Introduction to HASL Surface Finish
Hot air solder leveling and lead-free HASL (Hot Air Solder Leveling) are the two prominent surface finishes in the PCB Manufacturing and Assembly Process. However, there is a noticeable difference; Lead-Free HASL does not use tin and lead solder.
Yet, when choosing the right surface finish for your circuit boards, it is vital to choose a cost-effective and RoHS-compliant surface finish. Suppose you want to use HASL as your surface finish choice and need help deciding which surface finish to use. In that case, this guide examines the pros and cons differences between HASL and lead-free HASL.
What is PCB Surface Finish?
Surface Finish is metalizing the outer layer of a PCB being soldered. The function of PCB surface finish is to offer protection against corrosion on the copper circuitry. Also, it fosters easy soldering of circuit board components.
There are varied kinds of surface finishes employed in the PCB Industry. They are: Hot Air Solder Leveling (HASL), Electroless Nickel/Immersion Gold (ENIG), Immersion Silver (ImAg), Organic Solderability Preservative (OSP), and Immersion Tin (ImSn)
Hot Air Solder Leveling (HASL)
Hot air solder leveling (HASL) is the least expensive PCB surface finish. Many PCB Manufacturers commonly use this surface finish as it is economical and widely available. When applying Hot Air Surface Leveling on circuit boards, the board is dipped in molten solder and then scrapped off with a hot air knife.
PCB Manufacturers that employ through-hole technology or larger surface mount technology designs, hot air surface leveling excels in these designs. For smaller boards, it is not ideal. Also, The solder used is typically Tin-Lead solder, making it RoHS non-compliant.
LF Hot Air Solder Leveling or LF-HASL is identical to the standard HASL process. However, it does have an obvious difference, i.e., it does no use Tin and Lead Solder. Instead, you will use a Tin and Copper, Tin and Nickel, or Tin, Copper, and Nickel germanium.
This difference is what makes LF-HASL a cost-effective and RoHS compliant surface finish. However, similar to HASL, lead-free HASL is also not suitable for smaller components. For PCBs with smaller components, you can choose better surface finishes such as immersion coatings. They are a little more expensive but ideal for such purposes.
The lead-free HASL PCB surface finish became one of the most considered and frequently used surface finishes after immersion gold. It provided safer surface finish alternatives, but it never became the new standard and created a bit of hassle for the circuit board manufacturers.
PCB surface treatment of HASL/HASL lead-free
HASL/HASL(Lead free) is one of the major surface treatments in PCB fabrication industry. The process consist of emerging bare printed circuit board into tin lead alloy melting pot, and then use the “air knife” to blow hot air across the PCB board surface to remove excess solder.
Hot air solder leveling has an unexpected benefit that the process will make PCB exposure to the high temperature up to 265 ℃. This means that the process can well identify any potential delamiantion problem before assembling any expensive components to printed circuit board.
Basically the advantages and disadvantages for hot air solder leveling as below,
Advantages include:
• Low cost,
• Can be widely used
• Reworkable
• long shelf life
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