SMD packaging mos device reflow soldering anti-tin ball process method

Abstract

The application relates to a SMD packaging MOS tube device reflow soldering anti-tin bead process method, and belongs to the reflow soldering field of electronic assembly. In view of the technical problem that tin beads are generated at the bottom of a SMD packaging MOS tube device after reflow soldering in the prior art, the application provides a SMD packaging MOS tube device reflow soldering anti-tin bead process method. The generation of tin beads in the reflow soldering of the MOS tube device is reduced by designing a tinning tool, a tinned steel mesh and a reflow soldering steel mesh. The tinning tool and the tinned steel mesh are used to tin the surface of the welding end of the MOS tube device, then the reflow soldering steel mesh for preventing tin beads is designed for reflow soldering, tin paste printing of the pads on the printed board is completed through the reflow soldering steel mesh, MOS tube device mounting and reflow soldering are carried out, and reliable high-quality welding points are formed after the reflow soldering. Through the process method, the number of tin beads at the bottom of the MOS tube device after welding is greatly reduced. It is verified that the number of tin beads is reduced by 60% compared with the ordinary reflow soldering mode.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of reflow soldering of electronic assembly, and particularly relates to a reflow soldering tin bead prevention process method for SMD packaged MOS tube devices. BACKGROUND

[0002] With the increasing demand for the reliability of printed board assembly solder joints of electronic products, after reflow soldering of components, the bottom of the components is not allowed to have tin beads and other excess materials.

[0003] At present, in electronic products, ignition control products often use SMD packaged (surface mount package) MOS tube devices to control the ignition path switch, stabilize the voltage and protect the front circuit. Such products have common design features. In order to meet the functional requirements of ignition control, SMD packaged MOS tube devices are often used in design. In order to meet the requirements of miniaturization design, SMD-0.5 packaged MOS tubes are often selected in electrical design to achieve the use requirements of large current and high reliability and long service life. After SMD packaged MOS tubes are printed with tin paste and reflow soldered, good solder joints are formed. However, after the reflow soldering of such devices, tin beads are prone to appear in the T-shaped groove area at the bottom of the device. The free tin beads need to be cleaned after reflow soldering because they violate the minimum electrical clearance. The existence of tin beads at the bottom of the device is prone to cause short circuit of components or circuit connection, or cause breakdown of components under power-on. The tin bead problem is a key problem at present.

[0004] The tin beads at the bottom of the MOS tube device need to be observed by means of X-RAY equipment. The cleaning process of the tin beads needs to be repeated multiple times and observed by X-RAY, which consumes a lot of manpower and material resources. In addition, some small tin beads cannot be removed after multiple cleanings, which may cause potential quality risks. For example, the width of the T-shaped groove of some SMD packaged MOS tube devices is only 0.6 mm. According to the requirements of electrical safety clearance or product performance, the size of the tin bead should be no more than 0.06 mm or no free tin bead should exist. The cleaning process of the tin bead consumes a lot of manpower and material resources. In addition, during the reflow soldering process, some small tin beads are difficult to be completely removed by conventional cleaning methods due to their small size and hidden position. These small tin beads may have a potential impact on the electrical performance and reliability of the MOS tube device, thereby increasing the quality risk of the product and possibly leading to an increase in the failure rate of the end product. At present, the tin bead problem at the bottom of such devices is only improved by printing a steel mesh to prevent tin beads, adjusting the reflow curve, or investing more manpower and material resources in the cleaning process. The probability of tin bead generation at the bottom of the MOS tube device is still high, and the problem cannot be effectively solved. SUMMARY

[0005] The technical problem to be solved is:

[0006] In order to avoid the deficiencies of the prior art, the present application provides a SMD packaging MOS tube device reflow soldering tin bead prevention process method to solve the technical problem of tin bead excess at the bottom after SMD packaging MOS tube device reflow soldering in the prior art.

[0007] The technical scheme of the present application is: a SMD packaging MOS tube device reflow soldering tin bead prevention process method, comprising the following steps:

[0008] Step 1, design a tinning tool, and install MOS tube devices on the tinning tool;

[0009] According to the size of the body and the soldering end of the MOS tube device to be packaged, a SMD packaging component surface soldering end tinning tool is made; the tinning tool is provided with a plurality of MOS tube device placing grooves, one MOS tube device is placed in each placing groove, the soldering end face of the MOS tube device faces away from the bottom surface of the placing groove and is coplanar with the upper surface of the tinning tool;

[0010] Step 2, design a tinning steel mesh, and tin the soldering end of the MOS tube device;

[0011] The tinning steel mesh is provided with a plurality of groups of tinning mesh holes corresponding to the MOS tube device placing grooves of the tinning tool, which are used for printing tin paste on the soldering ends of the plurality of MOS tube devices installed on the tinning tool; each group of tinning mesh holes is three holes, corresponding to the three soldering ends of the MOS tube device, and respectively located at the central positions of the three soldering ends, and the opening area of each group of mesh holes is not greater than 75% of the soldering end area of the MOS tube device;

[0012] The tinning steel mesh is installed on the tinning tool provided with the MOS tube devices, each group of tinning mesh holes is ensured to correspond to each soldering end of the MOS tube device, tin paste is coated on the printing steel mesh, and a printing machine is used to print the tin paste to the soldering end of the MOS tube device;

[0013] Step 3, solidify after tinning the soldering end of the MOS tube device;

[0014] The tinning steel mesh is removed, the MOS tube device after printing tin paste is taken out together with the tinning tool, and tinning solidification is performed through a reflow furnace; the peak temperature of the tinning reflow furnace is at least 12℃ higher than the melting point of the tin paste, and the highest temperature cannot damage the performance of the MOS tube device;

[0015] Step 4, clean after solidifying the tinning soldering end of the MOS tube device to remove the residual flux after solidification of the tin paste;

[0016] Step 5, design a reflow soldering steel mesh, and print tin paste on the MOS tube pad of the printed board;

[0017] The reflow soldering steel net is provided with a plurality of groups of mesh holes corresponding to the MOS tube pads on the printed board, which are used for printing tin paste on the MOS tube pads of the printed board; each group of mesh holes is three holes, which correspond to the three pads of each group of MOS tubes on the printed board one by one, and the opening area of each group of mesh holes is 25% of the area of each group of MOS tube pads on the printed board;

[0018] Step 6, mounting MOS tube devices, and performing reflow soldering operation;

[0019] After the MOS tube devices cleaned in step 4 are mounted on the MOS tube pads of the printed board, the printed board with the mounted MOS tube devices is placed into a reflow furnace to perform reflow soldering, the tin paste is melted to form a welding point, and the welding end of the MOS tube device is welded with the MOS tube pad of the printed board.

[0020] Step 7, cleaning operation of the circuit board;

[0021] After the welding in step 6 is completed, the welding point is cleaned, and the cleaned circuit board is placed into an anti-static tray to be naturally dried.

[0022] A further technical solution of the present application is that the tinning tool body is plate-shaped, the two ends are provided with process edges, and the middle is provided with a device tray matching groove; the device tray matching groove is a rectangular annular groove matched with the circumferential edge of the MOS tube device tray, a plurality of MOS tube device placing grooves are uniformly distributed in the blocking area of the device tray matching groove, the position, spacing and number of the MOS tube device placing grooves are matched with the MOS tube device tray, and the MOS tube device placing grooves are used for placing the whole tray of MOS tube devices into the MOS tube device placing grooves of the tinning tool by docking the MOS tube device tray with the device tray matching groove; the two ends of the tinning tool are provided with four MARK points for positioning.

[0023] A further technical solution of the present application is that the depth of the MOS tube device placing groove is the same as the thickness of the MOS tube device, the length and width of the MOS tube device placing groove are both greater than the length and width of the MOS tube device by 0.1 mm, which is used for preventing the MOS tube device from being stuck.

[0024] A further technical solution of the present application is that the cleaning method in step 4 is that the MOS tube device is placed into an anti-static box containing anhydrous ethanol, the liquid surface of the anhydrous ethanol is higher than the welding end surface of the MOS tube device, the welding end of the MOS tube device is brushed with anhydrous ethanol after soaking for 5 min to clean the remaining flux after the tin paste of the welding end of the MOS tube device is solidified.

[0025] The further technical scheme of the present application is that the group of tinned steel meshes comprises a rectangular large soldering end mesh and two circular small soldering end meshes, the large soldering end mesh corresponds to the large soldering end of the MOS tube device, and the two small soldering end meshes correspond to the two small soldering ends of the MOS tube device respectively; the area ratio of the large soldering end mesh to the large soldering end of the MOS tube device is 3:4; and the area ratio of the small soldering end mesh to the small soldering end of the MOS tube device is 1:2.

[0026] The further technical scheme of the present application is that the group of tinned steel meshes comprises a rectangular large soldering end mesh and two circular small soldering end meshes, the large soldering end mesh corresponds to the large soldering end of the MOS tube device, and the two small soldering end meshes correspond to the two small soldering ends of the MOS tube device respectively; the area ratio of the large soldering end mesh to the large soldering end of the MOS tube device is 3:4; and the area ratio of the small soldering end mesh to the small soldering end of the MOS tube device is 1:2.

[0027] The further technical scheme of the present application is that the circuit board cleaning operation of step 7 is specifically that the circuit board is placed flat in a tray, anhydrous ethanol is poured, the soldering points of the circuit board components are covered, and after soaking for 15-20 min, the soldering points of the circuit board A and B are brushed with an anti-static brush; the cleaned circuit board is placed in an anti-static tray and naturally dried.

[0028] The further technical scheme of the present application is that the circuit board cleaning operation of step 7 is specifically that the circuit board is placed flat in a tray, anhydrous ethanol is poured, the soldering points of the circuit board components are covered, and after soaking for 15-20 min, the soldering points of the circuit board A and B are brushed with an anti-static brush; the cleaned circuit board is placed in an anti-static tray and naturally dried.

[0029] Beneficial effects

[0030] The application has the advantages that the SMD packaging MOS tube device reflow soldering tin bead prevention process method of the application reduces the generation of tin beads in the reflow soldering of the MOS tube device by designing a tinning tool, a tinning steel mesh and a reflow soldering steel mesh. The application uses the tinning tool and the tinning steel mesh, sets reasonable reflow furnace parameters, the peak temperature of the tinning reflow furnace is at least 12 DEG C higher than the melting point of the tin paste, the maximum temperature cannot damage the performance of the MOS tube device, the MOS tube device is solidified in the tinning reflow furnace, and a layer of tin is plated on the surface of the welding end of the MOS tube device. Then, the reflow soldering tin bead prevention reflow soldering steel mesh is designed and manufactured, the tin paste printing of the pads on the printed circuit board is completed through the reflow soldering steel mesh, the MOS tube device is attached and reflow soldered, and reliable high-quality welding points are formed after reflow soldering. Through the process method, the number of tin beads at the bottom of the welded MOS tube device is greatly reduced. It is verified that the number of tin beads is reduced by 60% compared with the ordinary reflow soldering mode.

[0031] The process method has the advantages of adaptability to mass production and good consistency. The process method has good compatibility, and the tinning tool and the tinning steel mesh matched with the MOS tube device can be manufactured according to the size of the MOS tube device. In practice, the process method can be applied to the reflow soldering process of MOS tube devices of different sizes, and the tinning tool, the tinning steel mesh and the reflow soldering steel mesh can be designed according to the size of the MOS tube device and the welding end. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 It is a tinning tool structure diagram of the SDM-0.5 packaging MOS tube device in the embodiment of the application.

[0033] Figure 2 It is a tinning tool structure diagram of the SDM-0.5 packaging MOS tube device in the embodiment of the application.

[0034] Figure 3 It is an assembly diagram of the SDM-0.5 packaging MOS tube device in the embodiment of the application.

[0035] Figure 4 It is a tinning steel mesh structure diagram of the SDM-0.5 packaging MOS tube device in the embodiment of the application.

[0036] Figure 5 It is a tinning steel mesh structure diagram of the SDM-0.5 packaging MOS tube device in the embodiment of the application.

[0037] Figure 6 It is a mesh hole diagram of the tinning steel mesh of the SDM-0.5 packaging MOS tube device in the embodiment of the application.

[0038] Figure 7 It is an assembly diagram of the tinning steel mesh and the tinning tool in the embodiment of the application.

[0039] Figure 8 Fig. 1 is a schematic diagram of a steel mesh structure for reflow soldering of a printed board of an SMD-0.5 packaged MOS device according to an embodiment of the present application;

[0040] Figure 9 Fig. 2 is a schematic diagram of a three-dimensional structure of a steel mesh for reflow soldering of a printed board of an SMD-0.5 packaged MOS device according to an embodiment of the present application;

[0041] Figure 10 Fig. 3 is a schematic diagram of a group of mesh hole structures of a steel mesh for reflow soldering of a printed board of an SMD-0.5 packaged MOS device according to an embodiment of the present application;

[0042] Figure 11 Fig. 4 is a schematic diagram of an outline size of an SMD packaged MOS device.

[0043] Fig. 1 is a schematic diagram of a steel mesh structure for reflow soldering of a printed board of an SMD-0.5 packaged MOS device according to an embodiment of the present application; DETAILED DESCRIPTION

[0044] The embodiments described below are exemplary and are intended to explain the present application, and should not be understood as limiting the present application.

[0045] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0046] The embodiment provides a SMD packaging MOS tube device reflow soldering tin bead prevention process method, and mainly solves the problem of tin bead at the bottom of a device in existing SMD packaging MOS tube device reflow soldering, which affects product quality. The application is characterized in that a tinning tool matched with the MOS tube device body and the welding end and a tinning steel mesh are designed, a certain thickness of tin is plated on the surface of the welding end of the MOS tube device through a reflow furnace, the flux on the surface of the MOS tube device after tinning is cleaned, then the reflow soldering steel mesh for preventing tin bead is designed according to the printed board pad of the MOS tube device, and the welding end of the MOS tube device after tinning is reflow soldered with the corresponding pad of the printed board. Compared with the ordinary reflow soldering mode, the number of tin beads at the bottom of the MOS tube device after welding is reduced by 60%, the method can be applied to SMD packaging MOS tube devices of different sizes, and is suitable for mass production.

[0047] The embodiment takes SMD-0.5 packaging MOS tube devices as an example to introduce the SMD packaging MOS tube device reflow soldering tin bead prevention process method. Referring to Figure 11 , the MOS tube device 2 is a hexahedral structure, and has three welding ends including one large welding end 21 and two small welding ends 22 at the bottom. The three welding ends of the MOS tube device need to be welded with the MOS tube device pads on the printed board, and a T-shaped groove 23 is formed between the three welding ends. By using the traditional process method, there are many tin beads in the T-shaped groove 23 at the bottom of the device after reflow soldering, which is difficult to clean and affects the product quality.

[0048] The SMD packaging MOS tube device reflow soldering tin bead prevention process method comprises the following steps.

[0049] Step 1, a tinning tool 1 is designed, and the MOS tube device 2 is installed on the tinning tool 1.

[0050] Referring to Figures 1-3 , the tinning tool 1 for the surface welding end of the SMD packaging component device is made according to the welding end size of the MOS tube device to be packaged. The main body of the tinning tool 1 is plate-shaped, and process edges 12 are arranged at both ends of the main body for placing the tinning tool 1 on the track of the reflow soldering equipment, and a device tray matching groove 13 is arranged in the middle. The device tray matching groove 13 is a rectangular annular groove matched with the edge of the MOS tube device tray. A plurality of MOS tube device placing grooves 11 are uniformly distributed in the blocking area of the device tray matching groove 13, and each placing groove 11 corresponds to one MOS tube device 2. The position, spacing and number of the MOS tube device placing grooves 11 are matched with the MOS tube device tray, so that the MOS tube devices 2 of the entire device tray can be flipped into the MOS tube device placing grooves 11 of the tinning tool 1 at one time when the MOS tube devices are installed on the tinning tool 1, and the installation efficiency is improved.

[0051] The depth of the MOS tube device placement groove 11 is the same as the thickness of the MOS tube device 2. When placed, the solder end of the MOS tube device 2 faces upwards, away from the placement groove, and its solder end is coplanar with the upper surface of the tinning tool, facilitating subsequent tinning of the tinned steel mesh covering the device solder end.

[0052] In this embodiment, taking SMD-0.5 devices as an example, the structure of the tinning tool is designed as a tool main body with a length of 176 mm and a width of 140 mm; a process edge with a width of 5 mm and a thickness of 1.5 mm; device tray matching grooves with adjacent groove widths of 5 mm and 5.5 mm; MOS tube device placement grooves 11 with a length of 7.6 mm and a width of 10.4 mm.

[0053] Step 2, design a tinning steel mesh 3 to tin the solder end of the MOS tube device 2.

[0054] Referring to Figures 4-6 The tinning steel mesh 3 is provided with a plurality of groups of tinning mesh holes corresponding to the placement grooves 11 on the tinning tool 1, which are used to print solder paste on the solder end of the plurality of MOS tube devices 2 installed on the tinning tool 1. Each group of tinning mesh holes is three holes, each group of tinning mesh holes corresponds to the three solder ends of the MOS tube device 2, and is respectively located at the central position of the three solder ends, and the opening area of each group of mesh holes is not greater than 75% of the solder end area of the MOS tube device 2. Specifically, one group of tinning mesh holes of the tinning steel mesh 3 includes a rectangular large solder end mesh hole 31 and two circular small solder end mesh holes 32, the large solder end mesh hole 31 corresponds to the large solder end 21 of the MOS tube device 2, and the two small solder end mesh holes 32 correspond to the two small solder ends 22 of the MOS tube device 2 respectively; the area ratio of the large solder end mesh hole 31 to the large solder end 21 of the MOS tube device is 3:4, and the mesh hole area ratio of the small solder end mesh hole 32 to the small solder end 22 of the MOS tube device is 1:2. By setting the opening position of the tinning steel mesh 3 in the solder end of the MOS tube device 2 and at the central position, it is ensured that the solder paste is located on the solder end of the device after printing, and will not stick to the device body or the T-shaped groove.

[0055] In order to match the solder end of the tinning tool 1 and the MOS tube device 2, the tinning steel mesh 3 is provided with mark points 33 matching the mark points of the tinning tool 1. In this embodiment, the thickness of the tinning steel mesh is designed to be 0.18 mm.

[0056] Referring to Figure 7 Install the tinning steel mesh 3 on the tinning tool 1 loaded with the MOS tube device 2, ensure that each group of tinning mesh holes corresponds to the solder end of each MOS tube device 2, apply solder paste to the printing steel mesh, and use a printer to print the solder paste, which will be printed on the solder end of the MOS tube device 2 through the openings of the tinning steel mesh 3.

[0057] Step 3, tin soldering and solidification of the MOS tube device soldering end after tin plating.

[0058] Remove the tin-plated steel mesh 3, and put the MOS tube device 2 printed with solder paste and the tin-plating tool 1 into the reflow furnace for tin soldering and solidification. High temperature makes the solder paste evenly spread on the soldering end surface of the MOS tube device 2, and the tin soldering process ends. The reflow furnace temperature curve is set according to the standard QJ3173-2003 and the recommended curve of the solder paste, and the temperature of the reflow zone needs to be higher than the melting point of the solder paste, and the peak temperature of the tin soldering reflow furnace is at least 12℃ higher than the melting point of the solder paste to ensure that the solder paste can melt, and the highest temperature cannot damage the performance of the MOS tube device.

[0059] Step 4, clean the MOS tube device 2 after tin soldering and solidification to remove the residual flux after the solder paste solidification.

[0060] Put the MOS tube device 2 into the anti-static box containing anhydrous ethanol, and the liquid level of the anhydrous ethanol is higher than the soldering end surface of the MOS tube device 2. After soaking for 5 minutes, use a soft brush to dip anhydrous ethanol to clean the residual flux on the soldering end of the MOS tube device 2 after the solder paste solidification.

[0061] Step 5, design the reflow soldering steel mesh 4 to print the solder paste on the MOS tube pad of the printed board.

[0062] Referring to Figures 8-10 , the reflow soldering steel mesh 4 is provided with a plurality of groups of mesh holes corresponding to the MOS tube pads on the printed board one by one, and the MOS tube pads on the printed board correspond to the soldering end of the MOS tube device 2. The reflow soldering steel mesh 4 is used to print the solder paste on the MOS tube pad of the printed board. Each group of mesh holes of the reflow soldering steel mesh 4 is three holes, which correspond to the three pads of each group of MOS tubes on the printed board one by one, and the opening area of each group of mesh holes is 25% of the area of each group of MOS tube pads on the printed board. Specifically, referring to Figure 10 , one group of mesh holes of the reflow soldering steel mesh 4 includes a large pad mesh hole 41 and two symmetrical small pad mesh holes 42. The large pad mesh hole 41 is rectangular, and its length is the same as the length of the large pad 6 on the printed board, and its width L3 is 1 / 4 of the width D3 of the large pad 6 on the printed board. The large pad mesh hole 41 is located at the end of the large pad 6 away from the small pad 5. The small pad mesh hole 42 is square, and its length L2 is 1 / 2 of the length D2 of the small pad on the printed board, and its width L1 is 1 / 2 of the width D1 of the small pad on the printed board. The small pad mesh hole 42 is located at the outer corner position of the small pad 5 away from the large pad 6. The opening position of the reflow soldering steel mesh 4 is away from the device edge of the T-shaped groove, which can avoid the tin beads formed by the tin paste splashing due to the volatilization of the flux during the reflow soldering process. The thickness of the reflow soldering steel mesh 4 in this embodiment is 0.12mm.

[0063] Solder paste is printed onto the MOS tube pad of the printed board through the reflow soldering steel mesh 4.

[0064] Step 6, mounting the MOS tube device 2, and performing reflow soldering.

[0065] After the MOS tube device is mounted on the MOS tube pad of the printed board after the solder paste is printed in step 5, the printed board with the mounted MOS tube device is placed into a reflow furnace for reflow soldering, the solder paste is melted to form a welding point, and the welding end of the MOS tube device 2 is welded to the MOS tube pad of the printed board.

[0066] Step 7, cleaning the circuit board.

[0067] After the welding in step 6 is completed, the welding point is cleaned, and the cleaned circuit board is placed into an anti-static tray for natural air drying. The specific cleaning process is as follows: the printed board, i.e., the circuit board, after welding is placed flat in the tray, and anhydrous ethanol is poured into the tray to cover the welding points of the components of the circuit board, and then the circuit board is soaked for 15-20 minutes, and then the welding points on the A and B sides of the circuit board are brushed with an anti-static brush. An appropriate amount of anhydrous ethanol is poured into another tray, and the welding points are carefully brushed with an anti-static brush. The cleaned circuit board is placed into an anti-static tray for natural air drying. For the MOS tube device with a T-shaped groove at the bottom, a spray gun filled with anhydrous ethanol is used to flush the T-shaped groove. The flushing air pressure ranges from 0.1 MPa to 0.2 MPa. When the tin beads at the bottom of the MOS tube are not cleaned, the circuit board is soaked in ethanol for 15-20 minutes again, and then the spray gun is used for flushing until the tin beads are cleaned.

[0068] The MOS tube device 2 is observed by X-RAY to confirm the inspection of the tin beads at the bottom of the MOS tube device, and it is ensured that the tin beads are cleaned.

[0069] In this embodiment, the amount of solder paste of the SMD-0.5 packaged MOS tube device surface welding end plated with the tin steel mesh 3 and the amount of solder paste of the printed board reflow soldering steel mesh 4 should meet the welding point reliability. For example, the total amount of solder paste required for the SMD-0.5 packaged device is 100% of the area of the device welding end, and the thickness of the solder paste is 0.15 mm. In this embodiment, the thickness of the tin steel mesh is made to be 0.18 mm, and the thickness of the anti-tin bead steel mesh for reflow soldering is made to be 0.12 mm.

[0070] The MOS tube device packaged by the SMD-0.5 is verified in this embodiment, and the MOS tube device is tested at three temperatures after being plated by using the process method of the present application and setting reasonable reflow soldering parameters. The alloy layer thickness of the welded device welding point is measured and a thrust test is performed, and the test results are all qualified, which can meet the high reliable welding requirements. The number of tin beads at the bottom of the MOS tube device is reduced by 60% compared with the ordinary reflow soldering method.

[0071] It should be noted that in another embodiment, the MOS device with SMD-1 and SMD-2 package can also use the process method of the present application. The difference is only that according to the MOS device body size and solder end matching tinning tool 1, tinning steel mesh 3, and the corresponding reflow solder steel mesh 4 on the MOS device pad on the printed board, different specifications of MOS devices can also exist on a circuit board.

[0072] Although the embodiments of the present application have been shown and described above, it should be understood by those skilled in the art that the above embodiments are exemplary and cannot be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments without departing from the principles and purposes of the present application within the scope of the present application.

Claims

1. A method for preventing solder balls during reflow soldering of SMD packaged MOSFET devices, characterized in that, Includes the following steps: Step 1: Design a tin plating fixture and install MOSFET devices on the tin plating fixture; Based on the body and solder terminal dimensions of the MOS transistor device to be packaged, a tin plating fixture for the solder terminals of the SMD packaged component is fabricated. The tin plating fixture has multiple MOS transistor device placement grooves, with one MOS transistor device placed in each groove. The solder terminal face of the MOS transistor device faces away from the bottom surface of the placement groove and is coplanar with the upper surface of the tin plating fixture. Step 2: Design a tin-plated stencil and tin-plat the solder ends of the MOSFET devices; The tin-plating steel mesh has multiple sets of tin-plating mesh holes that correspond one-to-one with the grooves for placing MOS transistors in the tin-plating fixture. These holes are used to print solder paste onto the solder ends of the multiple MOS transistors mounted in the tin-plating fixture. Each set of tin-plating mesh holes consists of three holes, corresponding one-to-one with the three solder ends of the MOS transistors, and each hole is located in the center of the three solder ends. The opening area of ​​each set of mesh holes is no more than 75% of the solder end area of ​​the MOS transistors. The tin-plated steel mesh comprises a set of tin-plated mesh holes, including rectangular large solder end mesh holes and two circular small solder end mesh holes. The large solder end mesh holes correspond to the large solder ends of the MOSFET device, and the two small solder end mesh holes correspond to the two small solder ends of the MOSFET device, respectively. The ratio of the area of ​​the large solder end mesh hole to the area of ​​the large solder end of the MOSFET device is 3:4; the ratio of the area of ​​the small solder end mesh hole to the area of ​​the small solder end of the MOSFET device is 1:

2. Install the tin-plated stencil onto the tin-plating fixture containing the MOSFET devices, ensuring that each set of tin-plated stencil holes corresponds to the solder terminal of each MOSFET device. Apply solder paste to the stencil and use a printer to print the solder paste onto the solder terminal of the MOSFET device. Step 3: Soldering the solder terminals of the MOSFET device and then curing it; Remove the tin-plating stencil, and then pass the printed solder paste MOSFET device along with the tin-plating fixture through a reflow oven for tin plating and curing. The peak temperature of the reflow oven for tin plating should be at least 12°C higher than the melting point of the solder paste. The maximum temperature should not damage the performance of the MOSFET device. Step 4: After the solder terminals of the MOSFET device are tinned and cured, clean them to remove any residual flux after the solder paste has cured. Step 5: Design the reflow soldering stencil and print solder paste on the MOS transistor pads of the printed circuit board; The reflow soldering stencil has multiple sets of mesh holes that correspond one-to-one with the MOSFET pads on the printed circuit board, used for printing solder paste onto the MOSFET pads on the printed circuit board; each set of mesh holes has three holes, corresponding one-to-one with the three pads of each group of MOSFETs on the printed circuit board, and the opening area of ​​each set of mesh holes is 25% of the area of ​​each group of MOSFET pads on the printed circuit board; The reflow soldering stencil has a set of mesh openings including a large pad mesh and two symmetrical small pad meshes. The large pad mesh is rectangular, with a length the same as the length of the large MOSFET pad on the printed circuit board and a width of 1 / 4 of the width of the large MOSFET pad on the printed circuit board. It is located at the end of the large pad away from the small pad. The small pad mesh is square, with a length of 1 / 2 the length of the small MOSFET pad on the printed circuit board and a width of 1 / 2 the width of the small MOSFET pad on the printed circuit board. The small pad mesh is located at the outer corner of the end of the small pad away from the large pad. Step 6: Mount the MOSFET devices and perform reflow soldering. After cleaning in step 4, the MOSFET device is mounted on the MOSFET pads of the printed circuit board. The printed circuit board with the MOSFET device mounted is placed in a reflow oven for reflow soldering. The solder paste melts to form solder joints, and the solder ends of the MOSFET device are soldered to the MOSFET pads of the printed circuit board. Step 7: Circuit board cleaning. After completing step 6, clean the solder joints and place the cleaned circuit board in an anti-static tray to air dry naturally.

2. The process method according to claim 1, characterized in that, The tin plating fixture is plate-shaped with process edges at both ends and a device tray matching groove in the middle. The device tray matching groove is a rectangular annular groove that matches the perimeter of the MOS transistor device tray. Multiple MOS transistor device placement grooves are evenly distributed within the enclosure area of ​​the device tray matching groove. The position, spacing, and number of MOS transistor device placement grooves match the MOS transistor device tray. This is used to flip the entire tray of MOS transistor devices into the MOS transistor device placement grooves of the tin plating fixture by connecting the MOS transistor device tray to the device tray matching groove. The tin plating fixture has four MARK points at both ends for positioning.

3. The process method according to claim 1, characterized in that, The depth of the groove for placing the MOS transistor is the same as the thickness of the MOS transistor. The length and width of the groove are both 0.1 mm greater than the length and width of the MOS transistor to prevent the MOS transistor from jamming.

4. The process method according to claim 1, characterized in that, The cleaning method in step 4 is as follows: Place the MOS transistor device in an anti-static box containing anhydrous ethanol, ensuring that the anhydrous ethanol level covers the solder end surface of the MOS transistor device. After soaking for 5 minutes, use a soft brush dipped in anhydrous ethanol to brush away the flux residue remaining after the solder paste on the solder end of the MOS transistor device has solidified.

5. The process method according to claim 1, characterized in that, The circuit board cleaning operation in step 7 is as follows: Place the circuit board flat in a tray, pour in anhydrous ethanol to cover the solder joints of the circuit board components, soak for 15-20 minutes, then use an anti-static brush to clean the solder joints on both sides of the circuit board A and B; place the cleaned circuit board in an anti-static tray to air dry naturally.

6. The process method according to claim 1, characterized in that, Another method for cleaning the circuit board in step 7 is as follows: Place the circuit board flat in a tray, pour in anhydrous ethanol to cover the solder joints of the circuit board components, soak for 15-20 minutes, and then use a spray gun filled with anhydrous ethanol to rinse the T-shaped groove. The rinsing pressure range is 0.1MPa-0.2MPa. If the solder beads at the bottom of the MOSFET are not cleaned, repeat the process of soaking the circuit board in ethanol for 15-20 minutes, and then rinse with a spray gun until the solder beads are clean.

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