JPH05285641A - Solder reflow furnace - Google Patents

Abstract

PURPOSE:To prevent a soldering ball from being generated during the reflow of a high density packaging printed circuit board. CONSTITUTION:The melting zone of a soldering reflow furnace 3 is surrounded by an inner case 4 to prevent the stirring by the hot wind from a fan 2, and the surface of the printed circuit board is uniformly preheated by the hot wind circulation by a heater 1 and a fan 3 at the preheated part. A printed circuit board 8 is uniformly preheated at the preheating part, and then, carried to a partitioned melting zone. This melting zone is kept in the windless condition, and static heating is executed by the far infrared radiation 6. This constitution allows the stirring by the hot wind from the surroundings to be shut off, preventing the molten solder from generating a soldering ball by the hot wind and also eliminating the parts from being erected. Since the cream solder can be melted while introducing the gaseous nitrogen into the inner case, packaging can be executed by using the cream solder of non-cleaning type which can not be used in the oxidizing atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder reflow furnace used for soldering a printed circuit board which constitutes an electronic circuit of an electronic device such as a computer and an information device.

[0002]

2. Description of the Related Art In recent years, the degree of integration of electronic devices has increased, and the degree of integration of printed circuit boards used in electronic devices has also increased. To solder such a highly integrated printed circuit board, a process different from the conventional one is required.

FIG. 3 shows the structure of a conventional hot air circulating type solder reflow furnace, and FIG. 4 shows the structure of a conventional far infrared ray type solder reflow furnace. As shown in the figure, a printed board 16 made of glass epoxy or the like having an electronic component 17 such as an IC mounted on its surface is conveyed by a conveyor belt 15. Above the conveyor belt, the heater 1 controlled to a predetermined temperature
1. Far-infrared heater and fan 12 that stirs the air in the furnace
A reflow furnace 13 having a built-in
6 passes through the reflow furnace 13 and is heated to reflow the cream solder.

The operation of the solder reflow furnace constructed as above will be described below. The cream solder should be printed on the land on the surface of the printed circuit board 16 that can be mounted on both sides using a metal plate, and then mounted on it.
An electronic component 17 such as C is placed on the printed circuit board 16
A conveyor belt 15 driven by a gear 14
Place it on top and move it. The printed circuit board 16 is heated by the heater when passing through the reflow furnace 13, the cream solder is melted, and after cooling, the electronic component 17 is fixed and the mounting is completed.

[0005]

However, in the conventional reflow furnace as described above, when the hot air circulation type is used, the air in the furnace is strongly agitated. Balls are easier to generate. Also,
In the far-infrared reflow furnace, there was a problem that the temperature distribution in the preheating part of the heater and the melting zone was poor, and many parts with poor solder wetting occurred. The solder balls exist on the printed circuit board as they are, and there is a problem that a short circuit between electrodes of the printed circuit board or a malfunction occurs during the subsequent processing steps or during the operation of the printed circuit board.

The present invention solves such a problem and eliminates solder balls and component standing that occur when solder is reflowed in a reflow furnace, and produces a printed circuit board that does not cause short circuit between electrodes or malfunction due to the solder balls. It is an object of the present invention to provide a solder reflow furnace which can be manufactured.

[0007]

In order to solve this problem, the present invention provides a conveyor for carrying a printed circuit board on which electronic components are fixed, and a preheating furnace provided over the conveyor and comprising a heater and a fan. , Comprising a melting zone containing a far infrared heater in an inner case provided in a part of the preheating furnace, heating the printed circuit board to a temperature below the melting point of solder in the preheating furnace, melting the solder in the melting zone, The electronic parts are mounted.

[0008]

According to this structure, the surface temperature of the printed circuit board is made uniform by circulating hot air in the preheating section, and the melting zone in the solder reflow furnace is surrounded by the inner case and partition plate to prevent disturbance by hot air from the surroundings. Melt the solder. The printed circuit board is first uniformly preheated in the above preheating part and then conveyed to the partitioned melting zone. In this melting zone, it is kept windless and is statically heated by far infrared rays. In this way, hot air circulation heating with a uniform temperature distribution preheats the solder to a temperature at which it does not melt, and then heats gently in a partitioned melting zone without disturbing phenomena until the solder melts. By this heating step, a solder reflow furnace with high reliability in which solder balls are not generated on the substrate surface and parts do not stand is realized.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A solder reflow furnace according to an embodiment of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 shows the structure of a solder reflow furnace of Embodiment 1. As shown in the figure, the heater 1 for heating the solder, the fan 2 for stirring the air in the furnace are the reflow furnace 3
A melting zone that is provided inside and that heats the cream solder until it is melted is formed by the inner case 4, and a far infrared heater 5 is built in the inner case. A printed circuit board 8 made of glass epoxy or the like is conveyed below the reflow furnace 3 by a conveyor 6. The conveyor 7 is driven by the gear 6,
A printed circuit board on which an electronic component 9 such as an IC is mounted is conveyed.

Next, the operation of the solder reflow furnace configured as described above will be described. A cream solder is printed on a land formed on the surface of the printed circuit board 8 by using a metal plate, and a component 9 to be mounted such as an IC is placed thereon. The printed circuit board 8 is driven by the gear 6 and the conveyor 7 is driven.
And then sent to the reflow furnace 3. The front part of the reflow furnace 3 is controlled so that the air heated by the heater 1 is agitated by the fan 2 and preheated at a temperature at which the cream solder does not melt. The printed circuit board 8 that has been further conveyed reaches the melting zone formed by the inner case 4. Here, the cream solder on the printed circuit board 8 is radiantly statically heated by the far-infrared heater 5 to melt, the electronic component 9 is soldered, and then cooled and mounted.

(Embodiment 2) FIG. 2 shows the structure of a solder reflow furnace of Embodiment 2. The reflow furnace of the second embodiment is provided with a gas introduction pipe 10 for introducing an inert gas such as nitrogen gas into the inner case 4, in addition to the solder reflow furnace of the first embodiment shown in FIG.

Next, the second embodiment constructed as described above
The operation of the solder reflow furnace will be described. Nitrogen gas is introduced into the inner case 4 from the outside through the nitrogen gas introduction pipe 10,
The oxygen gas concentration in the inner case 4 can be freely controlled. As a result, when the solder is melted in the melting zone where the temperature becomes high, the soldering can be performed without oxidizing the printed circuit board, the electronic component and the surface of the solder.

According to the above embodiment, the inner case 4 is provided in the reflow furnace 3 to block the disturbance caused by the hot air from the surroundings, so that the molten solder causes the hot air to generate the solder balls and the parts stand up. There is nothing to do. Further, since the cream solder can be melted while introducing the nitrogen gas into the inner case 4, it is possible to mount using the non-cleaning type cream solder which cannot be used in the oxidizing atmosphere.

[0015]

As is apparent from the above description of the embodiments, according to the present invention, the melting zone of the solder reflow furnace is surrounded by an inner case and a partition plate to prevent disturbance due to hot air from the surroundings.
In the preheating section, the surface temperature of the printed circuit board is made uniform by circulating hot air. The printed circuit board is first uniformly preheated in the above preheating part and then conveyed to the partitioned melting zone. In this melting zone, it is kept windless and is statically heated by far infrared rays. With this configuration, it is possible to block the disturbance caused by the hot air from the surroundings, and it is possible to prevent the molten solder from generating a solder ball or causing the component to stand up due to the hot air. Further, since the cream solder can be melted while introducing the nitrogen gas into the inner case, the non-cleaning type cream solder which cannot be used in the oxidizing atmosphere can be mounted.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a solder reflow furnace according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a schematic configuration of a solder reflow furnace according to the second embodiment.

FIG. 3 is a diagram showing a schematic configuration of a conventional hot air circulation type solder reflow furnace.

FIG. 4 is a view showing a schematic configuration of the far infrared solder reflow furnace.

[Explanation of symbols]

 1 Heater 2 Fan 3 Reflow Furnace 4 Inner Case 5 Far Infrared Heater 6 Gear 7 Conveyor 8 Printed Circuit Board 9 Electronic Component 10 Gas Inlet Pipe

Claims (2)

[Claims] 1. A conveyor for carrying a printed circuit board to which electronic components are fixed, a preheating furnace which is provided over the conveyor and includes a heater and a fan, and an inner case provided in a part of the preheating furnace. A solder reflow furnace having a melting zone containing an infrared heater, heating the printed circuit board to a temperature below the melting point of solder in the preheating furnace, melting the solder in the melting zone, and mounting electronic parts. 2. The inner case is provided with a gas introduction pipe penetrating outside the solder reflow furnace, and the solder is melted while introducing an inert gas into the inner case through the gas introduction pipe. Solder reflow oven.