A welding method and a structure before lamp bead welding

Abstract

The present invention belongs to the technical field of SMT welding patches, and in particular, relates to a welding method and a structure before welding of lamp beads. The welding method comprises the following steps: preparing lamp beads and circuit boards, wherein the circuit boards include a board body and a soldering pad arranged on the board body and opposite to the lamp beads and made of a conductive material, wherein the specific heat capacity of the board body is smaller than the specific heat capacity of the soldering pad; applying welding material to the circuit board and forming a welding layer, wherein a part of the soldering layer is applied to the soldering pad and does not completely cover the soldering pad and is located between the soldering pad and the lamp beads, and another part of the soldering layer is applied to the board body, and the soldering layer electrically connects the soldering pad and the lamp beads in a molten state. The present invention can prevent the light-emitting surface of the lamp beads from tilting after welding.

Description

Technical Field

[0001] The invention belongs to the technical field of SMT soldering patches, and in particular relates to a soldering method and a lamp bead pre-soldering structure. Background Art

[0002] See also Figures 1 to 3 LED display is a flat panel display, which is composed of small LED modules. With the rapid development of LED display industry, LED display products are diverse and widely used in various industries. At the same time, the market has higher and higher requirements for the quality and yield of LED display. LED module is composed of circuit board 30' through SMT (Surface Mounted Technology), and LED lamp beads 10' are welded on circuit board 30' to form a module that can display images. Therefore, the quality of LED lamp beads 10' mounted on circuit board 30' directly affects the production efficiency and yield, especially for LED display with smaller spacing. Because the spacing of LED lamp beads 10' is smaller, the precision requirement is higher and the mounting is more difficult.

[0003] See also Figures 1 to 3 In the existing LED display industry, the solder paste 40' has no uniform flow and climbing direction after melting, and the solder paste 40' is irregularly deposited under the lamp pin 11', causing the LED lamp bead 10' to float. Figure 2 After soldering with the solder paste 40', the lamp pin 11' floats up, so that the light-emitting surface 121' of the lamp body 12' is tilted relative to the horizontal plane. This often causes problems such as the LED lamp bead 10' being offset, tilted, the lamp pin 11' arching, warping, cold soldering and false soldering after LED mounting. This is especially true for TOP-packaged LEDs. Since these particles belong to bracket-type lamp pins 11', the lower lamp pins 11' have a certain curvature, so the lamp pins 11' are more likely to arch during reflow soldering. This phenomenon will cause the LED modules to be assembled into an LED display screen. When the display screen displays a white screen, when viewed from different angles in front of the display screen, the brightness of the display screen components will be inconsistent. This phenomenon is called "yin-yang surface" in the industry.

[0004] Figure 3 In the figure, there is a display screen composed of two LED modules with different light pins 11' floating in different directions. The light emitted by the two LED modules is tilted in different directions. When viewed from the L direction, the light of module a is brighter and the light of module b is darker; when viewed from the R direction, the light of module a is darker and the light of module b is brighter. This undesirable phenomenon caused by the floating height of the LED lamp pin 11' can be called "yin and yang surface", that is, the module brightness will show different degrees of brightness when viewed from different angles. Summary of the invention

[0005] The purpose of the present invention is to provide a welding method, aiming to solve the problem that LED lamp beads appear offset, tilted, and the lamp feet are arched and warped after welding, thereby causing the light-emitting surface thereof to tilt.

[0006] The present invention provides a welding method, comprising the following steps:

[0007] Prepare lamp beads and a circuit board, wherein the circuit board includes a board body and a solder pad arranged on the board body and opposite to the lamp beads and made of a conductive material, wherein the specific heat capacity of the board body is smaller than the specific heat capacity of the solder pad;

[0008] A welding material is applied to the circuit board to form a welding layer, a portion of the welding layer is applied to the welding pad and does not completely cover the welding pad and is located between the welding pad and the lamp bead, another portion of the welding layer is applied to the board body, and the welding layer electrically connects the welding pad and the lamp bead in a molten state.

[0009] The technical effect of the present invention is: by partially covering the pad with the welding layer, and then reflowing the circuit board, solder paste and lamp beads through the furnace, the pad area not covered by the welding layer has a fast heating rate. After the welding layer melts, the temperature of the pad area not covered by the welding layer is greater than the temperature of the board body, thereby causing the welding layer located on the board body to flow into the pad, that is, to produce a tin creeping effect. Due to the tin creeping effect, the welding layer located in the pad also flows together, so that the flow of the entire welding layer has regularity, and then the molten welding layer is evenly distributed in the pad, avoiding the problems of lamp bead deviation, tilt, lamp foot arching, warping, cold soldering and false soldering, and avoiding the tilt of the light-emitting surface of the lamp bead. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a schematic diagram of the structure of a lamp bead before welding in the prior art;

[0011] Figure 2 yes Figure 1 A schematic diagram of the structure of the lamp beads after welding in the prior art;

[0012] Figure 3 It is a schematic diagram of the principle of the positive and negative sides of a display screen in the prior art;

[0013] Figure 4 It is a schematic diagram of the principle of the soldering pad and the soldering layer provided in an embodiment of the present invention;

[0014] Figure 5 is a schematic diagram of the principle of a pad and a welding layer in another embodiment;

[0015] Figure 6 is a schematic diagram of the principle of a pad and a welding layer in yet another embodiment;

[0016] Figure 7 It is a structural schematic diagram of the structure of the lamp bead before welding provided by an embodiment of the present invention;

[0017] Figure 8 This is a structural schematic diagram of the structure of the lamp bead before welding in another embodiment;

[0018] Fig. 9 This is a schematic diagram of the structure of the lamp bead before welding in another embodiment;

[0019] Fig.10 is a structural schematic diagram of the structure of the lamp bead before welding in another embodiment;

[0020] Fig.11 It is a schematic diagram of the structure of the lamp bead before welding and after furnace reflow provided by an embodiment of the present invention.

[0021] The corresponding relationship between the numbers and names in the accompanying drawings is as follows:

[0022] 10', LED lamp beads; 12', lamp body; 11', lamp feet; 40', solder paste; 30', circuit board; 121', light-emitting surface;

[0023] 40, welding layer; 112, lamp bottom plate; 32, welding pad; 321, exposed area; 322, covering area; 41, shielding area; 42, shielding area; 10, lamp beads; 12, lamp body; 11, lamp foot; 111, lamp side plate; 30, circuit board; 31, board body; DETAILED DESCRIPTION

[0024] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0025] In the description of the present invention, it is necessary to understand that the orientation or positional relationship indicated by the terms "thickness", "up", "down", "vertical", "parallel", "bottom", "angle", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0026] In the present invention, unless otherwise clearly specified and limited, terms such as "installation" and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integrated connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements.

[0027] See also Figures 4 to 6 , an embodiment of the present invention provides a welding method, which can be used to weld a lamp bead 10 to a circuit board 30 .

[0028] Before explaining the specific process of this method, let's first explain the tin creeping effect. The so-called tin creeping effect is also called the SMT wick effect, which means that the flux has the characteristic of flowing to the place with higher temperature during the soldering process, thereby driving the solder to flow to the place with higher temperature.

[0029] The method comprises the following steps:

[0030] The lamp bead 10 prepared for welding, specifically, the lamp bead 10 of this embodiment is an LED lamp bead 10 .

[0031] Prepare a circuit board 30, the circuit board 30 is used to install the lamp bead 10, and the circuit board 30 includes a board body 31 and a solder pad 32 arranged on the board body 31 and opposite to the lamp bead 10 and made of a conductive material. The specific heat capacity of the board body 31 is smaller than the specific heat capacity of the solder pad 32, that is, the rate of temperature increase of the solder pad 32 is greater than the rate of temperature increase of the board body 31. Further, after the circuit board 30 is placed in a constant temperature environment and a predetermined time has passed, the temperature of the solder pad 32 is greater than the temperature of the board body 31.

[0032] A soldering material is prepared and applied to the circuit board 30 to form a soldering layer 40, the shape of the soldering layer 40 being adapted to the shape of the solder pad 32. Optionally, the soldering material is solder paste.

[0033] A portion of the soldering layer 40 is deposited on the soldering pad 32 and does not completely cover the soldering pad 32 and is located between the soldering pad 32 and the lamp bead 10 . Another portion of the soldering layer 40 covers the board body 31 . The soldering layer 40 electrically connects the soldering pad 32 and the lamp bead 10 in a molten state.

[0034] See also Figures 7 to 9, by partially covering the pad 32 with the solder layer 40, and then reflowing the circuit board 30, solder paste and lamp bead 10 through the furnace, the area of ​​the pad 32 not covered by the solder layer 40 has a fast heating rate. After the solder layer 40 melts, the temperature of the area of ​​the pad 32 not covered by the solder layer 40 is greater than the temperature of the board body 31, thereby causing the solder layer 40 located on the board body 31 to flow into the pad 32, that is, a creeping tin effect is generated. Due to the creeping tin effect, the solder layer 40 located in the pad 32 also flows together, so that the flow of the entire solder layer 40 has regularity, and then the melted solder layer 40 is evenly distributed in the pad 32, avoiding the problems of the lamp bead 10 being offset, tilted, the lamp foot 11 arching, warping, cold soldering and false soldering, and avoiding the tilt of the light-emitting surface of the lamp bead 10.

[0035] In one embodiment, the formation process of the welding layer 40 also includes preparing a printed board, which is stacked on the circuit board 30 and has a printing hole corresponding to the position of the pad 32, and the welding material is filled in the printing hole to form the welding layer 40. It is understandable that the printing board can be made of stainless steel material and is used to assist in the coating of the welding layer 40. The printing hole is opened on the printing board and the printing hole and the pad 32 are partially overlapped in the direction perpendicular to the circuit board 30. The shape of the printing hole is also adapted to the shape of the pad 32. After the welding layer 40 is formed, the printed board is detached from the circuit board 30, and the welding layer 40 is retained.

[0036] In one embodiment, the solder pad 32 has a covered area covered by the solder layer 40 and an exposed area 321 not covered by the solder layer 40, wherein the area of ​​the covered area is larger than the area of ​​the exposed area 321, so that most of the solder pad 32 is covered by the solder layer 40, which is beneficial to improving the soldering efficiency and the regular flow of the solder layer 40.

[0037] In one embodiment, the lamp bead 10 includes a lamp body 12 that generates light in a conductive state and a lamp foot 11 that connects the lamp body 12 and the welding layer 40 and is made of a conductive material. The lamp foot 11 includes a lamp side plate 111 and a lamp bottom plate 112 that is flatly arranged relative to the welding layer 40. One end of the lamp bottom plate 112 abuts against the welding layer 40 and is connected to the lamp side plate 111. The other end of the lamp bottom plate 112 extends out of the welding layer 40 and is arranged relative to the exposed area 321, that is, the other end of the lamp bottom plate 112 is located directly above the exposed area 321. It can be understood that the lamp bottom plate 112 is also made of metal material, so that the temperature of the lamp bottom plate 112 rises quickly when it is reflowed through the furnace, further improving the tin creeping effect, that is, improving the flow of the welding layer 40.

[0038] It can also be understood that the welding layer 40 covers the entire pad 32, the lamp base plate 112 abuts against the welding layer 40, the welding layer 40 near one end of the lamp base plate 112 is extended out of the pad 32, and the welding layer 40 at the other end of the lamp base plate 112 is cut off, that is, the welding layer 40 is arranged in an extension-introduction manner on the pad 32. This can prevent the lamp bead 10 from being offset, tilted, arched, and warped during welding, and at the same time, it can ensure that enough tin is accumulated on the upper and lower sides of the lamp pin 11 and the pad 32, so that the welding of the lamp pin 11 and the pad 32 is more firm.

[0039] See also Figure 10 to Figure 11 In one embodiment, the welding layer 40 has a shielding plate area 42 covering the shielding area and a shielding plate area 41 connecting the shielding plate area 42 and covering the board body 31, and the area of ​​the shielding plate area 41 is smaller than the area of ​​the shielding plate area 42. Optionally, the connection position of the lamp bottom plate 112 and the lamp side plate 111 is close to the shielding plate area 41, and the angle between the lamp bottom plate 112 and the lamp side plate 111 is an acute angle, that is, the end of the lamp bottom plate 112 connected to the lamp side plate 111 is sunken and close to the circuit board 30, and the end of the lamp bottom plate 112 away from the lamp side plate 111 is upturned and away from the circuit board 30. Therefore, when the welding material in the shielding area 41 reflows, a part of it will climb upward from the connection between the lamp base plate 112 and the lamp side plate 111 along one end of the lamp base plate 112 and flow to the plate surface of the lamp base plate 112 facing away from the welding layer 40, so that the welding layer 40 is fully welded to the lamp base plate 112, the welding quality is higher, and too much solder paste is prevented from being deposited under the lamp base plate 112, thereby preventing the lamp bead 10 from floating.

[0040] In one embodiment, the shape of the solder pad 32 and the solder layer 40 is rectangular, circular or elliptical.

[0041] See also Figures 4 to 6 In one embodiment, the pad 32 and the welding layer 40 are both rectangular, and the length of the welding layer 40 is greater than or equal to the length of the pad 32, and the width of the welding layer 40 is greater than or equal to the width of the pad 32. That is, F≥B.

[0042] In one embodiment, the length of the shielding area 41 along the length direction of the welding layer 40 ranges from 0.05 to 0.25 mm, that is, 0.05 mm ≤ D ≤ 0.25 mm.

[0043] In one embodiment, the length of the exposed area 321 along the length direction of the pad 32 is in the range of 0.05 to 0.20 mm. That is, 0.05 mm ≤ C ≤ 0.20 mm

[0044] In one embodiment, the difference between the width of the solder layer 40 and the width of the solder pad 32 is in the range of 0.05-0.1 mm, that is, 0.025 mm≤E≤0.05 mm.

[0045] See also Figures 4 to 11 The present embodiment also provides a lamp bead pre-welding structure manufactured by the above-mentioned welding method, the lamp bead pre-welding structure comprises a flatly arranged circuit board 30, a welding layer 40 formed by welding material, and a lamp bead 10 to be welded on the circuit board 30, the circuit board 30 comprises a board body 31 and a soldering pad 32 arranged on the board body 31 and opposite to the lamp bead 10 and made of a conductive material, the specific heat capacity of the board body 31 is smaller than the specific heat capacity of the soldering pad 32, the shape of the soldering layer 40 is adapted to the shape of the soldering pad 32, a part of the soldering layer 40 is deposited on the soldering pad 32 and does not completely cover the soldering pad 32, and the two side surfaces respectively abut the soldering pad 32 and the lamp bead 10, another part of the soldering layer 40 covers the board body 31, and the soldering layer 40 electrically connects the soldering pad 32 and the lamp bead 10 in a molten state.

[0046] By partially covering the pad 32 with the solder layer 40, when the circuit board 30, solder paste and lamp bead 10 are reflowed in the furnace, the area of ​​the pad 32 not covered by the solder layer 40 has a fast heating rate. After the solder layer 40 melts, the temperature of the area of ​​the pad 32 not covered by the solder layer 40 is greater than the temperature of the board body 31, thereby causing the solder layer 40 located on the board body 31 to flow into the pad 32, that is, a creeping tin effect is generated. Due to the creeping tin effect, the solder layer 40 located in the pad 32 also flows together, so that the flow of the entire solder layer 40 has regularity, and then the melted solder layer 40 is evenly distributed in the pad 32, avoiding the problems of the lamp bead 10 being offset, tilted, the lamp foot 11 arching, warping, cold soldering and false soldering, and avoiding the tilting of the light-emitting surface of the lamp bead 10.

[0047] In one embodiment, the structure before soldering of the lamp bead further includes a printed board with a printing hole, the printed board has a first state in which it is stacked with the circuit board 30 and a second state in which it is separated from the circuit board 30, and the printed board is in the first state for the soldering material to fill the printing hole and form the soldering layer 40. Optionally, the printed board is made of stainless steel. The shape of the printing hole is adapted to the soldering pad 32.

[0048] In one embodiment, the pad 32 has a covered area covered by the solder layer 40 and an exposed area 321 not covered by the solder layer 40 , wherein the area of ​​the covered area is larger than that of the exposed area 321 .

[0049] In one embodiment, the welding layer 40 has a shielding disk area 42 covering the shielding area and a shielding plate area 41 connecting the shielding disk area 42 and covering the plate body 31 , and the area of ​​the shielding plate area 41 is smaller than that of the shielding disk area 42 .

[0050] In one embodiment, the lamp bead 10 includes a lamp body 12 that generates light in a conductive state and a lamp foot 11 that connects the lamp body 12 and the welding layer 40 and is made of a conductive material. The lamp foot 11 includes a lamp side panel 111 that is vertically arranged and a lamp bottom panel 112 that is flatly arranged relative to the welding layer 40. One end of the lamp bottom panel 112 abuts the welding layer 40 and is connected to the lamp side panel 111, and the other end of the lamp bottom panel 112 extends out of the welding layer 40 and is arranged in the air relative to the exposed area 321.

[0051] In one embodiment, the lamp bead 10 includes a plurality of lamp pins 11 , and the lamp pins 11 are arranged in pairs, and the number of the soldering pads 32 and the soldering layers 40 are adapted to the number of the lamp pins 11 .

[0052] In one embodiment, the two exposed areas 321 in the same pair are adjacently arranged and are both located between the corresponding two welding layers 40. The flow directions of the two shielding areas are respectively as follows: Figure 7 The directions indicated by the two arrows in the figure, or the flow directions in the two baffle areas, are as follows: Fig. 9 The two arrows point to the direction.

[0053] In one embodiment, the two welding layers 40 in the same pair are arranged adjacent to each other and are both located between the corresponding two exposed areas 321. The flow directions of the two shielding areas are respectively as follows: Figure 8 The directions indicated by the two arrows in the figure, or the flow directions in the two baffle areas, are as follows: Fig.10 The two arrows point to the direction.

[0054] Specifically, when the lamp bead is soldered in the reflow soldering furnace, the solder paste melts due to the heat, and the solder paste in the shielding area 41 will flow toward the exposed area 321 in a liquid state, that is, the creeping solder effect is generated. Because the two lamp pins 11 are symmetrically arranged, that is, the solder paste in the shielding area 41 corresponding to the two lamp pins 11 flows toward or away from each other, the forces applied to the lamp bead 10 will offset each other, and the lamp bead 10 will not be relatively displaced due to the flow of the solder paste, and thus will not affect the soldering process of the lamp bead 10, and at the same time, it also avoids the soldering misalignment, tilting, arching, warping and other poor soldering phenomena caused by the irregular movement of the solder paste.

[0055] Furthermore, the free end of the lamp bottom plate 112 is tilted toward the lamp body 12, that is, the free end of the lamp bottom plate 112 is tilted relative to the circuit board 30. Therefore, during the flow process, the solder paste in the shielding area 41 can climb up the lamp bottom plate 112 from the lower end of the lamp bottom plate 112 and flow toward the free end of the lamp bottom plate 112, thereby improving the welding strength of the lamp bead 10, that is, the solder paste in the shielding area 41 climbs up the lamp bottom plate 112 from both sides of the lamp bottom plate 112 or the connecting end of the lamp bottom plate 112, thereby enhancing the firmness of the welding of the lamp bead 10, and greatly improving the SMT welding yield rate, solving the problem of the positive and negative sides of the LED display.

[0056] This embodiment also provides a display screen, which includes a plurality of lamp bead structures. The lamp bead structures are formed by reflowing the above-mentioned lamp bead pre-welding structures through a furnace.

[0057] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A welding method, characterized in that: The following steps are involved: Prepare lamp beads and a circuit board, wherein the circuit board includes a board body and a solder pad arranged on the board body and opposite to the lamp beads and made of a conductive material, wherein the specific heat capacity of the board body is smaller than the specific heat capacity of the solder pad; Apply welding material to the circuit board to form a welding layer, a part of the welding layer is applied to the welding pad and does not completely cover the welding pad and is located between the welding pad and the lamp bead, and another part of the welding layer is applied to the board body, the welding layer located on the board body flows into the welding pad in a molten state, and the welding layer located in the welding pad flows together, so that the flow of the entire welding layer has regularity, so as to electrically connect the welding pad and the lamp bead; The pad has a covered area covered by the soldering layer and an exposed area not covered by the soldering layer, wherein the area of ​​the covered area is larger than the area of ​​the exposed area; The lamp bead comprises a lamp body that generates light in a conductive state and a lamp foot that connects the lamp body and the welding layer and is made of a conductive material, the lamp foot comprises a lamp side plate and a lamp bottom plate that is laid flat relative to the welding layer, one end of the lamp bottom plate abuts against the welding layer and is connected to the lamp side plate, and the other end of the lamp bottom plate extends out of the welding layer and is arranged relative to the exposed area; the lamp bead comprises a plurality of lamp feet, and each of the lamp feet is arranged in pairs, and the two lamp feet of the same pair are symmetrically arranged, and the welding layers corresponding to the two lamp feet flow toward each other or flow away from each other; The free end of the lamp bottom plate is arranged to be tilted upward relative to the circuit board.

2. The welding method according to claim 1, characterized in that: The process of forming the welding layer further includes preparing a printing plate, which is stacked on the circuit board and has printing holes corresponding to the positions of the welding pads, and the welding material is filled in the printing holes to form the welding layer.

3. The welding method according to claim 1, characterized in that: The welding layer comprises a shielding disk area covering the shielding area and a shielding plate area connecting the shielding disk area and covering the plate body, wherein the area of ​​the shielding plate area is smaller than that of the shielding disk area.

4. The welding method according to claim 3, characterized in that: The shape of the pad and the welding layer is one of rectangular, circular or elliptical.

5. The welding method according to claim 4, characterized in that: The pad and the welding layer are both arranged in a rectangular shape, and the length of the welding layer is greater than or equal to the length of the pad, and the width of the welding layer is greater than or equal to the width of the pad.

6. The welding method according to claim 5, characterized in that: The length of the shield area along the length direction of the welding layer ranges from 0.05 to 0.25 mm.

7. The welding method according to claim 5, characterized in that: The length of the exposed area along the length direction of the pad ranges from 0.05 to 0.20 mm.

8. A lamp bead pre-welding structure, manufactured by the welding method according to any one of claims 1 to 7, characterized in that: include: A circuit board arranged flatly, a welding layer formed by welding material, and a lamp bead to be welded to the circuit board, the circuit board comprising a board body and a welding pad connected to the board body and arranged opposite to the lamp bead and made of conductive material, the specific heat capacity of the board body is smaller than the specific heat capacity of the welding pad, a part of the welding layer is laid on the welding pad and does not completely cover the welding pad, and the two side surfaces respectively abut the welding pad and the lamp bead, another part of the welding layer is laid on the board body, and the welding layer electrically connects the welding pad and the lamp bead in a molten state.

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