Hot Air Solder Leveling (HASL), commonly referred to as the PCB is  a widely used surface finishing technique in printed circuit board (PCB) manufacturing. This process involves coating the exposed copper pads of a PCB with a layer of molten solder, typically a eutectic alloy of 63% tin and 37% lead (though lead-free alternatives like tin-silver-copper are increasingly common), followed by leveling with hot air to ensure a smooth, uniform surface.

The HASL process begins with cleaning the PCB to remove oxides, oils, and contaminants from the copper surfaces, ensuring proper adhesion of the solder. The PCB is then preheated to around 150-200°C to evaporate any remaining moisture and prepare the copper for soldering. Next, the PCB is immersed in a bath of molten solder (at approximately 245-260°C for leaded solder or 250-270°C for lead-free alloys), allowing the copper pads to be fully coated. After immersion, high-velocity hot air knives blow across the PCB’s surface to remove excess solder, creating a flat, even layer that covers the pads while leaving the non-conductive areas (such as solder masks) clean.

One of the key advantages of HASL is its cost-effectiveness, making it suitable for high-volume production. The process also provides excellent solderability, as the tin-rich surface readily forms strong bonds with solder during component assembly. Additionally, HASL offers good protection against copper oxidation, ensuring the PCB remains functional during storage and handling.

However, HASL has limitations. The hot air leveling can result in slight variations in solder thickness, which may affect the precision of fine-pitch components (with pitches less than 0.8mm). Lead-free HASL alloys, while compliant with environmental regulations like RoHS, tend to be more brittle and have higher melting points, requiring careful control during assembly to avoid thermal damage to the PCB. Despite these drawbacks, HASL remains a popular choice for consumer electronics, industrial equipment, and other applications where cost and reliability are prioritized over ultra-fine pitch requirements.