JP2905331B2 - Double-sided board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double-sided substrate, and more particularly to a double-sided substrate having excellent adhesive strength at an interface between a conductive layer formed on both sides and an insulating film.

[0002]

2. Description of the Related Art In recent years, as electronic devices have become lighter, thinner, and smaller, there has been a demand for thinner and higher density circuit boards on which semiconductor elements and semiconductor devices are mounted. In order to respond to such demands, flexible wiring boards have also been improved in performance, and many single-sided boards and double-sided boards having a two-layer structure that do not use an adhesive for bonding a copper foil and an insulating film have been put on the market. I have. In a double-sided board, a conductive path is formed by through-hole plating in the thickness direction of an insulating film, and copper foil on both sides is electrically connected to further improve performance.

In order to conduct such a double-sided board to both sides, generally, first, a copper foil is laminated on both sides of an insulating film by means of heat and pressure to form a double-sided board, and then a drill or the like is used. Through holes are formed in the insulating film by a conventional mechanical method or a chemical method using wet etching with a chemical solution or photolithography of a photosensitive resin. Then, a thin film layer (seed layer) is formed on the inner wall surface of the formed through-hole by a method such as electroless plating or vapor deposition, and then the thin film layer is thickened by electrolytic plating or the like to form a conductive path. The method has been adopted.

[0004] In such a method, when the diameter of the through hole is small, the formation of a thin film on the inner wall surface of the through hole may occur, and the manufacturing process may be complicated. In particular, if the diameter of the through-hole is too small, the plating solution used for forming the conductive path does not sufficiently penetrate into the through-hole, not only does not ensure the conduction, but also is formed by plating the inner wall surface of the through-hole. In this case, the adhesiveness at the interface with the metal thin film layer is not sufficient, and the electrical resistance of the conductive path tends to increase. Furthermore, since the formation of through-holes is performed after the production of the double-sided board, the confirmation inspection of through-hole formation accuracy is performed in the latter half of the entire manufacturing process, so that defective product checking is delayed and the efficiency of manufacturing is never good. I can't say.

Further, when the above-mentioned through-hole plating method is used, it is not expected that the adhesive strength at the interface between the copper foil formed on both sides and the insulating film is further improved, so that the heating during the production of the double-sided board is difficult. Interfacial peeling may occur depending on the pressure bonding conditions.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems. In forming a conductive path in a double-sided substrate having a conductor layer on both sides, a metal substance is applied only to an insulating film. A structure in which a filled conductive path is formed to reduce the electric resistance value, and a metal protrusion protruding from the surface of the insulating film is formed at the end of the conductive path, and the protruding part is buried in the conductive layer and in contact with the conductive layer. By doing so, the problems of the conventional double-sided board have been solved at once.

[0007]

That is, the present invention relates to a double-sided substrate comprising an insulating film and conductive layers formed on both sides of the insulating film. Is formed by electrolytic plating, and a metal projection having a projection diameter larger than the diameter of the through hole is formed at least at one end of the conduction path by being buried in and contacting the conductive layer. It is intended to provide a double-sided substrate characterized in that:

The insulating film used for the double-sided substrate of the present invention may be any one which has substantially electric insulation. However, from the viewpoints of heat resistance, dimensional stability by heating, and mechanical strength, polyimide resin is used. Is preferably formed,
In particular, it is preferable to use a thermoplastic polyimide resin which can be heated and flowed by heating and pressing to surely adhere to the conductive layers formed on both surfaces, from the viewpoint of adhesion. The thickness of the insulating film is usually set to about 5 to 200 μm. The term “thermoplastic” in the present invention means that the glass transition temperature is 200 ° C. or higher, and the melt viscosity at a temperature 100 ° C. higher than the glass transition temperature has a value of 1 × 10 ⁸ poise or less. Defined.

The thermoplastic polyimide resin can be obtained, for example, by imidizing a polyamic acid obtained by a polycondensation reaction between the following tetracarboxylic dianhydride or a derivative thereof and the following diamine component.

Examples of the tetracarboxylic dianhydride or a derivative thereof include bis (3,4-dicarboxyphenyl) ether dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride, (3,4-dicarboxyphenyl) hexafluoropropane dianhydride,
3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, bis (3,4-dicarboxyphenyl) difluoromethane dianhydride An anhydride or the like, and at least one of these derivatives can be used.

On the other hand, bis [4-
(3-aminophenoxy) phenyl] sulfone, bis [4- (4-aminophenoxy) phenyl] sulfone,
Bis [4- (4-aminophenoxy) phenyl] hexafluoropropane, 3,3'-diaminodiphenylsulfone, 3,4'-diaminodiphenylsulfone, 4,
4'-diaminodiphenyl sulfone, bis [4- (3-
Aminophenoxy) phenyl] ether, bis [4-
(4-aminophenoxy) phenyl] ether, bis [4- (3-aminophenoxy) phenyl] propane,
Bis [4- (4-aminophenoxy) phenyl] propane, 3,3'-diaminodiphenylpropane, 3,3 '
-At least one of diaminobenzophenone and the like can be used.

The insulating film of the present invention has the thermoplastic polyimide resin layer on both outer layers,
As the inner layer, for example, an insulating resin layer such as a low linear expansion polyimide resin layer may be laminated to form a multilayer structure of three or more layers. By forming the layer having a low linear expansion property as the inner layer in this manner, the linear expansion coefficients of the conductive layer and the insulating film are approximated in the step of laminating the conductive layer such as a copper foil, so that the obtained double-sided substrate is formed. It is preferable because curling and warping can be prevented.

The low linear expansion polyimide resin is a polyimide resin having a linear expansion coefficient of 2.0 × 10 ⁻⁵ cm / cm / ° C. or less, and specifically, a tetracarboxylic acid component. 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride as
Bis (3,4-dicarboxyphenyl) sulfone dianhydride, 2,2′3,3′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride At least one kind is used, and as a diamine component, p-phenylenediamine, 4,4′-diaminodiphenyl ether, m-phenylenediamine,
It is preferable to use a polymer obtained by performing a polymerization reaction using at least one of 4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl ether, and 4,4′-diaminobiphenyl.

The double-sided substrate of the present invention has a conductive layer such as a copper foil formed on both sides of the above-mentioned insulating film, and has an independent conductive path in the thickness direction in the insulating film. As a method of laminating an insulating film and a conductive layer, a solution of a polyimide resin or a solution of a polyamic acid which is a precursor of the solution on one side of a conductive layer such as a copper foil is applied using a roll coater, a comma coater, a knife coater, a doctor blade, or the like. It can be used as an insulating film by coating and drying. Other methods such as forming a conductor such as metal in a layer on one or both sides of an insulating film prepared in advance by vapor deposition or plating, or applying heat and pressure to a copper foil or the like as a conductive layer are adopted. it can.

On the other hand, the conducting path is usually formed at a predetermined position on the insulating film at about 5 to 200 μm, preferably 10 to 1 μm.
It is formed by forming a through hole having a diameter of about 00 μm and filling the through hole with a metal substance.

Examples of the method of forming the through holes include a wet etching method using an alkali solution or the like, a dry etching method using a laser or plasma, and a mechanical processing method using punching or a drill. Among these, in consideration of processing accuracy, processing speed, variety of processing shapes, and the like, a laser processing method is preferable, and ablation using an ultraviolet laser having an oscillation wavelength of 400 nm or less is particularly preferable. As such an ultraviolet light laser, an excimer laser or a third harmonic of a YAG laser can be used.

Examples of the metal substance to be filled in the through-hole formed as described above include metals such as gold, silver, copper, nickel, cobalt, tin, lead, and indium, and various alloys containing these as main components. These metal substances are preferably filled by a plating method.

At least one end of the conduction path is formed with a metal projection made of the above-mentioned metal substance so as to be in contact with the conductive layer, and the metal projection is embedded in the conductive layer. The degree of embedding is 2 to 50 of the thickness of the conductive layer in contact.
% Is preferable in terms of reliable conduction and adhesion between the conductive layer and the insulating film. Such a metal projection can be formed by adjusting the plating time when filling the through hole with the metal substance. The height of the protrusion is usually adjusted to about 1 to 20 μm, and the diameter of the protrusion is preferably larger than the diameter of the through-hole, so that the conduction path can be reliably held in the insulating film.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The double-sided substrate of the present invention has the above-mentioned structure, and can be obtained, for example, by the method shown in the following embodiment. The double-sided board of the present invention is not limited to the following embodiments, and various modifications can be made without departing from the technical idea of the present invention.

Example 1 (See FIG. 1) Polyamide obtained by polymerizing 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride and p-phenylenediamine in N-methyl-2-pyrrolidone The acid solution was applied onto a copper foil, dried and imidized to prepare a single-sided substrate comprising an insulating film 1 having a thickness of 30 μm and a conductive layer 2 having a thickness of 18 μm.

K is applied to the surface of the insulating film 1 of the obtained substrate.
Irradiation of rF excimer laser light is performed, and only the insulating film 1 is dry-etched to have a diameter of 60 μm and a pitch of 200 μm.
m fine through holes were formed.

Next, a plating resist is applied to the surface of the copper foil 2 on the other side, immersed in a copper plating bath using the copper foil 2 as a cathode to perform copper plating, and copper is formed in the through-hole formed earlier. The conductive path 4 was formed by filling. The plating process was interrupted when the filled copper protruded 5 μm from the surface of the insulating film 1 to form a copper projection 3 on one surface of the conduction path 4. Copper protrusion 3 formed
Was 72 μm.

Next, the coating resist is peeled off, the surface of the insulating film 1 is subjected to a surface treatment with an alkaline chemical solution, and then a 3 μm thick copper is deposited on the surface by electroless plating. By plating, the conductive layer 2
Then, a copper layer having a thickness of 15 μm was formed to obtain a double-sided substrate of the present invention shown in FIG.

The peel strength at the interface between the copper foil and the insulating film in the obtained double-sided board was 1 kg / cm. All of the 20 conductive paths formed on the double-sided board are conductively connected to the front and back surfaces, and the connection resistance value of one conductive path is 0.1.
It was 5 mΩ or less.

Example 2 An insulating film was prepared using 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride and p-phenylenediamine / 4,4
It was formed from a 50 μm thick polyimide resin layer obtained by polymerizing 4′-diaminodiphenyl ether (60/40 molar ratio), and a conduction path was produced in the same manner as in Example 1. After the formation of the conduction path, a conductive layer made of a nickel layer having a thickness of 3 μm was formed on the surface of the insulating film by an ion plating method, to obtain a double-sided substrate of the present invention.

The peel strength at the interface between the copper foil and the insulating film in the obtained double-sided board is 1.1 kg / cm.
Met. All of the 20 conductive paths formed on the double-sided board were conductively connected to the front and back surfaces, and the connection resistance value of one conductive path was 1 mΩ or less.

Example 3 A polyimide resin layer using an insulating film in Example 1, bis (3,4-dicarboxyphenyl) sulfone dianhydride and bis [4- (4-aminophenoxy) phenyl] hexafluoro A double-sided substrate of the present invention was produced in the same manner as in Example 1, except that a laminated film (thickness: 30 μm) with a thermoplastic polyimide resin layer obtained by polymerizing propane was used.

The peel strength at the interface between the copper foil and the insulating film in the obtained double-sided board is 1.5 kg / cm.
Met. All the 20 conductive paths formed on the double-sided substrate were conductively connected to the front and back surfaces, and the connection resistance value of one conductive path was 0.5 mΩ or less.

Comparative Example 1 A double-sided substrate was obtained in the same manner as in Example 1 except that the filling of the through holes with copper and the formation of copper protrusions were not performed.

The peel strength at the interface between the copper foil and the insulating film in the obtained double-sided board was 1 kg / cm, and 18 out of 20 through holes had poor conduction. The remaining two were plated through-hole and were connected electrically, but the connection resistance value was 5 mΩ.

Comparative Example 2 A double-sided board was obtained in the same manner as in Example 2 except that the filling of the through holes with copper and the formation of copper projections were not performed.

The peel strength at the interface between the copper foil and the insulating film in the obtained double-sided board is 1.1 kg / cm.
13 out of the 20 through holes had poor conduction. The remaining seven electrodes were plated through-holes and electrically connected, but the connection resistance was 7 mΩ.

Example 4 (See FIG. 2) Thermoplastic polyamic acid obtained by polymerizing bis (3,4-dicarboxyphenyl) ether dianhydride and bis [4- (4-aminophenoxy) phenyl] sulfone The solution was applied on a copper foil 2, dried and imidized to prepare a single-sided substrate comprising an insulating film 1 having a thickness of 20 μm and a conductive layer 2 having a thickness of 35 μm. The glass transition temperature of this thermoplastic polyimide resin was 275 ° C., and the melt viscosity at 375 ° C. was 4 × 10 ⁶ poise.

On the surface of the insulating film 1 of the obtained substrate, K
Irradiation with rF excimer laser light is performed, and only the insulating film is dry-etched to have a diameter of 60 μm and a pitch of 200 μm.
20 fine through-holes were formed.

Next, a plating resist is applied to the surface of the copper foil 2 on the other side, and the surface of the copper foil exposed at the bottom of the through hole is polished in a hemispherical shape with a chemical polishing agent solution. The conductive path 4 was prepared by immersing in a gold plating bath as a cathode to perform gold plating, and filling the previously formed through holes with gold. In the plating process, the filled gold is 5μ from the surface of the insulating film 1.
When the protrusions m protruded, the gold protrusions 3 were formed in the conduction path 4. The diameter of the formed gold projection 3 was 70 μm.

Next, a copper foil 2 having a thickness of 18 μm was heated and pressed on the surface of the insulating film 1 on which the gold protrusions 3 were formed, to obtain a double-sided substrate of the present invention shown in FIG.

The peel strength at the interface between the copper foil and the insulating film in the obtained double-sided board is 1.4 kg / cm.
Met. All of the 20 conductive paths formed on the double-sided board were conductively connected to the front and back surfaces, and the connection resistance value of one conductive path was 0.1 mΩ or less.

Example 5 Except that an insulating film was formed from a thermoplastic polyimide resin obtained by polymerizing 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride and 3,3'-diaminodiphenyl sulfone. In the same manner as in Example 4, a double-sided substrate of the present invention was obtained. The glass transition temperature of this thermoplastic polyimide resin is 275 ° C., and the melt viscosity at 375 ° C. is 7
× 10 ⁶ poise.

The peel strength at the interface between the copper foil and the insulating film in the obtained double-sided board is 2.1 kg / cm.
Met. All of the 20 conductive paths formed on the double-sided board were conductively connected to the front and back surfaces, and the connection resistance value of one conductive path was 0.1 mΩ or less.

Comparative Example 3 A double-sided substrate was obtained in the same manner as in Example 4, except that the through holes were filled with gold and no gold protrusions were formed.

The peel strength at the interface between the copper foil and the insulating film in the obtained double-sided board is 1.4 kg / cm.
However, only three out of the twenty conductive paths were conductively connected.

Example 6 (see FIG. 3) As a low linear expansion polyimide resin, 3,3 ′, 4,4′-
Polymer of biphenyltetracarboxylic dianhydride and p-phenylenediamine (linear expansion coefficient: 0.6 × 10 ⁻⁵ cm /
cm / ° C) as a thermoplastic polyimide resin with a polymer of bis (3,4-dicarboxyphenyl) ether dianhydride and bis [4- (4-aminophenoxy) phenyl] sulfone (glass transition temperature 250 ° C, Using a melt viscosity of 4 × 10 ⁶ poise at 350 ° C., a thermoplastic polyimide resin layer 12 (10 μm
Thickness), low linear expansion polyimide resin layer 11 (30 μm
Thickness) and a thermoplastic polyimide resin layer 12 (10 μm thickness) were sequentially laminated to obtain a single-sided substrate having an insulating film 1 having a three-layer structure.

On the surface of the insulating film 1 of the obtained substrate, K
Irradiation of rF excimer laser light is performed, and only the insulating film 1 is dry-etched to have a diameter of 60 μm and a pitch of 200 μm.
m fine through holes were formed.

Next, a plating resist is applied to the surface of the copper foil 2 on the other side, and the surface of the copper foil 2 exposed at the bottom of the through hole is polished in a hemispherical shape with a chemical polishing agent solution. Was used as a cathode, immersed in a gold plating bath to perform gold plating, and gold was filled in the through-hole formed earlier to form a conductive path 4.
In the plating process, the filled gold is 5μ from the surface of the insulating film.
When the protrusions m protruded, the gold protrusions 3 were formed in the conduction path 4. The diameter of the formed gold projection 3 was 68 μm.

Next, a copper foil 2 having a thickness of 18 μm was heated and pressed on the surface of the insulating film 1 on which the gold protrusions 3 were formed, to obtain a double-sided substrate of the present invention shown in FIG.

The peel strength at the interface between the copper foil and the insulating film in the obtained double-sided board was 1.4 kg / cm.
Met. All of the 20 conductive paths formed on the double-sided board were conductively connected to the front and back surfaces, and the connection resistance value of one conductive path was 0.1 mΩ or less.

Example 7 As a low linear expansion polyimide resin, 3,3 ′, 4,4′-
Biphenyltetracarboxylic dianhydride and p-phenylenediamine / 4,4'-diaminodiphenyl ether (6
(0/40 molar ratio) (linear expansion coefficient 1.7 × 10
⁻⁵ cm / cm / ° C.) as a thermoplastic polyimide resin, a polymer (glass transition) of bis (3,4-dicarboxyphenyl) ether dianhydride and bis [4- (4-aminophenoxy) phenyl] sulfone Temperature 250 ° C, 350 ° C
Using a melt viscosity of 5 × 10 ⁶ poise), a thermoplastic polyimide resin layer (20 μm thick) on a 35 μm thick copper foil,
A low linear expansion polyimide resin layer (50 μm thickness) and a thermoplastic polyimide resin layer (20 μm thickness) were sequentially laminated, and a single-sided substrate having a three-layer insulating film was used.
A double-sided substrate of the present invention was obtained in the same manner as in Example 6.

The peel strength at the interface between the copper foil and the insulating film in the obtained double-sided board was 2.1 kg / cm.
Met. All of the 20 conductive paths formed on the double-sided board were conductively connected to the front and back surfaces, and the connection resistance value of one conductive path was 0.1 mΩ or less.

[0049]

As described above, the double-sided substrate of the present invention has a small electric resistance because the conductive path in the insulating film is formed by filling the metal material, and the metal protrusion is formed at the end of the conductive path. Since the metal protrusions are formed and embedded in the conductive layers on both surfaces, they are excellent in adhesion (adhesion) at the interface between the conductive layer and the insulating film, and have the effect of ensuring reliable conduction. Things.

[Brief description of the drawings]

FIG. 1 is a partially enlarged sectional view of a double-sided substrate of the present invention.

FIG. 2 is a partially enlarged sectional view of the double-sided board of the present invention.

FIG. 3 is a partially enlarged cross-sectional view of the double-sided board of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating film 11 Low linear expansion polyimide layer 12 Thermoplastic polyimide resin 2 Conductive layer 3 Metal protrusion 4 Conduction path

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-261193 (JP, A) JP-A-54-152163 (JP, A) JP-A-3-104185 (JP, A) 52059 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) H05K 1/11

Claims (4)

(57) [Claims] 1. A double-sided board made of an insulating film and a conductive layer formed on both surfaces thereof, conductive paths formed by filling a metal material in the through hole for independently in the thickness direction electrolyte in the insulating film A metal projection having a diameter larger than the diameter of the through hole is formed by plating , and at least one end of the conductive path is buried in the conductive layer and is in contact with the conductive layer. substrate. 2. The double-sided substrate according to claim 1, wherein the insulating film is formed from a thermoplastic polyimide resin. 3. The double-sided substrate according to claim 1, wherein the insulating film has a structure of three or more layers, and a layer in contact with the conductive layer is a thermoplastic polyimide resin layer. 4. The double-sided substrate according to claim 1, wherein the conductive layer on the side where the metal projections are embedded is formed by an electroless plating layer or a combination of an electroless plating method and an electrolytic plating method.