JP2006026665A - Laser boring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform narrow pitch penetration work with high quality, as regards a laser boring method. <P>SOLUTION: In laser boring work in which a hole 16 larger than a laser beam diameter is bored by rotating the laser beam 20 along the outer periphery of the hole, the boring is suspended for a predetermined period after the rotation of the laser beam 20 for a predetermined number of times and resumed for the predetermined number of times. This process is performed at least once. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a laser drilling method in which a hole larger than a laser beam diameter is formed by turning a laser beam along the outer periphery of the hole.

  As shown in FIG. 1, a printed wiring board (PCB) 10 having a thickness of about 0.1 to 0.4 mm, on which both sides of the insulating resin 12 containing glass fibers 13 are coated with a copper foil 14 as a conductor, Conventionally, when a through hole having a diameter of about 200 to 300 μm is formed, a mechanical method for controlling a mechanical drill (called a mechanical drill) by numerical control is generally used.

  On the other hand, in recent years, with the increase in density and miniaturization of printed wiring boards, there is an increasing demand for through holes having a small diameter of 100 μm or less. However, if such a small-diameter through hole is opened with a mechanical drill, the drill bit will be damaged in about 2000 holes, and the running cost will be high with a short life. Therefore, a diameter of about 100 μm is the limit for mass production, and smaller diameter machining is required. A construction method is desired. In addition, positional accuracy is required as the diameter is reduced, but in the case of a drill bit, the required accuracy of about ± 50 μm and ± 10 μm or less cannot be satisfied.

  In particular, as shown in FIG. 2 (A), the flip chip (FC) 6 having no lead is directly attached to the PCB 10 via the solder balls 8 as shown in FIG. 2 (B). This is a problem in the case of PCBs for use. That is, in the PCB for FC, as shown in an enlarged view in FIG. 3, the diameter D of the through holes 16 is about 75 μm, and the interval P of the through holes 16 is about 150 μm.

  On the other hand, a method of making a through hole using a laser beam has also been developed. For example, in the case of performing a through process using a UV laser, (1) a laser beam having a beam diameter (spot diameter) corresponding to the hole diameter D of the through hole 16. For example, a so-called burst method that continuously irradiates at a fixed frequency of 10 kHz, and (2) while drawing a turning trajectory with a laser beam 20 having a beam diameter (spot diameter) smaller than the diameter of the through hole 16 as shown in FIG. There is a so-called trepanning method (see Patent Documents 1 and 2) for processing a desired hole diameter D. In the figure, 22 is a processing lens made of, for example, an fθ lens, 24 is a processing head, and 26 is a chuck plate for fixing the PCB 10.

JP 2000-263263 A Japanese Patent Laid-Open No. 2004-87879

  However, in both methods, when the pitch P of the small-diameter through-holes 16 is narrowed, there is a problem that the insulating resin 12A between the holes 16 is broken due to the thermal effect, causing collapse or chipping as shown in FIG. Was.

  The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to carry out narrow pitch penetration processing with high quality.

  The present invention provides a laser drilling method in which a laser beam is swung a predetermined number of times in a laser drilling method in which a laser beam is swung along the outer periphery of the hole to thereby drill a hole larger than the laser beam diameter. The above-mentioned problem is solved by performing the step of turning again a predetermined number of times at least once.

  According to the present invention, the step of pausing the hole for a predetermined time after the laser beam is rotated a predetermined number of times is repeated a plurality of times.

  In the present invention, a pulse laser having a wavelength of 400 nm or less is used as the laser beam.

  According to the present invention, it is possible to alleviate the thermal effect on the insulating resin and to carry out narrow pitch penetration processing with high quality.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

In order to form the through hole, it is necessary to drill a copper foil layer (conductive layer). In order to directly process the copper foil 14 with the laser beam 20, a harmonic solid-state laser (UV laser) having a high absorption rate and a wavelength of 400 nm or less (for example, 355 nm) is suitable. A third harmonic solid-state laser is desirable, but a fourth harmonic or a fifth harmonic may be used. In order to protect the quality of the through-holes 16, it is necessary to reduce the bulge and scattering of the surface copper foil and increase the aperture ratio. As a result of the experiment, a through hole 16 having a hole diameter D = 75 μm is formed in the hole pitch P with respect to the PCB 10 having the thickness of the surface copper foil 14 of 9 μm, the thickness of the insulating resin 12 of 0.3 mm, and the thickness of the back surface copper foil 14 of 9 μm. = 150 μm, the beam diameter (spot diameter) is 50 μm or less in order to avoid thermal effects, and the pulse energy is 30 J / cm in energy density on the processed surface in order to improve the workability of the copper foil and glass material. It turned out that it is desirable to set it as ² or more. When the energy is low, the tip of the glass fiber 13 in the insulating resin 12 protrudes into the through hole 16 as illustrated in FIG.

  In order to realize the above energy density, when the spot diameter of the laser beam 20 is reduced to, for example, 30 μm and the through hole 16 having an outer diameter of 75 μm is formed, for example, trepanning is performed on the turning trajectory so that the outer periphery becomes 75 μm.

  More specifically, as shown in FIG. 7, when the laser beam is turned once (or even two turns) with respect to a certain hole A, another hole B is processed for a certain time (for example, 0.2 to 1 second). After drilling, the hole A is turned once again (two turns are also possible) and processed. As shown in FIG. 8, by repeating this method a predetermined number of times, the thermal effect on the insulating resin 12 can be alleviated, and narrow pitch penetration processing can be performed with good quality. In the case of a PCB having a thickness of 0.3 mm, it is preferable to repeat about 10 times to penetrate one hole.

  Here, as the laser beam having a wavelength in the ultraviolet (UV) region, the fourth or fifth harmonic of the Nd: YAG laser can be used in addition to the third harmonic of the Nd: YAG laser. A YLF laser or a YVO4 laser may be used instead of the Nd: YAG laser. Further, a fundamental wave of a KrF excimer laser or a XeCl excimer laser may be used.

  In the embodiment, the copper foil is processed. However, the processing target is not limited to this, and other metal foils such as an aluminum foil and a gold foil can be processed in the same manner. The PCB to be processed is not limited to FC.

Sectional drawing showing the configuration of the printed wiring board to be processed (A) Bottom view of flip chip and (B) Cross-sectional view showing a state attached to the substrate Similarly, an enlarged plan view of the main part of a flip chip substrate (A) sectional view and (B) plan view showing trepanning method Sectional drawing of the printed wiring board which shows the problem which this invention should solve Cross-sectional view of a printed wiring board showing other problems The time chart which shows the processing method of the embodiment of the present invention Cross-sectional view of a printed wiring board showing the processing state

Explanation of symbols

10 ... Printed wiring board (PCB)
DESCRIPTION OF SYMBOLS 12 ... Insulating resin 14 ... Copper foil 16 ... Through-hole 20 ... Laser beam

Claims (3)

In the laser drilling method of making a hole larger than the laser beam diameter by swirling the laser beam along the outer periphery of the hole,
A laser drilling method characterized in that, when the laser beam is swung a predetermined number of times, the processing of the hole is paused for a predetermined time, and the step of swirling the predetermined number of times is performed at least once.   2. The laser drilling method according to claim 1, wherein, when the laser beam is rotated a predetermined number of times, the step of pausing the hole for a predetermined time is repeated a plurality of times.   The laser drilling method according to claim 1 or 2, wherein a pulse laser having a wavelength of 400 nm or less is used as the laser beam.

Images