JP2700259B2 - Method of forming solder layer having recess in printed wiring board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a conductor circuit formed on a printed wiring board, and a protruding electrode of an electronic component such as a surface mount component, and a conductor circuit on the printed wiring board side. The present invention relates to a method for forming a solder layer having a recess used when connecting to a solder layer.

(Prior Art) When an electronic component such as a surface mount component is mounted on a conductor circuit formed on a printed wiring board, a solder layer formed on a surface of a predetermined portion of the conductor circuit is used. This solder layer
An electronic component can be mounted very easily by placing a protruding electrode of the electronic component thereon and heating and melting the same as it is.

The following two typical methods are typically used for forming such a conventional solder layer.

In the first method, as shown in FIGS. 5A to 5C, first, a solder resist is formed on a conductor circuit formed on a substrate except for a necessary portion of a solder layer ( I). Thereafter, solder paste is printed on the exposed conductor circuit (b). The solder paste printed in this manner is heated to a predetermined surface shape (c). In addition,
Instead of printing the solder paste, a method of immersing the printed wiring board in the molten solder is also adopted.

In the second method, as shown in FIGS. 6 and 7, a plating lead electrically integrated with a conductor circuit on a substrate is used. That is, in this method, a solder layer is formed at a predetermined location by performing plating with solder. For this purpose, a current is applied to a predetermined location of the conductor circuit, so that a plating lead electrically integrated with the conductor circuit is formed. You have to do it.

Specifically, prior to forming a conductor circuit on a substrate, as shown in FIG. 6, a design is made so that all the conductor circuits on which a solder layer is to be formed are connected to plating leads,
According to this, each conductor circuit (often a pad) is formed as shown in FIG. Then, as shown in FIG. 7, a plating resist is formed so as to expose only a portion where a solder layer is to be formed, and solder plating is performed while supplying electricity from a current supply portion of a plating lead. After the completion of the solder plating, the plating resist is removed to expose a conductor circuit generally formed of copper, and a predetermined lead cut is performed by selective etching of copper and solder forming the conductor circuit. .

Since the plating leads are completely unnecessary parts in the product, they are cut by performing external processing at the locations indicated by dotted lines in FIG. 6 after predetermined processing.

By the way, in recent years, in a printed wiring board, no matter what form it is, with the densification of the electronic component itself, it has become necessary to increase the density of the conductor circuit formed thereon. I have. This is not an exception even in a printed wiring board on which a solder layer is formed, and the actual situation is that the spacing between the conductor circuits is becoming increasingly smaller. When forming a solder layer under such a situation, the above two methods have problems that must be solved.

A problem that occurs in the first conventional method is that it is difficult to accurately form a solder layer on a high-density conductor circuit. That is, in the case of the representative example shown in FIG. 5 in which a solder paste is used, when printing the solder paste, the space existing between each conductor circuit and the solder resist is provided in FIG. As shown, air bubbles often remain. If the bubbles remain in this manner, as shown in FIG. 5 (c), when the solder paste is heated, the solder enters the space and the amount of solder on the conductor circuit decreases. When mounting electronic components, the amount of solder becomes insufficient, and it is a win. In order to avoid this, if the amount of the solder paste is increased, the solder pastes located on the left and right sides of the plating resist may come into contact with each other at the time of printing or melting. This becomes more remarkable as the density of the conductor circuits increases.

The problem that occurs in the second conventional method is that plating leads must be formed, and pads and plating leads must be connected by a conductor pattern. It is limited. That is, if the second method is adopted, it is difficult to achieve a sufficiently high density of the conductor circuit.

Therefore, the inventor of the present invention pays attention to the fact that the conventional method cannot sufficiently achieve a high density of the conductor circuit when forming a solder layer necessary for component mounting. They have been conducting diligent research.

As a result, before forming a plating resist, it is newly found that chemical plating is performed instead of the plating lead used in the conventional method, and that using this as a so-called plating lead produces good results, Japanese Patent Application No. 63-20021
A proposal was made in the issue to solve this.

By adopting the method proposed in Japanese Patent Application No. 63-20021, the above-mentioned problems of the first and second conventional methods could be sufficiently solved. Research has found that there may be inherent problems that need to be solved a bit more specifically.

That is, when the electronic component to be mounted on the printed wiring board is of a so-called surface mount type, the protruding electrode (21) as shown in FIG. 8 is formed on the electronic component (20). However, if the protruding electrode (21) is not securely positioned with respect to the solder layer formed on the conductor circuit on the printed wiring board side, reliable electrical connection may not be achieved. In other words, as shown in FIG. 9, when the solder layer is flat, the protruding electrode (21) of the electronic component (20) placed on it is slightly melted before it is melted. It is easily displaced from the solder layer due to vibration, shock, or the like.

The protruding electrodes (2
As a result of further research conducted by the inventors to prevent the misalignment of 1), a recess is formed on the surface of the solder layer so as to support the protruding electrode (21) of the electronic component (20). The present inventors have newly found that doing so produces good results, and have completed the present invention.

(Problems to be Solved by the Invention) The present invention has been made based on the above background, and the problem to be solved is to solve the problem of solder before melting in the protruding electrodes (21) of the electronic component (20). This is a position shift from the top of the layer.

The purpose of the present invention is to provide electronic components (2
The present invention provides a method of easily forming a solder layer on a printed wiring board in a shape capable of reliably positioning the protruding electrode (21) when the printed circuit board is mounted on the printed wiring board. It is in.

(Means and Actions for Solving the Problems) Means adopted by the present invention to solve the above-described problems will be described below with reference to FIGS. 1 to 4 corresponding to the embodiment. It is. That is, "a solder layer (16) having a recess (16a) for mounting a component (20) is added to a conductor circuit (12) on a printed wiring board (10) by the following (a) to (f). A method of forming through each process.

(A) A solder resist (13) having a thickness larger than the thickness of the conductor circuit (12) is formed between the conductor circuits (12) formed on the substrate (11), and the solder resist (13) is formed on the conductor circuit (12). A solder resist opening (13a) for exposing the conductive circuit (12) is formed at a portion where the solder layer (16) is formed on the conductive circuit (12).
A step of covering the other part except the upper solder resist opening (13a) with the solder resist (13); (b) a surface of the solder resist (13) and a conductor circuit (12) exposed from the solder resist opening (13a); Step of applying chemical plating (14) to the surface of ()); (c) Chemical plating of surface of solder resist (13) (14)
Forming a plating resist opening (15a) having a diameter larger than that of the solder resist opening (13a) and forming a plating resist (15) at a portion other than the plating resist opening (15a); Using the chemical plating (14) layer formed in the steps (d) and (b) as a plating lead, electrolytic solder plating is performed on the surface of the chemical plating (14) layer in the solder resist opening (13a) and the plating resist opening (15a). Steps: (e) removing the plating resist (15) formed in the step (c); chemical plating (14) exposed in the steps (f) and (e).
Step of removing a layer ”.

Next, each step of this means will be described in detail, taking into account its precautions. In this case, the following steps (a) to (f) correspond to (a) to (f) in FIG. 1, respectively.

First, a conductor circuit (12) is formed on a substrate (11). Among these conductor circuits (12), as shown in the right side of FIG. May be independent of each other.

(A) After forming each conductive circuit (12) on the substrate (11) as described above, a solder resist (13) having a thickness larger than the thickness of the conductive circuit (12) is formed between the conductive circuits (12). And a solder resist opening (13a) for exposing the conductor circuit (12) is formed at a portion where the solder layer (16) is formed on the conductor circuit (12), and a solder resist opening (13a) on the conductor circuit (12) is formed. Other parts except 13a) are covered with a solder resist (13). As a result, the solder resist (1
The surface of 3) is higher than the portion where the solder layer (16) is formed on the conductor circuit (12).

It is desirable that the surface of the solder resist (13) be roughened in order to make the chemical plating (14) adhere well in the next step.

In the step (b), chemical plating (14) is applied to the portion of the conductor circuit (12) exposed from the solder resist opening (13a) formed in the solder resist (13) and the surface of the solder resist (13). Is formed. As the chemical plating (14), a material mainly made of copper is employed, and its thickness is preferably about 0.3 μm to 30 μm, and more preferably 3 μm to 30 μm. Since the chemical plating (14) is a so-called plating lead for forming a plating solder (16) by energizing the chemical plating (14), if it is thinner than 0.3 μm, the resistance during the energization increases. This is because it becomes difficult to form the plated solder (16) under favorable conditions.

When copper is used as a material for the chemical plating (14), the copper diffuses into the plating solder (16) to some extent during reflow of the plating solder (16). Accordingly, when the chemical plating (14) is thin, for example, 0.3 μm to 3 μm, after reflowing the finally formed plating solder (16), as shown in FIG. Almost all of the chemical plating (14) formed in step (1) is diffused into the plating solder (16) and remains. Therefore, when the plating solder (16) is melted, the molten plating solder (16) adheres only to the conductor circuit (12) located immediately below. On the other hand, when the chemical plating (14) has a thickness greater than the above, the chemical plating (14) does not diffuse all into the plating solder (16), but a part of the plating does not diffuse. As shown in FIG. 4, it remains on the solder resist (13) side. Therefore, when the plating solder (16) is melted, the plating solder (16) is used not only for the conductor circuit (12) immediately below but also for the chemical plating (14) on the solder resist (13) side. It adheres due to surface tension. This is a great difference when the electronic components once connected by the plated solder (16) are replaced by melting the plated solder (16). That is, when the thickness of the chemical plating (14) is thin, most of the molten plating solder (16) adheres to the terminal side of the electronic component to be removed, and hardly remains on the conductor circuit (12). However, if the thickness of the chemical plating (14) is large, the molten plated solder (16)
Since a large amount remains on the upper side, mounting of another new electronic component can be reliably performed because sufficient plating solder (16) remains.

From the above, the thickness of the chemical plating (14) is 0.3 μm
The thickness is preferably 30 μm, but considering the replacement of electronic components, the thickness is more preferably 3 μm to 30 μm. In this case, the thickness can be adjusted by forming the same metal as the chemical plating component by electrolytic plating using the chemical plating as a plating lead.

(C) On the chemical plating (14) formed on the surface of the solder resist (13) as described above, a plating resist opening (15a) having a larger diameter is formed continuously from the solder resist opening (13a). Then, a plating resist (15) is formed in other portions except the resist opening (15a).

Thereby, the solder resist opening (13a) corresponding to the center of the solder layer (16) is formed low, and the plating resist opening (15a) corresponding to the peripheral portion of the solder layer (16) is formed high. The formation of the plating resist (15) so as to leave the plating resist opening (15a) larger than the solder resist opening (13a) at the center is performed by forming a plating recess on the solder layer (16) formed in a later step. To form the location (16a), but the solder resist opening (13a)
Solder layer (1) on the larger plating resist opening (15a)
When the solder layer (16) is formed, the solder layer (16) is depressed at a position corresponding to the solder resist opening (13a) of the solder resist (13).
a).

Needless to say, the plating resist (15) is used to prevent plating on unnecessary parts, and a resist that can serve as a resist for the plating solder layer (16) is used. Further, when a photosensitive resist formed in a sheet shape is used as the plating resist (15) and is formed by exposing and developing a desired portion, a resist having good positional accuracy can be obtained.

When the plating resist (15) is formed in this manner, when looking at the surface, the chemical plating (14) is exposed where the plating solder (16) is to be formed, and otherwise the plating resist ( 15) is covered by. Also,
Since each exposed chemical plating (14) itself remains on the entire surface, each of these chemical plating (14)
Are in an electrically connected state.

(D) Then, the chemical plating (1
4), that is, solder plating is applied to the solder resist opening (13a) and the plating resist opening (15a) using the chemical plating (14) as a plating lead, that is, the plating solder layer (16) is formed by electrolytic solder plating. ) Is formed. The periphery of the solder layer (16) corresponding to the plating resist opening (15a) is formed high, and the center corresponding to the solder resist opening (13a) is formed low, where the solder recess (16a) is formed. .

This plating solder layer (16) is used for the conditions of electrolytic solder plating,
For example, by setting the current density and the plating time, a solder layer having a desired amount of solder can be formed.

(E) When the formation of the plating solder (16) is completed, the plating resist (15) becomes unnecessary and is removed. The removal of the plating resist (15) is sufficient if a general stripping solution is used. As a result, the chemical plating (14) is exposed in portions other than the portion where the solder layer (16) is formed.

(F) Finally, the chemical plating (14) exposed on the solder resist (13) is removed by etching.
The removal of the chemical plating (14) is performed by an etching solution such as an aqueous ammonium chloride solution which can selectively etch copper and solder.

As described above, the plated solder layer (16) is exposed at a predetermined position, and the solder recess (16a) is formed at the center, and the other portions are protected by the solder resist (13). It becomes a wiring board (10).

(Examples) Next, the method according to the present invention will be described with reference to specific examples.

First, an etching resist is laminated on a single-sided copper-clad laminate using a glass / epoxy composite as a substrate (11), and after exposing and developing, the copper foil on the surface is etched with a cupric chloride solution to obtain a desired surface. Each conductor circuit (12) is formed by leaving the copper foil at the location.

Next, solder resist ink is printed on each conductor circuit (12), and the solder resist ink is thermally cured to form a solder resist (13). That is, the solder resist (13) formed between the conductor circuits (12) is formed to have a thickness larger than the thickness of the conductor circuit (12). A solder resist opening (13a) for exposing the conductor circuit (12) is formed in the solder layer (16) formation site on the conductor circuit (12), and the solder resist opening on the conductor circuit (12) is formed. Other parts except (13a) are covered with the solder resist (13). Therefore, the surface of the solder resist (13) is higher than the portion where the solder layer (16) is formed on the conductor circuit (12). (FIG. 1 (a)) Each conductor circuit (12) and solder resist (13) formed as described above and the solder resist opening (13a)
Chemical plating (1) on the conductor circuit (12) exposed from
4) Form (FIG. 1 (b)) In this embodiment, the chemical plating (14) is made of copper. Then, a plating resist opening (15a) having a larger diameter is formed continuously from the solder resist opening (13a) on the chemical plating (14) on the surface of the solder resist (13), and the plating resist (15 ) Is formed. (FIG. 1 (c)) Electrolytic solder plating is performed while energizing the chemical plating (14) on the substrate (11) as described above to form a plated solder (16) at a desired location. (FIG. 1 (d)) Thereafter, the unnecessary plating resist (15) is removed (FIG. 1 (e)), and the chemical plating (14) exposed on the surface is removed by etching ( FIG. 1 (f)).

(Effects of the Invention) As described in detail above, in the present invention, a solder layer (16) for mounting components is connected to a conductive circuit (12) on a printed wiring board (10) by a "printed wiring board". (10) A solder layer (16) having a recess (16a) for mounting a component (20) is formed on the upper conductive circuit (12) through the following steps (a) to (f). Method.

(A) A solder resist (13) having a thickness greater than the thickness of the conductor circuit (12) is formed between the conductor circuits (12) formed on the substrate (11). A solder resist opening (13a) for exposing the conductor circuit (12) is formed at the solder layer (16) formation site, and other portions except the solder resist opening (13a) on the conductor circuit (12) are formed on the solder resist (13). (B) a step of applying chemical plating (14) to the surface of the solder resist (13) and the surface of the conductor circuit (12) exposed from the solder resist opening (13a); (c) a solder resist (13) Surface chemical plating (14)
Forming a plating resist opening (15a) having a diameter larger than that of the solder resist opening (13a) and forming a plating resist (15) at a portion other than the plating resist opening (15a); Using the chemical plating (14) layer formed in the steps (d) and (b) as a plating lead, electrolytic solder plating is performed on the surface of the chemical plating (14) layer in the solder resist opening (13a) and the plating resist opening (15a). Steps: (e) removing the plating resist (15) formed in the step (c); chemical plating (14) exposed in the steps (f) and (e).
Layer removing step), so that the solder layer used when mounting electronic components can be securely used without adversely affecting the density of conductive circuits on the printed wiring board. Not only can it be easily formed, but also, when the electronic component (20) is mounted on the printed wiring board, the solder recess (16a) that can surely position the protruding electrode (21) can be surely formed. ) Can be provided.

[Brief description of the drawings]

1 (a) to 1 (f) are partially enlarged sectional views showing the method according to the present invention step by step, and FIG. 2 shows an embodiment of each conductor circuit to be formed in advance on a substrate. FIG. 3 is a partially enlarged plan view, FIG. 3 is a case where the chemical plating formed on the solder resist is relatively thin, and a partially enlarged sectional view showing a state in which the formed plated solder is reflowed. FIG. FIG. 3 is a view corresponding to FIG. 3 and is a partially enlarged cross-sectional view in a case where a chemical plating formed on a solder resist is relatively thick. 5 to 7 show a conventional method.
6A to 6C are partially enlarged sectional views showing a conventional first method for forming a solder layer in the order of steps, and FIG. 6 shows aspects of each conductor circuit to be formed in advance on a substrate. FIG. 7 is an enlarged plan view in the case where a solder resist is formed on the one shown in FIG. FIG. 8 is a partially enlarged cross-sectional view showing the relationship between the protruding electrodes of the electronic component and the solder layer, and FIG. 9 is a partially enlarged cross-sectional view showing a state where the protruding electrodes are displaced from the solder layer. EXPLANATION OF SYMBOLS 10: Printed wiring board, 11: Substrate, 12: Conductor circuit,
13 solder resist, 13a solder resist opening, 14 chemical plating, 15 plating resist, 15a
... Plating resist opening, 16 ... Plating solder, 16a ... Solder recess.

Claims (1)

(57) [Claims] A solder layer having a recess for mounting a component is formed on a conductive circuit on a printed wiring board by the following steps (a) to (f):
The method of forming through each process of. (A) A solder resist having a thickness larger than the thickness of the conductor circuit is formed between the conductor circuits formed on the substrate, and a solder resist opening for exposing the conductor circuit to a solder layer forming portion on the conductor circuit. Forming a solder resist on the conductive circuit and covering the other portions except the solder resist opening with a solder resist; (b) performing chemical plating on the surface of the solder resist and the surface of the conductive circuit exposed from the solder resist opening (C) a step of forming a plating resist opening having a diameter larger than that of the solder resist opening on the chemical plating on the surface of the solder resist and forming a plating resist at a portion other than the plating resist opening; (D) using the chemical plating layer formed in the step (b) as a plating lead, (E) removing the plating resist formed in the step (c); and (f) removing the plating resist formed in the step (e). Removing the layer.