JPS60187095A - Method of producing through hole circuit board - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing through-hole wiring boards used in general electronic equipment such as video tape recorders and televisions.

Conventional configurations and their problems In recent years, as the demand for smaller, lighter, and more reliable electronic equipment has increased, the demand for through-hole wiring boards has been increasing.

This through-hole wiring board electrically connects wiring circuit conductors formed on both the front and back surfaces of an insulating substrate by making the holes that pass through both conductive. Various methods have been used to manufacture this board. It has been implemented.

A typical manufacturing method thereof is through the manufacturing steps shown in FIGS. 1A to 1G.

That is, using a so-called double-sided copper-clad laminate in which copper is bonded to <2.2' on the entire front and back surfaces of an insulating substrate 1 made of glass epoxy, paper phenol, etc. as shown in FIG. Drill through-holes 3 at the predetermined locations where connections are required, as shown in Figure B, and then activate the substrate with a hydrochloric acid acidic solution of stannous chloride and palladium chloride, as shown in Figure 1C. An activation layer 4 made of palladium particle nuclei is formed on the entire surface of the substrate including the inner wall surface of the through hole by immersing it in a processing solution.
After adhering, as shown in the first diagram, this substrate is immersed in an electroless steel plating solution consisting of an alkaline solution of copper complex salt and formalin to deposit metallic copper 5 on the inner wall surface of the through hole and the entire surface of the substrate, Furthermore, as shown in FIG. 1E, electrolytic copper plating is performed to deposit metallic copper 6 to increase the conductor thickness.

Then, as shown in FIG. 1F, the through holes 3 and the wiring circuit are covered with an etching-resistant mask 7, and unnecessary parts of the copper are immersed in a ferric chloride solution or a cuprous chloride solution. By dissolving and removing it, a through-hole wiring board with conductive through-holes as shown in FIG. 1G is produced.

However, the through-hole wiring board manufactured by this method has the following drawbacks.

1. This manufacturing method requires wet processes such as activation treatment and electrolytic copper plating, which requires large-scale equipment for waste liquid treatment.

2. Manufacturing processes such as activation treatment, plating treatment, and punching are complicated and lack economic efficiency.

3. When a fairly thick copper layer is formed by plating and then a circuit conductor layer is formed by photoetching, side etching tends to occur on the line side of the circuit conductor layer, making it difficult to form fine wiring patterns.

4. Because the metal conductor layer is formed directly on the wall of the through hole,
The reliability of through-hole connections is greatly affected by the material of the insulating substrate used. Paper-based phenol substrates in particular have a large coefficient of thermal expansion, so the metal conductor layer cannot follow the expansion and contraction of the substrate, resulting in through-hole connections. Connection becomes less reliable.

5 In the electroless copper plating process, the deposition state of the plating is easily affected by the material of the insulating substrate and trace amounts of impurities contained in the insulating substrate. In particular, the plating is difficult to adhere to Teflon and polyimide substrates, which still contain impurities such as sulfur. This significantly inhibits the deposition of electroless copper plating, making it difficult to make good through-hole connections.

6 Activation treatment is performed by immersing the entire board with holes in the processing solution, so a conductor layer is formed on the side walls around the insulating substrate and through holes that do not require conductivity, so the punching process is not necessary. You need to do it twice.

As a through-hole wiring board that eliminates the above-mentioned drawbacks of the conventional example, wiring obtained by an additive method or an etching method, in which a wiring circuit conductor layer is directly formed on an insulating substrate and through-hole connections are made using only electroless copper plating, for example. Although methods such as filling silver paste into holes penetrating the circuit conductor layer and making through-hole connections have been implemented, none of these methods solves all of the above-mentioned drawbacks.

OBJECTS OF THE INVENTION In view of the above-mentioned drawbacks, an object of the present invention is to provide a manufacturing process that is relatively simple and economical, minimizes side etching to facilitate fine wiring, and improves the reliability of through-hole connections. It is an object of the present invention to provide a method for manufacturing a through-hole wiring board that can be significantly improved.

Structure of the Invention In order to achieve the above object, the through-ball wiring board of the present invention forms wiring circuit conductor layers on both the front and back sides of an insulating substrate, provides holes that penetrate through the wiring circuit conductor layers that require connection, and After applying insulating resin to the inner wall surface of the hole and fixing metal powder to the insulating resin layer, insulate both the front and back sides of the insulating substrate so that a part of the wiring circuit conductor layer around the through hole is exposed. It is made by forming a resist film and depositing a conductive metal layer on the metal powder fixed layer on the inner wall of the through hole and the exposed wiring circuit conductor layer by electroless plating.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIGS. 2A to 2E are cross-sectional views of main parts of a printed wiring board in each manufacturing process for explaining a method of manufacturing a through-hole wiring board in an embodiment of the present invention.

In the through-hole wiring board of the present invention, first, as shown in FIG. 2A, desired wiring circuit conductor layers 9 and 9' are formed on both the front and back surfaces of an insulating substrate 8.

In this embodiment, the insulating substrate 8 includes two paper base phenol resins, two paper base epoxy resins, two paper base polyester resins, a glass base epoxy resin, a glass base Teflon resin,
Synthetic resin substrates such as glass-based polyimide resin composite resins and metal substrates made of aluminum, iron, etc. are insulated with epoxy resin, etc., and the front and back surfaces of these various insulating substrates 8 are coated with copper foil, etc. A double-sided copper-clad laminate is made by gluing metal foils 9°9', and unnecessary copper foil is removed by a known method such as photo-etching using the copper-clad laminate, and an insulating substrate is created. Desired wiring circuit conductor layers 9°9' were formed on both the front and back surfaces of 8.

Then, as shown in FIG. 2B, through-holes 10 having a predetermined diameter are formed by drilling or punching in the areas where the wiring circuit conductor layers 9 and 9' formed on the front and back surfaces of the insulating substrate 8 need to be connected. As shown in FIG.
An insulating resin 11 is applied to a part of the through hole 10, and while the insulating resin 11 is not hardened, fine metal powder 12 is attached to its surface. Forms a fixed layer.

In this step, the insulating resin 11 applied to the inner wall surface of the through hole 10 not only has excellent adhesion to the various insulating substrates 8 used, but also has a high adhesion property that does not inhibit the electroless plating reaction in the next step. In this example, an epoxy resin is used as an insulating resin material that meets these requirements, and amines, imidazole, acid anhydrides, etc. are added to the hardening agent, and inorganic light is added. An insulating resin 11 whose viscosity has been appropriately adjusted using a filler material is applied to the inner wall surface of a through hole 10 made in an insulating substrate 8 by a screen printing method, and the substrate is coated with fine metal powder 12 while the insulating resin 11 is not cured. The fine metal powder 12 was allowed to adhere only to the surface of the insulating resin layer 11 by being left in a sprayed atmosphere, and then the insulating resin was cured to form a metal powder fixed layer.

Although various kinds of metals can be used as the fine metal powder 12, in this embodiment, flake-like or dendritic powder such as silver or copper was used.

Further, when an insulated metal substrate is used, the metal is exposed on the wall surface of the through hole, and it goes without saying that the insulating process must be applied to that portion by other means.

Next, as shown in the second diagram, an insulating resist 13 is selectively applied to both the front and back surfaces of the insulating substrate 80 so that the through hole 10 and parts of the wiring circuit conductor layers 9 and 9' in the vicinity thereof are exposed. and harden.

The insulating resist 13 used here needs to have sufficient resistance to the electroless plating process in the next step, and also needs to serve as a permanent mask and solder resist, so it has good heat resistance and Resin materials with excellent electrical insulation properties are required.

In order to satisfy such requirements, this example uses an insulating resist mainly made of epoxy resin or acrylic resin,
A dry film formed from an acrylic modified epoxy resin as a paste was used, and the insulating resist film 13 was formed by screen printing for the former and photo method for the latter.

Note that regarding the formation process of this insulating resist film 13,
In this embodiment, the process was carried out after forming the metal powder fixed layer 12 in the through hole 10, but it may be carried out before forming the metal powder fixed layer 1-2.

The substrate on which the insulating resist layer 13 is formed on both the front and back surfaces of the insulating substrate 8 in this way is finally subjected to electroless copper plating, and as shown in FIG.
2 and the exposed wiring circuit conductor layers 9, 9' by depositing a conductive metal layer 14 made of copper, a through-hole wiring board in which the front and back wiring circuit conductor layers 9, 9' were electrically connected was fabricated.

Electroless copper plating in this process uses a plating bath with the composition shown below, and is immersed in a plating bath with a pH of 12.5 to 13.0 at 60 to 90°C for 3 to 5 hours to deposit 10 to 16μ of copper. Ta.

[Electroless copper plating bath]

Copper sulfate 7 to 8 El/1 EDTA 1 to 15 g/l Caustic soda 8 to 10 g/7 Formalin 3 to 5 ml/ As described in detail of the invention, the through-hole wiring board according to the present invention includes:
A wiring circuit conductor layer is formed by etching copper foil adhered to both the front and back surfaces of an insulating substrate, a hole is made through both, and fine metal powder is fixed on the insulating resin layer on the inner wall surface of the hole. The conductive metal layer is formed by forming a layer and then performing electroless copper plating to deposit a conductive metal layer made of metallic copper on the wiring circuit conductor layer in the through hole and its surrounding area.

Therefore, the through-hole wiring board according to the present invention has the following effects compared to the conventional example.

1. No electrolytic plating process is required, and the activation process to make the through holes conductive is performed using a dry process using insulating resin and fine metal powder, which simplifies the manufacturing process and reduces manufacturing equipment. It is also highly economical as it does not require large equipment.

2. Since the metal powder fixed layer can be selectively formed only in the through-holes that require conductivity, it is possible to process the through-holes and external shape in advance that do not require conductivity, and therefore only one process is required, reducing the number of man-hours. It is possible to reduce the

3. Because the insulating substrate surface exposed on the inner wall surface of the through-hole is completely covered with insulating resin, impurities that act as catalyst poisons contained in the insulating substrate during the electroless copper plating process seep out, and the characteristics of the deposited copper deteriorate. It does not cause deterioration, and provides good conductivity even to insulating substrates made of resins (fluorinated resins, etc.) that originally have poor adhesion for electroless plating. Since metallic copper with extremely excellent adhesion is deposited, the reliability of the through-hole connection will not deteriorate against expansion and contraction of the insulating substrate due to heat cycles, regardless of the type of insulating substrate used.

4 Because the wiring circuit conductor layer is formed by etching a relatively thin metal foil (copper foil), there are fewer narrow lines in the circuit conductor width due to side etching, and a high-density through-hole wiring board with fine wiring is created. can get.

[Brief explanation of drawings]

Figures 1A and 1G are cross-sectional views of main parts of a printed wiring board in the main manufacturing process to explain the manufacturing process of a conventional through-hole wiring board, and Figures 2A-E are through-holes in an embodiment of the present invention. FIG. 3 is a cross-sectional view of a main part of a printed wiring board in a main manufacturing process for explaining a method for manufacturing a wiring board. 8... Insulating substrate, 9, 9'... Wiring circuit conductor layer, 10... Through hole, 11...
Insulating resin layer, 12... Metal fine powder, 13...
... Insulating resist film, 14 ... Conductive metal layer.

Claims (2)

[Claims] (1) a step of forming a wired circuit conductor layer on both the front and back surfaces of an insulating substrate, a step of providing a hole penetrating the wired circuit conductor layer that requires the connection, and applying an insulating resin to the inner wall of the through hole, a step of fixing metal powder to the insulating resin layer, a step of forming an insulating resist film on both the front and back surfaces of the insulating substrate so that a part of the circuit conductor layer around the through hole is exposed, and the metal powder fixing layer; A method for manufacturing a through-hole wiring board, comprising the step of depositing a conductive metal layer on an exposed wiring circuit conductor layer by electroless plating. (2) The through hole according to claim 1, characterized in that the wiring circuit conductor layer formed on both the front and back surfaces of the insulating substrate is made by a method of selectively dissolving and removing unnecessary parts of the metal foil. Method of manufacturing wiring boards.