Kovar is a nickel-iron-cobalt alloy featuring a coefficient of thermal expansion (CTE) nearly identical to borosilicate glass and ceramic materials. It is the core material for high-reliability hermetic packaging and glass-to-metal sealing in aerospace, vacuum electronics and semiconductor industries. Photochemical etching is the optimal manufacturing process for thin Kovar components, as it eliminates mechanical stress, thermal deformation and work hardening caused by stamping, laser cutting or CNC machining, fully retaining the alloy’s original thermal expansion and mechanical stability. Typical material thickness ranges from 0.03 mm to 0.5 mm, widely used for producing sealing frames, lead frames, precision shims and magnetic shielding parts.

Step-by-Step Kovar Photochemical Etching Workflow

1. DFM Design & Kovar Material Adaptation Review
Kovar has unique chemical etching characteristics different from stainless steel and iron-nickel alloys. Engineers optimize CAD patterns and calculate dedicated undercut compensation to offset isotropic wet etching. Strictly calibrate feature size, pitch and half-etch depth to ensure consistent CTE performance and sealing accuracy of finished parts.

2. Professional Surface Pre-treatment
Kovar surface is prone to uniform oxide film and oil contamination. Adopt customized degreasing and pickling processes to completely remove surface grease, fingerprints and oxide layers. Uniform surface activity ensures stable photoresist adhesion and consistent etching rate across the entire panel, avoiding local pattern defects.

3. Dual-sided Dry Film Lamination
High-precision photosensitive dry film is evenly laminated on both sides of the cleaned Kovar sheet under constant temperature and pressure to form a pinhole-free protective mask, meeting the requirements of fine micro-feature processing.

4. High-precision UV Exposure & Development
Transfer precision patterns including outlines, micro-slots, positioning holes and half-etch bend lines via UV exposure. The unprotected photoresist in the etching area is completely washed away by developer, exposing pure Kovar substrate for subsequent chemical etching.

5. Specialized Dual-sided Spray Etching (Core Step)
Adopt Kovar-specific ferric chloride mixed acid etching system with stable chemical ratio. Precisely control etching temperature, spray pressure and conveyor speed to achieve uniform metal removal. Support two processing modes:
• Through etching: Fully penetrate the sheet to form outer contours, sealing gaps and micro through-holes;
• Blind/half etching: Control partial-depth etching to form flexible bend lines and assembly grooves without penetrating the substrate.
The whole process is non-contact and non-thermal, completely retaining Kovar’s CTE matching performance and structural stability.

6. Resist Stripping & High-purity Rinsing
Strip the cured photoresist mask completely. Perform multi-stage deionized water rinsing and neutralization treatment to eliminate residual etchant, preventing surface corrosion and ensuring the airtightness and reliability of subsequent sealing assembly.

7. Precision Dimension & Performance Inspection
Inspect overall dimensions, feature tolerance, half-etch depth, flatness and edge quality. Focus on detecting aperture consistency and flatness to avoid CTE deviation caused by processing stress, ensuring high-precision matching with glass and ceramic materials.

8. Optional Post-processing
Support surface treatments such as gold plating, nickel plating and passivation to improve corrosion resistance, weldability and airtightness. Flat etched blanks can be secondarily bent and formed into finished sealing frames and shielding structures.

Core Advantages of Kovar Etching

1. Zero stress, fully retained CTE matching performance
Non-chemical contact processing introduces no residual stress, no work hardening and no heat-affected zone. It will not change the inherent thermal expansion coefficient of Kovar alloy, ensuring long-term stable airtightness of glass-to-metal and ceramic-to-metal sealing structures.

2. Burr-free, ultra-smooth sealing edges
Metal is removed at the molecular level, with smooth and flat edge contours, no micro-burrs, dross or tearing defects. It perfectly fits glass and ceramic sealing surfaces, effectively avoiding air leakage and failure of hermetic packaging.

3. High precision for fine micro-features
Capable of processing narrow slots, dense micro-holes, high-precision lead frame arrays and irregular sealing contours. The dimensional tolerance can reach ±0.005 mm, meeting the high-precision packaging requirements of microelectronic devices.

4. No hard tooling cost, fast R&D iteration
Only digital photomask is required without expensive custom molds. Design modification only updates CAD files, which is suitable for prototype verification, small-batch trial production and mass production of semiconductor packaging parts.

5. Excellent flatness & assembly consistency
Ultra-thin Kovar sheets maintain perfect flatness after etching without warping or deformation, ensuring uniform stress distribution during lamination and sealing assembly, and improving product yield.

6. Integrated multi-functional forming
Realize one-time forming of sealing contours, positioning holes, half-etch bend lines and micro-grooves, with high material utilization, effectively reducing the production cost of high-value Kovar alloy.

Typical Applications

• Semiconductor & Microelectronics: Kovar lead frames, hermetic sealing frames, chip carrier substrates, precision packaging shims

• Vacuum & Electronic Devices: Glass-to-metal sealing parts for vacuum tubes, X-ray tubes, microwave tubes and precision instrument sensors

• Aerospace & Military Industry: High-reliability hermetic packaging components, vacuum sealing structural parts, temperature-stable precision spacers

• Communication & Precision Equipment: Kovar magnetic shielding cans, high-stability conductive connecting pieces, micro precision assembly parts

Design Limitations & Notes

Kovar etching follows the isotropic wet etching principle, and lateral undercut compensation must be reserved in CAD design. The minimum feature size is limited by the substrate thickness. The alloy has special chemical activity, requiring strict control of etching solution ratio and process parameters to avoid over-corrosion or incomplete etching. The etching process is only suitable for thin and flat precision parts; for thick structural parts or complex 3D deep drawing structures, stamping or machining processes are more applicable. Etched Kovar parts need strict surface cleaning to ensure no residual impurities, which is the key to guaranteeing subsequent high-reliability sealing performance.