Investigate Immersion Silver Discoloration Before Assigning a Cause

Discoloration on immersion silver deserves a documented review, but color alone does not identify the chemistry or determine solderability. A useful investigation preserves the original surface and compares exposure patterns before deciding what testing is needed. Immediate wiping or polishing can remove the evidence required to explain the change.

Record the observation objectively

Photograph the board under consistent lighting and record which pads, regions and sides are affected. Include unaffected areas from the same board and reference boards when available. Describe the visible color and distribution rather than labeling every mark oxidation, contamination or a plating defect.

Uyemura’s technical discussion of immersion silver identifies sulfur exposure as a mechanism for silver-sulfide tarnish. That mechanism is a hypothesis to investigate when the exposure history fits; a photograph cannot establish it by itself. The article’s older specification references should not be used as current acceptance criteria.

Compare the exposure pattern

Build a chronology from finishing through storage and handling to the observation. Note when the surface was first seen to change and whether boards from the same lot followed different routes. Identify contact materials and unusual local exposures for review without assuming that any one item caused the condition.

Pattern comparison can be especially useful. Marks confined to contact areas suggest a different investigation from uniform change across exposed surfaces. If only boards from one storage interval are affected, retain that grouping in sample selection. Avoid combining all discolored boards into one untraceable sample bag.

Choose evidence for the actual decision

Agree with the supplier and assembler whether the immediate decision concerns appearance acceptance, surface chemistry or ability to complete the planned soldering process. Those questions may require different evaluations. Record the method, specimen selection and acceptance basis before submitting samples.

For solderability assessment, use representative features and relevant assembly conditions. A single hand-soldered demonstration can be informative, but it does not automatically represent fine-pitch paste printing or the full intended process. Preserve untreated samples for analysis while evaluating separate samples for process performance.

Keep remedial actions controlled

Do not introduce abrasive cleaning or an improvised chemical treatment as an undocumented production fix. Ask the finish supplier to assess any proposed recovery method and its effect on subsequent requirements. Record the before-and-after state and the verification needed to accept treated material.

The disposition should state the observed population, evidence obtained and reason for accepting, evaluating further or rejecting it. If a cause remains unconfirmed, say so. A clear distinction between a visible change, a confirmed surface reaction and measured assembly performance supports a stronger corrective action than a blanket claim that every tarnished pad is either harmless or unusable.