Kovar Hermetic Packages for Defense and Avionics Electronics
Defense and avionics electronics put a Kovar housing through the same sealing physics as any other hermetic package, but the surrounding expectations are different. A commercial sensor housing might need one good seal and a mill certificate. A radar module housing or an avionics connector body often needs a documented process trail, a realistic production volume plan and proof that the assembly survives a service thermal profile that is wider and less forgiving than a lab shelf life test. This guide picks up where Kovar glass to metal seal parts leaves off, on the assumption that the sealing chemistry there is already understood, and focuses on what a defense or avionics buyer specifically should plan for. See the aerospace and defense overview for the wider picture across alloys and applications.
Where Kovar packaging shows up in defense and avionics hardware
The parts a machine shop sees from this segment cluster into a few recognizable families, distinguished more by the assembly they sit in than by their geometry:
- RF and microwave module housings, machined boxes and lids that carry feedthroughs and windows for radar, EW and communications hardware, where the housing itself may be aluminum but the feedthrough body and seal ring are Kovar.
- Connector and header bodies, turned and milled parts that carry sealed pins through a bulkhead or a chassis wall on avionics and munitions electronics.
- Sensor and detector packages, housings and lids for infrared, optical and other detector elements that need a hermetic environment around the sensing element.
- Power and control electronics feedthroughs, pin carriers that bring power or signal lines through a sealed wall on flight or ground defense hardware.
The common thread is that the Kovar component is rarely the whole assembly. It is the sealing interface bolted, welded or brazed into a larger housing that may be aluminum, titanium or steel, which is part of why documentation on the Kovar piece specifically matters. A failure traced to the wrong component in a multi-material assembly is expensive to diagnose.
This also means the Kovar part’s drawing usually carries interface requirements that have nothing to do with sealing on their own: bolt patterns to a housing wall, a specific finish where a gasket or O-ring seats, or a ground path through the metal for EMI control. A shop quoting the seal itself needs to see the full drawing, not just the sealed feature, because a change to the mounting interface can affect how the part is fixtured and machined even though it never touches the glass.
Volume and quantity expectations: prototypes versus program production
Defense and avionics programs move through distinct quantity phases, and a shop’s fit for one phase does not guarantee fit for the next.
| Program stage | Typical quantity | What the shop needs to support |
|---|---|---|
| Concept and engineering build | 1 to 10 units | Fast turnaround, tight collaboration on drawing questions, tolerance for design changes between units |
| Qualification build | 10 to 50 units | Process repeatability, a documented first article, consistent heat treatment across the lot |
| Low rate initial production | Tens to low hundreds per year | Stable tooling and fixturing, lot traceability, predictable lead time |
| Sustained production | Steady annual volume over years | Long term material supply agreements, requalification if a process or material source changes |
A shop that is excellent at fast, flexible prototype work is not automatically the right fit for a program that needs the same part, unchanged, every quarter for a decade. Conversely, a production-oriented shop may be slow and expensive for a single engineering unit. State which phase your program is in on the RFQ so the match reflects the right kind of shop.
Long gaps between production lots are common on defense platforms with decades of service life, and they raise a question worth planning for early: whether the original shop, tooling and material source are still available when the next lot is ordered. A program that expects intermittent, spread-out production benefits from asking a shop up front how it handles requalification after a multi-year gap, rather than discovering the answer when the next order is placed.
Qualification expectations buyers bring from defense programs
Buyers coming from a defense or avionics background often expect a level of documentation that a purely commercial Kovar buyer would not ask for: a heat lot specific material certificate against ASTM F15 or the alloy’s UNS number, listed with the other low expansion alloys on the reference page of Invar specifications, a recorded anneal and oxidation cycle rather than a verbal description of the process, and a first article inspection report covering both dimensions and the seal-ready surface condition. None of this implies or requires that the shop hold a specific certification, and we do not claim that any matched shop is AS9100 certified, ITAR registered or qualified to a specific military standard. If your program requires a specific certification or registration, verify it directly with the shop, in writing, before you commit the order. The Invar machining for aerospace suppliers guide covers the general traceability and first article questions worth asking any shop on a program of this kind, and they apply here with the sealing-specific items from the Kovar glass to metal seal parts guide layered on top.
Thermal cycling in service: what a housing has to survive
A sealed Kovar package for ground or flight defense electronics often sees a wider and harsher thermal environment in service than the sealing process itself. Test programs commonly reference profiles similar in shape to those used across the defense electronics industry, cycling between a low temperature extreme and a high temperature extreme repeatedly with dwell time at each end, though the exact profile, dwell time and cycle count are set by the customer’s own specification, not by this article.
| Test parameter | Typical range referenced in industry practice | Why it matters to the housing |
|---|---|---|
| Low temperature extreme | As low as −55 °C for ground and airborne electronics | Seal materials contract; a mismatch in CTE opens a leak path |
| High temperature extreme | Up to 125 °C or higher depending on the platform | Repeated expansion can fatigue a marginal seal over many cycles |
| Cycle count | Tens to hundreds of cycles for qualification testing | A seal that survives one cycle can still fail after fifty |
| Dwell time at extremes | Minutes to tens of minutes per extreme | Ensures the part reaches thermal equilibrium, not just a brief temperature spike |
These figures describe common industry practice for reference only. The actual profile a given part must survive is set by the customer’s specification, and this article makes no claim that any specific part or shop meets a named military standard. The thermal cycling test guide covers how a cycling test is typically run and reported for these alloys in more detail.
Worked example: a connector body across a wide service swing
Take a hypothetical Kovar connector body with a 6 mm sealed pin, installed in a housing that sees an operational range from −55 °C to 125 °C, a swing of 180 K from a 25 °C assembly reference. The question is how far the seal interface itself moves across that range compared with the borosilicate glass bead sealing the pin.
Dimensional change of a 6 mm bore over 180 K = 6 mm × CTE × 180.
| Material | Typical CTE, ppm/°C | Change over 6 mm, mm | Mismatch to glass at about 5.0 ppm/°C, mm |
|---|---|---|---|
| Kovar body | 5.3 | 0.0057 | 0.0003 |
| Borosilicate sealing glass | 5.0 | 0.0054 | 0.0000 |
| 304 stainless (hypothetical alternative body) | 16.5 | 0.0178 | 0.0124 |
Values and the scenario are illustrative, not measured data from a real program. Across the full 180 K swing the Kovar body and the glass stay within a few microns of each other, which is what a properly annealed and oxidized seal is designed to absorb repeatedly. A stainless body in the same geometry would open a gap roughly forty times larger over the same swing, which is the practical reason Kovar, not a more common structural alloy, carries the sealed feedthrough even inside an otherwise all-metal housing.
What to put on the RFQ
- Program stage and expected volume, from a handful of engineering units through sustained annual production, so the match reflects a shop suited to that phase.
- Service temperature range and cycle expectations, even as a rough range, so the shop understands what the seal has to survive beyond the sealing process itself.
- Documentation required: heat lot certificate, recorded anneal and oxidation cycle, first article report, and whether you need per-lot or per-part records.
- Delivery condition: machined and cleaned, annealed and cleaned, or annealed, cleaned and oxidized to a stated sealing specification.
- Any certification or registration requirement, stated explicitly so it can be verified directly with the shop rather than assumed.
- STEP file, PDF drawing and quantity, with a realistic annual volume if the program is expected to reach production.
Send your drawing through our RFQ form, and we match it with up to three shops that machine Kovar for electronics packaging and can speak to your program’s volume and documentation needs. You verify certifications and manage program qualification directly with the shop.
Frequently asked questions
How is this different from a general glass-to-metal seal guide?
Kovar glass to metal seal parts covers the sealing physics and the anneal, clean and oxidize sequence that applies to any Kovar seal. This article assumes that background and focuses on what changes when the buyer is a defense or avionics program: volume expectations, documentation and the thermal cycling the housing sees once it is in service.
What quantities are typical for defense electronics Kovar parts?
It varies widely by program stage. Early qualification and engineering builds often run single digit to low dozens of units. Programs that reach production can run steady quantities over years as the platform stays in service, sometimes with long gaps between production lots that raise their own retooling and requalification questions.
Does a defense program require different heat treatment than a commercial Kovar part?
The underlying anneal, decarburize and oxidize sequence is the same physics regardless of end use. What differs is documentation: a defense or avionics program more often wants the process recorded, the furnace load traceable and the oxide inspection reported per part or per lot, rather than taken on trust.
Does thermal cycling testing certify a part for military use?
No single test qualifies a part for a program on its own. Thermal cycling demonstrates that a specific design and process survive a stated temperature profile without seal or dimensional failure. Program qualification is a broader process defined by the customer's specification, and this article does not claim any matched shop's parts are qualified to a specific program without that program's own review.
Do you machine or seal these parts yourselves?
No. We are a matching service. We connect your RFQ with up to three shops that machine Kovar for electronics packaging and can speak to the volume, documentation and thermal cycling your program needs. You place the order and manage qualification directly with the shop.
Reviewed against
Values in this guide are typical handbook figures for planning. The mill certificate for your heat lot and the shop's quote for your geometry govern.
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Get matched with an Invar shopKeep reading
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