Kovar Hermetic Packages for Telecom Electronics Manufacturers
A laser diode header, a TOSA or ROSA housing and a butterfly package for a telecom transceiver all share the same core requirement: a hermetic enclosure around an optical or optoelectronic component, sealed well enough to keep moisture out for the life of the product. Kovar carries that seal because its expansion tracks the glass and ceramic the package is built around. This guide covers the package geometries telecom manufacturers actually specify, what changes on the machine compared with a generic Kovar seal part, and when it makes sense to move from machined prototypes to stamped production parts.
Package types and where Kovar sits in each
Telecom optoelectronics packaging uses a handful of standard package families, and Kovar shows up in a specific role in each:
- TO-can headers, a round Kovar header with glass-sealed pins, used for laser diodes and photodiodes at lower channel counts. The header is often the only Kovar part; the can lid is typically a separate stamped or drawn metal cap.
- Butterfly packages, a rectangular Kovar or Kovar-based base with a pin row on each of two sides, used for cooled laser modules that need a thermoelectric cooler inside the package.
- DIP-style and box packages, used for some receiver and transceiver subassemblies, with a machined or stamped Kovar base and a seam-welded or soldered lid.
- TOSA and ROSA subassemblies, transmitter and receiver optical subassemblies that combine a sealed header with a barrel or sleeve, sometimes machined in Kovar and sometimes in a matched alloy chosen for the specific optical alignment hardware.
Across all of these, the glass-to-metal seal physics is the same as any other Kovar sealing application, covered in Kovar glass to metal seal machining. What is specific to telecom packaging is the geometry layered on top: seam weld ledges, TEC pass-throughs and pin counts driven by the module’s electrical interface rather than by a generic feedthrough design. The Invar specs reference lists Kovar’s specification and typical properties alongside Invar 36 and Alloy 42 if a mixed-material design is under consideration.
Package-specific geometry
| Feature | Typical requirement | Why it is telecom-specific |
|---|---|---|
| Seam weld ledge | Flat to 0.01 to 0.03 mm, consistent width around the perimeter | Uneven ledge height leaves a gap the seam welder cannot close, common failure mode on butterfly packages |
| Pin row spacing and count | Set by the module’s electrical interface, often 14 to 28 pins per side on butterfly packages | Pin layout is dictated by the transceiver or laser driver design, not a generic feedthrough pattern |
| TEC or thermal via pocket | Flat pocket floor, often with a separate thermal path spec | Cooled laser packages need a low thermal resistance path from the die to the base, which the machinist has to hold flat and clean |
| Optical window or fiber feedthrough boss | Position tolerance tied to the internal optical path, not just the outside of the package | Misalignment here affects coupling efficiency, not just hermeticity |
| Internal cavity depth and wall thickness | Set by the internal optical bench or submount that mounts inside | Package internal volume is driven by what has to fit inside, unlike a simple feedthrough connector |
The seam weld ledge is usually the tightest callout on the whole package, tighter in practice than the glass seal bores themselves, because a seam welder needs a continuous, flat, clean surface to close the weld without leaving a leak path. A shop unfamiliar with hermetic packages sometimes under-specifies this feature relative to the pin seals, which are the more obviously “precision” part of the drawing.
Machining vs stamping by volume
Most telecom hermetic packages start life machined and, if the design goes to volume, some or all of the metal parts move to stamping. The table gives typical guidance; actual figures depend on part complexity, tolerance and the shop or stamper’s own tooling cost.
| Factor | Machined base or lid | Stamped base or lid |
|---|---|---|
| Tooling cost | None beyond fixtures | Progressive die, often a meaningful upfront cost |
| Typical break-even volume | Prototype through low thousands per year | Low thousands per year and up |
| Design flexibility during development | High, easy to revise between lots | Low once the die is cut |
| Feature capability | Pockets, bosses, varied wall thickness | Best suited to uniform thickness with formed features |
| Lead time to first parts | Days to weeks | Weeks to months for die build, then fast per part |
| Typical fit | Prototype and pilot production, low-volume specialty modules | High-volume transceiver and laser module production |
The same tradeoff appears in Alloy 42 lead frames, covered in Alloy 42 machining for lead frames, where thin stamped parts and machined carriers or fixtures coexist in the same product. A telecom package program frequently runs the same pattern: machined Kovar bases for the first several thousand units, then a transition to stamped bases once volume and design stability justify the die.
Machining considerations specific to packages
Seam weld ledge flatness is held with the same fixturing discipline used on any thin or flat Kovar feature, described in Invar fixturing and workholding, which applies to Kovar bases and lids as well. Skim cuts after any stress-relieving step, rather than a single roughing pass, keep the ledge flat across its full perimeter.
Pin feedthroughs follow the seal bore practice in Kovar glass to metal seal machining: concentricity of the pin to the bore, a controlled edge break and a surface finish the glass wets evenly. On a butterfly package with two rows of a dozen or more pins, consistency across every bore matters more than any single bore’s absolute tolerance, since one out-of-family bore in a row of sealed pins is a single leak path in an otherwise good package.
Thermal via or TEC pocket flatness is a newer requirement compared with a generic Kovar seal part. The pocket floor has to sit flat against the thermoelectric cooler or submount with minimal air gap, which is closer to the flatness discipline used on thin Invar plates in Invar thin wall machining than to a typical seal feature.
Plating and hermeticity verification
Kovar packages are almost always plated after sealing, typically nickel as a barrier layer with gold on top for solderability and corrosion resistance on the surfaces that mate to a lid or a circuit board. The plating specification should state which surfaces are plated and to what thickness, since over-plating a seam weld ledge can change its dimensions enough to affect the weld, and under-plating a solder pad can cause adhesion problems downstream at the module assembler.
Hermeticity itself is verified by a helium leak test after sealing and, on some programs, after the seam weld as well, checking the completed package rather than assuming the seal and weld processes worked because the individual steps were in spec. A machine shop’s role ends before this test in most supply chains, since leak testing typically happens at the sealing house or at the module assembler, but the RFQ should still state the leak rate requirement so the shop and its sealing partner know what standard the finished part has to meet before it ships.
Qualifying a shop for telecom hermetic packaging
The general approach to qualifying an Invar or Kovar machine shop, covered in how to find an Invar machine shop with real experience, applies to package suppliers with two additions specific to this work:
- Has the shop machined seam weld ledges before, and can it describe the flatness it typically holds without a furnace-run stress relief step in between? Package lids and bases are often thin enough that the stress relief sequence used on a thick Invar 36 bracket does not apply the same way, and a shop should be able to explain its own approach rather than reciting a generic answer.
- Does the shop manage the sealing, plating and leak test chain, or does it deliver machined parts only? Telecom packaging supply chains vary widely in how much of this chain sits with the machinist versus a separate sealing house, and neither arrangement is wrong, but the RFQ and the quote need to agree on where the machine shop’s responsibility ends.
Worked example: butterfly package prototype to pilot run
Take a hypothetical 14-pin-per-side butterfly package for a cooled DFB laser module. The manufacturer needs 10 machined prototype bases for optical alignment and reliability testing, expects a pilot run of 200 to 500 units if testing passes, and projects several thousand units per year if the module is designed into a customer’s transceiver line.
| Stage | Typical approach | What is being decided |
|---|---|---|
| Prototype, 10 units | Machined from Kovar bar or plate | Fit of internal submount, seal integrity, seam weld process |
| Pilot, 200 to 500 units | Machined, same fixturing as prototype | Manufacturing repeatability before committing to tooling |
| Production, several thousand per year | Stamped base, possibly machined lid | Cost per unit at volume |
Figures are illustrative and a real program’s break-even point depends on the specific base geometry and the stamping tool cost quoted; see prototype vs production Invar and Kovar machining for how fixturing built during the machined stages typically carries into the tooling decision.
Back to the RF and telecom hardware overview
Hermetic packaging is one of several recurring needs across telecom and RF hardware programs, alongside custom connectors and waveguide components, covered together on the RF, microwave and telecom hardware overview.
What to put on the RFQ
- Package type and drawing, including the seam weld ledge dimensions and flatness callout.
- Pin count, spacing and which bores are seal-critical.
- Internal cavity features, TEC pocket, submount mounting and any thermal path requirement.
- Delivery condition, machined and cleaned, sealed, or sealed and plated, and who runs each step.
- Expected volume trajectory, so the shop can advise on the machining-to-stamping transition rather than quoting only the stage in front of it.
- Reliability and qualification testing the package must survive before production sign-off.
Send your drawing through the RFQ form, and we match it with up to three shops that machine Kovar hermetic packages and can speak to both the prototype stage and a later stamped production transition.
Frequently asked questions
Why do laser diode and transceiver packages use Kovar instead of aluminum or stainless?
Because the package is hermetically sealed, either by a glass or ceramic feedthrough for the electrical pins or by a seam-welded lid, and the seal only holds up over temperature cycling if the metal and the glass or ceramic expand at close to the same rate. Kovar's typical 5.0 to 5.5 ppm/°C CTE tracks borosilicate glass and alumina; aluminum at roughly 23 ppm/°C and even stainless at 16 to 17 ppm/°C would stress the seal on every thermal cycle.
Is the whole package machined from Kovar, or just the lid?
It depends on the design. Some packages machine the base, walls and lid all in Kovar for a uniform seal interface. Others use a machined or stamped Kovar base with pin header, paired with a Kovar or matched-alloy lid that seam welds to it. The base carrying the glass seal is almost always Kovar; the lid's material choice has more flexibility once the seam weld process is fixed.
At what volume does it make sense to switch from machining to stamping?
There is no fixed number, since it depends on part complexity and tooling cost, but the crossover for a simple lid or base typically falls somewhere in the low thousands of units per year. Below that, machining or a simple progressive tool is more economical than a full stamping die. Above it, the stamping die's upfront cost is repaid quickly by the much lower per-part time.
Can one shop handle both my prototype machined packages and a later stamped production run?
Some machine shops also run stamping or have a stamping partner and can carry a design from machined prototypes through a production tooling transition. Others focus on machining only and hand off the stamping decision to you. Ask directly during the RFQ which path the shop supports, since it affects how the prototype geometry should be designed for an eventual tooling transfer.
Are your matched shops certified for telecom or optoelectronics manufacturing?
We do not hold or claim any certification ourselves, and we do not certify shops in our network. Any certification, such as ISO 9001 or a customer-specific quality program, is described by the shop directly and should be verified with the shop before you commit to an order.
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.
Need a quote for this part?
Send the drawing. We match you with up to 3 shops that machine Invar and reply within 24 business hours.
Get matched with an Invar shop