Patent Publication Number: US-2021180867-A1

Title: Reflow furnace

Description:
RELATED APPLICATIONS 
     The present application claims the benefit of Chinese Patent Application No. 201911274713.6, filed Dec. 12, 2019, entitled “REFLOW FURNACE.” The entirety of Chinese Patent Application No. 201911274713.6 is expressly incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to the field of soldering, and in particular, to a reflow oven. 
     BACKGROUND 
     Reflow ovens are configured to solder elements on circuit boards to the circuit boards. Specifically, the reflow oven has a heating zone and a cooling zone. The heating zone is configured to heat the circuit board, such that solder paste (such as tin paste) on the circuit board is melted into a liquid state. The cooling zone is configured to solidify the liquid solder paste into a solid state, so that the solder paste is solidified in a selected area on the circuit board to solder an electronic element onto the circuit board. 
     SUMMARY OF THE DISCLOSURE 
     Exemplary embodiments of the present disclosure may solve at least some of the above problems. For example, the present disclosure provides a reflow oven. The reflow oven comprises a heating zone, a cooling zone, a barrier and exhaust zone, a gas exhaust passage, a gas exhaust power device, and a detection device. The heating zone comprises a heating zone inlet and a heating zone outlet. The cooling zone comprises a cooling zone inlet and a cooling zone outlet. The barrier and exhaust zone is located between the heating zone outlet and the cooling zone inlet. An inlet of the gas exhaust passage is communicated with the barrier and exhaust zone. The gas exhaust power device is disposed on the gas exhaust passage. The detection device is disposed on the gas exhaust passage and used for detecting parameters of gas in the gas exhaust passage, wherein the parameters of the gas reflect a blockage condition of the gas exhaust power device. 
     In the reflow oven according to the present disclosure, the reflow oven further comprises a control device. The control device is communicatively connected with the detection device. The detection device is configured to send a detection signal to the control device, and the control device is configured to receive the detection signal sent by the detection device. 
     In the reflow oven according to the present disclosure, the control device is communicatively connected with the gas exhaust power device, and the control device is configured to control the gas exhaust power device to turn on and turn off. 
     In the reflow oven according to the present disclosure, the reflow oven further comprises an audio or visual alarm device. The audio or visual alarm device is communicatively connected with the control device, the control device being configured to control the audio or visual alarm device to send audio or visual information based on the received detection signal sent by the detection device. 
     In the reflow oven according to the present disclosure, the reflow oven further comprises a heating device. The heating device is configured to heat the gas exhaust power device. 
     In the reflow oven according to the present disclosure, the control device is communicatively connected with the heating device, and the control device is configured to control the heating device to turn on and turn off based on a detection signal provided by the detection device. 
     In the reflow oven according to the present disclosure, the heating device comprises an electric heating wire, and the electric heating wire is arranged around the gas exhaust power device. 
     In the reflow oven according to the present disclosure, the detection device comprises a flow detection device for detecting quantity of flow of the gas in the gas exhaust passage. 
     In the reflow oven according to the present disclosure, the detection device comprises a pressure detection device for detecting pressure of the gas in the gas exhaust passage. 
     In the reflow oven according to the present disclosure, the gas exhaust power device comprises a vacuum generator, a fan or a pump. 
     The reflow oven according to the present disclosure can ensure that the gas containing soldering flux is sufficiently drawn out from the barrier and exhaust zone, thereby ensuring the production quality of a circuit board and improving the qualified rate of the circuit board. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of the present disclosure may be better understood by reading the following detailed description with reference to the accompanying drawings. The same reference numerals represent the same components throughout the accompanying drawings, in which: 
         FIG. 1  is a simplified system diagram of a reflow oven according to an embodiment of the present disclosure; 
         FIG. 2  is a simplified schematic diagram of an embodiment of a control device in  FIG. 1 ; 
         FIG. 3  is a schematic flow chart of control over a heating device of the reflow oven shown in  FIG. 1  by the control device; 
         FIG. 4A  is a perspective diagram of a pipe wall of a conventional gas exhaust power device without a heating device; 
         FIG. 4B  is a cross-sectional diagram of the pipe wall of the gas exhaust power device shown in  FIG. 4A  along a section line A-A in  FIG. 4A ; 
         FIG. 5A  is a perspective diagram of a pipe wall of a gas exhaust power device according to the present disclosure with a heating device; 
         FIG. 5B  is a cross-sectional diagram of the pipe wall of the gas exhaust power device shown in  FIG. 5A  along a section line B-B in  FIG. 5A ; and 
         FIG. 6  is a simplified system diagram of a reflow oven according to another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Specific embodiments of the present disclosure are described below with reference to the accompanying drawings which constitute part of this description. In the following accompanying drawings, the same reference numerals are used for the same components, and similar reference numerals are used for similar components. 
       FIG. 1  is a simplified system diagram of a reflow oven  1  according to an embodiment of the present disclosure. As shown in  FIG. 1 , the reflow oven  1  comprises a heating zone  10 , a barrier and exhaust zone  16 , and a cooling zone  18 . The heating zone  10  comprises a heating zone inlet  151  and a heating zone outlet  152 . The barrier and exhaust zone  16  comprises a barrier and exhaust zone inlet  153 , and a barrier and exhaust zone outlet  154 . The cooling zone  18  comprises a cooling zone inlet  155  and a cooling zone outlet  156 . The barrier and exhaust zone  16  is arranged between the heating zone  10  and the cooling zone  18 . More specifically, the barrier and exhaust zone  16  is arranged between the heating zone outlet  152  and the cooling zone inlet  155 . The barrier and exhaust zone inlet  153  is communicated with the heating zone outlet  152 , and the barrier and exhaust zone outlet  154  is communicated with the cooling zone inlet  155 . The barrier and exhaust zone  16  comprises a gas exhaust outlet  159  of the barrier and exhaust zone, which is configured to discharge gas in the reflow oven  1  out of the reflow oven  1 , so as to prevent heat from the heating zone  10  from being transferred to the cooling zone  18 . 
     The reflow oven  1  further comprises a hearth and a conveying component (not shown). The hearth is arranged to transversely pass through the heating zone  10 , the barrier and exhaust zone  16  and the cooling zone  18 , such that the heating zone  10 , the barrier and exhaust zone  16  and the cooling zone  18  are fluidly communicated with one another. The conveying component is arranged in the hearth and also transversely passes through the heating zone  10 , the barrier and exhaust zone  16  and the cooling zone  18 . The conveying component is configured to carry a circuit board, such that the circuit board enters the reflow oven  1  through the heating zone inlet  151 , sequentially passes through the heating zone  10 , the barrier and exhaust zone  16  and the cooling zone  18 , and then leaves from the reflow oven  1  through the cooling zone outlet  156 . 
     Specifically, the heating zone  10  and the cooling zone  18  may each comprise a plurality of sub-zones. In the embodiment shown in  FIG. 1 , the heating zone  10  comprises ten sub-zones. The ten sub-zones comprise colder zones  12  and hotter zones  14 . The hotter zones  14  have higher temperatures than the colder zones  12 . The colder zones  12  comprise two preheating zones  17 . The hotter zones  14  comprise four uniform temperature zones  13  and four peak zones  15 . The preheating zones  17 , the uniform temperature zones  13  and the peak zones  15  are arranged adjacent to one another. The heating zone  10  is configured to provide to the circuit board a temperature higher than the room temperature. The cooling zone  18  comprises four cooling sub-zones  11 . The cooling zone  18  is configured to provide to the circuit board a temperature lower than that of the heating zone  10 . 
     After the circuit board enters the reflow oven  1  through the heating zone inlet  151 , the circuit board can be gradually heated in the preheating zones  17  and the uniform temperature zones  13 . At least a part of soldering flux in solder paste on the circuit board will vaporize. In the peak zones  15 , the circuit board continues to be heated and the solder paste is melted. Next, the circuit board passes through the barrier and exhaust zone  16 . In the barrier and exhaust zone  16 , high-temperature gas escaping from the heating zone outlet  152  is discharged through the gas exhaust outlet  159  of the barrier and exhaust zone, such that the cooling zone  18  can be kept at a lower temperature without being affected by the high-temperature gas escaping from the heating zone outlet  152 . After passing through the barrier and exhaust zone  16 , the circuit board is transported into the cooling zone  18 . In the four cooling sub-zones  11 , the solder paste is cooled and solidified on a soldering area of the circuit board, thereby connecting an electronic element to the circuit board. 
     The reflow oven  1  further comprises a gas exhaust passage  115  and a gas exhaust power device  102 . The gas exhaust passage  115  comprises a gas exhaust passage inlet  161  and a gas exhaust passage outlet  162 . The gas exhaust passage inlet  161  is connected to the gas exhaust outlet  159  of the barrier and exhaust zone, thereby communicating the gas exhaust passage  115  with the barrier and exhaust zone  16 . The gas exhaust power device  102  is arranged on the gas exhaust passage  115  and is configured to provide power for drawing gas out of the barrier and exhaust zone  16 . As an example, the gas exhaust power device  102  may be a vacuum generator, a pump or a fan. 
     More specifically, the gas exhaust passage  115  comprises a first gas exhaust passage  171  and a second gas exhaust passage  172 . An inlet of the first gas exhaust passage  171  is the gas exhaust passage inlet  161  of the gas exhaust passage  115 , and is connected to the gas exhaust outlet  159  of the barrier and exhaust zone. An outlet of the first gas exhaust passage  171  is connected to an inlet of the gas exhaust power device  102 . An inlet of the second gas exhaust power device  172  is connected to an outlet of the gas exhaust power device  102 . An outlet of the second gas exhaust passage  172  is the gas exhaust passage outlet  162  of the gas exhaust passage  115 . 
     The reflow oven  1  further comprises a control device  120 . The control device  120  is communicatively connected with the gas exhaust power device  102 . The control device  120  can control the gas exhaust power device  102  to turn on and turn off 
     The reflow oven  1  further comprises a detection device  111 . The detection device  111  is disposed on the gas exhaust passage  115  and is used for detecting parameters of gas in the gas exhaust passage  115 , wherein the parameters of the gas can reflect a blockage condition of the gas exhaust power device  102 . In the embodiment of the present disclosure, the detection device  111  is disposed on the first gas exhaust passage  171 . The detection device  111  is a differential pressure detection device for detecting a difference between a pressure of the gas in the gas exhaust passage  115  and an atmospheric pressure at the location where the differential pressure detection device is located. The control device  120  is communicatively connected with the detection device  111 . The detection device  111  can provide a detection signal to the control device  120 . The control device  120  is configured to receive the detection signal sent by the detection device  111 . 
     The reflow oven  1  further comprises a heating device  132 . The heating device  132  is arranged to heat the gas exhaust power device  102 . The control device  120  is communicatively connected with the heating device  132 . The control device  120  can receive the detection signal provided by the detection device  111  and control the heating device  132  to turn on and turn off according to the detection signal. As an example, the heating device  132  may comprise an electric heating wire  133 , which is arranged around the gas exhaust power device  102 . When the electric heating wire  133  is energized, electric energy can be converted into thermal energy, thereby heating the gas exhaust power device  102  and the gas flowing through the gas exhaust power device  102 . 
     Through long-term observation, the inventor found that after the reflow oven runs for a long period of time, a residue is present on the soldered circuit board output from the cooling zone outlet. After analysis, the inventor found that the residue is liquid soldering flux or solid rosin in the soldering flux. The existence of such a residue will degrade the quality of the circuit board. After the reflow oven runs for a longer period of time, the amount of this residue will increase, and even reduce the qualified rate of the circuit board. According to the analysis of the overall operation of the reflow oven, the inventor found that this residue also exists on an inner side of a wall of the hearth in the cooling zone (i.e., on an inner side of a hearth housing), and most thereof exists on the inner side of the wall of the hearth in the cooling zone close to the barrier and exhaust zone. A large amount of accumulated residue will drip onto the circuit board, resulting in that the residue is also present on the circuit board. Through further analysis, the inventor believes that this situation is caused by the blockage of the gas exhaust power device. Specifically, the temperature in the heating zone is relatively high, generally reaching 280° C. As the first gas exhaust passage is fluidly communicated with the barrier and exhaust zone, the first gas exhaust passage is generally wrapped with a heat insulation material. However, the gas exhaust power device is often exposed to ambient air. A difference between the temperature of the ambient air and the temperature in the heating zone may reach 100° C. When the soldering flux gas comes into contact with the gas exhaust power device after being drawn out of the hearth, the soldering flux gas will be condensed into soldering flux solids and adhered to an inner wall of the gas exhaust power device due to the rapid temperature drop. With the accumulation of time, the flow area of the gas exhaust power device will decrease due to the adhesion of the soldering flux solids. This affects the gas exhaust effect of the barrier and exhaust zone, so that the soldering flux gas, that is generated in the heating zone and is unable to be sufficiently drawn out of the gas exhaust power device, enters the cooling zone and preferentially enters the cooling zone near the heating zone. After the temperature of the soldering flux gas gradually decreases in the cooling zone, the soldering flux gas is solidified into solids adhered to the wall of the cooling zone, and is partially condensed on the circuit board when passing through the cooling zone, thereby reducing the processing quality of the circuit board. 
     The heating device  132  in the reflow oven  1  of the present disclosure can heat the gas exhaust power device  102 , such that the soldering flux solid solidified inside the gas exhaust power device  102  is heated up again to become gas. When the heating device  132  is turned on, the gas exhaust power device  102  is also kept on, so that the soldering flux gas is discharged from the gas exhaust power device  102 . The gas exhaust power device  102  in the reflow oven  1  of the present disclosure can sufficiently draw the soldering flux gas out of the hearth, effectively preventing the soldering flux gas from condensing into the soldering flux solid and preventing the soldering flux gas from entering the cooling zone  18 , thereby ensuring the production quality of the circuit board and significantly improving the qualified rate of the circuit board. 
       FIG. 2  is a simplified schematic diagram of an embodiment of the control device  120  in  FIG. 1 . As shown in  FIG. 2 , the control device  120  comprises a bus  202 , a processor  204 , an input interface  206 , an output interface  208 , and a memory  214  having control programs  216 . Each component in the control device  120 , including the processor  204 , the input interface  206 , the output interface  208  and the memory  214 , is communicatively connected with the bus  202 , such that the processor  204  can control the operation of the input interface  206 , the output interface  208  and the memory  214 . Specifically, the memory  214  is configured to store programs, instructions and data, while the processor  204  reads programs, instructions and data from the memory  214  and can write data to the memory  214 . 
     The input interface  206  receives external signals and data, comprising the detection signal and data sent from the detection device  111 , through a connection line  218 . The output interface  208  sends control signals to the outside through a connection line  222 , including sending on-off control signals to the heating device  132  and the gas exhaust power device  102 . The memory  214  of the control device  120  stores data such as control programs and preset target setting values. Various parameters may be preset in production and manufacturing engineering, or may be set by manual input or data import when in use. 
       FIG. 3  is a schematic flow chart of control over the heating device  132  of the reflow oven  1  shown in  FIG. 1  by the control device  120 . A program of the flow chart shown in  FIG. 3  is stored in the memory  214  of the control device  120 . This control process can control the heating device  132  to turn on and turn off according to the detection signal sent by the detection device  111 . 
     As shown in  FIG. 3 , in step  301 , the processor  204  detects whether the gas exhaust power device  102  is operating. In other words, the processor  204  detects whether the gas exhaust power device  102  has been started. If the gas exhaust power device  102  is currently not in operation, the processor  204  switches the operation to step  301 . If the gas exhaust power device  102  is currently in operation, the processor  204  switches the operation to step  303 . 
     In step  303 , the processor  204  obtains a current differential pressure value from the detection device  111 . The processor  204  then switches the operation to step  304 . 
     In step  304 , the processor  204  determines whether the current differential pressure value is lower than a first set differential pressure value. If the current differential pressure value is not lower than the first set differential pressure value (that is, when the current differential pressure value is higher than or equal to the first set differential pressure value), the processor  204  switches the operation to step  303 . If the current differential pressure value is lower than the first set differential pressure value, the processor  204  switches the operation to step  306 . 
     In step  306 , the processor  204  turns on the heating device  132 . The processor  204  then switches the operation to step  308 . 
     In step  308 , the processor  204  obtains a current differential pressure value from the detection device  111 . The processor  204  then switches the operation to step  310 . 
     In step  310 , the processor  204  determines whether the current differential pressure value is higher than a second set differential pressure value. If the current differential pressure value is not higher than the second set differential pressure value (that is, when the current differential pressure value is lower than or equal to the second set differential pressure value), the processor  204  switches the operation to step  309 . If the current differential pressure value is higher than the second set differential pressure value, the processor  204  switches the operation to step  312 . 
     In step  312 , the processor  204  turns off the heating device  132 . The processor  204  then ends the control process. 
     It should be noted that, in the embodiment shown in  FIG. 3 , the gas exhaust power device  102  is operating while the heating device  132  is operating, because generally, when the gas exhaust power device  102  is operating, the soldering flux gas flows through the gas exhaust power device  102  and is solidified on the gas exhaust power device  102 . However, those skilled in the art can understand that the heating device  132  may also be turned on when the gas exhaust power device  102  is not operating, so as to remove the soldering flux solids adhered to the gas exhaust power device  102 . 
     As an example, the first set differential pressure value may be 80 Pa and the second set pressure value may be 180 Pa. When the current differential pressure value is lower than the first set differential pressure value of 80 Pa, it indicates that the gas exhaust power device  102  cannot provide an enough drawing capacity, and in this case, it is necessary to turn on the heating device  132  to heat the soldering flux solids in the gas exhaust power device  102  and turn the solids into soldering flux gas. As the soldering flux solids are heated to become soldering flux gas, the soldering flux solids adhered to the gas exhaust power device  102  gradually decrease, the gas flow area of the gas exhaust power device  102  increases, and the current differential pressure value also increases. When the current differential pressure value is higher than the second set pressure value of 180 Pa, it indicates that the gas exhaust power device  102  can provide at least a drawing capacity of 180 Pa, and in this case, the gas exhaust power device  102  can provide an enough drawing capacity, and the heating device  132  can be turned off. 
     It should be noted that although 80 Pa is set as the first set differential pressure value and 180 Pa is set as the second set pressure value in the present disclosure, those skilled in the art can understand that the first set differential pressure value and the second set pressure value may be specifically set according to a working condition of the reflow oven  1 . In addition, the magnitude of the first set differential pressure value may be different from that of the second set pressure value, or may be equal to that of the second set pressure value (i.e., the first set differential pressure value is equal to the second set pressure value). 
     It should also be noted that although the detection device  111  in the embodiment of the present disclosure is a differential pressure detection device (e.g., a differential pressure sensor), those skilled in the art can understand that the detection device  111  may also be a pressure detection device (e.g., a pressure sensor) for detecting pressure of gas in the gas exhaust passage  115 . Those skilled in the art can also understand that the detection device  111  may also be a flow detection device (e.g., a flow sensor) for detecting quantity of flow of the gas in the gas exhaust passage  115 . The blockage in the gas exhaust power device  102  is determined according to the flow value of the gas in the gas exhaust passage  115 , such that a first set flow value and a second set flow value (the first set flow value may be equal to the second set flow value) are set to control the heating device  132  to turn on and turn off.  FIG. 4A  is a perspective diagram of a pipe wall of a conventional gas exhaust power device without a heating device; and  FIG. 4B  is a cross-sectional diagram of the pipe wall of the gas exhaust power device shown in  FIG. 4A  along a section line A-A in  FIG. 4A . Dotted shadows indicate soldering flux solids adhered to the wall. It can be seen from  FIGS. 4A and 4B  that the flow area of the gas exhaust power device will be reduced by nearly 70%. This will greatly reduce the speed at which the soldering flux gas is discharged from the hearth and reduce the qualified rate of the circuit board. 
       FIG. 5A  is a perspective diagram of a pipe wall of a gas exhaust power device according to the present disclosure with a heating device; and  FIG. 5B  is a cross-sectional diagram of the pipe wall of the gas exhaust power device shown in  FIG. 5A  along a section line B-B in  FIG. 5A . Dotted shadows indicate soldering flux solids adhered to the wall. It can be seen from  FIGS. 5A and 5B  that almost no soldering flux solid is adhered to the wall of the gas exhaust power device. This can ensure that the actual flow area of the gas exhaust power device is consistent with a designed flow area thereof, thereby ensuring the speed at which the soldering flux gas is discharged from the hearth and greatly improving the qualified rate of the circuit board. 
       FIG. 6  is a simplified system diagram of a reflow oven  6  according to another embodiment of the present disclosure. The same parts of the reflow oven  6  of  FIG. 6  as those of the reflow oven  1  of  FIG. 1  will not be repeated herein. This reflow oven differs from the reflow oven  1  of  FIG. 1  in that the reflow oven  6  of  FIG. 6  comprises an audio or visual alarm device  611 , but does not comprise a heating device for heating the gas exhaust power device  102 . The audio or visual alarm device  611  is communicatively connected with the control device  120 . The control device  120  is configured to control the audio or visual alarm device  611  to send audio or visual information based on the received detection signal sent by the detection device  111 . Specifically, when the control device  120  receives gas parameters from the detection device  111  and determines that the gas parameters reflect that the gas exhaust power device  102  is blocked, the control device  120  will send a signal to the audio or visual alarm device  611 . The audio or visual alarm device  611  can send audio or visual information to alarm an operator. As an example, the audio or visual alarm device  611  comprises a tweeting device, a warning device, or a display device. When the operator is aware of the alarm from the audio or visual alarm device  611 , the gas exhaust power device  102  may be removed and replaced with a new gas exhaust power device, thereby ensuring the actual flow area of the gas exhaust power device, ensuring the speed at which the soldering flux gas is discharged from the hearth and greatly improving the qualified rate of the circuit board. 
     Although only some features of the present disclosure are illustrated and described herein, a person skilled in the art may make various improvements and changes. Therefore, it should be understood that the appended claims intend to cover all the foregoing improvements and changes that fall within the substantial spirit and scope of the present disclosure.