Multilayer Ceramic Capacitor (MLCC)

MLCCs consist of alternating layers of BaTiO₃ dielectric (very hard, ~1200-1500 HV) and thin metallic electrodes (Ni or Ag/Pd, much softer). The extreme hardness difference between ceramic and metal layers creates differential polishing challenges. Components are very small and must be encapsulated in epoxy before preparation. Precision grinding to the target cross-section plane is critical; over-grinding by even 50-100 μm can pass through the active area entirely.

Precision wafering only. For individual MLCCs, sectioning is typically not needed; the component is mounted whole in epoxy and ground to the target cross-section plane. For MLCCs on PCB assemblies, use a low-speed precision wafering saw with a thin diamond blade (0.15-0.3 mm) to section through or near the component of interest. Cutting speed: 100-200 RPM. Very low feed rate to avoid fracturing the brittle ceramic body. Position the cut 0.5-1.0 mm away from the target plane to allow grinding to the precise location.

Cold mounting with castable epoxy is required. For individual MLCCs, place the component in a small mold with the desired cross-section orientation, then fill with low-viscosity epoxy. Vacuum impregnation is strongly recommended to fill internal cracks, delaminations, and the gap between electrode terminations and the ceramic body. Use a low-shrinkage, edge-retaining epoxy formulation. For components on PCBs, mount the sectioned PCB piece with the component oriented so that grinding will approach the target plane from one side. Mark the target grinding depth on the mount for reference.

The very hard ceramic (1200-1500 HV) requires diamond grinding media. SiC paper wears too quickly and produces poor flatness on hard ceramics. Use bonded diamond discs. Disc speed: 200-300 RPM. Apply moderate pressure (20-30 N per 30 mm sample). Grind carefully toward the target cross-section plane; monitor progress frequently under a stereomicroscope.

Grinding sequence:

• 30μm diamond disc: Rapid material removal to approach the target plane (30-90 seconds). Check progress frequently.
• 15μm diamond disc: Approach the target plane more carefully (30-60 seconds). Measure remaining distance.
• 9μm diamond disc: Final approach to the target plane (15-30 seconds). Check under stereomicroscope after every few seconds of grinding.
• 6μm diamond disc: Fine adjustment to the exact target plane (10-20 seconds). The electrode pattern should be centered in the active area.

The softer metal electrodes will grind faster than the ceramic, so light pressure is important to minimize differential removal. Rotate specimen 90° between steps.

Use firm, napless cloths for all polishing steps. The hard ceramic requires longer polishing times than metals. The hardness contrast between BaTiO₃ and the metal electrodes can produce relief if napped cloths or excessive pressure are used.

Diamond polishing sequence:

• 6μm diamond: 3-5 minutes on a hard napless pad with moderate pressure (20-30 N per 30 mm sample).
• 3μm diamond: 3-5 minutes on a napless pad (20-25 N).
• 1μm diamond: 2-4 minutes on a napless pad (15-20 N). Check for relief around electrodes.

Final polishing:

• 0.05μm colloidal silica: 2-5 minutes on a soft pad with light pressure (12-18 N). This step is critical for revealing fine cracks in the ceramic that may be obscured by residual grinding damage. Vibratory polishing (4-8 hours) with colloidal silica produces the best results for crack and delamination analysis.

MLCCs are most commonly analyzed in the as-polished condition for electrode continuity, crack detection, and delamination. Etching is used when BaTiO₃ grain structure must be evaluated.

Thermal Etching - Primary method for grain structure:

• Conditions: Heat polished sample to 1100-1200°C in air or inert atmosphere for 15-30 minutes, then cool slowly.
• Reveals: BaTiO₃ grain boundaries by thermal grooving. Grain size measurement is critical for dielectric property correlation.
• Note: Thermal etching will oxidize Ni electrodes. If electrode integrity must be preserved, use chemical etching instead.

Dilute HF (Chemical Etching) - Alternative for grain structure:

• Composition: 0.5-2% HF in water (0.5-2 ml HF per 100 ml H₂O)
• Application: Immerse for 10-30 seconds. Very aggressive; start with lowest concentration and shortest time.
• Reveals: BaTiO₃ grain boundaries. Will also attack the metal electrodes, so use with caution.
• Safety: HF is extremely hazardous. Calcium gluconate gel must be available. Work in a fume hood with full PPE.