JPH0332464A - Reflow furnace - Google Patents

Abstract

PURPOSE:To prevent the generation of damages and soldering defects of parts by independently providing force convection type heating means respectively in a preheating area and regular heating area and forming the convection of the hot wind circulating in the transporting direction of materials to be heated in the preheating area and the regular heating area. CONSTITUTION:The heating area consisting of a panel heater 22 for temp. rising of the materials (substrates) 27 to be heated, the 1st, 2nd heating areas for soaking consisting of panel heaters 23, 24 and the heating area for the regular heating consisting of a panel heater 25 are disposed in series in the reflow furnace 21. The force convection type heating means are, thereupon, respectively independently provided in the heating area consisting of the heating areas for temp. rising and soaking and the regular heating area. The heating means are constituted of air heaters 32, 35, blowers 33, 36, pipes 31a, 31b, 34a, 34b, etc. The convection of the hot wind circulating in the same direction as the transporting direction of the materials. 27 to be heated is formed in the preheating area and regular heating area. The uniform soldering is executed while the generation of solder balls is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a reflow oven used for soldering electronic circuit boards and electronic circuit components.

(Prior Art) A method using a reflow oven (reflow soldering) is known as a method for surface mounting various semiconductor element parts on a circuit board by soldering. This soldering method involves placing electronic components whose joints are coated with solder in advance on a predetermined position on a circuit board, using a belt conveyor, for example, in a reflow oven consisting of multiple radiant heating zones arranged in series. In this method, electronic components are soldered at predetermined positions on the board by remelting the solder at the bonding portions using radiant heat from the heating area as the board passes through the furnace.

FIG. 3 shows an example of the configuration of a conventional reflow oven. Inside the reflow oven, four pairs of radiant heating areas 2 to 5 each consisting of a surface heater such as an infrared heater or a far-infrared heater are arranged in the oven length direction. The objects to be heated are placed on a belt conveyor 6 at predetermined intervals between these upper and lower heating areas 2 to 5,
That is, a substrate 7 on which various electronic components (not shown) are mounted is conveyed from an inlet 1a to an outlet 1b in the reflow oven. The joint between the electronic component and the board 7 is coated with solder. The belt conveyor 6 has a motor 8
The belt 11 is wound around a driving roller 9 connected to a drive roller 9 and three feeding rollers 10.

In the reflow oven 1 having this structure, the electronic components on the board 7 are soldered in a state where radiation heating from the surface heaters in each of the heating zones 2 to 5 described above and heating due to natural convection in the furnace atmosphere are combined. It will be done.

Here, in each heating zone 2 to 5, the heating zone 2 is the inlet 1
It functions as a temperature raising part arranged to rapidly raise the temperature of the substrate 7 carried into the furnace from a.

However, for example, there is a difference in heat capacity between the circuit board and the electronic components mounted thereon, and a temperature difference occurs between them.
A soaking section is formed in which 4 is arranged. Further, a heating area 5 for main heating as a main heating part is arranged after these heating areas 3 and 4, and here the board 7 and the electronic components mounted thereon are kept at a predetermined temperature, that is, soldering is carried out at a certain temperature. It is heated to perform soldering.

(Problems to be Solved by the Invention) By the way, as described above, the heat capacity of each part of the substrate 7 transported in the reflow oven 1 is not necessarily uniform, and furthermore, the heat capacity of the substrate 7 and the electronics mounted on the substrate 7 are not necessarily uniform. There are also differences in heat capacity between parts. Therefore, due to these differences in heat capacity, the temperature profile of the substrate and mounted components generally differs at each location within the furnace.

FIG. 4 shows an example of the temperature profile.

In the figure, the solid line indicates the temperature profile of the board, the dotted line indicates the mounted component, and the dashed-dotted line indicates the temperature profile of the package surface of the mounted component.

Generally, in order to effectively utilize the function of the flux in the cream solder used for soldering, it is preferable to maintain the temperature of the board in the soaking section at a predetermined temperature level, as shown in the figure.

However, in a reflow oven with a conventional structure as shown in Fig. 3, if the substrate temperature in the soaking section is managed as shown in Fig. 4, the temperature between the board and the mounted components will drop near the end of the soaking section. A temperature difference ΔT1 is generated, and a temperature difference ΔT2 is also generated in the main heating section.

This tendency becomes noticeable when components with large heat capacities are mounted, and even if the board reaches a predetermined temperature T1, the temperature of the mounted components is T! becomes significantly lower (△T.

This results in inconveniences such as defective soldering or impossibility of soldering.

By managing the temperature to raise the board temperature T in the main heating section and increasing the temperature T of the mounted components, it is possible to avoid a situation where soldering is impossible. This is disadvantageous because it causes thermal damage to the board and mounted components, resulting in loss of their functionality.

Also, the temperature difference △T! in the main heating section! In order to reduce the temperature difference and prevent soldering defects, it is necessary to reduce the temperature difference △ in the soaking area.
It is necessary to make T1 as small as possible. However, in the case of a reflow oven with a conventional structure, in order to reduce ΔT, it is necessary to either make the line speed extremely slow or increase the number of heating zones by increasing the oven length. Therefore, problems such as a decrease in manufacturing efficiency and an increase in the size of the furnace are unavoidable.

The present invention solves these problems and reduces the temperature difference △T1 between the components and mounted components in the soaking section and the temperature difference ΔT in the main heating section without increasing the size of the furnace. ! The present invention aims to provide a reflow oven having a structure that can be made small in size.

(Means for Solving the Problem) In order to achieve the above-mentioned object, in the present invention, a preheating area consisting of a heating area for raising the temperature of the object to be heated and a heating area for soaking, and a heating area for main heating are provided. In a reflow furnace in which the object to be heated is transported through the furnace arranged in this order, forced convection heating means are provided independently in each of the preheating area and the heating area for main heating, and the object to be heated is A reflow oven is provided, characterized in that a convection of hot air circulating in the same direction as the conveyance direction of the object is formed in the preheating area and the main heating area.

(Function) In addition to the radiant heat from the surface heater, hot air is forced to convect in the preheating area including the soaking section, so the speed of heat transfer to the heated object is faster than in the case of conventional natural convection. As a result, the ΔT1 in the soaking section can be reduced in a short time.

In addition, forced convection of hot air is also formed in the main heating section, so
The above ΔT there also becomes smaller.

As a result, even if the board temperature is kept flat at a predetermined temperature in the soaking section, the temperature difference between the board and mounted components in the main heating section where soldering progresses can be reduced, and cream soldering It becomes possible to perform reliable soldering without impairing the effectiveness of the flux.

(Example) Hereinafter, an example of the present invention will be described based on the accompanying drawings.

FIG. 1 shows a first embodiment of the present invention, in which a reflow oven 21
Inside, there is a heating area for raising the temperature consisting of a pair of upper and lower surface heaters 22 such as infrared heaters or far infrared heaters;
Similarly, a first soaking heating area includes a pair of upper and lower surface heaters 23, a second soaking heating area includes a pair of upper and lower surface heaters 24, and a heating area 25 for main heating consists of a pair of upper and lower surface heaters 25. are arranged in series in this order. Here, the heating area for temperature start-up, the first heating area for soaking, and the second heating area for soaking are used to properly solder the object to be heated in the heating area for main heating. Configure the preheating area.

A motor 28 is installed between the pair of surface heaters in each heating area.
A belt conveyor 26 wound around a driving rotor 29 and a feeding roller 30 connected to the belt conveyor 26 runs, and objects to be heated 27 are placed thereon at predetermined intervals, so that the objects to be heated 27 are reflowed. From the inlet 21a of the furnace 21 to the outlet 21
It is transported towards b.

The reflow oven inlet 21a side of the surface heater 22 and the surface heater 23
Pipes 31a and 31b are inserted into the furnace from above the object to be heated 27 at the boundaries of the surface heater 24, and
The pipe 31a is connected to the blower 33 via the air heater 32, and the pipe 31b is connected to the blower 33, and the entire system constitutes forced convection heating means in the preheating area.

Similarly, pipes 34a and 34b are inserted from above the object to be heated 27 before and after the surface heater 25 in the heating area for main heating, respectively, and the pipe 34a is connected to the blower 36 via the air heater 35, and the pipe 34b is connected to the blower 36 via the air heater 35. is connected to the blower 36, and as a whole constitutes forced convection heating means in the heating zone for main heating.

In any of these independent forced convection heating means, when the Pro 733.36 is operated, the hot air heated by the air heater 32.35 flows through the pipes 31a, 34a.
The air is blown into the furnace, flows in the direction of conveyance of the object to be heated 27, and is sucked into blowers 33, 36 through pipes 31b, 34b. That is, the hot air is heated in the preheating area,
In the heating area for main heating, they circulate independently as shown by arrows P+ and Pt, respectively.

Next, the effect will be explained.

The object to be heated 7 carried into the reflow oven 21 is heated by a surface heater 22.
The temperature is raised during the process of passing between the heating areas, and the heating area is transferred between the surface heaters of the first soaking heating area. Here, at the same time as being heated by the radiant heat of the surface heater 23, its upper surface is heated by the convecting hot air. Therefore, excessive temperature rise due to radiation heating is suppressed in parts of the object with a small heat capacity, while temperature rise in parts with a large heat capacity is promoted due to the synergistic effect of radiant heating and convection heating. Local temperature differences in the entire object become smaller.

Then, in the process of passing between the surface heaters 24 in the second soaking heating area, the overall temperature difference of the object to be heated becomes even smaller, and heating progresses.

The uniformly heated object 27 is then transferred between the surface heaters 25 in the heating area for main heating, and heated to a higher temperature than in the preheating area, but at this time as well, due to the action of hot air convection, the object to be heated is The local temperature difference of the heated object becomes smaller. In this way, by taking forced heating by convection of hot air into consideration, both the temperature difference ΔT1 in the soaking part and the temperature difference ΔT2 in the heating part become small, and no soldering defects occur.

Fig. 2 shows another embodiment of the present invention, and in the case of this reflow oven, the upper surface heater of the second soaking heating area is removed from the embodiment furnace of Fig. 1. , a hot air blowing section 38 connected to the air heater 37 is attached, and here,
The structure is such that hot air obtained by heating outside air with an air heater 37 is forcibly blown onto the upper surface of the object to be heated 27 being conveyed.

Such a structure is effective because the heating effect is further promoted.

(Effects of the Invention) As is clear from the above explanation, the reflow oven of the present invention has
Its configuration is a reflow process in which the object to be heated is conveyed through a furnace in which a preheating area consisting of a heating area for raising the temperature of the object to be heated and a heating area for soaking, and a heating area for main heating are arranged in this order. In the furnace, a forced convection type heating means is provided independently in each of the preheating area and the main heating heating area, and the convection of hot air circulating in the same direction as the conveying direction of the object to be heated is provided in the preheating area and the main heating area. Since it is formed in the heating area for main heating, for example, even if there is a 4° difference in heat capacity on the board surface depending on the type of electronic component mounted on the board surface, the temperature of this board surface in the soaking section is It becomes possible to suppress the temperature difference to an extremely small value, and as a result, it is possible to prevent defects such as damage to components and poor soldering in the heating section for main heating. In addition, when soldering on the surface of a board, any part of the joint quickly rises to a soaking temperature, and this temperature is maintained for a long time, so the flux contained in the cream solder becomes stable. As a result, phenomena such as the generation of solder balls are suppressed, and uniform soldering becomes possible.

[Brief explanation of drawings]

Figures 1 and 2 are block diagrams showing an embodiment of the reflow oven of the present invention, Figure 3 is a block diagram of a conventional reflow oven, and Figure 4 shows the temperature profile of the substrate and mounted components in the reflow oven. It is a graph. 21... Reflow oven, 21a... Inlet, 21b...
・Outlet, 22, 23, 24. 25... Surface heater, 26
... Belt conveyor, 27 ... Substrate (object to be heated),
28...Motor, 29...Driving roller, 30...
- Feeding loaf, 32° lower, 31a, 31b, 34a, 34b--pipe, 35.
37...Air heater, 33.36...Part 38...
Hot air blowing part.

Claims (1)

[Claims] In a reflow furnace in which the object to be heated is transported through a furnace in which a preheating area consisting of a heating area for raising the temperature of the object to be heated and a heating area for soaking, and a heating area for main heating are arranged in this order, A forced convection type heating means is provided independently in each of the preheating area and the heating area for main heating, and the convection of hot air circulating in the same direction as the conveyance direction of the object to be heated causes the heating in the preheating area and the heating area for main heating. A reflow oven characterized by being formed in a region.