Qualifying an Inkjet Legend on the Actual Soldermask

An inkjet legend should remain readable and attached through the operations the board will experience. Qualification therefore needs the actual soldermask and the complete later process. Printing a sharp label on an unrelated coupon establishes only a limited part of that requirement.

Identify the printed construction

Record the legend ink, soldermask, printer configuration and required curing method. Keep material identity separate from color. Two white inks can require different equipment or cure conditions even when their initial appearance is similar.

Peters’ inkjet marking-ink announcement identifies markings printed on solder resist and discusses compatibility with its solder-resist families. The announcement is not a universal approval for another supplier’s mask; the actual material combination needs suitable evidence.

Choose markings that challenge the process

Include the smallest required text, narrow strokes and any machine-readable symbols in the trial. Place them on representative local surfaces. A large logo on an open region may not represent fine polarity marks close to populated features.

Evaluate after the complete route

Use the selected material’s cure instructions and qualify the actual equipment settings. Then run representative later operations and repeat the relevant inspection. Do not call an ink acceptable only because it feels dry immediately after printing.

For example, a serial number may be legible before cleaning but lose contrast afterward. Retain before-and-after images under comparable lighting to distinguish changed material appearance from inconsistent inspection conditions.

If readability depends on a camera, include its illumination and recognition method in the qualification. Human-readable text and a machine-readable code may have different practical acceptance evidence.

Inspect markings near the production panel’s edges as well as its center when the printing trial calls for a positional comparison. Retain the print orientation so a location-related result can be investigated without confusing board coordinates with printer travel.

Control changes without losing identity

Review a replacement ink or mask with the existing print program, then identify any required program changes separately. This keeps a material change from being hidden by unrelated enlargement or repositioning of the legend.

Keep cure and material records with the accepted samples. When adhesion changes, the investigation needs both the printed ink and the surface beneath it.

The carbon-print registration guide covers another printed layer, while soldermask cure records help define the substrate received by the legend operation.