Welding stud structure, circuit board assembling method and circuit board assembly

Abstract

The invention relates to the technical field of electronic assembly, and provides a welding stud structure, a circuit board assembly method and a circuit board assembly.The welding stud structure comprises a stud body, the stud body is provided with a first end and a second end which are oppositely arranged, a preset length is formed between the first end and the second end, and the first end and the second end face each other in the direction from the end face of the first end to the second end; a threaded hole is formed in the stud body in the axial direction, a closed end for closing the threaded hole is formed at the second end of the stud body, the end face of the closed end is an arc face, and a welding part is formed on the cylindrical face close to the second end. The closed end for closing the threaded hole is formed at the second end of the stud body, so that the end face of the closed end is the cambered surface. When the stud body is assembled on the circuit board, a wave-soldering process can be used in an overlapping manner after an SMT (surface mount technology) process, so that tin waves can effectively fill tin in a welding cavity position of the SMT process, 100% tin penetration between the stud body and the hole wall of a welding hole of the circuit board is realized, the connection strength is improved, and a large current can pass through the stud body and the hole wall of the welding hole of the circuit board.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic assembly, in particular to a welding stud structure, a circuit board assembly method and a circuit board assembly. BACKGROUND

[0002] In the process of electronic assembly, a stud structure with a through threaded hole is usually adopted, when the stud is inserted into a printed circuit board (PCB), the threaded hole in the stud penetrates the upper and lower surfaces of the printed circuit board, and the welding process is limited by the physical structure. At present, the industry can only use the solder paste printing process in surface mount technology (SMT) to complete welding. Other mature welding processes such as wave soldering cannot be directly applied due to technical conflicts.

[0003] However, when relying solely on SMT solder paste printing, the solder material is difficult to fully fill the annular gap between the stud and the welding hole of the PCB, and welding voids (Voiding) are inevitably generated. If wave soldering is attempted, the liquid tin wave will flow into the threaded area inside the stud, causing the inner wall of the threaded hole to be left with solder, damaging the thread geometry, and making it impossible for the screw to be normally locked. Therefore, the present application provides a welding stud structure. SUMMARY

[0004] The present application provides a welding stud structure, a circuit board assembly method and a circuit board assembly to solve the above technical defects in the prior art, so that the stud body and the hole wall of the welding hole of the circuit board are 100% transparent to solder, the connection strength is improved, and the large current passing is met.

[0005] The first aspect of the present application provides a welding stud structure, comprising: A stud body having a first end and a second end arranged oppositely, having a predetermined length between the first end and the second end, from the end face of the first end to the direction of the second end, the inside of the stud body is provided with a threaded hole in the axial direction, the second end of the stud body forms a closed end closing the threaded hole, the end face of the closed end is an arc surface, and the cylindrical surface close to the second end forms a welding part.

[0006] According to the welding stud structure provided by the present application, the center of the virtual circle where the arc surface is located is located inside the threaded hole, and the center line of the arc surface coincides with the axis of the stud body.

[0007] According to the welding stud structure provided by the present application, in the case where the stud body is assembled to the circuit board: The length of the stud body remains unchanged, and the size of the stud body protruding from the circuit board is in a positive correlation with the radius of the virtual circle where the arc surface is located.

[0008] According to the welding stud structure provided by the application, two end points of the arc surface are a first end point A and a second end point B, the second end point B is located on an axis of the stud body, a reference straight line between the second end point B and a center O1 of a virtual circle where the arc surface is located is L, a perpendicular segment passing through the first end point A and being perpendicular to the reference straight line L, and a foot O2 of the perpendicular segment and the reference straight line L. Wherein, the first end point A, the center O1 and the foot O2 form a right triangle, and a radius R of the virtual circle where the arc surface is located is determined by the Pythagorean theorem.

[0009] According to the welding stud structure provided by the application, a diameter of a position where the welding part is located is smaller than a diameter of the stud body, and the diameter of the position where the welding part is located is larger than a hole diameter of the threaded hole.

[0010] The second aspect of the application provides a circuit board assembly method for assembling the welding stud structure to a circuit board, comprising the following steps: Printing tin paste on a welding area of a device surface of the circuit board; Inserting the welding stud structure into a through hole of the circuit board, so that a closed end of the stud body is exposed to a non-device surface of the circuit board; Welding the welding stud structure and the circuit board, so that the tin paste on the device surface of the circuit board is melted and flows downward by heat, and the solder on the non-device surface of the circuit board penetrates upward to fill the through hole of the welding stud structure and the circuit board.

[0011] According to the circuit board assembly method provided by the application, the welding of the welding stud structure and the circuit board, so that the tin paste on the device surface of the circuit board is melted and flows downward by heat, comprises: Using reflow welding technology to melt the printed tin paste, so that the melted tin paste fills the welding part of the stud body downward under capillary force to form an initial wetting layer.

[0012] According to the circuit board assembly method provided by the application, the welding of the welding stud structure and the circuit board, so that the solder on the non-device surface of the circuit board penetrates upward, comprises: Using wave soldering technology to push the solder to fill a gap between the welding part of the stud body and a hole wall of the through hole, drive the solder in the gap to fully mix and flow, and discharge all residual gas, so that the solder fills the entire gap.

[0013] According to the circuit board assembly method provided by the application, during the welding process using the wave soldering technology: The arc surface of the closed end of the stud body exposes the non-device surface of the circuit board, and the arc surface exposing the non-device surface of the circuit board guides molten solder to fill from the non-device surface of the circuit board to the device surface of the circuit board; When the wave crest descends and the welding point cools and solidifies, the arc surface exposing the non-device surface of the circuit board changes the surface tension distribution of the solder solidification point, and restrains the pull tip.

[0014] The third aspect of the present application provides a circuit board assembly comprising a circuit board and the soldering stud structure of any one of the aspects, the soldering stud structure being soldered to the circuit board; or being assembled by the circuit board assembly method of any one of the aspects.

[0015] The soldering stud structure provided by the present application forms a closed end of the second end of the stud body to form a closed threaded hole, so that the end surface of the closed end is an arc surface. In this way, when the stud body is assembled on the circuit board, the wave soldering process can be used after the SMT process, so that the tin wave effectively fills the soldering hollow position of the SMT process, and 100% tin penetration is achieved between the stud body and the hole wall of the soldering hole of the circuit board, the connection strength is improved, and large current passing is met.

[0016] Specifically, when the stud body is assembled on the circuit board, double-sided solder paste can be provided, that is, the wave soldering thrust cooperates with the printed solder paste from the device surface, so that the molten solder fully mixes and flows in the gap between the stud body and the soldering hole of the circuit board, and finally fills the entire hole, completely welding the stud body and the circuit board into one body, achieving 100% tin penetration, and ensuring that the mechanical connection and conductive performance of the circuit board assembly are reliable.

[0017] When wave soldering is performed, the molten solder contacts the arc surface of the closed end, and the arc surface guides the molten solder to fill more smoothly from the non-device surface to the device surface, which can increase the contact area and immersion angle of the solder with the stud body, enhance the capillary force, and facilitate the solder to climb. Moreover, the arc surface can provide a natural gas escape channel, so that bubbles cannot stably accumulate below the arc surface and are easily discharged upward along the curved surface edge, avoiding the formation of gas cavities. When the wave crest descends and the welding point cools and solidifies, the arc surface can change the surface tension distribution of the solder solidification point. The surface tension mainly acts on the inside of the solder, rather than being concentrated on a certain point at the bottom edge to pull upward forcibly, thereby significantly reducing the tendency of the pull tip to form; and the excess solder is more easily and evenly reflowed and gathered or collapsed, and the welding effect is better.

[0018] The circuit board assembly method provided by this invention, based on structural improvements to the stud body, allows for double-sided soldering. This enables the wave soldering thrust from the non-device side and the printed solder paste from the molten solder on the device side to fully mix and flow within the gap between the solder hole and the stud body. This allows the solder from both the device and non-device sides to ultimately merge, completing the filling of the entire hole (100% solder penetration). At this point, the curved surface structure ensures excellent solder wetting and flowability, reducing the possibility of cavitation and accelerating gas escape along the curved surface. When the circuit board leaves the wave crest and the solder joint cools and solidifies, the curved surface structure effectively disperses the surface tension during solidification, preventing the solder from being pulled up at the bottom edge to form spikes and significantly suppressing solder spikes.

[0019] The circuit board assembly provided by the present invention, having included the aforementioned solder stud structure, possesses all the advantages of the aforementioned solder stud structure. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 This is one of the structural schematic diagrams of the welded stud structure provided in the embodiments of the present invention.

[0022] Figure 2 This is the second schematic diagram of the welded stud structure provided in the embodiment of the present invention.

[0023] Figure 3 This is the third schematic diagram of the welded stud structure provided in the embodiment of the present invention.

[0024] Figure 4 This is a schematic diagram of the welded stud structure provided in an embodiment of the present invention.

[0025] Figure 5 This is a flowchart of a circuit board assembly method provided in an embodiment of the present invention.

[0026] Figure 6 This is a schematic diagram of a welding stud structure used in the circuit board assembly process according to an embodiment of the present invention.

[0027] Figure 7 This is one of the structural schematic diagrams of a welding stud structure used in the circuit board assembly process provided by the embodiments of the present invention.

[0028] Figure 8Fig. 2 is a structural schematic diagram of another embodiment of the welding stud structure used in the circuit board assembly process provided by the embodiment of the present application.

[0029] Figure 9 Fig. 1 is a structural diagram of the circuit board assembly provided by the embodiment of the present application.

[0030] Figure 10 Fig. 3 is a partial structural diagram of the circuit board assembly provided by the embodiment of the present application.

[0031] Reference signs: 10, stud body; 11, first end; 12, second end; 121, arc surface; 13, threaded hole; 14, welding portion; 20, circuit board; C, virtual circle. DETAILED DESCRIPTION

[0032] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be described clearly and completely below with reference to the drawings in the present application. Obviously, the described embodiments are some embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0033] In the description of the embodiments of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "connected", "connected" should be understood broadly, for example, it can be fixedly connected, or detachably connected, or integrally connected; it can be mechanically connected, or electrically connected; it can be directly connected, or indirectly connected through an intermediate medium. For those skilled in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0034] In the embodiments of the present application, unless otherwise explicitly specified and limited, the first feature is "on" or "under" the second feature, which can be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature "above", "over" and "on" the second feature can be that the first feature is directly above or obliquely above the second feature, or only means that the horizontal height of the first feature is higher than that of the second feature. The first feature "below", "under" and "under" the second feature can be that the first feature is directly below or obliquely below the second feature, or only means that the horizontal height of the first feature is less than that of the second feature.

[0035] In the description of the specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the embodiments of the present application. In the specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

[0036] The welding stud with a through threaded hole faces a fundamental contradiction under the traditional process, involving physical structure limitation, solder flow characteristics, process conflict and quality risk and the like problems.

[0037] For example, the adapter plate of the single-phase inverter inductor requires that the welding stud on the plate is 100% tin-penetrated. In actual operation, when the single-plate trial production is first carried out, the steel mesh uses a scheme of 0.15 mm + 0.5 mm expansion, and the back plate confirms that there is a 100% hollow area in the welding hole where the welding stud is located, and the tin amount is insufficient, which cannot meet the tin-penetration requirement of the welding hole where the stud is located. In the case of insufficient tin penetration, the through-flow between the stud and the PCB will be affected, and insufficient through-flow will in turn cause the temperature on the plate to be too high, causing serious problems such as board burning and machine explosion.

[0038] In view of the above problems, when the welding stud with a through threaded hole is used in the wave soldering process, the bottom of the stud (non-device side) is exposed to the tin wave, and the stud has no physical blockage in the direction of the PCB non-device side, and the through threaded hole becomes an open pipeline from the bottom of the PCB (non-device side) to the top (device side). When the non-device side of the PCB contacts the molten tin wave, the solder will uncontrollably rush into the threaded hole, causing the inside of the threaded hole to be blocked by the solder, and the subsequent screw cannot be screwed into the stud, resulting in failure of the function of the welding stud. Therefore, the welding stud with a through threaded hole cannot be used in the wave soldering process.

[0039] So, the welding stud with a through threaded hole can only use steel mesh printing (tin printing) in SMT process to apply solder paste on the device face pad of the stud, and there is an annular gap between the outer wall of the stud and the inner wall of the welding hole of the PCB, which needs to be filled with solder to realize electrical connection and mechanical strength. Since the solder paste can only be coated on the annular pad at the top of the welding stud, it cannot be directly injected into the bottom of the gap, therefore, it relies on the capillary action of the solder paste after reflow to flow down into the gap, and the amount of printed solder paste is limited by the opening of the steel mesh, which cannot provide enough volume to fill the entire hole gap with a depth-diameter ratio, and the area in the gap that cannot be completely filled with solder forms a void. The void means that the effective contact area between the welding stud and the circuit board is reduced, and the electrical and thermal connections between the welding stud and the wall of the welding hole on the circuit board are severely weakened; at the same time, the void destroys the integrity of the solder joint, resulting in insufficient bonding strength and reduced mechanical strength.

[0040] The above double contradictions result in that the welding stud with a through threaded hole cannot be double-sided soldered by wave soldering and SMT tin printing at present, which further reduces the current carrying capacity of the circuit board assembly and the welding strength, and the void reduces the effective cross-sectional area of the conductor and increases the resistance. When a large current passes through, the risk of local overheating increases dramatically, which may burn the solder joint or cause device failure. The void weakens the mechanical bonding force of the solder joint, and the stud is prone to loosen or even fall off when subjected to vibration, impact or torsion.

[0041] Figure 1 is one of the structure schematic diagrams of the welding stud structure provided by the embodiment of the present application. Figure 2 is another structure schematic diagram of the welding stud structure provided by the embodiment of the present application. Figure 3 is a third structure schematic diagram of the welding stud structure provided by the embodiment of the present application. Figure 4 is a physical schematic diagram of the welding stud structure provided by the embodiment of the present application.

[0042] Referring to Figures 1 to 4 , the embodiment of the present application provides a welding stud structure, which comprises a stud body 10, the stud body 10 has a first end 11 and a second end 12 arranged oppositely, and a threaded hole 13 is arranged in the stud body 10 in the axial direction from the end face of the first end 11 to the direction of the second end 12, and the second end 12 of the stud body 10 forms a closed end closing the threaded hole 13, which is equivalent to that the threaded hole 13 is a blind hole, the end face of the closed end is an arc face 121, which can be a dome-shaped, spherical or other structure, and a welding part 14 is formed on the cylindrical surface close to the second end 12, and the shape of the cross section of the welding part 14 can be circular or combined.

[0043] It can be understood that the welding stud structure provided by the embodiment of the present application forms the closed end of the second end 12 of the stud body 10 into a closed threaded hole 13, so that the end face of the closed end is an arc face 121. In this way, when the stud body 10 is assembled on the circuit board 20, the wave soldering process can be used after the SMT process, so that the tin wave effectively fills the soldering hollow position of the SMT process, and 100% tin penetration is achieved between the stud body 10 and the hole wall of the soldering hole of the circuit board 20, the connection strength is improved, and the large current passing is met.

[0044] Specifically, when the stud body 10 is assembled on the circuit board 20, double-sided tin supply can be performed, that is, the printed tin paste on the device surface is matched by the wave soldering thrust on the non-device surface, so that the molten tin is fully mixed and flows in the gap between the stud body 10 and the soldering hole of the circuit board 20, and finally the solder tin fills the entire hole, so that the stud body 10 and the circuit board 20 are completely welded into a whole, 100% tin penetration is achieved, and the mechanical connection and the electrical conductivity of the circuit board assembly are reliable.

[0045] When wave soldering is performed, the molten solder tin contacts the arc face 121 of the closed end, the arc face 121 guides the molten solder tin to fill from the non-device surface to the device surface more smoothly, can increase the contact area and the wetting angle of the solder tin and the stud body 10, enhance the capillary force, and is beneficial to the solder tin climbing. Moreover, the arc face 121 can provide a natural gas escape channel, so that the bubbles cannot stably gather below the arc face 121, but are easily discharged upward along the curved surface edge, avoiding the formation of air pockets. When the wave descends and the solder joint cools and solidifies, the arc face 121 can change the surface tension distribution of the solder tin solidification point. The surface tension mainly acts on the inside of the solder tin, rather than being concentrated on a certain point at the bottom edge to pull upward forcibly, thereby significantly reducing the tendency of the tip to form; and the excess solder tin is more easily and evenly reflowed and gathered or collapsed, and the welding effect is better.

[0046] Referring to Figure 2 and Figure 3 In some embodiments of the present application, the center of the virtual circle C where the arc face 121 is located is located inside the threaded hole 13, and the center line of the arc face 121 coincides with the axis of the stud body 10. The coaxial design ensures that the arc face 121 is symmetrically arranged, so that the thermal stress during welding solidification is uniformly distributed, the isotropic shrinkage during the solder tin solidification process is ensured (the crystal boundary segregation is eliminated), and unilateral stress concentration is avoided.

[0047] For example, when window welding is performed on the non-device surface, the axial symmetric flow field makes the solder tin rise in the hole by 360° synchronously, ensures that the solder tin is filled equally, and is beneficial to achieving 100% tin penetration.

[0048] Referring to Figure 2 and Figure 3In some embodiments of the present application, when the stud body 10 is assembled to the circuit board 20: the length of the stud body 10 remains unchanged, and the size of the stud body 10 protruding out of the circuit board 20 is positively correlated with the radius of the virtual circle C on which the arc surface 121 is located, that is, the larger the size of the stud body 10 protruding out of the circuit board 20, the larger the radius of the virtual circle C on which the arc surface 121 is located. Thus, the overall stress level is maintained within a safe range.

[0049] Continuing to refer to Figure 2 and Figure 3 In some embodiments of the present application, the two endpoints of the arc surface 121 are a first endpoint A and a second endpoint B, respectively, and the second endpoint B is located on the axis of the stud body 10. A reference straight line between the second endpoint B and the center O1 of the virtual circle C on which the arc surface 121 is located is L. A perpendicular segment is drawn from the first endpoint A to be perpendicular to the reference straight line L, and the intersection of the perpendicular segment and the reference straight line L is a foot O2. The first endpoint A, the center O1, and the foot O2 form a right triangle, and the radius R of the virtual circle C on which the arc surface 121 is located is determined by the Pythagorean theorem.

[0050] In the right triangle formed by the first endpoint A, the center O1, and the foot O2, the straight line between the first endpoint A and the center O1 is the radius R of the virtual circle C on which the arc surface 121 is located. The straight line between the first endpoint A and the foot O2 is the radius of the welding portion 14 of the stud body 10 protruding into the welding hole of the circuit board 20. The straight line between the foot O2 and the second endpoint B is the length H of the stud body 10, or the difference (H-h) between the length H of the stud body 10 and the length h of the stud body 10 protruding out of the circuit board 20.

[0051] Specifically, according to the conventional length of the stud body 10 protruding out of the circuit board 20, it can be understood as the size of the stud body 10 exposed on the non-device side of the circuit board 20, and the length H of the stud body 10 is generally controlled at 1.5 mm.

[0052] When the stud body 10 protrudes out of the non-device side of the circuit board 20, h is the length of the stud body 10 protruding out of the circuit board 20, which does not include the height of the arc surface 121, R is the radius of the virtual circle C on which the arc surface 121 is located, and r is the radius of the welding portion 14 of the stud body 10 protruding into the welding hole of the circuit board 20. According to the Pythagorean theorem: ; wherein r, H, and h are known numbers, and thus R can be calculated to determine the radius R of the virtual circle C on which the arc surface 121 is located.

[0053] As Figure 1 and Figure 2As shown in the figure, actual parameters are listed for verification, assuming that the radius r of the soldering portion 14 of the stud body 10 extending into the soldering hole of the circuit board 20 is 3.5 mm, the length H of the stud body 10 is 1.5 mm, and the length of the stud body 10 extending out of the circuit board 20 is 0.3 mm, then: It can be calculated that R = 5.7 mm, so the radius R of the virtual circle C where the arc surface 121 is located is determined to be 5.7 mm.

[0054] As shown in the figure, when the stud body 10 does not extend out of the non-device surface of the circuit board 20, R is the radius of the virtual circle C where the arc surface 121 is located, and r is the radius of the soldering portion 14 of the stud body 10 extending into the soldering hole of the circuit board 20, according to the Pythagorean theorem: Figure 3 ; wherein r and H are known numbers, and thus R can be calculated to determine the radius R of the virtual circle C where the arc surface 121 is located.

[0055] As shown in the figure, actual parameters are listed for verification, assuming that the radius r of the soldering portion 14 of the stud body 10 extending into the soldering hole of the circuit board 20 is 3.5 mm, and the length H of the stud body 10 is 1.5 mm, then: Figure 1 Figure 3 ; It can be calculated that R = 4.8 mm, so the radius R of the virtual circle C where the arc surface 121 is located is determined to be 4.8 mm.

[0056] Therefore, under the condition that the length of the stud body 10 is unchanged, the size of the stud body 10 extending out of the circuit board 20 is positively correlated with the radius of the virtual circle C where the arc surface 121 is located, that is, the larger the size of the stud body 10 extending out of the circuit board 20, the larger the radius of the virtual circle C where the arc surface 121 is located. By setting the arc surface 121 and determining the setting rule of the arc surface 121, in the actual processing process, the arc surface 121 is more easily recovered by the tin wave tension, so that the residual tin originally gathered on the plane can be quickly covered on the arc surface 121 after being separated from the tin in the tin groove under the action of the tension, forming a smooth circular surface.

[0057] Further, the size of the stud body 10 extending out of the circuit board 20 is h, wherein h ranges from 0 mm to 0.5 mm. According to the actual verification effect, the design of h ≤ 0.5 mm is preferred to ensure the effect of tin plating.

[0058] Please continue to refer to Figures 1 to 4 ​​​In some embodiments of the present application, the diameter of the position where the welding portion 14 is located is smaller than the diameter of the rest of the stud body 10, and the diameter of the position where the welding portion 14 is located is larger than the hole diameter of the threaded hole 13. That is, the outer surface of the stud body 10 and the welding portion 14 is a stepped shaft structure, and the welding portion 14 with a smaller diameter acts as a pin connection of the stud body 10.

[0059] In this way, the welding portion 14 formed after the size of the bottom of the stud body 10 is reduced can strengthen the flow guiding effect of the arc surface 121 on the solder, the welding portion 14 generates an ultra-strong capillary force to drive the solder paste to fill instantaneously, and the current density at the necking portion is increased. Moreover, the outer surface of the stud body 10 and the welding portion 14 forms a stepped structure, and after the welding portion 14 is inserted into the circuit board 20, it is limited by multiple surfaces of the circuit board 20, and at the same time, the welding portion 14 is connected with the circuit board 20 through the solder. Compared with the prior art in which the stud body 10 is directly connected with the circuit board 20, the connection part is first loosened and peeled off to fail, and the material of the stud body 10 is bent, deformed, or even directly broken to fail.

[0060] Figure 5 is a flowchart of the circuit board assembly method provided by an embodiment of the present application. Figure 6 is a structural schematic diagram of a welding stud structure of an embodiment used in the circuit board assembly process provided by an embodiment of the present application. Figure 7 is a structural schematic diagram of a welding stud structure of another embodiment used in the circuit board assembly process provided by an embodiment of the present application. Figure 8 is a structural schematic diagram of a welding stud structure of another embodiment used in the circuit board assembly process provided by an embodiment of the present application.

[0061] Referring to Figures 5 to 8 The present application also provides a circuit board assembly method for assembling the welding stud structure of any one of the above to a circuit board, which comprises the following steps S100, S200 and S300.

[0062] Step S100: printing solder paste on the welding area of the device surface of the circuit board 20.

[0063] It can be understood that, in the assembly process of the circuit board 20, the solder paste is printed on the annular pad of the device surface (i.e. the surface where the top end of the stud body 10 protrudes) of the circuit board 20 by using a steel mesh through printing (SMT solder paste printing), so as to provide a solder source from the device surface for the welding hole.

[0064] Specifically, the stainless steel mesh can be cut by laser to make the opening shape thereof accurately match the pad on the circuit board 20, the circuit board 20 is fixed on the printing machine table by an edge clamp or vacuum adsorption, and the optical positioning system identifies the reference point on the circuit board 20 and the mark of the steel mesh to realize accurate alignment.

[0065] Around the outer circle pad of the solder hole of the circuit board 20, the gap between the stud body 10 and the hole wall of the solder hole is filled with 1.5-2 times (compensate for reflow shrinkage), and high-activity flux is used to reduce the surface tension of the molten solder.

[0066] In order to solve the problem of incomplete tin filling in the solder hole, the thickness of the steel mesh can be increased, and the size of the steel mesh window can be expanded (the size of the steel mesh window in the conventional design is usually the same as or slightly smaller than the pad size). Increase the amount of tin printing, the specific thickness of the steel mesh and the size of the steel mesh window are determined according to the actual size of the surface pad, the thickness of the board, the diameter of the solder hole, and the diameter of the solder stud extending into the solder hole. The total amount of solder tin should be able to completely cover the surface pad and fill the gap between the solder hole and the solder stud. As shown in Figure 7 The embodiment of the present application adopts a scheme of 0.3mm steel mesh thickness and 1mm outward expansion of the steel mesh window, which can improve the amount of tin paste on the mounting surface.

[0067] Step S200: Insert the solder stud structure into the through hole of the circuit board 20, so that the closed end of the stud body 10 is exposed to the non-device surface of the circuit board 20.

[0068] It can be understood that this process requires pre-positioning of the stud body 10 and the circuit board 20, that is, the circuit board 20 is fixed first. Exemplarily, the circuit board 20 on which tin paste printing has been completed can be placed horizontally on a jig and fixed by vacuum suction holes or mechanical clamps.

[0069] Then identify the direction of the stud body 10, distinguish the closed end and the open end (locking end) of the stud body 10, and ensure that the closed end faces the non-device surface of the circuit board 20.

[0070] Clamp the stud body 10 so that the axis of the stud body 10 coincides with the axis of the solder hole on the circuit board 20, and the stud body 10 is perpendicular to the surface of the circuit board 20. Press the stud body 10 in the vertical direction so that the stud body 10 penetrates the solder hole of the circuit board 20.

[0071] It should be noted that the annular stepped surface can be a limiting reference surface for controlling the insertion depth of the stud body 10. At the same time, it can prevent the stud body 10 from sinking during reflow soldering, causing the height of the arc surface 121 to change.

[0072] Referring to Figure 6Some welding stud structures provided by the embodiments of the present application are assembled with circuit boards, the bottom of the threaded hole in the welding stud structure is closed, so that the threaded hole forms a blind hole, but the bottom of the welding stud is a flat surface, when wave soldering, the molten solder contacts the flat surface, gas (flux volatilization, air) is easily trapped between the bottom flat surface and the hole wall, forming an air pocket, hindering the upward filling of the solder (solder climbing), resulting in insufficient solder penetration, and the surface tension of the liquid solder forms a large upward pulling force at the edge of the flat surface.

[0073] When the solder joint is separated from the wave crest, it is easy to pull the solder into a sharp shape (sharp pulling) during solidification, causing the wave solder joint to be different, and the sharp pulling height often exceeds the bottom height limit, which needs to be repaired and processed. At the same time, when the bottom of the closed welding stud is a flat surface, the solder wave cannot effectively wet the solder pad of the circuit board and the bottom of the stud when passing through the solder wave, the solder covering effect is poor, resulting in a step difference between the solder pad at the bottom of the circuit board and the bottom of the stud, and the through-flow capacity and soldering strength are weakened.

[0074] Therefore, referring to Figure 1 The embodiments of the present application are innovative, and provide another welding stud structure, which optimizes the flat surface at the bottom of the closed end of the above welding stud structure into an arc surface (circular arc surface). The embodiments of the present application take the arc surface at the bottom of the closed end of the welding stud structure as an example to describe the circuit board assembly method.

[0075] When the annular stepped surface of the stud body 10 contacts the pad of the device surface of the circuit board 20 to achieve physical limiting, at this time, the vertex of the arc surface 121 of the closed end is determined to protrude from the non-device surface of the circuit board 20.

[0076] Step S300: welding the welding stud structure and the circuit board 20, so that the solder paste on the device surface of the circuit board 20 is heated and melted to flow downward, and the solder on the non-device surface of the circuit board 20 penetrates upward to fill the through hole of the welding stud structure and the circuit board 20.

[0077] It can be understood that during the reflow soldering implementation process, the circuit board 20 inserted into the stud body 10 is uniformly sent into the reflow soldering furnace. The printed solder paste is melted, and the molten solder is pulled into the annular gap between the welding part 14 of the stud body 10 and the inner wall of the welding hole by capillary force, covers the side surface of the stud body 10 and starts to fill downward, forming an initial wetting layer.

[0078] During the wave soldering implementation process, the circuit board 20 passes through the molten solder wave crest of the wave soldering machine in the direction of the non-device surface downward. A large amount of molten solder is provided for the welding hole, and the hole is filled with force from the non-device surface. The pressure of the wave crest pushes the solder into the hole, provides global heat, and makes the pre-printed solder paste on the device surface finally completely melt and reflow, and fuse with the solder flowing from the bottom.

[0079] At this time, the solder pressure of the bottom surge is greater and the heat is higher, which can drive the solder in the hole to fully mix and flow, and the downward flowing and upward penetrating molten solder meet at the welding hole to discharge the gas in the gap to both ends of the through hole: the gas escapes through the edge of the device surface pad, and the gas escapes through the root of the arc surface 121 located on the non-device surface to discharge all residual gas. The solder of the device surface and the non-device surface is finally merged to complete the filling of the entire hole.

[0080] Ensure that the downward flowing solder forms a bottom fillet below the stud step surface, and the upward penetrating solder forms a continuous metal plating on the inner wall of the through hole, and the solder in the intersection area solidifies to form a columnar solder body without cavities.

[0081] It can be understood that the circuit board assembly method provided by the embodiment of the application can be soldered by using double-sided solder based on the structural improvement of the stud body 10, so that the solder from the non-device surface and the printed solder paste of the device surface are fully mixed and flow in the gap between the welding hole and the stud body 10, so that the solder of the device surface and the non-device surface is finally merged to complete the filling of the entire hole (100% solder penetration). At this time, the arc surface structure ensures good solder immersion and flowability, reduces the possibility of air pocket formation, and accelerates the discharge of gas along the curved surface. When the circuit board 20 leaves the wave crest, the solder joint cools and solidifies, and the arc surface structure effectively disperses the surface tension when solidifying, prevents the solder from being pulled up to form a spike at the bottom edge, and significantly inhibits the spike.

[0082] That is, based on the structural improvement of the stud body 10, the wave soldering process is added to forcibly supplement the amount of solder, so that the stud body 10 and the circuit board 20 are completely soldered into one body, 100% solder penetration is achieved, the mechanical connection and conductive performance of the circuit board assembly are ensured to be reliable, and the problem of insufficient current carrying capacity in a large current scenario is improved.

[0083] Further, welding the stud structure and the circuit board 20 makes the solder paste on the device surface of the circuit board 20 heat and melt downward, comprising: using reflow soldering technology to melt the printed solder paste, so that the melted solder paste fills the welding part 14 of the stud body 10 downward under the capillary force to form an initial wetting layer.

[0084] Further, welding the stud structure and the circuit board 20 makes the solder on the non-device surface of the circuit board 20 penetrate upward, comprising: using wave soldering technology to push the solder to fill the gap between the welding part 14 of the stud body 10 and the hole wall of the through hole with strong pressure, drive the solder in the gap to fully mix and flow, and discharge all residual gas to make the solder fill the entire gap.

[0085] Further, in the wave soldering process, the arc surface 121 exposed on the non-device surface of the circuit board 20 guides the molten solder to fill from the non-device surface of the circuit board 20 to the device surface of the circuit board 20; when the wave crest descends and the solder joint cools and solidifies, the arc surface 121 exposed on the non-device surface of the circuit board 20 changes the surface tension distribution of the solder solidification point and inhibits the tip pulling.

[0086] Figure 9 The embodiment of the present application provides a physical structure diagram of the circuit board assembly. Figure 10 The embodiment of the present application provides a partial physical structure diagram of the circuit board assembly.

[0087] Referring to Figure 9 and Figure 10 , the embodiment of the present application further provides a circuit board assembly, which comprises a circuit board and the soldering stud structure of any one of the above, and the soldering stud structure is welded on the circuit board. Alternatively, the circuit board assembly is assembled by the circuit board assembling method described above.

[0088] From Figure 9 and Figure 10 , the circuit board assembly provided by the embodiment of the present application is known, the stud body 10 of the soldering stud structure adopts a non-through threaded hole 13, that is, a blind hole is used to replace a through hole, which fundamentally eliminates the risk of tin wave pouring and meets the processing requirement of double-sided tin supply. The bottom surface of the closed end adopts an arc surface 121, which solves the air pocket and tip pulling problem under the wave soldering and ensures the filling quality and appearance requirement.

[0089] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A welded stud structure, characterized in that, include: The stud body has a first end and a second end that are arranged opposite to each other, with a preset length between the first end and the second end. Starting from the end face of the first end and moving towards the second end, the stud body has a threaded hole arranged axially inside. The stud body forms a closed end at the second end that closes the threaded hole. The end face of the closed end is an arc surface, and a welded part is formed on the cylindrical surface near the second end.

2. The welded stud structure according to claim 1, characterized in that, The center of the virtual circle containing the arc surface is located inside the threaded hole, and the center line of the arc surface coincides with the axis of the stud body.

3. The welded stud structure according to claim 2, characterized in that, When the stud body is assembled to the circuit board: The lead length of the stud body remains constant, and the dimension by which the stud body extends beyond the circuit board is positively correlated with the radius of the virtual circle containing the arc surface.

4. The welded stud structure according to claim 3, characterized in that, The two endpoints of the arc surface are the first endpoint A and the second endpoint B. The second endpoint B is located on the axis of the stud body. The reference line between the second endpoint B and the center O1 of the virtual circle where the arc surface is located is L. A perpendicular line segment is drawn through the first endpoint A, perpendicular to the reference line L. The intersection of the perpendicular line segment and the reference line L is the foot of the perpendicular O2. Wherein, the first endpoint A, the center O1 and the foot of the perpendicular O2 form a right triangle, and the radius R of the virtual circle containing the arc surface is determined by the Pythagorean theorem.

5. The welded stud structure according to any one of claims 1 to 4, characterized in that, The diameter of the welded part is smaller than the diameter of the stud body, and the diameter of the welded part is larger than the diameter of the threaded hole.

6. A circuit board assembly method for assembling the solder stud structure according to any one of claims 1 to 5 onto a circuit board, characterized in that, Includes the following steps: Solder paste is printed on the soldering area of ​​the device side of the circuit board; The welding stud structure is inserted into the through hole of the circuit board, so that the closed end of the stud body is exposed on the non-device side of the circuit board; Soldering the solder stud structure and the circuit board causes the solder paste on the device side of the circuit board to melt and flow downwards, while the solder on the non-device side of the circuit board penetrates upwards to fill the through holes of the solder stud structure and the circuit board.

7. The circuit board assembly method according to claim 6, characterized in that, Soldering the solder stud structure and the circuit board, causing the solder paste on the device side of the circuit board to melt and flow downwards due to heat, includes: The printed solder paste is melted using reflow soldering technology. Under capillary force, the melted solder paste fills downward along the soldering part of the stud body to form an initial wetting layer.

8. The circuit board assembly method according to claim 6, characterized in that, Soldering the stud structure and the circuit board, such that the solder penetrates upwards from the non-device side of the circuit board, includes: Wave soldering technology is used to forcefully fill the gap between the welding part of the stud body and the wall of the through hole with solder, driving the solder in the gap to mix and flow fully, and expelling all residual gas, so that the solder fills the entire gap.

9. The circuit board assembly method according to claim 8, characterized in that, During the wave soldering process: The arc surface of the closed end of the stud body exposes the non-device surface of the circuit board, and the arc surface of the exposed non-device surface of the circuit board guides molten solder to fill from the non-device surface of the circuit board to the device surface of the circuit board. As the wave crest descends and the solder joint cools and solidifies, the arc surface of the non-device side of the circuit board alters the surface tension distribution of the solder solidification point, suppressing solder spikes.

10. A circuit board assembly, characterized in that, It includes a circuit board and a welding stud structure as described in any one of claims 1 to 5, wherein the welding stud structure is welded to the circuit board; or, it is assembled by the circuit board assembly method as described in any one of claims 6 to 9.

Images