Hot air solder leveling of hasl pcb, which is a process of coating molten tin-lead solder on the surface of the PCB and leveling (blow-out) with heated compressed air to form a coating layer that is resistant to copper oxidation and provides good solderability.
Hot air leveling is divided into two types: vertical and horizontal. Generally, the horizontal type is considered to be better. The horizontal hot air leveling coating is relatively uniform, which can realize automatic production. The general process is: micro-etching-> preheating-> coating flux-> spraying tin-> cleaning.
Currently, about 25% -30% of PCBs use the hot air leveling process. Hot air leveling is a dirty, unpleasant, and dangerous process, so it has never been a favorite process, but hot air leveling is an excellent process for larger components and larger spacing wires. In high-density PCBs, the flatness of hot air leveling will affect subsequent assembly; therefore, HDI boards generally do not use the hot air leveling process.
Poor leveling and hole plugging problems, high requirements for green oil, plate and lamination bonding, the existence of board bending, board warping potential problems, to avoid the need to use high Tg plate material and PP, only the cost of the plate increased by 100 yuan / m2 (to double-sided calculation)
HASL PCB is an advanced process developed in the 1980s. And by the mid-to-late 1990s, HASL PCB accounted for more than 90% of the entire PCB surface coating layer. Only in the late 1990s, due to the in-depth development of surface mount technology (SMT), the share of HASL gradually reduced down. However, the current share of HASL PCB in the PCB surface coating is still about 50%, still has a long life.
The most important advantage of HASL tin-lead alloy is that it has the same composition and composition ratio as the solder. At the same time, it protects the copper from oxidation and contamination by covering the fresh copper surface well. Therefore, HASL tin-lead alloy has excellent protection, solderability and reliability.
However, the HASL tin-lead alloy layer has encountered problems and challenges in SMT applications, mainly from the surface tension of the molten tin-lead alloy is too large and produces tin-copper intermetallic compounds at high temperatures and the PCB is subjected to high temperature thermal shock during the HASL process.
HASL PCB applications have worked well for many years, but with the advent of environmentally friendly green process requirements, the days of this process's existence are numbered. In addition to the lead-free issue, increasing PCB complexity and finer pitches have exposed the HASL PCB process to many limitations. However, being the lowest cost PCB surface process, it maintains solderability throughout the manufacturing process and has no negative impact on ICT.