Conveyance heating apparatus

Abstract

To reduce strains caused by the creep phenomenon of conveyor rails which are provided at cooling sections at the later stage of heating sections.SOLUTION: A conveyance heating apparatus comprises: heating sections including one or more heating furnaces and cooling sections successively aligned in the conveyance direction of an object to be heated; conveyor chains for conveying the object to be heated; conveyer rails for guiding the conveyor chains; and heat deformation absorption means provided at least at a part of each conveyer rail in each cooling section.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a conveying and heating device that is applied to a device that conveys an object to be heated by a conveying chain, such as a reflow device. [Background technology]

[0002] The running state of the conveyor chain is regulated by rails. For example, the conveyor chain is used in a reflow device to convey electronic components or printed circuit boards. The reflow device is equipped with a reflow furnace to which the object to be heated, such as a printed circuit board, is 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 a conveyance path from an inlet to an outlet. The multiple zones serve as heating zones, cooling zones, etc., depending on their functions.

[0003] 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 conveyor chain is guided by rails made of metal, such as aluminum alloy (hereinafter referred to as conveyor rails).

[0004] 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 a significant temperature difference between the upper and lower sides of the conveyor. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 3442597 Summary of the Invention [Problem to be solved by the invention]

[0006] 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 to metal at high temperatures, distortion increases over time, sometimes leading to fracture. This phenomenon is called creep.

[0007] 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, it could result in the PCBs being transported by the conveyor chain falling. To prevent this creep-related distortion over time, frequently used reflow soldering equipment adjusts or replaces the conveyor rails before significant distortion occurs. Furthermore, consideration must be given to the fact that the conveyor rails of reflow soldering equipment are used in different temperature environments, such as high-temperature heating sections and low-temperature cooling sections.

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a conveying and heating device that can deal with distortion and deformation caused by creep of a conveyor rail and thereby extend the service life of the conveyor rail. [Means for solving the problem]

[0009] The present invention is 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 portion of the conveying conveyor rail in the cooling section. [Effects of the Invention]

[0010] According to at least one embodiment, distortion and deformation of the conveyor rail due to creep can be reduced, and the service life of the conveyor rail can be improved. Note that the effects described herein are not necessarily limited, and any of the effects described in this disclosure may be used. Furthermore, the content of the present invention should not be interpreted as being limited to the effects exemplified in the following description. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram showing an example of a reflow apparatus to which the present invention can be applied. [Figure 2] FIG. 2 is a schematic diagram showing the configuration of the reflow furnace. [Figure 3] FIG. 3 is a graph showing an example of a temperature profile during reflow. [Figure 4] 4A and 4B are cross-sectional views showing an example of the configuration of a zone in the heating section. [Figure 5] 5A and 5B are cross-sectional views showing an example of the configuration of the zones in the cooling section. [Figure 6] 6A, 6B, 6C and 6D are cross-sectional views used to explain the transport conveyor rails. [Figure 7] 7A, 7B, and 7C are schematic diagrams showing examples of arrangement of transport conveyor rails used to explain one embodiment of the present invention. [Figure 8] FIG. 8 is a graph used to explain one embodiment of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described. Note that the embodiment described below is a preferred specific example of the present invention, and various technically preferable limitations are attached, but the scope of the present invention is not limited to these embodiments unless otherwise stated in the following description to the effect that the present invention is limited.

[0013] FIG. 1 shows a 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 a 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 FIG. 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 apparatus.

[0014] 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 FIG. 1) at a predetermined speed, and is finally removed from the carry-out exit 108. Although not shown, a substrate carry-in device for carrying in the substrate W is provided before the carry-in entrance 107, and a substrate carry-out device for sending the substrate W to the outside is provided after the carry-out exit 108.

[0015] FIG. 2 is a diagram showing a schematic configuration of the reflow furnace 102 of the reflow apparatus 101 shown in FIG. 1. The reflow furnace 102 is divided into, for example, nine zones Z1 to Z9 along a transport path 109 extending from an inlet 107 to an outlet 108, and these zones Z1 to Z9 are arranged in-line. Seven zones Z1 to Z7 from the inlet 107 side are heating zones, and two zones Z8 and Z9 from the outlet 108 side are cooling zones. Forced cooling units 112 are provided in association with the cooling zones Z8 and Z9. Note that the number of zones 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 a 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.

[0016] A throat 110 is provided between the reflow furnace 102 and the carry-in port 107, and a throat 111 is provided between the reflow furnace 102 and the carry-out port 108. The throats 110 and 111 function as seals that isolate the inside of the reflow furnace 102 from the outside and prevent an increase in the oxygen concentration inside the furnace. The throats 110 and 111 are configured as labyrinth seals, for example.

[0017] The above-mentioned multiple zones Z1 to Z9 control the temperature of the heated object according to a temperature profile during reflow. An example of a temperature profile is outlined in Figure 3. 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.

[0018] The temperature rise section R1 is a 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 a period during which the solder melts and the bond is completed. In the reflow section R3, the temperature must be raised to a temperature exceeding the solder melting temperature. Even after passing the preheat section R2, uneven temperature rise still exists, so heating to a temperature exceeding the solder melting temperature is required in the reflow section R3. The final cooling section R4 is a period during which the printed wiring board is rapidly cooled and the solder composition is formed. 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).

[0019] In Figure 3, curve P1 shows an example of a temperature profile for lead-free solder. Curve P2 shows an example of a temperature profile for Sn-Pb eutectic solder. 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.

[0020] In the reflow soldering equipment shown in Figures 1 and 2, the temperature control of the heating section R1 in Figure 3 is mainly handled by zones Z1 and Z2. The temperature control of the preheating section R2 is mainly handled by zones Z3, Z4, and Z5. The temperature control of the reflow section R3 is handled by zones Z6 and Z7. The temperature control of the cooling section R4 is handled by zones Z8 and Z9. The temperatures in zones Z8 and Z9 of the cooling section R4 are above 100°C.

[0021] An example of the configuration of the furnace body of 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.

[0022] The substrate W is transported by the transport chains 103 and 203 in the gap between the opposing upper and lower furnace bodies. As shown in the enlarged cross-sectional view of FIG. 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 to each other, and the substrate W is placed on pins that protrude from the link plates toward the transport surface and 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.

[0023] As shown in Fig. 4A, the upper furnace body is composed of a main heating source 12, an auxiliary 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 is, for example, similar to the upper furnace body, and is equipped with a main heating source 22, an auxiliary heating source 23, a blower 24, a heating panel 25, a hot air circulation duct 26, an opening 27, etc.

[0024] The blower 14 has a motor M5 and a rotary blade 18. Similarly, the blower 24 has a motor M15 and a rotary blade 28. As the blower, a centrifugal fan such as a turbo fan or a sirocco fan, or an axial blower may be used. The furnace bodies of the other heating units also have the same configuration as that shown in Figures 4A and 4B. Note that the configuration of the furnace body described above is an example, and other configurations may be used.

[0025] 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 a large number of holes formed therein, through which hot air passes (openings 17 and 27) and is blown onto the substrate W.

[0026] For example, in the upper furnace body, hot air is circulated by the blower 14. That is, the hot air circulates through the route (main heating source 12 → heating panel 15 → opening 17 → substrate W → hot air circulation duct 16 → auxiliary heating source 13 → hot air circulation duct 16 → blower 14 → main heating source 12). Similarly, in the lower furnace body, hot air circulates through the route (main heating source 22 → heating panel 25 → opening 27 → substrate W → hot air circulation duct 26 → auxiliary heating source 23 → hot air circulation duct 26 → blower 24 → main heating source 22).

[0027] An example of the configuration of a zone in the cooling section, for example, zone Z8, will be described with reference to Figures 5A and 5B. Figures 5A and 5B are schematic diagrams of a cross section perpendicular to the transport direction of the reflow soldering apparatus. Zone Z9 has the same configuration as zone Z8. Zone Z8 does not have a heating unit, but is provided with a motor M8, a blower 34 with rotating blades 38, and a rectifying plate 35 at its top for airflow. The rectifying plate 35 is a metal plate with many holes. Cool air circulates via the following route: blower 34 → rectifying plate 35 → opening 37 → substrate W → duct 36 → blower 34.

[0028] 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 FIG. 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 and in the buffer chamber between the heating section and the cooling section also have plates 43 and 143.

[0029] In one embodiment, in the above-described reflow soldering apparatus, one conveyor rail 41, 141 is provided throughout the entire section from the entrance 107 to the exit 108. If the conveyor rail is provided in two sections, connecting portions are created, and it becomes necessary to provide support and mounting portions for the conveyor rail at the connecting portions, which results in an increase in the number of parts and work processes.

[0030] A continuous conveyor rail can avoid this problem. However, it has been found that creeping of the conveyor rails is a significant issue in a reflow soldering machine with this configuration. To solve this issue, in one embodiment of the present invention, plates 43 and 143 are provided on the conveyor rails in the cooling section.

[0031] The material of the conveyor rails 41, 141 is an aluminum alloy. Pure aluminum is a soft metal, so 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 amount of magnesium and silicon, such as A6063, is used for the conveyor rails 41, 141. Other types of aluminum alloys can also be used.

[0032] 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. For example, the transport conveyor rail 41, which is an aluminum extrusion product, has a U-shaped cross-section in which an upper surface portion 51a, a bottom surface portion 51b, and a side surface portion 51c are continuously formed. A transport chain 103 is placed in a groove 51d between the upper surface portion 51a and the bottom surface portion 51b. Although the transport conveyor rail 41 will be described, a transport conveyor rail 141 also has a similar configuration.

[0033] 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, and welding, or a combination thereof. Furthermore, a groove extending in the longitudinal direction may be formed in the bottom surface 51b, and the plate 43 may be fitted into the groove.

[0034] Furthermore, as shown in Fig. 6C, a conveyor rail 41a may be used in which side surface portion 51c protrudes downward and protrusion portion 43a serves as a plate. Furthermore, the thermal deformation absorbing means is not limited to a plate protruding downward in the width direction, but as shown in Fig. 6D, a conveyor rail 41b provided with a plate 43b protruding downward in the thickness direction may be used.

[0035] The plate 43, protrusion 43a, and plate 43b are made of the same aluminum alloy as the conveyor rail. The thickness of the plate 43, protrusion 43a, and plate 43b is, for example, equal to or slightly greater than the thickness of the side surface 51c. The length of the 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.

[0036] The dimensions of plate 43, protrusion 43a, and plate 43b may be other than those described above. For example, plate 43 may be provided only in zone Z8, or a plate 43 shorter than the length of zone Z8 may be provided. Furthermore, plate 43 may be provided whose length is approximately equal to the length of conveyor rail 41 in the buffer chamber, zone Z8, and zone Z9 sections.

[0037] 7A, 7B, and 7C show schematic diagrams of the arrangement of conveyor rails in the entire reflow soldering equipment. One conveyor rail 41 is provided for all zones. The diagrams show an example of a reflow soldering equipment in which a buffer chamber BF is provided between the heating section and the cooling section.

[0038] The example shown in Figure 7A is an arrangement example where no special measures have been taken to prevent creep. A single transport conveyor rail 41 is installed throughout the entire section from the carry-in entrance 107 to the carry-out exit 108. As shown in Figure 6A, no plate 43 is provided for the transport conveyor rail 41.

[0039] 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 (e.g., zone Z7) before the buffer chamber BF. 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.

[0040] Figure 7C shows an arrangement according to 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.

[0041] 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 of heating to a high temperature of 300°C for about two hours and then cooling for about one hour was repeated 50 times. The horizontal axis of Figure 8 shows the number of times.

[0042] The vertical axis of Figure 8 shows the displacement (mm) of the transport conveyor rail, for example, the change in 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 distance between the reference plane and the underside of the substrate W is shown as the displacement. 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.

[0043] Graph 71 shows the measurement results for a conveyor rail 41 that does not have a thermal deformation absorbing means, as in the example arrangement shown in Figure 7A. Displacement increases rapidly, creep occurs, and there is a risk of the conveyor rail's lifespan being shortened.

[0044] Graph 72 shows the test results when conveyor rail 41 with plate 43 is used as the conveyor rail in zone Z7, the section preceding buffer chamber BF, as in the arrangement example shown in Figure 7B. The displacement is smaller than when no countermeasures are taken.

[0045] Graph 73 shows the test results when conveyor rails 41 with plates 43 are used as conveyor rails in 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.

[0046] As described above, according to one embodiment of the present invention, distortion and deformation of the conveyor rail due to creep can be suppressed, substrates can be prevented from falling off the conveyor rail, and the life of the conveyor rail can be extended.

[0047] Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications based on the technical concept of the present invention are possible. For example, in the present invention, since it is desirable to provide a thermal deformation absorbing means in the cooling section on a continuous transport conveyor spanning the heating section and the cooling section (including the buffer chamber), the transport conveyor rails arranged in other sections may be divided.

[0048] Furthermore, the present invention is not limited to printed circuit boards, but can also be applied to the reflow of flexible boards, boards formed by bonding rigid and flexible boards, and rigid-flex boards that combine these. The present invention can also be applied to reflow apparatuses with a single heating furnace (one zone). Furthermore, the present invention is not limited to reflow apparatuses, but can also be applied to heating devices 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. [Explanation of symbols]

[0049] 101... reflow device, 102... reflow oven, 103, 203... conveyor chain, W... substrate, 41, 141, 41a, 41b... conveyor rail, 43, 43a, 43b... plate

Claims

1. 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 thermal deformation absorbing means provided on at least a part of the conveyor rail in the cooling section; Conveyor heating device.

2. 2. The conveying and heating device according to claim 1, wherein the conveyor rail is provided continuously between the heating section and the cooling section.

3. 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.

4. 3. The conveying and heating device according to claim 1, wherein the thermal deformation absorbing means is provided on the bottom side of the conveyor rail.

5. 4. The conveying and heating device according to claim 3, wherein the thermal deformation absorbing means is provided on the bottom side of the conveyor rail.

6. 3. The conveying and heating device according to claim 1, 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 rail arranged in the buffer chamber and the cooling section.

7. 4. 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 part of the conveyor rails arranged in the buffer chamber and the cooling section.

8. 5. 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 part of the conveyor rails arranged in the buffer chamber and the cooling section.

9. 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.

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