telephone icon

Call +44 (0) 1342 717102



Materials & Plating Options



Materials & Plating Options


Materials generally

used by:

Seal Header - Body Electrodes Glass
Compression Seals

Cold Rolled steel
Stainless Steel

52 Alloy
Copper Cored 52 Alloy
42 Alloy
42-6 Alloy
Alkali Barium
Lead Silicate
Potash Sead
Soda Lime
Matched Seals Kovar
(hard glass - Alkali,
Barium, Soda, Potash)

Typical characteristics offered by our seal assemblies:

Breakdown voltage 40 VAC / 55 VDC per radial .001" of glass between header and electrode.

Hermeticity 1.04 x 10-8 Atm cc/sec, <.001 µ Cu. ft/Hr (Helium @ 1Atm)

Insulation resistance ranges @ 500VDC > 50 MΩ.


Seal Comparison Capabilities Cost Bracket

Continuous Upper
Temperature Limit

Reason for
Temperature Limit

Burst Pressure
(Bar) 6.5cm2

Compression Seals Least expensive and robust 230°C Expansion 870
Matched Seals More expensive and delicate 340°C Expansion 240


Plating & Material Options

Hermetic Seals can be provided in an extremely wide variety of materials which add corrosion resistance, improve solderability and enhance electrical performance to meet the requirements of the most demanding application. Various plating materials are available with either electroless (immersion) coatings or electrolytic selective plating.


The simplest seal comprises an outer body called a grommet, the insulating sealing medium (the glass) and the center pin or electrode. Without the electrode and using special glass the seal can be used as a sight glass.


Requirements and Typical Process for Compression Seals

  • Glass Bead: ID and OD determined by application, wall thickness limit: 0.38mm. We currently have a wide selection of standard beads. 
  • Preferred Materials:
    • Grommet - Cold rolled steel, inexpensive and strong (Grommet inner Ø must be <75% of the outer Ø (without sufficient wall the grommet will yield resulting in a failed seal.)
    • Electrodes - 52NiFe Alloy provides proper expansion characteristics.
  • Pre-Sealing Component Preparation Process – Grommets & Electrodes: Aqueous wash, dry, furnace anneal.
  • Firing and Sealing: Components are then loaded onto Graphite fixtures. The fixtures are loaded onto the furnace pallet and placed into the vacuum furnace. Heating takes place in our computer controlled, vacuum furnace (pre-programmed with appropriate parameters).
  • Quality Control: The fixtures are unloaded. Seals are inspected visually, followed by extensive sample assessment using our exacting testing equipment, all prior to being counted into our finished inventory.
  • Plating Process:
    • Electrodes can be plated selectively with specialized racks.
    • Entire seals can be processed.
    • Plating materials can include Nickel, Copper, Silver or Gold.
    • Plating to specific thicknesses or special finishes is also possible.


Please contact us at the number below if you would like to know more about our Hermetic Seals.

Willow Technologies Ltd. Unit 3 Borers Yard, Borers Arms Road, Copthorne, West Sussex, RH10 3LH, UK

Tel: +44 (0) 1342 717102, Email:

CORPORATE: Solid State Group

Privacy Policy • Cookie Policy