JP4528204B2 - Method for manufacturing printed wiring board - Google Patents

Description

  The present invention relates to a printed wiring board and a manufacturing method, and more particularly to a technique for drilling a copper foil with a laser beam.

  In recent years, with the reduction in size and weight of electronic devices, there has been a demand for higher density wiring of printed wiring boards. Therefore, a technique of a multilayer printed wiring board having a plurality of insulating layers and wiring layers has been advanced. In a multilayer printed wiring board manufacturing technique, an interlayer connection for electrically connecting wiring layers is an important factor.

  As an interlayer connection method, there are a method using a through hole which is a through hole or a blind via hole which is a non-through hole, a method using an interstitial via hole, and the like.

The hole forming method includes a drilling method, a laser processing method, and the like, but the laser processing method is mainly used from the viewpoint of reducing the diameter of the processing hole and high processing speed. CO ₂ lasers are the most prevalent having high laser energy among them.

In the wavelength region of the CO ₂ laser, laser light is reflected on the surface of the copper foil, so that it is difficult to process with the CO ₂ laser. Therefore, a conformal mask method is employed in which only the copper foil around the hole forming periphery is etched away before laser processing.

  However, the conformal mask method requires a copper foil patterning process and it is difficult to correct the misalignment of the holes, so there is a copper foil surface treatment technology for processing copper foil directly with a laser. It is being considered.

  As a method of increasing the laser light absorption rate on the copper foil surface, there are a method of providing a metal layer or an organic film having a high laser light absorption rate on the copper foil surface and a blackening treatment method of directly roughening the copper foil surface.

JP 2004-6611 A Toshiki Hirogaki and 4 other authors "Improvement of hole quality in Cu direct machining with carbon dioxide laser" The 14th Microelectronics Symposium October 2004

  The method of providing a different layer such as a metal layer or an organic film on the surface of the copper foil requires lamination of the different layers and peeling after drilling, and requires a significant increase in the number of steps. In addition, the blackening treatment method for roughening the copper foil surface is originally a copper foil surface treatment for adhesion between the inner wiring and the insulating layer, and therefore the laser light reflectance is as high as about 90% or more. Therefore, high laser energy is required for drilling a blackened copper foil. For this reason, an overhang occurs at the time of drilling, and the hole diameter dimensional accuracy decreases.

  An object of the present invention is to provide a method for manufacturing a printed wiring board capable of drilling a copper foil accurately and with low energy.

According to the present invention, in a method for manufacturing a printed wiring board including a step of simultaneously forming a hole in a copper foil and a resin of an outer layer using a laser on a laminated board in which a copper foil is bonded to a base resin, prior to laser processing, On the surface of the copper foil located in the outer layer, a copper oxide having a surface reflectance of 30 to 80% in a wavelength range of 9.3 to 10.6 μm and a thickness of 1.0 to 2.0 μm is formed. This copper oxide is formed at least with a treatment liquid having a sodium chlorite concentration of 100 to 160 (g / l) and a sodium hydroxide concentration of 60 to 100 (g / l).

  According to the present invention, it is possible to punch a copper foil accurately and with low energy.

  The printed wiring board of the present invention is not particularly limited, and may be a rigid or flexible generally known printed wiring board having copper foil on both sides or one side of resin including resin or glass cloth.

The laser device used in the method for producing a printed wiring board according to the present invention is a CO ₂ laser, and is preferably infrared light having a wavelength of 9.3 to 10.6 μm.

[Examples 1 to 12]
In Examples 1-12, the copper clad laminated board MCL-E679 which laminated | stacked copper foil on the glass cloth containing epoxy resin by Hitachi Chemical Co., Ltd. was used. The thickness of the copper foil is 18 μm. The copper clad laminate was first subjected to a copper foil surface treatment.

  The process of copper foil surface treatment is shown in FIG. First, in Step S1, degreasing treatment with a sodium hydroxide solution was performed at a liquid temperature of 50 ° C. for a treatment time of 3 minutes as washing of the copper foil surface of the copper clad laminate, and then washing with water was performed. Next, in step S2, the conditioner treatment with the surfactant solution was performed at a liquid temperature of 40 ° C. for a treatment time of 3 minutes, and then washed with water. In step S3, an ammonium persulfate-based Cu etching solution was treated at a liquid temperature of 30 ° C. for a treatment time of 1 minute, and then washed with water. In step S4, treatment was performed with a dilute sulfuric acid solution having a concentration of 5% at a liquid temperature of 25 ° C. for a treatment time of 1 minute, and then washed with water. Finally, in step S5, the copper foil surface treatment solution having a sodium chlorite concentration of 100 to 160 g / l and a sodium hydroxide concentration of 60 to 100 g / l is treated at a solution temperature of 70 ° C. and a treatment time of 7 minutes. Performed, washed with water and dried. In Examples 1 to 12, the liquid temperature of the copper foil surface treatment liquid was set to 70 ° C., but a predetermined surface shape and film thickness were ensured by performing the copper foil surface treatment in the liquid temperature range of 60 ° C. to 90 ° C. Is possible.

  FIG. 2 shows an example of the concentration of the copper foil surface treatment liquid in step S5. The sodium chlorite concentration is 100 to 160 g / l, and the sodium hydroxide concentration is 60 to 100 g / l.

Using a copper-clad laminate that had been subjected to copper foil surface treatment, drilling with a CO ₂ laser was performed to evaluate the workability. The target hole diameter is 50 μm and 80 μm. The results are shown in FIG. The workability is evaluated by measuring the energy required for drilling. As processing conditions, the laser energy was changed from 1.1 mJ to 25.2 mJ in one shot processing. The laser energy was measured when the 18μm thick copper foil reached the target hole diameter. This value indicates the laser energy required for drilling.

  In addition, as shown in FIG. 3, the reflectance of the surface of the copper oxide formed by the copper foil surface treatment and the film thickness of the copper oxide formed by the copper foil surface treatment were measured.

The surface reflectivity of the copper oxide was measured at an incident angle of 80 degrees by a highly sensitive reflection method using infrared absorption spectroscopy. The measurement wavelength was in the range of 9.3 to 10.6 μm, similar to the CO ₂ laser beam. The thickness of the copper oxide was measured using an electrochemical reduction potential method. The electrode area was 4.5 × 10 ⁻² cm ² , the electrolyte was a 0.1 mol / l NaOH aqueous solution, the reference electrode was a saturated KCl silver / silver chloride electrode, and the current value was 1 mA.

  According to the present invention, since the laser drilling is performed directly on the copper foil that has been subjected to the copper foil surface treatment, the removal amount of the insulating layer below the copper foil layer is large. Therefore, a so-called overhang occurs in which the hole diameter of the insulating layer is larger than the hole diameter of the outer layer copper foil. In order to evaluate this overhang, the copper-clad laminate after laser processing was subjected to cross-sectional polishing, and the ratio of the hole diameter of the outer layer copper foil to the hole diameter of the insulating layer was measured by cross-sectional observation. The results are shown in FIG.

[Comparative Example 1]
In Comparative Example 1, a blackening treatment that is a conventional technique was performed using the same copper clad laminate MCL-E679 as in Examples 1-12. Comparing the blackening treatment with the copper foil surface treatment of this example, the blackening treatment is the same as the copper foil surface treatment of this example up to steps S1 to S4 in FIG. 1, but in step S5, FIG. As shown in the figure, the sodium chlorite concentration is 90 g / l, and the sodium hydroxide concentration is 15 g / l. After performing the blackening treatment in this manner, laser drilling workability evaluation, copper oxide reflectance measurement, film thickness measurement, and overhang evaluation were performed in the same manner as in Examples 1-12. FIG. 3 shows the results of laser drilling workability evaluation, copper oxide reflectivity measurement, and film thickness measurement, and FIG. 4 shows the overhang evaluation results.

[Comparative Example 2]
In Comparative Example 2, the same copper clad laminate MCL-E679 as in Examples 1 to 12 was used. However, the copper foil surface treatment method is different from that in Examples 1-12. In Comparative Example 2, the copper clad laminate MCL-E679 was first treated with a cleaning liquid (MB-115 concentration 100 ml / l) at a liquid temperature of 50 ° C. for a treatment time of 3 minutes, and then washed with water. Next, after treatment with pre-dip solution (MB-100B concentration 20 ml / l, MB-100C concentration 29 ml / l) at a liquid temperature of 25 ° C. and a treatment time of 1 minute, a multibond solution (MB-100A concentration 100 ml / l, MB-100B concentration 80 ml / l, MB-100C concentration 43 ml / l, sulfuric acid concentration 50 ml / l), liquid temperature 32 ° C., treatment time 2 minutes, washed with water and dried. The multi-bond solution is a sulfuric acid / hydrogen peroxide-based copper roughening etching solution manufactured by Nihon McDermid.

  Next, with reference to FIG. 3 and FIG. 4, the results of laser drilling workability evaluation for Examples 1 to 12 and Comparative Examples 1 and 2 will be examined. Good drilling workability means that less energy is required for drilling. Low surface reflectance means that the ratio of energy used for laser processing is high. Therefore, it can be said that the low surface reflectivity also has good drilling workability.

  When Examples 1-12 are compared with Comparative Example 1, it can be confirmed that the laser processing energy is smaller than Comparative Example 1 for all Examples 1-12, and therefore the drilling workability is good.

  FIG. 5 illustrates the ranges of sodium chlorite concentration of 100 to 160 g / l and sodium hydroxide concentration of 60 to 100 g / l used in this example. Examples 1 to 12 are in a rectangular range indicated by a broken line. Therefore, in the rectangular range indicated by the broken line, the laser processing energy is smaller than that of Comparative Example 1, and therefore the drilling workability is good. In this range, the surface reflectance is about 30-80%. That is, except for Examples 6 and 9, the surface reflectance is about 30 to 65%.

  Among the present examples, the workability was particularly good in Example 1, Example 2, Example 3, Example 5, Example 8, and Example 10. These examples are in the rhombic hatched area surrounded by the points A to D shown in FIG. In this region, the laser processing energy is small and the surface reflectance is about 30 to 55%. Among them, Example 1 was able to obtain the best results.

  On the other hand, Comparative Example 1 will be examined. Comparing Comparative Example 1 and Example 1, the laser drilling workability evaluation at a target hole diameter of 50 μm required about 4 times as much laser energy as Example 1. From the overhang evaluation result, it was found that the hole diameter of the copper foil was halved relative to the hole diameter of the insulating layer, and the overhang was larger than that of Example 1. This is considered to be because the difference in the removal amount of the copper foil and the insulating layer is reduced by reducing the laser energy.

  The reflectance of the copper oxide of Comparative Example 1 is as high as 98%, which is about 3 times that of Example 1. The thickness of the copper oxide is 0.5 μm, which is 2.8 times thinner than that of Example 1. The crystal shape of the formed copper oxide is also a fine acicular crystal in Comparative Example 1, whereas Example 1 is an uneven crystal, and the size of one crystal is larger than Comparative Example 1. From these results, it was confirmed that the laser processing energy can be reduced and the overhang is reduced by the copper foil surface treatment of the present invention.

  Next, Comparative Example 2 will be examined. The surface reflectance of Comparative Example 2 is 50%, and the film thickness of the copper oxide is 0.02 μm. The feature of the copper foil surface treatment solution of Comparative Example 2 is that almost no copper oxide is formed on the copper foil surface.

  Comparative Example 2 is compared with Example 2 and Example 10. The surface reflectivities of the two are comparable, but the copper oxide film thickness is greater in Example 2 and Example 10 than in Comparative Example 2. However, in the laser drilling workability evaluation with a target hole diameter of 50 μm, the laser energy of Comparative Example 2 is higher. The cause of this is not known, but in Example 2 and Example 10, the formation of copper oxide on the surface of the copper foil prevents the thermal energy of the laser from diffusing into the atmosphere, and the processing efficiency by thermal energy Is presumed to be improved. The thermal conductivity of copper oxide is 0.003 gJ / cm · s · K compared to 4.01 gJ / cm · s · K, which is one hundredth smaller.

  From this result, it was confirmed that the thicker the copper oxide, the better the laser drilling workability, but there is a problem that the copper oxide has to be removed after drilling and the copper foil is thinned. The thickness of the copper oxide is preferably 1.0 to 2.0 μm.

  With reference to FIGS. 6-8, the manufacturing method of the printed wiring board by this invention is demonstrated. Here, the multilayer printed wiring board was produced using the copper foil surface treatment liquid of Examples 1-12. As shown in FIG. 6A, a copper clad laminate MCL-E679 was prepared as an inner layer base material 1 having a copper foil 3a on the surface. As shown in FIG. 6B, an inner layer circuit pattern made of a resist 2 is formed on the copper foil 3a. The copper foil 3a other than the portion covered with the resist 2 is removed by etching, and then the resist 2 is removed, whereby the inner layer circuit 3 is formed on the inner layer substrate 1 as shown in FIG. Formed. A copper foil with a resin not containing glass cloth was laminated on both sides of the inner layer base material by pressing to produce a four-layer copper-clad laminate. As shown in FIG. 7A, this copper-clad laminate has four layers of copper foil composed of two outer layer copper foils 5 and two inner layer copper foils 3. The thickness of the outer layer copper foil 5 was 9 μm.

Next, the copper foil surface treatment shown in FIG. 1 was performed on the outer layer copper foil 5 of this four-layer copper clad laminate. As shown in FIG. 7B, copper oxide 6 is formed on the surface of the outer layer copper foil 5. As shown in FIG. 7C, a blind via with a laser energy of 8 mJ and a hole diameter of 100 μm was formed by a CO ₂ laser. As shown in FIG. 8A, the copper oxide film 6 was removed with a copper etchant, a blind via desmear process was performed, and a copper plating film 7 of 15 μm was formed for interlayer conduction formation. Next, as shown in FIG. 8B, an inner layer circuit pattern made of the resist 2 is formed on the outer layer copper foil 5. The outer layer copper foil 5 other than the portion covered with the resist 2 is removed by etching, and then the resist 2 is removed, whereby the outer layer circuit 7 is formed on the insulating layer 4 as shown in FIG. Formed.

  FIG. 9 is a diagram schematically showing the structure of a multilayer printed wiring board. The positional deviation between the inner layer wiring and the hole of the multilayer printed wiring board produced in this way was measured by cross-sectional observation. In the measurement method, the holes of each multilayer printed wiring board were observed, and the maximum deviation between the inner layer wiring and the center of the hole was measured. The results are shown in FIG. In all of Examples 1 to 12, the maximum deviation between the inner layer wiring and the center of the hole was within 50 μm.

  The example of the present invention has been described above, but the present invention is not limited to the above-described example, and various modifications can be made by those skilled in the art within the scope of the invention described in the claims. It will be understood.

It is a figure which shows the copper foil surface treatment process by this invention. It is a figure which shows the composition conditions of the copper foil surface treatment liquid of the Example and comparative example of this invention. It is a figure which shows the measurement result of the laser drilling workability evaluation of the Example and comparative example of this invention, a reflectance, and a copper oxide film thickness. It is a figure which shows the result of the overhang evaluation of the Example and comparative example of this invention. It is a figure which shows the optimal concentration range of the copper foil surface treatment liquid by this invention. It is the schematic showing the manufacturing process of a multilayer printed wiring board. It is the schematic showing the manufacturing process of a multilayer printed wiring board. It is the schematic showing the manufacturing process of a multilayer printed wiring board. It is a bird's-eye view of a multilayer printed wiring board. It is a figure which shows the internal layer wiring by this invention, and the positional offset measurement result of a hole.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Inner layer base material, 2 ... Resist, 3 ... Inner layer circuit, 4 ... Insulating layer, 5 ... Outer layer copper foil, 6 ... Copper oxide, 7 ... Copper plating film, 8 ... Blind via

Claims (6)

In the method of manufacturing a printed wiring board including a step of forming a hole by laser processing in the copper foil of the outer layer of the laminated board obtained by laminating the copper foil to the base resin and the resin below the
Prior to drilling by laser processing, the surface reflectivity for infrared light in the wavelength range of 9.3 to 10.6 μm is 30 to 80% and the thickness is 1.0 to 2.0 μm on the surface of the outer copper foil. There row copper foil surface treatment to form a copper oxide, copper foil surface treatment on the surface of the copper foil of the outer layer, the concentration is sodium chlorite and the concentration of 100~160 (g / l) 60~100 ( method for manufacturing a printed wiring board, characterized in row Ukoto the treated with a surface treatment solution containing sodium hydroxide g / l).   2. The method of manufacturing a printed wiring board according to claim 1, wherein the surface reflectance of the copper oxide formed by the copper foil surface treatment is 30 to 55%. The manufacturing method of claim 1 Symbol mounting of the printed wiring board, the copper foil surface treatment method for manufacturing a printed wiring board, which comprises carrying out at a liquid temperature of 70 to 90 ° C.. In the laminated board for printed wiring board production in which copper foil is bonded to the base resin,
Prior to laser processing for forming holes using laser light in the wavelength range of 9.3 to 10.6 μm, the surface reflectance of infrared light in the range of wavelength 9.3 to 10.6 μm is 30 to 80 on the surface of the outer copper foil. The copper foil surface treatment is performed to form a copper oxide having a thickness of 1.0 to 2.0 μm, and the copper foil surface treatment has a concentration of 100 to 160 (g / g) on the surface of the outer copper foil. A laminated board for producing a printed wiring board, wherein the laminated board is treated with a surface treatment solution containing l) sodium chlorite and sodium hydroxide having a concentration of 60 to 100 (g / l) . In laminates for printed wiring board manufacture according to claim 4, laminated for printed wiring board manufacturing, wherein the surface reflectance of the copper oxide formed by the copper foil surface treatment is 30 to 55% Board.   In the surface treatment liquid used for the surface treatment performed prior to the step of forming the hole by laser processing on the copper foil of the laminated board in which the copper foil is bonded to the base resin and the resin therebelow, the concentration is 100 to 160 ( A surface treatment solution comprising sodium chlorite in g / l) and sodium hydroxide in a concentration of 60 to 100 (g / l).

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