JP5097979B2 - Method for manufacturing printed wiring board - Google Patents

Description

  The present invention relates to a method for manufacturing a printed wiring board in which a multilayer laminated board in which a resin layer and a copper layer are laminated is irradiated with laser light to form a via.

  Due to the recent miniaturization, higher density, and higher functionality of electronic devices, high-density circuit formation is also required for printed wiring boards. In order to satisfy this requirement, vias such as blind vias that are bottomed holes and through-hole vias that are through holes are formed in multilayer printed wiring boards for interlayer connection. The As a means for drilling at that time, laser processing such as a carbon dioxide laser is often adopted from the viewpoint of processing efficiency and cost.

  A conventional via forming method using laser processing will be described with reference to the drawings, taking a conformal mask method as an example. 3A to 3C to be referred to are cross-sectional views for each process for explaining the conformal mask method.

  First, a multilayer laminate as shown in FIG. 3A is prepared. In FIG. 3A, a core in which copper layers 1b are formed on both surfaces of an insulating base material 1a containing a resin such as a glass fiber reinforced epoxy resin impregnated substrate (glass epoxy substrate) or an aramid fiber reinforced epoxy resin impregnated substrate (aramid epoxy substrate). The material 1, the resin layer 2 made of prepreg containing glass reinforcing fibers and other resins, laminated on both surfaces of the core material 1, and the surfaces of the resin layers 2 opposite to the core material 1 are laminated. A multilayer laminate including the copper foil 3 is used. Usually, the copper layer 1b of the core material 1 is patterned to form a copper wiring.

  And the part 3a which forms the via in the copper foil 3 on the surface layer side is removed by etching (FIG. 3B). Next, the resin layer 2 positioned immediately below the via forming portion 3a is drilled with a laser (FIG. 3C) to form the blind via BV.

  On the other hand, in recent years, a direct laser method has been considered in which a laser is irradiated onto a copper foil on the surface layer side, and a hole is formed simultaneously in the copper foil and the resin layer to form a via. Since this direct laser method does not require an etching process for copper foil, there is no problem of copper remaining due to defective etching, and the alignment accuracy of circuits between copper layers is superior to the above-mentioned conformal mask method.

  However, in both the conformal mask method and the direct laser method, smear S (FIG. 3C) that is a residue of the resin layer 2 is generated inside the via during laser processing. If plating is performed in the via with the smear S remaining, there is a possibility that conduction between layers may not be achieved.

  Therefore, in the conventional via formation process, a desmear process for removing smear has been essential after laser processing. For example, in the conventional desmear process, the multilayer laminate after laser processing is swelled, then treated with a potassium permanganate solution, and further neutralized to reduce and remove potassium permanganate. It was removed (for example, refer to Patent Documents 1 to 3 below). Patent Document 4 below proposes a desmear process in which treatment with a potassium permanganate solution and ultrasonic cleaning are combined in order to enhance smear removability.

  However, the potassium permanganate used in the desmear process has a high possibility of environmental pollution and is a strong oxidizing agent, so that it is difficult to treat the waste liquid.

  For this reason, as a method not using an oxidizing resin solubilizer such as a potassium permanganate solution, a desmear process that uses an organic swelling agent and further removes smear by combining ultrasonic cleaning is proposed in Patent Document 5 below. Has been.

JP-A-6-314869 JP-A-5-167249 JP 2007-129147 A JP 2007-158238 A JP 2003-338679 A

  In the desmear process described in Patent Document 5, waste liquid treatment is easier than in the desmear process described in Patent Documents 1 to 4, but the smear removal effect is insufficient. For this reason, there has been a demand for a method that allows easy waste liquid treatment and a sufficient smear removal effect.

  In order to solve the above-described problems, the present invention provides a method for producing a printed wiring board that is easy to be treated with a waste liquid and that has a sufficient smear removing effect.

The method for producing a printed wiring board of the present invention is a method for producing a printed wiring board in which a via is formed by irradiating a laser beam to a multilayer laminated board in which a resin layer and a copper layer are laminated.
A swelling treatment step of immersing the multilayer laminate after irradiation with laser light in a non-oxidizing swelling agent;
A microetching treatment step for bringing a microetchant into contact with the multilayer laminate after the swelling treatment step;
An ultrasonic treatment step of applying an ultrasonic wave in a state where the multilayer laminated board after the microetching treatment step is immersed in a liquid.

  In addition, the “copper” in the present invention may be made of pure copper or a copper alloy. In this specification, “copper” refers to pure copper or a copper alloy.

  In the method for producing a printed wiring board according to the present invention, since a non-oxidizing swelling agent is used without using an oxidizing resin solubilizer such as a potassium permanganate solution, waste liquid treatment is facilitated. Further, by performing the swelling process step, the microetching process step, and the ultrasonic treatment step in this order, it is possible to reliably remove smear remaining inside the via.

  The present invention is applied to a method for manufacturing a printed wiring board in which a via is formed by irradiating a multilayer laminated board in which a resin layer and a copper layer are laminated with laser light. The laser processing method is not particularly limited, and known processing methods such as a conformal mask method and a direct laser method can be used. Also, the vias to be formed are not particularly limited, and can be applied to, for example, known vias such as blind vias and through-hole vias.Blind vias are particularly susceptible to smear remaining at the bottom of the via. The effect of the present invention is more effectively exhibited.

  Hereinafter, as an example of the present invention, an example in which the present invention is applied when a blind via is formed by a direct laser method will be described with reference to the drawings. 1A and 1B and FIGS. 2A to 2C to be referred to are cross-sectional views for each process for explaining a method for manufacturing a printed wiring board as an example of the present invention. In addition, the same code | symbol is attached | subjected to the component same as FIG. 3A-C mentioned above, and the description is abbreviate | omitted.

  First, a multilayer laminate similar to the above-described FIG. 3A is prepared (FIG. 1A). Then, a laser is irradiated onto the portion 3a where the via is formed in the copper foil 3 on the surface layer side to form a blind via BV (FIG. 1B). At this time, a smear S that is a residue of the resin layer 2 is generated at the bottom of the blind via BV (via bottom). Before the laser irradiation, a blackening treatment or a copper surface treatment described in JP-A-2007-129193 may be performed in order to reduce the reflection of the laser beam.

  The laser used in the process of FIG. 1B is not particularly limited, but a carbon dioxide laser is suitable from the viewpoint of processing efficiency and cost. The carbon dioxide laser uses a wavelength of 9.3 μm to 10.6 μm which is an infrared wavelength region. The processing energy can be appropriately selected depending on the thickness of the copper foil 3 on the surface layer side, and can be perforated by irradiation with one shot at, for example, 8 to 27 mJ. More preferably, the copper surface at the via bottom can be cleaned by irradiating the second shot at 2 to 5 mJ, which is a low processing energy. Here, the processing energy (J) of the carbon dioxide laser is calculated by dividing the output (W) required for processing by the frequency (Hz). Note that it is not always necessary to perform two-shot irradiation. If necessary, three or more shots may be irradiated.

  After the step of FIG. 1B, in order to improve the removal property of smear S, a swelling treatment step of immersing the multilayer laminate in a non-oxidative swelling agent (not shown) is performed, and the smear S is swollen as shown in FIG. 2A. Let The non-oxidizing swelling agent is not particularly limited as long as it is non-oxidizing and permeates into the resin to swell the resin. For example, a solution obtained by dissolving an organic solvent such as N-methyl-2-pyrrolidone, butyl cellosolve, N, N-dimethylformamide, glycols, methyl ethyl ketone, acetone or the like in an alkaline solution can be used. As the alkaline solution, an aqueous sodium hydroxide solution, an aqueous calcium hydroxide solution, an aqueous potassium hydroxide solution, or the like can be used. Further, an aqueous sodium hydroxide solution can be used alone as a non-oxidizing swelling agent. From the viewpoint of the swelling effect, those obtained by dissolving the above listed organic solvents in an aqueous sodium hydroxide solution are preferable. In addition, the pH of a non-oxidizing swelling agent is about 8-14, for example.

  35 to 70 degreeC is preferable and the process temperature in the said swelling process process has more preferable 40 to 50 degreeC. If processing temperature is 35 degreeC or more, the swelling effect will become high. On the other hand, if processing temperature is 70 degrees C or less, it is advantageous in terms of cost. The treatment time in the swelling treatment step is preferably 10 seconds to 300 seconds, more preferably 15 seconds to 60 seconds, from the viewpoint of the swelling effect. In addition, it is preferable to provide a water washing process after the swelling process process and before the microetching process process demonstrated below.

  After the swelling treatment step, a microetching treatment step is performed in which a microetching agent (not shown) is brought into contact with the multilayer laminate. As a result, as shown in FIG. 2B, the copper surface at the bottom of the via is slightly etched (microetching), and the smear S remaining at the bottom of the via is lifted. The microetching agent is not particularly limited as long as the copper surface can be microetched, but it is preferable to use a microetching agent in which hydrogen peroxide and sulfuric acid are dissolved in a solvent such as water because the via bottom can be uniformly microetched. As a method of bringing the microetching agent into contact with the multilayer laminate, a method by dipping or spraying can be adopted. However, the surface on which the via of the multilayer laminate is formed (in the case of FIG. 2B, the copper foil 3 on the surface layer side) ) Is preferable because the smear S can be sufficiently lifted without excessive etching of the via bottom.

  The etching amount of the via bottom in the microetching treatment step is preferably 1 to 7 μm, and more preferably 2 to 5 μm, in order to suppress the excessive etching of the via bottom and make the smear S rise. In order to control the etching amount of the via bottom within the above preferable range, for example, when spraying is employed, the temperature of the microetching agent is set to 20 ° C. to 35 ° C., the spray pressure is set to 0.05 MPa to 0.3 MPa, and the processing is performed. What is necessary is just to perform spray processing by setting time to 10 seconds-120 seconds. The etching amount can be obtained by observing a cross section of the via before and after the treatment.

  In the case of the direct laser method, at the time of laser processing, protrusions formed by copper scattering on the surface of the copper foil 3 around the via opening and copper burrs formed at the periphery of the via opening may remain. . If the copper plating process is performed in the next step without removing the scattered copper and burrs, defects such as abnormal deposition of plated metal may occur. In this case, if a microetching agent containing hydrogen peroxide and sulfuric acid (hereinafter simply referred to as “microetching agent”) is used as the microetching agent, the microetching treatment of the via bottom and the removal of scattered copper and burrs are performed. Can be performed simultaneously. Hereinafter, a microetching agent suitable for removing scattered copper and burrs will be described.

  When performing the microetching process by spraying, the surface of the copper foil 3 where the scattered copper and burrs are present is directly exposed to the microetching agent from the spray, so that the microetching agent is always replaced, that is, fresh. The micro-etching agent is always being supplied.

  On the other hand, since the inside of the via is a very narrow portion, the replacement of the microetching agent is small, and it is considered that the state is close to the immersion treatment using the microetching agent.

  Therefore, in order to prevent excessive etching of the inner copper layer 1b located at the bottom of the via, a microetching agent having a slow etching rate by dipping may be used.

  As the microetching agent that satisfies the above requirements, a microetching agent having an etching rate of 3 to 5 times that of the immersion treatment in the spraying treatment is preferable, and a microetching agent that is 3.5 to 4 times more preferable. According to such a microetching agent, it is possible to make the smear S float up while suppressing excessive etching of the via bottom, and to improve the removal of scattered copper and burrs.

  As for the etching rate in the spray process, an appropriate pressure is set from the range of spray pressure (0.05 to 0.3 MPa) normally set in the spray process, and the micro-etching agent is appropriately set in the range of 20 to 35 ° C. In a state where the temperature is maintained, the speed when etching is performed for a predetermined time (for example, 1 minute) is measured. On the other hand, the etching rate in the immersion treatment is measured by immersing in a microetching agent having the same temperature as the spray treatment to be compared and etching for the same time as the spray treatment to be compared. Then, the etching rate in the spray process is compared with the etching rate in the immersion process. The etching rate can be obtained by dividing the amount of weight loss of copper before and after etching when a general electrolytic copper foil is microetched by the etching time.

  In order to make the etching rate in the spray treatment 3 to 5 times the etching rate in the immersion treatment, for example, various additives such as a surfactant may be added to the microetching agent. Specifically, an aliphatic or alicyclic amine, an alcohol, a tetrazole compound, a methyl ester compound, a nonionic surfactant, or the like may be blended.

  The aliphatic amine is preferably an aliphatic amine having 1 to 12 carbon atoms, and specific examples include tri-n-butylamine, ethylenediamine, and 2-ethylhexylamine.

  Specific examples of the alicyclic amine include cyclohexylamine and dicyclohexylamine.

  Specific examples of the alcohol include glycols such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, and tripropylene glycol.

  Specific examples of the tetrazole compounds include 1H-tetrazole, 5-methyl-1H-tetrazole, 5-phenyl-1H-tetrazole, 5-mercapto-1H-tetrazole, and 1-methyl-5-ethyl-1H-tetrazole. Etc.

  Specific examples of the methyl ester compound include ethyl acetate, isopropyl acetate, butyl acetate and the like.

  Specific examples of the nonionic surfactant include propylene diglyceryl ether, polyethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether and the like.

  One or two or more of the above listed additives can be appropriately selected and used. For example, in order to increase the etching rate in the spray treatment, one or more kinds selected from aliphatic amines, alicyclic amines, alcohols, methyl ester compounds, and nonionic surfactants may be blended. . On the other hand, a tetrazole compound may be added to slow down the etching rate in the immersion treatment. In particular, when a tetrazole compound and an alicyclic amine are used in combination, excessive etching of the via bottom is effectively suppressed, copper scattered matters and burrs are more easily removed, and the via bottom is more uniformly micronized. This is preferable because it can be etched. Although the usage-amount of these additives is not specifically limited, 0.001-2 weight% is preferable with respect to the microetching agent whole quantity, and the range of 0.01-0.5 weight% is more preferable.

  In order to obtain a microetching agent having higher removability of scattered copper and burrs, the concentration of hydrogen peroxide in the microetching agent is preferably 1 to 15% by weight, and 2 to 10% by weight. More preferably, it is more preferably 2 to 5% by weight.

  Further, in order to obtain a microetching agent having higher removability of scattered copper and burrs, the concentration of sulfuric acid in the microetching agent is preferably 3 to 25% by weight, more preferably 5 to 20% by weight. More preferably, it is more preferably 6 to 10% by weight.

  After the micro-etching process, the smear S floating from the via bottom is removed by performing an ultrasonic process that applies ultrasonic waves while the multilayer laminate is immersed in a liquid (not shown). (FIG. 2C). As the liquid used in the ultrasonic treatment step, for example, any liquid such as an acid-soluble liquid, an alkaline solution, and water can be used as appropriate. However, when water is used, the safety is high and the management is easy. Is particularly preferable.

  The application condition of ultrasonic waves is, for example, when water (temperature 10 to 70 ° C.) is used, it is preferably applied at 28 kHz to 45 kHz for 10 seconds to 300 seconds, and applied at 28 kHz to 45 kHz for 20 seconds to 300 seconds. More preferably. If the frequency is within the above range, the removal of smear S can be improved without damaging the substrate. Moreover, if the application time is within the above range, the smear S can be reliably removed and the production efficiency can be improved.

  Although the illustration of the process of the multilayer laminate after the ultrasonic treatment is omitted, for example, the inner wall of the via is plated with copper, and the upper and lower copper foils 3 are patterned to form a copper wiring. It can be.

  Hereinafter, in order to facilitate understanding of the present invention, the present invention will be further described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

  R-1766 made by Matsushita Electric Works was used as the core material with copper layers formed on both sides of the insulating base material, and a prepreg having a thickness of 60 μm (R1661ED made by Matsushita Electric Works) was laminated on both sides of the core material. A copper foil having a thickness of 12 μm (3EC-III manufactured by Mitsui Mining & Mining) was laminated on the opposite side of the material to produce a multilayer laminate shown in FIG. 1A. However, since it is a test substrate, the following treatments were performed on both the outer layer and the inner layer without patterning (without forming wiring).

  First, the copper foil on the surface layer side of the test substrate was etched with a sulfuric acid / hydrogen peroxide-based laser processing pretreatment agent (MEC V bond manufactured by MEC Co., Ltd.), and the thickness of the copper foil on the surface layer side was set to 9 .6 μm. By performing this laser processing pretreatment, laser processing can be performed with low energy.

  Next, using a carbon dioxide laser machine (LC-2G212 / 2C manufactured by Hitachi Via Mechanics), the following processing is performed so that the diameter on the laser irradiation side (surface side) is 100 μm and the diameter on the bottom side is 80 μm to 100 μm. Vias were formed under conditions. In the description of the following conditions, before and after “/” indicate the first and second conditions when laser irradiation is performed by two-shot irradiation.

(Laser processing conditions)
Number of shots: 2 shots Frequency: 1000Hz
Processing energy: 17.75mJ / 3.60mJ
Pulse width: 36 μs / 10 μs

  Next, under the conditions shown in Tables 1 and 2, the test substrate after laser processing was processed in the order of the swelling treatment step, the microetching treatment step, and the ultrasonic treatment step. All the swelling treatment steps were treated by dipping, and all the microetching treatment steps were treated by spraying. However, in the microetching treatment step of Comparative Example 4, the treatment was performed by spraying using an etching agent for circuit formation instead of the microetching agent. Further, a water washing step was provided between the swelling treatment step and the microetching treatment step. In the ultrasonic treatment process, ULTRASONIC CLEANER VS-100III manufactured by Seiei Iuchi is used as an ultrasonic cleaner, and the test substrate is immersed in ion exchange water at a temperature of 25 ° C. in Tables 1 and 2. Ultrasonic waves were applied according to the conditions shown.

  Next, in order to facilitate confirmation of smear, platinum deposition was performed on the via bottom of the treated test substrate. Then, the cut surface of the via bottom was observed at a magnification of 3500 times with an FE-SEM (JSM-7000F, manufactured by JEOL Ltd.), and the maximum value of the length L (see FIG. 3C) of the smear remaining on the via bottom was measured. did. At this time, in each Example and each Comparative Example, the maximum value was measured for five vias, and the average value of these maximum values was calculated. About the obtained said average value, the smear removal property was evaluated by the following reference | standard.

(Evaluation criteria for smear removal)
The average value is less than 2 μm: ◎
The average value is 2 μm or more and less than 15 μm: ○
The average value is 15 μm or more and less than 30 μm: Δ
The average value is 30 μm or more: ×

  As shown in Table 1 and Table 2, in each of Examples 1 to 15, smear removability was improved as compared with Comparative Examples 1 to 4.

A and B are sectional views according to processes for explaining an example of the method for producing a printed wiring board of the present invention. AC is sectional drawing according to process for demonstrating an example of the manufacturing method of the printed wiring board of this invention. FIGS. 4A to 4C are cross-sectional views for each process for explaining the conformal mask method. FIGS.

Explanation of symbols

1 Core material 1a Insulating substrate 1b Copper layer 2 Resin layer 3 Copper foil BV Blind via

Claims (6)

In a method for manufacturing a printed wiring board in which a via is formed by irradiating a laser beam to a multilayer laminate in which a resin layer and a copper layer are laminated,
A swelling treatment step of immersing the multilayer laminate after irradiation with laser light in a non-oxidizing swelling agent;
A microetching treatment step for bringing a microetchant into contact with the multilayer laminate after the swelling treatment step;
Look including an ultrasonic treatment step of applying ultrasonic waves while dipping the multilayer laminate after the microetching step in the liquid,
A method for producing a printed wiring board, wherein smear is removed by the swelling treatment step, the microetching treatment step, and the ultrasonic treatment step without using an oxidizing resin solubilizer .   The method for manufacturing a printed wiring board according to claim 1, wherein the microetching agent is a microetching agent containing hydrogen peroxide and sulfuric acid.   The printed wiring board manufacturing method according to claim 2, wherein the microetching agent further includes a tetrazole compound and an alicyclic amine.   The method for manufacturing a printed wiring board according to any one of claims 1 to 3, wherein the microetching treatment step is a step of spraying the microetching agent onto a surface of the multilayer laminated board on which a via is formed.   The method for producing a printed wiring board according to claim 1, wherein the non-oxidizing swelling agent is an alkaline solution containing an organic solvent or an aqueous sodium hydroxide solution.   The method for producing a printed wiring board according to claim 1, wherein the ultrasonic treatment step is a step of applying ultrasonic waves in a state where the multilayer laminated board is immersed in water.