JPH11251728A - Printed board and method for coating cream solder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an electronic component mounting land from peeling, and to allow coating of a cream solder which requires no solder mask. SOLUTION: An insulating layer 3 of thickness of 20 μm or more from a land 2 surface is so formed as to cover the entire peripheral edge part of the land except for the central part of the land from the board surface with a part of the land overlapped. Thus, even if the peel strength of the land 2 is weak, reinforcement is made for retarding peeling. When, especially, the insulating layer is formed in thickness of 100 μm or more, the insulating layer is used instead of a solder mask to coat a cream solder on the printed board.

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 which effectively reinforces the peel strength of an electronic component mounting land (hereinafter referred to as "land"), a printed circuit board which does not require a solder mask in addition to the reinforcement of the peel strength. The present invention relates to a method for applying cream solder.

[0002]

2. Description of the Related Art In recent years, lands on a printed circuit board have been reduced in size due to high-density mounting of components, and the peel strength of the lands (resistance to peeling the lands from the printed circuit board) has been reduced. There is a tendency.

In general, a layer 103 of an insulating material called a solder resist (hereinafter, referred to as a resist layer) 103 is printed on the surface of a printed board 101 as shown in FIGS. And the like.

In the example shown in FIG. 4 and FIG.
, The resist layer 103 is formed on the substrate surface.

In the example shown in FIGS. 6 and 7, a resist layer 103 is formed from the surface of the substrate to a part of the land 102. When the resist layer 103 is formed over a part of the land 102 as described above, solder bridges are unlikely to occur even if the land pitch is narrowed to mount components having a narrow terminal pitch.

However, the conventional resist layer 103 cannot be expected to have an effect of reinforcing the peel strength. That is, (1) In the examples shown in FIGS. 4 and 5, the resist layer 103 does not reinforce the peel strength of the land 102 because the resist layer 103 escapes from the land 102. (2) In the examples shown in FIGS. 6 and 7, the resist layer 103 covers a part of the land 102, but the conventional solder resist has a property of spreading on the printed circuit board 101 in a fluid state before curing. Therefore, the thickness of the resist layer 103 is 10 μm or less at the maximum, and is as thin as approximately 0 μm depending on the location. Therefore, the effect that the resist layer 103 reinforces the peel strength of the land 102 can hardly be expected.

On the other hand, when components are mounted on the printed circuit board 101, conventionally, as shown in FIG. 8A, a cream solder printing mask (hereinafter, referred to as a solder mask) 106 is used for each component. The cream solder 104 is applied to the land 102.

The solder mask 106 is formed by forming a pattern 107 having an opening corresponding to a land on the printed board 101 on a thin plate of stainless steel or the like. Such a solder mask 106 is positioned and overlapped on the printed circuit board 101, and the cream solder 104 is placed near an end portion of the solder mask 106 outside a region where the pattern 107 exists (hereinafter, referred to as a pattern region). Next, a flat rubber plate 105 called a squeegee is moved toward the opposite end while being pressed against the cream solder 104 at an angle. Then, after moving the squeegee 105 to the outside of the pattern area near the opposite end, the solder mask 106 is separated from the printed circuit board 101. Thus, the cream solder 104 is printed on the land 102 of the printed circuit board 101 as shown in FIG.

After applying the cream solder, the printed circuit board 10
The components are placed on the substrate 1, and then the printed circuit board 101 and the components are heated and cooled to perform soldering.

[0010]

SUMMARY OF THE INVENTION As described above, a first object of the present invention is to provide a printed circuit board which can reinforce a land having a low peel strength so as not to peel off easily.

A second object of the present invention is to provide a printed circuit board and a method for applying cream solder which can apply cream solder without using a solder mask in addition to the above-mentioned reinforcement of peel strength. is there.

[0012]

According to a first aspect of the present invention, there is provided a printed board having a land, the printed board having an insulating layer formed on a surface of the board. It is formed so as to overlap a part of the land from the surface of the substrate so as to cover the entire periphery of the land except for the center part, and has a thickness of 20 μm or more from the surface of the land. Things.

A printed circuit board according to the present invention for solving the second problem is characterized in that the thickness of the insulating layer is 100 μm or more.

According to a second aspect of the present invention, there is provided a method of applying a cream solder to a printed circuit board on which an insulating layer having a thickness of 100 μm or more is formed by using the insulating layer instead of a solder mask. Is applied.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A printed board and a method for applying cream solder according to an embodiment of the present invention will be described below with reference to FIGS.

In the printed circuit board 1 shown in FIG. 1, an insulating layer 3 is formed so as to have a thickness t of 20 μm or more from the surface of the land 2 so as to overlap from the surface of the substrate to a part of the land 2. Like the resist layer 103 shown in FIG. 6, the insulating layer 3 is formed so as to cover the entire periphery of the land 2 except for the center of the land 2.

As described above, since the insulating layer 3 formed on the printed circuit board 1 over a part of the land 2 is as thick as 20 μm or more, even if the peel strength of the land 2 on the printed circuit board 1 is weak, the land 2 can be effectively formed. It can be reinforced to prevent peeling. In addition, solder bridges between lands can be prevented.

The insulating material used for forming the insulating layer 3 may be any material that has a property that it is less likely to spread on the printed circuit board 1 in a fluid state before curing than a conventional material for forming a resist layer. For example, a thick insulating layer 3 can be formed by using a conventional material for forming a resist layer to which an additive for increasing viscosity or an additive for increasing surface tension is added.

The insulating layer 3 does not necessarily have to have a single-layer structure, but may have a multilayer structure of two or more layers. For example, by applying an insulating material having a property that it is difficult to spread in a fluid state before curing on a printed circuit board on which a conventional resist layer is formed in advance, such as that shown in FIG. An insulating layer having a thickness of 20 μm or more may be formed from the surface. Alternatively, an insulating material having a property that is difficult to spread in a fluid state before curing is applied on an arbitrary printed circuit board, and an insulating material having a moisture-proof effect is further applied thereon, so that the entire surface is at least 20 μm from the land surface. May be formed. In the latter case, the printed circuit board hardly absorbs moisture.

Next, the printed circuit board 1 shown in FIG.
The insulating layer 3 is formed with a thickness t of 100 μm or more from the surface. This insulating layer 3 is also a resist layer 1 shown in FIG.
Similarly to 03, the land 2 is formed so as to cover the entire periphery of the land 2 except for the central part.

As described above, since the insulating layer 3 formed on the printed circuit board 1 over a part of the land 2 is as thick as 100 μm or more, the insulating layer 3 is used in addition to reinforcing the peel strength of the land 2 and preventing the solder bridge. Thus, the cream solder can be directly applied to the printed circuit board 1.

That is, the thickness of the solder mask is usually 100 μm.
Since the thickness is m to 200 μm, the insulating layer 3 having a thickness t of 100 μm or more can be used instead of a solder mask. Therefore, cream solder can be directly applied to the printed circuit board 1 using the insulating layer 3 without using a solder mask. Note that the insulating layer 3 may be used instead of the solder mask.
Is sufficient if the thickness t is 100 μm or more and 200 μm or less.

The insulating material used for forming the insulating layer 3 shown in FIG. 2 also has a property that it does not easily spread on the printed circuit board 1 in a fluid state before curing as compared with a conventional material for forming a resist layer. I just want it. For example, a thick insulating layer 3 can be formed by using a conventional material for forming a resist layer to which an additive for increasing viscosity or an additive for increasing surface tension is added.

The insulating layer 3 shown in FIG. 2 does not need to have a single-layer structure, and may have a multilayer structure of two or more layers.
For example, as described above, by applying an insulating material having a property that it is difficult to spread in a fluid state before curing on a printed circuit board on which a conventional resist layer is formed in advance, such as the one shown in FIG. As the entire two layers, an insulating layer having a thickness of 100 μm or more may be formed from the land surface. Alternatively, an insulating material having a property that is difficult to spread in a fluid state before curing is applied on an arbitrary printed circuit board, and an insulating material having a moisture-proof effect is further applied thereon, so that the entire surface is 100 μm from the land surface. An insulating layer having the above thickness may be formed. In the latter case, the printed circuit board hardly absorbs moisture.

Next, a method of applying cream solder to the printed circuit board 1 shown in FIG. 2 will be described with reference to FIG.

As shown in FIG. 3A, the printed circuit board 1
The cream solder 4 is directly placed near an end outside the region where the upper land 2 exists (hereinafter, referred to as a land region). Next, the squeegee 5 is angled and the cream solder 4
The squeegee 5 is moved toward the opposite end to the outside of the land area near the opposite end. Thus, the cream solder 4 is applied on the lands 2 of the printed circuit board 1 as shown in FIG.

If cream solder remains on the insulating layer 3 on the printed circuit board 1 except for the land 2, the surface of the insulating layer 3 may be polished in advance.

As a method of forming the insulating layer 3 having a thickness of 100 μm or more on the printed circuit board 1, a method of forming the insulating layer 3 using a mask as in the conventional resist layer formation, or a method not using a mask For example, there is a method of forming the insulating layer 3 by a curtain coating method.

[0029]

According to the present invention, an insulating layer is formed over a part of a land on a printed circuit board so as to have a thickness of 20 μm or more from the land, so that the land is reinforced so as not to peel even if the peel strength is weak. Can be. When the thickness of the insulating layer is as thick as 100 μm or more, cream solder can be directly applied to the printed circuit board using the insulating layer instead of a solder mask, in addition to reinforcing the peel strength.

[Brief description of the drawings]

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

FIG. 2 is a sectional view showing another example of the printed circuit board according to the embodiment of the present invention.

FIG. 3 is a view showing the application of cream solder to the printed circuit board shown in FIG. 2 as a cream solder application method according to an embodiment of the present invention.

FIG. 4 is a plan view showing an example of a conventional printed circuit board.

FIG. 5 is a sectional view of FIG. 4;

FIG. 6 is a plan view showing another example of a conventional printed circuit board.

FIG. 7 is a sectional view of FIG. 6;

FIG. 8 is a diagram showing a conventional cream solder printing method.

[Explanation of symbols]

 Reference Signs List 1 printed board 2 land 3 insulating layer 4 cream solder 5 squeegee

Claims (3)

[Claims] 1. A printed circuit board having a land for mounting electronic components (hereinafter, referred to as a land), comprising an insulating layer formed on the surface of the substrate. A printed circuit board which is formed so as to cover a part of the land from the surface of the substrate so as to cover a peripheral portion, and has a thickness of 20 μm or more from the surface of the land. 2. A printed circuit board, wherein the thickness of the insulating layer is 100 μm or more. 3. A method for applying cream solder to the printed circuit board according to claim 2, wherein the insulating layer of the printed circuit board is used instead of a solder mask.