Overview

Kovar lid etching forms hermetic sealing lids from Kovar sheet by photochemical machining, an iron-nickel-cobalt alloy (about 29% nickel, 17% cobalt) engineered to match the thermal expansion of glass and ceramic. The lid outline, sealing ring, internal steps and vent apertures are imaged onto a photoresist mask, developed, and the exposed metal is dissolved in an alloy-matched etchant. Since the metal is removed chemically, the lid emerges flat and burr-free, without the edge roll-over, work-hardening and residual stress that stamping leaves behind on the very surface that must be welded or soldered.

This matters because a sealing lid is a tolerance-critical part, not a simple cover. Kovar lid etching keeps the sealing land straight and square, which lets a seam-weld or solder preform close with a uniform, void-free joint; it keeps the lid flat so the seal ring seats evenly on the package wall; and it holds fine steps and slots that stamping cannot resolve. The result is a closure that survives the thermal cycling, mechanical shock and hermeticity testing that electronic packages are subjected to, and it comes with the tooling-free economics of a photographic process — every new lid shape is simply a new film.

Parameter Window

• Available Materials: Kovar (ASTM F-15 / UNS K94610), Alloy 42, Alloy 52, nickel
• Material Thickness Range: 0.05–0.4 mm
• Tolerance: ±0.025 mm on outline, ±0.02 mm on sealing edge width
• Minimum Feature: 0.08 mm line width, 0.15 mm step or slot at 0.15 mm stock
• Surface Options: electrolytic nickel, electroless nickel/gold, solderable tin finish, bare alloy
• Compliance: ISO 9001 process control, RoHS/REACH material traceability

Manufacturing Process / Workflow (8 Steps)

1. Drawing Review — Convert package drawings to vector artwork, check sealing-land width against stock thickness, and lock outline and step calls.
2. Material Selection — Confirm Kovar grade and temper; choose Alloy 42 or Alloy 52 where a different expansion match or lower cost is required.
3. Cleaning & Lamination — Degrease the sheet and laminate dry film resist so no bubbles sit under the sealing land or step edges.
4. UV Exposure — Expose through high-resolution film with the artwork registered to the sheet edge for panel-level accuracy.
5. Development — Wash out unexposed resist to open the lid outline, steps and slots, then inspect for under-developed edges.
6. Etching — Spray-etch in Kovar-matched chemistry; sidewall angle and edge straightness are set by time, temperature and conveyor speed.
7. Stripping & Plating — Remove resist, neutralize, then plate nickel or nickel/gold; stress-relief anneal is available where flatness must be restored.
8. Inspection & Packaging — Verify flatness, sealing-edge width, edge quality and plating against the approved sample, then pack in trays or waffle packs.

Core Advantages

1. Straight, square sealing edges: The etched edge is burr-free and true, so seam-weld and solder joints close with a uniform, void-free ring.
2. Flat and stress-free: Chemical removal introduces no dishing, curl or residual stress, keeping the lid flat for an even seal.
3. Matched thermal expansion: Kovar's CTE tracks glass and ceramic, so the seal survives thermal cycling and shock without cracking.
4. Fine steps and slots: Recesses, vent slots and alignment features hold at 0.15 mm without the distortion stamping causes.
5. Solderable and weldable surface: Nickel and nickel/gold plating provide a clean, wettable surface for brazing, soldering or seam welding.
6. Tooling-free iteration: Each package outline is a new film, so lid geometry can change in hours — kovar lid etching stays economical through every design revision.

Typical Applications

• Crystal oscillator lids: Thin Kovar closures for quartz crystal packages sealed under vacuum or inert gas.
• Sensor package lids: Sealing covers for pressure, gas and inertial sensor packages.
• MEMS package caps: Kovar lids for MEMS devices with matched expansion to silicon and glass.
• Optoelectronic covers: Lids with window apertures for laser diode and photodiode packages.
• Hybrid microcircuit lids: Covers for thick-film and hybrid circuit packages with matched expansion.
• Relay and transistor lids: Hermetic closures for power relays and transistors sealed by seam welding.

Design Notes & Process Considerations

1. Sealing-land width: Keep the sealing land at least 1.5 × material thickness wide, or the seam weld will not close reliably.
2. Flatness callout: State flatness per 10 mm, since a dished or curled lid cannot form a uniform seam-seal ring.
3. Plating specification: Name the plating and thickness; electrolytic nickel, electroless nickel/gold and tin all behave differently in solder and weld.
4. Expansion match: Verify the Kovar grade against the glass or ceramic CTE; a mismatch will crack the seal through thermal cycling.
5. Step and vent features: Specify half-etch depth for steps and slots, typically ±10% of stock thickness, and avoid blind pockets that trap etchant.
6. Panel layout: Group lids on one sheet with shared registration marks to reduce handling and keep unit cost down while preserving edge quality.