JPH03178190A - Method for mounting surface mount parts - Google Patents

Abstract

PURPOSE:To mount surface mount parts on a proper position free from positional deviation without reducing the amount of solder by supplying cream solder onto pads and, after the solder is once made to reflow and solidify, making the surface of the solder flat in advance by heating and pressing the solder with a heater chip of a pulse heater system. CONSTITUTION:Cream solder 2 is supplied onto pads 3 provided on a printed wiring board 4 for soldering leads 1 used as surface mount parts and, after the solder 2 is once made to reflow and solidify, the surface of the solder 2 is made flat in advance by heating and pressing the solder 2 with a heater chip 5 of a pulse heater system. Then parts with leads for surface mounting is placed on the board 4 and positioned to the pads 3 and, at the same time, the leads 1 of the parts are respectively soldered to the pads 3 by melting the solder 2 again by a local heating system of an optical beam method, thermopressing method, etc. Therefore, the positional deviation of leads can be prevented when parts with the leads are soldered and a trouble of soldering caused by a fine positional deviation at the time of mounting can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of mounting leaded components for surface mounting by soldering.

[Conventional technology]

One way to mount electronic components on a printed wiring board is to insert the leads of resistors, capacitors, and dual in-line package (DIP) type components into through-holes on the board, and then solder only the leads. There are two types of mounting methods: the insertion mounting method, in which electrodes are attached to the component itself without pulling out the leads, or the surface mounting method, in which the leads of a flat package are formed so that they can be placed on the board and then soldered. I can do it.

Specific surface mount components include resistors and capacitors in the form of cubes or rectangular parallelepipeds, as well as diodes, transistors, and flat parts with leads formed so that they can be mounted on the board. There are parts such as packages.

The method for soldering these surface mount components and boards is to powder the solder, mix it with a liquid solvent called 7lux, make it into a cream (hereinafter referred to as cream solder), and connect this to the components. The solder is supplied to a position on the board, the electrode part or lead part of each surface mount component to be mounted is placed on top of this, the solder is melted in a high temperature atmosphere, and once it is sufficiently melted, it is cooled. It is solidified (hereinafter this process is referred to as reflow), and the component electrodes and the board pads are connected by solder.

This reflow process can be roughly divided into two types depending on the method of applying heat: one is an overall heating method, and the other is a local heating method. The whole heating method is a method in which the board and the components mounted on the board are placed in a high-temperature atmosphere and reflowed.In this type of flow type, the entire board and the components mounted on the board are placed in a saturated steam bath containing an inert liquid and reflowed. There are paper phase soldering (VPS) and air reflow, which involves placing the solder in high-temperature air for reflow.

On the other hand, the local heating method heats and reflows only the part to be soldered, and examples of this method include, for example:
A pulse heat method applies a special heating head (hereinafter referred to as a heater chip) to the part you want to solder and applies a current to instantaneously heat it using Joule heat, followed by a cooling process. For example, there is a light beam method in which a beam of light is irradiated and heated to reflow.

When actually soldering, the actual situation is that soldering is done in a method that suits the purpose on a case-by-case basis.

Since flat package ICs for surface mounting are sensitive to heat, a local heating method is used in which only the leads are heated and soldered. In this case, the solder supply method is as follows:
Cream soldering is done using a dispenser or by printing. There is no problem when placing the lead directly on the cream solder and soldering it, but due to the design and process of the board, when the cream solder is heated, melted, and then cooled, and then a flat package IC is mounted. When the cream solder is reflowed, the surface becomes rounded, so when trying to solder a flat package IC using the local heating method, as shown in Figure 3(a), the lead (11) will be connected to the solder (12).
If the lead (11) is set in the center of the pad (13) of the board (14) as shown in Fig. 3(b), it will be bonded to the center part of the board (14) without any problem. If the solder (11) is set with even a slight deviation, the surface of the solder (11) is rounded, causing a defect due to positional deviation as shown in FIG. 4(b). As a countermeasure to this problem, if the surface is extremely rounded, there is a method of reducing the amount of solder, but reducing the amount reduces the bonding strength, which is not preferable.

[Problem to be solved by the invention]

The object of the present invention is to provide a flat package IC.
To enable soldering of lead-equipped parts for surface mounting, such as, without reducing the amount of solder, and to enable mounting at regular positions without positional deviation.

[Means to solve the problem]

As shown in FIG. 2, the present invention provides a printed wiring board (
4) Cream solder (2) is supplied onto the pad (3) provided on the pad (3) for joining the lead (1) of the surface mount component, and the cream solder is reflowed and once solidified,
As shown in Fig. 1, after flattening the upper part by heating and pressurizing it with a heater chip (5) using a pulse heater method, the parts with leads for surface mounting are aligned @1lfL, and the light beam method - A mounting method for a surface mount component characterized in that the solder (2) is remelted by a local heating method such as a thermocompression bonding method and the lead (1) of the component is joined.

In order to flatten the upper part of the solder using the pulse heating method used in the present invention, the tips (6) on both sides of the heater chip (5) are exposed as shown in Fig. 1, and the surface is reflowed. The center part of the heater chip (5) first touches the rounded solder (2°) top surface, and as shown in Figure 1(b), heat and pressure is applied so that the surface becomes the pad (3).
After the heater tip (5) has expanded beyond its dimensions and become flat, the protruding tip (6) touches the surface of the substrate (4) to prevent it from going down any further. The surface of the solder (2'') is melted, and when the surface becomes flat, it is rapidly cooled to fix the solder (2).

〔Effect of the invention〕

According to the present invention, it is possible to prevent misalignment of the leads during soldering of components with leads, and it is possible to eliminate defects caused by soldering due to minute misalignment during mounting.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the process of flattening the upper surface of the solder using a heater chip in the present invention. In addition, Figures 2 to 4 are schematic diagrams showing the process of placing component leads on top of the solder, remelting the solder, and joining.
Figure 2 shows a case where the lead position is slightly shifted on top of the solder whose top surface is flat according to the present invention, and Figure 3 shows a case where the lead is placed correctly on the top surface of the solder using the conventional method. Figure 4 shows the case where the lead is placed with a slight positional shift using the conventional method. (a) shows the lead placed on the top surface of the solder, and (b) shows the lead after remelting the solder. Shows the state in which they are joined.

Claims (1)

[Claims] (1) Cream solder is supplied onto the pads provided on the printed wiring board for joining the leads of surface mount components, and after the cream solder is reflowed and once solidified,
After the upper part is heated and pressurized using a heater chip using a pulse heating method to flatten it in advance, a component with leads for surface mounting is placed and aligned, and the solder is remelted using a local heating method to lead the said component. A method for mounting components for surface mounting, characterized by bonding.