Parallel seam welder is used to package integrated circuit chips. At present, the equipment used to package integrated circuit chips in China basically comes from the United States, Japan and other countries, which is expensive. Therefore, it is of far-reaching significance to make it localization and low price.
1. Main components and functions of the system
The system consists of upper computer (PC) and lower computer (single chip microcomputer). The hardware structure is shown in Figure 1.
The upper computer (PC) software adopts visual programming language VB6 0 development, using MSComm control to complete the data communication between PC and MCU, and transmit control information, status information and welding parameters; And using VB6 0 has the ability to operate various databases to realize the humanization of welding. The lower computer (single chip microcomputer) receives the command sent by the PC through the serial interface, starts the working program, and controls six stepping motors (including two X-axes, one Y-axis and two Z-axes) to rotate θ One shaft), which converts the angular displacement of the motor into linear displacement through the lead screw, drives the welding electrode to run according to the designed track, and transmits the current running state to the PC in real time. The main functions of the system include:
① The upper computer monitors the working state of the lower computer in real time and controls the working process of the lower computer; Set the working parameters of the lower computer, receive and send data information, control information and status information; Record the welding parameters of the history chip; When the system is powered on again, the latest welding parameters will be taken as the default value of this welding parameter; Conduct data processing, display data and working status, and guide the operation process;
② The lower computer controls the operation of 6 stepping motors and finally controls the movement of welding electrodes; Control the welding power and realize intermittent control; Realize the fine adjustment of welding electrode.
③ The accuracy of each welding axis direction of the system shall not be less than 0.1mm.
2. System resource utilization and communication mechanism
2.1 utilization of system resources
In order to make full use of the powerful data processing ability and massive storage space of PC and effectively play the role of MCU data memory, system resources must be allocated reasonably. One of the specific methods is that when sending welding data, the PC converts the welding parameters stored in floating point numbers into pulse numbers according to the step angle and lead screw ratio of the stepping motor and sends them to the single chip microcomputer; Second, when the number of bits occupied by the number of pulses is slightly greater than n bits of single byte integer times, on the premise of meeting the accuracy requirements, there are: the transmitted data = original data / 2n. At this time, the transmitted data is rounded. After the single chip microcomputer receives the integer data, the real data can be restored by moving n bits to the left. This not only improves the communication efficiency, but also reduces the occupation of MCU ram.
2.2 system communication protocol
The baud rate is set to 4800bps; The data frame structure is set as: start bit 1bit, data bit 8bit and stop bit 1bit.
The information package sent by PC to MCU includes data information package and control information package. The data packet structure is: it starts with “s” character, followed by 22 byte hexadecimal number. When sending, it is sent in ASCII code format (text format), and 44 ASCII codes are actually sent. After the lower computer receives it correctly, it sends “K” to the PC as a confirmation response signal. If the PC does not receive the “K” signal within the specified time, it will be retransmitted. If it fails three times, the display information will be given on the screen. The PC must ensure the packet length of 44 ASCII codes to avoid misoperation of the system. The structure of the control information packet is as follows: start with the capital “O”, followed by the control word of single byte hexadecimal number. Actually, two byte ASCII code is sent, and “K” is also used as the response signal, using the equal ratio code 3 / 8. When sending, the high order is in the front and the low order is in the back.
The main contents of the information packet structure received by PC from MCU are data information and status signal, and the data information and status information are sent at the same time. The packet starts with “s”, followed by 32 ASCII codes of 1-bit hexadecimal numbers, with “K” as the end signal. If the PC receives the complete information package sent by the single chip microcomputer, there will be a screen prompt to instruct the user to operate.
The above information is composed of double byte number and single byte number. Non hexadecimal ASCII code characters are used at the head and tail of the information packet to distinguish. The receiver unpacks according to the algorithm specified by both parties, and the sender groups packets according to the data structure specified by both parties.
3. Main modules and design idea of lower computer
3.1 communication module
The hardware composition of the communication module is relatively simple because only one MAX232 is used to complete the level conversion function, which eliminates the trouble caused by the use of ± 12V ~ 15V voltage in general chips. Moreover, the connection mode with PC is the simplest, there is no need for hard handshake, and a lot of work is completed by software.
The main programming methods are as follows:
① The lower computer receives the data packet sent by the PC and receives it in interrupt mode (and set as advanced interrupt) to meet the real-time requirements of communication. Here, only the execution of the receiving interrupt service program is triggered and the first byte is received. Once the interrupt program is entered, the remaining bytes are received by program query. The receive flag RI is set by hardware and reset by software. Therefore, after each byte is received, the instruction CLR RI needs to be executed. After receiving the data, decode and verify the data according to the protocol, and return the verification information to the PC. ② The subroutine that the lower computer sends the running state information to the PC is called according to the needs of the program working process. In the calling process, in order to ensure the clarity of the program logic and interrupt the CPU, use the program query sending flag Ti (the use of Ti is similar to RI), transform the data according to the protocol requirements and send a complete information packet, then interrupt the CPU, and the execution of the whole program is completed.
3.2 stepper motor control module
Stepper motor is one of the important actuators in mechatronics products. For three-phase reactive stepping motor, there are two working modes. The system adopts three-phase single and double six beat power on mode, which is not easy to lose step, is not easy to produce oscillation near the rotor balance position, has good operation stability, and the control accuracy is doubled. In order to make the stepper motor run more smoothly and control precision higher, the system uses a stepper motor driver with subdivision to control. The speed of the stepping motor depends on the frequency of the stepping pulse sequence. The hardware interface circuit is shown in Figure 2. The figure is only the connection diagram of the stepping motor on the left side of the x-axis. The connection mode of other motors is similar to that in the figure, but other pins of 8155a are used. CP + and CP – of stepping motor driver are stepping pulse input terminals, U / D + and U / D – are direction control input terminals, PD + and Pd – are offline control input terminals (not used in this system), and each has photoelectric isolation circuit, which is conducive to the safety and reliability of system operation, The common anode connection method is adopted because the current filling load capacity of logic circuit is usually greater than the pull current load capacity; DC and GND are power terminals, which are required to be DC 20 ~ 60V and current 4A; The output terminals a + and a -, B + and B -, C + and C – are respectively connected with the three-phase outgoing lines of stepping motor a, B and C. The control of stepping motor mainly includes logic control and speed control.
Logic control includes motor rotation direction control and sending step pulse sequence. Since the PA port and Pb port of 8155 need to be accessed in byte mode, according to the needs of rotation direction control and step pulse sequence transmission, two control words of logic setting and reset are formed and output to the corresponding port alternately, so as to realize the control of motor rotation. The system can control up to two motors to work at the same time, with a total of 16 control words. The specific programming idea is: the pulse number is proportional to the linear displacement through the step angle to the angular displacement, and then through the wire rod to the linear displacement.
The speed control is realized by inserting a delay subroutine during the alternating output of the set and reset control words, so the speed is determined by the execution time of the delay subroutine. In the low-speed area where the motor of the system works, the control line speed is 4mm / s during non welding operation; The linear speed during welding operation is 1 ~ 8mm / s, which is controlled by PC in real time according to the needs.
3.3 PWM module
In order to meet the technical conditions of IC chip seam welding, the power loading in the welding process is required to be intermittent. Therefore, a PWM pulse width modulation module is designed to realize the intermittent control of power. Figure 3 shows the circuit composition of this module. The core device is SG3524, and its output is periodic pulse sequence. Its cycle is controlled by RT, CT end to ground access resistance Rt and access capacitor CT, and the cycle T = 0.77rt × CT, so the digital potentiometer x9c104 is connected in series here to realize the control of T. According to the use method of digital potentiometer in the figure, the expression of resistance R is: r = (99-n) × 100k Ω, where n is controlled by programming. The duty cycle of the output signal of SG3524 is controlled by the D / a conversion circuit through programming. The system realizes t = 40ms ~ 80ms, the duty cycle is 0 ~ 100%, which is controlled by the upper computer.
3.4 welding power control module
In fact, the control of welding power is indirectly realized by controlling the output voltage. The single chip microcomputer outputs the digital signal to DAC0832 for digital / analog conversion. After the conversion result is controlled by the analog switch controlled by SG3524, the solid-state voltage regulating module evu-40a is controlled to make the output AC voltage linearly proportional to the input digital signal. The output voltage is connected to the welding transformer, converted into low voltage and high current, which is added to the welding electrode, and the IC chip is seam welded by generating high temperature. The implementation circuit is shown in Figure 4. In addition, there is residual voltage in the actual application of evu-40a voltage regulating module, resulting in ignition of electrode welding wheel when adjusting welding parameters, resulting in unnecessary loss. Therefore, AC solid-state relay gjh25-w is connected in series in the input circuit of voltage regulating module to block.
The programming method of welding power module control is as follows: the single chip microcomputer receives the power control information of the upper computer and writes it into DAC0832 chip with address of 6000h. At the same time, gjh25-w sends an effective control signal to make it conductive, and the welding electrode has corresponding power output for seam welding. When welding is not carried out, gjh25-w is cut off and 0ffh is sent to DAC0832 to realize complete and reliable disconnection of welding.
4. Experimental test results
10. The linear displacement / angular displacement of y-axis lead screw = 4mm / 360 degrees, the linear displacement / angular displacement of z-axis lead screw = 1.5mm/360 degrees, and the stepping angle is 0.36 degrees. The experimental method is to use the computer to send the number of pulses and calculate the theoretical value, and use the micrometer to actually measure and calculate the absolute error value (see Table 1). The analysis results meet the design requirements.
After a period of experimental operation, the system has proved that the communication has good real-time performance and high control precision, and meets the design requirements.
Responsible editor: GT