Alloy
Alloy 42 Machining: Controlled Expansion Without the Kovar Price
Alloy 42 (Fe-42Ni, ASTM F30) tracks alumina ceramic and softer sealing glasses at a lower cost and wider strip availability than Kovar. Most parts are thin, so fixturing decides the outcome, not the cutting. Send your drawing and we match it with shops that machine Alloy 42 and can hold it flat.
Why Alloy 42 and why the sequence matters
Alloy 42 is bought for a controlled expansion around 5 ppm/°C at a lower cost and wider strip availability than Kovar. It is the standard alloy for integrated circuit lead frames, and it also appears in ceramic-to-metal seals, ferrule and cap parts and bonded bimetal strip, anywhere a match to alumina or a softer sealing glass is worth more than the lowest possible expansion.
Most Alloy 42 parts a machine shop sees are thin: carriers, test fixtures, spacers and lids around a stamped lead frame, or short runs of a part too small a volume to justify a stamping die. On thin stock, rolling stress and cutting stress bow the part more easily than they would a thick Invar 36 block, so flatness is usually the harder problem, not the cutting.
Shops that machine Alloy 42 well remove stock evenly from both faces, clamp with low, even force, and stress relieve between roughing and finishing. Parts that plate or seal get an additional anneal to the plating or sealing spec. We match your RFQ with shops that already work this way.
Alloy 42 at a glance
Typical handbook values for planning. The mill certificate for your heat lot is the number to design to. Full cross-reference on the Invar specs reference.
| Property | Typical value |
|---|---|
| Composition | About 42 % Ni (41 to 43 typical), balance Fe. Co 0.5 % max, Mn 0.8 % max, Si 0.3 % max, C 0.05 % max (typical F30 limits) |
| Typical CTE | 4.0 to 6.0 ppm/°C from 30 to 300 °C, between Invar 36 and Kovar |
| Curie temperature | About 380 °C. Above it the alloy expands like a normal nickel steel |
| Density | 8.12 g/cm3 |
| Hardness, annealed | About 140 to 170 HB |
| Machinability | Roughly 45 to 55 % of B1112, similar band to Invar 36 and Kovar. Gummy, work hardens |
| Magnetic | Ferromagnetic at room temperature |
| Specs and names | ASTM F30, UNS K94100, historically referenced under MIL-I-23011 class 5. Trade names include Alloy 42, NILO 42, Pernifer 42, 1.3917 in the EN system |
| Stock forms | Strip and sheet are the common mill forms for lead frames. Round bar and plate exist in fewer sizes for machined parts |
How shops machine Alloy 42
The cutting is ordinary. The order of operations and what happens between them is what protects the property you are paying for.
Machine
Sharp positive tools, steady feeds, flood coolant and low clamping force on thin sections. Alternate passes on opposite faces so stock removal stays even and the part does not bow.
Stress relieve
A typical cycle holds thin flat parts near 400 to 480 °C for 30 to 60 minutes, longer for thicker carriers and fixtures. Skipping it is the most common cause of warped lids and carriers.
Finish and flatten
Light finishing passes, with lapping or grinding on faces that must stay flat. A flat vacuum plate or a soft jaw set spreads clamping force evenly across the part.
Anneal, clean and plate
Parts that seal or get plated are annealed in a protective atmosphere near 850 to 1000 °C to soften and decarburize the surface, then cleaned before plating. The plating or sealing spec sets the cycle.
| Operation | Tool | Speed | Feed | Note |
|---|---|---|---|---|
| Milling, carbide | Sharp positive rake, coated | 35 to 65 m/min | 0.05 to 0.12 mm per tooth | Keep the feed up on thin sections to avoid rubbing and heat buildup |
| Turning, carbide | Positive insert, small nose radius | 40 to 75 m/min | 0.1 to 0.2 mm/rev | Chip control matters, chips run long like Invar 36 |
| Drilling | HSS-Co or carbide, split point | 10 to 20 m/min | 0.05 to 0.15 mm/rev | Peck, flood coolant, do not dwell in thin sections |
| Lapping and grinding | Friable wheel, light passes | shop practice | light | Common for the final flat faces on carriers and lids |
Where Alloy 42 parts are used
Lead frames and IC packages
The frame itself is stamped or etched from strip. Machined carriers, test fixtures, spacers and lids surround it in the same package.
Ceramic and soft glass seals
Frames and headers that seal to alumina ceramic or to sealing glasses softer than hard borosilicate, where Kovar is not required.
Bimetal strip and thermostats
One layer of a bonded bimetal strip, paired with a higher expansion alloy so the assembly bends predictably with temperature.
Not for
Hard borosilicate glass seals and vacuum tight hermetic packages, where Kovar’s closer glass match and established sealing practice are the safer choice.
Typical tolerances on Alloy 42
What a stable, well fixtured part can hold after the right sequence. Tighter is possible on small features at real cost. See the tolerance guide.
| Feature | Typical | Note |
|---|---|---|
| Flatness on thin plates and lids | 0.02 to 0.05 mm | After stress relief, needs even stock removal from both faces and low clamping force |
| Bores and locating features | ±0.01 to ±0.03 mm | Finished in a second setup after stress relief, measured at 20 °C |
| Position of pin or lead patterns | 0.02 to 0.05 mm | Datum scheme on the drawing decides the fixture |
| Non-critical features | ±0.1 mm | Loosen it. Tight tolerances on thin Alloy 42 cost real time |
What to put on a Alloy 42 RFQ
Shops quote what they can read. These six lines get you comparable quotes. The full list is in the RFQ drawing checklist.
Alloy and spec: "Alloy 42 per ASTM F30" or the UNS number K94100.
Part thickness and which faces must stay flat, so the shop can plan stock removal and fixturing.
Heat treatment: "stress relieve after roughing", or the plating or sealing anneal spec if the part is plated or sealed.
Whether the part seals to glass or ceramic, and to what glass, since that can decide between Alloy 42 and Kovar.
Tolerances only on features that matter, with the inspection temperature (20 °C per ISO 1) called out.
A STEP file plus a PDF drawing. Quantity and a realistic yearly volume, since strip and bar minimums vary by mill.
Alloy 42 guides
- Materials
Machining Alloy 42 (ASTM F30): Thin Parts, Flatness and Alloy Choice
Alloy 42 machining: ASTM F30, typical CTE 4 to 6 ppm/°C, used in lead frames and ceramic packages. Thin part fixturing, stamping vs machining and alloy choice.
- Materials
Machining Kovar for Glass to Metal Seals: What the Seal Needs
Kovar glass to metal seal machining: why ASTM F15 Kovar matches borosilicate glass, how it machines, the anneal and oxide steps before sealing and the RFQ.
- Materials
Invar 36 vs Kovar vs Super Invar: Which Alloy for Your Part
Invar 36 vs Kovar vs Super Invar: typical CTE bands, Curie point, specs and machining notes, with a decision table for mounts, glass seals and space parts.
- Process
Thin-Wall Invar Parts: Machining Without Warping
Why thin Invar walls and webs are prone to distortion during machining, and the fixturing, sequencing and stress relief practices shops use to keep them flat.
- Process
Invar Fixturing and Workholding: Avoiding Distortion During Machining
Why workholding matters more on Invar parts than on steel or aluminum, and the fixturing practices shops use to avoid clamping distortion on thin or precision features.
- Process
Stress Relief for Invar Machined Parts: When and How Shops Do It
Why Invar parts move after roughing, typical stress relief and stabilization cycles, where they sit in the machining sequence and how to write the drawing note.
- Materials
Invar 36 by Other Names: Regional Trade Names and Specs
Why the same 36 percent nickel-iron alloy is called Invar 36, Pernifer 36, Nilo 36 or FeNi36 depending on the supplier and region, and how to match specs across them.
- Choosing a Supplier
Invar Mill Certifications: What a Certified Material Report Should Show
What a standard Invar 36 or Kovar mill cert includes, when to ask for measured CTE data, and how to read a certified material test report before it reaches your shop.
Have a Alloy 42 drawing ready?
Send the short version now. We will ask for anything missing. For full details up front use the full RFQ form. Reply within 24 business hours.
Your files go only to the shops we match. Ask for an NDA and nothing is shared until it is signed.
Questions about Alloy 42 machining
Something else? Email .
Is Alloy 42 the same as Kovar?
No. Both are iron-nickel controlled expansion alloys with a similar CTE, but Kovar adds cobalt (ASTM F15) and is the established choice for hard borosilicate glass seals. Alloy 42 (ASTM F30) costs less, is more widely stocked as strip, and suits ceramic seals, softer glass seals or parts that do not seal at all, like lead frames and bimetal strip.
Why are Alloy 42 parts hard to hold flat?
Most machined Alloy 42 parts are thin, so residual stress from rolling and from cutting bows them more easily than it would a thick block. Even stock removal from both faces, low clamping force and a stress relief between roughing and finishing are what keep a thin part flat, not the cutting itself.
Should my lead frame be machined?
No. Lead frames are stamped or chemically etched from strip in production volume. Machining suits the parts around the frame, carriers, test fixtures, spacers and lids, or short runs where a stamping die is not justified.
What tolerance can a shop hold on Alloy 42?
On a stable, well fixtured part, flatness of 0.02 to 0.05 mm and bore tolerances of ±0.01 to ±0.03 mm are common after stress relief. Thin, unsupported features cost more to hold tight and should get the loosest tolerance the design allows.
Do you machine Alloy 42 parts yourselves?
No. We are a matching service. We read your RFQ and connect you with up to three shops that have cut Alloy 42 and can fixture and stress relieve thin parts correctly. You place the order with the shop.