JPH06302954A - Manufacture of circuit board - Google Patents

Abstract

PURPOSE:To provide highly reliable conducting through holes by fixing a substrate to a supporting base having such recessed sections that can cover projecting sections at the locations corresponding to the through holes and polishing away the projecting sections. CONSTITUTION:After forming 1,150 through holes 2 through a substrate 1 made of a copper-clad epoxy laminated board whose base material is glass and filling the holes 2 with copper paste by a screen printing method as a curable conductive material 3, and then, solidifying the paste, the substrate 1 is fixed on a supporting base 4 composed of a copper-clad epoxy laminated board whose base material is glass. Then a positive etching pattern is formed by polishing the projecting parts of the solidified copper paste bodies from the nonsupported surface of the substrate 1 and plating electrolytic copper 5 to the smoothed surface of the substrate 1, and then, laminating a dry film as an etching resist 6 and performing exposure and development. Therefore, highly reliable conducting through holes can be obtained, because uniform and smooth polishing can be performed when the etching resist 6 is removed after etching.

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. More specifically, it is a method of manufacturing a circuit board that can reliably connect the surrounding wiring pattern to the through hole without plating the inside of the through hole.

[0002]

2. Description of the Related Art Conventionally, various methods are known for forming conductive through holes in a circuit board. For example, a through hole is formed in an insulating substrate having conductive layers on both sides (hereinafter, simply referred to as “substrate”), and a curable conductive material typified by copper paste / silver paste is projected from the substrate surface into the through hole. A method is known in which, after being filled and cured in the state, the protruding portion is removed by polishing to form a conductive through hole.

[0003]

Generally, a belt sander, slurry polishing,
A polishing method used for polishing an ordinary conductive layer such as buffing and scrubbing is preferably used. When the substrate is relatively thick, a good substrate can be manufactured. However, when the substrate is thin, for example, 1 mm or less, particularly 0.5 mm or less, the above-mentioned polishing causes the upper end of the through hole to be chipped, It was found that there is a problem that cracks and the like occur at the interface between the inner wall of the hole and the curable conductive material, and the reliability of through-hole connection is reduced.

[0004]

As a result of intensive studies to solve the above problems, the inventors of the present invention project a curable conductive material from the surface of a substrate into a through hole for a through hole provided in the substrate. After filling in the state, and then curing, when polishing the surface consisting of the cured body and the substrate surface smoothly, if the substrate thickness is thin, the protrusion on the substrate surface induces vertical shaking during polishing, It was confirmed that this was the cause of the crack. Therefore, in the present invention, the substrate is fixed by a supporting table having a concave portion that wraps the projecting portion at a position corresponding to the through hole, and the projecting portion on the substrate on the non-supporting table surface is removed by polishing. Provide what to do. In the present invention, it is possible to effectively suppress the occurrence of cracks at the upper end of the through hole, cracks at the interface between the inner wall of the through hole and the curable conductive material, and to form highly reliable conductive through holes with a high yield.

That is, according to the present invention, a through hole for a through hole provided in a substrate is filled with a curable conductive material so as to project from the surface of the substrate, and then the curable conductive material is cured, and then the through hole is filled in the through hole. Immobilizing the substrate with a support having a concave portion that wraps the protruding portion of the cured body at a corresponding position,
It is a method of manufacturing a circuit board, characterized in that the protruding portion on the substrate on the non-supporting base surface is removed by polishing.

In the present invention, as the substrate, an insulating plate having various known materials and structures and having conductive layers such as copper and nickel on both surfaces is used without particular limitation. As a typical example, a paper base material-phenolic resin laminated substrate,
Paper substrate-epoxy resin laminated substrate, paper substrate-polyester resin laminated substrate, glass substrate-epoxy resin laminated substrate, paper substrate-Teflon resin laminated substrate, glass substrate-polyimide resin laminated substrate, glass substrate-BT (Bismaleimide-triazine) Resin resin laminated substrate, synthetic resin substrate such as composite resin substrate, flexible substrate such as polyimide resin or polyester resin, or metal such as aluminum, iron or stainless steel covered with epoxy resin or the like for insulation treatment Examples include metal-based insulating substrates and ceramic substrates. The thickness of the conductive layer is not particularly limited, but generally 5 to 70 μm is suitable.

The thickness of the substrate used in the present invention is not particularly limited and may be selected from 0.1 mm to 2.0 mm. The present invention is particularly effective when the substrate has a thickness of 1 mm or less, preferably 0.5 mm or less.

First, a through hole for a through hole is provided on the above substrate. The diameter of the through hole is not particularly limited and can be set arbitrarily. In particular,
In the present invention, the diameter of the through hole is equal to or larger than the diameter of the hole capable of being filled with the curable conductive material, and is usually 0.3 mm.
Above, preferably, it can be selected from 0.3 to 2 mm. As the method of forming the through holes, known methods similar to those for manufacturing a usual circuit board such as drilling, punching, and laser processing are used without particular limitation.

In the present invention, the through hole is filled with a curable conductive substance which gives a cured product having conductivity and is cured. The curable conductive material is gold, silver, copper, nickel,
A known curable conductive substance that is made into a paste by mixing a conductive material such as lead or carbon with a crosslinkable thermosetting resin such as an epoxy resin or a phenol resin together with an organic solvent as necessary can be used without limitation. . Among these curable conductive substances, the etching solution used for etching, for example, ferric chloride etching solution, cupric chloride etching solution, ammonium persulfate etching solution, sodium persulfate etching solution, potassium persulfate etching solution, A material that gives a cured product that is not substantially dissolved by an etching solution such as a hydrogen peroxide / sulfuric acid etching solution or an alkaline etching solution containing ammonium sulfate complex ions as a main component is preferably used.

Further, the above-mentioned curable conductive material has an electric resistance after curing of 1 × in order to obtain good through-hole resistance.
It is preferable to select the conductive material and adjust the amount used so that it becomes 10 ⁻² Ω · cm or less.

The filling of the above-mentioned curable conductive material into the through holes of the substrate is carried out by filling the entire space of the through holes with the curable conductive material.
A little from both surfaces of the conductive layer, specifically, 0.1 mm
As described above, there is no particular limitation as long as it is a method of filling so as to project by 0.1 to 2 mm. A typical filling method of the curable conductive material is, for example, a method of applying one or more times by a printing method, a method of press-fitting with a pair of front and back squeegees from both sides of the substrate, a roll coater or a curtain coater. Means such as a method of filling and scraping off excess paint with a squeegee are preferably used.

Further, the curable conductive material filled in the through holes is cured by a known curing method such as a hot air oven, an infrared oven, a far infrared oven, an ultraviolet curing oven, an electron beam curing oven. What is suitable for curing may be appropriately selected and cured.

Next, in the present invention, the above-mentioned protruding portion is removed by polishing. In the polishing removal mode, only the protrusion may be removed by polishing, or both the substrate and the cured body of the curable conductive material may be removed by polishing to smooth the surface. A method of polishing and removing is not particularly limited, and a known polishing method can be used.
For example, methods such as belt sanding, slurry polishing, buff polishing, and scrub polishing are preferably used.

According to the present invention, when the above-mentioned polishing is performed, the substrate is fixed on a supporting table having a recessed portion that wraps the protruding portion of the cured body at a position corresponding to the through hole of the substrate, and the non-supporting surface of the substrate is fixed. It is particularly important to polish off the protrusions on the substrate.

As described above, the substrate after the predetermined through hole is filled with the curable conductive material and cured, has the protrusions of 0.1 mm or more in the portions corresponding to the through holes on both surfaces. In addition, a device for carrying out the above-mentioned polishing is generally a system in which a substrate is conveyed by a belt or a roll. Therefore, when the support is not used, the following problems occur due to the protrusion on the lower surface of the substrate when polishing the upper surface of the substrate. That is, in the polishing in the conveyance method by the belt, there is a gap between the lower surface of the substrate and the belt, and during the polishing,
Since the substrate is supported only by the protrusions on the lower surface, when pressure is applied from the upper surface of the substrate during polishing, bending stress is applied to the substrate portion in the vicinity of the through hole, and defects easily occur near the inner wall of the through hole. On the other hand, in the transfer method using a roll, since the substrate is lifted when the protruding portion on the lower surface of the substrate passes through the roll, fluctuations in the pressure during polishing easily cause uneven polishing. Further, the above problem is particularly remarkable when the thickness of the substrate is thin or when the strength of the substrate itself is substantially insufficient as in the case of using a flexible substrate or the like.

On the other hand, according to the present invention, a support base is used, the substrate is fixed on the support base, and polishing is performed, so that the stress on the substrate in the vicinity of the through hole generated during polishing is alleviated. Even when the thickness of the board is thin or when the strength of the board itself is substantially insufficient, such as when a flexible board is used, chipping at the upper end of the through hole, hardening of the inner wall of the through hole and curability The generation of cracks at the interface with the conductive material can be effectively suppressed, and uniform and smooth polishing can be performed.

The recess provided on the support base in the present invention is provided at a position corresponding to the through hole of the substrate.
Further, the shape and size of the concave portion are not particularly limited as long as the projections on both surfaces of the substrate can be completely accommodated, and may be a concave portion or a through hole.

In the present invention, the thickness, material and the like of the support base are not particularly limited as long as they can substantially withstand the stress during polishing according to various polishing methods. For example, a glass substrate-epoxy resin laminate having a plate thickness of 1.0 mm or more, an iron plate having a plate thickness of 0.5 mm or more, and the like can be preferably used.

If necessary, a plating layer may be formed on the smoothed surface of the substrate including the through holes. The plating layer is generally formed by electroless plating and / or electrolytic plating to form the plating layer on the entire surface of the substrate including the through holes. As the material of the electroless plating layer or the electrolytic plating layer used here, a known conductive metal is used without particular limitation, but in general, as a material of a curable conductive substance that gives a cured product having the conductivity, It is preferable to select the same material as the conductive metal used such as copper. The thickness of the plated layer is not particularly limited, but is preferably such that the reliability of the through hole due to plating is improved and uneven thickness of the plated layer does not occur. As a specific example, 100 μm or less is preferable, and 5 μm or more is preferable in consideration of improvement in reliability of through holes. Particularly preferably, it is 5 to 50 μm.

A wiring pattern is formed on the surface of the substrate including the through holes. The wiring pattern may be formed either before or after the step of filling and hardening the curable conductive material. As a method of forming the wiring pattern, a method of forming an etching pattern with an etching resist and performing etching is generally used. As the etching resist used here, a dry film, a resist ink or the like is used without particular limitation, and it may be appropriately selected and used depending on the fineness of the pattern. Further, as the etching resist pattern, a positive pattern or a negative pattern may be appropriately adopted by the etching method. For example, a positive pattern may be adopted in the etching method typified by the tenting method, and a negative pattern may be adopted in the etching method typified by the solder peeling method and the SES method.

[0021]

According to the method of the present invention, a conductive through hole can be formed without forming a plating layer inside the through hole. Also, during the manufacturing process of the substrate,
When polishing the surface of the substrate, by fixing the substrate on a support that has a recess at a specific position, uniform and smooth polishing can be performed, so a highly reliable conductive through hole can be obtained. . In addition, the conductive through hole can be easily formed even when the substrate is thin, or when the substrate itself is substantially insufficient in strength such as when using a flexible substrate or the like.

[0022]

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 curable conductive substance which gives a cured product having conductivity was prepared by the following method, and a circuit board was manufactured. That is, the average particle size is 6.8 μm and the tap density is 2.99 g / cm.
³ , dendritic electrolytic copper powder having a specific surface area of 4200 cm ² / g, linoleic acid to the copper powder surface 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,
Furthermore, after adding 2.8 parts by weight of 2-ethyl-4-methylimidazole to 100 parts by weight of the binder, 3
This roll mill kneaded the mixture for 30 minutes to obtain a copper paste.

Next, a circuit board was manufactured according to the steps shown in FIG. That is, (a) as the substrate 1, 300 ×
Using a glass-based epoxy resin copper clad laminate having a thickness of 340 mm and a thickness of 0.4 mm, (b) a through hole 2 having a diameter of 0.4 mm and 1150 holes per substrate was created by drilling. (C) The through-hole 2 was filled with the copper paste prepared by the above method as the curable conductive material 3 by the screen printing method. The copper paste is heated in a hot air oven at 50 ° C. 9
It was cured under conditions of 0 minutes and 180 ° C. for 100 minutes. The cured copper paste had a protrusion of 150 to 350 μm from the substrate surface. (D-1) Next, 300 × 340 having a through hole of 2.0 mmφ at a position corresponding to the through hole of the substrate.
mm, 1.6 mm in thickness, the above substrate is fixed on a support base 4 made of a glass-based epoxy resin copper clad laminate, and 320 buffs and 600 buffs are sequentially used using a buffing machine. The protruding portion of the copper paste cured product on the substrate on the non-support base was polished to smooth the substrate surface containing the cured product (d-3). (E) Then, the smoothed substrate surface was subjected to electrolytic copper plating 5 having a thickness of 15 μm. (F) Next, a dry film (“Aquamar CF” manufactured by Hercules Co., Ltd.) 1.
5 mil) was laminated, exposed and developed to form an etching positive pattern connected to the through hole portion.
(G) After that, etching was performed with a cupric chloride etching solution, and (h) the etching resist was peeled off to form a wiring pattern. The resistance value of the formed through hole was measured by the 4-terminal method between the wiring patterns connected to the through hole on the front and back sides. As a result, 3450 holes were measured, the average was 20.3 mΩ / hole, and the standard deviation was 2
The number of defective through holes of 8.3 mΩ / hole and 200 mΩ / hole or more was 0.

Example 2 In the process shown in FIG. 1, a supporting base used for polishing a hardened material protruding from the surface of the substrate was used as a recess having a diameter of 2.0 mm and a depth of 1.0 mm at a position corresponding to the through hole of the substrate. With a 2.0 mm thick stainless steel plate (d-
Wiring patterns were formed in the same manner as in Example 1 except that the above 2) was adopted. The resistance value of the formed through hole is 3
The average of 450 holes is 28.6 mΩ / hole, and the standard deviation is 13.
The number of defective through holes of 3 mΩ / hole and 200 mΩ / hole or more was 0.

Comparative Example 1 In the process shown in FIG. 1, a buffing machine was used to remove 32 without using a supporting base used for polishing a hardened material protruding from the substrate surface.
Other than polishing by sequentially using the 0th and 600th buffs,
A wiring pattern was formed in the same manner as in Example 1. The resistance value of the formed through holes was 50.0 mΩ / hole on the average of 3450 holes, the standard deviation was 106.2 mΩ / hole, and there were 57 defective through holes exceeding 200 mΩ / hole. When a cross-section was observed for this defective through hole and the cause of the defect was analyzed, it was observed that, in all through holes, the top of the through hole was chipped or a crack was generated at the interface between the inner wall of the through hole and the curable conductive material. Was done.

[Brief description of drawings]

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Through hole 3 Curable conductive substance 4 Support base 5 of the present invention 5 Plating layer 6 Etching resist

Claims (1)

[Claims] 1. A through hole for a through hole provided in a substrate is filled with a curable conductive substance in a state of protruding from the surface of the substrate, and then the curable conductive substance is cured, and then, at a position corresponding to the through hole. A method for manufacturing a circuit board, characterized in that the substrate is fixed with a support having a concave portion that surrounds the protruding portion of the cured body, and the protruding portion on the substrate on the surface of the non-supporting base is removed by polishing.