Oxidation of Electronic Components: Manifestations and Remedies

I. Typical Manifestations

    Visual Indicators
    • Leads or solder balls lose their metallic sheen, appearing dull, gray or speckled with black spots.
    • Surfaces become pitted, rough or discontinuous.
    Solderability Degradation
    • Under low-power magnification, solder refuses to wet the leads, resulting in non-wetting, dewetting or localized voids.
    • Per GJB360B solder-iron test: tinned area < 95 % or concentrated defects classify the part as oxidized.
    Electrical Drift (common in long-stored ICs)
    • Contact resistance rises, leakage current increases, and in extreme cases functionality is lost.

II. Severity Levels and Corresponding Actions

Level    Characteristics    Recommended Action
Level 0 (Acceptable)    Bright, contamination-free surface    Use as-is
Level 1 (Mild)    Slight graying, localized dulling    May be used directly; light de-oxidation if process demands are high
Level 2 (Obvious)    Large-area graying, reduced solderability    Mandatory de-oxidation (re-tinning, chemical cleaning, etc.)
Level 3 (Severe)    Blackened, heavily pitted, total luster loss    Scrap or re-plate / re-ball
III. Common De-Oxidation Methods

    Physical-Mechanical
    • Fine abrasive paper or eraser: gently rub along the lead, then clean with alcohol and re-tin. Suitable only for coarse-pitch components.
    • Blade or file: removes oxide but risks damaging the plating; not recommended for precision devices.
    Re-Tinning
    • Manual: 300 ± 20 °C iron, dip in rosin, quick drag-solder; cool one side before the other.
    • Solder pot: batch-immerse leads in 245 ± 2 °C solder for 2–3 s; efficient, requires continual dross removal.
    • Precautions:
    – Use heat-sink clips or pre-heat for heat-sensitive devices (glass diodes, tantalum capacitors).
    – Employ dedicated fixtures for BGAs/QFNs to prevent ball deformation.
    Chemical-Flux Method
    • Mix: ALPHA FLUX A88 or CSF898 flux : rosin = 3 : 1 by mass.
    • Steps:
    ① Brush the mixture evenly over the leads.
    ② Bake at 125 ± 3 °C for 2–3 min.
    ③ Rinse with anhydrous ethanol and air-dry.
    ④ Post-bake at 115 °C for 24 h to remove moisture.
    • Advantages: ideal for fine-pitch ≤ 0.5 mm parts, no bridging, no mechanical stress.
    Chemical Soak
    • Light oxidation: proprietary de-oxidizing solution for 5–10 s → dry.
    • Heavy blackening: strip plating → re-plate (leaded devices) or re-ball (BGAs).
    Protection & Prevention
    • Storage: vacuum bags + desiccant + nitrogen cabinet, RH ≤ 30 %; once opened, use promptly.
    • Handling: keep in ESD/moisture-proof boxes to minimize exposure time.
    • Process: implement AOI and solderability spot checks before SMT to prevent oxidized components from entering production.

IV. Workflow in Brief
“Look → Judge → Choose → Act → Verify”

    Look: screen visually with 5–10× loupe or microscope.
    Judge: classify per table or run solderability test.
    Choose: select mechanical, re-tinning or chemical method based on package type, oxidation level and volume.
    Act: strictly control temperature, time and ESD; run small samples first if necessary.
    Verify: after de-oxidation, sample for solderability, X-ray and functional tests to close the quality loop.