Introduction to SEMI F47

What is SEMI F47?

SEMI F47 is an industry standard for voltage sag immunity.

A voltage sag is a brief (longer than a cycle, shorter than a few seconds) reduction in AC mains voltage. Commonly caused by intermittent short circuits on utility lines, or by large loads starting in an industrial plant, voltage sags are the most common power quality event.

SEMI F47 says that all semiconductor manufacturing equipment must tolerate voltage sags to:

50% of nominal voltage for 200 milliseconds,
70% for 500 milliseconds,
and 80% for 1 second.

The percentage is the remaining voltage. A voltage sag to 80% on a 240 volt system drops to 192 volts.

In this context, what does "tolerate" mean?

In general, equipment is allowed to mis-operate during the voltage sag, provided it recovers without operator intervention. However, some customers have stricter interpretations. We will help you figure out what to do.

Where did these numbers come from?

During a three-year-long study of semiconductor fabrication sites around the world, thousands of voltage sags were recorded - roughly one per month at each site. Equipment that cannot meet the requirements of SEMI F47 fails about once per month. In contrast, equipment that meets SEMI F47 fails about once every 20 months.

What is the difference between a voltage sag and a voltage dip?

Nothing. The term "sag" is used in American English, and the term "dip" is used in British English, but they mean exactly the same thing.

My equipment already meets CE requirements, UL, and SEMI S2 - does that mean I already meet SEMI F47?

No. SEMI F47 is a more severe requirement, and has fewer exemptions, than the 61000-4-11 standard used for similar CE testing. And UL and SEMI S2 standards are related to safety, not performance. You need to independently test for SEMI F47.

Who enforces SEMI F47?

Customers. If you receive a Purchase Order from Intel, Motorola, Texas Instruments, IBM, etc. that requires SEMI F47, you need to comply. If not, you don't. There is no legal or safety requirement for SEMI F47 - it's purely a reliability and performance standard.

This means I need a UPS, right?

Absolutely not. SEMI F47 specifically discourages using Uninterruptible Power Supplies (UPS's). Instead, during SEMI F47 testing some minor design changes may be recommended - perhaps adding filter capacitors to the output of a power supply, or changing the style of contactor to one that is certified for SEMI F47. Power conditioning is always a last resort, because it's expensive and bulky.

What if my design already complies with SEMI F47?

Great! All you need to do, for most semiconductor customers, is obtain a third-party F47 Certificate from Power Standards Lab or other compliance lab. (Proper SEMI F47 testing and certification requires such specialized equipment that most compliance labs simply subcontract F47 work to Power Standards Lab.)

Aren't there other voltage sags in SEMI F47?

Yes. In addition to the required voltage sags listed above, SEMI F47 also recommends that equipment tolerate voltage sags to 0% (no voltage at all) for 1 cycle, and to 80% for 10 seconds.

Are there exemptions - maybe SEMI F47 doesn't apply to my system?

If your equipment, or component, runs from DC, it is exempt from SEMI F47, and there is no need to certify it. If there is no AC power input into your system (for example, it is strictly a gas or flow operated system), it is exempt from SEMI F47. But if there is an AC power cord, you need to comply.

How are the sags applied in three-phase systems?

The sags are applied between each pair of conductors, one pair at a time. For example, on a three-phase system with no neutral conductor, the sags are applied from L1 to L2, then from L2 to L3, then from L3 to L1. There is always at least one phase that is not disturbed.

How do I get started?

Skim through this CD-ROM. Take a brief look at the standards, the application notes, and the test equipment.
Contact Power Standards Lab and ask to speak to a SEMI F47 Engineer. TEL ++1-(510)658-9600, or e-mail F47@PowerStandards.com. We will be glad to help you figure out what to do.
Do some quick, simple tests to find out whether your equipment already passes. We will give you some helpful rules of thumb.
If necessary, hire PSL to work with you for one day. We will provide the test equipment, and a highly-experienced engineer who will work with you to solve any problems you might have. And we will train you to perform future tests yourself, safely and accurately, using our TestingPartner program.
PSL will issue you an electronic SEMI F47 Certificate, and optional Report, that you can e-mail to your customer, post on your web site, etc.

Start by calling us at ++1(510)658-9600.

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