JPH08242075A - Hot air blowoff heater - Google Patents

Abstract

PURPOSE: To uniformly heat the whole of a printed board by blowing off hot air from a blow-off port in both sides of a suction port at a center with the same amount and the same rate in a heater which is installed in a reflow furnace and blows off hot air. CONSTITUTION: In the title device, a suction port 3 is formed at the center of a box body 2, blowoff ports 4, 4 are formed at two positions before and behind with a suction port therebetween, sirocco fans 7, 7 are installed on both sides of a suction port, the sirocco fans 7, 7 are covered with scrolls 6, 6 and a scroll is extended before and behind and flow-out ports 9, 9 of a scroll are communicated with the blowoff ports 4, 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot air blowing heater for a reflow furnace for soldering a printed circuit board.

[0002]

2. Description of the Related Art Generally, there are an infrared type and a hot air type in a reflow furnace used for soldering a printed circuit board.

In the infrared system, infrared heaters are attached to the upper and lower parts of the tunnel, and the printed circuit board is heated by the infrared rays emitted from the infrared heater. Infrared rays go straight, so if there are thin lead wires on the backside of the printed circuit board, such as discrete components, the area around the leads can be heated without any problems.
Can be soldered without defects.

By the way, in recent electronic parts, surface-mounted parts are often used in which short leads are projected on the side surface or the back surface of the main body, or there are no leads and electrodes are formed on the ends or the back surface of the main body. Has become.

To solder the surface mount component, first, solder paste is applied to the land of the printed circuit board, the leads and electrodes of the surface mount component are placed thereon, and the surface mount component is attached by the adhesive force of the solder paste. Is held and then heated in a reflow furnace for soldering.

When a high-density mounting board on which a large number of surface-mounting components are mounted is heated in an infrared type reflow furnace, infrared rays go straight, so that the surface-mounting components having a high height penetrate into shadows and narrow gaps. Hard to do. Therefore, in the infrared type reflow furnace, the whole high-density mounting board could not be heated uniformly and sufficiently, and the solder paste was not completely melted, which could cause soldering failure. .

Further, in the infrared type reflow furnace, since the top of the electronic component having a high height approaches the infrared heater, the top receives an infrared ray stronger than that of the printed circuit board at the lower position and is heated more than necessary, so that the electronic component is heated. It may cause functional deterioration or crack the molding resin of electronic parts.

On the other hand, in the hot-air reflow oven, hot air can easily penetrate even between surface-mounted components that are densely packed,
Further, since the hot air spreads over the entire area of the printed circuit board, there will be no local insufficient heating or, conversely, no abnormally high temperature locally. Therefore, it can be said that the hot air method is most suitable for soldering a printed circuit board mounted with high density.

In recent years, soldering of printed circuit boards is often performed in an inert atmosphere in which a furnace is filled with nitrogen gas. This is because the printed circuit board after soldering can no longer be cleaned with solvents such as CFCs and trichlene, which have pollution problems, so low residue solder paste or weakly active solder paste that does not require cleaning after soldering is used. This is because they have come to do so. When these solder pastes are soldered in a reflow oven in the presence of oxygen, a large amount of unsoldered solder or fine solder balls without solder adherent are produced, and therefore these solder pastes must be used in an inert atmosphere reflow oven.

Conventionally, even hot air type reflow furnaces have been one in which the inside of the furnace is placed in an inert atmosphere for soldering. The conventional hot-air type reflow furnace has a propeller fan installed in the upper part of the tunnel (Japanese Patent Publication No. 61-38985 and Japanese Patent Application No. 63-296295), and a cross fan installed in the upper and lower parts of the tunnel. 63-180368, 63-278668) or a sirocco fan installed under the tunnel (Japanese Patent Laid-Open No. 1-215462).
No. 6-177532).

In the conventional hot air reflow furnace, when the inside of the furnace is made an inert atmosphere, the oxygen concentration can be reduced to some extent when the printed circuit board is not running in the furnace. When the printed circuit board was run after the concentration was lowered, the oxygen concentration sometimes increased.
This is because in the conventional reflow oven, when the printed circuit board is not running inside the furnace, the hot air blown out by the blower circulates from the top to the bottom without disturbance, but when the printed circuit board runs inside the furnace, the hot air flows Strikes the printed circuit board and redirects the flow laterally, affecting adjacent zones. When the hot air flows laterally in this way, it disturbs the flow of gas at the entrance and exit and causes outside air to enter the furnace.

Therefore, the inventor of the present invention blows out hot air so that it does not pass through the traveling position of the printed circuit board, heats the printed circuit board with the hot air, and then causes self-lubrication to return to the same hot air heater to perform the hot air flow. Japanese Patent Application No. 7-2861 for a hot air blowing heater for a reflow furnace that eliminates turbulence
Proposed in No. 71. This hot air blowing heater has an inlet in the center of the box and outlets before and after it, and a blower such as a cross fan or a sirocco fan is installed at the inlet. Here, the hot air sucked from the suction port is divided into the front and rear blow ports at the lower part and blown from the blow port toward the center. The hot air blown toward the center is self-circulated by being sucked from the suction port of the same hot air blowing heater regardless of the presence or absence of the printed circuit board.

The hot air blowing heater for self-circulation has an excellent feature that the hot air does not flow laterally when the printed circuit board is heated, so that the outside air does not enter from the entrance and exit and the stable low oxygen concentration is maintained. have.

However, since this hot air blowing heater has a structure in which the hot air sucked from the suction port is divided into the front and rear blowing ports at the lower part of the suction port, the hot air cannot be equally divided into the two front and rear blowing ports. there were. In a hot air blowing heater that blows hot air from two outlets, if hot air is not blown out uniformly, the hot air may hit the printed circuit board unevenly, causing a problem that the temperature distribution on the printed circuit board is not constant. .

Therefore, the present inventor has improved a hot air blowing heater having two air outlets, and provides a hot air air blowing heater for uniformly ejecting hot air from the two air outlets.

[0016]

According to the present invention, a suction port is formed in the center of the same surface of the box body, and two blow-out ports are formed in front of and behind the suction port with respect to the traveling direction of the printed circuit board. , There are holes on both side walls of the inlet of the box, and scrolls are installed on both outsides of the box, and the sirocco fan rotates inside each scroll in a state of being almost concentric with the hole on the wall. The sirocco fan is installed freely, and the two sirocco fans that are separated are connected by a single shaft.The scroll has outlets that extend in the front and rear directions, and these outlets are connected to the front and rear outlets. A hot air blower characterized by being connected to each other, an electric heater is installed inside the box, and a current-changing plate that flows hot air blown from here to the upper center is installed above the blow-out port. heater It is.

[0017]

[Operation] Sirocco fans are installed on both sides of the suction port, and the sirocco fans are made to flow hot air to the air outlets by a scroll having an outflow port in the front-rear direction, and the hot air flowing out from the air outlets on both sides is in the air outlets. Since they are made to join each other, an equal amount of hot air is blown out from each outlet.

Japanese Patent Laid-Open No. 6-177 discloses a hot air blowing heater in which a pair of sirocco fans are installed in the lower part of the furnace body.
No. 532. The hot air blowing heater described here raises the hot air sucked from the center along the furnace wall and lowers it from the upper part of the furnace. The hot air is reheated by an electric heater installed on the way down. The printed board is heated by applying hot air to the upper surface of the printed board passing under the electric heater, and the printed board is also heated by the electric heater.

In this hot-air blowing heater, the hot-air blowing port is parallel to the traveling direction of the printed circuit board and rises along the furnace wall, that is, it rises up on both sides of the printed circuit board, and it joins and descends at the upper part of the printed circuit board. To do. In this hot-air blowing heater, the hot air blown from the blow-out port does not directly hit the printed circuit board, but passes through the punching plate after being merged at the upper part and then hits the upper surface of the printed circuit board. Therefore, in this hot air blowing heater, the hot air blown out from the respective blowing ports does not have to be an equal amount, and even if the hot air blowouts from the pair of sirocco fans are somewhat uneven, there is almost no problem.

By the way, in the hot air blowing heater of the present invention, the hot air blows out in the direction perpendicular to the direction of travel of the printed circuit board and directly heats the front surface or the back surface of the printed circuit board. If the hot air is not uniform, the printed circuit board cannot be heated uniformly as described above. Therefore, the hot air blowing heater of the present invention is improved so as to equalize the amount of hot air blown out from the two blowout ports.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG.
1 is a perspective view of the hot-air blowing heater of the present invention, FIG. 2 is a sectional view taken along line XX of FIG. 1, FIG. 3 is a sectional view taken along line YY of FIG. 1, and FIG. 4 is a reflow furnace in which the hot-air blowing heater of the present invention is installed. FIG.

In the hot air blowing heater 1 of the present invention, a suction port 3 is formed in the center of a box body 2, and the suction port 3 is formed in the front-rear direction.
That is, blowout ports 4 and 4 are formed at two positions in the front-rear direction with respect to the traveling direction (arrow A) of the printed circuit board (not shown).

Holes 5 and 5 (one of which is not shown) are formed in both side wall surfaces of the box body 2, and scrolls 6 and 6 are installed on both outer sides of the box body 2. Inside the scrolls 6 and 6, the sirocco fans 7 and 7 are approximately concentric with the holes 5 and 5 on the wall surface.
Is installed. The pair of sirocco fans 7, 7 are connected by a single shaft 8 so that they rotate in the same direction (arrow B). Axis 8 is one scroll 6
And penetrates to the outside and is connected to the shaft of a motor (not shown).

As shown in FIG. 2, the scroll 6 extends in two front and rear directions, and its outlets 9, 9 communicate with the front and rear outlets 4, 4, respectively.

An electric heater 10 is installed in the box body 2. The electric heater is meandering inside the box in order to increase the contact area with the hot air and improve the thermal efficiency.

A large number of current-changing plates 11 are provided above the outlet 4.
... is installed. The current-changing plate 11 is a slanted louver, and changes the hot air blown from the blow-out port 4 toward the central suction port 3.

Next, the hot air blowing state of the hot air blowing heater of the present invention will be described.

When the electric heaters 10 and 10 are energized and the sirocco fans 7 and 7 are rotated in the direction of arrow B by a motor (not shown), the gas is first sucked from the suction port 3 by the sirocco fan. Then, the gas sucked by the sirocco fans 7, 7 flows evenly in the scrolls 6, 6 as shown by the arrows in FIG. Outlets 9 of scrolls 6 and 6
, Are open toward the outlets 4, 4, so that the gas flows into the outlet 4 from the outlets 9 of both scrolls 6, 6. At this time, since the sirocco fans 7 and 7 have the same shape and rotate, the gas of the same amount and the same speed flows from the outlets 9 into the outlets 4 and 4.

An electric heater 1 is provided in the outlets 4 and 4.
Since 0 and 10 are installed and the temperature inside the outlets 4 and 4 is high, the gas flowing therein is heated to become hot air and blown upward. In addition, outlets 4, 4
Since there are many current-changing plates 11 ...
Hot air is blown out toward the central suction port 3 as shown in FIGS. The hot air blown out above the suction port 3 is sucked into the suction port 3 because the upper portion of the suction port 3 has a negative pressure due to the sirocco fan.
That is, in the hot-air blowing heater of the present invention, the hot air blown out from the blowing outlet is sucked into the suction port of the same hot-air blowing heater, which is divided into two directions by scrolling and flows into two blowing outlets, and then from the blowing outlet again. Self-circulation is performed in which the hot air blown out is sucked into the suction port.

Therefore, since the hot air blowing heater of the present invention does not flow the hot air toward the other adjacent heaters or cooling devices, it does not cause turbulent flow in each heating zone or cooling zone and is stable. Can maintain an inert atmosphere.

Next, the heating state of the printed circuit board in the reflow furnace provided with the hot air blowing heater of the present invention will be described.

The inside of the reflow furnace 12 has a tunnel shape. A preheating zone P, a main heating zone R, and a cooling zone C are provided in the furnace, and a pair of chain conveyors 13 are provided in the furnace from the preheating zone P toward the main heating zone R (arrow A in FIG. 4). Running. The inlet of the preheating zone P and the outlet of the cooling zone C are air intrusion prevention zones K, K.

At the upper and lower portions of the preheating zone P and the main heating zone R, the hot air blowing heaters 1 of the present invention are installed. In the lower part of the cooling zone C, a cold air blowing type chiller 14 having the same structure as the hot air blowing heater of the present invention but without an electric heater is installed. Like the hot air blowing heater, the cooler also performs self-circulation in which the gas blown toward the center from both sides of the blower is sucked into the central suction port and is blown again from the blowing port. Therefore, the cooler can prevent the inflow of outside air from the outlet without hindering the self-circulation of the adjacent hot air blowing heater.

Above the cooling zone C, a turbulent flow prevention device 15 having a mountain-shaped cross section is installed. This is because when the printed circuit board advances and hits one of the blow-out port and the suction port of the cooler, the cold air blown out from the other blow-out port flows upward unless there is a turbulence prevention device on the upper part. The cold air that has flowed upward is changed in the mountain portion so that it does not flow out elsewhere.

The printed circuit board W enters from the entrance and is conveyed by the chain conveyor 13 in the direction of arrow A (FIG. 4). When the printed circuit board W arrives at the preheating zone P, it is heated by the hot air blown from the hot air blowing heaters 1 and 1 installed in the upper and lower portions of the tunnel with the chain conveyor 13 interposed therebetween. At this time, hot air is blown out obliquely upward from the two outlets 4 and 4 opened in the direction perpendicular to the direction of travel of the printed circuit board toward the central suction port 3. The front and back of the printed circuit board are heated by the hot air blown obliquely. The hot air after heating the printed circuit board is sucked from the suction port 3 at the center of the same hot air blowing heater 1.

Since the hot air blown out from the hot air blowing heater returns to the same hot air blowing heater,
It does not interfere with other hot air blowing heaters, and self-circulates so that hot air can be constantly sprayed. Moreover, since the hot air blowing heater of the present invention blows hot air of the same amount and the same speed from the two air outlets, it uniformly heats the printed circuit board.

The printed board preheated in the preheating zone P enters the main heating zone R, and is heated to a temperature higher than the melting temperature of the solder paste by the upper and lower hot air blowing heaters 1 and 1 in the same manner as in the preheating, and soldering is performed. Done. At this time as well, stable heating is performed without being interfered by the adjacent hot air blowing heater or cooler.

The printed circuit board which has been soldered in the main heating zone is sent to the cooling zone C, where it is cooled to below the melting temperature of the solder by a cooler. Here too, the cooler circulates itself, so a stable atmosphere is maintained.

A printed circuit board (thickness 1.2 mm, size 200 mm × 200 mm) on which surface-mounted components are mounted at high density in a reflow furnace equipped with the hot air blowing heater of the present invention.
When the temperature distribution was measured, the difference (Δt) between the maximum temperature and the minimum temperature of the surface mount component and the printed circuit board was 3 ° C., which was an extremely small value. Incidentally, Δt in the conventional reflow furnace is 5 to 6 ° C.

[0040]

As described above, since the hot air blowing heater of the present invention is a self-circulating system in which the hot air blown from the two blowing ports is sucked from the central suction port, the hot air blowing self-circulates. Not only does it prevent the outside air from flowing in by affecting other zones, but sirocco fans are installed on both sides of the inlet, and the hot air sucked by the sirocco fans is blown out in two by a scroll having an outlet in the front-rear direction. It has a structure that can be discharged to the mouth,
Since the hot air of the same amount and the same speed can always be blown out from the two air outlets, it has an unprecedented excellent effect of uniformly heating the printed circuit board.

[Brief description of drawings]

FIG. 1 is a perspective view of a hot air blowing heater according to the present invention.

FIG. 2 is a sectional view taken along line XX of FIG.

FIG. 3 is a sectional view taken along line YY of FIG.

FIG. 4 is a front sectional view of a reflow furnace in which the hot air blowing heater of the present invention is installed.

[Explanation of symbols]

 1 Hot Air Blow Heater 2 Box 3 Suction Port 4 Blowout Port 5 Hole 6 Scroll 7 Sirocco Fan 8 Shaft 9 Outlet 10 Electric Heater 11 Current Change Plate

Claims (1)

[Claims] 1. A suction port is formed in the center of the same face of the box body, and two blow-out ports are formed in front of and behind the suction port with respect to the printed circuit board advancing direction. Holes are bored in the wall surface, scrolls are installed on both outer sides of the box body, and a sirocco fan is rotatably installed in each scroll in a substantially concentric state with the hole in the wall surface, The two separated sirocco fans are connected by a single shaft, and the scroll has outlets that extend in the front and rear directions, and these outlets communicate with the front and rear outlets, and inside the box. An electric heater is installed in the hot air blowing heater, and a current changing plate is installed in the upper part of the blowing port to flow the hot air blown from here to the central upper part.