JPH05175650A - Manufacture of circuit board - Google Patents

Abstract

PURPOSE:To provide a method of manufacturing a circuit board by forming a through hole at an insulating board reduced in its permittivity by incorporating bubbles without reducing low permittivity effect due to the bubbles. CONSTITUTION:A penetrating hole 3 for a through hole is provided at a board 1 made of insulator containing bubbles, the inner wall of the hole is covered with paste having a viscosity of 1000 poises or more to form a coating layer 4, and then plated. Or, the hole is filled with curable conductive paste having a viscosity of less than 1000 poises to form a through hole.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method for manufacturing a circuit board. Specifically, it is a method of manufacturing a circuit board by forming through holes in an insulating substrate having a low dielectric constant by containing bubbles without reducing the effect of reducing the dielectric constant by the bubbles.

[0002]

2. Description of the Related Art The demand for high-frequency circuit boards is increasing due to the sophistication of communication equipment accompanying the development of an advanced information society. In particular, communication equipment such as satellite broadcasting, satellite communication, mobile radio, etc., which are expected to develop in the future, use high frequencies in the gigahertz band. Therefore, materials for circuit boards used in these communication equipment are in the gigahertz band. It is required to be a low dielectric constant material having excellent high frequency transmission characteristics. In addition, as information processing devices such as computers and magnetic devices are required to have higher sophistication and larger capacities, especially in terms of signal transmission speed, due to the low dielectric constant of the multilayer circuit board, high speed as a device is achieved. An approach is taken to improve the operability.

Conventionally, when viewed from the material of an insulating substrate intended for a low dielectric constant, a thermosetting resin such as an epoxy resin, a phenol resin, a polyimide resin or an unsaturated polyester resin as a base resin and a glass cloth as a reinforcing material. , Glass mats and paper are mainly used.
Further, there is polytetrafluoroethylene (PTFE) as a polymer material showing an extremely low dielectric constant, and the dielectric constant (hereinafter referred to as ε) is 2.1 and the dielectric loss tangent (hereinafter referred to as ta).
n 0) is 0.0002.

Further, recently, the development of further lowering the dielectric constant has been remarkable, and attempts have been made to further lower the dielectric constant of the insulating substrate by allowing bubbles to exist inside the insulating substrate. For example, a substrate in which a hollow body such as glass or resin is blended (JP-A-64-60648) or a foamed substrate (JP-A-62-69580) or 1969 U.S.A. L. Substrates (electronic materials, using expanded porous PTFE developed by GORE & ASSOCIATES)
The October 1991 issue, page 61, trade name "GORE-TEX") and the like have been proposed. Among them, the insulating substrate in which the resin contains a high proportion of bubbles (ε = 1) exhibits extremely low ε and tan δ. For example, in the case of “GORE-TEX”, it has continuous pores with a porosity of 80%, and ε = 1.16, t
An δ = 0.00003 is achieved.

On the other hand, in order to manufacture a double-sided circuit board using the above insulating substrate, a through hole forming step is required. As a method of forming a through hole, generally,
There is known a method in which a through hole is provided in an insulating substrate and the through hole is subjected to chemical plating, electroplating, or filling with a conductive paste.

[0006]

However, in the method of forming a conductor layer in a through hole of an insulating substrate by chemical plating or electroplating, air bubbles are trapped in a single hole or a continuous hole existing on the wall surface of the through hole, There is a problem that the plating solution permeates the wall surface of the through hole and a uniform plating layer cannot be formed, and the dielectric constant around the through hole where the plating solution permeates increases. In addition, in the method of filling the conductive paste, a solvent or an organic component permeates the wall surface of the through hole to swell the substrate, raises the dielectric constant, and in some cases causes a short circuit between the through holes. It was difficult to obtain a circuit board with

The above phenomenon becomes more prominent as the porosity increases and as the existence ratio of open cells increases.

[0008]

[Means for Solving the Problems] The inventors of the present invention have conducted research to solve the above problems in forming through holes in the production of a circuit board using an insulating substrate containing bubbles. By coating the inner wall of the through-hole for the through-hole provided in the insulating substrate with a paste having a specific viscosity, it is possible to reliably prevent the plating solution or the curable conductive paste from penetrating into the inner wall of the through-hole. It has been found that a circuit board having a highly reliable through hole can be reliably manufactured by performing normal plating or filling with a conductive paste in the through hole without increasing the dielectric constant. The invention has been provided.

That is, according to the present invention, a through hole for a through hole is provided in a substrate made of an insulator containing bubbles (hereinafter also simply referred to as an insulating substrate), and an inner wall of the through hole has a viscosity of 1000 poise or more (hereinafter, referred to as a paste). After coating with a high-viscosity paste), a plating treatment or a curable conductive paste having a viscosity of less than 1000 poise (hereinafter, also referred to as a low-viscosity curable conductive paste) is filled and cured to form a through hole. And a method for manufacturing a circuit board.

In the present invention, the insulating substrate containing bubbles is not particularly limited as long as it contains bubbles to the extent that the effect of reducing the dielectric constant is exhibited, and known materials and structures can be used without limitation. it can. Examples of typical materials include polytetrafluoroethylene (PTFE) and other fluororesins, polystyrene, ABS, polyethylene, polypropylene, polyacetal, acrylic resin, nylon, cellulosic resin, polycarbonate, phenoxy resin, polyester resin, polyurethane. , Thermoplastic resin such as, phenol / formaldehyde resin, urea resin, melamine / formaldehyde resin, epoxy resin,
Furan resin, xylene resin, unsaturated polyester resin,
Thermosetting resins typified by sillcone resin and diallyl phthalate resin, natural rubber, elastomers typified by chlorosulfonated polyethylene, chlorinated polyethylene, alumina, aluminum nitride, silica, cordierite, silicon nitride, silicon carbide Ceramics represented by, and the like are included. Further, the effect of the present invention is remarkably exhibited when the insulating substrate contains bubbles at a porosity of 70% or more, and in particular, an insulating substrate having open cells.

In the present invention, it is common to form conductive layers on both surfaces of the above insulating substrate prior to forming the through holes for through holes. The material of the conductive layer and the method of forming the conductive layer are not particularly limited. Examples of typical materials include copper, aluminum, iron and nickel. The forming method is generally a method of laminating copper foil, a method of electroless plating, or a method of combining electroless plating and electrolytic plating. Further, the thickness of the conductive layer is not particularly limited, but generally 5 to 100.
Micron is suitable.

Of course, if necessary, it is also possible to form through holes for through holes, form the through holes by the method of the present invention, and then form the conductive layer. In this case, a known method such as electroless plating may be used for forming the conductive layer without particular limitation.

In the present invention, the above-mentioned insulating substrate is provided with through holes for through holes. The diameter of the through hole is not particularly limited as long as it can be covered with the high-viscosity paste and filled with the low-viscosity curable conductive paste. Generally, it is preferable to select 0.3 mm or more, preferably 0.3 to 1.0 mm.

As the method for forming the through hole for through hole, known means such as drilling, punching, and laser processing are used without particular limitation.

In the present invention, before filling the through holes for forming the through holes with the low-viscosity curable conductive paste or performing the plating treatment, the inner wall of the through holes has a viscosity of 1000 poise or more, preferably 2000 to 5000 poise. It is important to coat with a viscous paste. That is, when the viscosity of the high-viscosity paste is less than 1000 poise, the high-viscosity paste easily permeates the inner wall of the through hole, and the permeation of the paste crushes the bubbles in the insulating substrate to increase the dielectric constant. The object of the present invention cannot be achieved.
Further, if the viscosity is too large, it becomes difficult to reliably coat the inner wall of the through-hole through hole, so it is preferable to set the viscosity to about 5000 poise.

It is also conceivable to use a highly viscous paste having conductivity as will be described later, and plug the through holes for through holes with the paste to form through holes. However, the above method can exhibit a sufficient effect when the filling is completely performed, but since the paste generally has a high viscosity, the through-hole through-hole can be formed with high reliability. Difficult to do. In the present invention, by coating only the inner wall with a high-viscosity paste, and then performing a highly reliable plating treatment or filling with a low-viscosity curable conductive paste, the plating solution in the above treatment, a low-viscosity cure It is possible to prevent the conductive conductive paste from penetrating into the inner wall of the through-hole for through-holes, and to form the through-holes reliably.

In the present invention, the high viscosity paste may be insulative or conductive as long as it has the above viscosity. For example, as the insulating high-viscosity paste, a paste composition in which a solvent is blended with the insulating resin as necessary and the viscosity range is adjusted is used without particular limitation. Examples of the insulating resin include epoxy resin, phenol / formaldehyde resin, unsaturated polyester resin, unsaturated compound containing at least one double bond in the molecule, urea resin, melamine / formaldehyde resin, furan resin, xylene resin, Curable resins such as silicone resins, diallyl phthalate resins, amide resins, imide resins and the like are commonly used. These resins can be used alone or
A combination of two or more species can be used.

As the conductive high viscosity paste,
The insulating high-viscosity paste with a conductive filler added thereto to give conductivity after curing is used without particular limitation. As the conductive filler, gold, silver,
Conductive materials such as copper, nickel, lead, solder, carbon are commonly used. The compounding amount of the conductive filler with respect to the insulating resin is not particularly limited, but generally 100 to 2 parts of the conductive filler are added to 100 parts by volume of the insulating resin.
It is preferable that the compounding amount be within the range of 000 parts by volume. The capacity part of the conductive filler is JIS K
It is calculated based on the value of the apparent density measured based on 2504.

In the present invention, the method of coating the inner wall of the through hole through hole with the high viscosity paste is not particularly limited. As a typical coating method, after filling the paste by the printing method, the excess paste is blown off from one side by decompressing or pressurizing air from one side, or the pin with the high-viscosity paste attached to the through hole for the through hole. There is a method of coating the inner wall thereof.

In the present invention, it is preferable that the high-viscosity paste is hardened immediately after coating. However, when the low-viscosity curable conductive paste is filled in the next step, the low-viscosity curable conductive paste is left unhardened. Filling may be performed and curing may be performed simultaneously with the low-viscosity curable conductive paste.

In the present invention, the through holes for through holes are coated with a high-viscosity paste and then plated or
A low-viscosity curable conductive paste having a viscosity of less than 1000 poise is filled and cured to form a through hole.

A known method can be used for the plating treatment without any particular limitation. For example, a method of performing electroless plating after performing electroless plating is recommended. The electroless plating generally forms a plating layer of the same material as the conductive layers formed on both surfaces of the insulating substrate. Also,
If necessary, the through-hole through-holes may be coated with a high-viscosity paste without forming conductive layers on both sides of the insulating substrate, and the above plating treatment may be performed to form conductive layers and through-holes. It is also possible to do it at the same time.

When the low-viscosity curable conductive paste is filled, the viscosity of the low-viscosity curable conductive paste is less than 1000 poise by increasing the viscosity of the conductive high-viscosity paste by increasing the amount of solvent to be blended. Preferably 200-5
Those having a viscosity adjusted to 00 poise can be used. In this case, the low-viscosity curable conductive paste has an electrical resistance of 1 × 1 after curing in order to obtain good through-hole resistance.
It is preferable to select the conductive material and adjust the amount to be used so that it becomes 0 ⁻² Ω · cm or less.

As a method for filling the low-viscosity curable conductive paste into the through-hole through hole, a known method can be adopted without any particular limitation. For example, there are a method of applying once or a plurality of times by a printing method, a method of press-fitting the paste from one side of the substrate, a method of automatically filling each hole by a dispenser, and the like. Further, the low-viscosity curable conductive paste filled in the through-holes for through-holes can be cured with a known low-viscosity curing method such as a hot-air oven, an infrared oven, a far-infrared oven, an ultraviolet curing oven, or an electron beam curing facility. A material suitable for curing the conductive conductive paste may be appropriately selected and cured. Further, after the low-viscosity curable conductive paste is cured, it is constituted by a cured body of the low-viscosity curable conductive paste and a conductive layer in order to facilitate the formation of a wiring pattern by laminating etching resist, etching, etc., which is subsequently performed. It is preferable to grind the surface to be smoothed.

In the present invention, after the plating treatment or the curing of the low-viscosity curable conductive paste, a wiring pattern is formed on the conductive layer including the through holes. As a method of forming the wiring pattern, a method of forming an etching pattern with a resist and performing etching is generally used. The resist used here is a dry film, a liquid resist,
Examples thereof include ink and photosensitive electrodeposition resist, which may be appropriately selected and used depending on the fineness of the pattern. Further, the photosensitive resist layer may be properly used as a positive type or a negative type depending on its use. In the present invention,
When the through holes for through holes are filled with a low-viscosity curable conductive paste and cured, it is preferable to protect the surface of the cured product with a liquid resist or the like, if necessary.

After forming the resist layer, the conductive layer is etched with an etching solution such as ferric chloride, cupric chloride, persulfates, hydrogen peroxide / sulfuric acid, and alkali etchant to form a wiring pattern. After that, the resist layer is stripped using an appropriate treatment liquid such as an alkaline aqueous solution, alcohols, and a chlorine-based organic solvent. However, when the resist layer is a permanent mask for the purpose of protection or insulation, peeling is not necessary.

In the above method, the method of forming the through hole before the formation of the wiring pattern was mainly described, but the present invention can also form the through hole in the same manner after the formation of the wiring pattern. Is. In this case, in order to protect the wiring pattern when forming the through holes, it is preferable to cover the wiring pattern with a plating resist and perform plating in the case of plating.

[0028]

According to the present invention, a circuit board is manufactured by forming through holes in an insulating substrate having a low dielectric constant by containing bubbles without reducing the effect of reducing the dielectric constant by the bubbles. It is possible. Therefore, the substrate obtained by the present invention can be suitably used for applications such as a double-sided circuit substrate and a multilayer circuit substrate that utilize the characteristics of such an insulating substrate.

[0029]

EXAMPLES Examples will be shown below for specifically explaining the present invention, but the present invention is not limited to these examples.

Example 1 A circuit board was manufactured by the method shown in FIG. First,
As the insulating substrate 1 having the conductive layers 2 on both sides, a stretched porous polytetrafluoroethylene (trade name “GORE-TEX Copper Clad Laminate GTL-1000” manufactured by Japan GORE-TEX Co., Ltd.) was used. (A) Through-holes 3 having a thickness of 1.0 mm and a diameter of 0.4 mm were formed in series by drilling. The inner wall gap of the through hole 3 for through hole was 3.0 mm. (B) Next, a high-viscosity paste (Sartomer 3000 (epoxy diacrylate, viscosity 10000 poise (measured value at 25 ° C.)) and O.
After filling a mixture of 5 wt% (wt%) benzoyl peroxide, manufactured by SARTOMER, one side is depressurized to remove the excess high-viscosity paste in the through holes 3 to form the inner wall of the through holes. A coating layer 4 of high-viscosity paste was formed on. Then, it heated in nitrogen at 80 degreeC for 2 hours, and hardened the high viscosity paste. (C) Next, the low-viscosity curable conductive paste obtained by the method shown below is screen-filled into the through-holes 3 for through holes and heat-cured at 180 ° C. for 10 minutes in a far-infrared furnace. A cured product 5 was obtained. (D) A resist layer 6 corresponding to the wiring pattern (a thermosetting etching resist ER-402 manufactured by Tamura Manufacturing Co., Ltd.) is formed on both surfaces of the thus-prepared substrate.
C-7) was screen-printed and then cured by curing at 125 ° C. for 4 minutes. (E) Then, the exposed copper foil (conductive layer 2) is etched with an etching bath of ferric chloride, and (f) the resist layer 6 is peeled off with a 2% NaOH aqueous solution at 40 ° C. to produce a circuit board. did.

The through-hole resistance value of the obtained circuit board was measured and found to be 30 mΩ to 50 mΩ / hole. Also,
When the cross section of the through hole was observed, no penetration of the high-viscosity paste 4 and the conductive paste 5 was observed inside the insulating substrate 1 1 mm or more from the inner wall of the through hole for the through hole, and the insulating substrate 1 had the original shape of the continuous hole. It was confirmed that the low dielectric constant was not affected.

Even if the circuit board was immersed in an oil bath at 20 ° C. and 260 ° C. 10 times for 20 seconds each, the through-hole resistance hardly changed. Further, as a migration test, a DC voltage of 50 V was applied between the through holes in an atmosphere of 60 ° C. and 90% RH, and the insulation resistance was measured 1000 hours later. The insulation resistance was 2 × 10 ⁹ Ω, which was good and the appearance was not abnormal. It was

(Composition of low-viscosity curable conductive paste) Average particle size 6.8 μm, tap density 2.99 g / cm ³ ,
Resinous electrolytic copper powder with a specific surface area of 4200 cm ² / g, linoleic acid to the copper powder surface area, 0.25 × 10 ^-5 mmol
/ Cm ² and compounded in a mortar for 15 minutes under a nitrogen atmosphere. The pretreated copper powder thus obtained was used with respect to 100 parts by weight of a binder of neopentyl glycol diglycidyl ether (epoxy equivalent = 150) / novolac type phenol resin (hydroxy equivalent = 105) = 74/26 (weight ratio). Add 456 parts by weight,
After adding 2.8 parts by weight of 2-ethyl-4-methylimidazole to 100 parts by weight of the binder, 3
The mixture was kneaded with this roll mill for 30 minutes to form a paste.
The viscosity of the obtained paste was 350 poise.

Example 2 Instead of the high viscosity paste used in Example 1, SP-40
60 (Product name: 5-functional epoxy acrylate, viscosity / 2
The same procedure as in Example 1 was performed except that 5 ° C. = 2500 poise: manufactured by Showa High Polymer Co., Ltd. was used.

The through hole resistance value of the obtained circuit board was measured and found to be 30 mΩ to 50 mΩ / hole. When the cross section of the through hole was observed, no penetration of the high-viscosity paste 4 and the low-viscosity curable conductive paste 5 was observed inside the insulating substrate 1 1 mm or more from the inner wall of the through-hole for through hole, and the insulating substrate 1 was continuous. It was confirmed that the original shape of the hole was maintained and the low dielectric property was maintained.

Further, even if the circuit board was immersed in an oil bath at 20 ° C. and 260 ° C. 10 times for 20 seconds each, the through-hole resistance was hardly changed. As a migration test, a DC voltage of 50 V was applied between the through holes in an atmosphere of 60 ° C. and 90% RH, and the insulation resistance was measured 1000 hours later. The insulation resistance was 2 × 10 ⁹ Ω, which was good and the appearance was not abnormal. It was

Further, in the present invention, substantially the same result was obtained even when the high viscosity paste having a viscosity of 1500 poise, or 2500 poise as described above was used. The effect was remarkable when it was more than poise.

Comparative Example 1 Instead of the high viscosity paste used in Example 1, EBEC
RYL264 (trade name: trifunctional urethane acrylate,
Viscosity / 25 ° C. = 450 poise: manufactured by Daicel UCB Co., Ltd., except that the same procedure as in Example 1 was performed.

The through-hole resistance value of the obtained circuit board was measured and found to be 60 mΩ to 350 mΩ / hole. The cross section of the through hole was observed, and it was 10 mm from the inner wall of the through hole.
Penetration of the high-viscosity paste 4 and the conductive paste 5 was also confirmed inside the insulating substrate 1 containing the above. This allows
It was confirmed that the low dielectric constant of the insulating substrate 1 was not maintained. As a migration test, 60
A direct current of 50 V was applied between the through holes in an atmosphere of 90 ° C. and 90% RH, and the insulation resistance after 200 hours was measured.
The hole showed 1 kΩ or less, and there was a problem in reliability.

Example 3 In Example 1, after curing the low-viscosity curable conductive paste (c), the surface constituted by the cured body 5 and the conductive layer 2 was ground smoothly, and then electroless copper plating was performed. Example 1 was repeated except that electroplating was performed to form uniform plated layers on both sides.

The through-hole resistance value of the obtained circuit board was measured and found to be 30 mΩ to 60 mΩ / hole. Also,
When observing the cross section of the through hole, 1m from the inner wall of the through hole
No penetration of the high-viscosity paste 4 and the conductive paste 5 was observed inside the insulating substrate 1 containing m or more.
It was confirmed that the original shape of the continuous hole was maintained and the low dielectric property was maintained.

Further, even if the circuit board was immersed in an oil bath at 20 ° C. and 260 ° C. 10 times for 20 seconds each, the through-hole resistance hardly changed. Further, as a migration test, a direct current of 50 V was applied between the through holes in an atmosphere of 60 ° C. and 90% RH, and the insulation resistance after 1000 hours was measured, which was 1 × 10 ⁹ Ω and was good, and the appearance was not abnormal. It was

[Brief description of drawings]

FIG. 1 is a process showing a representative embodiment of the method of the present invention.

[Explanation of symbols]

 1 Insulating Substrate 2 Conductive Layer 3 Through Hole Through Hole 4 Covering Layer with High Viscosity Paste 5 Cured Body of Low Viscosity Curable Conductive Paste 6 Resist Layer 8 Wiring Pattern

Claims (1)

[Claims] 1. A through hole for a through hole is provided in a substrate made of an insulator containing bubbles, and the inner wall of the through hole has a viscosity of 1000.
After coating with paste of poise or more, plating treatment,
Alternatively, a method for manufacturing a circuit board is characterized in that a curable conductive paste having a viscosity of less than 1000 poise is filled and cured to form a through hole.