HASl or hot air solder level is the finish of the PCB used on board. The board is put in a bath of molten solder that exposes the copper surface covered with soldered. Extra solder was removed through the moving board with hot air knives. HASL can used with or without lead and lead-free is RoHS compliant.
How to Apply HASL on PCB Surface
HASL is a metallic surface finishing method that is used on the external layer of the PCB board for the protection of copper layers where components are soldered.
HASL coating is made with Tin 63 percent and 37 percent lead and at the time of assembly coating is dissolved with solder materials
- HASL started with putting the board in the molted tin or lead solution and opening the area of the board coated with the solution.
- After that Hot air leveler make sure to make uniform solder deposition by removing extra solder on board with use of high-pressure hot air knives. That makes a uniform and thin layer on board.
- Coated protects copper traces from corrosion until the board not used for the assembly process
Features of HASL
- In this process, board surface detection can done with direct eye observance.
- HASL offers good wetting at the time of soldering.
- The board that comes with HASL has features to work for a temperature range of 265 degrees Celsius
- It has levels of oxidized copper on the printed circuit board.
- This type of board finishing is easy to access.
- The finish type increases board working life.
- materials for this finish are low-cost and easy to access.
- It can applied without certain requirements
Lead-free HASL
Lead-free hot air solder leveling is a surface finish type that employs lead-free alloys as compared to tin-lead alloys that are used for HASL.
In this process, molten solder is applied on the baord to get wet with the use of hot air knives.
After the application of solder, it becomes soling and the remaining flux is removed through the passes board in the washer.
The use of this finishing has a positive affect on boards but it is not used as commonly with other finishing such as  ENIG and OSP.HA
Differences between HASL and Lead-Free HASL
- HASL finish comes with lead-tin alloy that has a bad effect on environmental and human health while leading free not have these toxic materials that have a bad effect
- Lead has a higher melting point than tin and the melting point of lead-free HASl is higher as compared to HASL due to the use of lead.
- HASL finish has a shining surface and lead-free HASL has a matte surface finish.
- Both HASL and lead-free HASL provide some mechanical features.
- HASL finish has 37 percent lead and lead free has about 0.5% lead.
- Lead provides easy handling of tin wires at the time of soldering but lead-free also provides about the same results
Features | HASL | Lead free HASL |
Lead | 37% of lead |
lead less than 0.5%
|
Reflow soldering temperatures | 210℃ to 245℃ | 240℃ to 270℃ |
Wave soldering temperatures | 250℃ | 260℃ |
Pad Working | Glossy | Dim |
Solderability | Good | Mid |
Solder Alloy | Tin-Lead |
Tin-Copper, SAC
|
Wettability | Good |
Moderate
|
Melting Temperature | 183°C | 217-232°C |
Solder Bath Temperature | 200-210°C | 240-255°C |
Coating Thickness | 100-300 μin |
50-100 μin
|
Solderability | Excellent |
Good to Excellent
|
Ductility/Hardness | Soft |
Harder
|
Pros of Lead-free HASL
- It is low-cost finishing and provdie good soldering features.
- It is used for larger through hole circuits.
Cons of Lead-free HASL
- The temperature range of lead-free HASL is about 260 ℃ to 270 ℃
- It is not good to use for small-level boards
- It has a high difference between small and large pad thickness.
Advantages of HASL
- The result of HASL is flat and uniform solder which provides good soldering features. The connection of components on board is according to requirements
- HASL is a low-cost surface finish than other types of finishing gold or immersion. It is a simple and easy process taht can also used for larger PCB manufacturing.
- It is the basic type of PCB finishing and is preferred in the industry.
HASL Disadvantages
- HASL is not preferred for SMT since it makes irregular surfaces
- It faces high temperatures that can damage some components
- It is not good to use for line binding
- It does not have features to handle close tolerance on plated holes.
What is the difference between HASL and ENIG finish?
- The main benefit of HASL is easy to afford has high thermal resistance featues and can managed for low-budget projects.
- ENIG finish comes with RoHS compliance, and best option for high-frequency applications, fine-pitch components
What is the HASL method?
- HASL is a finish type used for PCB where the board is dipped in a molted solder bath that covers all open parts of the board with solder. Extra solder is removed after passing the board in hot air knives.
What is the standard thickness of HASL?
- HASL comes with variable thickness metallic alloy coating that is about 25 to 2000 µ thick and is used for making solderable surfaces and sustaining soldering features for a longer time.
What is the difference between HASL and immersion tin?
- HASL uses an alloy of tin and comes with two components lead and lead-free. Pure tin provide high melting point and is not used.
- Immersion tin finish uses a tin slat and is made in an acidic solution having tin.
What is ENIG in PCB?
- ENIG comes with two two-layer metallic surface finishes that have a thin layer of gold plated on nickel layers.
What is OSP surface finish?
- OSP is a PCB finish that defines organic solderability preservative. The surface finish of PCB is used for 2 causes to make srue soldering featues and to protect exposed copper circuitry.
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