Steel mesh for SMT welding

Abstract

The utility model provides a steel mesh for SMT (Surface Mount Technology) welding, which comprises a steel mesh body with the thickness of 0.04 mm-0. 12mm; the steel mesh opening is used for being matched with each regular long-strip-shaped bonding pad on the surface of the chip, the steel mesh opening comprises a long side direction and a short side direction, at least one V-shaped sawtooth is configured in the long side direction, and the tip end of the V-shaped sawtooth extends inwards from the steel mesh body on the edge of the long side; the area of the opening of the steel mesh is not less than 85% of the area of the corresponding long-strip-shaped bonding pad. The V-shaped sawteeth are arranged at the edge of the opening of the steel mesh, so that the solder paste printed on the surface of the PCB from the opening of the steel mesh is not a long strip shape completely consistent with the shape of a chip bonding pad, but a V-shaped notch is formed in the long edge, and bubbles generated after the solder paste is melted can be easily contacted with the notch extending into the solder paste, so that the solder paste is prevented from falling off. And gas accumulated in the solder paste is discharged through a gap, so that the welding reliability is improved.

Description

TECHNICAL FIELD

[0001] The utility model relates to electronic technical field especially a steel net for SMT welding. BACKGROUND

[0002] SMT (Surface Mount Technology, surface mount technology) is widely applied in the assembly of electronic devices, and is a common way of welding components directly on the surface of PCB, and the welding process is as follows: tin paste is printed on the surface of the solder pad of the PCB, and electronic components are accurately placed on the surface of the PCB printed with tin paste through patching, at this time, the solder pad on the surface of the PCB is connected to the bottom of the tin paste, and the solder pad of the electronic component is connected to the top of the tin paste, and then the tin paste is melted in the reflow furnace at high temperature, so that the components and the PCB are firmly bonded together. However, since the tin paste contains air, water and flux, etc., these components become gas when the tin paste is melted at high temperature, and because the upper and lower solder pads cannot be discharged in time, bubbles and cavities are prone to occur after welding. SUMMARY

[0003] In order to overcome the above shortcomings, the utility model provides a steel net for SMT welding, which solves the technical problem that the gas in the tin paste cannot be discharged in time.

[0004] The technical scheme provided by the utility model is as follows:

[0005] The utility model provides a steel net for SMT welding, which comprises:

[0006] The thickness of the steel net body is 0.04mm-0.12mm;

[0007] The steel net opening is used to adapt to the regular long strip-shaped solder pad on the surface of the chip, and the steel net opening comprises a long edge direction and a short edge direction, at least one V-shaped sawtooth is arranged in the long edge direction, and the tip of the V-shaped sawtooth extends from the steel net body of the long edge edge to the inside; the area of the steel net opening is not less than 85% of the area of the corresponding long strip-shaped solder pad.

[0008] Further preferably, at least one pair of V-shaped sawteeth is symmetrically arranged in the two long edge directions of the steel net opening.

[0009] Further preferably, a plurality of pairs of V-shaped sawteeth are symmetrically arranged in the two long edge directions of the steel net opening, and a plurality of V-shaped sawteeth are uniformly arranged in the single long edge direction.

[0010] Further preferably, the surface of the chip is provided with positive long strip-shaped solder pads and negative long strip-shaped solder pads which are the same in size and shape, and a plurality of steel net opening pairs matched with the chip solder pads are regularly arranged on the steel net body.

[0011] Further preferably, the length of the short side direction of each steel mesh opening is not greater than 0.8mm.

[0012] Further preferably, the depth of the V-shaped sawtooth is less than half of the length of the short side of the pad.

[0013] Further preferably, the maximum width of the V-shaped sawtooth is 0.1mm-0.3mm.

[0014] The steel mesh for SMT welding provided by the present application has V-shaped sawtooth extending from the steel mesh body in the long side direction of the steel mesh opening, and the tip of the V-shaped sawtooth extends from the long side edge of the steel mesh opening to the inside, so that the tin paste printed from the steel mesh opening to the surface of the PCB board is not a long strip shape completely consistent with the shape of the chip pad, but has a V-shaped notch in the long side, and the bubbles generated after the tin paste melts can easily contact the notch extending into the tin paste, and the gas accumulated in the tin paste is discharged from the notch, improving the reliability of welding. At the same time, the area of the steel mesh opening is not less than 85% of the area of the corresponding long strip pad, which ensures that the bubbles can be quickly discharged, and the device can be firmly connected to the surface of the PCB board by soldering. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 Fig. 1 is a top view of the prior art steel mesh of the present application;

[0016] Figure 2 Fig. 2 is a top view of the steel mesh in an embodiment of the present application;

[0017] Figure 3 Fig. 3 is a structure enlargement view in the A frame of Fig. 2. Figure 2 Fig. 4 is a structure enlargement view in the B frame of Fig. 2.

[0018] REFERENCE NUMERALS:

[0019] 1-steel mesh body, 2-steel mesh opening, 3-V-shaped sawtooth. DETAILED DESCRIPTION

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the specific embodiments of the present application will be described below with reference to the drawings. Obviously, the drawings described below are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to these drawings without creative labor, and other embodiments can also be obtained.

[0021] The utility model discloses a kind of steel mesh for SMT welding, comprising: steel mesh body, the thickness of steel mesh body is 0.04mm~0.12mm;Steel mesh opening for adapting each regular long strip-shaped pad on chip surface, steel mesh opening includes long side direction and short side direction, at least one V-shaped sawtooth is configured in long side direction, and the tip of V-shaped sawtooth extends from the steel mesh body of long side edge to inside;The area of steel mesh opening is not less than 85% of corresponding long strip-shaped pad area.

[0022] The steel mesh in the embodiment is used for printing tin paste in SMT process, and the opening position on the steel mesh body corresponds to the position of the pad on the PCB board. The shape and size of the steel mesh opening correspond to the long strip-shaped pad on the surface of the chip to be welded. Generally, the pad to be welded on the surface of the PCB board is also a long strip-shaped pad consistent with the chip, and the shape and size are consistent with the pad on the surface of the chip. The embodiment adopts a small-size chip. The short side length of the long strip-shaped pad in the chip is not greater than 0.8 mm, and the length of the long side is not limited. According to the shape of the chip itself, the long side may be 2-5 times the short side. The shape of the steel mesh opening needs to correspond to the chip pad. Therefore, the length of the short side direction in each steel mesh opening is not greater than 0.8 mm. The chip referred to herein includes but is not limited to LED chip and the like. The number of surface pads may be one (such as a vertical structure chip) or two (such as a flip structure chip). The corresponding steel mesh opening can be designed according to the pad of the chip. One steel mesh opening corresponds to one pad. Since the size of the chip itself is small, the size of the pad is also small, and the length of the short side direction is not greater than 0.8 mm. For the long strip-shaped pad of the chip, it is not appropriate to further design an exhaust passage structure on the pad, otherwise it may cause the chip to be unable to be normally attached.

[0023] Therefore, without changing the chip pad and the pad on the surface of the PCB board, the embodiment changes the shape of the steel mesh opening, extends the V-shaped sawtooth from the steel mesh body to the steel mesh opening, and configures the V-shaped sawtooth structure with the tip extending to the inside of the steel mesh opening in the long side of the steel mesh opening. When the tin paste printed subsequently is printed to the surface of the pad on the PCB board through the steel mesh opening, due to the blockage of the V-shaped sawtooth, the tin paste is not filled in the V-shaped sawtooth extending out of the long side, but forms a concave notch consistent with the shape of the V-shaped sawtooth. That is, between the pad on the PCB board and the chip pad, the tin paste is not a long strip-shaped pad completely consistent with the shape of the chip pad, but has a notch consistent with the shape of the V-shaped sawtooth in the long side. During the welding process, when the high-temperature molten tin paste, the notch can be used as an exhaust passage for the gas in the tin paste. Even if the tin paste is sandwiched between the long strip-shaped chip pad and the PCB pad, the generated bubbles can easily contact the V-shaped notch extending into the tin paste and be quickly discharged from the V-shaped notch, improving the reliability of welding. Compared with the prior art, the embodiment has the advantages that the tin paste is not filled in the V-shaped sawtooth extending out of the long side, but forms a concave notch consistent with the shape of the V-shaped sawtooth in the long side. During the welding process, when the high-temperature molten tin paste, the notch can be used as an exhaust passage for the gas in the tin paste. Even if the tin paste is sandwiched between the long strip-shaped chip pad and the PCB pad, the generated bubbles can easily contact the V-shaped notch extending into the tin paste and be quickly discharged from the V-shaped notch, improving the reliability of welding. Figure 1The V-shaped serration design can significantly improve the problem of gas discharge in the solder paste; that is, the steel mesh with the long edge of the steel mesh opening in the embodiment having the V-shaped serration structure can effectively promote the discharge of gas in the solder paste.

[0024] Generally speaking, the more the number of V-shaped serrations and the longer the depth, the more conducive to the discharge of bubbles in the solder paste; but the area occupied by the V-shaped serrations itself will cause the area of the solder paste to decrease, which is not conducive to the firm welding of the chip, and under the condition that the shape of the V-shaped serration is unchanged, the more the number of V-shaped serrations, the smaller the soldering area, and the more likely to cause the welding to be not firm; since the thickness of the steel mesh body is 0.04mm-0.12mm, the thickness of the printed solder paste is consistent with the thickness of the steel mesh body, therefore, under such thin solder paste thickness, it is necessary to ensure that the solder pad area covered by the solder paste is not less than 85%, to ensure that the final soldering area reaches more than 85%, so as to ensure that the electronic components can be firmly connected with the PCB board, that is, the area of the steel mesh opening is not less than 85% of the corresponding long strip-shaped pad area, and the total area of the V-shaped serrations used should be less than 15% of the pad area. For the shape of a single V-shaped serration, too long V-shaped serration depth can also affect the flow and final distribution of the solder paste, in the embodiment, the depth of the V-shaped serration is less than half of the length of the short side of the pad, and the maximum width of the V-shaped serration is 0.1mm-0.3mm, that is, the length of a single V-shaped serration occupies 0.1mm-0.3mm on the long side of the steel mesh opening, and the width gradually decreases with the inward extension, and the inward extension distance is less than half of the length of the short side of the pad. In addition, in order to avoid uneven distribution of the printed solder paste, affecting the overall welding performance, if there are multiple V-shaped serrations, the V-shaped serration structure is uniformly distributed. Therefore, when designing the shape of the steel mesh opening, the size and distribution position of the V-shaped serration should be determined by considering factors such as soldering area, bubble discharge, solder paste distribution, etc.

[0025] The chip pad is long strip-shaped, and the general shape of the steel mesh opening is also long strip-shaped, the V-shaped serrations are usually symmetrically distributed, at least one pair of V-shaped serrations are symmetrically arranged in the direction of the two long sides of the steel mesh opening, that is, the two long sides of the steel mesh opening are symmetrically tooth comb-shaped, the serrations occupy a length of 0.1mm-0.3mm from the edges of the two long sides of the steel mesh opening, and simultaneously penetrate into the middle along the width direction (the left serration penetrates into the right side, and the right serration penetrates into the left side), and the serrations of the two long sides are symmetric about the center line of the short side. When multiple pairs of V-shaped serrations are symmetrically arranged in the direction of the two long sides of the steel mesh opening, and multiple V-shaped serrations are uniformly arranged in the direction of a single long side, there is a certain gap between adjacent V-shaped serrations, the distance between the V-shaped serrations remains the same, and the length of the entire long side is evenly divided into several segments by the serrations.

[0026] This embodiment is an improvement on the previous one. In this embodiment, the chip surface is equipped with two pads, typically a positive and a negative elongated pad of the same size and shape. The positive and negative pads are parallel to each other with a certain gap and do not contact each other. To solder the two pads of the chip to the pads on the PCB board one-to-one, the stencil for printing solder paste is also designed with a pair of stencil openings that match the two pads of the chip. The gap between the two stencil openings in this pair of stencil openings is consistent with the gap between the positive and negative elongated pads, and their shapes and sizes correspond to the positive and negative elongated pads, respectively. The two stencil openings are the same size and shape, and the V-shaped serrations on their long sides are also distributed in the same way. The distribution of the V-shaped serrations in the stencil opening pair is described in detail below through an example:

[0027] like Figure 2 and Figure 3 ( Figure 3 for Figure 2 As shown in the enlarged schematic diagram at point A, there are 12 pairs of stencil openings arranged in a 3*4 array in the stencil body 1. Each pair of stencil openings corresponds to one positive pad and one negative pad of the chip. The two stencil openings in the same pair are the same size and have a small gap between them. The individual stencil opening 2 is basically long and narrow, but the two long sides are symmetrical comb-shaped with V-shaped serrations extending inward from the stencil body, occupying part of the area of ​​the long pad. There are 3 evenly distributed V-shaped serrations on each long side. The V-shaped serrations 3 extend from the stencil body at the location of the long side into the interior of the stencil opening. The V-shaped serrations on the two long sides are symmetrical about the center line of the short side and are evenly distributed. The distance between the tips of the two V-shaped serrations that are symmetrical on both sides of the center line of the short side is 0.2mm, that is, a width of 0.1mm is left on both sides of the center line of the short side to prevent the V-shaped serrations from extending in, so as to avoid affecting the flow and distribution of solder paste. When used for printing solder paste, each stencil opening prints solder paste onto the PCB board pad surface with symmetrical V-shaped notches on its two long sides. The width of the notches gradually expands from the central tip to the left and right sides, which helps air bubbles in the solder paste to be quickly discharged from the notches.

[0028] It should be noted that the above embodiments can be freely combined as needed. The above are merely preferred embodiments of this utility model. It should be pointed out that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this utility model, and these improvements and modifications should also be considered within the protection scope of this utility model.

Claims

1. A stencil for SMT soldering, characterized in that, include: The steel mesh body has a thickness of 0.04mm to 0.12mm; The stencil opening is used to adapt to the regular elongated pads on the chip surface. The stencil opening includes a long side direction and a short side direction. At least one V-shaped serration is provided in the long side direction, and the tip of the V-shaped serration extends from the stencil body at the edge of the long side inward. The area of ​​the stencil opening is not less than 85% of the area of ​​the corresponding elongated pad.

2. The steel mesh as described in claim 1, characterized in that, At least one pair of V-shaped serrations are symmetrically arranged along the two long sides of the opening of the steel mesh.

3. The steel mesh as described in claim 2, characterized in that, The steel mesh opening has multiple pairs of V-shaped saw teeth symmetrically arranged along its two long sides; and along a single long side, multiple V-shaped saw teeth are evenly arranged.

4. The steel mesh as described in any one of claims 1-3, characterized in that, The chip surface is provided with positive and negative long strip pads of the same size and shape, and the stencil body has regularly arranged pairs of stencil openings that match the chip pads.

5. The steel mesh as described in any one of claims 1-3, characterized in that, In each opening of the steel mesh, the length of the shorter side shall not exceed 0.8mm.

6. The steel mesh as described in any one of claims 1-3, characterized in that, The depth of the V-shaped serrations is less than half the length of the short side of the pad.

7. The steel mesh as described in any one of claims 1-3, characterized in that, The maximum width of the V-shaped saw teeth is 0.1mm to 0.3mm.

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