JP2715267B2 - Hot air blowout heater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Generally, a reflow furnace used for soldering a printed board includes an infrared ray method and a hot air method.

In the infrared method, infrared heaters are attached to upper and lower portions of a tunnel, and a printed circuit board is heated by infrared rays emitted from the infrared heater. Infrared rays go straight, so for thin parts such as discrete parts that only emerge on the back side of the printed circuit board, heat the area around the leads without any problem,
Defect soldering is possible.

In recent years, as electronic components, surface-mounted components in which short leads protrude from the side and back surfaces of the main body, or no leads are formed, and electrodes are formed on the end and back surfaces of the main body, are often used. It has become

[0005] Soldering of a surface mount component is performed by first applying a solder paste to a land of a printed circuit board, placing leads and electrodes of the surface mount component on the land, and applying the adhesive force of the solder paste to the surface mount component. Is held and then heated in a reflow furnace to perform soldering.

When a high-density mounting board on which a large number of surface-mounted components are mounted is heated in an infrared-type reflow furnace, the infrared rays travel straight, so that the high-surface-mounted components enter shadows and narrow gaps due to the high surface-mounted components. Hard to do. For this reason, in the infrared type reflow furnace, the entire high-density mounting substrate cannot be heated uniformly and sufficiently, and the solder paste does not completely melt, which may cause a soldering failure. .

In an infrared reflow furnace, the top of a high electronic component approaches the infrared heater, so that the top is heated more than necessary by receiving infrared rays stronger than a printed circuit board located at a lower position. In some cases, functional deterioration may occur, or the mold resin of the electronic component may crack.

On the other hand, a hot-air reflow furnace allows hot air to easily penetrate even between high-density surface-mounted components.
In addition, since the hot air spreads over the entire area of the printed circuit board, there is no local shortage of heat, or conversely, an abnormally high temperature. Therefore, it can be said that the hot-air method is optimal for soldering a printed circuit board mounted at high density.

In recent years, soldering of printed circuit boards has often been performed in an inert atmosphere filled with a nitrogen gas in a furnace. This is because it is no longer possible to clean the printed circuit board after soldering with a solvent such as chlorofluorocarbon or trichlene, which has a problem of pollution, so a low-residue solder paste or a weakly active solder paste that does not need to be cleaned after soldering is used. This is because they are starting to do so. When these solder pastes are soldered in a reflow oven in which oxygen is present, a large amount of unsoldered or minute solder balls to which no solder adheres is generated. Therefore, they must be used in an inert atmosphere reflow oven.

Conventionally, even in a hot-air reflow furnace, there has been a method in which the inside of the furnace is soldered with an inert atmosphere. Conventional hot-air reflow furnaces have a propeller fan installed in the upper part of the tunnel (Japanese Patent Publication No. 61-38985 and Japanese Patent Application Laid-Open No. 63-296295), and a cross fan installed in the upper and lower parts of the tunnel (Japanese Patent Application Laid-Open No. 63-296295). 63-180368 and 63-278668, or a sirocco fan installed at the lower part of a tunnel (JP-A-1-215462).
No. 6-177532).

In a conventional hot-air reflow furnace, when the inside of the furnace is set to 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 is run after the concentration has been reduced, the oxygen concentration may increase.
The cause is that in a conventional reflow furnace, when the printed circuit board is not traveling in the furnace, the hot air blown out by the blower circulates from top to bottom without disturbance, but when the printed circuit board runs in the furnace, the hot air Strikes the printed circuit board and changes the flow laterally, affecting adjacent zones. When the hot air flows sideways in this way, it disturbs the flow of gas at the entrance and exit, causing outside air to enter the furnace.

The inventor of the present invention blows out hot air so as not to pass through the running position of the printed circuit board, and after heating the printed circuit board with the hot air, performs self-lubrication so as to return to the same hot air heater. Japanese Patent Application No. Hei 7-2861 discloses a hot air blowout heater for a reflow furnace which eliminates turbulence.
No. 71 proposed. This hot air blowout heater has a suction port in the center of the box, and blowout ports before and after the suction port, and a blower such as a cross fan or a sirocco fan is installed in the suction port. Here, the hot air sucked from the inlet is divided into lower and front outlets at the lower part, and is blown toward the center from the outlet. The hot air blown toward the center is self-circulated such that the hot air is drawn in from the suction port of the same hot air blowing heater regardless of the presence or absence of the printed circuit board.

The self-circulating hot air blowout heater has an excellent feature that when the printed circuit board is heated, the hot air does not flow laterally, so that no outside air enters from the entrance and exit and a stable low oxygen concentration is maintained. have.

However, since the hot air blowout heater has a structure in which the hot air sucked from the suction port is divided into the front and rear blowout ports at the lower portion of the suction port, the hot air may not be equally divided into the two front and rear blowout ports. there were. In a hot air blowout heater that blows out hot air from two outlets, if the hot air is not blown out uniformly, the hit of the hot air to the printed circuit board becomes uneven, which sometimes causes a problem that the temperature distribution of the printed circuit board is not constant. .

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

[0016]

According to the present invention, a suction port is formed at the center on the same surface of a box, and two outlets are formed in front of and behind the suction port with respect to the direction of travel of the printed circuit board. Holes are drilled on both side walls of the suction port of the box, and scrolls are installed on both outer sides of the box, and the sirocco fan rotates in each scroll in a substantially concentric state with the hole on the wall. The sirocco fan is installed freely, and the two sirocco fans are separated by a single shaft, and the scroll has two outlets extending in the front and rear directions. An electric heater is installed inside the box, and an electric heater is installed inside the box, and a current changing plate is installed above the outlet to let the hot air blown out from it flow to the upper center. heater It is.

[0017]

[Function] A sirocco fan is installed on both sides of a suction port, and the sirocco fan is caused to flow hot air to an outlet by a scroll having an outlet in the front-rear direction. Because they are merged, a uniform amount of hot air is blown from each outlet.

A pair of sirocco fans installed in the lower part of the furnace with a hot air blower heater is disclosed in JP-A-6-177.
No. 532. The hot-air blowing heater described here raises 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 circuit board is heated by applying hot air to the upper surface of the printed circuit board passing under the electric heater, and the printed circuit board is also heated by the electric heater.

In this hot air blowout heater, the hot air blowout port rises along the furnace wall in parallel to the printed circuit board traveling direction, that is, rises through both sides of the printed circuit board. Is what you do. In this hot air blowout heater, the hot air blown out from the blowout port does not directly hit the printed circuit board, but after joining at the upper part, passes through the punching plate and hits the upper surface of the printed circuit board. Therefore, in this hot air blowout heater, the amount of hot air blown out from each blowout port does not need to be an equal amount, and there is almost no problem even if the blowout of the hot air from the pair of sirocco fans is somewhat uneven.

In the hot air blowout heater of the present invention, since hot air blows out at right angles to the traveling direction of the printed circuit board and directly heats the front surface or the back surface of the printed circuit board, it is blown out from two outlets. If the hot air is not uniform, the printed circuit board cannot be heated uniformly as described above. Therefore, in the hot air blowout heater of the present invention, improvements have been made to equalize the amount of hot air blown from two outlets.

[0021]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG.
2 is a perspective view of the hot air blowout 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. FIG.

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

Holes 5 and 5 (one is not shown) are formed on both side walls of the box 2, and scrolls 6 and 6 are provided on both outer sides of the box 2. In the scrolls 6, 6, the sirocco fans 7, 7 are formed substantially concentrically with the holes 5, 5 on the wall surface.
Is installed. The pair of sirocco fans 7, 7 are connected by one shaft 8, and rotate in the same direction (arrow B). Axis 8 is one scroll 6
, And protrudes to the outside, and is connected to a motor shaft (not shown) outside.

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

A large number of current change plates 11 are provided above the outlet 4.
… Is installed. The current change plate 11 is an inclined louver, and changes the flow of hot air blown out from the blowout 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), first, gas is 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 arrows in FIG. Outlet 9 of scroll 6, 6
Are open toward the outlets 4, 4, so that gas flows into the outlets 4 from the outlets 9 of both scrolls 6, 6. At this time, since the sirocco fans 7 have the same shape and the same rotation, the same amount of gas at the same speed flows into the outlets 4 from all the outlets 9.

The electric heater 1 is provided in the outlets 4 and 4.
0 and 10 are installed, and since the insides of the outlets 4 and 4 have a high temperature, the gas flowing into the outlets is heated and becomes hot air, and is blown upward. Also, outlets 4, 4
Are installed at the upper part of the
The hot air is blown out by the current change plate in the direction of 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 part of the suction port 3 is under negative pressure by the sirocco fan.
In other words, in the hot air blowout heater of the present invention, the hot air blown out from the blowout port is sucked into the suction port of the same hot air blowout heater, divided into two directions by the scroll and flown into the two blowout ports, and again from the blowout port. The self-circulation that the blown-out hot air is sucked into the suction port is performed.

Therefore, the hot-air blowing heater of the present invention does not cause hot air to flow in the direction of another adjacent heater or cooling device, so that it does not cause turbulence in each heating zone or cooling zone and is stable. An inert atmosphere can be maintained.

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

The inside of the reflow furnace 12 has a tunnel shape. The inside of the furnace has a preheating zone P, a main heating zone R, and a cooling zone C. In the furnace, a pair of chain conveyors 13 extends from the preheating zone P toward the main heating zone R (arrow A in FIG. 4). I am running. The entrance of the preheating zone P and the exit 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, hot air blowout heaters 1 of the present invention are provided. Further, a cool air blowout type cooler 14 having the same structure as the hot air blowout heater of the present invention but having no electric heater is installed below the cooling zone C. Like the hot air blowout heater, the cooler also performs self-circulation in which gas blown toward the center from the blowout ports on both sides is sucked into the suction hole in the center, and blown out from the blowout port again. Therefore, the cooler does not hinder the self-circulation of the adjacent hot-air blowing heater, and can also prevent outside air from entering from the outlet.

Above the cooling zone C, a turbulence 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 outlets and the inlet of the cooler, the cool air blown out from the other outlet flows upward without the turbulence prevention device at the upper part. The upwardly flowing cold air is changed at the mountain-shaped portion so as not to flow out.

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 blowout heaters 1 and 1 installed above and below the tunnel with the chain conveyor 13 interposed therebetween. At this time, hot air blows obliquely upward from the two outlets 4, 4 opened in a direction perpendicular to the printed board traveling direction toward the central suction port 3. The front and back sides of the printed circuit board are heated by the hot air that blows 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 blowout heater 1.

Since the hot air blown out from the hot air blowout heater returns to the same hot air blowout heater,
Self-circulation without any interference by other hot-air blowout heaters enables stable hot-air blowing at all times. Moreover, the hot-air blowing heater of the present invention uniformly heats the printed circuit board because the same amount of hot air is blown from the two blowing ports at the same speed.

The printed circuit board preheated in the preheating zone P enters the main heating zone R, and is heated above 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, so that soldering is performed. Done. Also at this time, stable heating is performed without interference by the adjacent hot air blowing heater or cooler.

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

Printed circuit board (1.2 mm thick, 200 mm × 200 mm) on which surface mount components are mounted at high density in a reflow furnace equipped with a hot air blowout 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-mounted component or the printed circuit board was an extremely small value of 3 ° C. Incidentally, Δt in the conventional reflow furnace is 5 to 6 ° C.

[0040]

As described above, the hot air blowout heater of the present invention is of a self-circulation type in which the hot air blown out from the two blowout ports is sucked from the central suction port. In addition to preventing the outside air from influencing other zones, sirocco fans are installed on both sides of the suction port, and the hot air sucked by the sirocco fan is blown out by a scroll having an outlet in the front-rear direction. It is a structure that can be discharged into the mouth,
Since the same amount of hot air can always be blown out from the two blow-out ports in the same amount and at the same speed, the present invention has an unprecedented excellent effect of uniformly heating the printed circuit board.

[Brief description of the drawings]

FIG. 1 is a perspective view of a hot air blowout heater of 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. 1;

FIG. 4 is a front sectional view of a reflow furnace provided with a hot air blowout heater of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hot-air blower heater 2 Box 3 Suction port 4 Blow-out port 5 Hole 6 Scroll 7 Sirocco fan 8 Axis 9 Outlet 10 Electric heater 11 Current transformer

Claims (1)

(57) [Claims] An inlet is formed at the center on the same surface of the box, and two outlets are formed before and after the inlet with respect to the printed circuit board traveling direction. Holes are drilled in the wall surface, scrolls are installed on both outer sides of the box, and in each scroll, a sirocco fan is installed rotatably 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 extending in the front and rear directions, and these outlets communicate with the front and rear outlets, and also inside the box. Is equipped with an electric heater, and a hot air blower heater is provided above the outlet, and a current transformer plate for flowing hot air blown out from the outlet to the upper center.