JPS5826839B2 - printed wiring board - Google Patents

Description

Detailed Description of the Invention The present invention relates to a double-sided printed wiring board in which conductor layers provided on both sides of an insulating substrate are connected by through-hole conductors provided in through holes of the insulating substrate, This relates to a printed wiring board such as a multilayer printed wiring board in which the above-mentioned large number of insulating substrates are connected by through-hole conductors provided in the through-holes of the upper insulating substrate, and its purpose is to improve the reliability of the through-hole conductors. There is a particular thing.

Generally, in printed wiring boards such as double-sided printed wiring boards and multilayer printed wiring boards, through-hole conductors are used as a means of electrically shorting between multiple conductor layers, and the through-hole conductors are formed by electroplating or chemical plating. I was creating it.

However, the electroplating method requires a hidden electrode and requires the use of expensive power supply equipment, while the chemical plating method does not require expensive power supply equipment, but requires the use of a plating solution. There has been a problem in that conditions such as temperature and pH have a strong tendency to electrically and mechanically embrittle the base material of printed wiring boards.

Moreover, in the normal case where copper metal is applied to both electroplating and chemical plating to maintain properties, the expansion and contraction rates of the copper conductor and the base material of the printed wiring board are different. Attachment of components to the board often causes fatigue disconnections due to repeated temperature cycle factors that occur during use of printed wiring boards.

Therefore, as the base material for the printed wiring board, it is necessary to avoid using paper-based phenolic resin laminates, which have a high expansion and contraction rate, and instead use expensive glass cloth-based epoxy resin laminates, which have a low expansion and contraction rate and are close to that of copper. It was something I couldn't get.

The present invention solves these conventional drawbacks,
The present invention will be described below with reference to drawings of embodiments.

FIG. 1 shows an embodiment of the printed wiring board of the present invention.
is a first insulating substrate, and a conductive layer 3 made of conductive paint is formed on one surface of the first insulating substrate.

A second insulating substrate 4 is attached to the surface of the first insulating substrate 1 on which the conductor layer 3 is formed, and a through hole 6 is provided corresponding to the conductor layer 3 .

And the above 1. Window 1 consisting of through hole 6 of multilayer printed wiring board 12 consisting of the pasting structure of second insulating substrates 1 and 4
3 is filled with a through-hole conductor 14 made of conductive paint, and is formed into a dome shape with a concave center as shown in the figure.

A conductor layer 15 is provided on the surface of the insulating substrate 4 including the dovetail-shaped surface of the through-hole conductor 14 by chemical plating of copper.

At this time, the conductor layer 15 also has a concave shape with a concave center.

That is, this conductor layer 15 is connected to the conductor layer 3 provided on the surface of the first insulating substrate 1 via the through-hole conductor 14.

When configuring the multilayer printed wiring board 12 having such a structure, first, as a first step, as shown in FIG.
Prepare a paper-based phenolic resin laminate with a size of 120~13 mm and print epoxy resin paint on one side of it.
Cured at 0°C for 30 to 60 minutes to form resin base layer 2.
form.

Then, a conductive layer 3 is formed on the surface of the resin base layer 2 by a printing method using 5504 manufactured by DuPont as a conductive paint, and cured at 160° C. for 30 minutes.

As a second step, as shown in Fig. 3, a paper-based phenolic resin laminate with a thickness of 0.5 plate of JIS standard PP-7 is prepared as the second insulating substrate 4, and one side of the paper-based phenolic resin laminate is coated with epoxy resin. Print resin paint at 120-130℃.

A resin base layer 5 is formed by curing for 30 to 60 minutes, and a through hole 6 with a diameter of 1.0 mm is formed in the second insulating substrate 4 including the resin base layer 5.

The third step is the above-mentioned 4. Second insulating substrate 1°4
A window 1 consisting of the above-mentioned through hole 6 is pasted between the two paper edge substrates 1 and 4 using an adhesive 7 or 8 provided on either one of the surfaces.
A multilayer printed wiring board 12 having a single-sided structure having a thickness of 3 is prepared.

At this time, the adhesive 7 or 8 is formed on the first or second insulating substrate 1 or 4 except for the ceiling portion of the through hole 6.

The adhesive 7 or 8 may be thermoplastic, but considering the possibility of using a chemical plating bath, a thermosetting epoxy resin is used and cured at 150'C.
．． It is desirable to permanently attach the second insulating substrates 1 and 4.

As a fourth step, as shown in FIG. 4, a metal mask 16 is placed on the single-sided multilayer printed wiring board 12, and the window 13 is printed using DuPont's 5504 as a conductive paint. Through-hole conductor 1 inside
4, press a pin into the center to make a concave shape, and cure at 160°C for 30 minutes.

The conductive paint used as the through-hole conductor 14 has a property of not being attacked by a strong alkaline plating bath, and does not allow the plating liquid to penetrate into the hole wall of the window 13.

As a fifth step, as described above, the through-hole conductor 14 is
Multilayer printed wiring boards 12, 12 having a single-sided structure are temporarily bonded back to back using an adhesive adhesive 10.

As a sixth step, as shown in FIG. 5, a plating resist layer 9 is formed on each surface of the multilayer printed wiring boards 12, 12, and a copper conductor layer 15 is formed on the through-hole conductor 14 by a known chemical plating method. Form including parts.

At this time, the pattern forming surface of the multilayer printed wiring board 12.12 and the surface of the through-hole conductor 14 are subjected to sensitization and catalyzing treatment, for example, in the following electroless copper deposition bath at 558C for 50 hours to 25μ A thick copper plated conductor layer 15 is formed.

Copper sulfate 0.03 mol/l Soda 0.125 n Sodium cyanide 0.0004 tt Formaldehyde
o, os 〃Cyamin titoacetic acid 0.
036 1/Remaining amount of water Then, finally, by separating both printed wiring boards 12, 12 from the adhesive 10, the two conductor layers 15 are removed.
, 3 are connected by through-hole conductors 14, thereby obtaining a multilayer printed wiring board 11.

In the above embodiment, the multilayer printed wiring board 11 has a single-sided structure.
However, in the case of a double-sided multilayer printed wiring board, a thermosetting adhesive may be used in place of the tacky adhesive 10 for permanent bonding.

As described above, according to the present invention, the through-holes of the insulating substrate are filled with a through-hole conductor made of conductive paint, and the conductor layer provided on one surface of the through-hole conductor is connected with the conductor layer formed by chemical plating of copper. , various additives (
e.g. gelatin, dextrin, etc.)
This greatly contributes to reducing the cost of plating solutions.

In particular, in the present invention, the center of the surface of the filled through-hole conductor is recessed to form a dome shape, and a chemically plated conductor layer is provided on top to form a dome shape, so that heat is not applied during the soldering process etc. It is capable of dispersing thermal stress.

That is, if the surface of the through-hole conductor is flattened, there is a great fear that the hardened conductive paint will crack due to thermal stress or the like, and the chemically plated copper conductor layer will also be cut.

In contrast, in the configuration of the present invention in which the through-hole conductor is formed into a dovetail shape, the through-hole conductor does not crack due to thermal stress or the like, and reliability can be greatly improved.

Furthermore, even if the through-hole conductor is a conductive paint containing silver, its surface is covered with a chemically plated conductor layer, so the solder resist or molten solder itself does not come into direct contact with the conductive paint, causing silver migration. It is possible to prevent this and further improve reliability.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a printed wiring board showing an embodiment of the present invention;
FIGS. 2 to 5 are diagrams for explaining the manufacturing method of the printed wiring board. 1.4...Insulating substrate, 13...Window, 1
4...Through-hole conductor, 15...Copper chemical plating conductor layer.

Claims (1)

[Claims] 1 Filling the through holes provided in the insulating substrate with a through-hole conductor made of conductive paint in the form of a mortar with a concave center, and covering the surface of the through-hole conductor in the form of a mortar on at least one exposed surface side of the insulating substrate. A chemically plated conductor layer of copper is provided in the form of a dovetail, one end of the through-hole conductor is connected to a conductor layer provided on one side of the insulating substrate, and the other end is provided on the other side of the insulating substrate. 1. A printed wiring board, characterized in that the conductor layer is connected to the copper chemically plated conductor layer.