Prevent defect generation by monitoring pcb process variables

- Oct 18, 2019-

1. When the prototype pcb process starts to shift and lose control, the engineering technician can analyze and judge according to the real-time data (it is the question of the thermocouple itself, the problem of measuring the terminal connection point, or the sub-temperature out of control, the transmission speed, the air volume occurs. The change...) is then processed according to the judgment result.


2. Prevent the occurrence of defects by quickly adjusting the surface mount pcb assembly process parameters.


3. Software and equipment that can continuously monitor the temperature curve of reflow soldering furnace are also becoming more and more popular.


An example of two reflow process controls is described below.


(1) Use reflow soldering process control tools


The temperature monitoring system introduced by KIC in the United States - KIC Vision is a system for automatically measuring the temperature curve of the furnace.


The system includes hardware and software. With this system, the reflow oven can be monitored in real time for 24 hours, and it can be used to continuously measure the temperature profile, thus increasing production speed and productivity. The basic principle of the system is to install thermocouples (15-20 thermocouples per side) inside the furnace along the PCB transfer track near the plane of the PCBA for collecting temperature data and installing on the side of the furnace. Receiving system. The KIC247 system features a Thermocouple Measurement Data Processor (TPU) that not only records the temperature measured by 30 to 40 thermocouples to the hard disk, but also displays the measured hot air temperature profile on a computer: In addition, the KIC247 is equipped with a fiber optic sensor for follow-up recording of each surface mount pcb assembly board entering the furnace.


An automatic curve system for regular inspection of reflow soldering and curing furnaces


When using the KIC247 real-time monitoring system, when the temperature adjustment PCBA (temperature measuring plate) passes through the position of each thermocouple, the thermocouple will measure the temperature of the hot air in the furnace at that time, and measure the thermocouple with the test panel. The actual measured temperature conditions were compared, recorded and simulated. After the PCBA has completely passed through the entire furnace, that is, after the entire welding process is completed, the fixed thermocouple inside the furnace can simulate the same temperature curve (called the pseudo-curve) of the mountain and the actual temperature measuring plate. With this virtual standard curve, when each PCBA is reflowed, all fixed thermocouples in the furnace continuously measure the temperature of the hot air and continuously simulate the temperature curve on each PCBA. At the same time, the temperature and time parameters on the virtual curve are calculated, and the process state in each PCBA welding process is displayed and recorded. Then, using the specific relationship existing between the real-time temperature curve and the virtual temperature curve, the software risk is calculated by PWI, CPK, etc. to represent the process risk or capability information. Users can set warning and alert criteria, and the system can issue an alarm when a PCBA has a problem during the welding process or an impending problem. The parameter changes of each PCBA during the welding process will also be recorded and used for quality information tracking management. Although the KIC247 real-time monitoring system provides a good tool for reflow quality control, it is not a panacea. Can the quality of reflow soldering be truly controlled, the key is whether the correct "virtual standard temperature curve" can be set. Setting the “virtual standard temperature curve” can not be completely in accordance with the temperature curve given by the solder paste factory, but also combined with the specific conditions of each batch of assembled boards, combined with the actual welding quality of the “temperature measuring board” (or “first piece”). Pcc prototype China modulates a theoretically and practically ideal "virtual standard temperature profile" so that the quality of the weld is truly controlled.


(2) Using AOI software technology


AO1's software technology has process control capabilities, and AOU has become an effective process control tool. Depending on the product, the AOI can be placed in the production line after solder paste printing, before reflow soldering, and after reflow soldering. Multiple varieties and small batches can be disconnected. AOI's software technology has process control capabilities and has become an effective process control tool. Although the long-term reliability of lead-free solder joints still has uncertain factors, lead-free reflow soldering is more difficult than lead reflow soldering. As long as we apply the welding theory, we can correctly set the reflow soldering temperature curve and master the correct SMT process control method can ensure the quality of solder joints and ensure that components and PCBs are not damaged.


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