JP2872453B2 - Drilling method of printed circuit board by laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the drilling of a printed circuit board by a laser for forming a blind hole for forming a conductive layer for electrically connecting an outer layer copper foil of a multilayer printed circuit board and an underlying copper foil. It relates to a processing method.

[0002]

2. Description of the Related Art A printed circuit board is formed, for example, on a surface of an insulating material obtained by impregnating and curing an epoxy resin into a net-like woven fiber bundle in which 40 to 60 glass fibers each having a diameter of several micrometers are bundled. It is composed by attaching copper foil. As shown in FIG. 4, the multilayer printed circuit board is formed by bonding the above-mentioned printed circuit boards to several sub-layers such that the copper foil 1 and the insulating material 2 are alternately located.

In such a multilayer printed circuit board, when electrically connecting the outer layer copper foil 1 and the inner layer copper foil 1, conventionally, as shown in FIG. A hole penetrating the copper foil 1 of the inner layer to be connected was formed, and the conductive layer 3 by copper plating was formed in this hole. However, when the hole is drilled in this way, the contact between the copper foil 1 of the inner layer and the conductive layer 3 becomes
Since there is only the inner peripheral surface of the hole of the inner layer copper foil 1, the contact area is small and the reliability of the electrical connection is lacking.

In order to eliminate such a problem, as shown in FIG. 6, it is desired to form a blind hole leaving an inner copper foil 1 and to form a conductive layer 3 in the blind hole. As a method of forming such a blind hole, it has been proposed to perform a drilling process by using a carbon dioxide laser and a laser beam. In this drilling method, as shown in FIG. 6, a window hole 4 is previously formed in an outer copper foil 1, and a laser beam 5 is irradiated through the window hole 4 as shown in FIG. The glass fiber and the epoxy resin constituting the material 2 are removed to expose the inner layer copper foil 1.

[0005]

However, when a drilling process using a carbon dioxide gas laser is performed, the laser beam 5 applied to the printed circuit board is reflected by the copper foil 1, so that the inner layer copper foil 1 is processed. However, when the irradiation amount of the laser beam 5 increases, the copper foil 1 is heated, so that the inner copper foil 1
The epoxy resin below melts or evaporates, and the copper foil 1 of the inner layer rises from the insulating material 2 thereunder, or the laser beam 5 reflected from the copper foil 1 of the inner layer as shown in FIG.
As a result, the insulating material 2 is eroded, making it difficult to form a conductive layer, and lowering the reliability of electrical connection. When the irradiation amount of the laser beam 5 is reduced, the epoxy resin remains on the inner copper foil 1 and, as shown in FIG.
Or the contact area of the
The reliability of the electrical connection is reduced.

In view of the above circumstances, an object of the present invention is to provide a method for boring a printed circuit board with a laser for forming a blind hole capable of forming a good conductive layer.

[0007]

In order to achieve the above object, in the present invention, a processing laser pulse having a relatively long oscillation time and a cleaning laser pulse having a relatively short oscillation time are set. After processing a hole reaching the copper foil below the opening with a processing laser pulse, a laser pulse for cleaning is irradiated into the hole.

[0008]

A laser beam for processing is first radiated to a window hole formed on a printed circuit board to form a hole reaching the copper foil below the opening, and a cleaning hole is formed in the hole. The laser pulse is applied to remove the epoxy resin remaining inside the hole.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will now be described with reference to FIGS.
It will be described based on. In the figure, 1 is a copper foil. 2 is an insulating material. The copper foil 1 and the insulating material 2 are alternately laminated to form a printed board. Reference numeral 4 denotes a window hole formed so as to penetrate the outer layer copper foil 1. 5a is a laser pulse for processing. 5b
Is a laser pulse for cleaning. Reference numeral 6 denotes a hole for forming a conductive layer.

First, as shown in FIG. 1, a window hole 4 penetrating the outer copper foil 1 of a printed circuit board is formed by a drill (not shown). Next, as shown in FIG.
Irradiates the laser pulse 5a to the printed circuit board through
The hole 6 is formed by removing the insulating material 2 between the outer layer copper foil 1 and the inner layer copper foil 1. Finally, the epoxy resin remaining on the inner layer copper foil 1 is removed by irradiating a laser pulse 5b. Since the epoxy resin does not remain on the bottom surface of the hole 6 thus formed, that is, on the inner layer foil 1, the conductive layer formed in a subsequent step and the inner layer foil 1 can be securely connected. You can get a connection.

In the above embodiment, the diameter of the hole 4 is 0, 1
mm, when the thickness of the insulating material between the outer copper foil 1 and the inner copper foil 1 is 0, 3 mm, the laser pulse 5a is supplied with a pulse width of 0,
45-0, 55 (ms), output energy 100-1
50 (mJ), laser pulse 5b, pulse width 0.2
0 to 3 (ms), output energy 15 to 25 (m
J), and using air as an assist gas, 20 L / m
In the process, the laser pulses 5a and 5b were irradiated by one pulse at a time, and as shown in FIG. 3, there was no residual resin on the inner layer copper foil 1 and the insulating material 2 could be eroded. No good holes could be formed.

The window hole 4 in the above embodiment is not limited to drilling, but may be formed by etching or the like.

Although the above embodiment has been described with reference to a multilayer printed circuit board, a double-sided printed circuit board can also be processed in the same manner as in the above embodiment by using an inner-layer copper foil as a reverse-sided foil.

[0014]

As described above, according to the present invention, after a hole reaching a copper foil under an opening is machined by a machining laser pulse, a laser beam for cleaning is irradiated into the hole. Since the blind holes are formed, it is possible to form a good hole without residual resin on the inner layer copper foil and without eroding the insulating material.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a printed circuit board in a state before processing according to the present invention.

FIG. 2 is a side cross-sectional view of a printed circuit board showing a state of drilling processing according to the present invention.

FIG. 3 is a side sectional view of a printed circuit board showing a state of a cleaning process according to the present invention.

FIG. 4 is a side sectional view of a multilayer printed circuit board.

FIG. 5 is a side sectional view of a conventional printed circuit board on which a conductive layer is formed.

FIG. 6 is a side sectional view of a printed circuit board on which a desired conductive layer is formed.

FIG. 7 is a side sectional view of a printed circuit board showing a state before laser processing in the related art.

FIG. 8 is a side sectional view of the printed circuit board showing a laser processing state.

FIG. 9 is a side cross-sectional view of a printed circuit board showing a hole shape processed by excessive laser irradiation.

FIG. 10 is a side sectional view of a printed circuit board showing a hole shape processed due to insufficient laser irradiation.

[Explanation of symbols]

1 same foil, 2 insulating materials, 4 window holes, 5a, 5b
Laser pulse.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H05K 3/00

Claims (1)

(57) [Claims] 1. A printed circuit board from which a copper foil in an opening of a hole has been removed in advance by irradiating a laser beam to form a blind hole reaching the copper foil below the opening. In the drilling method, a laser pulse for processing with a relatively long oscillation time and a laser pulse for cleaning with a relatively short oscillation time are set, and the laser pulse for processing reaches the copper foil below the opening. A method for forming a hole in a printed circuit board by using a laser, comprising forming a blind hole by irradiating a laser pulse for cleaning into the hole after processing the hole.