HOT AIR SOLDER LEVELING
HASL PCB Manufacturing
Leaded and lead-free solder finishes for circuit boards built for assembly.
FLJ manufactures HASL-finished PCBs from prototype quantities to production. Molten solder wets the exposed copper, hot air removes the excess, and the retained coating protects the lands before component soldering.
HASL FABRICATION AT A GLANCE
- Two finish routes
- Leaded and lead-free HASL
- 0.6–3.5 mm
- HASL-route board thickness
- Panel processing
- Smaller boards carried in larger workpieces
FROM LIQUID SOLDER TO FINISHED LANDS
How Hot Air Solder Leveling Forms the Surface
The finished contour begins with wetting and ends with the solder left after leveling. FLJ prepares the exposed copper, applies the solder coating and clears the excess before the board moves into final inspection and packing.
Wetting the Exposed Copper
Solder-mask openings define the copper that receives the finish. Cleaning removes surface contamination and oxides; the flux supports wetting when the board contacts molten solder. Thermal preparation is set for the selected process and construction.
Liquid solder wets the prepared lands and plated-hole surfaces. A copper–tin interfacial region forms where solder contacts copper. This is bare-board finishing: component placement and joint formation follow in assembly.
Removing Excess Solder and Clearing Holes
As the board leaves the solder, air knives drive off surplus liquid. The air also clears solder from the hole openings while retaining a coating on the intended copper surfaces. Too much retained solder can alter land height or obstruct a hole; insufficient coverage leaves an unsuitable exposed area.
The solder must remain mobile while the air removes it. Solder temperature and board movement affect the interval available for leveling before the coating solidifies; air direction, flow and knife position control how the excess leaves the features. These conditions are set together to retain usable coverage and open holes while limiting thermal and mechanical stress on the board.
Cooling solidifies the remaining solder. Cleaning and examination then address residual process material, coating coverage and the openings that must remain usable for the next manufacturing stage.
THE SURFACE THE ASSEMBLY WILL USE
HASL Coating, Pad Geometry and Assembly
Air leveling removes surplus solder, but the retained material can still form a curved profile. Coverage at one point and the relative height of several lands answer different questions about the finished board.
Through-Hole Coverage and SMT Pad Topography
For a through-hole component, the finished plated hole needs a solderable surface and an opening that accepts the intended lead. A set of SMT lands must also support paste printing, component seating and solder-joint formation across the complete footprint.
The solder contour varies with exposed geometry and position. A thickness value at a hole entrance cannot describe the height at a pad centre, and one pad reading does not define a common mounting plane across a package. The underlying copper and board shape remain part of that geometry.
Small lands, close spacing and a demanding coplanarity requirement can make a flatter deposited surface such as ENIG the more suitable choice. Land size and spacing, permitted height variation and the planned paste-printing and placement process determine the appropriate choice across that footprint.
FLJ carries the selected board finish into SMT assembly, with paste printing, placement and reflow prepared around the supplied lands and components.
Thermal Exposure and Solderability
The board experiences a thermal excursion during HASL before later assembly heating begins. Laminate and mask selection therefore consider finishing together with the expected first and second reflow cycles, selective soldering and rework.
Alloy choice alone does not determine the board’s response. Construction, moisture condition and the rate and duration of heating also matter. Manufacturing and assembly are planned together so that the delivered surface fits the build sequence.
Finished-board inspection examines solder coverage, bridging, blocked holes, surface condition and board shape. Physical coating examination addresses the material left on the board; a wetting evaluation asks how that surface behaves when soldered.
Where the project needs additional evidence, solderability, microsection or thermal verification is defined around the question and sample scope. Appearance, a thickness reading and electrical continuity each provide useful information without replacing the others.
LEADED & LEAD-FREE FABRICATION
HASL Manufacturing Capabilities
These finishing dimensions describe the processing route. Small finished PCBs can be carried in a larger panel through surface treatment; the processing-panel minimum is not the minimum delivered board size.
On smaller screens, scroll the table horizontally to compare both finishes.
| Manufacturing item | Leaded HASL | Lead-free HASL | What the dimension describes |
|---|---|---|---|
| Maximum processing size | 520 × 650 mm | 520 × 650 mm | Panel / workpiece size for surface treatment |
| Minimum processing panel | 150 × 230 mm | 150 × 230 mm | Smaller finished boards are processed in larger panels |
| Board thickness | 0.6–3.5 mm | 0.6–3.5 mm | Board thickness for the HASL finishing route |
| BGA pad diameter reference | 10 mil / 0.254 mm | 12 mil / 0.3048 mm | Pad diameter, not package pitch or inter-pad clearance |
Dimensions stay with their physical object. The pad-diameter references do not qualify an entire footprint. Board geometry, construction and assembly requirements determine the workable combination.
Specify Your HASL PCB Build
Send the PCB fabrication data, selected finish and quantity. FLJ quotes the board construction and finishing route, with component assembly included when required.