JP5839876B2 - Copper plate for laser processing, printed circuit board using the copper plate for laser processing, and laser processing method for copper plate - Google Patents

Description

  The present invention relates to a copper plate for laser processing whose both surfaces are roughened.

In recent years, lead-free solder has been used for joining printed circuit boards to terminals and the like in consideration of the environment. Lead-free solder is concerned about the problem of short circuit due to the occurrence of whiskers. Laser welding is an example of a joining technique that can avoid this problem. However, the copper plate used for the printed circuit board is used for the laser light having a fundamental wavelength of 10600 nm for a CO ₂ laser often used as an infrared laser for welding, a fundamental wavelength of 1064 nm for an Nd: YAG laser, and a fundamental wavelength of 1084 nm for a fiber laser. Since it has a reflectance of 90% or more, it is difficult to perform laser welding with an infrared laser that is often used in welding applications.

  On the other hand, in the electrolytic copper foil for printed wiring boards, the surface of the copper foil is blackened to enable drilling with a laser, the surface of the copper foil is roughened with a chemical solution, and the surface of the copper foil is iron. Various attempts have been made in the past to improve laser light absorptivity, such as forming a coating layer made of tin, nickel, cobalt, zinc, or the like (Patent Document 1).

Japanese Patent Application Laid-Open No. 2004-339531

  However, even if the electrolytic copper foil can improve the laser light absorptivity of the surface, it is very difficult to join terminals and the like by laser welding because the thickness is as thin as about 30 to 40 μm. In addition, since it is difficult to simultaneously treat both surfaces of an electrolytic copper foil in order to improve both the laser light absorption and the resin adhesion, a resin adhesion surface 13 is formed on one surface of the copper foil 12 as shown in FIG. After bonding with the resin 5, the surface 14 was subjected to a treatment for forming a coating layer 15 having good laser light absorption.

  The problem to be solved by the present invention is to provide a copper plate for laser processing that is suitable for laser welding and has good resin adhesion, and in particular, a copper plate for laser processing that can be manufactured by simultaneously processing both surfaces of a copper plate It is to provide.

  In order to solve the above-described problems, the copper plate for laser processing according to the present invention is formed with fine granular protrusions on both sides of the copper plate in order to improve the laser light absorption of one surface and improve the resin adhesion of the other surface. It is characterized by that.

  In the copper plate for laser processing of the present invention, it is desirable that the L value of the one surface is 50 or more and 75 or less. And it is desirable for the average particle diameter of the particle | grains which comprise the fine granular protrusion of said one surface to be 0.3 micrometer or more and 3 micrometers or less. Moreover, you may prescribe | regulate the average particle diameter of the said particle | grain as 0.1 micrometer or more and below the wavelength of the laser beam used for a process.

  In addition, the fine granular protrusions are formed by electrolysis that generates copper fine particles on both sides of the copper plate and plating treatment that fixes the copper fine particles on both sides of the copper plate after the electrolytic treatment. It is desirable to be formed by carrying out the process of 1 cycle or more.

  According to the present invention, it is possible to provide a copper plate for laser processing in which one surface is suitable for laser welding and the other surface has good resin adhesion.

  The copper plate for laser processing of the present invention has one cycle of electrolytic treatment for generating copper fine particles on both sides of the copper plate by electrolysis and plating treatment for fixing the copper fine particles on both sides of the copper plate after the electrolytic treatment, By carrying out these treatments for one cycle or more, it is possible to simultaneously produce both sides of the copper plate.

Sectional drawing which shows notionally the structure of the printed circuit board using the copper plate for laser processing of this invention The figure which shows the relation between the laser output and the irradiation time which can join the terminal and the copper plate The figure which shows the relationship between L value and the penetration depth of a copper plate by laser beam irradiation Electron micrograph showing surface state of conventional electrolytic copper foil Electron micrograph showing the surface state of the copper plate for laser processing (roughened copper plate) of the present invention Process drawing which illustrates the manufacturing method of the copper plate (roughened copper plate) for laser processing of this invention Process drawing which illustrates another manufacturing method of the copper plate for laser processing (roughened copper plate) of this invention Electron micrograph showing the cross-sectional structure of the laser processing copper plate (roughened copper plate) of the present invention Electron micrograph showing the cross-sectional structure of a comparative example of a roughened copper plate Electron micrograph showing the cross-sectional structure of another comparative example of a roughened copper plate Sectional drawing which shows the structure of the printed circuit board using the conventional electrolytic copper foil conceptually

Hereinafter, embodiments of the present invention will be described.
[Copper plate for laser processing]
FIG. 1 is a sectional view conceptually showing the structure of a printed circuit board using a laser processing copper plate of the present invention. This printed circuit board is obtained by bonding the copper plate 1 for laser processing of the present invention to the surface of a resin substrate 5. The copper plate 1 for laser processing is formed with fine granular protrusions 2a and 3a on both surfaces 2 and 3 of the copper plate 4 in order to improve the laser light absorption of one surface 2 and improve the resin adhesion of the other surface 3. Do it. Hereinafter, the one surface is referred to as a “laser light absorbing surface” and the other surface is referred to as a “resin bonding surface”. The thickness of the copper plate 4 is 70 μm to 200 μm.

  FIG. 2 shows the relationship between the laser output (fundamental wavelength) capable of joining the terminal and the copper plate and the irradiation time. The measurement results were as follows: a fiber laser with a fundamental wavelength of 1084 nm was used, irradiation times were set to 1 second, 0.5 seconds, and 0.24 seconds, a 640 μm square brass terminal and a 200 μm thick copper plate at each irradiation time. Is a result of measuring the unprocessed copper plate and the laser processing copper plate (roughened copper plate) of the present invention. The L value of the roughened copper plate used in this embodiment is 63. From this measurement result, the laser processing copper plate (roughened copper plate) of the present invention can be welded to the terminal and the copper plate with a laser output smaller by 20 to 30 W than the untreated copper plate, and the laser output can be reduced. Comparing the results of about 65 W, it can be seen that the irradiation time can be reduced to about half at the same laser output.

  FIG. 3 shows the relationship between the L value and the penetration depth of the copper plate by laser light irradiation. The measurement results were obtained by preparing nine sample copper plates with different L values, and laser-beaming the laser light having a fundamental wavelength of 1084 nm and an output of 100 W to each copper plate at a processing speed of 2 m / sec. It is the result of measuring the depth of the fusion | melting area | region in the cross section of an irradiation location. From this measurement result, it is understood that when the L value of the laser light absorption surface 2 is 50 or more and 75 or less, a penetration depth of 10 to 60 μm required for welding can be obtained. If the L value of the laser light absorption surface 2 is greater than 75, the laser absorption rate of the laser light absorption surface 2 is insufficient, and it is unsuitable for welding with a fiber laser. Further, when the L value of the laser light absorbing surface 2 is less than 50, there arises a problem that the particles are easily separated. The L value of the laser light absorbing surface 2 is more preferably 55 or more and 70 or less from the viewpoint of absorption of laser light and prevention of peeling of fine particles. Incidentally, the L value of the glossy copper plate is approximately 80.

In addition, it is desirable that the average particle diameter φ of the particles constituting the fine granular protrusions 2a of the laser light absorbing surface 2 is 0.3 μm or more and 3 μm or less. When the average particle diameter φ is 0.3 μm or more and 3 μm or less, a high laser as shown in the result of FIG. 2 although the L value of the laser light absorption surface 2 is a relatively bright value of 50 or more and 75 or less. Light absorption characteristics can be realized. This is because relatively large irregularities due to the fine granular protrusions 2a are formed on the laser light absorbing surface 2 and a relatively large number of gaps are formed between the particles constituting the fine granular protrusions 2a (see FIG. 8). It is thought that this is because the absorption of incident light is promoted by the unevenness due to 2a and the numerous gaps between the particles.
If the average particle diameter φ is 0.1 μm or more, the structure consisting of fine granular protrusions such as the roughened copper plate according to the present invention and a large number of gaps, the laser light absorption characteristics as fine particles as shown above are remarkably exhibited. High laser light absorption characteristics can be obtained (see FIGS. 5, 8, 9, and 10). In addition, when the average particle diameter φ is equal to or less than the wavelength of the laser beam used for processing (in the case of an infrared laser having a wavelength of about 1 μm, φ is 1 μm or less), the laser light absorption characteristics are most excellent. However, if the average particle diameter φ is 3 μm or less, good laser light absorption characteristics can be obtained not only for CO ₂ laser but also for laser light having a wavelength of about 1 μm.
In addition, as shown in FIGS. 8 to 10, there is a tendency that the space between the particles is filled with the plating material by increasing the plating current in order. In the state of FIG. 8, since the particles on the surface of the copper foil retain the original shape, good laser light absorption characteristics can be obtained for the above reason. As shown in FIGS. 9 and 10, when the space between the particles is filled with the plating material, the laser light absorption characteristic gradually decreases, but as shown here, the structure composed of fine granular protrusions and a large number of gaps is maintained. By doing so, the effects of the present invention are exhibited. On the other hand, in the case of FIG. 8, when the adhesion strength of the particles is reduced and the plating becomes weaker than in the cases of FIGS. As described above, the plating conditions are determined so as to achieve both laser light absorbability and particle adhesion.

[Method for producing copper plate for laser processing]
Next, the manufacturing method of the copper plate 1 for laser processing is demonstrated.
The copper plate 1 for laser processing of the present invention is one cycle of electrolytic treatment for generating copper fine particles on both surfaces of the copper plate 4 by electrolysis and plating treatment for fixing the copper fine particles on both surfaces of the copper plate 4 after the electrolytic treatment. As a result, the above process is performed for one cycle or more.

  FIG. 4 is an electron micrograph showing the surface state of a conventional electrolytic copper foil. FIG. 5 is an electron micrograph showing the surface state of a copper plate subjected to electrolytic treatment and plating treatment for one cycle or more. It can be seen that the latter has a smaller particle size of the copper fine particles than the former, and there are many irregularities and gaps between the particles due to the fine granular protrusions 2a.

  There are two methods illustrated in FIGS. 6 and 7 for manufacturing the copper plate 1 for laser processing while controlling the L value of the laser light absorption surface 2 and the resin bonding surface 3 by electrolytic treatment and plating treatment, respectively.

[First manufacturing method]
FIG. 6 shows a first manufacturing method of the laser processing copper plate 1. In FIG. 6, 6 is an electrolytic cell, 7 is an electrolytic copper plating solution accommodated in the electrolytic cell 6, 8A and 8B are a plurality of pairs (two pairs in the illustrated example) insoluble in the electrolytic copper plating solution 7. Electrodes (anode electrodes), 9A and 9B are a plurality of pairs (three pairs in the illustrated example) of copper electrodes (cathode electrodes) disposed opposite to each other in the electrolytic copper plating solution 7, and 4 is a copper plate whose surface is to be roughened. The insoluble electrodes 8A and 8B and the copper electrodes 9A and 9B are arranged in tandem with each other. The copper plate 4 is plated between the insoluble electrodes 8A and 8B while being held at the cathode, and is placed between the copper electrodes 9A and 9B while being held at the anode. Thus, electrolytic treatment is performed. As the plating solution 7, additives such as 40 to 250 g / l copper sulfate, 30 to 210 g / l sulfuric acid, 10 to 80 ppm hydrochloric acid, and a brightener are used.

The current density and current value in the plating process ((a), (c) and (e)) are constant. Moreover, the current density and current value in the electrolytic treatment process ((b) and (d)) are also constant. When the current density and current value in the plating process are 1.2 to 2.0 A / dm ² and 25 to 40 A, respectively, the current density and current value in the electrolytic process are 1.7 to 2.5 A / dm ² , respectively. 35 to 50 A is desirable. The time required for each process is 2.5 to 5 minutes.

First, as shown in (a), by placing the copper plate 4 between the insoluble electrodes (anode electrodes) 8A and 8B while keeping the copper plate 4 at the cathode, a plating treatment for relaxing the rolling stripes on the surface of the copper plate 4 is performed. Do. Next, (b), the copper electrode (cathode) 9A while maintaining the copper plate 4 to the anode, by placing between 9B, copper constituting the fine particle-like projections 2a on the surface of the copper plate 4 An electrolytic treatment for generating fine particles is performed. Thereafter, as shown in (c), the copper plate 4 is kept again as a cathode, and is disposed between the insoluble electrodes (anode electrodes) 8A and 8B to perform plating. This plating, copper particles formed on the surface of the copper plate 4 is fixed to the copper plate 4, the fine particle-like projections 2a on the surface of the copper plate 4 is formed. Thereafter, as shown in (d), the electrolytic treatment is performed by placing the copper plate 4 between the copper electrodes (cathode electrodes) 9A and 9B while keeping the copper plate 4 at the anode again. At this time, a resin baffle plate 10 is provided so as to hide the resin bonding surface 3 of the copper plate 4. Since the baffle plate 10 is provided on the resin bonding surface 3 side of the copper plate 4, the generation of copper fine particles on the resin bonding surface 3 is suppressed. As a result, more copper fine particles than the resin bonding surface 3 are generated on the laser light absorbing surface 2. Thereafter, as shown in (e), plating is performed by placing the copper plate 4 between the insoluble electrodes (anode electrodes) 8A and 8B while keeping the copper plate 4 at the cathode. Also at this time, the baffle plate 10 is provided so as to hide the resin bonding surface 3 of the copper plate 4. By providing the baffle plate 10 on the resin bonding surface 3 side of the copper plate 4, fixing of the copper fine particles on the resin bonding surface 3 is suppressed. As a result, more copper fine particles than the resin bonding surface 3 are fixed to the laser light absorbing surface 2.

  Through the series of processes described above, the copper plate 4 for laser processing having the laser light absorption surface 2 and the resin bonding surface 3 is manufactured by simultaneously processing both surfaces of the copper plate 4. The L value of the laser light absorbing surface 2 and the L value of the resin bonding surface 3 can be controlled by adjusting the current density and current value in the plating process, the current density and current value in the electrolytic process, and the time required for each process. It is.

[Second manufacturing method]
FIG. 7 shows a second manufacturing method of the laser processing copper plate 1. In the method of FIG. 7, the baffle plate 10 is not used. Instead, in the electrolytic treatment step (b), a copper electrode (cathode electrode) 9A is formed between the laser light absorbing surface 2 side and the resin bonding surface 3 side of the copper plate 4. , 9B, a difference in current value and current density is provided.

The current density and current value in the plating step (a) are the same on both sides 2 and 3. When the current density and the current value in the plating process are 1.2 to 2.0 A / dm ² and 25 to 40 A, respectively, between the electrode 9A on the laser light absorption surface 2 side and the copper plate 4 in the electrolytic process (b). The current density and the current value are 1.7 to 2.5 A / dm ² and 35 to 50 A, respectively. The current density and the current value between the electrode 9B on the resin bonding surface 3 side and the copper plate 4 are the laser light absorption surface 2. Smaller than the side. The time required for each step is 2.5 to 5 minutes.

By repeating the plating treatment step (a) and the electrolytic treatment step (b), the laser processing copper plate 1 is manufactured. At that time, the rolling stripe on the surface of the copper plate 4 is first relaxed by the plating step (a). Next, by electrolytic process step (b), to produce a copper fine particles constituting the fine particle-like projections 2a on the surface of the copper plate 4. Since the current value and the current density towards the laser light absorbing surface 2 side of the resin adhesive face 3 side is large, many generated laser light absorbing surface 2 than copper particulate resin bonding surface 3 constituting the fine particle-like projections 2a Is done. Thereafter, the copper fine particles on the surface of the copper plate 4 are fixed to the copper plate 4 again by the plating treatment step (a). Thus, the fine particle-like projections 2a on the surface of the copper plate 4 is formed. Thereafter, copper fine particles are further generated on the surface of the copper plate 4 again by the electrolytic treatment step (b). Also at this time, more copper fine particles are generated on the laser light absorption surface 2 than on the resin bonding surface 3. Thereafter, the copper fine particles on the surface of the copper plate 4 are fixed to the copper plate 4 by a plating process (a).

  Through the series of processes described above, the copper plate 4 for laser processing having the laser light absorption surface 2 and the resin bonding surface 3 is manufactured by simultaneously processing both surfaces of the copper plate 4. The L value of the laser light absorbing surface 2 and the L value of the resin bonding surface 3 are the current density and current value in the plating process, and the current density and current value on the laser light absorbing surface 2 side and the resin bonding surface 3 side in the electrolytic process. Control is possible by adjusting the time required for each process.

  In the above example, as a method of manufacturing the laser processing copper plate 1 of the present invention, a manufacturing method using both electrolytic treatment and plating treatment has been described. However, the method of manufacturing the laser processing copper plate 1 of the present invention is as follows. It is not limited to this. For example, it is also possible to manufacture the laser processing copper plate 1 having the laser light absorption surface 2 and the resin bonding surface 3 by simultaneously roughening both surfaces of the copper plate 4 only by electrolytic treatment. However, a decrease in fixability of the copper fine particles on the surface of the copper plate 4 due to not performing the plating treatment is inevitable.

1 Laser processing copper plate (roughened copper plate)
2 Laser light absorption surface (one surface)
2a Fine granular protrusion 3 Resin bonding surface (the other surface)
3a Fine granular protrusion 4 Copper plate 5 Resin

Claims (10)

A copper plate having a thickness of 70 μm or more,
In order to improve the laser light absorbability of one surface of the copper plate and to improve the resin adhesion of the other surface, fine grain protrusions are formed on both surfaces of the copper plate,
The fine granular protrusion is composed of copper fine particles,
The copper plate for laser processing, wherein the copper fine particles are more on one surface than the other surface of the copper plate.   The copper plate for laser processing according to claim 1, wherein the L value of the one surface is 50 or more and 75 or less.   The copper plate for laser processing according to claim 1 or 2, wherein an average particle diameter of particles constituting the fine granular protrusion on the one surface is 0.3 µm or more and 3 µm or less. The average particle diameter of the particles is 0.1 μm or more, which is less than the wavelength of the laser beam used for processing,
The copper plate for laser processing according to claim 1 or 2, wherein a wavelength of laser light used for the processing is 1084 nm or less. 5. The fine granular protrusion according to claim 1, wherein one or more sets of the copper fine particles and the plating layer for fixing the copper fine particles are formed as one set . Copper plate for laser processing.   A printed circuit board, wherein a resin substrate is bonded to the other surface of the laser processing copper plate according to claim 1. In order to improve the laser light absorption of one surface and improve the resin adhesion of the other surface, it has fine granular projections composed of copper fine particles on both sides,
The copper fine particles are more on the one surface than on the other surface,
Using a copper plate with a thickness of 70 μm or more,
A laser processing method for a copper plate, wherein one surface of the copper plate is irradiated with laser light, the laser light is absorbed by the fine granular protrusions, and the copper plate is welded.   The laser processing method of the copper plate according to claim 7 whose L value of said one side is 50 or more and 75 or less.   The laser processing method for a copper plate according to claim 7 or 8, wherein a wavelength of the laser beam is larger than a particle diameter of the copper fine particles.   The copper plate laser processing method according to claim 9, wherein a wavelength of the laser light is 1084 nm or less.

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