JPH11307896A - Printed wiring board and mounted circuit board using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printed wired board which has high reliability in connecting through holes, excellent heat and chemical resistance, and good electrical properties, and further provide a mounted circuit board using the printed wired board. SOLUTION: An electrical insulating board 2 is formed of a film which is molded of polymer enabling formation of optically antisotropic molten phase, and the thermal expansion coefficient of the thickness direction of the board 2 is substantially identical with the thermal expansion coefficient of a conductor 5 which is used as plating material of a through hole 4 formed through the board 2 in the thickness direction. When the thermal expansion coefficient of the conductor which is used as plating material of the through hole 4 is P×10<-6> cm/cm/ deg.C, the thermal expansion coefficient of the thickness direction of the above film preferably ranges from (P-10)×10<-6> to (P+10)×10<-6> cm/cm/ deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board having excellent through-hole connection reliability and a mounting circuit board using the same. More specifically, the printed wiring board of the present invention is an excellent material derived from a film formed from a polymer capable of forming an optically anisotropic molten phase (hereinafter, referred to as a liquid crystal polymer) used as an electrically insulating substrate. It has both heat resistance, chemical resistance and electrical properties, and is particularly useful as a multilayer printed wiring board and a mounted circuit board.

[0002]

2. Description of the Related Art Numerous methods have been proposed as processes for manufacturing printed wiring boards, particularly multilayer printed wiring boards, but at present, industrial bases such as equipment and materials have been prepared in accordance with the plating through hole method. I have. This method
Each pattern is electrically connected by forming conductive patterns on the surface and inside of the electrically insulating substrate and plating the inner walls of through holes formed between the patterns. Electroless copper plating and electrolytic copper plating are sequentially performed for plating of this through hole, and the plating thickness is usually about 30 μm except for special cases.

[0003]

Conventionally, a thermosetting resin such as an epoxy resin or a polyimide resin has been frequently used as a material of an electric insulating layer constituting a substrate of a printed wiring board. Here, FR-4, which is a substrate containing an epoxy resin,
Has a thermal expansion coefficient (linear expansion coefficient) in the thickness direction of about 40 × 1 around a glass transition temperature of about 140 to 160 ° C.
0 ⁻⁶ cm / cm / ° C. to about 130 × 10 ⁻⁶ cm / cm /
° C. The FR-4 is a copper-clad laminate in which a glass cloth base material is impregnated with an epoxy resin, and copper foils are adhered on both upper and lower surfaces thereof. The coefficient of thermal expansion in the thickness direction of the polyimide resin is a glass transition temperature of 210-3.
Approximately 30 × 10 ^-6 cm / cm / ° C.
To about 130 × 10 ⁻⁶ cm / cm / ° C. On the other hand, the coefficient of thermal expansion of copper used for plating the through holes is 17 × 10 ⁻⁶ cm / cm / ° C., which is extremely higher than the coefficient of thermal expansion of the thermosetting resin at or above the glass transition temperature. small.

[0004] The thermal expansion coefficient in the thickness direction of a printed wiring board, particularly an electrically insulating substrate constituting the printed wiring board, has a great effect on the connection reliability of the through hole. That is,
If the coefficient of thermal expansion of the electrically insulating substrate and the conductor plated on the inner wall of the through hole are significantly different, the heat cycle causes cracks in the conductor and eventually leads to disconnection. Therefore, in order to improve the connection reliability of the through holes, it is necessary to make the thermal expansion coefficient of the electrically insulating substrate of the printed wiring board as close as possible to that of the conductor.

In recent years, as a new electrically insulating substrate material for printed wiring boards, it has excellent features such as low moisture absorption, heat resistance, chemical resistance, and electrical properties (electrical insulating properties, dielectric properties, etc.). Liquid crystal polymer films have attracted attention. In particular, since the liquid crystal polymer film has extremely low hygroscopicity as compared with the above-mentioned thermosetting resin, it is difficult for the material to be destroyed due to the explosive evaporation of the hygroscopic water at the time of solder reflow, and at the same time, It has features such as extremely small dimensional change due to moisture absorption. However, when such a liquid crystal polymer film is used as an electrically insulating substrate, the thermal expansion coefficient of the conventional one is larger than the thermal expansion coefficient of the conductor applied to the inner wall of the through hole. Cracks may occur and lead to disconnection.

The inventors of the present invention have continued to study the use of a liquid crystal polymer film having the above-mentioned excellent characteristics as an electrically insulating substrate material of a printed wiring board. The inventors have found that the melting point and the coefficient of thermal expansion can be arbitrarily adjusted, and have completed the present invention. SUMMARY OF THE INVENTION It is an object of the present invention to provide a printed wiring board which is excellent in connection reliability of through-holes, and is also excellent in heat resistance, chemical resistance and electrical properties, and a mounted circuit board using the same. is there.

[0007]

In order to achieve the above object, the printed wiring board of the present invention has an electric insulating substrate formed of a liquid crystal polymer film, and penetrates the electric insulating substrate in a thickness direction. In the printed wiring board in which the holes are formed, a thermal expansion coefficient in a thickness direction of the liquid crystal polymer film is substantially equal to a thermal expansion coefficient of a conductor used for plating the through holes.

By subjecting the liquid crystal polymer film to heat treatment, the coefficient of thermal expansion in the thickness direction can be adjusted to be substantially the same as the coefficient of thermal expansion of the conductor used for through-hole plating. As a result, the conductor does not crack even by the heat cycle, and the connection reliability of the through hole of the printed wiring board is improved. Moreover,
Printed wiring boards have the excellent heat resistance, chemical resistance and electrical properties of liquid crystal polymer films. The heat treatment may be performed before or after laminating the metal foil on the film, or may be performed before or after performing through-hole plating. However, due to heat treatment,
As a result of expansion or contraction of the through-hole plating in the thickness direction, the through-hole plating may be disconnected. The temperature of the heat treatment is not particularly limited as long as the liquid crystal polymer film is not thermally degraded. However, in order to obtain a practical effect, the temperature should be 20 ° C. lower than the melting point of the liquid crystal polymer film and 20 ° C. lower than the melting point. Temperature ranges up to higher temperatures can be employed. Further, the means for the heat treatment is not particularly limited, and examples thereof include a hot air circulation furnace, a hot roll, a ceramic heater, and a hot press.

The liquid crystal polymer film is obtained by extruding a liquid crystal polymer. Although any method can be used for the extrusion, the well-known T-die method, inflation method and the like are industrially advantageous. In particular, in the inflation method, stress is applied not only in the mechanical axis direction of the film (hereinafter, abbreviated as the MD direction) but also in a direction orthogonal to the machine axis direction (hereinafter, abbreviated as the TD direction). A film is obtained which has a good balance of mechanical and thermal properties.

The above-mentioned liquid crystal polymer film can have any thickness. For example, a plate or sheet having a size of 5 mm or less is also included. However, when a liquid crystal polymer film is used alone as the electrically insulating substrate of the printed wiring board, the film thickness is preferably in the range of 10 to 150 μm, and more preferably in the range of 15 to 75 μm. If the thickness of the film is too thin, its rigidity and strength will be reduced, so it will be deformed by pressure when mounting electronic components on the obtained printed wiring board, and the position accuracy of the wiring will be deteriorated and defects will occur. Cause. Further, as the electrically insulating substrate of the printed wiring board, a composite of the above film and another electrically insulating material, for example, a glass cloth base material can be used. In addition, additives such as a lubricant and an antioxidant may be added to the film as long as the effects of the present invention are not lost, that is, as long as the physical properties of the film are not impaired.

The printed wiring board is formed by laminating a metal foil such as a copper foil on at least one surface of a liquid crystal polymer film serving as an electrically insulating substrate. At this time, as a material of the metal foil to be used, a metal used for electrical connection is suitable, and in addition to copper, gold, silver, nickel, aluminum and the like can be mentioned. Copper foil is rolled,
Any of those produced by electrolysis can be used, but those produced by electrolysis having a large surface roughness are preferred. The metal foil may have been subjected to a chemical treatment such as acid cleaning usually performed on the copper foil. The thickness of the metal foil used is 10 to 100 μ
m, more preferably 10 to 35 μm.

In laminating the liquid crystal polymer film and the metal foil, a method of bonding using an epoxy adhesive or the like, a method of directly forming the metal foil on the film by vapor deposition, sputtering, plating, etc., and other vacuum pressing equipment And a method of thermocompression bonding using the method described above.

As a method of forming a through hole in a printed wiring board, there are a drilling process, a carbon dioxide laser,
Processing using a laser such as a YAG laser or an excimer laser can be used. When the liquid crystal polymer melts and precipitates inside due to the heat generated during the formation of the through-hole, it is preferable to chemically dissolve and remove it using a general-purpose commercial chemical.

As a method of plating the through holes, a conventionally known method can be used. For example, electroless copper plating and pattern plating with electrolytic copper and / or panel plating are sequentially performed.

In order to further improve the reliability of the connection of the through hole to the heat cycle, the thermal expansion coefficient of the conductor used for the through hole plating should be P × 10 ⁻⁶ cm / cm.
cm / ° C., the coefficient of thermal expansion in the thickness direction of the liquid crystal polymer film is (P−10) × 10 ⁻⁶ cm / cm / ° C.
It is preferable to adjust the temperature to within the range of (P + 10) × 10 ⁻⁶ cm / cm / ° C. Outside of this range, the incidence of cracks in the conductor on the inner surface of the through-hole increases. Here, the P value of a typical conductor such as copper or aluminum is 11 to 30.

The liquid crystal polymer film preferably has a molecular orientation degree SOR of 1.3 or less. The liquid crystal polymer film having the degree of molecular orientation SOR in this range has a better balance of mechanical and thermal properties between the MD direction and the TD direction, and is therefore more practical.

The degree of molecular orientation SOR (Segment Orie)
The term “ntation ratio” refers to an index that gives the degree of molecular orientation of a segment constituting a molecule, and is a conventional M
Unlike OR (Molecular Orientation Ratio), it is a value irrelevant to the thickness of the object. This molecular orientation degree SOR
Is calculated as follows.

First, in a well-known microwave molecular orientation measuring instrument, a liquid crystal polymer film is inserted into a microwave resonant waveguide such that the film surface is perpendicular to the traveling direction of the microwave. The electric field intensity (microwave transmission intensity) of the transmitted microwave is measured, and an m value (referred to as a refractive index) is calculated by the following equation based on the measured value. m = (Z ₀ / Δz) × [1−ν _MAX / ν ₀ ] where Z ₀ is a device constant, Δz is the average thickness of the object, and ν _MAX is the maximum micro-wave when the frequency of the microwave is changed. The frequency that gives the wave transmission intensity, ν _0, is the frequency that gives the maximum microwave transmission intensity when the average thickness is zero (that is, when there is no object).

Next, when the rotation angle of the object with respect to the microwave oscillation direction is 0 °, that is, the microwave oscillation direction and the direction in which the molecules of the object are most oriented, and the minimum microwave transmission m ₀ to m value when the direction that gives strength meets a m value when the rotation angle is 90 ° as m _90, orientation ratio SOR is calculated by m ₀ / m _90.

The required degree of molecular orientation SOR is naturally different depending on the application field of the liquid crystal polymer film of the present invention. However, when SOR ≧ 1.5, the film becomes hard due to the remarkable deviation in the orientation of the liquid crystal polymer molecules. And easily torn in the orientation direction. In the case of a printed wiring board or a multilayer printed wiring board that requires dimensional stability such as no warpage during heating, it is desirable that SOR ≦ 1.3. Especially when it is necessary to almost eliminate the warpage during heating, SO
It is desirable that R ≦ 1.03.

The liquid crystal polymer used in the present invention is not particularly limited, and specific examples thereof include known compounds derived from compounds (1) to (4) and derivatives thereof as exemplified below. Thermotropic liquid crystal polyester and thermotropic liquid crystal polyesteramide can be mentioned. However, it goes without saying that a suitable combination of repeating units is required to obtain a liquid crystal polymer.

(1) Aromatic or aliphatic dihydroxy compounds (see Table 1 for typical examples)

[0023]

[Table 1]

(2) Aromatic or aliphatic dicarboxylic acids (see Table 2 for typical examples)

[0025]

[Table 2]

(3) Aromatic hydroxycarboxylic acid (see Table 3 for typical examples)

[0027]

[Table 3]

(4) Aromatic diamine, aromatic hydroxyamine or aromatic aminocarboxylic acid (see Table 4 for typical examples)

[0029]

[Table 4]

(5) Representative examples of liquid crystal polymers obtained from these starting compounds include copolymers (a) to (e) having the structural units shown in Table 5.

[0031]

[Table 5]

As a liquid crystal polymer, for the purpose of imparting high heat resistance and processability to a film, about 200
In the range of from about 250C to about 400C, especially from about 250C to about 350C.
Are preferred, while liquid crystal polymers having a relatively low melting point are more preferred from the viewpoint of film production. Therefore, when higher heat resistance and a higher melting point are required, a film is manufactured using a liquid crystal polymer having a lower melting point, and the film is subjected to heat treatment to increase the heat resistance and the melting point to the desired values. To explain an example of the condition of the heat treatment, even if the melting point of the obtained film is 283 ° C., if the film is heated at 260 ° C. for 5 hours, the melting point becomes 320 ° C.
become.

The printed wiring board obtained as described above can be obtained by a pin insertion mounting method for mounting electronic components with leads through through holes, a mounting method for mounting electronic components with a case on a pattern surface without passing through through holes, or a bare mounting method. Various electronic components are mounted by a known method such as an IC chip mounting method of mounting an IC chip on a pattern surface to form a mounted circuit board.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a printed wiring board 1. The wiring board 1 uses a liquid crystal polymer film 2 as its electrically insulating substrate, and adheres and laminates metal foils on upper and lower surfaces thereof, and etches these metal foils. The conductive pattern 3 is formed by performing such processes. In addition, a through hole 4 is formed between the conductive patterns 3 and 3 on the upper and lower surfaces so as to penetrate in the thickness direction of the film 2, and a conductor 5 made of, for example, copper is formed on the inner surface. As a result, the upper and lower conductive patterns 3, 3 are electrically connected to each other. An electronic component 6 is soldered to the conductive pattern 3 via, for example, its terminal 7 to form a mounted circuit board 8.

[0035]

EXAMPLES Next, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples. Example 1 First, p-hydroxybenzoic acid and 6-hydroxy-2-
A liquid crystal polymer having a melting point of 283 ° C., which was a copolymer of naphthoic acid, was melt-extruded, and a liquid crystal polymer film having a film thickness of 50 μm and a molecular orientation degree SOR of 1.05 was produced by inflation molding. Next, a copper foil (electrolytic copper) having a thickness of 18 μm, which is a metal foil, was heat-pressed at 300 ° C. on both sides of the liquid crystal polymer film to form a laminate comprising a combination of copper foil / liquid crystal polymer film / copper foil. Produced. Table 6 shows the results of examining the thermal expansion coefficient of the laminated plate in the thickness direction of the film and the reliability of through-hole connection of the laminated plate.

Example 2 The liquid crystal polymer film used in Example 1 was heated at 260 ° C. for 5 hours to increase the melting point to 320 ° C., and a 18 μm thick copper foil (electrolytic copper) was applied to the film at 340 ° C. To produce a laminate comprising a combination of copper foil / liquid crystal polymer film / copper foil. Table 6 shows the results obtained by examining the above properties of the laminate.

Example 3 A laminate having the combination of copper foil / liquid crystal polymer film / copper foil obtained in Example 1 was heated at 260 ° C. for 20 hours to obtain a laminate having a melting point raised to 350 ° C. Was. Table 6 shows the results obtained by examining the above properties of the laminate.

Example 4 A liquid crystal polymer having a melting point of 330 ° C., which is a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, is melt-extruded and has a film thickness of 5 by inflation molding.
A liquid crystal polymer film having a thickness of 0 μm and a degree of molecular orientation SOR of 1.03 was produced. Then, a copper foil (electrolytic copper) having a thickness of 18 μm was heat-pressed at 355 ° C. on both surfaces of the liquid crystal polymer film to prepare a laminate composed of a combination of copper foil / liquid crystal polymer film / copper foil. Table 6 shows the results obtained by examining the above properties of the laminate.

Example 5 The same procedure as in Example 1 was carried out except that the heat and pressure were applied at 290 ° C.
A laminate comprising a combination of copper foil / liquid crystal polymer film / copper foil was prepared. Table 6 shows the results obtained by examining the above properties of the laminate.

Comparative Example 1 An 18 μm-thick copper foil (electrolytic copper) was heated and pressed at 320 ° C. on both sides of the liquid crystal polymer film used in Example 1,
A laminate comprising a combination of copper foil / liquid crystal polymer film / copper foil was prepared. Table 6 shows the results obtained by examining the above properties of the laminate.

Comparative Example 2 A copper foil (electrolytic copper) having a thickness of 18 μm was heat-pressed at 320 ° C. on both sides of the liquid crystal polymer film used in Example 4,
A laminate comprising a combination of copper foil / liquid crystal polymer film / copper foil was prepared. Table 6 shows the results obtained by examining the above properties of the laminate.

The melting point of the liquid crystal polymer film was obtained by observing the thermal behavior of the film using a differential scanning calorimeter. That is, after the film is raised at a rate of 20 ° C./min and completely melted, the melt is heated at a rate of 50 ° C./min.
° C, and the position of an endothermic peak that appeared when the temperature was raised again at a rate of 20 ° C / min was recorded as the melting point of the film.

In measuring the thermal expansion coefficient in the thickness direction of the liquid crystal polymer film, first, copper foil was removed from the film with a ferric chloride solution. Then, using a thermomechanical analyzer (TMA), a pin having a diameter of 1 mmΦ is pressed against the film with a compression load of 5 g, and the temperature is raised from room temperature to a temperature 80 ° C. lower than the melting point at a rate of 5 ° C./min.
Based on the thickness at the time of cooling to 30 ° C. (abbreviated as T1) at a rate of 1 minute, the temperature was raised again to a temperature (abbreviated as T2) at which the pins penetrate the film at a rate of 5 ° C./min. The thermal expansion (abbreviated as TE) was measured, and TE / (T2-T
1) (unit: cm / cm / ° C.) was recorded as the coefficient of thermal expansion in the thickness direction.

In measuring the through hole connection reliability of the laminated plate, 5000 holes having a diameter of 0.3 mm were drilled in the laminated plate, and then electroless copper plating and a resist pattern were formed. By sequentially performing each operation of formation, pattern plating, resist peeling, etching,
A through-hole having a land diameter of 0.5 mmΦ and a hole-wall copper plating thickness of 30 μm was formed. Next, after measuring the resistance value of 5000 through-hole plating by a four-terminal method, a thermal shock test was performed in which one cycle of immersing alternately in an oil bath at 25 ° C. and 260 ° C. for 20 seconds and 5 seconds, respectively, was performed. 2000
The resistance value at the time of repeating the cycle was measured. The rate of increase of the resistance value after the thermal shock test with respect to the initial resistance value is measured. Through holes having an increase rate of 10% or more are regarded as defective, and the number of defective through holes for all 5,000 pieces is defined as a defective rate (unit%). Recorded.

[0045]

[Table 6]

As apparent from Table 6 above, Comparative Examples 1 and 2
According to No. 2, the coefficient of thermal expansion of the liquid crystal polymer film is limited to the coefficient of thermal expansion (1
7 × 10 ⁻⁶ cm / cm / ° C.). As a result, the failure rate after the through-hole connection reliability test also increases. On the other hand, according to Examples 1 to 5, the coefficient of thermal expansion of the liquid crystal polymer film can be made substantially the same as the coefficient of thermal expansion of copper used for plating of the through-hole, so that it can be substantially the same after the through-hole connection reliability test. Defective rate can be reduced to zero.

[0047]

According to the present invention, it is possible to obtain a printed wiring board which is excellent in connection reliability of through holes, and is excellent in heat resistance, chemical resistance and electrical properties, and a mounted circuit board using the same. .

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a printed wiring board according to an embodiment of the present invention.

[Explanation of symbols]

2 ... electric insulating substrate (liquid crystal polymer film), 4 ... through hole, 5 ... conductor, 6 ... electronic parts.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Kiyomichi Hagiwara 1-12-39 Umeda, Kita-ku, Osaka Kuraray Co., Ltd.

Claims (4)

[Claims] An electrically insulating substrate is formed by a film formed from a polymer capable of forming an optically anisotropic molten phase, and a through hole is formed through the electrically insulating substrate in a thickness direction. A printed wiring board, wherein the coefficient of thermal expansion in the thickness direction of the film is substantially the same as the coefficient of thermal expansion of a conductor used for plating the through hole. 2. The film according to claim 1, wherein the thermal expansion coefficient of the conductor used for plating the through holes formed in the film is P × 10 ⁻⁶ cm / cm / ° C. Thermal expansion coefficient is (P-10) × 10 ^-6 cm
/ Cm / ° C to (P + 10) × 10 ^-6 cm / cm / ° C. 3. The printed wiring board according to claim 1, wherein the film has a molecular orientation of 1.3 or less. 4. A printed circuit board comprising an electronic component mounted on and connected to the printed wiring board according to claim 1.