Summary: what is SEMI F47?
SEMI F47 is a voltage sag immunity specification from SEMI, the global semiconductor industry association. It was approved in 1999, and the current version is F47-0706. It requires semiconductor process, metrology, and automated test equipment to pass three test points: voltage at 50% for 200 ms, 70% for 500 ms, and 80% for 1 s, with no shutdown and no operator intervention. Test methods depend on equipment current: IEC 61000-4-11 (16 A per phase or less) or IEC 61000-4-34 (above 16 A).
What does SEMI F47 cover?
SEMI F47 was driven jointly by EPRI (Electric Power Research Institute), utilities, chipmakers, and equipment makers, and approved in 1999 (EPRI, 2013). It sets the "minimum" voltage sags that semiconductor process, metrology, and automated test equipment must ride through, with a simple goal: when a sag hits, equipment keeps running without operator intervention.
Know what it doesn't cover, too: F47 doesn't address product quality, and doesn't cover swells, high-frequency transients, or other power disturbances (Advanced Energy, AN1401). Facility systems have a separate guide, SEMI F49, and utility-side sag performance is covered by SEMI F50.
The F47 curve: three test points
| Remaining voltage | Duration | Cycles at 50 Hz | Cycles at 60 Hz |
|---|---|---|---|
| 50% | 200 ms | 10 cycles | 12 cycles |
| 70% | 500 ms | 25 cycles | 30 cycles |
| 80% | 1 s | 50 cycles | 60 cycles |
The percentage means "how much voltage remains during the sag." For example, a 70% sag on a 200 V system means voltage falls to 140 V, not 60 V.
F47-0706 also lists three "recommended but not required" points: 0% remaining for 1 cycle (20 ms), 80% for 10 s, and continuous operation at 90% (Advanced Energy, AN1401).
F47-0706 vs. F47-0200
The 2006 revision removed the old "50% for 50 ms" test point and changed compliance to "passing the three test points," rather than "riding through everything above the curve." It also states explicitly that simultaneous three-phase sag testing is not required. In its 2011–2012 review, the standard was judged to need no technical changes and remains in effect (Lewis Bass, history of the SEMI F47 standard).
| Item | F47-0200 (old) | F47-0706 (current) |
|---|---|---|
| Published | February 2000 | July 2006; reviewed 2011–2012, unchanged |
| 50% for 50 ms | Included | Removed |
| Required points | From 50% / 50 ms up to 80% / 1 s | 50% / 200 ms, 70% / 500 ms, 80% / 1 s |
| Compliance | Everything above the curve | Pass 3 points |
| 3-phase sags | Not specified | Not required |
The last four digits of the version number are the publication month and year: 0200 = February 2000, 0706 = July 2006. Which version your equipment spec or purchase documents cite changes how acceptance works, so clarify it first.
How F47 is tested
The following procedure is based on F47-0706 requirements and a publicly available test report (PULS TP960.241 SEMI F47 test report, 2024):
Test conditions
Record the equipment under test's rated voltage, frequency, and load. Testing must be done under a load that "represents actual use"; passing with no load means nothing. Both 50 Hz and 60 Hz must be considered; in the report above, 50 Hz was the more demanding condition.
Test method
Equipment drawing 16 A per phase or less is tested under IEC 61000-4-11; above 16 A, under IEC 61000-4-34. In IEC 61000-4-34, the three F47 test points fall under the "user-defined" Class X (EPRI, 2013).
Test setup
Power the equipment from a programmable AC source or sag generator, measure input voltage with an oscilloscope and differential probes, measure input current with a current probe, and monitor the equipment's output and status signals. The test source's peak current capability must also meet IEC requirements.
Apply the sags
For single-phase equipment, the sag is applied between phase and neutral; for three-phase equipment without a neutral, it's applied to one phase-to-phase pair (for example, L1–L2). The test equipment can control the phase angle at which the sag starts; for exact phase angles and repetitions, refer to the standard.
Pass or fail
The criterion for complete equipment is "no interruption": no fault or shutdown that requires outside intervention to recover. Components (such as power supplies) are judged against the a, b, and c criteria in the next section.
Extra checks and report
A good test report also records inrush current at the moment the sag ends and voltage recovers (to confirm the fuses are correctly sized), and results at different ambient temperatures.
Pass criteria: tools vs. parts
The pass criterion for complete semiconductor equipment is "no interruption." Subsystems and components can be specified to meet one of the following, depending on their use (Advanced Energy, AN1401):
| Class | During the sag | Recovery | May send fault signals |
|---|---|---|---|
| a | Full rated output | Unaffected | — |
| b | May drop below full load | Recovers on its own | Not allowed |
| c | May drop below full load | Recovers on its own | Allowed |
6 things to check in a SEMI F47 test report
Standard version
Does it state SEMI F47-0706, and whether IEC 61000-4-11 or IEC 61000-4-34 was used?
Same conditions as your site?
Are the test voltage, frequency, and load the same as your actual conditions? A report only proves a pass "under the conditions stated in the report."
Where the sag was applied
For three-phase equipment, which phase-to-phase pair was tested? Keep in mind that F47 doesn't require simultaneous three-phase sags.
Which pass class
Was the component judged against class a, b, or c, and is its "pass" good enough for your complete equipment?
Stated limits
Component reports often note that "the system integrator must determine applicability." The power supply report above, for example, states that F47 certification isn't designed for this type of component and leaves compatibility to the integrator.
Effects of aging
A power supply's hold-up time shortens as components age. The report above estimates hold-up time may drop by about 15% at end of life. Passing when new doesn't mean passing ten years later.
If it passes SEMI F47, why can it still stop on a sag?
Because F47 is only a "minimum" requirement. EPRI points out that SEMI F47, IEC 61000-4-11, and IEC 61000-4-34 don't require testing simultaneous three-phase sags (EPRI, 2013), while real grid faults can drop all three phases at once. Other common reasons: sags deeper than 50% or longer in duration, sags in quick succession, peripheral components and facility systems outside F47's scope, and equipment aging. For how to cover this gap, see SEMI F47 gaps and sag protection.
FAQ
What are the three SEMI F47 test points?
50% voltage remaining for 200 ms, 70% for 500 ms, and 80% for 1 s. Equipment must keep running under all three without operator intervention.
How do you read the SEMI F47 ride-through curve?
The horizontal axis is how long the sag lasts; the vertical axis is how much voltage remains during it. The F47-0706 curve consists of three required test points: 50% for 0.2 s, 70% for 0.5 s, and 80% for 1 s. Equipment must keep running through any sag above the curve (shallower or shorter). Sags below the curve are outside F47's requirements but can still occur on the real grid.
How does SEMI F47 relate to IEC 61000-4-34?
SEMI F47 defines "which sags to ride through"; IEC 61000-4-11 and IEC 61000-4-34 define "how to test." Equipment at 16 A per phase or less uses IEC 61000-4-11; above 16 A, IEC 61000-4-34.
If older equipment fails SEMI F47, does it have to be replaced?
Not necessarily. Most older equipment trips because a few components can't hold on, such as AC control relays, contactors, or control power supplies. Finding and hardening those components one by one, or adding a voltage sag compensator to just the control circuits, usually fixes it.
Can a power supply get a SEMI F47 certificate?
Components usually come with a report tested to F47 rather than a whole-equipment certificate. One public power supply test report, for example, notes that F47 certification isn't designed for this type of component, and the equipment integrator must decide whether the report applies to the complete equipment.