"Hermetic" sounds binary and is not. It is a statement about a leak rate — how fast gas crosses the seal — and a package either meets a specified rate or it does not. MIL-STD-883 Method 1014 is the standard that turns the word into a measurement, and understanding what it tests is the difference between specifying a seal and hoping for one.
Why there are two tests, not one
Method 1014 covers fine leak and gross leak testing, and they exist separately because they fail differently and no single test catches both.
Fine leak testing finds the slow paths. A package is pressurised in helium, held, then measured on a mass spectrometer for helium escaping. Helium is used because its small atom finds paths larger molecules would not, so the test is deliberately more sensitive than the service condition — that is the point, not a flaw.
Gross leak testing finds the obvious ones. A large enough breach lets the tracer gas out so quickly that a fine leak test can read it as sealed — the helium is simply gone before measurement. So gross leak is checked by a different mechanism, typically immersion in a heated fluorocarbon fluid where a stream of bubbles makes the breach visible.
This is the counter-intuitive part worth remembering: a badly broken package can pass a fine leak test. That is exactly why the standard specifies both, and why "we leak tested it" is an incomplete statement without saying which.
What the numbers mean
A fine leak result is a rate, expressed in atmosphere-cubic-centimetres per second of helium, and the acceptable rate depends on the internal cavity volume — a small cavity tolerates less absolute leakage than a large one for the same service life, because the same flow changes its internal atmosphere faster. That relationship is written into the standard rather than left to judgment.
What that means in practice: a leak rate is not meaningful without the cavity volume beside it, and a supplier quoting a rate without one is quoting half a specification.
What leak testing does not tell you
Method 1014 tests the seal. It does not test what is inside the seal, and the distinction matters in real failure investigations.
A package can pass leak testing with contamination sealed inside it — moisture adsorbed on surfaces before the lid went on, or volatiles that a polymer inside the cavity will keep releasing over the part's life. The seal is doing its job perfectly; it is holding the wrong atmosphere in. This is a large part of why eutectic and metal-system attach methods show up in hermetic builds: they put nothing organic inside the cavity to outgas in the first place.
Nor does a leak rate at time zero say anything about the seal after temperature cycling. Thermomechanical stress is how a seal that passed becomes a seal that leaks, which is why a leak test after environmental stress tells a different and more useful story than one before it.
How the seal gets made
The seal method determines what the leak test is likely to find. We run solder and epoxy seals, eutectic seam sealing in Au-Si, Au-In and Sn-Ag systems, Kovar lids, glass-to-metal seals and seam welding — matched to the cavity, the internal components and the temperature the assembly can take. Hermetic testing is available on request, and MIL-STD qualification work is part of the same conversation.
Where to start
Three things scope a hermetic build:
- The internal cavity volume, because the acceptable leak rate depends on it.
- What is inside the cavity — anything organic changes the attach and seal strategy regardless of what the leak numbers say.
- The environmental profile the part has to survive, since a leak rate before thermal cycling and one after are different claims.
More on seal methods, lid options and testing on our hermetic packaging page. If the cavity contents are what is driving the decision, eutectic versus epoxy die attach covers the other half of it.
Answered.
What does MIL-STD-883 Method 1014 test?
It is the standard method for seal testing on hermetic microelectronic packages, and it covers two separate tests: fine leak, which finds slow leak paths using a helium tracer and a mass spectrometer, and gross leak, which finds large breaches by a different mechanism such as immersion in heated fluorocarbon fluid.
Why are fine leak and gross leak tested separately?
Because a large breach can let the tracer gas escape before measurement, so a badly broken package can read as sealed on a fine leak test. Gross leak testing uses a different mechanism specifically to catch that case. Saying a package was "leak tested" is incomplete without saying which of the two.
What is an acceptable helium leak rate for a hermetic package?
It depends on the internal cavity volume, and the standard defines the relationship rather than leaving it to judgment — the same absolute leak changes a small cavity's internal atmosphere faster than a large one's. A leak rate quoted without the cavity volume beside it is half a specification.
Does passing a leak test mean the inside of the package is clean?
No, and this is a common source of confusion. A package can pass leak testing with moisture or outgassing volatiles sealed inside it. The seal is working correctly; it is holding the wrong atmosphere in. It is one of the main reasons hermetic builds favour attach methods that put nothing organic inside the cavity.
Which hermetic seal methods do you offer?
Solder and epoxy seals, eutectic seam sealing in Au-Si, Au-In and Sn-Ag systems, Kovar lids, glass-to-metal seals and seam welding — matched to the cavity, its contents and the temperature the assembly can tolerate. Hermetic testing is available on request, in Halethorpe, Maryland, on US soil.