thermal shock test (X-sensitivity test) by oil dipping, and inspecting the positional deviation on the upper and lower surfaces of the substrate.

The energization check is carried out by applying current to the through hole and measuring its resistance value.If it is 50 mΩ or more, it is considered "good", and "good" is determined per 100 through holes.
Table 1 shows the number of through holes that have been certified as such.

Further, in the thermal shock reliability test, after repeating immersion in oil at 260° C. for 5 seconds 10 times, a current check was performed. Table 1 shows the number of through holes that could no longer conduct electricity per 50 through holes.

Further, the positional accuracy was measured by measuring relative coordinate points on the back and front sides with the reference hole as the origin, and the deviation from the theoretical value was within ±10 scales.

Example 2 YAG with a wavelength of 1.06 μm instead of carbon dioxide laser
Using a laser, the irradiation conditions were: average output 1OW, frequency 5, 2, spot diameter 0.08 mmφ, irradiation time 0.5.
Through-holes were formed in the same manner as in Example 1 except that the time was changed to 2 seconds.

Table 1 shows the results of the evaluation of the obtained through-hole in the same manner as in Example 1.

Comparative Example A through hole was formed in the double-sided copper-clad glass epoxy substrate used in Example 1 using a drilling drill with a diameter of 0.1 ma+ at a feed rate of 2.5 m/min, and the resulting through hole was A conductive material layer was coated in the same manner as in Example 1 to obtain a through hole.

Table 1 shows the results of the evaluation of the obtained through-hole in the same manner as in Example 1.

Table 1 [Effects of the Invention] According to the method of the present invention, since drilling by an energy beam is not used for drilling holes in the substrate, it is possible to drill holes with minute diameters efficiently and easily. In addition, through-holes can be formed without causing problems associated with drilling by machining with a drill or the like.

Furthermore, in the method of the present invention, finishing processing using plasma treatment is combined with drilling using an energy beam, so that the inner wall of the through-hole is coated with a conductive material with good uniformity and adhesion. formed in the state,
Highly reliable through holes can be obtained.

[Brief explanation of drawings]

FIGS. 1(a) to 1(d) are partial sectional views of a substrate showing the main steps of an example of the method of the present invention. Figure 42 (a) and (
b) is a partial sectional view of a substrate showing the main steps of a conventional method using machining. 1: Conductive material layer (copper layer) 2: Composite material layer 3: Energy beam 4: Black carbide 5: Plasma 6: Drill 7: Conductive material coating layer

Claims (1)

[Claims] 1) A process of forming a through hole in a substrate made of a composite material using an energy beam, a process of finishing the inside of the formed through hole by plasma treatment, and a process of forming a conductive material on the inner wall of the finished through hole. 1. A method for forming a through hole, the method comprising the step of forming a through hole by coating a transparent material. 2) The method for forming a through hole according to claim 1, wherein the plasma treatment includes cleaning the inner wall of the through hole and smoothing unevenness. 3) A method for forming through-holes in which the composite material is formed by impregnating glass fiber with resin and curing it.