JPH0621644A - Reflow furnace with excellent temperature controllability - Google Patents

Abstract

PURPOSE:To properly control the temperature of inactive gas atmospheres in respective tanks of reflow furnace so as to prevent soldering failures by introducing inactive gases in respective tanks of reflow furnace from upper feeding ports through the centers of respective tanks into their bottom side and circulating them upwardly from the periphery by means of propellers. CONSTITUTION:In a reflow furnace 1 consisting of a preheating zone three tanks, a reflow zone tank and a cooling zone tank, inactive gas feeding ports are provided on the ceilings of respective tanks so that fed inactive gases may be introduced through their centers to the bottom sides by propellers 2 prepared on the upper center parts inside respective tanks. Then the inactive gases are heated in respective tanks of the preheating zone and reflow zone by heaters 3 provided on both sides thereof and circulated/stirred upwardly along the both-side walls in the cooling zone. Further an opening part 5 is formed on the lower side of the reflow furnace 1 in a manner to have a minimum area where works and transfer unit may pass through thereby suppressing flowing-in of outside air to the utmost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflow furnace for soldering in an inert gas atmosphere, and more particularly to a reflow furnace capable of obtaining an inert gas atmosphere at a stable temperature.

[0002]

2. Description of the Related Art Conventionally, so-called flow soldering, which is a plane dipping method or a jet soldering method, has been often performed as a soldering method for a printed circuit board in a factory. After the flux is applied to the solder, the side to be soldered is dipped in the molten solder for a predetermined time.

However, recently, portable devices such as VTRs with built-in cameras and headphone stereos, various measuring devices, communication devices such as facsimiles, telephones and exchanges, word processors, personal computers, large computers, automobile devices, control devices for machine tools, etc. As found in applications, it has become necessary to mount electronic components more densely on printed circuit boards.

As a soldering technique for accurately connecting fine parts in order to mount such electronic parts at high density,
Reflow soldering is often used in which cream solder is applied to a printed circuit board by screen printing or the like, and then surface-mounted components are mounted and soldering is performed using a reflow furnace. In the reflow soldering, the cream solder is usually melted in the air to perform the soldering process. In this case, the surface of the printed circuit board and the cream solder are easily oxidized, which hinders the soldering and weakens the strength of the soldered part, or impairs the conductivity. It is often not possible to fully demonstrate.
As a countermeasure, a method has been proposed in which the atmosphere in the reflow furnace is made into a non-oxidizing gas, especially an inert gas, and each manufacturer is now actively studying it.

As described above, the reflow soldering is usually performed in the air, but the printed circuit board surface and the cream solder are oxidized to cause many soldering defects. As a countermeasure against this, a method of making the atmosphere in the reflow furnace a non-oxidizing gas, particularly an inert gas, is proposed.
In this case, the oxygen concentration is lowered to the extent that the printed circuit board surface and the cream solder are not oxidized and soldering failure does not occur, and the temperature of the inert gas atmosphere is maintained at a value necessary for the soldering process. Is very difficult.

When soldering is performed by the reflow soldering apparatus, external air flows into the reflow furnace as the work is carried into the reflow furnace and conveyed between the tanks in the reflow furnace, and the oxygen concentration and temperature are increased. Since the inert gas of another tank flows into the adjacent tank, the oxygen concentration and temperature of the atmosphere of the inert gas in each tank change, and become inconsistent. Due to these effects, defects such as remaining solder balls, wicking, and component standing occur.

In order to prevent these drawbacks, it has been proposed to attach a curtain that can be opened and closed to the work inlet and outlet of the reflow furnace and the opening between the tanks (Japanese Patent Laid-Open No. 61-82965). ), Not only this is not enough effect, but when this curtain carries in the work, the lead is inserted into the through hole of the printed circuit board and bent (inserted mounting), or the electronic component is bonded to the printed circuit board with an adhesive or paste. Then, there is a drawback in that a temporarily fixed product (surface mounting) may be misaligned to become a defective product, or a solder bridge may be generated due to the misalignment.

[0008]

The present invention solves the above-mentioned problems by a reflow soldering apparatus for soldering in an inert gas atmosphere, and more specifically, two or more tanks. In a reflow furnace consisting of a preheating zone, a reflow zone of one or more tanks and a cooling zone of one or more tanks, and the temperature of the inert gas atmosphere in each tank is different, the inert gas supplied from the top (ceiling) of each tank By propelling the central part of the tank downward with a propeller and circulating it so as to rise around it, by reducing the opening of each tank to a size that allows the work and its transfer equipment to pass, Since the flow of the active gas is suppressed as much as possible, the temperature of each tank can be maintained at a predetermined value, which allows stable reflow soldering.

[0009]

As described above, according to the present invention, the propeller is provided at the center of each tank of the reflow furnace for soldering in the inert gas atmosphere, and the inert gas is caused to flow downward in the center of the tank and the surrounding area is maintained. By circulating so as to ascend and at the same time making the opening to the minimum required size, an inert gas atmosphere with stable temperature was obtained in each tank of the reflow furnace, and soldering failure could be completely prevented. Further, since this reflow furnace has a simple structure, maintenance is extremely easy.

[0010]

FIG. 1 shows an embodiment of the reflow furnace (1) of the present invention with the front cover removed. FIG. 2 is a lateral cross-sectional view of the preheating zone or reflow zone of the reflow furnace (1) of the present invention. This reflow furnace comprises 3 tanks of preheating zone, 1 tank of reflow zone and 1 tank of cooling zone. There is an inert gas supply port on the ceiling of each tank, and the inert gas supplied from this is sent downward through the central part by a propeller (2) provided in the upper central part of the tank. In each tank of the preheating zone and the reflow zone, they are heated by the heaters (3) arranged on both sides,
Further, in the cooling zone, it is circulated and stirred upward along both side walls. On the other hand, the lower part of the reflow furnace is provided with an opening (5) through which a work (a printed circuit board on which electronic parts are temporarily placed) and its transportation equipment are passed.
In order to suppress the inflow of external air as much as possible and to prevent the flow of inert gas with different temperature in other tanks, make the size small enough for the work and the transfer equipment to pass through. Furthermore, the bottom of this reflow furnace is an inverted trapezoid for the purpose of storing inert gas.

[0011]

As described above, the present invention relates to a reflow furnace of a reflow soldering device that performs soldering in an inert gas atmosphere, and supplies the inert gas flow in each tank of the reflow furnace to the upper part (ceiling). The temperature of the inert gas atmosphere in each tank is improved by circulating it with a propeller so that it descends from the mouth through the center of the tank and rises from its surroundings, and by making the size of the opening as small as possible. Since it can be controlled, soldering defects have been drastically reduced. In addition, this reflow furnace has a simple structure, so the cost can be reduced.

[Brief description of drawings]

FIG. 1 is an elevational view of a reflow oven of the present invention with a front cover removed.

FIG. 2 is a lateral cross-sectional view of the preheating zone or reflow zone of the reflow furnace of the present invention.

[Explanation of symbols]

 1 Reflow oven 2 Propeller 3 Heater 4 Work (printed circuit board with electronic parts temporarily placed) 5 Opening

Claims (2)

[Claims] 1. A reflow furnace comprising two or more tank preheating zones, one or more tank reflow zones and one or more tank cooling zones in which the temperatures of the inert gas atmospheres are all different, and the upper part of each tank ( Inert gas supplied from the ceiling is circulated so that the propeller flows downward in the center of the tank and rises around it, and the opening of each tank is a work (this is a print with electronic parts temporarily stored). A reflow furnace with good temperature control, characterized in that it is made small enough to pass the substrate) and its transfer equipment. 2. The reflow furnace according to claim 1, wherein heaters are provided on both sides of each tank of the preheating zone and the reflow zone.