JP2665293B2 - Printed circuit board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed circuit board used in the field of electronic materials and the like.

[0002]

2. Description of the Related Art Conventionally, in a printed circuit board subjected to a solder reflow process, only a portion necessary for component mounting is coated with a solder, as shown in FIG. In addition, a portion (wiring circuit portion) other than the portion serving as the component mounting portion 3 is covered with the solder resist 4.

[0003]

However, in recent years, as high-density mounting has been demanded and the area of the component mounting portion has become smaller, the molten solder has come into contact with the metal portion during the reflow process. In addition, a problem that solder does not adhere to a predetermined portion has occurred, and improvement thereof has been desired. An object of the present invention is to solve the above-described problems, and a wiring circuit capable of coating a predetermined solder during a reflow process even if the area of a metal portion is reduced by high-density mounting. It is to provide a substrate.

[0004]

According to the study by the inventors, as described above, although the molten solder is in contact with the metal layer during the reflow process, the solder is formed at a predetermined location. The problem of non-sticking occurs because the ratio of the area of the metal layer surface of the component mounting part to the height of the resist layer surrounding it decreases with the increase in density. This is because the balance between the wettability of the solder and the metal layer portion, the force with which the resist layer repels the solder, the surface tension of the solder, and the like is lost, in addition to the reason that the wraparound of the solder to the portion is hindered. Such a problem is ameliorated if the step between the surface of the metal layer serving as the component mounting portion and the surface of the resist layer is eliminated or reduced , but the surface of the metal layer is formed of the resist layer.
If it is arranged at a position higher than the surface, it is surely solved.

Therefore, a printed circuit board according to the present invention is a printed circuit board in which a portion other than a metal layer serving as a component mounting portion is covered with a solder resist, and the surface of the solder resist layer is formed on the component mounting portion. characterized that you have been placed at a position lower than the surface of the metal layer becomes. The printed circuit board according to the present invention, the surface of the pre-SL component mounting portion and comprising a metal layer by the other solder resist
Ru can be higher than the surface of the metal layer of the coated portion Te.

Hereinafter, the printed circuit board according to the present invention will be specifically described. FIG. 1 shows an example of a printed circuit board according to the present invention. As can be seen from the drawing, in this wired circuit board, unlike the conventional one shown in FIG. 5, the metal layer 2 formed on the surface of the substrate 1 is
The surface of the part to be the component mounting part 3 is higher than the surface of the other part (wiring circuit part). Therefore, the surface of the solder resist 4 is lower than the surface of the metal layer to be the component mounting part 3. positioned.

In the printed circuit board according to the present invention, as long as the surface of the part to be the component mounting part 3 is higher than the surface of the other part (wiring circuit part), the circuit shown in FIG. there need not necessarily stomach. Such a printed circuit board can be manufactured, for example, by the following two methods.

First, the first method will be described with reference to the flow steps shown in FIG. A substrate on which a metal layer having a predetermined thickness is formed over the entire surface is prepared, and a positive resist is applied.
Here, the positive resist is not particularly specified as long as it does not hinder the subsequent plating step, and may be a dry film type, an ED type, or a liquid. Even if it is a type, it can be used properly according to the situation.

Then, by photolithography, only a portion requiring solder coating (a portion of a metal layer to be a component mounting portion) in a later reflow step is exposed and developed. Next, plating is performed on the metal layer portion (component mounting portion) exposed by removing the resist, and the metal layer is thickened to have a predetermined thickness. That is, the positive resist is used as a plating resist.

In this plating step, the positive resist formed in the previous step is further exposed and developed in the next step, so that it is necessary to work in a yellow room or the like so as not to be irradiated with ultraviolet rays. In the present plating step, there is no particular designation for the metal to be plated, and furthermore, any one of electrolytic plating and electroless plating may be used. Next, a positive resist is formed on the exposed metal layer surface or the entire substrate surface. This resist formation, for example,
This can be dealt with by applying a liquid resist.

Next, exposure and development are performed on portions other than the circuit portion of the positive resist, the exposed metal layer is etched, and the remaining positive resist is removed. Finally, the portion other than the metal layer serving as a component mounting portion formed by the above process, so that the such a position lower than the surface of the surface of the metal layer, when coated with solder resist, as shown in FIG. 1 A simple printed circuit board can be obtained.

Next, according to the flow process diagram shown in FIG.
The second method will be described. First, a printed circuit board as shown in FIG. 4 which has been subjected to predetermined patterning and metallization by a full additive method is prepared. In the figure, 1 is a substrate, 2 is a metal layer, and 4 is a resist. Next, the metal layer 2 at a location other than the location where the component mounting portion 3 is to be formed.
Is covered with a resist 4 to obtain a printed circuit board as shown in FIG. Then, by forming (thickening) a metal layer on the component mounting portion 3 of the printed circuit board by electroless plating or the like, the surface of the metal layer at that portion becomes higher than the surface of the solder resist layer. By doing so, a printed circuit board as shown in FIG. 1 is obtained.

In the case where all portions requiring thickening of the metal are electrically conductive, the thickening can be performed by an electroplating method. Here, even with the conventional printed circuit board as shown in FIG. 4 obtained by the full additive method, there is no problem with respect to the solder wettability at the time of reflow to the metal part, but it has the following disadvantages. . That is, in the conventional full-additive method, since the wiring coating is also applied to the wiring circuit portion other than the portion where the component is to be mounted at the time of reflow, for example, a multi-layer wiring circuit board is to be manufactured by bonding to another wiring circuit board. In such a case, inconveniences such as short-circuiting between the wirings due to the melting of the solder, or contact with a portion other than the contact portion with the wiring circuit board to be bonded are caused.

[0014]

In the printed circuit board according to the present invention, the surface of the metal layer serving as the component mounting portion is higher than the surface of the solder resist layer.
Is also located at a higher position, so that the wettability of the molten solder during solder reflow is improved.

[0015]

An embodiment of the printed circuit board according to the present invention will be described below in more detail. Example 1 A ceramic substrate having a copper layer of a predetermined thickness formed on the entire surface was prepared, and a printed circuit board was manufactured according to the flow process shown in FIG.

First, a positive type liquid resist was applied to the ceramic substrate by a dipping method, and exposure and development were performed only on a part to be a component mounting portion by using a photolithographic method. In addition, in this example, in order to evaluate the solder wettability at the time of reflow, a test pattern was prepared such that the component mounting portion had a diameter of 0.2 to 2 mmφ. The copper exposed in the previous process is subjected to copper sulfate electroplating in a yellow room,
A μm thick copper was applied.

Next, the same positive type liquid resist as that used in the previous step was coated on the entire surface to a thickness of about 3 μm, and subsequently, a portion to be a circuit was exposed and developed. Next, the copper layer exposed in the previous step was removed using a copper chloride etching solution, and the remaining resist was subsequently peeled off with a solution of sodium carbonate. Then, finally, a region other than the metal portion serving as the component mounting portion was covered with a paste-like solder resist to obtain the printed circuit board shown in FIG.

After the obtained printed circuit board was preheated in a preheating furnace, it was passed through a solder reflow bath set at 250 ° C. and solder coating was performed. Uniform solder coating was performed on all round parts.

Example 2 A glass epoxy copper wiring circuit board having a structure as shown in FIG. 4 is prepared by a conventional full additive method.
The printed circuit board of FIG. 1 was manufactured according to the flow process diagram shown in FIG. That is, specifically, in this embodiment,
In order to evaluate the solder wettability at the time of reflow in the same manner as in Example 1, a test pattern having a component mounting portion having a diameter of 0.2 to 2 mmφ was prepared. First, a plating resist and a photo solder resist were applied to the above-mentioned glass epoxy copper wiring circuit board by a screen printing method to a thickness of 20 μm, and portions other than the component mounting portion were covered by exposure and development.

Next, using an electroless copper plating solution of a thick type, only the exposed copper layer is thickened, and the thickness is shown in FIG.
As described above, the printed circuit board having the structure shown in FIG. 1 was obtained in such a manner that the surface of the copper layer serving as the component mounting portion was higher than the surface of the solder resist. After pre-heating the obtained wiring circuit board in a pre-heating furnace, it was passed through a solder reflow tank set at 230 ° C. to perform solder coating.
Uniform solder coating was able to be performed on all the round portions of 0.2 to 2 mmφ prepared as the component mounting portions.

Example 3 Two types of ceramic printed circuit boards having a thickness of 0.3 mm produced in the same manner as in Example 1 were soldered to the surface of a copper layer serving as a contact portion of each printed circuit board by a reflow process. After coating, the respective substrates were bonded together at a solder melting temperature to obtain a multilayered printed circuit board.

When an electrical continuity test was conducted on the printed circuit board having the laminated multilayer structure, it was confirmed that all the contact portions were connected well. -Comparative Example 1- An evaluation of the solder wettability in the reflow process was performed on the ceramic printed circuit board having the same pattern as in Example 1 and manufactured by the conventional method shown in FIG. 5 under the same conditions as in Example 1. . The height difference (step) between the surface of the copper layer of the component mounting portion and the surface of the solder resist in the printed circuit board used in this comparative example was 20 μm.

As a result of the evaluation of the solder wettability, it was found that no solder coating could be performed at all on the round portion of 0.2 mmφ, and some portions could not be coated on the round portion of 0.5 mmφ. Comparative Example 2 Two types of ceramic printed circuit boards were bonded together under the same conditions as in Example 3 except that they were manufactured by the conventional method as shown in FIG. 5 to obtain a printed circuit board having a multilayer structure. When an electrical continuity test similar to that of Example 3 was performed on this multilayered wiring circuit board, a conduction failure that was partially due to an insufficient amount of solder coating was observed.

[0024]

In the printed circuit board according to the present invention, the surface of the metal layer serving as the component mounting portion is located higher than the surface of the solder resist layer. A predetermined amount of solder can be coated without hindering contact. for that reason,
Performs uniform solder coating after the reflow process, without causing defects such as uneven solder amount on the metal surface that will be the component mounting part or partial lack of solder coating. You can do it.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of the structure of a printed circuit board according to the present invention.

FIG. 2 is a flowchart showing an example of a method for manufacturing a printed circuit board according to the present invention.

FIG. 3 is a flowchart showing another example of the method of manufacturing a printed circuit board according to the present invention.

FIG. 4 is a cross-sectional view illustrating an example of a printed circuit board manufactured by a full additive method.

FIG. 5 is a cross-sectional view showing an example of the structure of a conventional printed circuit board.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Metal layer 3 Component mounting part 4 Solder resist layer

Claims (2)

(57) [Claims] 1. A printed circuit board in which a portion other than a metal layer serving as a component mounting portion is covered with a solder resist, wherein a surface of the solder resist layer is lower than a surface of the metal layer serving as the component mounting portion. printed circuit board, characterized that you have been placed in the position. Wherein the surface of the pre-SL component mounting portion and comprising a metal layer,
The printed circuit board according to claim 1, wherein the wiring circuit board is higher than the surface of the metal layer in a portion covered with the other solder resist .