JPH0365908B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for forming a circuit board used in the assembly of electronic equipment.

Conventional structure and its problems When soldering to a printed wiring layer on a circuit board, either alone or together with individual components, the solder layer on the printed wiring layer is used as a mask material to selectively form the solder layer. A solder resist layer may be provided in the non-selected portions. This solder resist layer is usually selectively formed using a screen printing method using a thermosetting resin such as melamine resin or epoxy resin, or a photocuring resin such as acrylated epoxy resin or acrylated melamine resin. The material is hardened by heating or ultraviolet irradiation to obtain heat resistance when it comes into contact with a solder bath. This solder resist layer was left on the circuit board even after the solder layer was formed.

However, conventional solder resist layers are often incomplete due to voids caused by air bubbles entrained during coating layer formation, the presence of free chlorine, etc., and this also reduces insulation resistance.

Purpose of the Invention The present invention provides a method for forming a circuit board, which includes a step of selectively forming a solder layer on a wiring layer on a circuit board using a solder resist layer, and then removing the solder resist layer. In particular, it provides a method for easily removing the solder resist layer.

Structure of the Invention The present invention forms a base layer that can be decomposed at the solder melting temperature on a circuit board having a wiring layer, and forms a solder resist layer that selectively covers the wiring layer via the base layer. A method for forming a circuit board, comprising the steps of: forming a solder layer on a part of the wiring layer; and removing the solder resist layer after forming the solder layer, and thereby:
In the solder layer forming process, the base layer interposed directly below the solder resist layer is appropriately decomposed, and after the solder layer is formed, the solder resist layer and the base layer residue can be easily removed.

In the present invention, the base layer has a boiling point temperature of 180°C.
By using the above rosin oil, it is possible to perform solder bath treatment at a solder melting temperature of 220° C. to 300° C. during solder layer formation. Furthermore, an epoxy resin containing an aromatic amine compound is optimally used for the solder resist layer.

DESCRIPTION OF EMBODIMENTS The present invention will be described in more detail with reference to the process cross-sectional views of FIGS. 1 to 4.

As shown in FIG. 1, a layer of rosin oil 3 whose boiling point temperature is adjusted to 183 DEG C. or higher is applied to a uniform thickness over the printed wiring layer 2 on the insulating circuit board 1. This rosin oil layer 3 does not require a strong drying process, and will harden appropriately even if left alone.

Next, as shown in FIG. 2, a solder resist layer 4 is applied by printing through the rosin oil layer 3. This solder resist layer 4 is made of epoxy resin-based epichlorohydrin-bisphenol A (for example,
50 parts by weight of Shell Oil Co. product name: 808), an aromatic amine adduct as a curing agent (for example,
A mixture of 50 parts by weight of Nippon Gosei Kako Co., Ltd. (product name: H-84) with a viscosity of approximately 350 poise was selectively printed and coated using a 180 mesh polyester cloth screen. ℃ for 15 minutes to form a finished thickness of approximately 8 mm.

Next, as shown in FIG.
It is formed on the printed wiring layer 2. The process of forming this solder layer involves using a bath of tin-lead eutectic solder (melting point 183°C).
Keep the temperature at 260℃ and apply it to this solder liquid surface for about 5 seconds.
It is done by contact method. At this time, the rosin oil layer 3 begins to dissolve or decompose during this treatment process, and the exposed portion acts as a solder flux, and the adhesion strength as a base layer in the portion immediately below the solder resist layer 4 is significantly reduced. Therefore, when this circuit board is cleaned with alcohol at 25° C. and rapidly cooled, the solder resist layer 4 becomes peeled off.

Finally, by cleaning with a solvent such as triclene or fluoroethylene, a circuit board with the rosin oil residue and solder resist layer removed can be obtained as shown in FIG. Experience has shown that the durability of the circuit board obtained in this example sufficiently exceeds that of the conventional example.

Effects of the Invention According to the present invention, a solder resist layer is provided on a printed wiring layer on a circuit board via a base layer that can be decomposed at the solder melting temperature, and then a solder layer is formed. After formation, the underlayer and solder resist layer can be easily removed, greatly improving product stability and durability of the finished circuit board.

[Brief explanation of drawings]

1 to 4 are cross-sectional views in the order of steps of an embodiment of the present invention. 1... Insulating circuit board, 2... Printed wiring layer, 3
...Rosin oil layer, 4...Solder resist layer,
5...Solder layer, 6...Individual components, 7...Lead terminal.

Claims (1)

[Claims] 1. Forming a base layer that can be decomposed at the solder melting temperature on a circuit board having a wiring layer, and forming a solder resist layer that selectively covers the wiring layer via the base layer. a step of forming a solder layer on a part of the wiring layer; and a step of removing the solder resist layer after forming the solder layer. 2. The method for forming a circuit board according to claim 1, wherein the base layer is a rosin oil layer. 3. The method for forming a circuit board according to claim 1, wherein the solder resist layer is made of an epoxy resin containing an aromatic amine compound.