JPH057072A - Printed wiring board - Google Patents

Abstract

PURPOSE:To increase the bond strength of land pads onto the title printed-wiring board by a method wherein the outer periphery of the land pads is also coated with a resist. CONSTITUTION:The whole surface of the title printed-wiring board 1 is copper plated. Later, the circuit composed of the elements including land pads 2 and patterns 3 and the white and black inversed circuit are made of dry film, etc. Next, the circuit parts are copper-plated further to form an etching resist on the copper plating. Next, the land pads 2 are independently formed by further etching step. At this time, the area of the land pads 2 is made larger than that specified by the soldered surface size of the terminal of an electronic part. Next, a resist 4 is formed by coating not only the parts excluding the land pads 2 but also the parts entering inside the land pads 2 by the depth of 0.2-1.0mm with the resist 4. Through these procedures, the bond area of the land pads 2 onto the printed-wiring board can be increased thereby enabling the bond strength to be increased resultantly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a land pad of a printed wiring board for fixing terminals of electronic parts in a conductive state.

[0002]

2. Description of the Related Art FIG. 2A is an enlarged plan view of a part of a conventional printed wiring board, and FIG.
It is b sectional drawing. Formed on the upper surface of the printed wiring board 1 is a land pad 2 for fixing a terminal of an electronic component (not shown) in a conductive state by a method such as soldering. The land pad 2 is made of copper foil and is continuous with the copper foil pattern 3 to form an electric circuit. A portion of the upper surface of the printed wiring board 1 other than the land pad 2 is covered with the resist 4. The resist 4 is made of an insulating coating layer formed of a highly insulative plastic ink, and is for preventing short-circuiting or bridging between terminals of soldered electronic components.

The size of the land pad 2 to which the terminal of the electronic component is fixed by soldering or the like is about 0.5 to 2.0 mm larger than the soldering surface of the terminal of the electronic component. I needed it. Further, the resist 4 was located at a position further away from the land pad 2 by 0.1 to 0.5 mm. These dimensions improve solderability and prevent short circuits between terminals of electronic components and bridging between the land pads 2.

[0004]

However, the above-mentioned conventional techniques have the following problems.

When an electronic component is fixed to the land pad 2 by soldering or the like, even if the fixing strength between the terminal and the land pad 2 is sufficient, the land pad 2 and the upper surface of the printed wiring board 1 are joined together. Since the strength is weak, there is a problem that the land pad 2 is separated from the printed wiring board 1 when an external force is applied to the fixed electronic component in the lateral direction. This problem occurs more and more as the terminals of electronic parts become smaller, and in recent years, due to the development of IC development, etc., it frequently occurs in printed wiring boards for fixing electronic parts having ultra-small terminals with fine pitch. It's coming. When the through-hole is formed in the land pad 2, a large bonding strength can be obtained by continuously forming the land-pad on both sides of the edge of the through-hole.
In the case of the microminiature terminal, the area of the land pad is also small and it is often impossible to form a through hole.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide an excellent printed wiring board capable of increasing the bonding strength between the land pad and the printed wiring board and preventing the peeling of the two. And

[0007]

In order to achieve the above object, the present invention has a structure in which the resist also covers the outer periphery of the land pad.

[0008]

The exposed area of the land pad for fixing the terminal of the electronic component requires a large predetermined area with respect to the soldering surface of the terminal. Therefore, by coating the outer periphery of the land pad with a resist as in the present invention, the actual area of the land pad can be made larger than the predetermined area, and the land pad and the printed wiring board can be increased by the increased amount. The joint strength of can be increased.

[0009]

FIG. 1 shows an embodiment of the present invention. The same figure (a)
Is a plan view of a part of the printed wiring board according to the present embodiment, and FIG. 6B is a sectional view taken along the line bb of FIG.

The printed wiring board 1 is usually formed in a plate shape using a glass epoxy material or a paper phenolic material, and the plate thickness is usually about 0.5 mm to 2.0 mm, and it is a very thin plane surface. Forming the body. Then, the land pad 2 is formed on the upper surface of the printed wiring board 1 by a method usually called a subtractive method. That is, copper is plated on the gold surface of the upper surface of the printed wiring board 1, and then a circuit that is the reverse of the circuit including the land pad 2 and the pattern 3 is formed with a dry film or printing ink. Then, the exposed part, that is, the part of the real circuit is plated with copper, and after forming an etching resist on it, by etching,
Land pads having a thickness of 20 to 40 μm are independently formed.
The land pad 2 has an area larger than a predetermined area determined by the size of the soldering surface of the terminal of the electronic equipment. Next, the resist 4 is formed by screen printing or photo printing, and 0.2 to 1.0 mm is entered not only in the portion other than the land pad 2 but also from the outer periphery 2a of the land pad 2 toward the inside of the land pad 2. It is formed by covering up to a part.

As a result, the bonding area between the land pad 2 and the printed wiring board 1 can be increased, and therefore the bonding strength can be increased. That is, conventionally, it is determined by the size of the soldering surface of the terminal of the electronic component, and if it is too large, problems such as bridging between the land pads 2 occur. On the other hand, according to the present embodiment, the actual area of the land pad 2 can be increased to some extent, and the exposed area for fixing the electronic component is the area of the resist 4 that also covers the outer periphery of the land pad 2. It will be determined by the shape of the plane. The exposed portion 2b of the land pad 2 is about 0.1 to 1. outside the soldering surface of the terminal of the electronic component.
It has a range of 0 mm larger and resists outside this range 4
Is formed. 0.1 to 0.5 mm further than this range
An actual land pad is formed in a large area on the outside.
Therefore, the land pad 2 having a larger area than the conventional one is formed by the amount larger by 0.1 to 0.5 mm. The bonding strength between the land pad 2 and the printed wiring board 1, that is, the force required to cause peeling is normally calculated by 1.6 kg × bonding area and is in a proportional relationship with the bonding area. Therefore,
As described above, the bonding strength can be increased by increasing the area of the land pad 2.

The land pad 2 is covered with the resist 4 by covering the outer periphery of the land pad 2 with the resist 4.
Further pressing down can be expected to have the effect of supplementarily increasing the strength of the joint surface.

As described above, according to the above-described embodiment, the area of the land pad 2 is increased to enhance the bonding strength with the printed wiring board 1 and the peeling is less likely to occur. Further, since the area of the land pad 2 is increased, the soldering itself is improved, and the peeling between the land pad 2 and the electronic component can be suppressed.

Further, since the shape and area of the exposed portion 2b of the land pad 2, that is, the portion which plays the role of the actual land pad can be defined by the planar shape of the resist 4, the shape of the land pad 2 itself. In addition, the area can be freely set to some extent, the constraint in circuit design is weakened, and highly accurate design can be performed relatively easily.

Further, according to this embodiment, the resist also covers the outer periphery of the land pad 2, so that the resist 4 covers as compared with the conventional case, so that the area of the resist 4 increases and the area between the land pads 2 increases. This has the effect of further preventing bridging when soldering.

It is considered that the conventional method of forming a resist by the screen printing method is not suitable for the present invention because it has a large amount of bleeding. However, in the recently developed photo printing, the resist method does not cause a bleeding. Therefore, it can be said to be particularly suitable for the present invention.

[0017]

As is apparent from the above-described embodiment, the present invention can increase the actual area of the land pad as compared with the conventional one, and accordingly, increase the bonding strength between the land pad and the printed wiring board. Between them, it has the effect of suppressing peeling.

[Brief description of drawings]

FIG. 1A is a plan view of a part of a printed wiring board according to a first embodiment of the present invention, and FIG. 1B is a sectional view taken along line bb of FIG.

FIG. 2A is a plan view of a conventional printed wiring board, and FIG. 2B is a bb sectional view of FIG.

[Explanation of symbols]

 1 Printed wiring board 2 Land pad 3 Pattern 4 Resist

Claims (1)

Claim: What is claimed is: 1. A land pad for fixing a terminal of an electronic component in a conductive state, and a resist for covering a portion other than the land pad and an outer periphery of the land pad for insulation. Printed wiring board.