JPH06112633A - Circuit board - Google Patents

Abstract

PURPOSE:To obtain a circuit board which is so constituted as to have a very high resistance against corrosive gas and humidity. CONSTITUTION:A circuit pattern 2 is formed on a printed board 1. A first resist layer 3 is applied to a part of the circuit pattern 2. A conducting layer 4 (a plating layer of metal such as solder, nickel or gold) is applied to the part of the circuit pattern 2 which is not covered with the first resist layer 3. A boundary 10 between the first resist layer 4 and the conducting layer 1 is covered with a second resist layer 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board having a solder resist.

[0002]

2. Description of the Related Art FIG. 3 is a plan view showing a conventional example of a circuit board having a solder resist, and FIG.
FIG. In addition, FIG. 2A is a diagram showing a part of the process of producing the circuit board.

[0003] Conventionally, in equipment such as fire detectors, which is installed in places where gas is generated or humidity is extremely high, it is necessary to have a structure that can withstand a corrosion test using a corrosive gas such as sulfurous acid gas. Therefore, a solder resist is formed on the surface of the printed circuit board to protect the printed circuit board from being corroded and destroyed by the sulfurous acid gas. As described above, a circuit board formed by applying a solder resist to the surface of the printed circuit board 1 is conventionally used, for example, as shown in FIG.
Alternatively, there is one as shown in FIG. That is, in the printed circuit board 1 having a circuit pattern 2 made of copper laid on the surface thereof, the circuit board has a conductive layer 4 attached to the surface of an element connecting portion for soldering a circuit element, and the conductive layer 4 is removed. A resist layer 3 made of epoxy resin or the like is attached to the entire surface of the printed circuit board 1. It should be noted that, for example, on the surface of the circuit pattern 2 to which the semiconductor chip is wire bonded, the conductive layer 4 is formed by metal plating such as nickel or gold, and other general electronic elements are connected to the circuit pattern by soldering. The conductive layer 4 is formed on the surface 2 by soldering.

Conventionally, in order to produce a circuit board having the above-mentioned structure, first, as shown in FIG.
The resist layer 3 is deposited on the surface portion of the printed circuit board 1 other than the element connection portion of FIG. 2, and then, as shown in FIG. 2B, the resist layer 3 is deposited using the resist layer 3 as a mask. The conductive layer 4 is deposited on all the remaining portions, that is, the element connection portions of the circuit pattern 2 by soldering or metal plating.

[0005]

However, in the conventional structure, the conductive layer 4 on the circuit pattern 2 is used.
At the boundary 10 between the resist layer 3 and the resist layer 3, it is easy to form a pinhole reaching the circuit pattern 2. If there is any pinhole, the circuit pattern 2 is corroded from the pinhole during the corrosion test. There has been a serious problem that the circuit pattern 2 is cut off. Further, if there is a pinhole at a place other than the boundary 10, the circuit pattern 2 is corroded from the pinhole, which is a serious problem. Further, there is a problem that moisture enters from the pinholes and rust is generated on the circuit pattern 2.

The present invention has been made in view of the above problems, and an object thereof is to provide a circuit board having a structure extremely resistant to corrosive gas and humidity.

[0007]

In order to solve the above-mentioned problems, the present invention comprises a first resist layer and a conductive layer deposited on the surface of a circuit pattern laid on a substrate, and the first resist. The circuit board is characterized in that a boundary between the layer and the conductive layer is covered with a second resist layer.

[0008]

According to the present invention, the substrate can be completely protected from corrosive gas and moisture.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. The same components as those of the conventional example are designated by the same reference numerals.

FIG. 1 (b) is a plan view showing a circuit board according to an embodiment of the present invention, and FIG. 1 (a) is an A- line in FIG. 1 (b).
FIG.

The circuit board of the embodiment of the present invention comprises two layers of solder resist, and the resist layer 3 (hereinafter referred to as "first resist layer") of the circuit board of the conventional example shown in FIG. 3 ") is further coated with a second resist layer 5 by means of which the first resist layer 3
The boundary 10 between the conductive layer 4 and the conductive layer 4 is covered. The first resist layer 3 and the second resist layer 5 are made of an insulating resin such as an epoxy resin as in the conventional case.

In producing the circuit board of the embodiment of the present invention, first, as in the conventional case, the first resist layer 3 is applied to the surface portion of the printed board 1 other than the element connection portion of the circuit pattern 2. . In order to deposit the first resist layer 3 on the printed circuit board 1, a printing plate having holes is used to apply the insulating resin to the printed circuit board 1 and cure it.

Thereafter, using the first resist layer 3 as a mask, all the portions where the first resist layer 3 is not deposited,
That is, the conductive layer 4 is deposited on the element connection portion of the circuit pattern 2 by soldering or metal plating of nickel, gold or the like to form the conventional structure shown in FIG.

After that, the position of the printing plate is shifted from the first resist layer 3 and the insulating resin is printed and adhered and cured to form the second resist layer 5. At this time, the position of the printing plate is shifted by the thickness of the second resist layer 5 so that the boundary 10 between the first resist layer 3 and the conductive layer 4 is completely covered with the insulating resin. Print the insulating resin. Thereby, as shown in FIG. 1, a boundary 10 between the first resist layer 3 and the conductive layer 4 is formed.
A second resist layer 5 is deposited to cover. The second resist layer 5 completely shields the pinholes generated at the boundary 10 from the outside air, so that corrosive gas such as sulfurous acid gas or humidity does not reach the circuit pattern 2 and the circuit is prevented. It is possible to reliably prevent the corrosion and rust of the pattern 2.

The second resist layer 5 in the circuit board of this embodiment not only covers the boundary 10 between the first resist layer 3 and the conductive layer 4, but also the first resist layer 3
Since most of them are covered so as to be hidden from the appearance, pinholes other than the boundary 10 can be covered, and there can be almost no pinhole reaching the circuit pattern 2. It is possible to construct a circuit board that is extremely strong against. Further, even if the circuit board is used under high humidity conditions, moisture does not enter from the pinhole as in the conventional case, so that the generation of rust or the like in the circuit pattern 2 can be prevented. Circuit boards are also extremely resistant to moisture.

[0016]

According to the present invention constructed as described above, it is possible to construct a circuit board which is extremely resistant to corrosive gas, moisture and the like.

[Brief description of drawings]

FIG. 1 is a sectional view showing a circuit board according to an embodiment of the present invention (a).
And a plan view (b). In addition, (a) shows the AA sectional view of (b).

FIG. 2 is a cross-sectional view showing a circuit board of a conventional example (b) and a cross-sectional view showing a part of a process of producing the circuit board (a).
3B is a sectional view taken along the line BB in FIG. 3 and also shows a part of the process of producing the circuit board of the embodiment of the present invention.

FIG. 3 is a plan view showing a conventional circuit board.

[Explanation of symbols]

 1 Printed Circuit Board 2 Circuit Pattern 3 First Resist Layer 4 Conductive Layer 5 Second Resist Layer 10 Boundary

Claims (1)

[Claims] 1. A surface of a circuit pattern laid on a substrate is coated with a first resist layer and a conductive layer, and a boundary between the first resist layer and the conductive layer is formed by a second resist layer. A circuit board characterized by being covered.