Overview

A custom kovar hermetic lid is a precision cover, formed by photochemical etching, that seals semiconductor, optoelectronic and RF packages against moisture and gas ingress. Kovar (ASTM F15, Fe-Ni-Co) is chosen because its thermal expansion closely matches borosilicate glass and alumina ceramics, so a glass-to-metal or ceramic-to-metal seal stays hermetic across temperature cycling. Photochemical machining dissolves the unprotected metal through a photoresist mask rather than shearing it, so lids leave the line flat, burr-free and free of the stress and recast layer that stamping or laser cutting would introduce into a sealing surface.

For a packaging engineer, a custom kovar hermetic lid solves three recurring problems: sealing faces that must be mirror-flat and scratch-free to wet the braze or glass evenly, fine features such as alignment notches, vent windows and marking pockets that cannot be punched without distorting a thin sheet, and plating or brazing cladding that must survive a 400 °C sealing cycle without blistering. Because the geometry is defined by artwork, a new package outline is a new film rather than a new die, so prototype-to-volume iterations stay economical. Supplied from 0.10 mm to 1.0 mm stock, these lids are typically nickel- or gold-plated after etch to protect the Kovar surface and support wire bonding or die attach downstream.

Parameter Window

• Available Materials: Kovar (ASTM F15 / 4J29), Alloy 42, stainless 316L on request
• Material Thickness Range: 0.10–1.0 mm
• Tolerance: ±0.02 mm on sealing-ring flatness, ±0.03 mm on outline profile
• Minimum Feature: 0.12 mm slot width and 0.20 mm notch radius at 0.25 mm stock
• Surface Options: electroless nickel, electrolytic Ni/Au, bright anneal, passivation, glass-bead blast
• Compliance: ISO 9001 process control, RoHS/REACH material traceability

Manufacturing Process / Workflow (8 Steps)

1. Artwork & DFM Review — Convert the package drawing to vector artwork, check slot-to-thickness ratios and confirm seal-ring width and corner radii.
2. Alloy & Temper Selection — Match Kovar lot, cold-rolled temper and flatness to the sealing method and the downstream plating spec.
3. Cleaning & Lamination — Degrease and micro-etch the sheet, then laminate dry-film resist under controlled heat and pressure.
4. UV Exposure — Expose both faces through registered high-resolution film so front-side pockets align to back-side outlines.
5. Development & Inspection — Develop the resist and inspect for pinholes or scumming on the sealing land before etching.
6. Controlled Etching — Spray-etch in ferric-chloride chemistry tuned for Fe-Ni-Co; time, temperature and conveyor speed set wall profile.
7. Stripping, Anneal & Plating — Strip resist, hydrogen anneal to relieve stress, then apply electroless Ni or Ni/Au to the sealing surface.
8. Flatness & Leak Verification — Measure seal-land flatness, outline and burr, then pack in trays or on tape for cleanroom transfer.

Core Advantages

1. Seal-ready flatness: Chemical removal leaves no roll-over or burr, so the sealing land wets braze or glass evenly and leak rates stay low.
2. No hard tooling: A new package outline is a new phototool, not a stamping die, which keeps low-volume and revision-heavy programs affordable.
3. Stress-free edges: Etched parts carry no mechanical work-hardening or heat-affected zone that could warp a thin lid during the sealing cycle.
4. Fine package features: Alignment notches, vent windows, index marks and shallow marking pockets hold at 0.12 mm on 0.25 mm stock.
5. Plating-friendly surface: A uniform, oxide-controlled Kovar surface accepts dense Ni/Au plating with consistent braze wetting.
6. Batch-to-batch repeatability: A custom kovar hermetic lid produced from one approved film etches identically from first article to high-volume lots, simplifying incoming qualification.

Typical Applications

• Ceramic package lids: Covers for hermetic ceramic IC and MEMS packages sealed by glass frit or AuSn braze.
• TO and metal-can headers: Flat lids for transistor-outline and optoelectronic cans that need a weldable sealing ring.
• RF and microwave modules: Shielded cavity covers with etched vent patterns and grounded sealing lands.
• Sensor and detector housings: Hermetic closures for infrared detectors, pressure sensors and vacuum devices.
• Laser diode and VCSEL packages: Lids with optical apertures and alignment fiducials for active alignment.
• Hybrid microcircuits: Covers for thick-film and thin-film substrates requiring a controlled-atmosphere seal.

Design Notes & Process Considerations

1. Seal-land width: Keep the continuous sealing land at least 0.6 mm wide, or 2.5 × material thickness, to guarantee a reliable wetting area.
2. Flatness callout: Specify seal-surface flatness per 25 mm and overall bow; thin Kovar can distort during annealing if not fixtured.
3. Corner radii: Use internal radii ≥ 0.20 mm to avoid resist trapping and stress concentration at package corners.
4. Plating specification: State nickel underplate thickness, gold thickness and whether plating covers edges, cavities or only the sealing face.
5. Cladding and brazing: Note any braze preform or clad layer, plus the peak sealing temperature, so the alloy temper is chosen accordingly.
6. Panelization and marking: Group lids on a shared registration grid and add orientation marks; a custom kovar hermetic lid with clear fiducials speeds automated pick-and-place and seal alignment.