JPS63273398A - Reflow soldering method for printed substrate - Google Patents

Abstract

PURPOSE:To rigidly solder the electrode of a chip component to a printed substrate by so provide a cream solder as not to fill between the land of the substrate and the electrode of the component, and then thermally melting the solder. CONSTITUTION:A section of the land 2 of a printed substrate 1 where a chip component 4 is not placed is coated with cream solder 3. The component is so placed as not to fill the solder between the electrode 5 of the component 4 and the land 2. When the center of the component 4 is fixed with an adhesive 6, its position is not displaced. When it is heated, solder flux flows out to be invaded between the land 2 and the electrode 5 by means of capillary phenomenon, powder solder is then melted to follow to the flux, thereby completely filling between the land 2 and the electrode. The solder 3 is bonded to the side of the electrode to solder it at both the inner and outer surfaces of the bonded part without malfunction so that no void is generated between the component and the land, thereby increasing the bonding strength.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of soldering a printed circuit board and a chip component using cream solder.

[Conventional technology]

Modern electronic devices are becoming smaller and lighter, so the electronic components used in them are also very small, such as chip components and flatback components (hereinafter simply referred to as chip components). It's starting to look like this.

Chip components cannot be soldered with a soldering iron because the soldering area is small, so ``dip soldering'' and ``reflow soldering'' are generally used to solder chip components.

Dip soldering is a method in which chip components are temporarily fixed in place on a printed circuit board with adhesive in advance.
After coating it with black and preheating it, it is dipped in molten solder and soldered. Furthermore, the reflow soldering method is a method in which cream solder is applied to the runt of a printed circuit board, a chip component is mounted thereon, and then soldering is performed by heating and melting the cream solder.

The dip soldering method requires large-scale soldering equipment, and during soldering, flux frames remaining on the sides of the chip prevent molten solder from penetrating into the lands and corners of the chip components. There was a problem of poor soldering. The reflow soldering method is often used this time because it does not cause soldering defects like the dip soldering method.

In the conventional reflow soldering method, as shown in Figure 6, cream solder (3) is applied to the entire land (2) of the printed circuit board (1), and then the chip component (4) is applied on top of the cream solder (3).
(Fig. 7) and heated with a heating device such as a reflow oven or a high-temperature steam tank to perform soldering.

[Problem that the invention seeks to solve]

With conventional reflow soldering methods, chip components often peel off easily with the slightest impact after soldering, even if the solder appears to be completely adhered.

Furthermore, printed circuit boards soldered using conventional reflow soldering methods sometimes have poor insulation resistance, which can sometimes reduce the reliability of electronic devices.

[Means for solving problems]

When observing the peeled surface of a printed circuit board and a chip component soldered using the conventional reflow soldering method, so-called voids, which are not completely filled with solder, may occur.

As a result of intensive studies by the inventors regarding the occurrence of voids, the following findings were discovered. In other words, in the conventional reflow soldering method, as shown in Figure 7, cream solder (3), which is a mixture of powdered solder and liquid flux, is already present between the land of the printed circuit board and the electrode of the chip component. When the printed circuit board is heated to melt the cream solder, liquid flux is formed at the soldering area formed by the land (2) of the printed circuit board and the electrode (5) of the chip component (4), as shown in Figure 10. (F) is surrounded by the molten solder (S), and the flux cannot be extracted, resulting in voids (8). Furthermore, the reason why printed circuit boards soldered using conventional reflow soldering methods have poor insulation resistance is that cream solder is already present between the lands of the printed circuit board and the electrodes of the chip components. This phenomenon occurs because the chip component (4) is placed on top of the cream solder (3) as shown in Figure 7.
Cream solder extruded by chip components adheres to areas other than the lands of the printed circuit board, and this melts and remains as a large ball (Q) outside the lands, or it disperses into small balls and adheres to the outside of the lands. , these are what lowered the insulation resistance.

Therefore, the present inventors completed the present invention by focusing on the fact that if cream solder does not exist between the land of the printed circuit board and the electrode of the chip component from the beginning, the generation of voids and the decrease in insulation resistance can be suppressed. Ta.

The feature of the present invention is a method of soldering a printed circuit board and chip components using cream solder, in which cream solder is applied to the land of the printed circuit board other than the part where the chip components are mounted. , the chip component is placed on the printed circuit board so that the cream solder is not caught between the lands of the printed circuit board and the electrodes of the chip component, and then the printed circuit board is heated to melt the cream solder to connect the printed circuit board. It is a reflow soldering method for printed circuit boards that connect chip components.

[Effect]

Since there is no cream solder between the land of the printed circuit board and the electrode of the chip component from the beginning, the flux in the cream solder is not surrounded by molten solder.

Furthermore, since the cream solder applied to the land is pushed out by the chip components and does not adhere to the outside of the land, balls do not occur outside the land.

〔Example〕

The present invention will be explained below based on the drawings. FIG. 1 is a diagonal flow diagram illustrating the application state of cream solder in the present invention;
2 to δ are cross-sectional views illustrating the soldering process of the present invention, and FIG. 9 is a plan view illustrating the flow of flux and molten solder during soldering in the present invention.

First, cream solder is applied to the lands (2) of the printed circuit board (1) using silk screen printing, metal screen printing, a dispenser, etc. (FIG. 2). The cream solder is applied here where the electrodes of the chip component are not placed when the chip component is placed on the printed circuit board.

Next, a predetermined chip component is placed on the land coated with cream solder, making sure that the cream solder is not caught between the electrode (5) of the chip component and the land (2) of the printed circuit board. figure). At this time, it is preferable to fix the approximately central portion of the chip component to the printed circuit board with an adhesive (6) so that the chip component does not shift.

When the cream solder is applied in this way and the printed circuit board on which the chip components are mounted is heated in a heating device such as a reflow oven or a high-temperature steam bath, the flux (F) in the cream solder first flows out. , it penetrates between the land (2) of the printed circuit board and the electrode (5) of the chip component due to capillary action (Fig. 4).

As the heating progresses further, the powdered solder in the cream solder melts and flows following the flux that flowed out earlier (Figure 9), completely filling the space between the land (2) and the electrode (5) with solder. I come to do it. The solder (5) also adheres to the side surfaces of the electrodes, resulting in defect-free soldering on both the inner and outer surfaces of the joint (FIG. 5).

〔Effect of the invention〕

According to the present invention, since voids are not generated between the land of the printed circuit board and the electrode of the chip component, a soldered portion with strong adhesive strength can be obtained.

Further, according to the present invention, since no balls remain on the printed circuit board other than the lands, insulation failure does not occur.
We can provide reliable electronic equipment.

[Brief explanation of the drawing]

Fig. 1 is a perspective view illustrating the cream solder application state in the present invention, Figs. 2 to 5 are sectional views illustrating the soldering process of the present invention, and Figs. 6 to 8 are the process of the conventional reflow soldering method. 9 is a plan view illustrating the flow of flux and molten solder during soldering in the present invention, and FIG. 10 is a plan view illustrating the occurrence of voids and balls in the conventional reflow soldering method. be. 1... Printed circuit board 2... Land 3... Cream solder 4... Chip parts 5... Electrode
6... Adhesive Figure 1 Figure 6 Figure 17 Figure 8 Figure 2BQ jI9 Flash Figure 10

Claims (1)

[Claims] A method of soldering a printed circuit board and chip components using cream solder, which comprises: applying the cream solder to lands of the printed circuit board other than the areas on which the chip components are mounted; The chip component is mounted on the land so that it is not caught between the land of the printed circuit board and the electrode of the chip component, and then the printed circuit board and the chip component are bonded by heating the printed circuit board and melting the cream solder. How to reflow solder a printed circuit board.