JP7832041B2 - Substrate warping prevention device and transport heating device - Google Patents

Description

This invention relates to a substrate warping prevention device and a transport heating device, for example, to a reflow apparatus.

A reflow apparatus is used in which a solder composition is pre-supplied to electronic components or printed circuit boards, and the boards are transported into a reflow oven by a transport conveyor such as a transport chain. The reflow apparatus comprises a transport conveyor for transporting the boards and a reflow oven body into which the material to be heated, such as a printed circuit board, is supplied by the transport conveyor. The reflow oven is divided into multiple zones along a transport path from the inlet to the outlet, and these multiple zones are arranged in a line. The multiple zones have roles such as heating zones and cooling zones, depending on their function.

In the heating zone, hot air is blown onto the workpiece (the object to be heated), melting the solder in the solder composition and soldering the electrodes of the printed circuit board to the electronic components. In a reflow soldering apparatus, the desired soldering is achieved by controlling the heating temperature according to a desired temperature profile. Specifically, the first section is a heating section where the temperature rises due to heating, the next section is a preheating section where the temperature remains nearly constant, the following section is the reflow (main heating) section, and the final section is a cooling section.

In this type of reflow soldering assembly method, the recent miniaturization and thinning of electronic devices has resulted in thinner printed circuit boards (PCBs), making them more susceptible to warping. To prevent PCB warping (downward warping, hereafter the same), a warping prevention device is known that supports the underside of the PCB as it is being transported within the reflow soldering machine using protrusions. These protrusions are attached to a warping prevention chain that is synchronized with the transport chain used for transporting the PCB. A warping prevention rail extending in the transport direction is provided to support and guide the warping prevention chain. Because the warping prevention rail is long, rail guides are provided at predetermined locations (intervals) within the furnace, perpendicular to the transport direction (referred to as the width direction), to suppress deflection. The rail guides support the warping prevention rail by receiving it over a surface area.

In reflow soldering equipment, flux fumes are generated during production. These fumes condense upon cooling. In particular, on the rail guides in areas where the temperature drops, such as between the heating and cooling zones, the flux fumes accumulate as a viscous substance. While there is no impact during production in the reflow soldering equipment because the furnace is exposed to a high-temperature environment, the temperature inside the furnace drops during product changeovers after production is complete. This can cause the anti-warping rail and rail guide to stick together due to the flux. Specifically, because the surfaces of the rail guide and the anti-warping rail are in contact, the impact of flux adhesion is significant.

In reflow soldering equipment, when changing the size of printed circuit boards due to product changes, the spacing of the transport chains in the width direction is variable. Since the anti-warping element is most effective when positioned in the center of the back surface of the printed circuit board, it becomes necessary to change the position of the anti-warping rails in the width direction in response to changes in the transport chain spacing. However, if the position of the anti-warping rails is changed while they are fixed together with the rail guides, the fixed flux can cause the anti-warping rails to bend, potentially having a significant impact on subsequent production.

For example, Patent Document 1 describes a flux application apparatus in which, in order to solve the problem of the screw shaft becoming unable to rotate relative to the nut due to the solidification of the flux, a portion of the screw threads of the nut is cut out to form a non-engaging portion.

Japanese Patent Publication No. 2016-215276

The invention described in Patent Document 1 is intended and configured for the smooth rotation of a screw shaft, and therefore differs in purpose and configuration from the solution to the problem of the anti-warping rail and rail guide becoming stuck together as described above. Furthermore, while it is conceivable to provide roller guides at the contact points between the anti-warping rail and rail guide, roller guides would increase the cost of the reflow machine.

Therefore, the object of the present invention is to provide a substrate warping prevention device and a transport heating device that can suppress the loss of production opportunities due to flux adhesion.

The present invention relates to a heating device comprising a plurality of heating furnaces arranged in a row and configured to blow hot air onto an object to be heated by the heating furnaces, and a conveying heating device having a conveying conveyor for transporting the object to be heated to the heating device,
It is equipped with a warp prevention rail that guides a warp prevention body that suppresses downward warping of the object being heated, and a rail guide that supports the warp prevention rail from below.
This is a conveying and heating device in which rail guides are present between multiple heating furnaces, and the anti-warping rails have protrusions on the contact surface with the rail guides.
Furthermore, the present invention is a warp prevention device comprising a warp prevention body that supports the lower surface of an object to be heated while being transported, a warp prevention chain to which the warp prevention body is attached, a warp prevention rail having a chain guide that guides the warp prevention chain, a rail guide that supports the warp prevention rail from below, and rib-shaped projections formed on the contact surface of the warp prevention rail with respect to the rail guide and extending in the direction of extension of the warp prevention rail.

According to at least one embodiment, the anti-warping rail expands and contracts due to heating and cooling, and the displacement of the anti-warping rail can scrape off the accumulated flux, preventing the anti-warping rail and rail guide from becoming stuck together by the flux. The effects described herein are not necessarily limited, and any of the effects described in the present invention may be used. Furthermore, the effects illustrated in the following description should not be interpreted as limiting the scope of the present invention.

Figure 1 is a schematic diagram showing a conventional reflow apparatus to which the present invention can be applied. Figure 2 is a graph showing an example of a temperature profile during reflow. Figures 3A, 3B, and 3C are schematic diagrams, cross-sectional views of the anti-warping device and the anti-warping rail, respectively, used to illustrate an anti-warping device to which the present invention can be applied. Figure 4 is a top view of the workpiece transport surface of the reflow machine. Figure 5 is an enlarged plan view of a portion of Figure 4. Figures 6A and 6B are cross-sectional and bottom views of an example using rail guide fittings, and Figures 6C and 6D are cross-sectional and bottom views of an example using rail guide fittings. Figures 7A and 7B are side and bottom views of the portion where the rail guide fitting and the rail guide are in contact, and Figure 7C is a plan view of an example of a rail guide. Figures 8A, 8B, and 8C are cross-sectional and bottom views of the rail guide fitting, and a front view of the rail guide fitting, while Figures 8D, 8E, and 8F are cross-sectional and bottom views of the rail guide fitting, and a front view of the rail guide fitting. Figures 9A and 9B are side and bottom views of the portion where the rail guide fitting and the rail guide are in contact.

The present invention will be described below in the following manner, following embodiments.
<1. An example of a reflow oven>
<2. One Embodiment>
<3. Variations>
The embodiment described below is a preferred example of the present invention and is subject to various technically preferred limitations. However, the scope of the present invention is not limited to these embodiments unless otherwise specified in the following description.

<1. An example of a reflow oven>
Figure 1 shows a schematic configuration of a conventional reflow apparatus to which the present invention can be applied. A workpiece, with surface-mount electronic components mounted on both sides of a printed circuit board, is placed on a conveyor belt and transported into the heating chamber of the reflow apparatus from the entrance 101. The conveyor belt transports the workpiece at a predetermined speed in the direction of the arrow (from left to right in Figure 1), and the workpiece is removed from the exit 102. The transport direction of the conveyor belt is horizontal.

The heating device is configured such that multiple heating furnaces are arranged along the transport path from the inlet 101 to the outlet 102, and hot air (heated atmospheric gas) is blown onto the workpiece by the heating furnaces. Multiple heating furnaces (referred to as zones) are arranged in a line. Seven zones Z1 to Z7 from the inlet side are heating zones, and two zones Z8 and Z9 on the outlet side are cooling zones. A forced cooling unit 103 is provided in relation to cooling zones Z8 and Z9. Each of the heating zones Z1 to Z7 has an upper heating furnace and a lower heating furnace, each including a blower, heater, and blowing panel. Note that this number of zones is an example, and a configuration with a different number of zones is also possible.

The aforementioned zones Z1 to Z9 control the workpiece temperature according to the reflow temperature profile. Figure 2 shows a schematic example of a temperature profile. The horizontal axis represents time, and the vertical axis represents the surface temperature of the workpiece, such as a printed circuit board with electronic components mounted on it. The first section is the heating section R1 where the temperature rises due to heating; the next section is the preheating section R2 where the temperature remains nearly constant; the following section is the reflow (main heating) section R3; and the final section is the cooling section R4.

The heating section R1 is the period during which the substrate is heated from room temperature to the preheating section R2 (e.g., 150°C to 170°C). The preheating section R2 is a period for activating the flux, removing the oxide film from the surface of the electrodes and solder powder, and eliminating uneven heating of the printed circuit 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 bonding is completed. In the reflow section R3, heating to a temperature exceeding the solder melting temperature is required. Even after passing through the preheating section R2, uneven temperature rise may exist, so heating to a temperature exceeding the solder melting temperature is necessary in the reflow section R3. The final cooling section R4 is the period during which the printed circuit 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 R3 will be higher (e.g., 240°C to 260°C).

In Figure 2, curve 1 shows an example of the temperature profile for lead-free solder. An example of the temperature profile for Sn-Pb eutectic solder is shown by curve 2. Since the melting point of lead-free solder is higher than that of eutectic solder, the set temperatures in the preheating section R2 and reflow section R3 are higher compared to those for eutectic solder.

In the reflow apparatus shown in Figure 1, the temperature control of the heating section R1 in Figure 2 is primarily handled by zones Z1 and Z2. The temperature control of the preheating section R2 is primarily 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. Gaps exist between the multiple heating furnaces (zones) described above.

<2. One Embodiment>
Each zone is equipped with an upper heating furnace and a lower heating furnace facing each other. Workpieces with surface-mount electronic components mounted on one or both sides of a printed circuit board are transported by a conveyor belt within the gap between the upper and lower heating furnaces. The upper and lower heating furnaces are filled with an atmospheric gas, such as nitrogen (N2). The upper heating furnace heats the workpiece by blowing hot air (heated atmospheric gas) downwards through a blowing panel, while the lower heating furnace heats the workpiece by blowing hot air upwards through a blowing panel. Infrared radiation may also be used along with the hot air. The upper and lower heating furnaces each have a fan (rotating blades) and heaters, which are rotated by a motor.

A warp prevention device, as shown in Figures 3A, 3B, and 3C, is provided for the workpiece W, such as a printed circuit board. The warp prevention device comprises a warp prevention body 11, a warp prevention chain 12 to which the warp prevention body 11 is attached, and a warp prevention rail 13 that guides the warp prevention chain 12. The warp prevention chain 12 is, for example, a roller chain. The movement of the conveyor that transports the workpiece W and the movement of the warp prevention chain 12 are synchronized.

The anti-warping chain 12 is transported at a position below (lower than) the height of the conveying surface of the conveyor. An anti-warping body 11, which prevents downward warping by supporting the lower surface of the workpiece W, protrudes upward from the anti-warping chain 12. The anti-warping body 11 is, for example, a metallic plate-shaped or rod-shaped body attached to each link plate of the anti-warping chain 12. Because the lower surface of the workpiece W is supported by the anti-warping body 11, the workpiece W is prevented from bending downward due to the weight of the mounted electronic components when heated. It is preferable that the anti-warping body 11 contacts the lower surface of the workpiece W at multiple points in the conveying direction of the workpiece W. Since the feeding of the workpiece W and the anti-warping body 11 are synchronized, the anti-warping body 11 can stably support the workpiece W.

The anti-warping rail 13 is a rail that extends in the conveying direction, located approximately in the center between the two conveying belts, and has a lower guide 14 and an upper guide 15 for guiding the anti-warping chain 12. The anti-warping rail 13 is made of a metal such as stainless steel, aluminum, or iron. Since the anti-warping rail 13 is a long rail installed within the conveying range of the workpiece W, it is supported from below by a rail guide 21 to prevent bending.

As shown in Figure 3C, a composite anti-warping rail may be used in which a lower resin guide 17 is fitted into a metal rail 16. Although not shown, the upper guide is also made of resin. The upper and lower resin guides 17 are, for example, molded products of polyamide-imide resin. Polyamide-imide resin has excellent properties of wear resistance, heat resistance, and durability. Furthermore, it does not contain carbon and is non-conductive. Therefore, since the debris generated by friction between the upper and lower resin guides 17 and the anti-warping chain 12 is resin (non-conductive), there is no risk of a short circuit occurring on the substrate due to the debris.

Figure 4 is a top-down plan view of the workpiece transport surface of a reflow apparatus. While the reflow apparatus in Figure 1 has nine zones Z1 to Z9, the reflow apparatus in Figure 4 has ten zones Z1 to Z10. Zones Z1 to Z9 are heating zones, and zone Z10 is a cooling zone. Two transport conveyors 22a and 22b (simply referred to as transport conveyor 22 when there is no need to distinguish between the two transport conveyors) are provided parallel to each other on the upper surface of the blowout panel of the lower heating furnace in each zone for transporting workpieces.

A warp prevention rail 13 is installed parallel to the conveyor belts 22, approximately in the center of the space between them. In the height direction, the warp prevention rail 13 is positioned lower than the conveyor belts 22 so that the tip of the warp prevention body 11 contacts the underside of the workpiece. The spacing between the conveyor belts 22 is adjustable in the width direction according to the width of the workpiece. When the spacing between the conveyor belts 22 is changed, the positional relationship between the warp prevention rail 13 and the conveyor belts 22 is maintained.

The rail guides 21 are installed at predetermined intervals in the transport direction in the gaps between zones (heating furnaces). For example, they are installed between zone Z1 and zone Z2, between zone Z3 and zone Z4, between zone Z5 and zone Z6, between zone Z7 and zone Z8, and between zone Z9 and zone Z10. Two rail guides 21 are installed between zone Z9 and zone Z10. As an example, the rail guides 21 protrude inward from the side where the transport conveyor 22b is installed, with their tips protruding further towards the transport conveyor 22a side than the anti-warping rail 13. The length of the rail guides 21 is such that they protrude slightly outward from the center position when the transport conveyor 22 is spaced at its maximum. The rail guides 21 are metal brackets with an L-shaped cross-section.

Figure 5 shows a magnified view of section A, circled in Figure 4. In this example, a rail guide support, such as a metal rail guide fitting 23A with a U-shaped cross-section, is attached to the anti-warping rail 13. For example, the anti-warping rail 13 is made up of multiple divided anti-warping rails connected by the rail guide fittings 23A. The support surface of the rail guide 21 is in contact with a projection provided on the bottom surface of the rail guide fitting 23. Note that the anti-warping rail 13 is not limited to a configuration of connected divided sections; it may also be a single rail.

If flux adheres to the contact point or vicinity between the support surface of the rail guide 21 and the bottom surface of the rail guide fitting 23A (or the bottom surface of the anti-warping rail 13), the viscosity of the flux may increase or the flux may solidify as a result of cooling during product changeover, causing the rail guide 21 and the rail guide fitting 23A to stick together. In this state, if the anti-warping rail 13 is moved in the width direction to change the width of the workpiece, the stuck point will not move, causing the anti-warping rail 13 to bend, which will hinder subsequent production.

However, in one embodiment of the present invention, a projection is provided on the bottom surface of the rail guide fitting 23A, that is, on the contact surface with the rail guide 21, thereby avoiding this problem. An example of the projection is described below.

Figures 6A and 6B show a cross-sectional and bottom view of an example in which a rail guide fitting 23B, having an L-shaped cross-section that closely contacts the side and bottom surfaces of a rail guide support, such as a warp-prevention rail 13, is fixed to the warp-prevention rail 13 with bolts. A rib-shaped projection 24 is formed approximately at the center of the width direction of the bottom surface of the rail guide fitting 23B, extending parallel to the extension direction of the warp-prevention rail 13 (workpiece transport direction). The projection 24 has a rectangular cross-section, and its tip surface contacts the support surface of the rail guide 21.

Figures 6C and 6D show a cross-sectional and bottom view of an example where a rail guide fitting 23C, having an I-shaped cross-section that closely contacts the bottom surface of the anti-warping rail 13, is fixed to the anti-warping rail 13 with bolts. A rib-shaped projection 24 is formed approximately at the center of the width direction of the bottom surface of the rail guide fitting 23B, extending parallel to the extension direction of the anti-warping rail 13 (workpiece transport direction). The projection 24 has a rectangular cross-section, and its tip surface contacts the support surface of the rail guide 21.

Figures 7A and 7B are side and bottom views of the portion where the rail guide fitting 23B and the rail guide 21 are in contact, and Figure 7C is a plan view of an example of the rail guide 21. As can be seen from Figure 7B, the surface area of the contact surface between the rail guide 21 and the projection 24 can be made smaller compared to the example where the projection 24 is not formed. During production in the reflow oven, flux fumes are generated, causing flux to adhere to and accumulate on the anti-warping rail 13, rail guide 21, and rail guide fitting 23B. When production is stopped, such as during product changeovers, the inside of the furnace cools, increasing the viscosity of the flux and causing it to solidify.

As described above, the contact surface between the rail guide 21 and the projection 24 can be made smaller, thus reducing the amount of flux accumulated within and near the contact surface. Furthermore, the temperature changes caused by heating and cooling result in contraction and thermal expansion of the anti-warping rail 13, as indicated by the arrows in Figures 7A and 7B. Since one side of the anti-warping rail 13 is fixed, it contracts and expands in the transport direction. This sliding motion due to contraction and expansion can release the sticking between the rail guide fitting 23B and the rail guide 21, and scrape off the flux accumulated within and near the contact surface. As a result, the anti-warping rail 13 can be prevented from bending when it moves in the width direction. The rail guide fitting 23C has a similar function to the rail guide fitting 23B.

Figures 8A, 8B, and 8C show a cross-sectional view and a bottom view of an example where the rail guide fitting 23A is fixed to the anti-warping rail 13 with bolts, as well as a front view of the rail guide fitting 23A having a U-shaped cross-section that makes close contact with both sides and the bottom surface of the anti-warping rail 13. Similar to rail guide fittings 23B and 23C, the rail guide fitting 23A has a rib-shaped projection 24 extending parallel to the extension direction of the anti-warping rail 13 (workpiece transport direction) at approximately the center of the width direction of the bottom surface. The tip surface of the projection 24 contacts the support surface of the rail guide 21.

Figures 8D, 8E, and 8F show a cross-sectional view and a bottom view of an example where a rail guide support, such as a rail guide fitting 23D, is fixed to the anti-warping rail 13 with bolts, and a front view of a rail guide fitting 23D having a U-shaped cross-section similar to that of rail guide fitting 23A. Like other rail guide fittings, the rail guide fitting 23D has rib-shaped projections 25 extending in the direction of extension of the anti-warping rail 13 (the direction of workpiece transport). The tip surface of the projection 25 contacts the support surface of the rail guide 21. This projection 25 differs from projection 24 in that it is formed in an inclined direction with respect to the center line in the width direction of the bottom surface.

Figures 9A and 9B are side and bottom views of the portion where the rail guide fitting 23D and the rail guide 21 are in contact. As can be seen from Figure 9B, the contact surface between the rail guide 21 and the projection 25 can be made smaller. Therefore, since the contact surface between the rail guide 21 and the projection 25 can be made smaller, the amount of flux accumulated in and around the contact surface can be reduced. Furthermore, as indicated by the arrows in Figures 9A and 9B, the temperature changes caused by heating and cooling cause contraction and thermal expansion of the anti-warping rail 13. Since one side of the anti-warping rail 13 is fixed, the anti-warping rail 13 contracts and expands in the transport direction, and this sliding due to contraction and expansion can relieve the sticking between the rail guide fitting 23B and the rail guide 21, and scrape off the flux accumulated in and around the contact surface. As a result, it is possible to prevent the anti-warping rail 13 from bending when it moves in the width direction. Furthermore, since the projection 25 on the bottom surface of the rail guide fitting 23D is formed in an inclined direction, it slides in the width direction of the anti-warping rail 13 due to the sliding of the anti-warping rail 13 in the transport direction. Therefore, the area over which flux can be scraped off can be wider compared to a straight projection 24.

Furthermore, surface treatment such as plating may be applied to the entire rail guide fittings 23A, 23B, 23C, or 23D, or to a portion including the tip surface of the projection 24 (projection 25), to reduce frictional resistance between the rail guide 21 and the rail guide fitting, and to suppress the generation of metal shavings due to friction. Alternatively, projections may be formed on the bottom surface of the anti-warping rail 13 itself without providing rail guide fittings. In this case, projections may be formed only near the area where the anti-warping rail 13 contacts the rail guide 21.

<3. Variations>
Although embodiments of the present invention have been specifically described above, the invention is not limited to the embodiments described above, and various modifications are possible based on the technical concept of the present invention. For example, the present invention can also be applied to a configuration with multiple lanes in which multiple transport furnaces are arranged in parallel. Furthermore, the present invention is not limited to printed circuit boards, but can also be applied to the reflow of flexible circuit boards, circuit boards made by bonding rigid circuit boards and flexible circuit boards, and rigid-flex circuit boards that combine these. Moreover, it is not limited to reflow equipment, but can also be applied to heating equipment for curing resins, etc. Furthermore, the configurations, methods, processes, shapes, materials, and numerical values given in the embodiments described above are merely examples, and different configurations, methods, processes, shapes, materials, and numerical values may be used as needed. In addition, the configurations, methods, processes, shapes, materials, and numerical values of the embodiments described above can be combined with each other as long as they do not depart from the spirit of the present invention.

Z1-Z10... Zones, 101... Entrance, 102... Exit, 103... Forced Cooling Unit, 11... Anti-Warping Body, 12... Anti-Warping Chain, 13... Anti-Warping Rail, 21... Rail Guide, 23A, 23B, 23C, 23D... Rail Guide Fittings, 24, 25... Protrusions

Claims (7)

A heating device comprising a heating device having multiple heating furnaces arranged in a row and configured to blow hot air onto an object to be heated by the heating furnaces, and a conveying conveyor for transporting the object to be heated to the heating device,
The system includes a warp-preventing rail that guides a warp-preventing body that suppresses downward warping of the object to be heated, and a rail guide that supports the warp-preventing rail from below.
A conveying and heating device in which the rail guides are located between the plurality of heating furnaces, and the warp prevention rail has a projection on the contact surface with the rail guides. The conveying and heating apparatus according to claim 1, wherein a rail guide support is attached to the anti-warping rail, and the projection is formed on the rail guide support. The conveying and heating apparatus according to claim 2, wherein the anti-warping rail is configured in which divided anti-warping rails are connected by the rail guide support. The conveying and heating device according to any one of claims 1 to 3, wherein the projection is a rib-shaped projection extending in the direction of conveying the object to be heated. The conveying and heating device according to any one of claims 1 to 3, wherein the projection is a rib-shaped projection extending in a direction inclined with respect to the conveying direction of the object to be heated. A warp prevention device comprising: a warp prevention body that supports the lower surface of an object to be heated and transported; a warp prevention chain to which the warp prevention body is attached; a warp prevention rail having a chain guide that guides the warp prevention chain; a rail guide that supports the warp prevention rail from below; and rib-shaped projections formed on the contact surface of the warp prevention rail with respect to the rail guide, extending in the direction of extension of the warp prevention rail .
The anti-warping device according to claim 6, wherein the chain guide is formed of resin.