JP2006203074A - Circuit board and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a circuit board whereby occurrence of smear can be reduced and sufficiently eliminated, as formed inside of blind vias and at the surrounding of opening edges caused when the blind vias are formed through the emission of a laser beam and to provide the circuit board. <P>SOLUTION: The circuit board includes a resin layer and a conductor layer, and is formed with the blind vias. The resin layer is provided with a protection layer for protecting the resin layer on a side opposite to the side of the conductor layer. The manufacturing method of the board includes a step of forming the blind via holes by emitting the laser beam to the resin layer and the protective layer, and a step of removing the protection layer after the forming of the blind vias. The emission of the laser beam is carried out in a manner of defocusing the focus so as to be deviated in an optical axis direction with respect to the surface of the protection layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a circuit board manufacturing method and a circuit board.

In recent years, with the increase in the density of electronic devices, there has been a demand for multilayered and thinned circuit boards used therefor. The process of manufacturing a multilayer circuit board includes a process of bonding substrates by bump plating, and is performed as follows.
Blind vias are formed on the insulating layer of the substrate with a UV laser or the like, bump plating is performed on the blind vias, the substrates are stacked, and the layers are multilayered to obtain conduction between the substrates.

When blind vias are formed by this laser light irradiation, smears may remain inside or around the vias.
If smear remains in or around the blind via, it may be difficult to perform plating in the next process with good quality and shape.
In particular, at the bottom of the blind via, the copper foil partially melts due to the variation in energy density in the depth direction of the blind via of the laser beam to irradiate. Smear may remain. In addition, smear remains around the opening edge of the blind via due to thermal damage caused by laser light irradiation and oxidation of the insulating layer, or decomposition sublimates of the insulating layer strongly adhered by the laser light. There is a case.

  Therefore, in order to remove the smear around and around the via formed by laser processing or the like, the smear was dissolved and removed by immersion in a permanganic acid solution (for example, see Patent Document 1). However, for smears that adhere firmly to the bottom or the periphery of blind vias, we have devised processing solutions and optimized processing conditions such as repeated processing, but it may be difficult to remove smears sufficiently. there were.

JP 2004-146533 A

  An object of the present invention is to provide a circuit board manufacturing method capable of reducing the generation of smear around the blind via and around the opening edge, which is generated when a blind via is formed by laser light irradiation, and sufficiently removing the smear. And providing a circuit board.

Such an object is achieved by the present invention described in the following (1) to (12).
(1) A method of manufacturing a circuit board comprising a resin layer and a conductor layer, wherein a blind via is formed, wherein the resin layer includes a protective layer that protects the resin layer on the side opposite to the conductor layer And the step of irradiating the resin layer and the protective layer with a laser beam to form a blind via hole, and the step of removing the protective layer after the formation of the blind via, The circuit board manufacturing method is performed in a state of being defocused so that the focal point is shifted in the optical axis direction with respect to the surface of the protective layer.
(2) A method of manufacturing a circuit board comprising a resin layer and a conductor layer, wherein a blind via is formed, and a protective layer for protecting the resin layer on the side opposite to the conductor layer on the resin layer A step of providing a laser beam to the resin layer and the protective layer to form a blind via hole, and a step of removing the protective layer after the formation of the blind via. The circuit board manufacturing method is performed in a state where the focus is defocused so as to be shifted in the optical axis direction with respect to the surface of the protective layer.
(3) The method for manufacturing a circuit board according to (2), wherein the step of forming the protective layer is a step of laminating the resin film or a step of sputtering the metal layer.
(4) The circuit board manufacturing method according to any one of (1) to (3), wherein a distance between the focal point and the surface of the protective layer is 0.01 to 3 mm.
(5) The method according to any one of (1) to (4), wherein the focal point is located on a side opposite to the resin layer from a surface of the protective layer.
(6) The method for manufacturing a circuit board according to any one of (1) to (5), wherein a beam diameter of the laser light is 20 to 80 μm.
(7) The method for manufacturing a circuit board according to any one of (1) to (6), wherein the blind via has an internal cross-sectional area that increases toward the opening.
(8) The circuit board manufacturing method according to any one of (1) to (7), wherein a taper angle formed by a side wall of the blind via with respect to a surface of the conductor layer is 10 to 25 degrees.
(9) The method for producing a circuit board according to any one of (1) to (8), wherein the protective layer is a resin layer or a metal layer made of a resin composition.
(10) The method for manufacturing a circuit board according to (9), wherein the resin composition includes an acrylic resin.
(11) The method for manufacturing a circuit board according to (9), wherein the metal layer is made of a metal containing copper.
(12) A circuit board obtained by the method for manufacturing a circuit board according to any one of (1) to (11).

According to the present invention, a method of manufacturing a circuit board capable of reducing and sufficiently removing smear around the blind via and around the opening edge that occurs when forming a blind via by laser light irradiation. And a circuit board can be provided.
Moreover, when the position of the focus of the laser beam in the defocused state is located on the side opposite to the resin layer from the surface of the protective layer, the size of the bride via can be made more accurate.

Hereinafter, the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.
FIG. 1 is a cross-sectional view illustrating an example of a process of forming a protective layer on a circuit board including a resin layer and a conductor layer. FIG. 2 is a cross-sectional view showing an example in which a protective layer is formed on a circuit board including a resin layer and a conductor layer. FIG. 3 is a cross-sectional view schematically showing a state in which the circuit board is irradiated with laser light. FIG. 4 is a cross-sectional view showing an example in which blind vias are formed on a circuit board. FIG. 5 is an energy intensity distribution diagram schematically showing the energy density distribution of the laser light. FIG. 6 is a cross-sectional view schematically showing a state in which a circuit board is irradiated with laser light by a conventional method.

  Hereinafter, each process will be described.

In the step of forming the protective layer, a laminator 10 covers the resin layer 3 of the laminate 4 in which the conductor layer 2 and the resin layer 3 provided on one side of the conductor layer 2 are laminated as shown in FIG. A protective layer 31 is formed.
The protective layer 31 is used to easily remove smear attached to the surface of the resin layer 3 (surface opposite to the conductor layer 2). That is, smears adhering to the surface of the resin layer 3 of the blind via can be removed together with the protective layer 31 by irradiation with a laser beam 5 described later.

The material used for the protective layer 31 is not particularly limited as long as it is a material that can be removed after irradiation with laser light, such as a resin layer made of a resin composition or a metal layer made of a metal material. Specifically, thermosetting of acrylic resin, polyester resin, epoxy resin, urethane resin, polystyrene resin, polyethylene resin, polyamide resin, polyimide resin, ABS resin, polycarbonate resin, silicone resin, etc. Examples thereof include a resin layer composed of a resin composition containing a conductive resin or a thermoplastic resin, and a metal layer composed of a metal material such as copper, nickel, cobalt, and chromium. Among these, in the said resin layer, the resin layer comprised with the resin composition containing acrylic resin is preferable. Thereby, it can be set as the shape of a dry film resist, and formation and removal of the protective layer 31 can be made easy by it. That is, in the case of the dry film resist, the protective layer 31 can be easily formed by thermocompression using a laminator, and the protective layer 31 can be easily removed by caustic soda.
Moreover, in the said metal layer, the metal layer comprised with copper is preferable. Thereby, the protective layer 31 can be easily formed by sputtering. Further, the protective layer 31 can be easily dissolved and removed by an etching solution such as sulfuric acid hydrogen peroxide.

  When the protective layer 31 is the resin layer, the thickness is not particularly limited, but is preferably 5 to 40 μm, and particularly preferably 7 to 25 μm. If the thickness is less than the lower limit value, it may be removed by thermal energy generated when the laser beam 5 is irradiated. If the thickness exceeds the upper limit value, the bottom portion of the blind via 6 due to variations in the density of the laser beam 5 to be irradiated. Resin residue may occur in 61.

  When the protective layer 31 is the metal layer, the thickness is not particularly limited, but is preferably 0.5 to 3 μm, particularly preferably 1 to 2 μm. When the thickness is less than the lower limit value, it may be removed by thermal energy generated when the laser beam 5 is irradiated, and when the thickness exceeds the upper limit value, the conductor layer 2 may be etched.

In this way, the protective layer 31 is formed to protect the conductor layer 2 as shown in FIG. 2, the resin layer 3 provided on one side of the conductor layer 2, and the resin layer 3 on the side opposite to the conductor layer 2. The circuit board 1 provided with the protective layer 31 to be obtained is obtained.
In this embodiment, the step of forming the protective layer 31 is included. However, the circuit board 1 on which the protective layer 31 is formed in advance may be used.

A circuit is formed on the conductor layer 2 later by etching or the like.
Examples of the conductor layer 2 include copper foil and aluminum. Among these, copper foil is preferable. Thereby, an arbitrary wiring pattern can be easily formed.

  Although the thickness of the conductor layer 2 is not specifically limited, 5-70 micrometers is preferable and 9-35 micrometers is especially preferable. When the thickness is within the above range, the circuit formability by the etching process is particularly excellent.

The resin layer 3 is used to hold an insulating layer between the conductor layer 2 and other layers.
Examples of the resin layer 3 include resin films such as a polyimide film, a polyether ether ketone film, a polyether sulfone film, and a liquid crystal polymer film, a laminated plate such as an epoxy resin laminated plate, a phenol resin laminated plate, and a cyanate resin laminated plate. Can be mentioned. Among these, a resin film represented by a polyimide film is preferable. Thereby, heat resistance can be improved. Furthermore, flexibility can be exhibited.

  Although the thickness of the resin layer 3 is not specifically limited, 9-100 micrometers is preferable and 12-25 micrometers is especially preferable. When the thickness is within the above range, it is possible to shorten the plating time for forming the bump plating in order to conduct the blind via 6 described later.

  In the step of forming the via hole, the blind via 6 as shown in FIG. 4 is formed by irradiating the laser beam 5 from the protective layer 31 side of the circuit board 1 as shown in FIG. The laser light used in the present invention is not parallel light but focused light. That is, the laser beam is focused toward the front of the beam. In this case, the laser beam 5 is defocused so that its focal point (condensing point) 51 is shifted in the optical axis direction with respect to the surface 311 of the protective layer 31 (hereinafter simply referred to as “defocused state”). To do. Thereby, it is possible to prevent the smear in which the conductor layer 2 and the smear are mixed and firmly adhered to the bottom 61 (conductor layer 2 portion) of the blind via 6 by the irradiation of the laser beam 5. The reason will be described in detail below.

Conventionally, when irradiating a substrate with laser light, laser processing has been performed by focusing the laser light 5 on the surface of the resin layer 3 as shown in FIG. However, when the laser beam is irradiated in the just focus state, the laser beam 52 having a relatively high energy density is irradiated as shown in FIG. When the laser beam 52 having such high energy density is irradiated, the bottom of the blind via (that is, the conductor layer) is greatly damaged due to the variation in the profile of the laser beam 52. As a result, the conductive layer and smear generated at the bottom (conductor layer portion) of the blind via may be mixed and smear may be generated.
On the other hand, when the laser beam 5 is irradiated in a defocused state, the energy density of the laser beam 53 irradiated to the resin layer 3 can be reduced as shown in FIG. Therefore, the bottom 61 of the blind via 6 can be prevented from being damaged, so that the bottom of the blind via 6 does not melt and smear that adheres firmly does not occur. Furthermore, since the protective layer 31 is provided, the shape of the opening edge 62 can be sharpened.

  The separation distance between the position of the focal point 51 of the laser beam 5 and the surface 311 of the protective layer 31 in the defocused state is not particularly limited, but is preferably 0.01 to 3 mm, particularly preferably 0.1 to 2.8 mm. The most preferable is 1.5 to 2.7 mm. When the position of the focal point 51 is within the above range, the size of the upper end portion of the blind via 6 can be made accurate.

  Further, the position of the focal point 51 of the laser beam 5 in the defocused state may be located on the resin layer 3 side from the surface 311 of the protective layer 31 or may be located on the opposite side to the resin layer 3. The resin layer 3 is preferably located on the opposite side. Thereby, the size of the blind via 6 can be made more accurate.

  In forming the blind via 6, it is preferable to irradiate the laser beam 5 while moving the vicinity of the center of the blind via 6 formed by the focal point 51 of the laser beam 5 in the horizontal direction. Thereby, the blind via 6 having a diameter of about 50 μm can be easily formed.

Examples of the laser beam 5 include an infrared region laser such as a carbon dioxide laser (CO ₂ laser) and a YAG laser. Examples of the ultraviolet region laser include a YAG laser, a YLF laser, a YAP laser, A YVO ₄ laser, an excimer laser, etc. are mentioned. Among these, YAG laser is preferable. Thereby, the small diameter processing of 50 micrometers or less can be made easy. Furthermore, it can be processed whether the protective layer 31 is a metal layer or a resin layer.

  The shape of the blind via 6 formed in the process of forming the blind via 6 is not particularly limited, but it is preferable that the internal cross-sectional area is widened toward the opening. More specifically, the taper angle formed by the side wall of the blind via 6 with respect to the surface 21 of the conductor layer 2 is preferably 10 to 25 degrees, and particularly preferably 12 to 23 degrees.

  After the blind via 6 is formed, a desmear process is performed by a permanganate solution, a plasma process, or the like in a process of performing a desmear process. In particular, dry-type plasma treatment is preferable. As a result, it is possible to sufficiently remove smear from a small-diameter blind via.

Next, in the step of removing the protective layer 31, as described above, the protective layer 31 is removed by peeling and removing with caustic soda or the like, etching with hydrogen peroxide sulfate or the like. Thereby, the smear adhering to the periphery of the opening edge 62 of the blind via 6 can be removed together with the protective layer.
The step of removing the protective layer 31 may be performed before the desmear process.

Next, plating is deposited on the blind via 6 to protrude from the surface of the resin layer 3. And it coat | covers with a brazing material so that the protruding plating part may be covered. Thereby, the conduction | electrical_connection between the conductor layer 2 and another layer can be aimed at.
Then, another conductor layer is laminated so as to be joined to the brazing material to form a multilayer circuit board.

EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example and a comparative example, this invention is not limited to this.
Example 1
1. Formation of protective layer A single-sided circuit board (Ube Industries: SE1310) composed of a 12 μm-thick copper foil as a conductor layer and a 25 μm-thick polyimide film as a resin layer, and a 20 μm-thick dry layer as a protective layer A film resist (acrylic resin, manufactured by Asahi Kasei: AQ2075) was thermocompression bonded with a dry film laminator.

2. Next, the surface of the protective layer is irradiated with UV laser light (laser beam diameter: 22 μm) in a defocused state so that the focal point of the laser light is shifted 2 mm toward the front side in the optical axis direction. A blind via having a diameter of 50 μm was formed (a separation distance of 2 mm between the surface of the protective layer and the focal point of the laser beam). The shape of the blind via was such that the internal cross-sectional area expanded toward the opening.

3. Peeling of the protective layer 2% of caustic soda was sprayed at 40 ° C. with a spray pressure of 0.15 MPa for 30 seconds to peel off the protective layer.

4). Desmear treatment After forming the blind via, the desmear treatment was performed using a parallel plate type plasma apparatus. In a state where the degree of vacuum was 50 Pa or less, 200 sccm was introduced, 2,500 W was applied between the electrodes, and the mixture was held for 2 minutes.

5. Plating treatment and solder coating After the desmear treatment, a copper sulfate solution was used at a current density of 10 A / dm ² for 15 minutes to make the length of the copper plating protrusions from the resin layer 8 μm. Next, treatment was performed for 10 minutes at a current density of ² A / dm ² so as to cover the projected copper plating protrusions, and the solder coating amount from the resin layer was set to 15 μm.

(Example 2)
Example 1 was performed except that the focal position of the laser beam was changed as follows.
The laser beam was irradiated with UV laser light in a defocused state so that the focal point of the laser beam was shifted by 0.05 mm toward the near side in the optical axis direction (a separation distance of 0.5 mm between the surface of the protective layer and the focal point of the laser beam).

(Example 3)
Example 1 was performed except that the focal position of the laser beam was changed as follows.
The laser beam was irradiated in a defocused state so that the focal point of the laser beam was shifted 3 mm toward the near side in the optical axis direction (a separation distance of 3 mm between the surface of the protective layer and the focal point of the laser beam).

Example 4
Example 1 was performed except that the focal position of the laser beam was changed as follows.
UV laser light was applied in a defocused state so that the focal point of the laser beam is shifted by 2 mm toward the resin layer in the optical axis direction (a separation distance of 3 mm between the surface of the protective layer and the focal point of the laser beam).

(Example 5)
A copper foil was used as the protective layer, and the same procedure as in Example 1 was performed except that the protective layer was formed as follows.
The copper foil was sputtered using a sputtering apparatus (manufactured by Shimadzu Corporation) so as to have a thickness of 1 μm.

(Comparative Example 1)
The same procedure as in Example 1 was performed except that the protective layer was not provided and the focal point was positioned on the surface of the protective layer when the laser beam was irradiated (the surface of the protective layer and the laser beam). The separation distance from the focal point is 0 mm).

(Comparative Example 2)
Example 1 was repeated except that the protective layer was not used.

The circuit board obtained in each example and each comparative example was evaluated as follows. The evaluation items are shown together with the contents.
1. Residue of Resin Layer The state after removing the resin layer with laser light was visually evaluated. Each code is as follows.
A: The resin layer could be removed.
○: A part of the resin layer remains, but it was in a range that can be removed by desmear treatment.
Δ: A part of the resin layer remained and could not be removed even by desmear treatment.
X: Many resin layers remained.

2. Residual smear amount The residual smear amount at the opening edge and the bottom of the blind via was visually evaluated for the blind via after the desmear treatment. Each code is as follows.
A: Almost no residual smear.
○: Residual smear is partially present, but there is no practical problem.
Δ: Some residual smear is present and impractical.
X: There is a residual smear amount.

3. Plating shape The plating shape after the plating treatment was visually evaluated. Each code is as follows.
A: A uniform plating layer can be formed.
○: There is a plating layer portion that is partially uneven, but there is no practical problem.
(Triangle | delta): There exists a nonuniform plating layer part, and it cannot use it.
X: A plating layer cannot be formed.

4). Heat resistance Heat resistance was evaluated by performing a temperature cycle test (hot oil 260 ° C. 10 seconds⇔normal temperature 20 seconds 100 cycles), measuring appearance and conduction resistance. Each code is as follows.
A: There is no abnormality in the appearance, and the rate of change from the initial value of the conduction resistance is less than ± 5%.
A: There is no abnormality in the appearance, and the rate of change from the initial value of the conduction resistance is ± 5% or more and less than ± 8%.
(Triangle | delta): There is no abnormality in an external appearance and the change rate from the initial value of conduction | electrical_connection resistance is more than +/- 8% and less than +/- 10%.
X: Abnormality such as swelling and peeling in appearance, or change rate from initial value of conduction resistance is ± 10% or more.

As is clear from Table 1, Examples 1 to 5 were able to reduce the amount of residual smear.
In addition, since the amount of residual smear could be reduced, the plating shape was good.
In Examples 1 and 5, the resin layer could be substantially removed without damaging the conductor layer after laser light irradiation.

It is sectional drawing which shows an example of the process of forming a protective layer in a circuit board provided with a resin layer and a conductor layer. It is sectional drawing which shows an example which has formed the protective layer in the circuit board provided with a resin layer and a conductor layer. It is sectional drawing which shows typically the state which irradiates a circuit board with a laser beam. It is sectional drawing which shows an example in which the blind via is formed in the circuit board. It is an energy intensity distribution figure which shows distribution of energy density of a laser beam typically. It is sectional drawing which shows typically the state which irradiates a laser beam with the conventional method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Circuit board 10 Laminator 2 Conductor layer 21 Conductor layer surface 3 Resin layer 31 Protective layer 311 Protective layer surface 4 Laminate 5 Laser beam 51 Focus 52 Laser beam with high energy density 53 Laser beam with low energy density 6 Blind via 61 Bottom 62 Opening edge

Claims (12)

A method for manufacturing a circuit board comprising a resin layer and a conductor layer, wherein a blind via is formed,
The resin layer is provided with a protective layer for protecting the resin layer on the side opposite to the conductor layer,
Irradiating the resin layer and the protective layer with laser light to form blind via holes;
Removing the protective layer after the blind via formation,
The method of manufacturing a circuit board is characterized in that the laser beam irradiation is performed in a defocused state so that the focal point is deviated in the optical axis direction with respect to the surface of the protective layer. A method for manufacturing a circuit board comprising a resin layer and a conductor layer, wherein a blind via is formed,
Providing the resin layer with a protective layer for protecting the resin layer on the side opposite to the conductor layer;
Irradiating the resin layer and the protective layer with laser light to form blind via holes;
Removing the protective layer after the blind via formation,
The method of manufacturing a circuit board is characterized in that the laser beam irradiation is performed in a defocused state so that the focal point is deviated in the optical axis direction with respect to the surface of the protective layer.   The method for manufacturing a circuit board according to claim 2, wherein the step of forming the protective layer is a step of laminating the resin film or a step of sputtering the metal layer.   The method for manufacturing a circuit board according to claim 1, wherein a distance between the focal point and the surface of the protective layer is 0.01 to 3 mm.   The circuit board manufacturing method according to claim 1, wherein the focal point is located on a side opposite to the resin layer from a surface of the protective layer.   6. The method for manufacturing a circuit board according to claim 1, wherein a beam diameter of the laser light is 20 to 80 [mu] m.   The method for manufacturing a circuit board according to claim 1, wherein the blind via has an internal cross-sectional area extending toward the opening.   The circuit board manufacturing method according to claim 1, wherein a taper angle formed by a side wall of the blind via with respect to a surface of the conductor layer is 10 to 25 degrees.   The method for manufacturing a circuit board according to claim 1, wherein the protective layer is a resin layer or a metal layer made of a resin composition.   The method for manufacturing a circuit board according to claim 9, wherein the resin composition includes an acrylic resin.   The method for manufacturing a circuit board according to claim 9, wherein the metal layer is made of a metal containing copper.   A circuit board obtained by the method for manufacturing a circuit board according to claim 1.

Images