JP4355248B2 - Wiring board manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing a wiring board.

  There are two types of package substrates for mounting integrated circuit chips: organic wiring substrates and ceramic wiring substrates. In recent years, in the field of organic wiring substrates, a build-up method in which a resin insulating layer and a conductor layer are formed one by one on a core substrate has become mainstream. The build-up method is advantageous for finer wiring and has excellent productivity. On the other hand, ceramic wiring boards also have many advantages over organic wiring boards, such as excellent high-frequency characteristics and heat dissipation.

  In recent years, development of a wiring board having a structure that can make use of the characteristics of both, that is, a wiring board in which a resin insulating layer and a conductor layer are formed on a ceramic core board by a build-up method has been promoted (for example, Patent Document 1) below.

In the build-up method, electrical connection between layers is generally made by vias, and this method is also applied to a build-up wiring substrate having a ceramic core substrate. As the via forming method, a laser processing method is one mainstream. When a via is formed by laser processing, a resin residue (smear) is generated on a conductor exposed in the via. Therefore, it is removed by a treatment liquid such as an alkaline permanganate solution or ultrasonic cleaning (for example, the following) Non-patent document 1). This operation is called desmear processing.
JP 2001-284805 A Kiyoshi Takagi "Build-up multilayer printed circuit board technology" Nikkan Kogyo Shimbun, first edition p68-p69

  By the way, the surface conductor of the ceramic core substrate is formed by firing a metal paste containing Ag, W, or the like. Conductors formed by firing often have minute voids. If an attempt is made to expose the surface conductor having such voids by laser processing, the resin may bite into the voids and may not be completely removed by normal desmear treatment. If smears remain, the via electrical connectivity will be adversely affected.

  An object of the present invention is to provide a method for reliably removing smear generated on a surface conductor of a core substrate in a method for manufacturing a build-up wiring substrate using a ceramic core substrate.

Means for Solving the Problems and Effects of the Invention

  In order to solve the above-described problems, the present invention is conducted on a core substrate having a surface conductor formed of a fired metal on the main surface, and is electrically connected to the surface conductor by a resin insulating layer and vias formed in the resin insulating layer. In a method of manufacturing a wiring board provided with a conductor layer, a resin insulation layer forming step of forming a resin insulation layer on the core substrate so as to cover the surface conductor and the main surface; and a resin insulation layer so that the surface conductor is exposed A via forming step for forming a via, a desmear treatment step for removing a resin residue in the via, and a cleaning step for cleaning the inside of the via are performed in this order. In the cleaning step, the inside of the via is washed with a cleaning solution containing hydrofluoric acid. After cleaning, the main feature is to further clean the inside of the via with water. Examples of the fired metal include those mainly composed of Ag. As the core substrate, one using ceramic as a dielectric can be shown. For the via formation step, a laser via process in which via drilling is performed with laser light is suitable. Further, “mainly” means containing the largest amount by mass%.

  In the present invention, in addition to the desmear process after the via formation step, the inside of the via is washed with a cleaning liquid containing hydrofluoric acid, and further, the inside of the via is washed with water. According to this procedure, first, a resin residue is easily removed by cleaning with a cleaning solution containing hydrofluoric acid, and then water is allowed to flow there. That is, the removal efficiency is extremely high as compared with a method of simply washing with water. Since the resin residue can be reliably removed, it is possible to prevent the occurrence of defects such as poor via conduction.

  Further, the core substrate has a structure in which an inner layer conductor and a ceramic dielectric layer are laminated, and a surface conductor is formed on a main surface formed by the ceramic dielectric layer, and the ceramic dielectric layer is made of a low-temperature fired ceramic. What was comprised is suitable. According to the low-temperature fired ceramic, there is an advantage that the core substrate can be produced by a simultaneous firing process using a highly conductive metal such as Ag or Cu.

  The cleaning with water can be performed by spraying pure water toward the bottom of the via. By using pure water, the adhesion of impurities can be prevented as much as possible. Further, by spraying pure water toward the bottom of the via, the resin residue can be removed more efficiently.

  Further, it is desirable that the above-described cleaning liquid further contains nitric acid. Using a nitric hydrofluoric acid-based cleaning solution, even if the resin residue is strongly biting into the void formed at the bottom of the via, hydrofluoric acid dissolves the glass component, and nitric acid is a metal (Ag, Cu) Combined with the action of dissolving the components, the effect of raising the resin residue is high.

  Further, the desmear treatment process can be a process of removing the resin residue in the via with a non-nitric hydrofluoric acid treatment liquid having an etching ability with respect to the resin material constituting the resin insulating layer. In the cleaning process, the cleaning liquid adjusted so that the total amount of nitric acid and hydrofluoric acid is smaller than water in terms of mass is used, and the cleaning time with the cleaning liquid is shorter than the processing time with the processing liquid in the desmear processing process. It is desirable to be In the cleaning process in the via, it is inherently desirable that only the resin residue can be removed. Therefore, the cleaning process using a nitric hydrofluoric acid-based cleaning solution should be performed under the condition that the etching of the surface conductor proceeds slowly. For this purpose, as described above, a cleaning solution having a relatively low etching ability should be used. Is appropriate. In addition to this, it is possible to prevent the surface conductor exposed at the bottom of the via from being excessively etched by shortening the processing time using the processing liquid in the desmear processing step.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 schematically shows a cross-sectional structure of a wiring board 1 according to an embodiment of the present invention. The wiring substrate 1 includes a core substrate 2 having a multilayer structure in which ceramic dielectric layers 50, 51, 52 and conductor layers 60, 61, 62, 63 are alternately stacked, and a first main surface CP of the core substrate 2. On the side, a build-up wiring laminated portion 3 disposed on the core substrate 2 is provided. The buildup wiring laminated portion 3 includes buildup resin insulation layers 7 and 9 and conductor layers 8 and 10.

  The core substrate 2 is provided with a plurality of via conductors 4 that electrically connect the conductor layers 60 to 63 so as to penetrate each of the ceramic dielectric layers 50 to 52 in the thickness direction. These via conductors 4 provide electrical connection between layers. The conductor layers 60 to 63 include surface conductors 63 and 60 provided on the main surfaces CP and DP of the core substrate 2 and inner layer conductors 61 and 62. The surface conductor 60 on the second main surface DP side of the core substrate 2 has a mounting pin 14 brazed with a brazing material 16 (including solder), and serves as a mounting pad for electrical connection with another mounting substrate or the like. It's being used. Further, as shown in the figure, a passive element such as a chip capacitor 18 may be mounted on the core substrate 2 with brazing materials 20 and 20. In the present embodiment, a single-sided wiring board in which a resin insulating layer and a conductor layer are laminated only on one side of the core substrate 2 is shown, but a resin insulating layer and a conductor layer can be laminated on both sides of the core substrate 2. .

  The first buildup resin insulation layer 7 is disposed so as to cover the first main surface CP of the core substrate 2, and has a portion in contact with the ceramic dielectric layer 52 and a portion in contact with the surface conductor 63. Furthermore, a conductor layer 8 is formed on the surface of the first buildup resin insulation layer 7 by Cu plating. The conductor layer 8 and the surface conductor 63 of the core substrate 2 are connected to each other through vias 34. The via 34 in FIG. 1 shows a filled via in which the hole is filled with Cu plating. However, conformal vias in which Cu plating is applied only to the inner walls of the holes can also be employed.

  A second buildup resin insulation layer 9 is further provided on the conductor layer 8. The second buildup resin insulation layer 9 can be composed of a resin composition having the same composition as the first buildup resin insulation layer 7. On the surface of the second buildup resin insulation layer 9, a conductor layer 10 is further formed by Cu plating. Part or all of the conductor layer 10 is used as a metal terminal pad. The conductor layer 8 and the conductor layer 10 disposed above and below the second buildup resin insulation layer 9 are connected to each other by filled vias 34 penetrating the second buildup resin insulation layer 9 vertically.

  The second buildup resin insulation layer 9 is covered with a solder resist layer SR1 having an opening so that the conductor layer 10 is exposed. The conductor layer 10 exposed from the opening of the solder resist layer SR1 is subjected to Ni / Au plating, Sn-Pb eutectic solder, Sn-Ag, Sn-Cu, Sn-Ag-Cu, Sn-Sb, etc. Solder bumps 11 made of solder substantially containing no Pb are provided. A similar solder resist layer SR2 is formed on the second main surface DP side of the core substrate 2.

  Build-up resin insulation layers 7 and 9 and solder resist layers SR1 and SR2 are manufactured, for example, as follows. That is, a photosensitive resin film obtained by forming a photosensitive resin composition varnish into a film is laminated, and a transparent mask (for example, a glass mask) having a pattern corresponding to the via 34 is overlaid and exposed. The film portion other than the via 34 is cured by this exposure, while the via 34 portion remains uncured, so if it is removed by dissolving it in a solvent, the via 34 can be easily formed in the desired pattern. (So-called photovia process). Further, instead of the photo via process, a laser via process for drilling with a laser can be adopted.

  The build-up resin insulation layers 7 and 9 are made of a resin composition mainly composed of one kind of resin selected from the group consisting of a liquid crystal polymer, a polyimide resin, an epoxy resin, and a fluorine resin. Such a resin composition is obtained by blending a resin as a substrate with additives such as a curing agent and a stabilizer, a filler, and the like as necessary. Examples of the filler include inorganic fillers such as silica powder and glass fiber. The linear expansion coefficient changes according to the amount of filler mixed. When the linear expansion coefficient of the buildup resin insulation layer 7 is close to the core substrate 2, the buildup resin insulation layer 7 has excellent peeling resistance. That is, the build-up resin insulation layer 7 and the core substrate 2 are unlikely to peel off when heat reception and heat dissipation from an integrated circuit chip or the like mounted via the solder bumps 11 are repeated. In addition, both photosensitive and thermosetting can be employ | adopted for the above-mentioned resin composition. In addition, any of a technique of laminating a resin composition formed into a film on the core substrate 2 or the like and a technique of applying a liquid resin composition to the core substrate 2 or the like can be employed.

  The dielectric layers 50 to 52 constituting the core substrate 2 include dielectric loss even in a high frequency region such as alumina ceramic, mullite ceramic, aluminum nitride ceramic, silicon nitride ceramic, silicon carbide ceramic, glass ceramic, low temperature fired ceramic, etc. Is preferably used in the present invention. In particular, it is desirable to use a composite material of glass and a ceramic filler other than glass (hereinafter referred to as glass ceramic) or a high-purity alumina ceramic in terms of excellent surface smoothness upon baking of the dielectric substrate surface. .

  Ceramic dielectric layers 50 to 52 are configured such that the linear expansion coefficient in the temperature range of −55 ° C. or more and 125 ° C. or less is, for example, 3 ppm / ° C. or more and 20 ppm / ° C. or less. The conductor layers 60 to 63 of the core substrate 2 are made of a metal that can be fired simultaneously with the ceramic dielectric layers 50 to 52. Specifically, when firing at a high temperature is required, a refractory metal such as W or Mo is employed. When the ceramic dielectric layers 50 to 52 are composed of a low-temperature fired ceramic (for example, having a firing temperature of 1000 ° C. or less), Ag, an Ag alloy (for example, Ag—Pt, Ag—Pd), Au, Ni, Cu Further, a highly conductive metal such as a Cu alloy can be used. In this embodiment, Ag or an Ag alloy is used.

Hereinafter, the manufacturing process of the wiring board 1 will be described.
First, the core substrate 2 is produced. The core substrate 2 is manufactured using a ceramic green sheet. The ceramic green sheet can be produced by a known doctor blade method. First, raw material ceramic powder made of dielectric ceramic (for example, in the case of glass ceramic powder, mixed powder of borosilicate glass powder and ceramic filler powder such as alumina, BaTiO _3, etc .: average particle size is about 0.3 μm to 1 μm ) Solvent (acetone, methyl ethyl ketone, diacetone, methyl isobutyl ketone, benzene, bromochloromethane, ethanol, butanol, propanol, toluene, xylene, etc.), binder (acrylic resin (eg, polyacrylic ester, polymethyl methacrylate)) , Cellulose acetate butyrate, polyethylene, polyvinyl alcohol, polyvinyl butyral, etc.), plasticizer (butyl benzyl phthalate, dibutyl phthalate, dimethyl phthalate, phthalate ester, polyethylene Glycol derivatives, tricresol phosphate, etc.), peptizers (fatty acids (glycerin triolates, etc.), surfactants (benzenesulfonic acid, etc.), wetting agents (alkyl allyl polyether alcohol, polyethylene glycol ethyl ether, nithyl phenyl glycol, A mixture of additives such as polyoxyethylene ester) is kneaded to form a slurry, which is applied onto a back sheet such as PET using a doctor blade and dried appropriately, thereby producing a ceramic green sheet. Get.

  Next, a metal paste for forming via conductors (hereinafter referred to as via conductor paste) is prepared. The metal powder to be used can be the above-described highly conductive metal, and those having an average particle diameter adjusted in the range of 2 μm to 20 μm are preferable. A via conductor paste can be obtained by blending and preparing an organic solvent such as butyl carbitol in the metal powder so as to obtain an appropriate viscosity.

Next, a metal paste (hereinafter referred to as a conductor layer paste) used for forming the conductor layers 60 to 63 is prepared. The metal powder to be used is preferably the same type as that used in the via conductor paste and having an average particle size adjusted to be as small as 0.1 μm to 3 μm. To this metal powder, an inorganic compound powder having an average particle size of 500 nm or less (preferably 100 nm or less, more preferably 50 nm or less) is blended in the range of 0.5% by mass or more and 30% by mass or less. A metal paste for forming a conductor layer can be obtained by blending and preparing a binder and an organic solvent such as butyl carbitol so as to obtain an appropriate viscosity. The inorganic compound powder may be a ceramic green sheet raw material ceramic powder, or at least one of aluminum oxide (Al ₂ O ₃ ), silicon dioxide (SiO ₂ ), and titanium oxide (TiO ₂ ). You may mix | blend and use the inorganic compound powder (average particle diameter of 100 nm or less, desirably 50 nm or less) which consists of seeds.

  Using the ceramic green sheet and the metal paste produced as described above, the core substrate 2 is produced as follows. As shown in FIG. 2, an unfired via conductor 4 is formed by forming a through hole at a predetermined position of a ceramic green sheet 25 prepared in advance by a technique such as punching or laser and filling via conductor paste. After that, the unfired conductor layer 61 is formed by printing the conductor layer paste on the main surface of the ceramic green sheet 25 by a method such as screen printing. When the formation of the via conductor 4 and the conductor layer 61 is completed in this way, another ceramic green sheet 25 is stacked on the via conductor 4 and the process of pattern printing / ceramic green sheet lamination is repeated to obtain the unfired substrate 20. If this is fired, the core substrate 2 is obtained.

  After producing the core substrate 2 as described above, a silane coupling agent or a titanate coupling agent is applied to the first main surface CP of the core substrate 2 to improve the adhesion to the resin film. The coupling agent is thinly applied to the surface of the core substrate 2 using a spin coater and then dried. After performing the surface treatment in this way, the buildup wiring laminated portion 3 is formed on the first main surface CP side of the core substrate 2 by a known buildup method.

Specifically, as shown in FIG. 3, a semi-cured resin film 7 ′ is laminated on the core substrate 2 so as to cover the surface conductor 63 and the first main surface CP, and then a temperature of 100 ° C. to 200 ° C. Heat to cure. Thereby, the buildup resin insulating layer 7 is formed (resin insulating layer forming step). Subsequently, the build-up resin insulation layer 7 is excavated by laser processing to form a via 34 so that the conductor below one layer, that is, the surface conductor 63 of the core substrate 2 is exposed (via formation step). For laser processing, a gas laser such as a CO ₂ laser or an excimer laser, or a solid-state laser such as an Nd: YAG laser can be used. After completion of the via formation process, a desmear treatment process is performed to remove the resin residue (smear) adhering to the bottom of the via 34, that is, the surface conductor 63.

The method of desmear treatment is roughly divided into a dry type and a wet type. The dry method is a method of removing smear with plasma of O ₂ , CF ₄ or the like. The wet method is a method in which the wiring board workpiece W is immersed in a chromic acid bath, a concentrated sulfuric acid bath, or a permanganate bath. Preferably, as shown in the upper part of FIG. 4, a method of dipping the wiring board workpiece W in an alkaline potassium permanganate solution 40 that is gentle in processing, does not require equipment costs, and is environmentally friendly can be employed. The alkaline potassium permanganate solution 40 that is processing the wiring board workpiece W may be appropriately stirred. Since the alkaline potassium permanganate solution 40 has an etching ability with respect to a resin material constituting the build-up resin insulation layer 7, for example, an epoxy resin, the above desmear treatment and a roughening treatment for forming irregularities on the resin surface Can be used together. In the series of desmear treatment steps, the build-up resin insulation layer 7 is swollen with a liquid containing an organic solvent, and then treated with an alkaline potassium permanganate solution 40 to perform neutralization, washing with water, and drying. After that, it ends.

  Even when the desmear process is sufficiently performed as described above, the resin residue on the surface conductor 63 exposed in the via 34 may not be completely removed. This is because the surface conductor 63 is obtained by firing a metal paste, so that voids are likely to occur. When a laser beam is irradiated to a place where such a void is present, the resin bites into the void and is very difficult to remove. Therefore, in the present invention, the resin residue is surely removed by performing the cleaning process described below following the desmear process.

  First, as shown in the middle part of FIG. 4, the inside of the via 34 of the wiring board workpiece W (see FIG. 3) is cleaned using a fluoric acid-based cleaning solution 42. In the present embodiment, the inside of the via 34 is cleaned by immersing the wiring board workpiece W in the cleaning liquid 42 and stirring the cleaning liquid 42 appropriately, but a method of spraying the cleaning liquid 42 onto the wiring board work W may be used. The nitric hydrofluoric acid-based cleaning liquid 42 contains nitric acid, hydrofluoric acid, and water. In the present embodiment, the cleaning liquid 42 is substantially composed of them.

  The composition of the nitric hydrofluoric acid-based cleaning liquid 42 is desirably adjusted so that the total amount of nitric acid and hydrofluoric acid is smaller than water in terms of mass. Usually, a mixed acid of nitric acid and hydrofluoric acid is strongly acidic and has a strong etching ability. However, in the present invention, since a gentle etching ability is expected, it is preferable to use a material that is greatly diluted with water. For example, by mixing commercially available nitric acid (concentration: about 68%), commercially available hydrofluoric acid (concentration: about 46-50%) and pure water at a ratio of 1: 1: 10, a suitable cleaning solution 42 is obtained. Obtainable.

  Furthermore, it is preferable that the cleaning time with the cleaning liquid 42 having the composition adjusted as described above be shorter than the processing time with the alkaline potassium permanganate solution 40 in the desmear processing step. This can prevent the surface conductor 63 from being etched excessively. Further, the cleaning step can be performed at room temperature, or may be performed within a range of room temperature to several tens of degrees Celsius.

  Next, as shown in the lower part of FIG. 4, pure water 44 is sprayed toward the wiring board workpiece W. Thereby, the resin residue which has not been completely removed in the desmear treatment process is surely removed. One reason why the resin residue removal easiness is improved is that the cleaning liquid 42 corrodes the glass component or metal component around the resin residue that has penetrated into the void, thereby generating a gap between the void and the resin residue. It is done. That is, it can be said that the resin residue can be efficiently removed because water is blown vigorously to the place where the resin residue is slightly lifted.

In addition, the use of pure water 44 can prevent contamination and the like from adhering to the via 34, and is therefore preferable for ensuring better plating properties. The pure water 44 can be sprayed using, for example, a commercially available water jet device (for example, a device that discharges water with a plunger pump). The pressure of the washing water by the water jet device is 50 kgf / cm ² in this embodiment, but can be adjusted to, for example, 10 kgf / cm ² or more and 100 kgf / cm ² or less.

  After performing the cleaning process as described above, the cyan cleaning process and the drying process are performed. If the Ag surface is roughened by performing the cyan cleaning treatment, the adhesion of the Cu film is improved. Next, a thin Cu film is formed in the via 34 and on the surface of the buildup resin insulating layer 7 by Cu sputtering (Cu film forming step). Note that a Cu film can be formed by electroless Cu plating instead of Cu sputtering. Even in that case, the smear in the via 34 is surely removed, so that the plating property is good.

  After the Cu film is formed, the plating resist is patterned and an electrolytic Cu plating process is performed. Then, an unnecessary portion of the underlying Cu film is removed by etching, and the conductor layer 8 of the build-up resin wiring portion 3 is formed. Furthermore, by providing the buildup resin insulating layer 9 and the conductor layer 10, the buildup resin wiring portion 3 is formed. Thereafter, solder resist layers SR1 and SR2 and solder bumps 11 are formed, and mounting pins 14 and chip capacitors 18 are attached to obtain wiring board 1 of FIG.

  In the above-described embodiment, the cleaning process is performed using the nitric hydrofluoric acid-based cleaning liquid 42. However, the cleaning process may be performed using a cleaning liquid composed of hydrofluoric acid and pure water. Also in this case, since there is an effect of floating the resin residue that has penetrated into the via bottom, it is possible to obtain a high resin residue removal effect by performing in combination with water jet cleaning. The mixing ratio of hydrofluoric acid and pure water can be, for example, 1: 5. Further, the remaining steps can be the same as in the case of the nitric hydrofluoric acid-based cleaning liquid 42 already described.

The cross-sectional schematic diagram of the wiring board which has a ceramic core board. Manufacturing process explanatory drawing of the wiring board of FIG. Manufacturing process explanatory drawing following FIG. Manufacturing process explanatory drawing following FIG.

Explanation of symbols

1 Wiring board 2 Core board 7, 9 Build-up resin insulation layer 8, 10 Conductor layer 34 Via 40 Alkaline permanganate solution (treatment liquid)
42 Cleaning liquid 44 Pure water 50, 51, 52 Ceramic dielectric layers 61, 62 Inner layer conductors 60, 63 Surface conductor CP First main surface

Claims (5)

Manufacture of a wiring board in which a resin insulating layer and a conductor layer electrically connected to the surface conductor by a via formed in the resin insulating layer are provided on a core substrate having a surface conductor formed of a fired metal on the main surface In the method
A resin insulation layer forming step for forming the resin insulation layer on the core substrate so as to cover the surface conductor and the main surface, and via formation for forming the via in the resin insulation layer so that the surface conductor is exposed Performing a process, a desmear treatment process for removing the resin residue in the via, and a cleaning process for cleaning the inside of the via in this order,
In the cleaning step, after the inside of the via is cleaned with a cleaning liquid containing hydrofluoric acid, the inside of the via is further cleaned with water.   The core substrate has a structure in which an inner layer conductor and a ceramic dielectric layer are laminated, the surface conductor is formed on the main surface formed by the ceramic dielectric layer, and the ceramic dielectric layer is fired at a low temperature. The method for manufacturing a wiring board according to claim 1, which is made of ceramic.   3. The method of manufacturing a wiring board according to claim 1, wherein the cleaning with water is performed by spraying pure water toward the bottom of the via.   The method for manufacturing a wiring board according to claim 1, wherein the cleaning liquid in the cleaning step further contains nitric acid. The desmear treatment step is a step of removing a resin residue in the via with a non-nitric hydrofluoric acid treatment liquid having an etching ability with respect to a resin material constituting the resin insulating layer,
In the cleaning step, the cleaning liquid adjusted so that the total amount of nitric acid and hydrofluoric acid is smaller than water in terms of mass is used, and the cleaning time by the cleaning liquid is longer than the processing time by the processing liquid in the desmear processing step. The method for manufacturing a wiring board according to claim 4, wherein the wiring board is also shortened.

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