SMT patch refers to the abbreviation of a series of process processes based on PCB. PCB (Printed Circuit Board) is a printed circuit board.
SMT is the abbreviation of Surface Mounted Technology, which is the most popular technology and process in the electronic assembly industry. Electronic circuit surface assembly technology (Surface Mount Technology, SMT) is called surface mount or surface mounting technology. It is a method of installing leadless or short-lead surface-mounted components (referred to as SMC/SMD, called chip components in Chinese) on the surface of a printed circuit board (PCB) or other substrate. A circuit assembly technology that is assembled by soldering using methods such as reflow soldering or dip soldering.
In the SMT welding process, nitrogen is extremely suitable as a protective gas. The main reason is that its cohesive energy is high, and chemical reactions will only occur under high temperature and high pressure (>500C, >100bar) or with the addition of energy.
Nitrogen generator is currently the most suitable nitrogen production equipment used in the SMT industry. As on-site nitrogen production equipment, the nitrogen generator is fully automatic and unattended, has a long lifespan, and has a low failure rate. It is very convenient to obtain nitrogen, and the cost is also the lowest among the current methods of using nitrogen!
Nitrogen Production Manufacturers - China Nitrogen Production Factory & Suppliers (xinfatools.com)
Nitrogen has been used in reflow soldering before inert gases were used in the wave soldering process. Part of the reason is that the hybrid IC industry has long used nitrogen in reflow soldering of surface-mount ceramic hybrid circuits. When other companies saw the benefits of hybrid IC manufacturing, they applied this principle to PCB soldering. In this type of welding, nitrogen also replaces the oxygen in the system. Nitrogen can be introduced into every area, not just in the reflow area, but also for cooling of the process. Most reflow systems are now nitrogen-ready; some systems can be easily upgraded to use gas injection.
Using nitrogen in reflow soldering has the following advantages:
‧Fast wetting of terminals and pads
‧Little change in solderability
‧Improved appearance of flux residue and solder joint surface
‧Quick cooling without copper oxidation
As a protective gas, nitrogen's main role in welding is to eliminate oxygen during the welding process, increase weldability, and prevent re-oxidation. For reliable welding, in addition to selecting the appropriate solder, the cooperation of flux is generally required. The flux mainly removes oxides from the welding part of the SMA component before welding and prevents re-oxidation of the welding part, and forms excellent wetting conditions for the solder to improve solderability. . Tests have proven that adding formic acid under nitrogen protection can achieve the above effects. The ring nitrogen wave soldering machine that adopts a tunnel-type welding tank structure is mainly a tunnel-type welding processing tank. The upper cover is composed of several pieces of openable glass to ensure that oxygen cannot enter the processing tank. When nitrogen is introduced into the welding, using the different proportions of the protective gas and air, the nitrogen will automatically drive the air out of the welding area. During the welding process, the PCB board will continuously bring oxygen into the welding area, so nitrogen must be continuously injected into the welding area so that the oxygen is continuously discharged to the outlet.
Nitrogen plus formic acid technology is generally used in tunnel-type reflow furnaces with infrared enhanced convection mixing. The inlet and outlet are generally designed to be open, and there are multiple door curtains inside with good sealing, which can preheat and preheat components. Drying, reflow soldering and cooling are all completed in the tunnel. In this mixed atmosphere, the solder paste used does not need to contain activators, and no residue is left on the PCB after soldering. Reduce oxidation, reduce the formation of solder balls, and there is no bridging, which is extremely beneficial to the welding of fine-pitch devices. It saves cleaning equipment and protects the global environment. The additional costs incurred by nitrogen are easily recouped from cost savings derived from reduced defects and labor requirements.
Wave soldering and reflow soldering under nitrogen protection will become the mainstream technology in surface assembly. The ring nitrogen wave soldering machine is combined with formic acid technology, and the ring nitrogen reflow soldering machine is combined with extremely low activity solder paste and formic acid, which can remove Cleaning process. In today's rapidly developing SMT welding technology, the main problem encountered is how to remove oxides, obtain a pure surface of the base material, and achieve reliable connection. Typically, flux is used to remove oxides, moisten the surface to be soldered, reduce the surface tension of the solder, and prevent re-oxidation. But at the same time, flux will leave residue after soldering, causing adverse effects on PCB components. Therefore, the circuit board must be thoroughly cleaned. However, the size of SMD is small, and the gap between non-soldering parts is getting smaller and smaller. Thorough cleaning is no longer possible. What is more important is environmental protection. CFCs cause damage to the atmospheric ozone layer, and CFCs as the main cleaning agent must be banned. An effective way to solve the above problems is to adopt no-clean technology in the field of electronic assembly. Adding a small and quantitative amount of formic acid HCOOH to nitrogen has proven to be an effective no-clean technique that does not require any cleaning after welding, without any side effects or any concerns about residues.
Post time: Feb-22-2024
