JP4522322B2 - Laser processing method - Google Patents

Description

  The present invention relates to a laser processing method for determining a rotation angle of a pair of mirrors for deflecting an optical axis of a laser beam based on an XY coordinate value of a target position and processing holes in a first layer and a second layer of a workpiece. It is about.

  In a laser processing apparatus for drilling a printed circuit board, which is an example of a laser apparatus having a function of scanning a laser beam, a laser using a carbon dioxide laser having a wavelength of 9 μm to 10.6 μm or a UV laser having a wavelength of 355 nm or 266 nm is used as the laser. Is applied to the printed circuit board in a pulsed manner to form holes for connecting the conductor layers of the circuit board.

Hereinafter, a conventional laser processing apparatus for drilling a printed circuit board will be described.
FIG. 3 is a configuration diagram of the laser processing apparatus.
The outer shape of the laser beam 2 emitted from the laser oscillator 8 is shaped by the aperture 9, reflected by the galvanometer mirrors 6 and 7, incident on the fθ lens 1, condensed by the fθ lens 1, and collected on the XY processing table 4 A hole is processed in the printed circuit board 3 arranged in the above. The laser beam 2 can be moved in the Y direction on the printed circuit board 3 by rotating the galvanometer mirror 6, and the laser beam 2 can be moved in the X direction on the printed circuit board 3 by rotating the galvanometer mirror 7. .

  The size of the processing region 11 (galvano scanning region) determined by the galvanometer mirrors 6 and 7 and the fθ lens 1 is about 50 mm × 50 mm. When the processing of the hole in one processing region 11 ′ is completed, the XY table 4 is moved and the next processing region 11 ′ is positioned with respect to the fθ lens 1. Thereafter, the above operation is repeated until the processing of the entire printed circuit board 3 is completed.

  The control device 13 controls the galvanometer mirrors 6 and 7, the laser oscillator 8, and the CCD camera 12.

  For example, the first layer and the third layer of the printed circuit board in which the first layer (surface layer) is a copper foil, the second layer under the first layer is an insulator, and the third layer under the second layer is a copper foil. Are electrically connected, the first layer and the third layer are electrically connected by forming a hole reaching the third layer from the first layer and plating the hole. When the second layer is processed with a laser beam having an intensity capable of processing holes in the first layer, the holes formed in the second layer are formed in a beer barrel shape, and the plating quality is deteriorated. Therefore, the second layer is processed by reducing the intensity of the laser beam (Patent Document 1).

Next, the function of the fθ lens 1 will be described.
FIG. 4 is a function explanatory diagram illustrating the function of the fθ lens 1.
In the figure, F1 is a front focal point (deflection point), and F2 is a rear focal point, both of which are on the central axis O of the fθ lens 1. F is the focal length of the fθ lens 1. As indicated by a solid line in the figure, the optical axis of the light passing through the front focal point F1 and incident on the central axis O at an angle θ (that is, light incident on the fθ lens 1 at an incident angle θ) has an optical axis of From the center axis O of the plane H perpendicular to the center axis O at the rear focal point F2 in parallel with the center axis O and emitted from the fθ lens 1 L = fθ (1)
An image J0 of the aperture 9 is formed on a surface K which is condensed at a position M of L represented by

  Therefore, when the surface of the printed circuit board 3 is aligned with the surface K, a hole having a desired diameter can be formed in the printed circuit board 3. Moreover, since the axis line of the hole processed into the printed circuit board 3 becomes perpendicular | vertical with respect to the surface of the printed circuit board 3, the hole excellent in quality can be processed. In general, the size of the image J0 is several tenths of the diameter of the aperture 9, and the distance g is about 0.1 to 0.3 mm.

  On the other hand, as indicated by a dotted line in FIG. 8, a laser beam that does not pass through the front focal point F1 but has an angle θ with respect to the central axis O of the optical axis is also condensed at the position M, and an image J1 of the aperture 9 is formed on the surface K. Kyuzo. However, since the optical axis is inclined by the angle ε with respect to the central axis O, the position of the image J1 is deviated from the image J0. The image shift caused by the angle ε is called a telecentric error. Due to the telecentric error, the optical axis of the incident light when the incident light intersects the central axis O on the front side of the front focal point F1 (the side far from the fθ lens 1) approaches the central axis O below the surface H. On the other hand, when the incident light intersects the central axis O on the rear side of the front focal point F1 (side closer to the fθ lens 1), the optical axis of the incident light is separated from the central axis O below the surface H.

  Processing for forming a desired image on the surface of the processing portion is hereinafter referred to as focus processing.

  As is clear from the above description, it is ideal to match the reflecting surfaces of the galvanometer mirrors 6 and 7 with the front focal point F1 of the fθ lens 1. However, the reflecting surfaces of the two mirrors cannot be arranged at the same position. Therefore, normally, the galvanometer mirror 6 and the galvanometer mirror 7 are arranged before and after the front focal point F1, and the reflecting surfaces of the galvano mirror 6 and the galvano mirror 7 are arranged as close as possible to the front focal point F1, and the axis of the hole to be processed Is perpendicular to the printed circuit board. The magnitude of the telecentric error can be obtained by calculation if the distance between the galvanometer mirrors 6 and 7 and the fθ lens 1 is determined.

However, the mounting position of the galvanometer mirror 6 and the galvanometer mirror 7 varies depending on the ambient temperature. Therefore, prior to processing or at certain time intervals, the coordinates are set on the acrylic plate 10 shown in FIG. 3 (for example, 5 mm pitch), the hole is processed, and the coordinate value of the center of the processed hole is measured by the CCD camera 12. Deviations in the XY directions with respect to the target value are obtained, and the obtained deviations are stored as correction values. At the time of machining, the correction value stored in the XY coordinate value of the machining position specified by the machining program is added to obtain the XY coordinate value of the target position, and the angles of the galvanometer mirrors 6 and 7 are based on the coordinate value of the target position Is stipulated. The operation for obtaining the correction value is hereinafter referred to as “correction value acquisition operation”.
JP-A-3-27855

  In the case of laser processing, the emission position of the laser beam output from the laser oscillator changes only by changing the output of the laser oscillator or changing the frequency of the laser beam. For this reason, it is not a good idea to change the output of the laser oscillator when processing the second layer.

  Since the laser beam focused on the surface H expands as the distance from the surface H increases, the intensity per unit area of the laser beam can be reduced by moving the printed circuit board relatively away from the fθ lens. However, the irradiation position is shifted due to a telecentric error. Although the position of the optical axis of the laser beam can be measured on both the surface K and the surface away from each other and the respective correction values can be stored, the measurement takes time and the processing efficiency cannot be improved.

  An object of the present invention is in the case of laser processing (hereinafter referred to as “defocus processing”) in which the energy intensity per unit area of the laser beam is changed by changing the distance between the printed circuit board and the fθ lens. The present invention also provides a laser processing method capable of efficiently processing a hole having excellent quality.

  According to the present invention, the deviation of the actual irradiation position from the designed irradiation position is obtained in advance as a correction value, and the correction value is added to the XY coordinate value of the center of the hole designated by the machining program to obtain the target position XY. A coordinate value is determined, a rotation angle of a pair of mirrors is determined based on an XY coordinate value of a determined target position, and a laser beam whose position is determined by the pair of mirrors is condensed by an fθ lens, and a plurality of materials are collected. In a laser processing method for processing a hole reaching the third layer through the second layer under the first layer from the first surface of the workpiece on which the different layers are laminated, a desired shape is obtained on the surface of the workpiece After forming a hole in the first layer and forming a hole in the first layer, the distance between the fθ lens and the workpiece surface is increased by a predetermined distance, and based on the XY coordinate value of the target position where the first layer is processed. The target position when processing the second layer Defining a Y coordinate value, characterized by machining a hole in the second layer based on the XY coordinate value determined.

  Since it is possible to position the optical axis of the laser beam at the approximate center of the hole to be processed without actually measuring the deviation of the optical axis during the defocus processing, it is possible to efficiently process a hole with excellent quality.

  First, the principle of the present invention will be described in the case of the galvanometer mirror 6 that determines the X coordinate value.

  FIG. 1 is a principle explanatory diagram for explaining the principle of the present invention. Components having the same or the same functions as those in FIG. The thickness of the fθ lens 1 is 0, and the laser beam shows only the optical axis. The distance between the reflecting surface of the galvanometer mirror 6 and the front focal point F1 of the fθ lens 1 is dx, and the surface of the printed circuit board 3 is positioned on the surface K.

  Assuming that the X coordinate of the processing position specified by the processing program is Lx0, the optical axis of the designed laser beam passes through the front focal point F1 and the point M as indicated by the alternate long and short dash line x11, and the point on the surface K An aperture image is formed on Lx0 (hereinafter simply referred to as “image formation”). Further, the actual laser beam reflected by the galvanometer mirror 6 passes through the point M and forms an image at the point Lx1 where the X coordinate value on the plane K is Lx1, as indicated by the alternate long and short dash line x12.

If the distance of the point Lx1 from the point Lx0 is a, the correction value a for the X coordinate value Lx0 is obtained by the correction value acquisition operation. At the time of processing, Lx2 (where Lx2≈Lx0 + a) is determined as a target coordinate, and the galvanometer mirror 6 is
α = Lx2 / f (2)
Is positioned at an angle α represented by

  When the rotation angle of the galvanometer mirror 6 is the angle α, the optical axis of the designed laser beam passes through the front focal point F1 and the point M1 as shown by the dotted line x21 and forms an image at the point Lx2 on the surface K. Further, the optical axis of the actual laser beam reflected by the galvanometer mirror 6 passes through the point M1 and forms an image at the point Lx0 on the plane K as indicated by a dotted line x22.

  Next, in order to process the second layer, the surface of the printed circuit board 3 is positioned on the surface Q below the surface K by z. Then, the optical axis x22 of the actual laser beam reflected by the galvanometer mirror 6 enters the point Px1 on the surface Q.

Here, when the angle with respect to the central axis O of the optical axis x22 emitted from the fθ lens 1 is β, the coordinate value Px1 of the angle β and the point Px1 is
tan β = dx · tan α / f (3)
Px1 = Lx2- (z + g) · tanβ (4)
It is represented by

In order to perform processing with excellent quality, the optical axis of the actual laser beam reflected by the galvanometer mirror 6 must be incident on the point Px0 whose coordinates on the plane Q are Lx0. That is, the coordinate value Lx3 of the target position is expressed as Lx3 = Lx2 + (z + g) · tan β (5)
It must be a value represented by.

  Here, since the angle α is ± 0 to 10 degrees, when tan α is replaced with α, Equation 3 can be transformed into Equation 6.

tan β = dx · α / f (6)
Substituting Equation 6 into Equation 5 and ignoring g sufficiently smaller than z,
Lx3 = Lx2 + z · dx · α / f (7)
Is obtained.

Substituting Equation 2 into Equation 7,
Lx3 = Lx2 + z · dx · (Lx2 / f) / f
= Lx2 (1 + z · dx / f ² ) (8)
Is obtained.

  In Expression 8, dx and f are values determined in advance by the apparatus, and z is a predetermined value. Therefore, the X coordinate value Lx3 of the target position when processing the second layer can be determined from the X coordinate value Lx2 of the target position when processing the first layer.

  As shown in the figure, the optical axis x31 of the designed laser beam passes through the front focal point F1 and the point M3, and the optical axis x32 of the actual laser beam reflected by the galvanometer mirror 6 passes through the point M3 and passes through the surface Q. An image is formed at a point Px0 where the upper X coordinate value is Lx0.

Also, the Y coordinate can be determined in the same manner as the procedure for obtaining the X coordinate value. That is, if the distance between the reflecting surface of the galvano mirror 7 and the front focal point F1 of the fθ lens 1 is dy, and the Y coordinate value of the target position when processing the first layer is Ly2, the target when processing the second layer The Y coordinate value Ly3 of the position is
Ly3 = Ly2 (1-z · dy / f ² ) (9)
Equation 9 can be used.

  In the above, the signs of dx, dy, α, θ, Lx, Ly are determined as follows.

  That is, with reference to the front focal point F1, dx on the side far from the fθ lens 1 is plus, dy on the side near the fθ lens 1 is minus, and α and θ are descending to the right with respect to the central axis 0. Is positive when incident on the left, and negative when incident on the left-hand side. When the center axis 0 is set at the center (origin) of the machining area, Lx is positive in the right direction, negative in the left direction, Ly is positive in the upward direction, and negative in the downward direction.

Next, the operation of the present invention will be described.
Prior to processing, correction value acquisition work is performed. Next, the laser beam is positioned at the corrected coordinate values (Lx2, Ly2) instead of the coordinate values (Lx0, Ly0) specified by the machining program, and a hole is machined in the first layer. When all the processing of the first layer is completed, the distance between the printed circuit board 3 and the fθ lens 1 is increased by z, and Lx2 and Ly2 and Expressions 8 and 9 are used instead of the coordinate values (Lx0, Ly0) specified by the processing program. The laser beam is positioned at the coordinate values (Lx3, Ly3) obtained using, and a hole is processed in the second layer.

  As described above, according to the present invention, since the processing of the correction information for both the focus processing and the defocus processing is completed by measuring the amount of displacement of the processing hole position under the focus condition, the work efficiency can be improved.

  FIG. 2 is a diagram for explaining the effect of the present invention. The target when the second layer is processed using Lx2 and Ly2 and the processing is performed using Lx3 and Ly3 when z is 3.5 mm. It is a value obtained by actually measuring the displacement with respect to the position. The processing area is 50 mm × 50 mm, and the processing pitch is 10 mm.

  As is apparent from the figure, the amount of deviation in the case of processing the second layer according to the present invention, that is, with the coordinate value of the target position as (Lx3, Ly3) is in the range of −8 μm to +7 μm. On the other hand, when the second layer is the position where the first layer is processed, that is, when the coordinate value of the target position is (Lx2, Ly2), the deviation amount is in the range of −56 μm to +84 μm. Yes. Therefore, when processing a hole having a small diameter, for example, 50 μm, if the energy density of the laser beam for processing the second layer is ¼ (the diameter is twice) that for processing the first layer, the laser beam is desired. The hole cannot be machined because it is out of the machining position.

It is a principle explanatory drawing for demonstrating the principle of this invention. It is a figure explaining the effect of this invention. It is a block diagram of a laser processing apparatus. FIG. 2 is a function explanatory diagram for explaining functions of an fθ lens 1.

Explanation of symbols

1 fθ lens 3 Printed circuit board

Claims (1)

A deviation of the actual irradiation position from the designed irradiation position is obtained in advance as a correction value, and the XY coordinate value of the target position is determined by adding the correction value to the XY coordinate value of the center of the hole designated by the machining program. The rotation angle of the pair of mirrors is determined based on the XY coordinate value of the determined target position, and the laser beam whose position is determined by the pair of mirrors is condensed by the fθ lens, and a plurality of layers made of different materials are formed. In the laser processing method for processing a hole that penetrates the second layer under the first layer from the surface first layer of the stacked workpieces and reaches the third layer,
After forming a desired shape on the workpiece surface and machining a hole in the first layer, the distance between the fθ lens and the workpiece surface is increased by a predetermined distance to process the first layer. A laser which defines an XY coordinate value of a target position when processing the second layer based on an XY coordinate value of a target position, and processes a hole in the second layer based on the determined XY coordinate value Processing method.

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