JPH0240489A - Re-flow furnace - Google Patents

Abstract

PURPOSE:To restrain a temperature difference in the surface of a substrate in an uniformly heating section to a minimum value and prevent the generation of defects such as the damage or faulty soldering of a part and the like by providing a forced convection type heating means in the uniformly heating zone. CONSTITUTION:A temperature rise-up section consisting of an infrared ray heater 22, an uniformly heating section consisting of a hot air forced convection means 23 and the infrared ray heater 24 and a main heating section consisting of the infrared ray heater 25 are arranged sequentially in series in a re-flow furnace 31. A substrate 7, transferred into the re-flow furnace 31, passes through the temperature rise-up section and, thereafter, is heated by the radiation heat of the heater 24 and the convection of hot air in the uniformly heating section. According to this method, the surface of the substrate, which is provided with a small heat capacity, is restrained in temperature rise due to the radiation heating while the temperature of a part having a large heat capacity is risen by the synergistic effect of the radiation heat and the convection whereby a temperature difference in the whole of the substrate becomes small. Accordingly, the generation of defects may be prevented.

Description

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

(Prior Art) A method using a reflow oven (reflow soldering) is known as a method for surface mounting various element parts on a circuit board by soldering. This method of soldering involves passing a circuit board on which electronic components whose joints have been coated with solder in advance are passed through a reflow oven in which multiple radiant heating zones are arranged side by side, using a belt conveyor, for example. In this method, the solder at the joint is remelted by radiant heat from the heating zone, and soldering is performed at the contact position.

FIG. 4 shows an example of the configuration of a conventional reflow oven. Inside the reflow oven 1, four pairs of radiant heating zones 2 to 5 made of, for example, infrared heaters are disposed vertically. A substrate 7 carrying various electronic components (not shown), that is, an object to be heated, is placed on a belt conveyor 6 at predetermined intervals between the reflow oven 1 and the reflow oven 1, from the inlet 1a to the outlet 1b.
It is transported by The joint between the electronic component and the board 7 is coated with solder. Belt conveyor 6 is
It consists of a driving roller 9 connected to a motor 8 and a belt 11 wound around three feeding rollers 10.

The functions of each of the heating zones 2 to 5 of the reflow oven 1 include, for example, the heating zone 2 raising the temperature of the circuit board 7 (hereinafter referred to as
), heating zone 3. ．． A heating zone 4 uniformizes the temperature (hereinafter referred to as a "heat equalizing section"), and a heating zone 5 performs main heating for soldering (hereinafter referred to as a "heat equalizing section").
The main heating section is divided into two parts. Normally, the flux contained in cream solder used for soldering electronic components loses its effectiveness when the temperature exceeds 170°C. Therefore, before the main heating is performed, the substrate temperature is 1
It is not preferable for the temperature to rise above 70''C. Therefore, the above-mentioned temperature equalization section is provided to equalize the substrate temperature and maintain it at a predetermined temperature.

(Problem to be Solved by the Invention) By the way, the heat capacity of each part of the board 7 being transported in the reflow oven l is not necessarily uniform, and furthermore, the heat capacity between the board 7 and the electronic components mounted on the board 7 is not necessarily uniform. There is also a difference in heat capacity. Therefore, it is common to have different a degree profiles at each location within the furnace due to these differences in heat capacity. FIG. 5 shows, by way of example, the temperature profiles of the board 7 and components with thermal capacity on this board, in which the solid lines represent the board and the broken lines represent the electronic components, respectively. In other words, the temperature rise of electronic components is slower than that of the board, and furthermore, the temperature difference ΔT with the board near the end of the soaking section is
1, there is a temperature difference ΔT2 between the main heating section and the substrate.

In order to reduce the temperature difference ΔT2 in the main heating section and prevent soldering defects, it is necessary to make the temperature difference ΔTl in the soaking section as small as possible. However, in the conventional reflow furnace 1, in order to reduce ΔTl, the line speed must be extremely slowed or the furnace length must be increased to increase the number of heating zones, which reduces manufacturing efficiency. This has the disadvantage of causing the furnace to become larger.

The present invention has been made in view of such conventional problems, and it reduces the temperature difference between the substrate and components in the soaking section as much as possible without increasing the size of the furnace or reducing manufacturing efficiency, and as a result, the main heating An object of the present invention is to provide a reflow oven that can reduce the temperature difference between parts.

(Means for Solving the Problems) In order to achieve the above object, according to the present invention, a heating zone for raising the temperature of the object to be heated, a heating zone for soaking, and a heating zone for main heating are arranged in this order. The reflow furnace in which the object to be heated is transported is configured to include forced convection heating means in the soaking heating zone.

(Function) When the board moves inside the reflow oven and passes through the soaking section,
Heat equalization is performed by forced convection heating of hot air, and convection of the hot air occurs near the surface of the opening plate, so that excessive temperature rise is suppressed in parts of the substrate surface with small heat capacity. Temperature rise is promoted in the portions with large heat capacity, and as a result, the temperature difference across the entire substrate becomes small. Therefore, the temperature difference between each part of the board in the subsequent main heating section is also small, and the occurrence of soldering defects is prevented.

(Example) Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows a first embodiment of the present invention, in which a reflow oven 21
Inside, there is a temperature raising section consisting of a pair of upper and lower infrared heaters 22, a heating section consisting of a hot air forced convection means 23 disposed at the upper part and an infrared heater 24 disposed at the lower part, and a temperature equalization section consisting of a pair of upper and lower infrared heaters 22. The main heating sections including heaters 25 are arranged in parallel in this order. In the hot air forced convection means 23,
The outside air is turned into hot air by the heater 26 and is blown onto the substrate 7 as a convection current from above.

The action will be explained below.

The substrate 7 transferred to the reflow oven 21 passes through a temperature raising section and is then transferred to a soaking section where it is heated from below by radiant heat from an infrared heater and from above by convection of hot air. Ru. Therefore, excessive temperature rise due to radiation heating is suppressed in parts of the substrate surface with small heat capacity, while temperature rise in parts with large heat capacity is promoted by the synergistic effect of radiant heat and convection, resulting in a temperature difference across the board. ΔT1 becomes small.

In the above embodiment, instead of the heater 24 disposed below the soaking section, a hot air forced convection means for generating convection of hot air from below to above may be disposed, or the heater 24 A heat insulating member may be provided instead.

2 and 3 show other embodiments of the present invention, in which the same components as in FIG. 1 are denoted by the same reference numerals. In the reflow oven 31 shown in FIG. 2, hot air blown into the furnace by forced hot air convection means 23 disposed in a soaking section is circulated through the soaking section by a blower 32.

The reflow oven 41 shown in FIG. 3 is provided with forced hot air convection means 42 in the horizontal direction in addition to forced hot air convection means 23 in the vertical direction of the soaking section.

The hot air forced convection means 42 is configured to horizontally circulate hot air blown from a blower 44 through a heater 45 between a pair of upper and lower heaters 43.

In each of the above-mentioned embodiments, it is also possible to improve the temperature rise speed by providing a U⊕ irradiation means in the temperature rise part and using a heater and UV irradiation in combination. Furthermore, the main heating section may be of a hot air forced convection type, or heating by an infrared heater and heating by a hot air forced convection means may be used in combination.

(Effects of the Invention) As explained above, according to the present invention, a heating zone for raising the temperature of the object to be heated, a heating zone for soaking, and a heating zone for main heating are arranged in this order in the furnace. In the reflow oven in which the object to be heated is transported, the soaking heating zone is equipped with a forced convection heating means, so that, for example, differences in heat capacity occur on the surface of the substrate depending on the type of electronic component mounted on the surface of the substrate. Even in such a case, the temperature difference on the surface of the board in the soaking section can be kept extremely small, and as a result, there is an advantage that defects such as damage to components and defective soldering are prevented from occurring.

[Brief explanation of the drawing]

Figures 1 to 3 are block diagrams showing an embodiment of the reflow oven of the present invention, Figure 4 is a block diagram of a conventional reflow oven, and Figure 5 is a temperature profile based on the difference in heat capacity between the board and the mounted component. This is a graph showing the difference between 6...belt conveyor, 7
... M provisional, 2 ll, 31.41 ... reflow oven,
22.24.25.43...Infrared heater, 23.4
2...Hot air forced convection means. Figure 1

Claims (1)

[Claims] In a reflow furnace in which the object to be heated is transported through a furnace in which a heating zone for raising the temperature of the object to be heated, a heating zone for soaking, and a heating zone for main heating are arranged in parallel in this order, the heating for soaking is performed. A reflow oven characterized by having a zone equipped with forced convection heating means.