Anyone involved within the printed circuit board (PCB) industry understand that PCB have copper finishes on their surface. If they are left unprotected then the copper will oxidize and deteriorate, making the circuit board unusable. The surface finish forms a critical interface between the component and the PCB. The finish has two essential functions, to protect the exposed copper circuitry and to provide a solderable surface when assembling (soldering) the components to the printed circuit board.

      Hot Air Solder Leveling (HASL) was once the tried and true method of deliver consistent assembly results. However, the ever-increasing circuit complexity and component density has stretched the capabilities of even horizontal solder levelling systems to their limits.
As component pitches became finer and a need for a thin coating became greater, HASL represented a process limitation for PCB manufacturers in PCB Assembly. As an alternative to HASL, alternative coatings have been around for several years now, both electrolytic and immersion processes.

       HASL is the predominant surface finish used in the industry. The process consists of immersing circuit boards in a molten pot of a tin/lead alloy and then removing the excess solder by using ‘air knives’,

  which blow hot air across the surface of the board.
One of the unintended benefits of the HASL process is that it will expose the PCB to temperatures up to 265°C which will identify any potential delamination issues well before any expensive components are

attached to the board.
Advantages:
Low Cost
Widely Available
Re-workable
Excellent Shelf Life
Disadvantages:
Uneven Surfaces
Not Good for Fine Pitch
Contains Lead (HASL)
Thermal Shock
Solder Bridging
Plugged or Reduced PTH’s (Plated Through Holes)
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