Micro-strip surface-mounted high-temperature welding spot laser welding method

Abstract

The invention relates to a micro-strip surface-mounted high-temperature welding spot laser welding method, belongs to the technical field of laser welding, and solves one of the problems that in the prior art, welding spots are poor in morphology consistency, welding uniformity and welding performance, a micro-strip is prone to falling off, welding time is difficult to control, and dependence on operators is high. According to the micro-strip surface-mounted high-temperature welding spot laser welding method, efficient welding of a micro-strip welding pad and an antenna in a high-temperature environment is achieved through the steps of fixing of the welding pad and a to-be-welded part, spot coating of welding flux, setting of a multi-section welding process curve, automatic welding and the like, the welding spots are highly consistent in morphology, welding uniformity is good, and welding performance is excellent; and the welding process does not depend on operators, so that the production cost is reduced, and the production capacity is improved while manual operation is removed.

Description

Technical Field

[0001] The invention relates to the technical field of laser welding, and in particular to a microstrip surface mounted high temperature solder joint laser welding method. Background Art

[0002] The welding of micro-high-temperature solder joints has always been a difficult problem in electrical assembly technology. Position accuracy, welding temperature, welding time, solder quantity, etc. all require precise control to ensure the quality of the solder joints. According to the structural characteristics of the product, the use of automatic equipment for laser soldering is currently the best solution. This method is a laser welding technology that uses laser as a heat source to heat the laser soldering solder paste. Using the laser as a heat source, the leads and pads are radiated, and heat is transferred to the substrate through the solder, thereby reaching the soldering melting point temperature, and the solder is wetted to form solder joints. The spot area is adjustable, the heat area has little impact, the heating speed is fast, and it is non-contact welding. It is widely used in the assembly of tiny solder joints and the welding of substrate devices in difficult-to-reach areas.

[0003] The assembly requirements of existing dual-polarized antennas are constantly increasing with the application environment of the products. The solder joints are mainly welded by hand, because the melting point of the solder is high, the solderability is poor, and the solder joints are affected by the structure space, the aperture and the pad are limited, so the welding is difficult. In addition, the assembly rate of such antennas is extremely sensitive to the morphology of the solder joints. Many factors restrict the assembly efficiency of such antennas.

[0004] The manual welding method used in the existing technology has the disadvantages of poor consistency of solder joint morphology, poor welding uniformity, poor welding performance, easy detachment of microstrip pads, difficult to control welding time, and strong dependence on the operator. Summary of the invention

[0005] In view of the above analysis, an embodiment of the present invention aims to provide a microstrip surface mount high temperature solder joint laser welding method to solve one of the problems of inconsistent solder joint morphology, poor welding uniformity, poor welding performance, easy curling of microstrips, and strong dependence on operators.

[0006] The present invention discloses a microstrip surface mount high temperature solder joint laser welding method, the specific steps of which are:

[0007] S1: Align the workpiece to be welded through the fixed fixture and clamp it on the welding equipment, close to the microstrip pad;

[0008] S2: adjusting the tin discharge amount of the solder paste valve so that the width of the solder paste discharge matches the size of the workpiece to be welded and the microstrip pad, and applying solder to the workpiece to be welded;

[0009] S3: In the process window interface of the automatic laser brazing equipment, the laser welding temperature and time are set in sections to form a multi-section gradually increasing temperature welding process curve;

[0010] S4: performing microstrip surface mount high-temperature automatic laser welding on the workpiece to be welded according to the welding process curve.

[0011] Specifically, the welding process curve is divided into five sections, which are welding at 200±10°C for 1s, welding at 220±10°C for 1s, welding at 245±10°C for 5s, welding at 260±10°C for 0.5s and welding at 350±10°C for 1.5s.

[0012] Specifically, the width of the solder paste in step S2 is 0.4-0.45 mm.

[0013] Specifically, the morphology requirements of the solder dot coating in step S2 are that the workpiece to be welded is in close contact with the microstrip pad, the tin creeping on both sides and ends of the workpiece to be welded is not less than 1 / 2 of the height of the workpiece body to be welded, and the workpiece to be welded has no overall offset relative to the microstrip pad.

[0014] Specifically, the liquidus of the solder is greater than 300°C.

[0015] Preferably, the solder is Sn5Pb 95 , its liquidus is 312℃.

[0016] Specifically, the microstrip pad has a size of 1 to 3 mm in length and 0.2 to 0.5 mm in width.

[0017] Specifically, the microstrip pad has a size of 2 mm in length and 0.3 mm in width.

[0018] Specifically, the workpiece to be welded is a round copper wire with a diameter of 0.15 to 0.3 mm.

[0019] Specifically, the automatic laser brazing equipment is a laser brazing equipment with the functions of process parameter setting, automatic solder paste spraying, automatic temperature measurement, automatic temperature control, automatic welding, automatic flow connection between processes, and real-time monitoring of the process.

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0021] 1. Good welding uniformity and welding performance, the microstrip is not easy to deform and fall off. By setting a multi-stage gradual heating curve, local overheating can be effectively avoided, so the welding uniformity is good, and the microstrip is not easy to deform or fall off; using controllable multi-stage high-temperature welding, the IMC layer generates a uniform tin-silver alloy on the round copper wire side and a uniform tin-copper alloy on the pad side at the connection between the solder and the weldment, so the welding is firm and the welding performance is good.

[0022] 2. Good consistency of welding morphology. By adjusting and curing the width of the tin valve, spraying air pressure, spraying time and other parameters, the amount of solder coating can be controlled and the solder width consistency is high; laser automatic welding uses a unified welding temperature and time, and laser welding avoids traditional manual contact heat transfer, the welding effect is better, and it helps to form a uniform and beautiful welding morphology. Therefore, the consistency of welding morphology is greatly improved, which is conducive to the assembly of antennas in subsequent processes and improves the matching rate.

[0023] 3. Eliminate manual labor, improve production efficiency and weld yield rate. Traditional manual operation is highly dependent on people, and production efficiency and yield rate are limited by the operator's production skills. The uneven morphology of the welds also restricts the consistency of the performance of the subsequent assembled antenna. The laser welding method disclosed in the present invention can effectively avoid the above defects and realize the elimination of manual labor in welding.

[0024] 4. Save labor costs, lower the threshold for operators, and shorten the production cycle. Effectively improve the dependence of the production unit on people in this process. The work that previously required 3 to 4 highly skilled personnel can now be completed by 1 to 2 operators with ordinary skills. The production cycle is significantly shortened and the controllability is greatly improved.

[0025] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0027] Figure 1 It is a schematic diagram of the process of laser welding method for microstrip surface mounted high temperature solder joints;

[0028] Figure 2 This is a photo of the welded parts after straightening in Example 1;

[0029] Figure 3 This is a photo of the solder spot coating morphology of Example 1;

[0030] Figure 4 This is a photo of the solder joint morphology after soldering in Example 1;

[0031] Figure 5 This is the metallographic image of the solder joint of Example 1;

[0032] Figure 6 This is a SEM photo of the solder joint of Example 1;

[0033] Figure 7 This is a welding morphology photo of Comparative Example 1;

[0034] Figure 8 This is a welding morphology photograph of Comparative Example 4. DETAILED DESCRIPTION

[0035] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0036] The invention discloses a microstrip surface-mount high-temperature solder point laser welding method.

[0037] Before implementing a specific welding operation, first select the appropriate solder according to the working environment of the solder joint, and select the size of the microstrip pad according to the size of the workpiece to be welded.

[0038] The working environment conditions of the solder joint are closely related to the selection of solder. For example, an important application scenario of the present invention is the welding of the microstrip pad of the dual-polarized antenna. Given that the working environment of the final product is about 290°C, in order to avoid secondary melting failure of the solder joint, it is more reliable to select solder with a liquidus greater than 300°C when welding the corresponding weldment. The size of the weldment and the size of the microstrip pad can be selected according to actual needs.

[0039] The specific steps are:

[0040] S1: Align the workpiece to be welded through the fixed fixture and clamp it on the welding equipment, close to the microstrip pad;

[0041] S2: adjusting the tin discharge amount of the solder paste valve so that the width of the solder paste discharge matches the size of the workpiece to be welded and the microstrip pad, and applying solder to the workpiece to be welded;

[0042] S3: In the process window interface of the automatic laser brazing equipment, the laser welding temperature and time are set in sections to form a multi-section gradually increasing temperature welding process curve;

[0043] S4: performing microstrip surface mount high-temperature automatic laser welding on the workpiece to be welded according to the welding process curve.

[0044] In step S1, the weldment is straightened in advance by using conventional fixed tooling that is currently widely used, which can effectively improve the welding yield rate.

[0045] In step S2, by adjusting the tin outlet width of the solder paste valve, the solder paste width can fully cover the width and length of the welding body and the pad, otherwise it is very easy to cause exposed solder joints and rework. By matching the solder paste outlet width with the size of the workpiece to be welded and the microstrip pad, the solder joint is full and well wetted, and the weldment, pad and solder are more fully combined. Since the solder has a high melting point and the pad is in the shape of a microstrip, in order to ensure the consistency of the solder joint morphology, the precise control of the solder cannot be ignored, and a slight deviation will cause a large change in the morphology. The present invention achieves consistent control of the amount of tin by adjusting the air pressure and the spot coating time. This control method is a conventional adjustment operation in the industry. In the present invention, a 0.3mm solder paste needle is selected, the air pressure is adjusted to 30-55kPa, and the spot coating time is 1.5s to meet the spot coating requirements.

[0046] Specifically, in step S3, the welding process curve is divided into five sections, which are welding at 200±10℃ for 1s, welding at 220±10℃ for 1s, welding at 245±10℃ for 5s, welding at 260±10℃ for 0.5s and welding at 350±10℃ for 1.5s.

[0047] Experiments show that when the process curve has more than 5 sections, the effect is not significantly improved; when the process curve has less than 5 sections, the temperature rise effect is abrupt and the welding morphology deteriorates; through the above welding process, better welding morphology and welding effect can be obtained.

[0048] The first two sections of this process curve are basic preheating, which makes the temperature difference between the weldment and the solder smaller; the third section is further preheating to activate the flux; the fourth section realizes the wetting of the solder pad and the weldment by the flux, and the wetting process can remove the oxide layer on the surface of the solder pad and the weldment to achieve the purpose of enhancing the welding effect. Since the solder at 250℃ begins to change its shape, too long a temperature in this section will cause solder accumulation and solder splashing, so the temperature is directly raised to 260℃; in the fifth section, the temperature is raised to 350℃ to start welding, and the solder liquefies and merges with the solder pad and the weldment, forming an alloy on the contact surface, and becomes a qualified solder joint after sufficient wetting. Because the pad is small, when the temperature is greater than 250℃ (i.e., the fourth and fifth sections of this process curve), in order to avoid damage to the pad, the welding time should not exceed 3s; and in order to ensure the best welding effect and avoid raw welding, the welding time of the fourth section is set to 0.5s, and the welding time of the fifth section is set to 1.5s.

[0049] Specifically, in step S2, the solder paste width is 0.4-0.45 mm. For a common microstrip pad with a width of 0.3 mm, the solder paste width can completely cover the workpiece to be welded and the pad, avoiding too little or too much solder.

[0050] Specifically, in step S2, the morphology requirements of the solder dot coating are: the workpiece to be welded is in close contact with the microstrip pad, the tin creeping on both sides and the end of the workpiece to be welded is not less than 1 / 2 of the height of the body of the workpiece to be welded, and the workpiece to be welded has no overall offset relative to the microstrip pad. If the weldment is offset, the consistency of the solder joint morphology will deteriorate; if the weldment is not completely in close contact with the pad, the solder will be filled in the unclosed part, resulting in the lack of solder in other parts, poor solder joint morphology and affecting the welding effect. The tin creeping height setting on both sides and the end of the workpiece to be welded of the present invention takes into account both welding performance and welding morphology aesthetics.

[0051] Specifically, the liquidus of the solder is greater than 300° C. An important application scenario of the present invention is the welding of dual-polarized antenna microstrip pads. Given that the working environment of the final product is about 290° C., in order to avoid secondary melting failure of the solder joint, it is more reliable to select a solder with a liquidus greater than 300° C. when welding the corresponding weldment.

[0052] Preferably, the solder is Sn5Pb 95 , and its liquidus is 312°C. The alloy solder joints produced by high-lead solder and pads and weldments have better wettability, more beautiful solder joint morphology, and better solder joint quality.

[0053] Specifically, the size of the microstrip pad is 1 to 3 mm long and 0.2 to 0.5 mm wide. The microstrip pad is generally made of copper-plated gold. This size range is the optimal welding performance range of the welding method of the present invention. If it exceeds this range, the welding performance may decrease. Exemplarily, the pad length can be 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8 (unit: mm); the width can be 0.3, 0.4 (unit: mm).

[0054] It is worth emphasizing that the laser spot size should be consistent with the pad size, and it is not advisable to set a too small spot. If the spot is too small, it will lead to reciprocating welding, which may easily cause solder joint delamination, raw welding, and incomplete wetting.

[0055] Specifically, the microstrip pad has a size of 2 mm in length and 0.3 mm in width.

[0056] Specifically, the workpiece to be welded is a round copper wire with a diameter of 0.15 to 0.3 mm. The diameter of the round copper wire is a common size for antenna assembly, generally made of copper plated with silver, and exemplary copper wire diameters may be 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29 (unit: mm).

[0057] Specifically, the automatic laser brazing equipment is a laser brazing equipment with the functions of process parameter setting, automatic solder paste spraying, automatic temperature measurement, automatic temperature control, automatic welding, automatic flow connection between processes, and real-time monitoring of the process. At present, such equipment is generally integrated and customized by relevant manufacturers according to the required functions and specific parameters, and the relevant process is very mature. For example, laser welding integration manufacturers such as Han's Laser Technology Industry Group Co., Ltd. and Shenzhen Aibet Electronic Technology Co., Ltd. can provide customized equipment that meets the implementation requirements of the present invention.

[0058] Preferred specific embodiments and comparative examples of the present invention are as follows:

[0059] The general parameter settings are shown in Table 1:

[0060] Table 1 General parameter settings

[0061]

[0062] Example 1

[0063] Step 1: For the dual-polarized antenna working environment at 300°C, select the solder alloy composition as Sn5Pb 95 , liquidus 312℃.

[0064] Step 2: Select a microstrip pad with a length of 2 mm and a width of 0.3 mm. The laser spot size should be the same as the pad size.

[0065] Step 3: Straighten the round copper wire with a diameter of 0.2 mm through a fixing fixture, and clamp it on the welding equipment, close to the microstrip pad.

[0066] Step 4: Test and adjust the amount of solder paste applied to the fixed round copper wire in the laser equipment software interface. The application time is 1.5s. The air pressure is fine-tuned (30-55kPa) without changing the time until the solder paste width requirement is met. In this embodiment, the solder paste width is finally adjusted to 0.4-0.45mm.

[0067] Step 5: Apply solder paste. The round copper wire is covered with solder paste. Figure 3 shown.

[0068] Step six, set the welding process curve into five sections, namely welding at 200±10℃ for 1s, welding at 220±10℃ for 1s, welding at 245±10℃ for 5s, welding at 260±10℃ for 0.5s, and welding at 350±10℃ for 1.5s.

[0069] Step 7: Laser weld the microstrip surface mount high temperature solder joints according to the above process. Figure 4 shown.

[0070] According to IPC-TM-650 and GB / T 16594-2008, a professional testing agency was commissioned to observe the solder joints of this embodiment using a metallographic microscope and measure the thickness of the IMC using a SEM.

[0071] Metallographic photos such as Figure 5 As shown in the SEM photos Figure 6 As shown, the inspected solder joints have no abnormalities such as non-wetting and cracking, the tin-lead two phases are evenly distributed and diffused, the IMC layer generates tin-silver alloy on the round copper wire side, and tin-copper alloy on the pad side. The IMC thickness is 0.2-0.5μm, and intermetallic compounds have been formed with uniform morphology.

[0072] The solder joint morphology is observed at 100 times magnification through the printed circuit board inspection system microscope inspection (360-degree inspection is possible). The tin creeping height on the side and end of the weld is not less than 1 / 2 of the body height. The weld body has no warping or offset. The solder joint is well wetted with a wetting angle of no more than 30 degrees. There are no pull tips or pinholes in the solder joint, and there is no crack at the junction of the microstrip and the substrate.

[0073] Comparative Example 1

[0074] The process curve is set to two sections, and the specific parameters are: welding at 210±10°C for 2.5s and welding at 315±10°C for 4.5s; the remaining steps and parameters are the same as those in Example 1.

[0075] like Figure 7 As shown in the figure, visual observation revealed raw soldering, pad detachment, and tin bead splashing.

[0076] Comparative Example 2

[0077] The spot size was set to 0.3*1 mm, and the remaining steps and parameters were the same as those in Example 1. Visual observation showed reciprocating welding, and the solder joints showed slight delamination and complete wetting.

[0078] Comparative Example 3

[0079] The solder paste width was adjusted to 0.3 mm, and the remaining steps and parameters were the same as those in Example 1.

[0080] There is no solder between the welding pad and the welding pad, no alloy layer is formed, and the welding joint is unqualified. The welding pad is too narrow, smaller than the diameter to be welded, the welding joint quality is poor, and the weldment is easy to break.

[0081] Comparative Example 4

[0082] The spraying pressure was set to 20 kPa, the time was set to 1 s, and the remaining steps and parameters were the same as those in Example 1. Figure 8 As shown, the amount of tin output is too small, the solder cannot completely cover the weldment after welding, the tin creeping height of the weldment end and side is less than 1 / 3, and the solder joint is unqualified and may even cause the solder joint to open.

[0083] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A microstrip surface mount high temperature solder joint laser welding method, characterized in that: The steps include: S1: Align the workpiece to be welded through the fixed fixture and clamp it on the welding equipment, close to the microstrip pad; S2: adjusting the tin discharge amount of the solder paste valve so that the width of the solder paste discharge matches the size of the workpiece to be welded and the microstrip pad, and applying solder to the workpiece to be welded; S3: In the process window interface of the automatic laser brazing equipment, the laser welding temperature and time are set in sections to form a welding process curve with multiple sections of gradually increasing temperature; S4: performing microstrip surface mount high-temperature automatic laser welding on the workpiece to be welded according to the welding process curve.

2. The microstrip surface mount high temperature solder joint laser welding method according to claim 1, characterized in that: The welding process curve is divided into five sections, which are welding at 200±10°C for 1s, welding at 220±10°C for 1s, welding at 245±10°C for 5s, welding at 260±10°C for 0.5s and welding at 350±10°C for 1.5s.

3. The microstrip surface mount high temperature solder joint laser welding method according to claim 1, characterized in that: The width of the solder paste in step S2 is 0.4 to 0.45 mm.

4. The microstrip surface mount high temperature solder joint laser welding method according to claim 1, characterized in that: The morphology requirements of the solder dot coating in step S2 are: the workpiece to be welded is in close contact with the microstrip pad, and the tin creeping on both sides and ends of the workpiece to be welded is not less than 1 / 2 of the height of the body of the workpiece to be welded.

5. The microstrip surface mount high temperature solder joint laser welding method according to claim 1, characterized in that: The liquidus of the solder is greater than 300°C.

6. The microstrip surface mount high temperature solder joint laser welding method according to claim 1, characterized in that: The solder is Sn5Pb 95 , its liquidus is 312℃.

7. The microstrip surface mount high temperature solder joint laser welding method according to claim 1, characterized in that: The microstrip pad has a length of 1 to 3 mm and a width of 0.2 to 0.5 mm.

8. The microstrip surface mount high temperature solder joint laser welding method according to claim 1, characterized in that: The microstrip pad has a length of 2 mm and a width of 0.3 mm.

9. The microstrip surface mount high temperature solder joint laser welding method according to claim 1, characterized in that: The workpiece to be welded is a round copper wire with a diameter of 0.15 to 0.3 mm.

10. The microstrip surface mount high temperature solder joint laser welding method according to claim 1, characterized in that: The automatic laser brazing equipment is a laser brazing equipment with the functions of process parameter setting, automatic solder paste spraying, automatic temperature measurement, automatic temperature control, automatic welding, automatic flow connection between processes, and real-time monitoring of the process.

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