The overall control system of nitrogen reflow soldering adopts Windows operating system, Chinese and English interface, easy to operate and easy to learn. There are two control methods, computer control and emergency manual control, with safety guarantee function. The communication between PC and PLC (single chip) adopts PC/PP protocol , Stable work, no crash. Powerful software function, online temperature measurement of PCB board, and data curve analysis, storage and printing at any time. Automatic monitoring, display equipment working status, which is conducive to monitoring equipment at any time. The following is the detailed control system introduce.
1. Reflow soldering transportation system
PCB products are conveyed through the reflow oven by transport system. The transportation system is mainly composed of transportation guide rails, transmission sprockets, chains and transmission mesh belts. The conveyor mesh belt is a standard 440mm (Max560mm) stainless steel mesh belt, and the transmission speed is steplessly regulated by the control software. The width of the transport guide rail can be adjusted freely through the reverser, screw and nut drive according to the size of the PCB board, and the width can be adjusted to 400mm (maximum 460mm). It adopts chain network transmission, and the drive device is installed at the outlet of the furnace. The drive device includes a drive motor, a drive shaft, a drive chain and sprocket, a guide screw and other guide rail transport elements.
2. The composition of the inner temperature zone of the reflow soldering furnace
The furnace body of nitrogen reflow furnace is mainly composed of inlet, preheating zone, heat preservation zone, reflow zone and cooling zone. With the guide rail as the center, the upper and lower temperature zones independently circulate and control the temperature independently. The airflow in each independent temperature zone is accelerated, pressurized and heated, and then uniformly acts on the upper and lower sides of the PCB through the rectifier plate. All heating zones have upper and lower heating modules with independent circulation and independent temperature control. Each temperature zone adopts the same modular structure, which is easy to maintain and replace.
3. Reflow cooling zone
After the recirculation zone, the cooling zone is a specially-made cooling module with an external chiller to achieve efficient cooling. Double cooling zone cooling is adopted in nitrogen installation: the gas cooled by heat exchange is applied to the PCB board from above through devices such as water-cooled heat exchanger, cooling fan and air curtain at the outlet. After the PCB board is forced to cool in the cooling zone, it is sent out of the furnace by the transportation system to complete the reflow soldering. The heat exchanger has a filtering effect on the flux, which can ensure the circulation of clean gas in the furnace; the air volume of the cooling fan is appropriate, which can maintain a stable inert gas content in the cooling zone. Adopting modular structure, the maintenance of heat exchanger, cooling fan and rectifier orifice is convenient.
4. Reflow soldering transport speed control
The speed of the reflow oven transportation system can be set according to the user's needs and controlled by the software. The control accuracy can reach ±2mm/min.
5. Reflow soldering temperature control
The set temperature of each temperature zone is set by software operation, the actual temperature of each temperature zone is transmitted and displayed on the PC monitor screen through the thermocouple installed in each temperature zone, and the control signal is also fed back to the solid state in the electric control box. The relay provides enough power to maintain the temperature at the set value.
6. Reflow soldering temperature measurement line interface
The reflow oven temperature measurement line interface is installed on the operation control panel on the front of the machine. The input end of the temperature measurement line is connected to the temperature measurement card on the industrial computer, and the temperature curve during welding is captured through the reflow oven control software, and the temperature curve can be displayed, printed and stored.
7. Reflow soldering temperature out-of-tolerance alarm protection
When the actual temperature exceeds the upper and lower limits of the set temperature, the system will send an alarm signal and display the alarm information through software control, and all heating zones will stop heating at the same time (the temperature in the cooling zone will only alarm when the temperature is out of tolerance, but will not stop heating) (if the temperature in the temperature zone is set It is set to 200℃, when the upper and lower temperature limits are set to 10℃, an alarm will be issued when the actual temperature exceeds 210℃ or is lower than 190℃), the transportation system continues to operate, and the PCB board is safely sent out of the reflow oven. After the cause of the fault is eliminated, turn on the heating switch again for heating.
8. Nitrogen control in reflow oven
Nitrogen reflow ovens require gas controls because clean nitrogen or air is supplied to the oven. Gas control devices include: inlet and outlet air curtains; inlet and exhaust devices and control software; flowmeter and oxygen concentration analyzer (optional for nitrogen type); optional flux recovery device.
