Printed Circuit Board HASL Process Analysis
ASL is the leading leaded surface treatment process used in the industry. This process is formed by immersing the plate in a lead-tin alloy. Excessive solder is removed by the "air knife". The so-called air knife is the hot air blown on the board. For the PCA process, HASL has many advantages: it is the cheapest PCB that can be soldered by multiple reflow soldering, cleaning and storage of the back side layer. For ICT, HASL also provides a process for solder to automatically cover test pads and vias. However, the smoothness or uniformity of the HASL surface is poor compared to existing alternative methods. There are now some lead-free HASL replacement processes that are becoming more popular due to the natural replacement properties of HASL. The HASL application has been running for many years, but with the emergence of "green" green process requirements, this process is only a few days. In addition to lead-free issues, increasing board complexity and finer pitches expose the HASL process to many limitations.
Advantages: The lowest cost PCB surface process maintains solderability throughout the manufacturing process with no negative impact on ICT.
Disadvantages: Lead-based processes are often used, and lead-containing processes are now limited and will eventually be eliminated by 2007. For fine pin pitch (<0.64mm), solder bridging and thickness issues can result. Surface irregularities can cause uniformity issues during assembly.