| Electronic manufacturing continues to develop in small quantities and diversified ways,which requires the process of electronic manufacturing to be more flexible.As a kind of surface array package which is widely used,the ball grid array packaging is also facing more and more problems of flexible ball planting.The current BGA welding process,there are some unstable factors,easily lead to welding failure;second,because the chip temperature rise,circuit board aging,external shocks and other factors,resulting in defects of solder ball holes,originally existing solder joint offset,coplanarity poor evolved into the chip and PCB circuit board connection is destroyed.These chips can be more efficient and economical to solve the problems of BGA chips in small batch,stable and rapid re implantation.Single point and multi-point existing ball planting methods,planting the corresponding equipment are difficult to meet the flexibility,stability and low cost,this article from the flexible reballing process of design,a new method of industrial robot ball.The new ball planting method is modeled on the FDM technology,the use of solder wire instead of solder and solder paste as a solder ball in the process of melt molding become balls required for solder ball,called the molten tin wire ball method.The ball grafting method can better adapt to the BGA chip with wider diameter of the welding pad,and has the unique characteristics of the solder specifications.The application of this method to the design of the ball robot pad corresponding BGA chip is characteristic of rectangular array,the movement structure of rectangular coordinates,and equipped with the ability to meet the needs of the flexible ball ball system and visual system,the automatic completion of various specifications of BGA ball as the goal,to expand the research and design on the robot.The movement system structure design,using X,Z two axis linkage and individual movement Y axis layout mode,the 42 BYGH hatchback phase hybrid stepping motor through Aluminum Alloy winding coupling,to drive the ends of radial fixed trapezoidal screw rotation,with driving nut consumption difference function of linear motion at trapezoidal screw,thus driving the melting execution device or BGA chip fixture reaches the designated position coordinates system.The DRV8825 integrated motor driver chip as the stepper motor drive in motion control system,high precision to achieve 32 times subdivision drive;the stroke switch adopts EE-SX674-WR type photoelectric switch OMRON,so as to ensure the motion mechanism in various directions of accurate location and spacing.In the design of ball system,the clamping mechanism of BGA chip is used to connect the spring clamp clamping screw top and slider,makes the clamping mechanism drive motor has enough time to avoid blocking change phenomenon,also can according to the operating current of the motor to control the spring tension force;four the connecting rod lifting mechanism of BGA chip fixture by the parallelogram lifting action to drive the chip platform,the use of photoelectric switches to sense the target chip vegetation sphere,thereby positioning chip platform height.Cleaning device using sponge roller to clean the nozzle on the residual liquid tin,the use of wire rod as the rotating shaft to drive the tank frame,which will sink to complete lifting and rotating movement from the device,convenient maintenance personnel to clean the sink.The feeding device is provided with a gripping and releasing mechanism,and the shaft ends of the roller wheels used for placing the solder wire rolls are fixed and moved so as to facilitate the replacement of the solder wire rolls.The remote feeding device uses 1:8's small teeth difference planetary reducer to improve the wire feed accuracy.The two sides of the friction feeding wheel are equipped with photoelectric sensors to induce the penetration of the solder wire and the position in the material tube.Installed in the heating aluminum block on the electric heating wire and a thermistor to control and detect the melt temperature of the cavity melt actuating device,the heating aluminum block is installed above the radiator,while using Teflon as the connector,thereby preventing solder wire in the tube material due to thermal deformation of pipe blockage.In the design of the visual system,lighting on chip LED light source low angle mounting pad,using 1/6 inch 3.6mm lens with OV7670 CMOS sensor to shoot BGA chip;in order to match the AVR data transmission speed of MEGA128 MCU and CMOS sensor,the use of the model as a buffer for the FIFO memory chip AL422B;use the SD card to expand the microcontroller in the image storage capacity.Image processing and analysis of the hardware platform based on PC,to run the image data processing program and image feature analysis procedures for processing and analysis of the BGA chip pad features,then generate reballing robot action G-Code.In the control system,the control board with AVR MEGA32 as the core and the communication mainboard with AVR MEGA128 as the core are responsible for the action and communication of the robot.The control board has four DC motor drive circuit,four stepper motor drive circuit,temperature measurement circuit and 12 V driving circuit;Wi-Fi circuit with LCD,human-computer interaction module,USB serial communication circuit and CMOS circuit board,a communication unit ball robot.The closed loop control of temperature of melt molding,the NTC thermistor is used in the control system of the resistance temperature curve,using LabVIEW graphical programming method,the parameters of the fitted equations were calculated,obtained 200 degrees error fitting curve of 7.25%;the use of critical proportion method,the PID controller on the temperature of melt molding proportional integral differential parameters are set,and have a good step response.The characteristics of BGA pad extraction procedures,using C++ language based on OpenCV the preliminary design of the BGA pad features extraction procedures,Canny edge detection to get the contour of form of circle Hough transform to extract the circular feature pad has a great influence;thus adding morphological filtering in open operation improved Hough circle transformation can extract the circular feature number and size consistency.In order to evaluate the ball planting quality of the ball bearing robot,a method of evaluating the shape of BGA welding ball was found out by referring to the ball implant defect detection technology of BGA ball mill.This circular feature evaluation method through the quantitative ring lighting mode of solder ball,so the statistics feature vector of BGA ball shape,and then through the standard features and potential defects of known vector comparison,get the percentage deviation of the feature vector,and then get the target defect trends of BGA solder ball shape,and the relative possibility of occurrence. |
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