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SMT itself is a complex system engineering, it has a series of technical equipment such as SMT machine, solder paste printer, reflow soldering machine, printing, solder paste, cleaning and other technical technologies, solder paste, screen, cleaning agent and other processes Organization and management of materials. Want to install and solder good PCB components in batches and inexpensively.
In addition to equipment for paste welding with good performance, proper process materials should be selected, strict management system should be established, and the research of process technology should also be paid attention to. Many people think that SMT equipment and materials are very important, but do you also think that SMT chip proofing processing technology is very important?
SMT patch proofing processing
Process technology is also called process method and process. The focus of this technology is to achieve the goal of balanced and stable production of high-quality products by controlling equipment parameters, environmental conditions, production process preparation, selection of raw materials and auxiliary materials, and production process quality. We call equipment parameters, environmental parameters, process parameters, and auxiliary materials as process materials, and production processes as process flow. Therefore, we can also refer to process technology as process preparation, process material selection and process parameter control technology.
We say that the SMT patch proofing process is not the most difficult, which is relatively speaking. Generally speaking, this process has two process requirements: one is high installation accuracy; the other is high installation accuracy. The other is the low leakage rate. High installation accuracy requires that the metalized end or printed circuit of the equipment covers more than 2/3 of the area of the printed circuit board pad. The installation accuracy mainly depends on the installation accuracy and its related performance. The loss of solder paste is caused by the collapse of fragments. The placement machine has good performance and achieves the leakage rate.
SMT patch proofing processing
How to make the placement machine have high precision and low loss rate? This is also a technical problem, there are "tricks", but it depends more on the equipment. It is different from solder paste printing and soldering. Many process parameters in printing and welding are determined by field technicians based on experience and experiments. The process level varies greatly, so SMT patch proofing processing is not a simple matter.
PCB soldering is a lubricating process in mechanism, a temperature and time control process. It is a complex physical and chemical change process for reflow soldering machine, solder, flux, parts, and printing plates. The purpose of welding is to form high-quality solder joints. The solder joints of the sheet-shaped parts simultaneously play the role of electrical connection and mechanical fixation. Therefore, the solder joints are required to have a certain degree of mechanical strength, and no false soldering or missing soldering is allowed. The main factors affecting the quality of solder joints are the solderability and heat resistance of components and printing plates, as well as the properties of solder paste, flux and other processing materials.
SMT patch proofing processing
In this process, the above technical indicators and materials must be strictly controlled, which is the basic condition for the success of the welding process. The remaining problem is that the technician has to specify the ideal process (temperature) curve, which is divided into three parts: preheating, welding and cooling. Do not preheat too fast, otherwise it is easy to produce solder balls and spatter; if the soldering temperature is too high, exceeding the heating temperature of the printing plate will cause overheating and discoloration. If the welding time is too long, the welding time will be too short and the welding temperature will be too low. Excessive cooling will cause thermal stress.
Even the ideal process (temperature) curve is not enough. The melting furnace in the actual PCB circuit board is a surface, not a line, and its edge is different from the temperature of ZTE. Because the heat of the shell, components, wires, and soldering boards of various materials is different, the temperature of each point varies greatly, so The whole soldering process is a technician who controls the soldering materials, solder and flux, temperature and time. After comprehensive balance and comprehensive adjustment, high-quality solder joints can be obtained.
The pass rate of a solder joint can reach 99.99%, that is, 10,000 solder joints are just a bad solder joint. If there are about 2000 solder joints on the computer motherboard, that is to say, there are defective products according to one of the above five indicators, the repair rate can reach 20%. This is much higher than the 5% maintenance rate of foreign computer motherboards. This shows that the PCB soldering process is not simple.
