JP2025153204A - Transport heating device - Google Patents

Abstract

The present invention aims to reduce distortion due to creep of a transport conveyor rail provided in a cooling section subsequent to a heating section.
[Solution] A conveying and heating device comprising a heating section and a cooling section including one or more heating furnaces arranged sequentially in the conveying direction of the heated object, a conveying chain for conveying the heated object, a conveying conveyor rail for guiding the conveying chain, and a thermal deformation absorbing means provided on at least a part of the conveying conveyor rail in the cooling section.
[Selection diagram] Figure 6

Description

The present invention relates to a conveying and heating device that is applied to devices that convey objects to be heated using a conveying chain, such as reflow machines.

The running state of the conveyor chain is regulated by rails. For example, conveyor chains are used in reflow machines to convey electronic components or printed circuit boards. The reflow machine is equipped with a reflow furnace to which heated objects, such as printed circuit boards, are supplied by the conveyor chain. The reflow furnace is configured, for example, with multiple heating furnaces (furnace bodies) corresponding to multiple zones arranged in sequence along the conveyance path from the inlet to the outlet. Depending on their function, the multiple zones serve as heating zones, cooling zones, etc.

In the heating zone, hot air is blown onto the board, melting the solder and soldering the electrical wiring circuit of the printed circuit board to the electrodes of the electronic components. In the reflow device, the heating temperature is controlled according to the desired temperature profile to achieve the desired soldering. The transport chain is guided by rails made of metal, such as aluminum alloy (hereinafter referred to as transport conveyor rails).

One known solution to the problem caused by thermal expansion of conveyor rails is described in Patent Document 1. The technology described in this document involves forming a groove on the upper side of the conveyor rail to solve the problem of warping of the conveyor rail due to the significant temperature difference between the upper and lower sides of the conveyor.

Patent No. 3442597

The technology described in Patent Document 1 solves the problem of thermal expansion of conveyor rails. However, conveyor rails also suffer from the problem of creep, which is separate from thermal expansion. When a certain load is applied to metal at room temperature, distortion stops at a certain point. However, when a certain load is applied at high temperatures, distortion increases over time, sometimes leading to fracture. This phenomenon is known as creep.

Reflow soldering equipment uses conveyor rails that are exposed to high temperatures. Because conveyor rails are typically made of aluminum alloy, consideration must be given to creep. Compared to other metals such as iron, aluminum creeps at lower temperatures, such as around 100°C. If creep causes the conveyor rail to bend, there is a risk that printed circuit boards being transported by the conveyor chain may fall. In frequently used reflow soldering equipment, conveyor rails are adjusted or replaced before significant distortion occurs, due to distortion over time caused by creep. Furthermore, consideration must be given to the fact that conveyor rails in reflow soldering equipment are used in different temperature environments, such as high-temperature heating sections and low-temperature cooling sections.

Therefore, the object of the present invention is to provide a conveyor heating device that can address distortion and deformation caused by creep in conveyor rails, thereby extending their service life.

The present invention is a conveying and heating device equipped with a heating section and a cooling section, each including one or more heating furnaces arranged sequentially in the conveying direction of the heated object, a conveyor chain for conveying the heated object, a conveyor rail for guiding the conveyor chain, and a thermal deformation absorbing means provided on at least a portion of the conveyor rail in the cooling section.

According to at least one embodiment, it is possible to reduce distortion and deformation of the conveyor rail due to creep, thereby improving the service life of the conveyor rail. Note that the effects described here are not necessarily limited to those described herein, and any of the effects described in this disclosure may be applicable. Furthermore, the content of the present invention should not be interpreted as being limited to the effects exemplified in the following description.

FIG. 1 is a schematic diagram showing an example of a reflow apparatus to which the present invention can be applied. FIG. 2 is a schematic diagram showing the configuration of the reflow furnace. FIG. 3 is a graph showing an example of a temperature profile during reflow. 4A and 4B are cross-sectional views showing an example of the configuration of the zones in the heating section. 5A and 5B are cross-sectional views showing an example of the configuration of zones in the cooling section. 6A, 6B, 6C and 6D are cross-sectional views used to explain the transport conveyor rails. 7A, 7B, and 7C are schematic diagrams showing examples of arrangement of transport conveyor rails used to explain one embodiment of the present invention. FIG. 8 is a graph used to explain one embodiment of the present invention.

Embodiments of the present invention are described below. Note that the embodiment described below is a preferred specific example of the present invention and is subject to various technically desirable limitations. However, the scope of the present invention is not limited to these embodiments unless otherwise specified in the following description to the effect that the present invention is limited.

Figure 1 shows the schematic configuration of a conventional reflow apparatus 101 to which the present invention can be applied. The reflow apparatus 101 includes a reflow furnace 102, a conveyor chain 103 that passes an object to be heated, such as a printed circuit board (hereinafter simply referred to as the board) W with surface-mount electronic components mounted on both sides, through the reflow furnace 102, rotating bodies (idlers, sprockets, etc.) 105a, 105b, 105c, and 105d that define the movement path of the conveyor chain 103, and an outer plate 106. Note that Figure 1 shows only one of two parallel conveyor chains, conveyor chain 103. For example, a roller chain is used as conveyor chain 103. The outer plate 106 is a case that covers the entire structure.

After being carried into the reflow furnace 102 through the carry-in entrance 107, the substrate W is transported by the transport chain 103 in the direction of the arrow (from left to right in Figure 1) at a predetermined speed, and is finally removed from the unloading exit 108. Although not shown, a substrate carry-in device for carrying the substrate W is provided before the carry-in entrance 107, and a substrate unloading device for sending the substrate W to the outside is located after the unloading exit 108.

Figure 2 is a diagram showing the schematic configuration of the reflow furnace 102 of the reflow apparatus 101 shown in Figure 1. The reflow furnace 102 is divided into, for example, nine zones Z1 to Z9 along the transport path 109 from the inlet 107 to the outlet 108, and these zones Z1 to Z9 are arranged in-line. Seven zones Z1 to Z7, counting from the inlet 107 side, are heating zones, and two zones Z8 and Z9, counting from the outlet 108 side, are cooling zones. Forced cooling units 112 are provided in association with cooling zones Z8 and Z9. Note that the number of zones shown is merely an example, and other numbers of zones may be provided. The multiple zones Z1 to Z9 control the temperature of the substrate W according to the temperature profile during reflow. Each of the heating zones Z1 to Z7 has an upper heating unit and a lower heating unit, each including a blower.

A throat section 110 is provided between the reflow furnace 102 and the inlet 107, and a throat section 111 is provided between the reflow furnace 102 and the outlet 108. The throat sections 110 and 111 function as seals that isolate the interior of the reflow furnace 102 from the outside and prevent an increase in the oxygen concentration inside the furnace. The throat sections 110 and 111 are configured, for example, as labyrinth seals.

The multiple zones Z1 to Z9 described above control the temperature of the heated object according to a temperature profile during reflow. Figure 3 shows an example of a temperature profile. The horizontal axis represents time, and the vertical axis represents the surface temperature of the heated object, such as a printed wiring board with electronic components mounted on it. The first section is the temperature rise section R1, where the temperature rises due to heating, the next section is the preheat section R2, where the temperature is almost constant, the next section is the reflow section R3, and the final section is the cooling section R4.

The temperature rise section R1 is the period during which the board is heated from room temperature to the preheat section R2 (e.g., 150°C to 170°C). The preheat section R2 is a period during which isothermal heating is performed, for example, to activate the flux, remove oxide films from the electrodes and solder powder surfaces, and eliminate uneven heating of the printed wiring board. The reflow section R3 (e.g., peak temperature of 220°C to 240°C) is the period during which the solder melts and the bond is completed. In the reflow section R3, the temperature must be raised to a temperature above the solder's melting temperature. Even after the preheat section R2, uneven temperature rise still exists, so the reflow section R3 requires heating to a temperature above the solder's melting temperature. The final cooling section R4 is the period during which the printed wiring board is rapidly cooled to form the solder composition. Note that in the case of lead-free solder, the temperature in the reflow section is even higher (e.g., 240°C to 260°C).

In Figure 3, curve P1 shows an example of a temperature profile for lead-free solder. An example of a temperature profile for Sn-Pb eutectic solder is shown by curve P2. Because the melting point of lead-free solder is higher than that of eutectic solder, the set temperatures in preheat section R2 and reflow section R3 are higher than those for eutectic solder.

In the reflow soldering equipment shown in Figures 1 and 2, temperature control of the heating section R1 in Figure 3 is primarily handled by zones Z1 and Z2. Temperature control of the preheating section R2 is primarily handled by zones Z3, Z4, and Z5. Temperature control of the reflow section R3 is handled by zones Z6 and Z7. Temperature control of the cooling section R4 is handled by zones Z8 and Z9. Note that the temperatures in zones Z8 and Z9 of the cooling section R4 are above 100°C.

An example of the configuration of the furnace body in zone Z5 will be described with reference to Figures 4A and 4B. Figures 4A and 4B are schematic cross-sectional views perpendicular to the transport direction of the reflow apparatus. The furnace body is filled with atmospheric gas, such as nitrogen (N2) gas. The furnace body heats the substrate W by blowing hot air (heated atmospheric gas) onto the substrate W. Infrared rays may also be irradiated along with the hot air.

Walls W are transported by transport chains 103 and 203 within the gap between the opposing upper and lower furnace bodies. As shown in the enlarged cross-sectional view of Figure 4B, the transport chains 103 and 203 are respectively arranged in grooves formed in the transport conveyor rails 41 and 141. The transport chains 103 and 203 have link plates that connect the rollers, and the boards W are placed on pins that protrude from the link plates toward the transport surface and are transported. Although not shown, guides that support the rollers of the transport chains 103 and 203 are arranged in the grooves of the transport conveyor rails 41 and 141.

As shown in Figure 4A, the upper furnace body is composed of a main heating source 12, a sub-heating source 13, a blower 14, a heating panel 15, a hot air circulation duct 16, an opening 17, etc. The opening 17 is formed by a number of holes formed in the heating panel. The lower furnace body, for example, is similar to the upper furnace body and is equipped with a main heating source 22, a sub-heating source 23, a blower 24, a heating panel 25, a hot air circulation duct 26, an opening 27, etc.

Blower 14 has motor M5 and rotary blades 18. Similarly, blower 24 has motor M15 and rotary blades 28. The blower may be a centrifugal fan such as a turbo fan or a sirocco fan, or an axial blower. The furnace bodies of the other heating sections also have a configuration similar to that shown in Figures 4A and 4B. Note that the furnace body configuration described above is an example, and other configurations are possible.

Hot air is blown onto the substrate W through openings 17 and 27. Main heating source 12, main heating source 22, sub-heating source 13, and sub-heating source 23 are composed of, for example, electric heaters. Heating panel 15 and heating panel 25 are made of, for example, an aluminum alloy and have many holes formed through which hot air passes (openings 17 and 27) and is blown onto the substrate W.

For example, in the upper furnace body, hot air is circulated by the blower 14. That is, the hot air circulates via the following route: (main heating source 12 → heating panel 15 → opening 17 → substrate W → hot air circulation duct 16 → sub-heating source 13 → hot air circulation duct 16 → blower 14 → main heating source 12). Similarly, in the lower furnace body, hot air circulates via the following route: (main heating source 22 → heating panel 25 → opening 27 → substrate W → hot air circulation duct 26 → sub-heating source 23 → hot air circulation duct 26 → blower 24 → main heating source 22).

With reference to Figures 5A and 5B, an example of the configuration of a zone in the cooling section, such as zone Z8, will be described. Figures 5A and 5B are schematic diagrams of a cross section perpendicular to the transport direction of the reflow device. Note that zone Z9 has the same configuration as zone Z8. Zone Z8 does not have a heating unit, and is provided with a motor M8, a blower 34 with rotating blades 38, and a rectifying plate 35 at the top for blowing air. The rectifying plate 35 is a metal plate with many holes formed in it. Cool air circulates via the following path: (blower 34 → rectifying plate 35 → opening 37 → substrate W → duct 36 → blower 34).

A forced cooling unit 112, such as a heat exchanger 39, is provided below the substrate W. In zone Z8, as shown in the enlarged cross-sectional view of Figure 5B, transport chains 103 and 203 are placed in grooves formed in transport conveyor rails 41 and 141, respectively. The transport conveyor rails 41 and 14 in zone Z8 have plates 43 and 143 on their bottom surfaces as thermal deformation absorbing means. As will be described later, the transport conveyor rails 41 and 141 located in another zone Z9 in the cooling section, as well as in the buffer chamber between the heating section and the cooling section, also have plates 43 and 143.

In one embodiment, the reflow soldering device described above has a single conveyor rail 41, 141 running the entire length from the inlet 107 to the outlet 108. If the conveyor rail were divided into sections, connecting sections would be created, which would require support and attachment parts for the conveyor rail at the connecting sections, resulting in an increase in the number of parts and work processes.

Continuous conveyor rails can avoid this problem. However, it has been found that in reflow soldering equipment with this configuration, creep can have a significant effect on the conveyor rails. To solve this problem, one embodiment of the present invention provides plates 43 and 143 on the conveyor rails in the cooling section.

The material of the transport conveyor rails 41, 141 is an aluminum alloy. Because pure aluminum is a soft metal, its strength can be improved by alloying it with copper, manganese, silicon, magnesium, zinc, nickel, etc. As an example, an aluminum alloy containing a certain ratio of magnesium and silicon, such as A6063, is used for the transport conveyor rails 41, 141. Other types of aluminum alloys can also be used.

The transport conveyor rail will be described with reference to the cross-sectional views of Figures 6A to 6D. Figure 6A shows a cross-section of an example of a transport conveyor rail 41. The transport conveyor rail 41, which is made of extruded aluminum, for example, has a U-shaped cross-section with a top surface 51a, a bottom surface 51b, and a side surface 51c formed continuously. The transport chain 103 is placed in a groove 51d between the top surface 51a and the bottom surface 51b. Note that while the transport conveyor rail 41 will be described, the transport conveyor rail 141 also has a similar configuration.

Figure 6B shows a conveyor rail 41 in which a plate 43 serving as a thermal deformation absorbing means is attached to the bottom surface 51b. The attachment method can be any one of screwing, soldering, or welding, or a combination thereof. Furthermore, a groove extending longitudinally can be formed in the bottom surface 51b, and the plate 43 can be fitted into the groove.

Furthermore, as shown in Figure 6C, a conveyor rail 41a may be used in which the side surface 51c protrudes downward, and the protrusion 43a serves as a plate. Furthermore, the thermal deformation absorbing means is not limited to a plate that protrudes downward in the width direction, but as shown in Figure 6D, a conveyor rail 41b may be used that has a plate 43b that protrudes downward in the thickness direction.

The above-mentioned plate 43, protrusion 43a, and plate 43b are made of the same aluminum alloy as the conveyor rail. The thickness of plate 43, protrusion 43a, and plate 43b is, for example, equal to or slightly greater than the thickness of side portion 51c. Furthermore, the length of plate 43, protrusion 43a, and plate 43b is, for example, approximately equal to the length of the conveyor rail 41 in the buffer chamber and zone Z8.

The dimensions of the plate 43, protrusion 43a, and plate 43b may be other than those described above. For example, the plate 43 may be provided only in zone Z8, or a plate 43 shorter than the length of the zone Z8 section may be provided. Furthermore, a plate 43 approximately equal in length to the conveyor rail 41 in the buffer chamber, zone Z8, and zone Z9 sections may be provided.

Figures 7A, 7B, and 7C show a schematic diagram of the arrangement of conveyor rails in the entire reflow soldering device. One conveyor rail 41 is provided for all zones. This figure shows an example of a reflow soldering device in which a buffer chamber BF is provided between the heating section and the cooling section.

The example shown in Figure 7A shows an arrangement where no special measures have been taken to prevent creep. A single conveyor rail 41 is installed throughout the entire section from the entrance 107 to the exit 108. As shown in Figure 6A, no plate 43 is provided for the conveyor rail 41.

Figure 7B shows a reference example. As shown in Figure 6B, a plate 43 is attached to the conveyor rail 41 in the heating section before the buffer chamber BF (for example, the section of zone Z7). The length of the plate 43 may be shorter. Note that the configuration shown in Figure 6C or Figure 6D may also be used for the conveyor rail in this section.

Figure 7C shows the arrangement in one embodiment of the present invention. As shown in Figure 6B, a plate 43 is attached to the transport conveyor rail 41 in the section between buffer chamber BF and zone Z8. Note that the configuration shown in Figure 6C or 6D may also be used for the transport conveyor rail in this section.

Figure 8 is a graph showing the results of a test conducted to investigate the creep phenomenon of the transport conveyor rail 41. A6063 aluminum alloy was used for the transport conveyor rail 41. By controlling the reflow equipment, a thermal cycle process was performed 50 times, in which the temperature was heated to a high temperature of 300°C for approximately two hours, followed by cooling for approximately one hour. The horizontal axis of Figure 8 shows the number of times.

The vertical axis in Figure 8 shows the displacement (mm) of the transport conveyor rail, for example, the progression of displacement in zone Z7, where the displacement is greatest. The reference plane is set to the same height as the surface where the opening 27 of the heating panel 25 of the lower furnace body is formed, and the displacement is shown as the distance between the reference plane and the underside of the substrate W. The distance before the first test is set to zero. Therefore, the smaller the displacement value, the greater the deformation (downward sagging) of the transport conveyor rail.

Graph 71 shows the measurement results for a conveyor rail 41 that does not have a thermal deformation absorption means, as in the example arrangement shown in Figure 7A. Displacement increases rapidly, leading to significant creep and the risk of shortening the lifespan of the conveyor rail.

Graph 72 shows the test results when a conveyor rail 41 with a plate 43 is used as the conveyor rail in zone Z7, the section preceding the buffer chamber BF, as in the example arrangement shown in Figure 7B. The displacement is smaller than when no countermeasures are taken.

Graph 73 shows the test results when conveyor rails 41 with plates 43 were used as conveyor rails for buffer chamber BF and zone Z8 of the cooling section, as in the arrangement of one embodiment shown in Figure 7C. The best results were obtained, with smaller displacement compared to the reference example.

As described above, one embodiment of the present invention can suppress distortion and deformation of the conveyor rail due to creep, prevent boards from falling off the conveyor rail, and extend the life of the conveyor rail.

The above describes specific embodiments of the present invention, but the present invention is not limited to the above-mentioned embodiments, and various modifications based on the technical concept of the present invention are possible. For example, in the present invention, it is desirable to provide a thermal deformation absorbing means in the cooling section of a continuous conveyor spanning the heating section and the cooling section (including the buffer chamber), so the conveyor rails located in other sections may be divided.

The present invention is not limited to printed circuit boards, but can also be applied to the reflow of flexible boards, boards made by bonding rigid and flexible boards, and rigid-flex boards that combine these. The present invention can also be applied to reflow equipment with a single heating furnace (one zone). Furthermore, the present invention is not limited to reflow equipment, but can also be applied to heating equipment for curing resins, etc. The configurations, methods, processes, shapes, materials, and values described in the above-described embodiments are merely examples, and different configurations, methods, processes, shapes, materials, and values may be used as needed. The configurations, methods, processes, shapes, materials, and values described in the above-described embodiments can be combined with each other as long as they do not deviate from the spirit of the present invention.

101... reflow device, 102... reflow furnace, 103, 203... conveyor chain, W... substrate, 41, 141, 41a, 41b... conveyor rail, 43, 43a, 43b... plates

Claims (9)

A heating section and a cooling section including one or more heating furnaces sequentially arranged in a conveying direction of the object to be heated, and a conveying chain for conveying the object to be heated;
a conveyor rail that guides the conveyor chain;
A conveying and heating device comprising a thermal deformation absorbing means provided on at least a part of the conveyor rail in the cooling section. The conveying and heating device according to claim 1, wherein the conveyor rail is provided continuously between the heating section and the cooling section. In the heating section, a fan and a heater are provided on the upper and lower sides, respectively;
3. The conveying and heating device according to claim 1, wherein a blower is provided above the cooling section. The conveying and heating device according to claim 1 or 2, wherein the thermal deformation absorbing means is provided on the bottom side of the conveyor rail. The conveying and heating device described in claim 3, wherein the thermal deformation absorbing means is provided on the bottom side of the conveyor rail. The conveying and heating device according to claim 1 or 2, wherein a buffer chamber is provided between the heating section and the cooling section, and the thermal deformation absorbing means is provided on at least a portion of the conveyor rails arranged in the buffer chamber and the cooling section. The conveying and heating device according to claim 3, wherein a buffer chamber is provided between the heating section and the cooling section, and the thermal deformation absorbing means is provided on at least a portion of the conveyor rails arranged in the buffer chamber and the cooling section. The conveying and heating device according to claim 4, wherein a buffer chamber is provided between the heating section and the cooling section, and the thermal deformation absorbing means is provided on at least a portion of the conveyor rails arranged in the buffer chamber and the cooling section. 6. The conveying and heating device according to claim 5, wherein a buffer chamber is provided between the heating section and the cooling section, and the thermal deformation absorbing means is provided on at least a part of the conveyor rails arranged in the buffer chamber and the cooling section.