JPH06112644A - Method of soldering printed wiring board - Google Patents

Abstract

PURPOSE:To eliminate solder balls and avoid a pattern short-circuit, etc., when an electronic component is soldered onto a printed wiring board. CONSTITUTION:When an electronic component 1 is soldered onto a printed wiring board 2, the printed wiring board 2 is inserted into a soldering heating apparatus 3 having an evacuation mechanism and the soldering is performed in a reducing gas 4 atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for soldering an electronic component onto a printed wiring board. In recent years, electronic components have become increasingly narrower and more compact. Solder, which has many advantages, is used as the material for joining and connecting the electronic component and the printed wiring board.

With the realization of high-density mounting, electronic parts have been changed to surface-mounted parts and printed wiring boards have been made into fine patterns.

[0003]

2. Description of the Related Art In surface mounting of electronic parts, solder is formed into a paste and supplied on the surface of a printed wiring board by screen printing. Electronic components are mounted on this printed wiring board and soldered by the reflow method. Then, the conventional method is to wash the flux with an organic solvent.

[0004]

However, from the viewpoint of environmental protection, CFCs and 1.1.1. Regulations on the use of trichloroethane etc. have begun, and solvents for cleaning flux, and
The cleaning method has become a big problem.

The purpose of cleaning this flux is
In addition, halogen in the flux is removed to prevent corrosion and migration of the copper foil on the printed wiring board and electrodes of electronic parts, etc. Secondly, to prevent pattern short-circuiting of the wiring due to solder balls, and thirdly, the optical system. The fourth purpose is to prevent diffuse reflection by the resin in the visual inspection, and fourthly to prevent non-contact of the contact pins.

Therefore, a soldering method in a nitrogen atmosphere has already been implemented, and it is effective in preventing the copper foil of the printed wiring board, the electrode part of the electronic component, and the solder particles from being oxidized.

However, there is no ability to actively remove oxides. In view of the above problems, it is an object of the present invention to provide a method for soldering that prevents the generation of solder balls and prevents wiring pattern short circuits and the like.

[0008]

FIG. 1 shows a soldering heating apparatus having an evacuation mechanism of the present invention. In the figure,
1 is an electronic component, 2 is a printed wiring board, 3 is a soldering heating device having an evacuation mechanism, 4 is a reducing gas, 5 is a substrate conveying belt, 6 is an infrared heating lamp, 7 is a gas inlet, and 8 is exhaust. Mouth, 9 is a heating chamber, 10 is an inlet door, 11 is an inlet chamber, 12 is an outlet door, 13 is an outlet chamber, 14 is a gate valve, and 15 is a valve.

For the problem of the solder paste itself, which is the first purpose of flux cleaning, a type of flux containing a small amount of halogen is used. The generation of the second solder balls is a manufacturing problem, and if the solder balls can be eliminated, the surface mounting board can be made non-cleaning.

The third and fourth problems can be solved by using a low residue flux. The generation mechanism of solder balls is as follows: First, the amount of solder is too large to protrude from the solder joint. The particles remain between the wiring patterns after being extruded. Thirdly, the solvent content in the solder paste evaporates rapidly due to heating, so that the solder particles are repelled. Fourthly, the surface of the solder particles is oxidized. Therefore, the solder particles do not fuse with each other.

Therefore, in order to prevent the generation of solder balls, in the present invention, the printed wiring board 2 on which the electronic component 1 to be soldered is surface-mounted is soldered in the soldering heating device 3 having a vacuum exhaust mechanism.

The solder paste supplied by screen printing to the printed wiring board 2 is evacuated and heated to
The solvent in the paste is gradually evaporated. As a result, the above-mentioned second and third problems at the time of heating are solved. Moreover, the fourth problem is solved by reducing with a mixed gas of argon (Ar) and hydrogen (H ₂ ), and the copper foil of the printed wiring board 2 and the oxide of the electrode part of the electronic component are removed.

As described above, the vacuum and the reducing gas make it unnecessary to add halogen to the solder paste. Further, since the resin component in the paste is not carbonized in a vacuum or the atmosphere of the reducing gas 4, the solder paste is transparent, and the appearance inspection does not cause any problems.

That is, when the electronic component 1 is soldered to the printed wiring board 2, the printed wiring board 2 is inserted into a soldering heating device 3 having a vacuum evacuation mechanism as shown in FIG. It is achieved by soldering in an atmosphere of reducing gas 4.

[0015]

In the present invention, soldering of electronic components to a printed wiring board is performed in a reducing gas atmosphere, so that solder balls are not generated.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of a heating device having a vacuum exhaust mechanism of the present invention, and FIG. 2 is a soldering temperature profile.

In the figure, 1 is an electronic component, 2 is a printed wiring board, 3 is a soldering heating device having an evacuation mechanism, 4 is a reducing gas, 5 is a substrate conveying belt, 6 is an infrared heating lamp, and 7 is gas. Inlet, 8 exhaust, 9 heating chamber, 10 inlet door, 11 inlet chamber, 12 outlet door,
13 is an outlet chamber, 14 is a gate valve, and 15 is a valve.

An embodiment of the present invention will be described with reference to FIGS. First, the solder paste is applied to the copper foil of the printed wiring board 2 by screen printing. The electronic component 1 is mounted thereon, placed on the substrate transfer belt 5 of the soldering heating device 3 having a conveyor furnace type vacuum exhaust mechanism, and inserted into the device.

The inside of the heating chamber 9 of this apparatus is heated by the infrared heating lamp 6. The apparatus is evacuated to a vacuum of 0.1 Pa, and a mixed gas of argon and hydrogen, which is the reducing gas 4, is introduced at a rate of 250 to 500 sccm from the gas inlet 7 to maintain the degree of vacuum at 1 to 10 Pa.

No heating mechanism is attached to the inlet chamber 11 and the outlet chamber 13, and the inlet chamber 11, the heating chamber 9,
A gate valve 14 is provided between the outlet chambers 13 to shut off each chamber.

A printed wiring board 2 in which an electronic component 1 is placed on a predetermined copper foil of the printed wiring board 2 in the inlet chamber 11.
Is set, and after the atmosphere becomes the same as that of the heating chamber 9, the gate valve 14 is opened and the printed wiring board 2 is put into the heating chamber 9.

In the heating chamber 9, the printed wiring board 2
The solvent in the upper solder paste evaporates due to vacuum and heating. The temperature profile of soldering is as shown in FIG.

First, in the preheating section, 150 to 16 for 40 to 60 seconds
Preheat to 0 ° C. Next, 230 to 240
The electronic component 1 is soldered to the printed wiring board 2 by heating at 40 ° C. for 40 to 80 seconds.

The printed wiring board 2 is cooled in the outlet chamber.
The temperature profile is such that it is performed in 13 and does not cool rapidly. This is to prevent the printed wiring board 2 from warping due to the rapid cooling and from causing problems such as a bridge in soldering.

[0025]

According to the present invention, when soldering, no solder balls are generated, it is not necessary to add halogen to the flux, and solder voids are not generated.

Therefore, cleaning with an organic solvent after soldering is unnecessary, corrosion of copper foil and electrodes does not occur, and problems such as migration do not occur. In addition, the resin in the solder paste is not carbonized, which facilitates visual inspection.

For the above reasons, the baking process by moisture absorption of the thin resin package becomes unnecessary.

[Brief description of drawings]

FIG. 1 is a soldering heating device having an evacuation mechanism of the present invention.

[Figure 2] Soldering temperature profile

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electronic component 2 Printed wiring board 3 Soldering heating device having a vacuum exhaust mechanism 4 Reducing gas 5 Substrate transport belt 6 Infrared heating lamp 7 Reducing gas inlet 8 Exhaust port 9 Heating chamber 10 Entrance door 11 Entrance chamber 12 Exit door 13 Outlet chamber 14 Gate valve 15 Valve

Claims (1)

[Claims] 1. When soldering an electronic component (1) to a printed wiring board (2), the printed wiring board (2) is inserted into a soldering heating device (3) having an evacuation mechanism to reduce reducibility. A method for soldering a printed wiring board, which comprises performing soldering in a gas (4) atmosphere.