JPH0931886A - Base paper for electrical insulating laminated sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject base paper, improved in silver migration resistance and useful for printed wiring substrates, etc., without deteriorating the suitability to processing such as varnish impregnating properties and heat resistance and characteristics of laminated sheets by adding zeolite to a pulp raw material for the base paper used in the laminated sheet. SOLUTION: This base paper for electrical insulating laminated sheets is obtained by adding zeolite into a raw material slurry before wet forming a sheet of paper, impregnating or coating the resultant base paper after forming the sheet with a zeolite dispersion, reducing residual Na<+> ions in the base paper and reducing the advance rate of the migration of Ag<+> ions advancing in the circuit substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a base paper for electrically insulating laminates, which is a material for printed wiring boards and the like, and more specifically, it is suitable for impregnating varnish, heat resistance and the like, and impairing laminate properties. And a laminated base paper having improved silver migration resistance.

[0002]

2. Description of the Related Art Ordinary laminates, especially laminates for electrical insulation, are obtained by impregnating a laminate base paper with a thermosetting resin such as phenol resin or epoxy resin, and heating and drying it into a prepreg of a semi-cured resin. It is manufactured by laminating a plurality of these prepregs and thermocompressing them together with a metal foil. Such a laminated plate is relatively inexpensive and almost satisfies the performance required for use in ordinary electric or electronic devices, and is therefore mainly used for household electric appliances.

However, due to the recent lighter, thinner, shorter, and smaller electric products, the packaging density of electric parts has increased, and the conductor patterns of printed wiring boards have become finer. Furthermore, even in printed wiring boards using paper as a base material, the conductor patterns are becoming double-sided, and silver through holes have been used for the purpose of electrical connection between the front and back. Therefore, not only the workability, dimensional stability, and punchability of the laminated plate,
The deterioration of electrical insulation due to the migration phenomenon of silver has become a problem, and demands for improvement of silver migration prevention performance (hereinafter referred to as silver migration resistance) are becoming more and more strict.

Conventionally, pulp used for laminated board base paper has been unbeaten bleached kraft pulp (LBK) made from hardwood wood.
P) is generally used, but depending on the application, it may be blended with bleached softwood kraft pulp to increase the strength of the laminated base paper, or blended with unbleached pulp for the purpose of cost reduction, or high In some cases, sulfite pulp (SP) is used for whitening. Such pulp is made by a known paper machine, and the density of the laminated base paper obtained is as low as 0.45 to 0.55 g / cm ³ .

In order to improve the migration of silver in a printed wiring board, the properties required for the base paper are that there are few residual ions in the base paper that contribute to the ionization of silver and the precipitation as metallic silver, and a thermosetting resin. The good impregnating property is. In particular, the base paper generally contains 100 to 200 ppm of Na ⁺ as residual impurity ions, which is considered to be the cause of increasing the occurrence frequency of the silver migration phenomenon. Therefore, it is necessary to reduce the residual Na ⁺ ions in the base paper. Is considered to be very effective as a measure for improving the resistance to silver ion migration of the laminated sheet using the base paper.

In order to solve the above problems, a method of using a resin varnish containing an inorganic ion exchanger (JP-A-2-
JP-A-133442 and JP-A-5-162245) are known, but in the case of a paper-based phenolic resin laminated board using laminated board base paper, the laminated board base paper is manufactured from pulp fibers. In the above method, the inorganic ion exchanger does not take time to sufficiently remove the impurity ions in the pulp, so it is not a fundamental solution and the silver migration resistance is not sufficient. .

In Japanese Patent Laid-Open No. Hei 5-162245, an inorganic ion exchanger layer is provided on the surface of a laminated plate so that residual metal ions in the base paper do not affect the metal foil. However, no effect can be obtained for suppressing migration between through holes. In Japanese Patent Laid-Open No. 63-1452, a filter for removing ions from various solutions is designed to carry an inorganic ion exchanger between pulp fibers, but this method results in a large particle size. Inorganic ion-exchanger particles or inorganic ion-exchanger particles that have undergone secondary agglomeration in the wet papermaking raw material are present in the paper substrate, resulting in poor phenol varnish impregnation,
It cannot be easily adopted because it causes poor heat resistance after molding.

On the other hand, a method of impregnating a glass nonwoven fabric with an organic binder containing a metal migration inhibitor is proposed in a laminate using a glass nonwoven fabric as a substrate (Japanese Patent Laid-Open No. 6-158492). In the case of board base paper, it is difficult to adopt it because of the large cost increase.

[0009]

SUMMARY OF THE INVENTION In view of the above situation, the present inventors have found that in order to suppress silver migration of a printed wiring board, the relationship between the silver migration resistance of the laminate and the residual ions in the base paper and the silver ion trapping agent. As a result of various studies on the effect of the above, it was found that the silver migration resistance can be significantly improved by adding zeolite to the electric insulating laminate base paper, and the present invention has been completed.

It is an object of the present invention to provide a laminated base paper having good silver migration resistance without deteriorating the processability such as varnish impregnation property, heat resistance and the like and laminated plate properties.

[0011]

The present invention includes the following aspects. [1] An electrical insulating laminated board base paper obtained by wet-making paper using pulp as a main raw material, and containing zeolite. [2] The electrical insulating laminate base paper according to [1], wherein the zeolite is a zeolite in which sodium in the composition is replaced with hydrogen.

[3] Zeolite is contained in an amount of 1 to 10% by weight based on the weight of absolutely dry pulp [1] or [2].
The electrical insulating laminated board base paper described. [4] The electrically insulating laminated board raw paper according to [1] or [2], wherein the zeolite is an A-type zeolite.

[5] Maximum particle size of zeolite is 50 μm
An electrically insulating laminated board raw paper according to [1], [2], [3] or [4] below. [6] Pulp contains hardwood bleached kraft pulp [1]
The electrical insulating laminated board base paper described.

[7] An electrically insulating laminated sheet obtained by laminating two or more prepregs impregnated with a thermosetting resin on the electrically insulating laminated sheet base paper as one of [1] to [6] and integrating them.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, it is important to reduce residual Na ⁺ ions in the base paper by adding zeolite to the pulp raw material for the base paper for laminated board. That is,
Since zeolite acts as a very effective inorganic ion exchanger, zeolite is added to the raw material slurry before wet papermaking, or by impregnating or coating the zeolite dispersion on the raw paper after papermaking, Residual N
It can be presumed that the a ⁺ ion can be reduced and the silver ion migration resistance can be improved.

Further, in the present invention, by adding zeolite to the pulp raw material for laminated board base paper, Ag ⁺ ions advancing in the circuit board are trapped in the zeolite, and there is also an effect of decreasing the migration progressing speed. . That is,
The migration that occurs in a laminated plate made of paper and a resin such as a phenol resin as a raw material proceeds near the pulp fiber (fiber-phenol resin interface) and in the pulp fiber, but zeolite is a very effective Ag ⁺ ion trapping agent. Since it acts as an agent, by adding zeolite to the raw material slurry before wet papermaking, or by impregnating or coating the raw paper after papermaking with the zeolite dispersion liquid, Ag ⁺ ions that proceed in the circuit board It is estimated that it will be captured in.

The zeolite used in the present invention is
It is a crystalline aluminosilicate, and its general structural formula is as follows. xM _n O · Al ₂ O ₃ · ySiO ₂ · zH ₂ O Here, M represents a metal ion such as sodium, x,
y and z show the molar ratio of each component.

Currently available synthetic zeolites are A type (x = arbitrary, y = 2, z = 4.5), X type (x = arbitrary, y = 2.5, z = 6), Y type (x = arbitrary) , Y = 4.8,
z = 8.9), MFI type (M = Na, x = 1, y = 10 to 100)
, Z = arbitrary), etc., and the zeolite used in the present invention is not particularly limited to the above specific type.

However, since the A type zeolite is excellent in the ability to capture Ag ⁺ ions, the zeolite used in the present invention is preferably the A type zeolite. on the other hand,
Although cheap natural zeolite is also commercially available, its composition is not constant, and the ion exchange capacity and Ag ⁺ ion trapping capacity vary greatly depending on the place of production and the time. Therefore, the zeolite used in the present invention is a synthetic product. Preferably there is.

Further, usually commercially available zeolite contains sodium as a metal ion (M). Such a normal zeolite has a crystal structure of N
a ⁺ ions release, since the adsorption of Ca ^{2 +,} Mg ^{2 +} ions, are often used as detergent builders. However, the zeolite used in the present invention,
It is preferable that exchange ions such as Na ⁺ → H ⁺ have been subjected to a substitution treatment in advance such as zeolite used for a catalyst. This substitution-treated product is obtained by subjecting zeolite synthesized by a usual method to acid treatment and then drying, and the substitution rate can be improved by repeating the same treatment. The zeolite used in the present invention has a Na ⁺ → H ⁺ substitution ratio of 70.
% Or more is more preferable. By using a zeolite having a substitution rate of 70% or more, it is possible to prevent an increase in the amount of Na ⁺ ions in the base paper and more effectively prevent the deterioration of silver migration resistance.

In addition, the maximum particle size of the zeolite used in the present invention is preferably 50 μm or less. If the maximum particle size exceeds 50 μm, when the base paper is impregnated with, for example, phenol varnish or the like to form a laminate, a minute impregnation defect occurs around the zeolite particles, which adversely affects the physical properties of the laminate after forming. May give. However, the maximum particle size of zeolite is determined as follows.

A slurry was prepared by dispersing the zeolite sample to be measured in pure water, and the particle size distribution was measured using a Shimadzu laser diffraction particle size distribution analyzer SALD-1100 (manufactured by Shimadzu Corporation). The integral volume% of the obtained distribution is 99.
The maximum grain size is defined as the grain size at the upper limit of the distribution region of 5%.

However, the smaller the average particle size, the lower the yield in the paper when dispersed and mixed in the raw material. Therefore, when the zeolite is contained in the paper by internal addition, the average particle size of the zeolite used The diameter is preferably 3 μm or more, more preferably the average particle diameter is 5 μm or more.
However, the average particle size is more preferably about 20 μm or less.

As a measure for preventing secondary agglomeration in the raw material dispersion liquid, an appropriate dispersant may be appropriately selected and used, but it does not have adsorption / reaction activity at the Na ⁺ ion trapping point of the zeolite, or Care must be taken to select one that does not bring in new Na ⁺ ions into the system. Specific examples include carbonic acid diphenyl, dibenzyl terephthalate, oxalic acid di-P-methylbenzyl ester, diisobutylene maleic anhydride copolymer ammonium salt (eg, Tespil KP-225W manufactured by Hitachi Chemical Co., Ltd.).

Zeolite is preferably added in an amount of 1 to 10% by weight based on the weight of absolutely dry pulp. If the addition amount is low, the Na ⁺ ion trapping effect is low, and if the addition amount is high, the impregnation rate tends to be lowered during the resin varnish impregnation step, and this may cause a defective impregnation portion.

When the zeolite is added internally, it is desirable to take a sufficient stirring time after the zeolite is added to the raw material slurry so that the zeolite has a large contact time with the pulp and many opportunities. As a result, the ability of zeolite to adsorb Na ⁺ ions is fully exerted, and the effect of improving silver migration resistance is more effectively exhibited. For this stirring, a suitable stirrer such as a low-concentration mixer, a medium-concentration mixer or a static mixer may be appropriately selected and used. Further, in order to maximize the ability of zeolite to adsorb Na ⁺ ions, the zeolite retention temperature in the raw material is 10 to 70 ° C., and the pH during the treatment is 4.0 to 6.0.
Is preferred.

As a method for incorporating zeolite into the base paper, zeolite is added to the raw material slurry as described above.
There are an internal addition method of dispersing and forming a sheet by a normal wet papermaking method, an external addition method of impregnating or coating a zeolite dispersion liquid on a base paper which has already been made into a sheet, and adding the same. Use /
Either method may be used by appropriately selecting in consideration of quality / manufacturing conditions.

The raw material for papermaking of the present invention is not particularly limited, and kraft pulp obtained from wood chips,
Sulfite pulp, mechanical pulp, dissolving pulp, linter, non-wood pulp such as hemp, etc. are used, and synthetic fibers, internal fillers, glass fibers, etc. can be appropriately selected and blended according to the application and quality. .

The method for producing a laminated board from the laminated board base paper of the present invention is not particularly limited, but for example, the laminated board base paper is impregnated with a thermosetting resin and dried, and the prepreg obtained as described above is used. One or more sheets are laminated and molded and integrated at a predetermined temperature and pressure. As the thermosetting resin, a resol type phenol-formaldehyde resin is generally used, but the thermosetting resin is not limited to this, and other examples include ordinary phenol-formaldehyde resin, melamine-formaldehyde resin, urea-formaldehyde resin. Can be illustrated, and is appropriately selected and used.

The conditions of the heating and pressurizing operations for thermosetting are as follows:
It is adjusted according to the type and amount of the thermosetting resin, the structure and dimensions of the laminate, and is not particularly limited. Generally 150-180 ° C
At a temperature of 80 to 120 kg / cm ^{2 and} a pressure of 30 to 60
Done for a minute.

[0031]

The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is of course not limited thereto. In the examples and comparative examples,%
Represents% by weight unless otherwise specified. The pulp, zeolite and treatment method used in the examples are as follows. (1) Pulp Bleached kraft pulp using a mixed material of domestic hardwood.

(2) Zeolite As the zeolite, (a) Mizusawa Chemical Co., Ltd. synthetic zeolite "Mizukashi"
Leaves Y-420 (Y type, Na⁺→ H⁺Ion exchange processing
)): Maximum particle size = 21 μm, average particle size 6 μm. (B) Mizusawa Chemical Co., Ltd. synthetic zeolite "Mizukashi"
Leaves 4A (A type, Na ⁺→ H⁺Ion exchange processing
)): Maximum particle size = 24 μm, average particle size 6 μm. (C) N of Mizusawa Chemical Co., Ltd. synthetic zeolite (B)
a⁺→ H⁺Ion exchange product (exchange rate = 72%): maximum particle size =
23 μm, average particle size 7 μm. (D) Granules of synthetic zeolite (C) manufactured by Mizusawa Chemical Industry Co., Ltd.
Diameter-changed product: maximum particle size = 48 μm, average particle size 19 μm. (E) Granules of synthetic zeolite (C) manufactured by Mizusawa Chemical Industry Co., Ltd.
Diameter-changed product: maximum particle size = 70 μm, average particle size 23 μm. of
Five types were used.

(3) Addition treatment method A predetermined amount of pulp is put in a poly bucket and the pulp concentration is 3%.
Then, the zeolite dispersion was added with a predetermined amount per absolute dry pulp weight, and stirred with a mixer for 45 minutes at room temperature.

Example 1 The above zeolite (a) was contained in an amount of 1.2% based on the weight of the absolutely dry pulp, and the addition treatment of the above (3) was performed. Melamine resin (trade name: Sumirez Resin AC8: manufactured by Sumitomo Chemical Co., Ltd.) was internally added to the pulp after the treatment as a papermaking raw material, and the basis weight was 125 g / m ² , the density was 0.50 g / cm ³
The laminated base paper of No. 3 was made into paper. The residual Na ⁺ of this laminated board base paper
The ion concentration was measured. Further, a laminated board was prepared from this laminated base paper and evaluated for silver migration resistance and heat resistance.

Example 2 A laminated base paper having a basis weight of 125 g / m ² and a density of 0.50 g / cm ^{3 was} prepared in the same manner as in Example 1 except that the type of zeolite treated for pulp was changed to (b). Paper-made. The residual Na ⁺ ion concentration of this laminated base paper was measured. Also, a laminated board was prepared from this laminated board base paper, and silver migration resistance,
The heat resistance was evaluated.

Example ³ A laminated base paper having a basis weight of 125 g / m ² and a density of 0.50 g / cm ^{3 was} prepared in the same manner as in Example 1 except that the type of zeolite treated for pulp was changed to (c). Paper-made. The residual Na ⁺ ion concentration of this laminated base paper was measured. Also, a laminated board was prepared from this laminated board base paper, and silver migration resistance,
The heat resistance was evaluated.

Example 4 A laminated base paper having a basis weight of 125 g / m ² and a density of 0.50 g / cm ^{3 was} prepared in the same manner as in Example 1 except that the type of zeolite treated for pulp was changed to (d). Paper-made. The residual Na ⁺ ion concentration of this laminated base paper was measured. Also, a laminated board was prepared from this laminated board base paper, and silver migration resistance,
The heat resistance was evaluated.

Example 5 A laminated base paper having a basis weight of 125 g / m ² and a density of 0.50 g / cm ^{3 was} prepared in the same manner as in Example 1 except that the type of zeolite treated for pulp was changed to (e). Paper-made. The residual Na ⁺ ion concentration of this laminated base paper was measured. Also, a laminated board was prepared from this laminated board base paper, and silver migration resistance,
The heat resistance was evaluated.

Examples 6 to 9 The above-mentioned zeolite (c) was used in an amount of 0.5% (Example 6), 5.0% (Example 7), 9.0 based on the weight of the absolutely dried pulp.
% (Example 8) and 15.0% (Example 9) were added, and the above treatment was performed. Melamine resin (trade name: Sumiretsu AC8: manufactured by Sumitomo Chemical Co., Ltd.) is used as a papermaking raw material after the treatment, and 1% of the pulp is internally added to the pulp, and the basis weight is 125 g / m 2.
^2. A laminated board base paper having a density of 0.50 g / cm ³ was produced. The residual Na ⁺ ion concentration of this laminated base paper was measured. Further, a laminated board was prepared from this laminated base paper and evaluated for silver migration resistance and heat resistance.

Comparative Example 1 Same as Example 1 without adding zeolite to pulp
Method of basis weight 125g / m^Two, Density 0.50g / cm^ThreeStack of
A board raw paper was made into paper. Residual Na in this laminated base paper ⁺ion
The concentration was measured. Also, a laminated board is made from this laminated board base paper.
Then, the silver migration resistance and the heat resistance were evaluated.

<Method of Measuring Residual Na ⁺ Ions in Base Paper> 100 ml of 0.
Add 1N hydrochloric acid and boil for 1 hour. Then, the solution was filtered and the Na ⁺ ion in the extract was measured by the atomic absorption method and converted into the concentration in the base paper.

<Manufacturing Method of Laminated Plate> A laminated plate base paper is impregnated with a commercially available water-soluble phenolic resin (trade name: Shonor BRL-2854: Showa Highpolymer Co., Ltd.), and a dryer is used. A primary prepreg having a resin / base material ratio of 15:85 was prepared by drying with a commercially available oil-modified phenolic resin (trade name Shonor BLS-3122: Showa Highpolymer Co., Ltd.). Manufactured) and dried to prepare a prepreg having a ratio of the resin and the base material of the water-soluble phenolic resin and the oil-modified phenolic resin of 50:50. Next, stack 8 prepregs, 1
A phenol resin laminate was obtained by pressure molding at 65 ° C. and 100 kg / cm ² for 60 minutes.

<Evaluation Method of Silver Migration Resistance of Laminated Plate> A comb-shaped electrode having a line width of 1 mm and a line gap of 1 mm was formed on the laminated plate with a silver paste, and an ion migration evaluation system (AMI-025-P: Tabai Espec Co., Ltd. was used. ) Made in 50 ° C at 40 ° C and 93% RH in constant temperature and humidity.
The insulation resistance between the electrodes was measured while applying the DC voltage. To prevent condensation at the start of the test, 6
The sample was allowed to stand at 0 ° C. for 1 hour, and after the sample was sufficiently stabilized at that temperature, the humidity was set and the measurement was started 1 hour after the humidity was set. As an evaluation standard, the insulation resistance between electrodes was continuously measured, and it was determined that migration had occurred on the substrate having a resistance of 10 ⁶ Ω or less. From this continuous measurement data, the time until the first migration occurred (failure occurrence time) was used as a criterion for evaluation.

When an ordinary commercially available circuit board is evaluated,
Under the above conditions, durability of 1000 hours or more is required, but when the substrate is not subjected to moisture resistance treatment at all as in the above-mentioned laminated board manufacturing method, one having durability of 250 hours or more is generally good. Is judged.

<Heat Resistance Evaluation Method> The heat resistance of the laminate is evaluated by measuring the solder heat resistance by the following method. 25 (± 1) m based on JIS standard C6481
Create a laminated plate test piece with dimensions of mx 25 (± 1) mm,
It is floated on a molten solder bath at 260 (+2 to −0) ° C., and the time (seconds) until the laminate swells is measured.

Usually, a product having a heat resistance of 10 seconds or more is preferable as a product.

The results obtained in the examples are shown in Tables 1 and 2. As is clear from Tables 1 and 2, a laminate produced from an electrically insulating laminate base paper, which is characterized in that zeolite is added to the paper raw material, has significantly improved silver migration resistance. Understand (Examples 1 to 1
9). Further, it is possible to further improve the silver migration resistance by adopting Na ⁺ → H ⁺ ion exchange treatment as the zeolite used (comparison between Example 2 and Examples 3 to 5). Furthermore, the maximum particle size is 50μ
By adopting a zeolite having a size of m or less, it is possible to improve the silver migration resistance while maintaining the heat resistance of the laminate (compare Examples 3, 4 and 5).
In addition, the amount of zeolite added to the pulp raw material is 1 to 1
A laminate produced from 0% by weight (weight of absolute dry pulp) of the electrically insulating laminate base paper is particularly excellent in heat resistance of the laminate and can improve silver migration resistance.

[0048]

[Table 1]

[0049]

[Table 2]

[0050]

INDUSTRIAL APPLICABILITY The present invention is a laminated board base paper most suitable for producing a laminated board having good heat resistance after processing a laminated board and good silver migration resistance of a printed wiring board. The significance is extremely large.

Claims (3)

[Claims] 1. A base paper for an electrically insulating laminated board, which is a raw paper for an electrically insulating laminated board obtained by wet papermaking using pulp as a main raw material, and containing zeolite. 2. The electrically insulating laminated board base paper according to claim 1, wherein the zeolite is a zeolite in which sodium in the composition is replaced by hydrogen. 3. Zeolite is 1 per weight of absolutely dry pulp.
The electrical insulating laminated board base paper according to claim 1 or 2, which comprises 10 to 10% by weight.