Microstrip surface mount high temperature solder joint laser welding method

Abstract

The present application relates to a kind of microstrip surface high temperature solder joint laser welding method, belong to laser welding technical field, solve the poor consistency of the weld appearance in prior art, poor welding uniformity, welding performance is poor, microstrip is easy to produce shedding, welding time is difficult to control, one of the problems such as strong dependence on operator.The present application discloses a kind of microstrip surface high temperature solder joint laser welding method, by the fixation of solder pad and to be welded piece, solder point coating, setting multiple welding process curve, automatic welding etc., realize the efficient welding of microstrip pad and antenna under high temperature environment, the weld appearance is highly consistent, welding uniformity is good, welding performance is excellent, welding process does not need to rely on operator, reduce production cost, improve production capacity while dehumanization.

Description

Technical Field

[0001] This invention relates to the field of laser welding technology, and in particular to a laser welding method for high-temperature solder joints of microstrip surface mounts. Background Technology

[0002] Soldering micro-sized high-temperature joints has always been a challenging problem in electrical assembly technology. Precise control of positional accuracy, soldering temperature, soldering time, and solder quantity is required to ensure reliable solder joint quality. Based on the product's structural characteristics, automated laser soldering equipment is currently the best solution. This method uses a laser as a heat source to heat the laser soldering paste. The laser radiates heat to the leads and pads, transferring heat to the substrate through the solder, reaching the solder's melting point temperature, and the solder wets and forms the solder joint. The laser spot area is adjustable, the heat field has minimal impact, the heating speed is fast, and it is a non-contact soldering method, widely used in the assembly of micro-joints and the soldering of substrate components in hard-to-reach areas.

[0003] As the application environment of existing dual-polarized antennas becomes increasingly demanding, the assembly requirements are mainly based on manual soldering. This is because the solder has a high melting point and poor solderability, and the aperture and pad size of the solder joints are limited by the structural space, making soldering difficult. Furthermore, the assembly ratio of this type of antenna is extremely sensitive to the solder joint morphology, and these factors restrict the assembly efficiency of such antennas.

[0004] The existing manual welding methods have drawbacks such as poor weld point morphology consistency, poor welding uniformity, poor welding performance, easy detachment of microstrip pads, difficulty in controlling welding time, and strong dependence on operators. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a laser welding method for high-temperature solder joints of microstrip surface mounts, in order 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] This invention discloses a laser welding method for high-temperature solder joints of microstrip surface mount devices, the specific steps of which are as follows:

[0007] S1: Align the workpiece to be welded using a fixing fixture and clamp it onto the welding equipment, making it close to the microstrip pad;

[0008] S2: Adjust the solder paste valve to dispense solder so that the solder paste width matches the size of the workpiece to be soldered and the microstrip pad, and apply solder dots to the workpiece to be soldered;

[0009] S3: In the process window interface of the automatic laser brazing equipment, the laser welding temperature and time are set in segments to form a welding process curve with gradual heating in multiple segments.

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

[0011] Specifically, the welding process curve is divided into five segments: welding at 200±10℃ for 1 second, welding at 220±10℃ for 1 second, welding at 245±10℃ for 5 seconds, welding at 260±10℃ for 0.5 seconds, and welding at 350±10℃ for 1.5 seconds.

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

[0013] Specifically, the morphology requirements for solder dotting in step S2 are as follows: the workpiece to be soldered is in close contact with the microstrip pad, the solder creep on both sides and the end of the workpiece to be soldered is not less than 1 / 2 of the height of the workpiece body, and the workpiece to be soldered has no overall offset relative to the microstrip pad.

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

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

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

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

[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 functions such as 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. Excellent welding uniformity and performance, preventing microstrip deformation and detachment. By setting multiple progressively increasing temperature curves, local overheating is effectively avoided, resulting in excellent welding uniformity and preventing microstrip deformation and detachment. Controllable multi-segment high-temperature welding is adopted, and at the connection between the brazing filler metal and the pad / workpiece, the IMC layer forms a uniform tin-silver alloy on the round copper wire side and a uniform tin-copper alloy on the pad side, resulting in strong welding and excellent welding performance.

[0022] 2. Excellent weld morphology consistency. By adjusting and fixing parameters such as the width of the solder outlet valve, spraying air pressure, and spraying time, the amount of solder applied is controllable, resulting in high consistency in solder width. Laser automated welding uses uniform welding temperature and time, and avoids traditional manual heat transfer, leading to better welding results and contributing to a uniform and aesthetically pleasing weld morphology. Therefore, the significantly improved weld morphology consistency is beneficial for antenna assembly in subsequent processes, increasing the assembly rate.

[0023] 3. Eliminating manual labor and improving production efficiency and weld yield. Traditional manual operations are highly dependent on human labor, and production efficiency and yield are limited by the operator's skills. Inconsistent weld joint morphology also restricts the consistency of antenna performance in subsequent assembly. The laser welding method disclosed in this invention can effectively avoid the above defects and achieve welding without manual labor.

[0024] 4. Saves labor costs, lowers the threshold for operators, and shortens the production cycle. Effectively reduces the dependence of the production unit on human resources for this process. What used to require 3 to 4 highly skilled workers can now be completed by 1 to 2 ordinary skilled operators, significantly shortening the production cycle and greatly improving controllability.

[0025] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0026] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0027] Figure 1 A schematic diagram of the laser welding method for high-temperature solder joints of microstrip surface mount devices;

[0028] Figure 2 This is a photograph of the workpiece to be welded after straightening in Example 1;

[0029] Figure 3 Photographs showing the solder dot coating morphology in Example 1;

[0030] Figure 4 This is a photograph of the weld morphology after welding in Example 1;

[0031] Figure 5 Metallographic image of the solder joint in Example 1;

[0032] Figure 6 Here is a SEM image of the solder joint in Example 1;

[0033] Figure 7 The image shows the welding morphology of Comparative Example 1.

[0034] Figure 8 This is a photograph of the welding morphology for Comparative Example 4. Detailed Implementation

[0035] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form 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 intended to limit the scope of the present invention.

[0036] This invention discloses a laser welding method for high-temperature solder joints of microstrip surface mounts.

[0037] Before performing specific welding operations, first select the appropriate solder based on the working environment of the welding point, and select the microstrip pad size based on the size of the workpiece to be welded.

[0038] The working environment of the solder joints is closely related to the choice of solder. For example, one important application of this invention is the soldering of microstrip pads for dual-polarized antennas. Given that the final product's working environment is approximately 290°C, to avoid secondary melting and failure of the solder joints, it is more reliable to choose solder with a liquidus temperature greater than 300°C when soldering the corresponding components. The size of the component and the microstrip pad can be selected according to actual needs.

[0039] The specific steps are as follows:

[0040] S1: Align the workpiece to be welded using a fixing fixture and clamp it onto the welding equipment, making it close to the microstrip pad;

[0041] S2: Adjust the solder paste valve to dispense solder so that the solder paste width matches the size of the workpiece to be soldered and the microstrip pad, and apply solder dots to the workpiece to be soldered;

[0042] S3: In the process window interface of the automatic laser brazing equipment, the laser welding temperature and time are set in segments to form a welding process curve with gradual heating in multiple segments.

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

[0044] In step S1, the conventional fixed fixtures that are currently widely used are used to straighten the weldment in advance, which can effectively improve the welding yield.

[0045] In step S2, the solder paste width is adjusted to ensure it fully covers the soldering body and the width and length of the pads. Otherwise, exposed solder joints are likely to occur, requiring rework. Matching the solder paste width to the dimensions of the workpiece and the microstrip pads ensures full, well-wetted solder joints and a more complete bond between the workpiece, pads, and solder. Due to the high melting point of solder and the microstrip shape of the pads, precise control of the solder is crucial to ensure consistent solder joint morphology; even slight deviations can significantly alter the morphology. This invention achieves consistent solder quantity control through adjustments to air pressure and application time, a standard industry practice. In this invention, a 0.3mm solder paste nozzle, an air pressure of 30–55 kPa, and an application time of 1.5 seconds are sufficient to meet the application requirements.

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

[0047] Experiments show that when the process curve has more than 5 segments, the effect is not significantly improved; when it has less than 5 segments, the heating effect is abrupt and the weld morphology deteriorates; the above welding process can achieve better weld morphology and welding effect.

[0048] The first two sections of this process curve are preheating, which reduces the temperature difference between the workpiece and the solder. The third section further preheats, activating the flux. The fourth section wets the solder pads and workpiece with flux, removing the oxide layer from their surfaces and enhancing the soldering effect. Since the solder begins to change its shape at 250℃, prolonged heating in this section can cause solder buildup and spatter; therefore, the temperature is directly raised to 260℃. In the fifth section, the temperature is raised to 350℃ to begin soldering. The solder liquefies and fuses with the solder pads and workpiece, forming an alloy at the contact surface. After thorough wetting, a qualified solder joint is formed. Because the solder pads are small, when the temperature exceeds 250℃ (i.e., the fourth and fifth sections of this process curve), the soldering time should not exceed 3 seconds to avoid damaging the pads. To ensure optimal soldering results and avoid undersoldering, the soldering time for the fourth section is set to 0.5 seconds, and the soldering time for the fifth section is set to 1.5 seconds.

[0049] Specifically, in step S2, the solder paste width is 0.4–0.45 mm. For common microstrip pads with a width of 0.3 mm, this solder paste width can completely cover the workpiece and the pad, avoiding insufficient or excessive solder.

[0050] Specifically, in step S2, the morphology requirements for solder dotting are as follows: the workpiece to be soldered is tightly attached to the microstrip pad; the solder creep on both sides and ends of the workpiece is not less than 1 / 2 of the height of the workpiece body; and the workpiece is not offset relative to the microstrip pad. If the workpiece is offset, the consistency of the solder joint morphology will deteriorate; if the workpiece is not completely attached to the pad, the solder will fill the unattached areas, resulting in missing solder in other areas, poor solder joint morphology, and affecting the soldering effect. The solder creep height setting on both sides and ends of the workpiece in this invention balances soldering performance and aesthetic soldering morphology.

[0051] Specifically, the liquidus temperature of the solder is greater than 300°C. One important application of this invention is the soldering of microstrip pads for dual-polarized antennas. Given that the final product's operating environment is approximately 290°C, to avoid secondary melting and failure of the solder joints, it is more reliable to select a solder with a liquidus temperature greater than 300°C when soldering the corresponding components.

[0052] Preferably, the solder is Sn5Pb. 95 Its liquidus temperature is 312℃. High-lead solder produces alloy solder joints with better wettability, more aesthetically pleasing morphology, and better quality.

[0053] Specifically, the microstrip pads are 1–3 mm long and 0.2–0.5 mm wide. The microstrip pads are generally made of gold-plated copper. This size range represents the optimal welding performance range for the welding method of this invention; exceeding this range may result in a decrease in welding performance. For example, the pad length can be 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, or 2.8 mm; the width can be 0.3 or 0.4 mm.

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

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

[0056] Specifically, the workpiece to be soldered 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 used for antenna assembly, and it is generally made of silver-plated copper. Exemplary copper wire diameters can 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, and 0.29 (unit: mm).

[0057] Specifically, the automatic laser brazing equipment is a laser brazing device with functions such as 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. Currently, such equipment is generally integrated and customized by relevant manufacturers according to the required functions and specific parameters, and the relevant processes are very mature. Laser brazing 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 requirements of this invention.

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

[0059] 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 operating environment of 300℃, select Sn5Pb solder alloy composition. 95 The liquidus temperature is 312℃.

[0064] Step 2: Select a microstrip pad that is 2mm long and 0.3mm wide, and make sure the laser spot size is the same as the pad size.

[0065] Step 3: Straighten the 0.2mm diameter round copper wire using a fixing fixture, and clamp it onto the welding equipment, making sure it is close to the microstrip pad.

[0066] Step four: On the laser equipment software interface, test and adjust the amount of solder paste applied to the fixed round copper wire. The application time is 1.5 seconds. While keeping the time constant, fine-tune the air pressure (30-55 kPa) until the solder paste width requirement is met. In this embodiment, the final solder paste width is adjusted to 0.4-0.45 mm.

[0067] Step 5: Apply solder paste, covering the round copper wires with solder paste, such as... Figure 3 As shown.

[0068] Step 6: Set the welding process curve into five segments, namely welding at 200±10℃ for 1 second, welding at 220±10℃ for 1 second, welding at 245±10℃ for 5 seconds, welding at 260±10℃ for 0.5 seconds, and welding at 350±10℃ for 1.5 seconds.

[0069] Step 7: Perform laser welding on the high-temperature solder joints of the microstrip surface mount according to the above process. The solder joint morphology is as follows. Figure 4 As shown.

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

[0071] Metallographic photographs such as Figure 5 As shown, the SEM image is as follows Figure 6 As shown, the inspected solder joints showed no abnormalities such as non-wetting or cracking. The tin-lead two-phase distribution and diffusion were uniform. The IMC layer formed a tin-silver alloy on the round copper wire side and a tin-copper alloy on the solder pad side. The IMC thickness was 0.2-0.5μm, and all had formed intermetallic compounds with uniform morphology.

[0072] The solder joint morphology was observed under a microscope (360-degree inspection) using a PCB inspection system with 100x magnification. The solder creep height on the side and end of the solder joint was not less than 1 / 2 of the body height. The solder joint body had no warping or displacement. The solder joint was well wetted with a wetting angle of no more than 30 degrees. There were no spikes or pinholes in the solder joint. There were no cracks at the junction of the microstrip and the substrate.

[0073] Comparative Example 1

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

[0075] like Figure 7 As shown, visual inspection reveals issues such as raw soldering, solder pad detachment, and solder ball splattering.

[0076] Comparative Example 2

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

[0078] Comparative Example 3

[0079] Adjust the solder paste width to 0.3mm, and the remaining steps and parameters are the same as in Example 1.

[0080] There is no solder between the solder pad and the solder joint, and no alloy layer has been formed, resulting in an unqualified solder joint. If the solder pad is too narrow, smaller than the diameter to be soldered, the solder joint quality will be poor, and the workpiece will easily break.

[0081] Comparative Example 4

[0082] The spraying air pressure was set to 20 kPa, and the time was 1 second. The remaining steps and parameters were the same as in Example 1. Figure 8 As shown, if the amount of solder is too small, the solder cannot completely cover the workpiece after soldering, and the solder height at the end and side of the workpiece is less than 1 / 3. This can result in substandard solder joints or even solder joint breakage.

[0083] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for laser welding high-temperature solder joints of microstrip surface mount devices, characterized in that, Includes the following steps: S1: Align the workpiece to be welded using a fixing fixture and clamp it onto the welding equipment, making it close to the microstrip pad; S2: Adjust the solder paste dispensing amount of the solder paste valve so that the width of the dispensing solder paste matches the size of the workpiece to be soldered and the microstrip pad, and apply solder to the workpiece; the liquidus of the solder is higher than the operating temperature of the product; use a 0.3mm solder paste nozzle, adjust the air pressure to 30-55kPa, and the dispensing time is 1.5s; the width of the dispensing solder paste in step S2 is 0.4-0.45mm; the solder creep on both sides and the ends of the workpiece to be soldered is not less than 1 / 2 of the height of the workpiece body; S3: In the process window interface of the automatic laser brazing equipment, the laser welding temperature and time are set in segments to form a welding process curve with gradual temperature increase in multiple segments; wherein, the size of the laser spot is consistent with the size of the microstrip pad; The welding process curve is divided into five segments, namely welding at 200±10℃ for 1 second, welding at 220±10℃ for 1 second, welding at 245±10℃ for 5 seconds, welding at 260±10℃ for 0.5 seconds, and welding at 350±10℃ for 1.5 seconds. S4: Perform micro-strip surface-mount high-temperature automatic laser welding on the workpiece according to the welding process curve; The solder is Sn5Pb. 95 Its liquidus temperature is 312℃.

2. The laser welding method for high-temperature solder joints of microstrip surface mount devices according to claim 1, characterized in that: The morphology requirement for the solder dot coating in step S2 is that the workpiece to be soldered is in close contact with the microstrip pad.

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

4. The laser welding method for high-temperature solder joints of microstrip surface mount according to claim 1, characterized in that: The microstrip pads are 1-3 mm long and 0.2-0.5 mm wide.

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

6. The laser welding method for high-temperature solder joints of microstrip surface mount devices 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.

7. The laser welding method for high-temperature solder joints of microstrip surface mount according to claim 1, characterized in that: The automatic laser brazing equipment is a laser brazing equipment with functions such as 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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