Was studied by metallography, scanning electron microscopy (sem) and tensile test USB connector laser brazing process parameters on the quality and strength of the joint connection. The results show that the laser from coke is 27.5 mm, current is 120 A, with the increase of pulse width joint strength increases first and then, when the pulse width range of 1.4 ~ 2.0 ms joint strength meet the industry standards, and when the pulse width is 1.7 ms joint maximum tensile force is 29.63 N. In laser from coke is 27.5 mm, width is 2.0 ms, with the increase of the electric current, the joint strength increased first and then, when the current range is 130 ~ 150 A joint strength meet the industry standards. The optimal welding parameters of metal components pin and conductor fully wetting by solder, solder splash and welds, less tin tin and even less defects.

Modern electronic products manufacturing, electronic components of connector pin (pin) and the connection between the conductor usually adopt the welding technical implementation. At present, the electronic product manufacturing technology is developing in the direction of the small, miniaturization. Traditional connection technology, such as tin tin welding, hot air welding, hot melt welding (hot bar), etc., usually small components and wire damage, is difficult to meet the welding operation of miniature electric connector. Many improvements in technology, using laser micro connections is a distinctive research direction, in recent years, with the introduction of laser soft soldering (laser Soldering). Commonly used connection technology usually lead to high rejection rate, and the use of the soft laser brazing solder joints with complete structure, strong and durable, good conductivity, etc. In the process of laser welding heat source local centralized heating by a laser beam to the workpiece, and can rapidly cooling after melting. Therefore laser soft soldering welding technology can meet the tiny core solder connection request, and can contribute to the organization of solder joint elaboration, has been a sharp increase in the mechanical properties of the solder joints.

USB cable in laser welding electric connector, copper wire and metal pipe connection after welding quality between the feet will greatly affect the quality of the USB signal transmission. Solder copper wire and the interface between the metal tube feet often. Welding defects, these defects and solder, welding process parameters, material composition and other factors. Therefore, you can through the research of welding technology and welding defects to analyze the reasons of the interface, and targeted to the whole optimization process, improve product quality. For laser welding electric connector, the main factor that affects the core solder joint quality is all kinds of welding process parameters, is one of the most important process parameters Light energy and welding time. Laser energy, which is decided by the laser current and pulse width of pulse width refers to maintain the length of the laser energy, pulse width, the greater the heat input welding process, the greater the size of solder joints with bigger. Laser from coke and welding protective gas can also affect the welding quality, including from coke determines the diameter of the laser beam of light and energy. Therefore it is necessary for the USB electric connector to do laser soft braze welding process test research.

This paper designed the pack card USB electric connector and wire welding jig, and has made the core of electric connector and tube feet after welding tensile test, to study the influences of laser parameters on the effect of welding, comparative and obtained the optimal welding process parameters. At the same time also to under the optimal process parameters of welding joint microstructure analysis, to explore the mechanism of the good joint properties.

1 Laser soft brazing fixture design

The laser brazing of the USB electric connector is an extremely fine process, both laser beam and core wire are millimeter level. In order to ensure the accuracy and stability of the laser welding process, a welding fixture is designed to fix the electronic connector and core wire. The specific design requirements are as follows:

1) The fixture must be able to effectively secure the connector to the core wire, allowing the metal pin to contact the front end of the core wire for easy welding;

2) There is a certain stability, can ensure that the welding core wire will not be loose, dislocation;

3) A window of about 1mm × 7mm is reserved for the incidence of laser beam to facilitate the laser beam to act on the core wire.

4) The electrical connector and the core wire can be easily installed and disassembled to improve efficiency.

According to the above requirements, the welding jig is designed. The overall structure is composed of 6 parts, namely core wire groove, cable press plate, upper and lower plates, electrical connector press plate, clip wire groove and push device. The cable press plate is used to keep the cable flat; The upper and lower plates can adjust the vertical position of the core wire and the metal pin; The electric connector press plate can ensure the connector is stable; The clamping groove is used to separate the core wires and make the front of each wire contact with the metal pin and fix it. The push device helps to remove the electrical connector after welding.

2 Soft laser brazing test

The test chose wuhan chutian laser (group) co., LTD. Production of Nd: YAG gx JHM - 1-400 - e pulse laser. The laser laser diameter, working current and pulse width adjustable, main parameters are shown in table 1. Test the USB electrical connector size of 14.2 mm x 7.0 mm x 4.5 mm, each electric connector requires welding metal tube with a total of 10 foot. Testing needs to be paired with electric connector 10 coaxial cables with pin for welding operation in turn. Electric connector metal foot width is 0.6 Mm, spacing of 0.8 mm. The laser beam on a narrow tube feet, so need to adjust the laser welding process to between 0.4 ~ 0.6 mm in diameter, both to ensure the welding effect, and won't ablation metal near the foot of PCB board. Test with seven conductor of the coaxial cable for copper, every seven core diameter is about 0.5 ~ 0.6 mm, and constitute a small cable insulation rubber package.

Before welding, the cable front 10 is needed Mm possible impurities of partial nephrectomy, and artificial stripping processing. The cable has been stripped conductor and electric connector metal tube feet clean with alcohol, to remove impurity and oil on the surface of the. The above stay before soldering tin welding materials, and then each conductor with fixture fixed and contact with the metal tube feet and filling flux. Using coaxial visual monitoring system to determine whether a laser speckle and good contact with core, adjust the good welding parameter can implement welding operation. Butt joint after the effective judgment, joint effectiveness judgment standard is: (1) after soldering tin pin point full; There is no solder paste in the front end of the welded pin; After welding, the welding interface does not produce too much tin beads; (4) there is no joint with tin and less tin defects.

The test was divided into groups A and B, with 10 effective welded joints in each group, respectively using different laser soft brazing process parameters. Group B, the coke quantity to 27.5 mm, width 2.0 ms, variables for the current, a. to test by tensile test of welded joint of two groups, using automatic hydraulic servo universal testing machine, testing mechanical properties of solder joints, stretching rate in the tensile test samples are set to 10 mm, min ¹ . Scanning electron microscopy (SEM) analysis was carried out on the welded joint, to observe the study the microscopic structure.

3 Results and analysis

3.1 Analysis of joint mechanical properties

Tensile test is designed to measure the maximum tensile strength of welding joint of two groups, in order to determine the process parameters of mechanical properties after welding joint whether meet the industry standards. According to the standard stipulated in the USB electric connector industry, need A connector to withstand A tensile force should be 20 or more N, and the static suspension time not less than 1 min. The tensile test of A and B group joint on the maximum tensile force.

A, B group of experiments the influence of process parameters on the solder joint maximum tensile force. In group A, from the coke with constant current and pulse width change of circumstances, can make the solder joint mechanical performance meet the industry standards of pulse width in the range of 1.4 ~ 2.0 ms, and within the scope of the pulse width of solder joint can withstand tensile force of not less than 20 N. If gradually enhance the value of pulse width, solder joint maximum tensile force will increase when the pulse width up to 1.7 ms, solder joint maximum tensile force increases to 29.63 N. Then continue to ascend pulse width value, solder joints of maximum tensile force will gradually decline, until the laser energy is too high, interrupt conductor. In group B, the amount of coke and the pulse width is constant, the current change of circumstances, can make the solder joint mechanical performance meet the industry standards of current in the range of 130 ~ 150 A, within the scope of the solder joint can withstand tensile force of not less than 20 N. If A gradual increase in current value, in the current 130 A, conductor of the solder joint will obtain the best mechanical properties; If the current value continues to increase, the maximum tensile force of the solder joint will gradually decrease, and even when the current is greater than 150 A, the laser beam energy is too large and the core wire is directly fused.

In conclusion, the optimal technological parameters of laser-capable soft brazing were obtained by group A and group B tests, that is, the defocusing amount was 27.5mm, the current was 120a, the pulse width was 1.7ms, and the maximum tensile force of the joint welding spot was 29.63n.

3.2 Joint morphology analysis

Welding test of some process parameters under the welded joint are found in weld defects, through the analysis of the solder joint were observed on the welding joint, found in solder joints defects such as solder splash, tin tin and even less. A coke deposition process parameters in the 27.5 mm, the current 120 a, pulse width 2.1 ms under joint weld defects, and the parameters of joint mechanical performance is unqualified. B for the parameters of welded joint fracture morphology in the tensile test of welded joint can be found in the tensile test fracture in interface layer, show that the joint interface intermetallic compounds (intermetallic Due to the high concentration of laser beam energy in laser soft brazing, the welding temperature increases rapidly, which will increase the dissolution and diffusion rate of Cu in the metal pin in the molten solder. And in the study of Sn content in the use of lead-free solder is higher than Sn, Pb solder and Cu melt and diffusion rate can be increased. Both increases the solder and the interface between the metal tube feet formation rate of IMC. Generally speaking, a small amount of IMC is formed between filler metals and metal tube feet can increase solder on the substrate wetting, enhance the adhesion strength of the solder, but due to the intrinsic brittleness IMC, with the increase of the thickness of the IMC, the mechanical properties of joint will be severely weakened, lead to solder joint failure ahead of time. Therefore, the process parameters under a thick IMC interface layer has weakened the tensile properties of the joint, joint mechanical performance is unqualified.

Is the optimal process parameters (defocus 27.5 mm, current 120 A, pulse 1.7) Ms) of the electric connector welded specimen. After soldering tin metal tube feet point even full, almost no PCB solder splash, tin tin and even less phenomenon, joint welding effect is better. The internal distribution of copper wire is in good condition, is located in the joint as a whole, not obvious deviation, completely after molten solder around the wire, and closely integrated with the solder joint integrity interface, the overall state of a semicircle or approximate circle. At the interface between IMC, metal tube feet interface clear, complete with brazing material not found not welded or not melting phenomenon, show that metal tube feet and core fully wetting by the molten solder in welding, with good metallurgical bonding .

4 conclusion

1) A reasonable positioning mechanism and welding jig are designed, which can effectively fix the USB electric connector and the core wire and prevent the core wire from loosening during welding.

2) In laser from coke and current under the condition of constant value (120 A) from focal measured 27.5 mm, current, pulse width when the range of 1.4 ~ 2.0 ms joint strength meet the industry standards, the maximum when the pulse width is 1.7 ms joint maximum tensile force 29.63 N. In the laser from coke and pulse width is fixed value (27.5 mm from the coke, pulse width 2.0 ms), when the current range is 130 ~ 150 A joint strength meet the industry standards.

3) The optimal welding technological parameters (27.5 mm of coke, the current 120 A, pulse width 1.7 ms) of the electric connector welding effect is better, the metal Pin and joint core fully wetting by solder, solder splash, happen less and less tin and tin defect. And not qualified under the technological parameters of weld defects is serious, and solder joints on tensile test interruption in the IMC interface layer.