JP5378954B2 - Prepreg and multilayer printed wiring boards - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a prepreg for buildup that can suppress exposure of a base material by suppressing dissolution of an insulating resin layer exposed on an inner peripheral surface of a via hole during desmear processing, and also secure continuity reliability by suppressing remaining of a resin between a conductor circuit of an inner-layer circuit board on a bottom surface of the via hole and plating in the via hole, and a multilayer printed wiring board using the same. <P>SOLUTION: The prepreg for buildup includes a low-solubility resin layer containing the base material in a low-solubility resin in a B stage which is low in solubility in chemicals during the desmear processing and a high-solubility resin layer provided on one surface of the low-solubility resin layer and composed of a high-solubility resin in the B stage relatively higher in solubility in the chemicals during the desmear processing than the low-solubility resin. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a prepreg and a multilayer printed wiring board using the prepreg, and more particularly to a prepreg for buildup and a multilayer printed wiring board using the prepreg.

  Printed wiring boards used in electronic devices, electrical devices, computers, communication devices, etc. are becoming thinner, smaller, and more highly integrated and dense in circuits. Accordingly, multilayer printed wiring boards are used. It is like that.

  And in response to demands for thinning, etc., there is a build-up method in which an inner layer circuit board is used as a core material, and insulating resin layers and conductor circuits are alternately stacked on this surface to form a multilayer printed wiring board. It has been put into practical use (see Patent Documents 1 and 2).

  In the build-up method, for example, the insulating resin layer and the conductor circuit are stacked as follows. An inner layer circuit board provided with a conductor circuit on the surface is used. First, an insulating resin layer and a conductor layer such as copper foil are provided on the surface of the inner layer circuit board.

  Next, a via hole is formed in the insulating resin layer with a laser or the like, a plating layer is formed on the inner peripheral surface of the via hole, a circuit is further formed on the conductor layer, and the inner and outer conductor circuits on both sides of the insulating resin layer are formed by the via hole. Are connected with each other. This build-up process is repeated as necessary to form a desired number of layers of conductor circuits, and a multilayer printed wiring board is produced.

  As a material for forming the insulating resin layer, a metal foil with resin that does not contain a reinforcing base material such as glass cloth may be used. A prepreg produced by impregnating a base material such as a glass cloth with a thermosetting resin and drying it from the viewpoint that rigidity can be imparted to the wiring board is used.

  In such a build-up method, after drilling a via hole, as a pre-processing step for metal plating, the resin residue (smear) remaining in the via hole when removing holes by laser or the like is removed, and the inner and outer conductor circuits are plated Desmear processing is performed for smooth connection.

  In the desmear treatment, a chemical such as an aqueous oxidant solution is mainly used. By treating with such a chemical, the smear of the resin in the via hole is dissolved and removed.

  During this desmear treatment, if the insulating resin layer exposed on the inner peripheral surface of the via hole is excessively dissolved by the chemicals, not only smear, but the substrate such as glass cloth is exposed on the inner peripheral surface of the via hole, and uniform plating is performed. It may become impossible to form a layer. Therefore, conventionally, a prepreg that can form an insulating resin layer that is relatively difficult to dissolve in a chemical during desmear treatment is used to suppress dissolution of the inner peripheral surface of the via hole due to desmear treatment.

JP 2004-356232 A JP 2003/086941 A

  However, when using a prepreg that can form an insulating resin layer that is difficult to dissolve in chemicals during desmear treatment, it remains attached to the conductor circuit of the inner circuit board at the bottom of the via hole, and the resin smear also dissolves. It will be difficult. Therefore, the resin tends to remain between the conductor circuit of the inner layer circuit board and the plating. If the resin remains between the conductor circuit of the inner layer circuit board and the plating, the conduction reliability may be lowered.

  The present invention has been made in view of the circumstances as described above, suppresses dissolution of the insulating resin layer exposed on the inner peripheral surface of the via hole during the desmear process, suppresses the exposure of the base material, and the bottom surface of the via hole. Provided are a prepreg for build-up that can prevent the resin from remaining between the conductor circuit of the inner layer circuit board and the plating in the via hole, and can ensure conduction reliability, and a printed wiring board using the prepreg It is an issue.

  The present invention is characterized by the following in order to solve the above problems.

1stly, the prepreg of this invention is a prepreg for buildup, Comprising: The low solubility resin layer which contains a base material in the low solubility resin of B-stage with low solubility to the chemical | medical agent at the time of a desmear process, Provided on one side of the low-solubility resin layer, and has a high-solubility resin layer made of B-stage high-solubility resin, which has relatively higher solubility in chemicals during desmear treatment than the low-solubility resin. The prepreg is placed on one or both surfaces of the inner layer circuit board with the highly soluble resin layer facing the inner layer circuit board .

Second, in the first prepreg, the base material of the low-solubility resin layer is unevenly distributed from the center in the thickness direction of the low-solubility resin layer to the side opposite to the high-solubility resin layer, and the thickness direction of the base material The distance between the center of the substrate and the surface of the low-solubility resin layer on the side where the base material is unevenly distributed is 0.1 to 0.3 as a ratio to the total thickness of the low-solubility resin layer. The thickness is 20 to 100 μm .

  Third, in the multilayer printed wiring board of the present invention, at least a part of the insulating resin layer in the buildup layer is formed using the first or second prepreg as a material.

  According to the first aspect of the invention, the insulating resin layer is formed by laminating the highly soluble resin layer of the prepreg toward the surface of the inner circuit board, the via hole is drilled by the laser, and then the desmear treatment is performed by the chemical. The low-solubility resin layer exposed to the inner peripheral surface of the via hole can suppress the dissolution of the insulating resin layer and suppress the exposure of the base material, and a uniform plating layer can be formed on the inner peripheral surface of the via hole. Can be formed. Furthermore, since a low-solubility resin layer is located near the bottom surface of the via hole, even if this low-solubility resin remains as a smear in the conductor circuit on the bottom surface of the via hole, it can be easily removed by desmear treatment, It is possible to ensure conduction reliability by suppressing the resin from remaining between the conductor circuit of the inner circuit board and the plating in the via hole.

  According to the second invention, the base material of the low-solubility resin layer is unevenly distributed from the center in the thickness direction of the low-solubility resin layer to the side opposite to the high-solubility resin layer. In addition to the effect of the invention, the base material is positioned in the vicinity of the surface of the insulating resin layer, and the rigidity of the surface is further improved. Therefore, workability at the time of producing the printed wiring board can be improved, and further, warpage in the reflow process can be reduced.

  According to the third aspect, since at least a part of the insulating resin layer in the buildup layer is formed using the first or second prepreg as a material, a uniform plating layer is formed on the inner peripheral surface of the via hole. And conduction reliability can be ensured.

  Hereinafter, the present invention will be described in detail.

  In the present invention, the terms “low-solubility resin” and “high-solubility resin” refer to those having a relatively low dissolution rate when immersed in the same chemical during desmear treatment for the same time. "Resin", the fast one is expressed as "highly soluble resin".

  In the present invention, a resin used for a resin composition for forming a low-solubility resin layer of a prepreg (hereinafter referred to as “resin composition for a low-solubility resin layer”) is used as an electronic insulating material. Although it will not specifically limit if it is a high molecular resin which can be used, For example, thermosetting resins, such as an epoxy resin, a polyimide resin, a phenol resin, a bismaleimide resin, an unsaturated polyester resin, can be used. These may be used alone or in combination of two or more. In addition to these thermosetting resins, thermoplastic resins such as polycarbonate resins, polyphenylene sulfide resins, polyethylene terephthalate resins, and liquid crystal polymers can be used in combination.

  The resin composition for a low-solubility resin layer can be blended with other components in addition to the above-mentioned resin within the range not impairing the effects of the present invention. Examples of such other components include a curing agent, a curing accelerator, an inorganic filler, a modifier, an organic solvent, and the like conventionally blended in a resin composition for a printed wiring board.

  In the present invention, an epoxy resin composition is preferably used as the resin composition for the low-solubility resin layer from the viewpoint of excellent heat resistance and adhesive properties.

  The epoxy resin blended in the epoxy resin composition is not particularly limited. For example, bifunctional epoxy resins such as bisphenol A type epoxy resin and bisphenol F type epoxy resin, and novolac type epoxy resins such as cresol novolac type epoxy resin. , Dicyclopentadiene type epoxy resin, bimethyl type epoxy resin such as tetramethylbiphenyl type epoxy resin, trifunctional type epoxy resin, polyfunctional type epoxy resin such as tetrafunctional type epoxy resin, hydroquinone type epoxy resin, and bromination of these A type or the like can be used. These may be used alone or in combination of two or more.

  A curing agent and, if necessary, a curing accelerator are blended in the epoxy resin composition. Although it does not specifically limit as a hardening | curing agent, For example, phenol resins, such as a novolak-type phenol resin, dicyandiamide, an acid anhydride, amines, etc. are mentioned. These may be used alone or in combination of two or more. Considering solder heat resistance and the like, for example, the curing agent can be blended so that the functional group of the curing agent is in the range of 0.8 to 1.2 equivalents with respect to 1 equivalent of the epoxy group of the epoxy resin. .

  Although it does not specifically limit as a hardening accelerator, For example, an imidazole type compound, an organophosphorus compound, a tertiary amine, a quaternary ammonium salt etc. are mentioned. These may be used alone or in combination of two or more.

  Moreover, an inorganic filler can be mix | blended with an epoxy resin composition from points, such as heat resistance improvement. The inorganic filler is not particularly limited, and examples thereof include synthetic silica, natural silica, glass powder, aluminum hydroxide, magnesium hydroxide, talc, calcined talc, kaolin, calcined kaolin, clay, and calcined clay. These may be used alone or in combination of two or more.

  These inorganic fillers may be subjected to a surface treatment with a silane coupling agent or the like, and the interface strength with the resin can be improved by performing such a surface treatment.

The inorganic filler preferably has an average particle size of 0.3 to 30 μm. If the average particle size is too small, flow characteristics and the like may be deteriorated. If the average particle size is too large, clogging may occur in a filter process for removing foreign substances in the varnish of the epoxy resin composition. The average particle size can be measured by the laser diffraction / scattering method based on the Mie scattering theory. Specifically, the particle size distribution of the inorganic filler is created on a volume basis using a laser diffraction particle size distribution measuring device. Then, the median diameter (d ₅₀ ) is measured, and this median diameter can be used as the average particle diameter.

  Such a resin composition for a low-solubility resin layer such as an epoxy resin composition is blended with a resin as exemplified above, usually with an organic solvent, and further with other components as necessary. These can be prepared by, for example, mixing uniformly using a mixer, nanomill or the like.

  Then, the obtained resin composition for the low-solubility resin layer is impregnated into a base material, and dried in a dryer at, for example, 100 to 180 ° C., so that the semi-cured state (B-stage) low-solubility resin layer Can be produced.

  As the substrate, a sheet-like fiber substrate can be used. Such a sheet-like fiber substrate is not particularly limited, for example, a cloth substrate such as a glass cloth, an aramid cloth, a polyester cloth, a nonwoven fabric substrate such as a glass nonwoven fabric, an aramid nonwoven fabric, a polyester nonwoven fabric, pulp paper, Linter paper or the like can be used.

  At this time, with the substrate as a boundary, the resin layer formed on one surface of the substrate is dried so that the thickness of the resin layer is thicker than the resin layer formed on the other surface to be in a semi-cured state. Thereby, the position of the thickness direction of a base material can be unevenly distributed to one surface side from the center of the thickness direction of a low solubility resin layer. Thus, the base material is located near the surface of the insulating resin layer by unevenly distributing the position in the thickness direction of the base material and positioning it on the side opposite to the highly soluble resin layer described later. The rigidity is further improved. Therefore, workability at the time of producing the printed wiring board can be improved, and further, warpage in the reflow process can be reduced.

  In addition, when the base material such as glass cloth is unevenly distributed in the conventional prepreg as described above, the via hole shape may be distorted after the desmear treatment, which may not be desirable, but the high solubility resin described later on one side of the low solubility resin layer. In the structure of the present invention provided with a layer, the balance of solubility in chemicals in the thickness direction is good, and an appropriate via hole shape can be obtained after desmear treatment.

  The distance between the center in the thickness direction of the base material and the surface of the low-solubility resin layer on the side where the base material is unevenly distributed is a ratio with respect to the thickness of the entire low-solubility resin layer from the viewpoint of improving the rigidity of the surface. It is preferable that it is 0.1-0.3.

  Moreover, it is preferable that the thickness of a low solubility resin layer is 20-100 micrometers. If the thickness is too small, insulation reliability in the thickness direction may not be ensured, and if the thickness is too large, there may be cases where the demand for thinning the printed wiring board cannot be satisfied.

  A highly soluble resin layer can be comprised by the composition similar to said low solubility resin layer, for example. The solubility of the resin can be appropriately changed by a combination of an epoxy resin, a curing agent, a curing accelerator, an inorganic filler, a modifier, etc., but the solubility of the high solubility resin is changed to the solubility of the low solubility resin. It is desirable to make it 4 to 10 times as large. If the solubility of the highly soluble resin is too small, it may be difficult to suppress the resin from remaining between the conductor circuit of the inner circuit board on the bottom surface of the via hole and the plating in the via hole. If the solubility of the high-solubility resin is too high, desmearing may occur up to the interface at the bottom of the via hole, resulting in liquid residue and the like, which may affect the heat resistance.

  The highly soluble resin layer can be produced, for example, as follows. 1stly, the resin composition for high solubility resin layers is thinly apply | coated to one side of a low solubility resin layer with a roll coater etc., and it is set as B stage. Alternatively, second, a B-stage low-solubility resin layer and a B-stage high-solubility resin layer are separately prepared in advance, and a high-solubility resin layer is disposed on one side of the low-solubility resin layer. Laminate with a roll or the like under heat and pressure to integrate.

  The thickness of the highly soluble resin layer is preferably 2 to 5 μm in consideration of smear removability, characteristics as an insulating resin layer, shape retention of the via hole after desmear treatment, manufacturing points, and the like.

  Thus, a prepreg for build-up, a low-solubility resin layer containing a base material in a B-stage low-solubility resin having low solubility in chemicals during desmear treatment, and a low-solubility resin A prepreg of the present invention having a high-solubility resin layer comprising a B-stage high-solubility resin provided on one side of the layer and having relatively higher solubility in chemicals during desmear treatment than a low-solubility resin can get.

  Using the prepreg of the present invention, a multilayer printed wiring board can be produced as follows.

  First, an inner-layer circuit board in which a conductor circuit is formed on one or both sides of a laminated board, or a multilayer inner-layer circuit in which conductor circuits and insulating resin layers are alternately laminated and a conductor circuit is formed on one or both sides of the outermost layer Prepare a board. Here, the surface of the conductor circuit of the inner layer circuit board is preferably subjected to a roughening treatment in advance by a blackening treatment or the like from the viewpoint of improving the adhesion with the insulating resin layer.

  The inner layer circuit board is not particularly limited. For example, a circuit board having a conductor circuit formed on one or both surfaces of a substrate such as a glass epoxy resin substrate, a polyester substrate, a polyimide substrate, a BT resin substrate, or a thermosetting polyphenylene ether substrate. Can be used.

  Next, on one side or both sides of this inner layer circuit board, the prepreg of the present invention is placed so that the highly soluble resin layer is in contact with the inner layer circuit board, and further, if necessary, a metal foil is placed on the outside thereof, for example, Lamination molding is performed by heating and pressing under vacuum. Lamination molding can be performed, for example, under conditions of a temperature of 100 to 200 ° C., a pressure of 0.5 to 5 MPa, and a time of 20 to 100 minutes.

  Next, a hole is formed in the insulating resin layer formed on the surface of the inner layer circuit board by laser processing using a carbon dioxide gas laser, a YAG laser, or the like to form a via hole (blind via).

  For example, a conformal method can be used for drilling the via hole. First, using a dry film or the like, only the metal foil present on the surface of the via hole forming portion is removed by etching. When the portion where the metal foil is removed is irradiated with laser, the remaining surrounding metal foil becomes a conformal mask, and a via hole can be formed only in the portion where the metal foil is removed.

  Alternatively, when a metal foil is not used, a via hole can be formed by directly irradiating a laser only on the surface of the via hole forming portion without using a conformal mask.

  Next, desmear processing in the via hole is performed. As the chemical for desmear treatment, for example, an oxidizing agent aqueous solution or the like can be used, and specifically, for example, an alkaline aqueous solution of potassium permanganate or sodium permanganate, an aqueous sulfuric acid solution of chromic acid or sodium dichromate, or the like. Can be used.

  In addition, before processing with these chemical | medical agents, you may pre-process in a via hole using the alkali swelling liquid known conventionally.

  After the desmear treatment, after neutralizing with a predetermined neutralization solution, the desmeared via hole is subjected to conduction treatment. As the conduction treatment, treatment by dry plating such as vapor deposition, sputtering, ion plating, etc. may be performed, but wet processing such as electroless plating (for example, chemical copper plating), electrolytic plating (for example, electrolytic copper plating), etc. The treatment by plating is preferable in consideration of mass productivity.

  In the case of conducting a wet plating process as the conduction process, an electroless plating is performed on the inner peripheral surface of the via hole, and then a plating layer is formed by electroplating, and a dry film is used in the subtractive method. A circuit is formed on the conductor layer by a tenting method or the like. As a result, the inner and outer conductor circuits on both sides of the insulating resin layer can be connected by the via holes.

  Further, a conductive circuit can be provided on the surface of the insulating resin layer by using an additive method for forming a circuit by performing electroless plating, a semi-additive method for forming a circuit by combining electroless plating and electrolytic plating, or the like.

  As described above, a multilayer printed wiring board is obtained in which conductor circuits and insulating resin layers are alternately laminated, and at least part of the insulating resin layer in the buildup layer is formed using the prepreg of the present invention as a material. The above process can be further repeated to obtain a multilayer printed wiring board having a larger number of layers.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples at all.
<Example 1>
[Preparation of resin composition for low-solubility resin layer and high-solubility resin layer]
The following epoxy resin composition was prepared as a resin composition for a low solubility resin layer. The following were used as a compounding component of the epoxy resin composition. As epoxy resin, 40 parts by mass of “Epiclon HP-7200” manufactured by DIC Corporation, 40 parts by mass of “Epiclon N-690” manufactured by DIC Corporation, and 20 parts by mass of “YDB-400” manufactured by Toto Kasei Co., Ltd. 40 parts by mass of “Phenolite KH-6021” manufactured by DIC Corporation as a curing agent and 0.1 part by mass of “Curesol 2E4MZ” manufactured by Shikoku Kasei Kogyo Co., Ltd. as a curing accelerator What was diluted with MEK was stirred and homogenized to obtain a varnish of an epoxy resin composition.

The following epoxy resin composition was prepared as a resin composition for a highly soluble resin layer. The following were used as a compounding component of the epoxy resin composition. 40 parts by mass of “DER530” manufactured by Dow Chemical Co., Ltd. as epoxy resin, 45 parts by mass of “YD-128” manufactured by Toto Kasei Co., Ltd., and 15 parts by mass of “YDB-400” manufactured by Toto Kasei Co., Ltd. are cured. 40 parts by mass of “Tamanol 752” manufactured by Arakawa Chemical Industries, Ltd. as an agent, and 0.1 part by mass of “Curesol 2E4MZ” manufactured by Shikoku Kasei Kogyo Co., Ltd. as a curing accelerator were diluted with MEK, an organic solvent. Were stirred and homogenized to obtain a varnish of an epoxy resin composition.
[Preparation of prepreg]
A glass cloth (“WEA1078” manufactured by Nittobo Co., Ltd.) was used as a base material, and this glass cloth was impregnated with the above-described epoxy resin composition varnish for the low-solubility resin layer at room temperature, and then about 130 By heating at ˜170 ° C., the organic solvent in the varnish was removed by drying, and the epoxy resin composition was semi-cured to prepare a prepreg. The amount of resin in the prepreg was adjusted to be 200 parts by mass of the resin with respect to 100 parts by mass of the glass cloth. Moreover, it adjusted so that a glass cloth might be located in the center of a prepreg thickness direction.

Next, after applying a varnish of an epoxy resin composition for a highly soluble resin layer on one side of the prepreg using a roll coater, the organic solvent in the varnish is dried by heating at about 130 to 170 ° C. By removing and semi-curing the epoxy resin composition, the low-solubility resin layer of 80 μm thickness containing the base material in the low-solubility resin of B-stage and the thickness of 3 μm consisting of the high-solubility resin of B-stage A prepreg having a highly soluble resin layer was prepared.
[Production of multilayer printed wiring boards]
An inner layer circuit is formed by forming a circuit on a copper foil on both sides of a double-sided copper-clad laminate ("3EC-III" manufactured by Mitsui Mining & Smelting Co., Ltd., thickness 0.2 mm, copper foil thickness 35 μm) and providing an inner layer copper circuit. A plate was made.

  Next, after the blackening treatment liquid is applied to the copper circuit of the inner layer circuit board to perform the roughening treatment, the above-described prepreg is applied to the surfaces on both sides of the inner layer circuit board, and the highly soluble resin layer is applied to the inner layer circuit board. The copper foil (thickness: 12 μm) was placed on the outside, and was heated and pressed under conditions of 170 ° C. and 2.9 MPa.

  Next, an opening having a diameter of 300 μm was formed by dry film exposure and etching at a location where a copper foil via hole on the outermost surface was to be formed.

  A via hole having a diameter of 100 μm was formed in the insulating resin layer exposed at the opening using a carbon dioxide laser processing machine “ML505GT” manufactured by Mitsubishi Electric Corporation.

  Next, a desmear treatment process was performed. The desmear treatment was performed by the MacDermid's desmear process. This desmear process is carried out by swelling treatment with “Macuizer 9204” (35 ° C., 7 minutes), treatment with “Macuizer 9275” (75 ° C., 15 minutes), and neutralization treatment with “Macuizer 9279” (43 ° C., 5 minutes) Minutes).

Next, electroless copper plating (chemical copper plating) was applied to form an electroless plating layer in the via hole, and further electrolytic copper plating (electro copper plating) was applied to form an electrolytic plating layer (thickness 15 μm). Thereafter, an outer layer conductor circuit was formed by a tenting method to produce a multilayer printed wiring board.
<Example 2>
In Example 1, when the base material impregnated with the resin composition for the low-solubility resin layer is dried as described above, it is dried using a horizontal dryer as a dryer, and an uncured varnish-like resin By moving the composition downward as a whole by gravity and drying in such a state to make it semi-cured, the thickness of the resin layer formed on the lower surface of the substrate is formed on the upper surface with the substrate as the boundary A prepreg thicker than the thickness of the resin layer to be formed was produced. The distance between the center in the thickness direction of the base material and the surface of the low-solubility resin layer on the side where the base material is unevenly distributed was 0.2 as a ratio to the thickness of the entire low-solubility resin layer.

Otherwise, in the same manner as in Example 1, the 80-μm-thick low-solubility resin layer containing the base material in the B-stage low-solubility resin and the high-solubility 3 μm-thickness composed of the B-stage high-solubility resin A prepreg having a conductive resin layer and a multilayer printed wiring board using the prepreg were prepared.
<Comparative Example 1>
In Example 1, a prepreg composed only of a low-solubility resin layer without using a high-solubility resin layer was prepared, and a low-solubility resin layer having a thickness of 80 μm containing a base material in a B-stage low-solubility resin And a multilayer printed wiring board using the prepreg.

The following evaluation was performed about said Example and the comparative example.
[Solubility in chemicals during desmear treatment]
The high-solubility resin and the low-solubility resin were immersed in an aqueous oxidizer solution of the chemical during the desmear treatment for the same time, and evaluated according to the following criteria from the relative dissolution rate.
○: A high-solubility resin has a faster dissolution rate than a low-solubility resin.
X: Other than the above.
[Laser processability]
A surface treatment (blackening treatment) of a copper foil of a FR-4 grade double-sided copper clad laminate (copper foil thickness 35 μm) having a substrate thickness of 0.2 mm was used as the inner layer substrate. The prepreg produced as described above was laminated on both surfaces of the inner layer substrate, and heat-pressed under conditions of 170 ° C., 2.9 MPa, and 90 minutes to produce a multilayer board. Thereafter, the copper foil on the surface was removed by etching to obtain a sample for laser processing.

Next, using a laser processing machine “ML505GT” manufactured by Mitsubishi Electric Corporation, the pulse frequency is 1500 Hz, the pulse width is 20 μs, the output is 5.4 mj / pulse, and the number of irradiation pulses is 3 shots as described above. After drilling the obtained laser processing sample, the above desmear treatment was performed, and the inside of the hole was observed using a scanning electron microscope SEM to confirm the presence or absence of a resin residue.
[Conduction reliability: Oil dip test]
The multilayer printed wiring boards for evaluation of Examples 1 and 2 and Comparative Example 1 were immersed in 260 ° C. oil for 30 seconds and then immersed in water at 25 ° C. for 15 seconds for 100 cycles. The number of occurrences of disconnection in 20 test pieces was determined.
[Warpage amount due to reflow process]
A surface treatment (blackening treatment) applied to a copper foil of a FR-4 grade double-sided copper clad laminate (copper foil thickness 35 μm) having a substrate thickness of 0.2 mm was used as the inner layer substrate. The prepreg produced as described above is laminated on both surfaces of the inner layer substrate, and heat-pressed under conditions of 170 ° C., 2.9 MPa, and 90 minutes to produce a multilayer plate for warpage evaluation having a size of 150 mm × 150 mm. did. About this multilayer board for warpage evaluation, the processing which exposes for 10 seconds in the atmosphere of 230 ° C as reflow processing was performed, and the amount of warpage was evaluated. As the amount of warpage, the maximum amount of lifting when a multilayer board for warpage evaluation having a size of 150 mm × 150 mm was placed on a horizontal board was measured.

  The evaluation results are shown in Table 1.

  From Table 1, in Examples 1 and 2 using a prepreg having a low-solubility resin layer containing a substrate and a high-solubility resin layer, there is no resin residue after desmear treatment, and laser workability is good. It also had conduction reliability. In Example 2 in which the glass cloth of the low-solubility resin layer was unevenly distributed from the center in the thickness direction of the low-solubility resin layer to the side opposite to the high-solubility resin layer, the amount of warping due to the reflow process was Example 1. Was significantly reduced.

  On the other hand, in Comparative Example 1 using a prepreg not provided with a highly soluble resin layer, resin residues were observed after desmear treatment, and conduction reliability was also lowered.

Claims (3)

A prepreg for build-up, which is provided on one side of a low-solubility resin layer and a low-solubility resin layer containing a base material in a B-stage low-solubility resin with low solubility in chemicals during desmear treatment is, possess a high solubility resin layer solubility in chemicals during desmear treatment than the low-soluble resin is made of a high solubility resin relatively high B- stage, the inner layer circuit board one or both sides of the A prepreg characterized by disposing the prepreg on the surface with a highly soluble resin layer facing the inner circuit board . The base material of the low-solubility resin layer is unevenly distributed from the center in the thickness direction of the low-solubility resin layer to the side opposite to the high-solubility resin layer, and the base in the thickness direction of the base material and the side where the base material is unevenly distributed The distance from the surface of the low-solubility resin layer is 0.1 to 0.3 as a ratio to the thickness of the entire low-solubility resin layer, and the thickness of the low-solubility resin layer is 20 to 100 μm. The prepreg according to claim 1.   A multilayer printed wiring board in which at least a part of an insulating resin layer in a buildup layer is formed using the prepreg according to claim 1 or 2 as a material.