Reflow furnace

Abstract

To provide a reflow furnace which can suppress power consumption.SOLUTION: A heating chamber 4 is temperature-controlled by phase control. In control of a reflow furnace 100, control modes of each heating chamber 4 and each cooling chamber 6 are switched by an in-furnace position of a workpiece W. In the reflow furnace 100 in a stand-by state, when a workpiece detection sensor S detects the workpiece W, a first heating chamber 4(1) closest to an inlet In is switched from the stand-by mode to an operation mode. In heating chambers 4(2) to 4(5) on and after the second one and the two cooling chambers 6, the stand-by mode is continued.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a reflow furnace for soldering electronic components mounted on a printed circuit board via reflow soldering.

Background Art

[0002] A reflow furnace is used for soldering a substrate (hereinafter referred to as a "workpiece") on which electronic components are mounted. A reflow furnace for continuous processing has a plurality of chambers in the furnace, and soldering is completed when the workpiece passes through these chambers. Patent Documents 1 and 2 disclose a reflow furnace that employs an endless chain as a conveyor for conveying the workpiece. The workpiece is conveyed through the furnace at a constant speed by the endless chain.

[0003] In a vapor-phase reflow furnace that uses hot air for soldering, the ambient gas in each chamber is circulated by a fan arranged for each chamber. In the heating zone inside the furnace, the ambient gas whose temperature is adjusted by a heater is discharged toward the workpiece (Patent Documents 3 and 4). Then, the temperature of each chamber is controlled according to a preset temperature profile (Patent Document 5).

[0004] In the temperature control of the heating chamber that constitutes the heating zone, a solid state contactor is employed. Also, a conventional reflow furnace generally employs a sheathed heater as a heat source. Here, the sheathed heater is composed of a nichrome wire of a heating element, insulating powder, and a metal pipe containing these. That is, the sheathed heater has a metal pipe that surrounds the nichrome wire, and the metal pipe is filled with insulating powder (a typical example is magnesium oxide powder) to prevent contact between the metal pipe and the nichrome wire.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] Recently, the warming problem has posed a major issue for reflow ovens. That is, it is to further reduce the power consumption of reflow ovens. The object of the present invention is to provide a reflow oven capable of suppressing power consumption. [Means for Solving the Problems]

[0007] The above problems are achieved by providing the following reflow oven. That is, The reflow oven of the present invention has a plurality of rooms in the furnace, and in a vapor-phase reflow oven for soldering a workpiece composed of a substrate on which electronic components are mounted by passing through these rooms, a conveyor for conveying the workpiece, a fan installed in each of the plurality of rooms for circulating the atmosphere gas in each room, a motor for driving the fan, a nozzle installed in each of the plurality of rooms for discharging the atmosphere gas in each room toward the workpiece, a heater for heating the atmosphere gas in a heating chamber constituting a heating zone in the furnace, and a controller for individually controlling the temperature of each of the plurality of rooms, The controller has an operation mode and a standby mode as controls for each of the plurality of rooms, In the standby mode, the motor is controlled under a standby target temperature lower than the operation target temperature set in the operation mode. In the standby mode of the heating chamber, the heater is controlled under a standby target temperature lower than the operation target temperature set in the operation mode. The controller has an individual mode switching control unit that switches the control of each room from the operation mode to the standby mode or from the standby mode to the operation mode according to the position of the workpiece conveyed by the conveyor. The effects and other objects of the present invention will become apparent from the description of the preferred embodiments of the present invention.

Brief Description of the Drawings

[0008]

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Embodiment for Carrying Out the Invention

Example

[0009] The attached drawings are related to the reflow furnace 100 of the embodiment. The illustrated reflow furnace

[100] is a gas-phase reflow furnace that performs reflow processing using hot air. Fig. 1 is a schematic diagram of the overall configuration of the reflow furnace

[100] . Referring to Fig. 1, the reflow furnace

[100] has a heating zone [Hz] and a cooling zone [Cz]. Further, the reflow furnace

[100] has an inlet-side buffer chamber [InBF] located upstream of the heating zone [Hz], and in addition to this, it has an outlet-side buffer chamber [OutBF] located downstream of the cooling zone [Cz].

[0010] The reflow furnace 100 has a plurality of partition walls 2 arranged at intervals in the flow direction of the work piece W, and a plurality of rooms are formed by these partition walls 2 to constitute each zone. Specifically explaining the rooms inside the furnace, the reflow furnace 100 has, in order from the inlet In to the outlet Out, an inlet side buffer chamber InBF, first to fifth heating chambers 4(1) to 4(5), first and second cooling chambers 6(1), 6(2), and an outlet side buffer chamber OutBF. In the following description, when collectively referring to the plurality of heating chambers 4(1) to 4(5), the reference symbol "4" is used, and when collectively referring to the plurality of cooling chambers 6(1), 6(2), the reference symbol "6" is used.

[0011] The reflow furnace 100 has an endless chain 10 as the in-furnace transfer means Tr of the work piece W, that is, a conveyor. The endless chain 10 is continuously operated at a constant speed. The reflow furnace 100 has a work detection sensor S arranged near the inlet In. The position of the work piece W in the furnace can be detected based on the elapsed time since the work piece W was detected by the sensor S.

[0012] The work piece W placed on the endless chain 10 is soldered by passing through the furnace at a constant speed by the endless chain 10. Each of the rooms 4(1) to 4(5), 6(1), 6(2) of the reflow furnace 100 is individually controlled. And the control of each room has two operation modes, an operation mode and a standby mode, and each of the rooms 4(1) to 4(5), 6(1), 6(2) can be individually switched from the operation mode to the standby mode and from the standby mode to the operation mode according to the presence / absence of the work piece W and the in-furnace position of the work piece W.

[0013] In each heating chamber 4 and each cooling chamber 6 of the reflow furnace 100, a fan Fn for circulating the atmosphere gas inside the chamber is arranged, and the atmosphere gas of each room is circulated by each fan Fn, and the atmosphere gas is blown onto the work piece W through the nozzle 14.

[0014] A heater H is disposed in each heating chamber 4. The heater H is composed of a nichrome wire heater 12 obtained by omitting a metal pipe and insulating powder from a sheathed heater. That is, in each heating chamber 4, the heater H is composed of a nichrome wire heater 12 with an exposed heat source.

[0015] Each of the rooms 4 and 6 has a pair of fan cases 30 (FIG. 2) disposed above and below with a conveyance path constituted by an endless chain 10 therebetween, and a fan Fn is accommodated in each fan case 30. FIG. 2 is a front view of each of the rooms 4 and 6. In FIG. 2, reference numeral 2a indicates an opening formed in each partition wall 2. The opening 2a has a size that preferably allows the workpiece W to pass through and is the minimum necessary size. In FIG. 1, each fan Fn is rotationally controlled by an electric motor M disposed in relation thereto. A heater H (nichrome wire heater 12) is accommodated in the fan case 30 disposed in each heating chamber 4. Each fan case 30 has a nozzle 14.

[0016] FIGS. 2 to 4 are diagrams for explaining an example of the fan case 30. The illustrated fan case 30 is made of a stainless steel plate. In FIG. 2, the illustration of the heater H (nichrome wire heater 12) accommodated in the fan case 30 is omitted. The fan case 30 has a split structure including an upper portion that accommodates the fan Fn and a lower portion in which the nozzle 14 is formed.

[0017] Note that the fan case 30 disposed in the cooling chamber 6 does not have a built-in heater H (nichrome wire heater 12) unlike the heating chamber 4. In each cooling chamber 6, the ambient gas is circulated by the fan Fn, and the circulated gas is discharged toward the workpiece W through the nozzle 14.

[0018] FIG. 3 is a perspective view of the lower structure of the fan case 30 as viewed from above, and FIG. 4 is a perspective view of the lower structure illustrated in FIG. 3 with the top and bottom reversed. Since the fan case 30 is described in detail in Patent Document 2, refer to Patent Document 2 if necessary.

[0019] Referring to FIG. 4, the fan case 30 has a nozzle forming member 32 made of a stainless steel plate. The nozzle forming member 32 has a plurality of gas passages 34 formed by bending the stainless steel plate into a wave shape. The plurality of gas passages 34 extend in parallel with each other, and both ends of each gas passage 34 are open. The nozzle forming member 32 also has a plurality of through holes (FIG. 4) associated with each gas passage 34, and these through holes constitute the nozzle 14.

[0020] Regarding the upper and lower structures of the fan case 30 including the nozzle forming member 32, conventionally, it has been made of a stainless steel plate with a thickness of 1.2 mm or 1.0 mm. In the reflow furnace 100 of the embodiment, the fan case 30 including the nozzle forming member 32 is made of a stainless steel plate with a thickness of 0.8 mm or thinner, which is 20% thinner than the conventional one.

[0021] The outline of the control of the reflow furnace 100 is described as follows. (1) Operation mode: In order to perform reflow processing on the workpiece W, the user sets the operation target temperature for each of the rooms 4(1) to 4(5), 6(1), and 6(2). In the operation mode, under this operation target temperature, the temperature of each of the rooms 4(1) to 4(5), 6(1), and 6(2) and the rotation speed of the fan Fn are controlled.

[0022] (2) Standby mode: For each of the heating chambers 4(1) to 4(5) and each of the cooling chambers 6(1) and 6(2), the user sets a standby target temperature lower than the above operation target temperature. In the control of the heating chamber 4, in the standby mode, under the standby target temperature, the heater H (nichrome wire heater 12) and the fan Fn are controlled for each of the heating chambers 4(1) to 4(5). Also, in the control of the cooling chamber 6, in the standby mode, the fan Fn is controlled for each of the cooling chambers 6. Specifically, in the heating chamber 4 and the cooling chamber 6, in the standby mode, the control of the motor M is set to a rotation speed lower than that in the operation mode. Thereby, the fan Fn rotates at a lower speed than in the operation mode.

[0023] (3) Phase control: In a conventional reflow oven, a solid-state contactor is adopted for temperature control of a heating zone as described above. The reflow oven 100 of the embodiment employs phase control for temperature management of each heating chamber 4(1) to 4(5). By adopting phase control, precise temperature control of each heating chamber 4(1) to 4(5) becomes possible, and there is less overshoot when switching from the standby mode to the normal mode, and the operating target temperature can be reached quickly. As a result, when switching to the operating mode, the time until each heating chamber 4(1) to 4(5) stabilizes can be substantially eliminated. Also, during operation in the operating mode, overshoot and undershoot can be significantly reduced even when the temperature of each heating chamber 4 is stable.

[0024] (4) Combination of phase control and nichrome wire heater 12: In the reflow oven 100 of the embodiment, as the heater H, a nichrome wire heater 12 is arranged in each heating chamber 4 instead of the sheathed heater described in the conventional example. As described above, the sheathed heater includes insulating powder or a metal pipe outside the nichrome wire of the heat source. Therefore, even when power is supplied to the sheathed heater, it takes time for the sheathed heater to generate heat and reach a predetermined temperature. On the other hand, the nichrome wire heater 12 adopted in the embodiment has no insulating powder or metal pipe around it and is exposed to the outside, so it generates heat simultaneously with the power-on. By combining this with phase control, the temperature of each heating chamber 4(1) to 4(5) can be controlled more precisely and quickly.

[0025] (5) Combination of phase control, nichrome wire heater 12, and fan case 30: As described with reference to FIGS. 2 to 4, the fan case 30 included in the embodiment is made of a thinner steel material than before. Thereby, the heat capacity of the fan case 30 can be reduced. Therefore, the temperature of each heating chamber 4 can be controlled more precisely and more quickly.

[0026] An example of the control of the reflow furnace 100 will be described with reference to FIGS. 5 to 13. In FIGS. 5 to 13, the control states of each of the rooms 4 and 6 are identified by the presence or absence of coloring. That is, the rooms 4 and 6 that are controlled in the standby mode are colored gray. Conversely, each of the rooms 4 and 6 that are controlled in the operation mode is not colored. Note that in FIGS. 5 to 13, the illustration of the motor M is omitted.

[0027] FIG. 5 is a diagram for explaining a state in which the rooms 4 and 6 of the reflow furnace 100 are controlled in the standby mode. As described above, the endless chain 10 is operated at a constant speed. The position of the workpiece W in the furnace can be detected by the elapsed time from the time when the workpiece detection sensor S disposed near the inlet In is turned on, as described above. In the control of the reflow furnace 100, the control modes of each heating chamber 4 and each cooling chamber 6 are switched according to the position of the workpiece W in the furnace. An example of the switching timing of the control modes of each heating chamber 4 and each cooling chamber 6 will be described with reference to FIGS. 6 to 13, but this is merely an example.

[0028] FIG. 6 is a diagram for explaining the control of the reflow furnace 100 when the workpiece detection sensor S detects the workpiece W. When the workpiece detection sensor S detects the workpiece W, the first heating chamber 4(1) closest to the inlet In is switched from the standby mode to the operation mode. The second and subsequent heating chambers 4(2) to 4(5) and the two cooling chambers 6 continue the standby mode.

[0029] FIG. 7 is a diagram for explaining the control state of the reflow furnace 100 when the workpiece W enters the first heating chamber 4(1). In the control of the reflow furnace 100, the second heating chamber 4(2) is switched from the standby mode to the operation mode. Therefore, in the reflow furnace 100, the first and second heating chambers 4(1) and 4(2) are controlled in the operation mode, and the other chambers continue the standby mode.

[0030] FIG. 8 is a diagram for explaining the control state of the reflow furnace 100 when the workpiece W exits the first heating chamber 4(1). In the reflow furnace 100, the first heating chamber 4(1) is switched from the operation mode to the standby mode. On the other hand, the third and fourth heating chambers 4(3), 4(4) are switched from the standby mode to the operation mode. Therefore, the control of the reflow furnace 100 is such that the second to fourth heating chambers 4(2), 4(3), 4(4) are controlled in the operation mode, and the first heating chamber 4(1), the fifth heating chamber 4(5), and the two cooling chambers 6 are controlled in the standby mode.

[0031] FIG. 9 is a diagram for explaining the control state of the reflow furnace 100 when the workpiece W exits the second heating chamber 4(2). In the reflow furnace 100, the second heating chamber 4(2) is switched from the operation mode to the standby mode. On the other hand, the fifth heating chamber 4(5) is switched from the standby mode to the operation mode. Therefore, the control of the reflow furnace 100 is such that the third to fifth heating chambers 4(3), 4(4), 4(5) are controlled in the operation mode, and the first and second heating chambers 4(1), 4(2), and the two cooling chambers 6 are controlled in the standby mode.

[0032] Thereafter, the control modes of the respective chambers 4, 6 are continued or switched according to the position of the workpiece W in the furnace. FIG. 10 is a diagram for explaining the control state of the reflow furnace 100 when the workpiece W exits the fourth heating chamber 4(4). In the reflow furnace 100, the first to fourth heating chambers 4(1), 4(2), 4(3), 4(4) are controlled in the standby mode. On the other hand, the fifth heating chamber 4(5) continues to be in the operation mode. The first and second cooling chambers 6(1), 6(2) are switched from the standby mode to the operation mode.

[0033] FIG. 11 is a diagram for explaining the control of the reflow furnace 100 when the workpiece W exits from the fifth heating chamber 4(5). When the workpiece W exits from the fifth heating chamber 4(5), the reflow furnace 100 switches the fifth heating chamber 4(5) from the operation mode to the standby mode. Therefore, the reflow furnace 100 controls all the heating chambers 4 in the standby mode. On the other hand, the first and second cooling chambers 6(1) and 6(2) are controlled in the operation mode.

[0034] FIG. 12 is a diagram for explaining the control of the reflow furnace 100 when the workpiece W exits from the first cooling chamber 6(1). When the workpiece W exits from the first cooling chamber 6(1), the control of the first cooling chamber 6(1) is switched from the operation mode to the standby mode. Therefore, the reflow furnace 100 controls all the heating chambers 4 and the first cooling chamber 6(1) in the standby mode. At this time, only the second cooling chamber 6(2) is controlled in the operation mode.

[0035] FIG. 13 is a diagram for explaining the control of the reflow furnace 100 when the workpiece W exits from the second cooling chamber 6(2). When the workpiece W exits from the second cooling chamber 6(2), the control of the second cooling chamber 6(2) is switched from the operation mode to the standby mode. Therefore, the reflow furnace 100 controls all the heating chambers 4 and all the cooling chambers 6 in the standby mode. That is, the inside of the reflow furnace 100 is in the standby state.

[0036] 14 is a functional block diagram related to the control of the reflow furnace 100. Each of the chambers 4 and 6 is provided with one or more temperature sensors 40, as in the conventional case. Information from the temperature sensors 40 in each chamber and the above-mentioned workpiece detection sensors S is input to a control unit 44 of a controller 42. The controller 42 has a target temperature input unit 50, through which the user sets the target temperatures in the operation mode and standby mode for each of the chambers 4 and 6, a memory unit 52 that stores the target temperatures in the operation mode and standby mode for each of the chambers 4 and 6 input through the target temperature input unit 50, and a timer 54. The control unit 44 includes an individual mode switching control unit 56. This individual mode switching control unit 56 individually controls the temperature (heaters H in heating chambers 4(1) to 4(5)) including the rotation speed of the fans Fn in each room 4 and 6 of the reflow furnace 100, and individually switches between standby mode and operation mode for each room 4(1) to 4(5), 6(1), and 6(2).

[0037] In the above embodiment, the position of the workpiece W in the furnace is indirectly detected based on the elapsed time since the workpiece detection sensor S was turned ON. As a modified example, a plurality of workpiece position detection sensors may be arranged at intervals along the workpiece transport path formed by the endless chain 10, and the position of the workpiece W in the furnace may be directly detected by these workpiece position detection sensors. The endless chain 10, which functions as a conveyor for transporting the workpiece W, is driven by a motor not shown. A sensor may be provided to detect the number of rotations of the motor, and the travel distance of the endless chain 10 may be calculated based on the number of rotations of the motor detected by this sensor, thereby detecting the position of the workpiece W in the furnace.

[0038] In the reflow oven 100, a method is adopted in which the work piece W is soldered while being passed through a plurality of chambers 4 and 6 in the furnace at a constant speed by an endless chain 10. As a modification, a reflow oven that intermittently conveys the work piece W and allows the work piece W to stay in each chamber in the furnace for a certain period of time may be used. This type of reflow oven is disclosed in Japanese Patent Application Laid-Open No. 2015-82630. Note that Japanese Patent Application Laid-Open No. 2015-82630 discloses a fluxless formic acid reflow oven. The present invention can also be preferably provided for a fluxless formic acid reflow oven. Of course, the present invention can also be preferably applied to a reflow oven using N2 gas as the atmosphere gas.

Explanation of Signs

[0039] 100 Reflow oven of the embodiment W Work piece 4 Heating chamber 6 Cooling chamber Fn Fan M Fan drive motor H Heater 10 Endless chain (conveyor) 12 Nichrome wire heater 14 Nozzle 30 Fan case 42 Controller 56 Individual mode switching control unit

Claims

1. In a vapor-phase reflow furnace for soldering a work piece composed of a substrate on which electronic components are mounted by having a plurality of chambers in the furnace and passing the work piece through these chambers, a conveyor for conveying the work piece, a fan installed in each of the plurality of chambers for circulating the atmosphere gas in each chamber, a motor for driving the fan, a nozzle installed in each of the plurality of chambers for discharging the atmosphere gas in each chamber toward the work piece, a heater for heating the atmosphere gas in a heating chamber that constitutes a heating zone in the furnace, and a controller for individually controlling the temperature of each of the plurality of chambers, wherein the controller has an operation mode and a standby mode as controls for each of the plurality of chambers, in the standby mode, the motor is controlled under a standby target temperature lower than the operation target temperature set in the operation mode, in the standby mode of the heating chamber, the heater is controlled under a standby target temperature lower than the operation target temperature set in the operation mode, the reflow furnace is characterized in that the controller has an individual mode switching control unit for switching the control of each chamber from the operation mode to the standby mode or from the standby mode to the operation mode according to the position of the work piece conveyed by the conveyor.

2. The reflow furnace according to Claim 1, wherein the heating chamber is controlled by phase control.

3. The reflow furnace according to Claim 2, wherein the heater is composed of a nichrome wire heater.

4. The reflow furnace according to Claim 3, wherein the heating chamber has a fan case that houses the fan and the heater and is provided with the nozzle, and the fan case is made of a stainless steel plate with a thickness of 0.8 mm or less.

5. The reflow furnace according to any one of Claims 1 to 5, wherein in the standby mode, the rotation speed of the motor is lower than that in the operation mode.

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