Kovar is an iron-nickel-cobalt (Fe-Ni-Co) controlled low-expansion alloy. Its thermal expansion coefficient closely matches borosilicate glass and alumina ceramics, making it the primary material for hermetic glass-to-metal sealing in high-reliability electronics. Kovar photochemical etching is a precision subtractive manufacturing method to produce thin, complex Kovar components without mechanical cutting force. Unlike stamping or CNC machining, this etching process avoids work hardening, burrs and residual stress, preserving the alloy’s stable thermal expansion performance.

Process Workflow

1. Material preparation: Select annealed Kovar foil/sheet, perform ultrasonic degreasing to remove oil and surface contaminants.
2. Photoresist lamination: Apply dry film photoresist evenly on both sides of the cleaned Kovar sheet.
3. Exposure & development: UV exposure transfers the custom part pattern from photomask onto photoresist; development removes unexposed resist to expose the Kovar surface.
4. Kovar chemical etching: Immerse the patterned sheet into customized ferric chloride based etchant with corrosion inhibitors. Exposed metal is dissolved isotropically to form required contours, holes and slots.
5. Stripping & cleaning: Strip remaining photoresist, rinse thoroughly with DI water to eliminate residual etchant.
6. Post-treatment & inspection: Surface passivation, dimensional metrology, visual defect check for critical dimension, edge quality and hole uniformity.

Core Advantages

• Zero burr & stress-free: No mechanical impact, eliminates work hardening that often appears in stamping; maintains Kovar’s original low-CTE property.
• Complex thin geometries: Capable of fine holes, narrow slots, intricate outlines and dense array patterns on thin Kovar foils down to 0.02mm thickness.
• Consistent dimensional stability: Batch processing delivers tight tolerance, ideal for mass production of hermetic packaging parts.
• No custom hard tooling: Pattern changes only require new phototool, drastically cuts prototyping cost and shortens lead time.
• Preserves sealing performance: Uniform, smooth etched edges and surfaces maintain reliable glass-metal sealing integrity for high-reliability packages.

Application Fields

• Semiconductor hermetic packaging: Kovar headers, sealing rings, package lids and micro lead frames.
• Optoelectronic components: Optical feedthroughs, vacuum packaging parts for lasers and image sensors.
• Aerospace & defence: Precision low-expansion spacers, shielding parts and sealed feedthrough assemblies.
• MEMS & micro sensors: Thin Kovar structural frames and sealing components for micro-electromechanical devices.
• Vacuum & microwave devices: Micro wave tube parts, vacuum chamber gaskets and precision shims.

Design & Process Considerations

• Kovar is sensitive to corrosion; etchant formula must use dedicated inhibitors to control surface roughness and avoid over-etching.
• Material annealing state matters. Hard cold-rolled Kovar will cause uneven etching; annealed Kovar sheet is preferred for consistent etch rate.
• Feature size is limited by material thickness: standard design rule: minimum hole width ≥ 1.2× sheet thickness.
• Post-processing options: nickel plating, gold plating or passivation can be applied after etching to improve corrosion resistance and soldering performance.
• Thermal cycle test should be validated for etched Kovar sealing parts to confirm CTE matching with glass/ceramic after etching.