How to deal with defective SMT patch processing
The main maintenance methods of SMT patch processing include: soldering iron, focused IR and warm air. Warm air and focused IR are generally composed of a bottom plate and a furnace. The function of the bottom plate is to radiate heat to the printed circuit board, and the function of the furnace is to generate partial heating on the top of the parts. For most parts of reflow soldering equipment, hot compressed air or nitrogen with extremely high temperature is used.
Any heating method should prevent excessive heating of SMT chip processing or poor compensation of different coefficients of thermal expansion (CTE) to prevent the pads from lifting, damage to parts, internal metal formation and scorching. On the contrary, if the flux is not heated sufficiently, it will cause harm to the whole process, resulting in virtual solder joints.
SMT patch processing methods to supplement solder include spot coating or printing solder paste, application of flux, and the use of solid-core wire or preform. In most cases, there is no need to fill in solder paste. For example, in the case of bridging, you only need to redistribute the current solder paste without adding solder paste.
Special attention: the solder paste that needs to be used at the beginning of SMT patch processing and printing will not be suitable for maintenance. Different but compatible solder pastes can be used. Some manufacturers use low melting point alloys to prevent over-temperature. If the alloy used in SMT patch processing and maintenance is not harmful, the flux is sufficiently heated (can be activated), and the residue left behind will not cause damage (no cleaning), this is also a good way.
Even in the same workshop and the same process, the flux SMT patch processing and distribution methods are quite different. Common methods include painting, squirt bottle, spray, and felt pen. In addition, the type of flux is also different, there are active flux and low-activity nitrogen wave flux. For this reason, a variety of diversified materials are mixed in the whole process of SMT patch processing and maintenance. Depending on the maintenance materials and methods, manufacturing processes such as cleaning, hand washing, saponification/solvent rinsing, etc., or chemical reactions that may cause harm are avoided.