PCB Hot air leveling process introduce
The general process of hot air leveling process is: micro-etching → pre-heating → coating flux → spraying tin → cleaning.
Hot air leveling, also known as hot-air solder leveling (commonly known as spray tin), is the process of applying molten tin (lead) solder on the surface of a PCB and heating (or blowing) flat air to form a layer that resists copper oxidation. It also provides a good solderability coating. When the hot air is leveled, the solder and copper form a copper-tin intermetallic compound at the junction. When the PCB is hot-air levelled, it sinks into the molten solder; the air knife blows the liquid solder before the solder solidifies; the air knife minimizes the meniscus of the solder on the copper surface and prevents solder bridging.
Hot air leveling is divided into vertical and horizontal types. It is generally considered that the horizontal type is better, mainly because the horizontal hot air leveling coating is relatively uniform and can realize automatic production.
Advantages: Longer storage time; After the PCB is completed, the copper surface is completely wet (completely covered with tin before welding); suitable for lead-free welding; mature technology, low cost, suitable for visual inspection and electrical testing
Disadvantages: not suitable for wire bonding; due to surface flatness issues, there are limitations on SMT; not suitable for contact switch design. When the tin was sprayed, the copper dissolved, and the board was subjected to a high temperature. Specially thick or thin plates, sprayed tin has limitations, and production operations are inconvenient.