Comparing Local Land Heights on a HASL-Finished PCB

If a component appears to sit unevenly on a HASL-finished board, determine which surfaces are being compared before changing the assembly process. Local solder coating geometry, overall board shape and component terminal geometry are separate contributors. A single photograph may combine all three.

Identify the surface that supports the component

American Standard Circuits describes HASL as a solder coating leveled with hot air and notes that pad geometry, orientation and equipment affect uniformity. This supports examining the actual land arrangement rather than assigning one height to every finished pad.

Record the board state before paste printing or placement. Measurements made after reflow cannot automatically be used to reconstruct the incoming surface.

Choose a useful reference

Record how the board is supported during measurement. Flattening it forcefully may conceal a condition present during printing or placement, while allowing it to rock may add a measurement artifact.

Compare matched pad groups

Inspect the relevant component footprint and a comparable region on another panel location. Retain pad orientation and incoming panel direction if available. A large test pad elsewhere may not represent the same geometry.

For example, a connector with lands running in two directions offers a useful local comparison. Measure the required surfaces consistently instead of judging the brighter or duller group by appearance alone.

Connect the result to the assembly concern

1. Confirm whether the observed geometry exceeds an agreed requirement.
2. Review the matching component terminal information.
3. Check printing and placement evidence at the affected footprint.
4. Evaluate a controlled fabrication or assembly change.
5. Verify the resulting joints and process repeatability.

Changing paste volume may improve one assembly symptom without resolving the incoming geometry. If that becomes the approved solution, qualify it deliberately with the actual board and component combination.

Do not claim a universal acceptable height difference from an unrelated package or finish comparison. The drawing, assembly process and functional joint requirements define the needed decision.

Document whether solder mask is included in the chosen reference surface. Using nearby mask as a convenient zero can mix mask geometry into a question about metal lands; a clearly defined datum makes the resulting comparison much easier to interpret.

Retain incoming measurements alongside the completed trial so future lots can be compared before assembly. The finish-selection guide supports broader material decisions; the measurement-location guide illustrates why a reported thickness needs a precise physical definition.