JPH0750480A - Soldering method for electronic component - Google Patents

Abstract

PURPOSE:To decrease the height of an electronic components after soldering and mounting, by printing solder paste on only the peripheral region of a mounting part of an electronic component on an electrode pad of a printed circuit board, mounting the electronic component on the pad surface to be in direct contact, and reflowing solder. CONSTITUTION:On the surface of an electrode pad 1, solder paste 2 is applied, by a printing method, to only the peripheral region of the part on which an electronic component 3 is to be mounted. The electronic component 3 is directly mounted on the part where the solder paste is not applied and the electrode pad 1 is exposed as it is. The electronic parts is mounted lower than the peripheral solder paste by the amount that the solder paste 2 is not present in the mounting part. When solder is subjected to reflow by heating in this state, the solder paste 2 is melted and rises up along the side end surface of the electronic component 3. Solder 5 fixes the electronic component 3 so as to hold both ends thereof. It does not occur that a solder ball is generated by the solder paste 2 pushed out from the lower part of the electronic component 3, and the height of the upper surface of the electronic component 3 becomes always constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for printing and applying a solder paste on an electrode pad of a printed circuit board to solder a surface mounting component.

[0002]

2. Description of the Related Art The method of soldering components on the surface mounting of components on a printed circuit board includes a flow method of applying molten solder to the components and the substrate, and a method of soldering the components or the substrate in advance and then applying heat. It is roughly classified into a reflow method in which the solder is melted by applying heat, cooled and soldered.

If the amount of solder for joining the components is too small, the joint strength between the components and the substrate will be weak, and if it is too large, for example, in a 0.5 mm pitch molded IC or the like, a short circuit will occur between electrodes by soldering. Therefore, it is important to keep the amount of solder within a certain range, since problems such as electrical failure will occur. When the flow method is used, it is not possible to control the amount of solder adhered, so in surface mounting, the reflow method is usually used for soldering.

As a method of supplying solder by the reflow method, solder is made into particles and mixed with a solvent to form a cream-like solder paste, which is applied to a substrate.
There are a dispenser method and a printing method for applying. Among them, in the dispenser method, it is difficult to quantitatively control the amount of solder applied due to the influence of temperature and pressure, and thus the printing method is usually used.

A mask is used in the printing method, but a screen mask is printed by blocking a portion other than a predetermined portion of a mesh-like sheet to prevent the solder from coming out, and a predetermined portion of a metal plate is hollowed out to solder only that portion. There is a metal mask to make it appear. Printing of the solder paste uses a metal mask to which more solder is applied.

In order to solder an electronic component for surface mounting, conventionally, as shown in FIG. 2, a solder paste (2) is formed on the entire surface of an electrode pad (1) of a printed circuit board (4).
Was printed and applied, and the electronic component (3) was placed on the solder paste (2) as shown in FIG. Therefore, the electronic component is soldered to a higher position by the amount of the solder paste (2) below the electronic component (3). This is fine if there are no height restrictions,
If the height after soldering is limited, the solder under the component causes height problems.

When the height is always constant, it may be designed in consideration of the height, but it is not always easy to attach the component depending on the surface condition of the component or the pad. For example, if a part of the copper surface is oxidized, it is difficult for solder to attach to that part, so that the solder concentrates on other parts and the parts are abnormally high even though the amount of solder is the same. There was a problem attached. Further, depending on the amount of force applied when the electronic component (3) is placed on the solder paste (2), the electronic component bites into the layer of the solder paste (2), and the solder paste corresponding to that amount of the electronic component (3). As a result of being extruded into the lower space, the extra solder paste was melted and curled during reflow to form a solder ball (6) as shown in FIG. 2C, which could be a cause of defects.

[0008]

SUMMARY OF THE INVENTION The present invention has been made as a result of studies in view of such drawbacks of mounting electronic components by a conventional solder paste, and an object thereof is to provide an electronic component after soldering mounting. Lower the height of the parts,
This is to eliminate variations in soldering height and generation of solder balls.

[0009]

That is, according to the present invention, the solder paste is printed and applied only on the peripheral area of the mounting portion of the electronic component on the electrode pad of the printed circuit board, and the electronic component is directly attached to the electrode pad surface. It is a method of soldering an electronic component, which is characterized in that the electronic components are placed in contact with each other and the solder is reflowed.

As shown in FIG. 1A, the solder paste (2) is printed only on the peripheral region of the surface of the electrode pad (1), leaving a portion for mounting the electronic component (3). Give. FIG. 1B shows a state in which the electronic component (3) is directly placed on a portion where the electrode pad (1) is exposed without applying the solder paste (2). It can be seen that it is placed lower than the surrounding solder paste because there is no paste. When heating and reflowing the solder in this state, the solder paste (2) melts,
As shown in FIG. 1C (side sectional view), the electronic component (3) rises along the side end surface of the electronic component (3), and the solder (5) holds both ends of the electronic component (3) so as to be fixed.

Therefore, there is no problem in terms of the joint strength of the electronic component (3) by soldering. Further, unlike the conventional method shown in FIG. 2, solder balls (6) are not generated by the solder paste extruded from the lower portion of the electronic component, and the height of the upper surface of the electronic component (3) is always constant. .

[0012]

According to the present invention, the height of the electronic component after soldering can be reduced and the variation can be eliminated.
Further, since it is possible to suppress the generation of solder balls generated in the lower part of the electronic component, the yield after solder reflow is significantly improved, which is a great industrial advantage.

[Brief description of drawings]

1A and 1B are views for explaining a method of the present invention, in which FIG. 1A is a top view of an electrode pad, FIG. 1B is a side view of a state where electronic components are placed, and FIG. 1C is a state after solder reflow. FIG.

FIG. 2 is a diagram for explaining a conventional method, (a) is a top view of an electrode pad in a state where a solder paste is printed,
(B) is a side view of a state where electronic components are placed, and (c) is a side sectional view showing a state after solder reflow.

[Explanation of symbols]

 1 Electrode Pad 2 Solder Paste 3 Electronic Component 4 Printed Circuit Board 5 Solder 6 Solder Ball

Claims (1)

[Claims] 1. A solder paste is printed and applied only on a peripheral region of a mounting portion of an electronic component on an electrode pad of a printed circuit board, and the electronic component is directly placed on the electrode pad surface to be mounted and solder reflow is performed. A method for soldering an electronic component, comprising: