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SEMI E129-1103 © SEMI 2003 22 R2-9 Problem of Controlling Static Charge in Manufacturing Equipment R2-9.1 The interior of high-speed pro duction equipment is a challenge to static control method s. The high cost of produ…

SEMI E129-1103 © SEMI 2003 21

additional requirements to the ESD-protective

packaging properties. Some of these considerations

may actually preclude the ability to provide ESD

protection. Therefore, there may often be a tradeoff

between ESD protection, cleanliness, and other required

material properties.

R2-8.1.2 The dissipative property for ESD protection

requires some type of chemical, metallic or elemental

additive to the bulk of the material or the surface of an

ESD-protective item. Adding a highly conductive layer

within the structure of the material or item provides the

electrostatic-shielding property. Any additive or

treatment may contribute to contamination concerns for

application in cleanrooms.

R2-8.1.3 Making a material low charging (“antistatic”)

requires modification of the surface to decrease surface

resistance and reduce friction. Often, low charging

materials allow a transfer of materials to contacting

surfaces to make the actual surfaces similar in

chemistry. Materials with chemically similar surfaces

usually do not show high levels of charge generation

when placed into contact and then separated from each

other. A downside to this process is the potential

contamination issue that may be involved if the

materials are used in clean areas. Take care in selecting

low-charging materials if cleanliness is a major issue.

This concern includes ionic contamination, non-

volatile-residue and outgassing.

R2-8.2 Material Guidelines

R2-8.2.1 Physical Guidelines — The required material

physical properties depend on the application involved.

The selection process for a packaging material or

system should consider all of the physical attributes

generally associated with protecting an item during

transit or storage. The physical requirements normally

evaluated for any packaging system and associated test

methods are shown in Table R2-1.

Table R2-1 Packaging System Physical Properties

Physical Properties Test Method

Tensile Strength ASTM D882

Elongation ASTM D882

Tear Strength ASTM D1922

Puncture Resistance FED-STD-101/2065

Seam Seal Strength (if

applicable)

ASTM F88

Light Transmission ASTM F1003

Moisture Vapor Transmission

(if applicable)

ASTM F1249

Light Transmission Rate (if

applicable)

ASTM D1003

R2-8.2.2 ESD-Protective Packaging Guidelines — The

type of packaging required for ESD-susceptible items

depends on where the item is going. Packaging

materials used inside of an ESD-protected work area

are static dissipative or low charging. When sensitive

items are moved outside of the protected area, the level

of protection should increase to include electrostatic

discharge shielding. Some extremely sensitive items

may require additional EMI or RFI protection provided

by heavier layers of shielding. Materials that provide

increased shielding may also provide moisture barrier

protection for enclosed items. The necessary electrical

properties for packaging materials that are normally

evaluated are shown with their associated test methods

in Table R2-2.

Table R2-2 ESD-Protective Packaging Properties

Electrical Properties Test Method

Surface Resistance ESD STM11.11

Volume Resistance ANSI ESD STM11.12

Shielding ANSI ESD S11.31

Static Decay FED-STD-101/4046

R2-8.2.3 Contamination Control Guidelines —

Contamination issues are not limited to particles.

Plastic processing additives to plastic packaging and

handling materials, chemical and molecular

compatibility should also be of concern. Users can

evaluate plastic packaging and handling materials using

published standard test methods. There are multiple

test methods and procedures to identify contamination

properties, as shown in Table R2-3. The user is advised

to select the method best suited to their products that

require protection.

Table R2-3 Contamination Control Properties

Contamination Properties Test Method

Particles ISO Std 14644

IEST-STD-CC1246D

IDEMA M9

ARP 598

KSC-C-123

Non-Volatile Residue IDEMA M7

ASTM E1235

ASTM F331

IPA extraction method

Outgassing IDEMA M11 Dynamic

Headspace Analysis

ASTM E595

Ionics IDEMA M12

Extractable/leachable cation

levels by ion chromatography

SEMI E129-1103 © SEMI 2003 22

R2-9 Problem of Controlling Static Charge in

Manufacturing Equipment

R2-9.1 The interior of high-speed production

equipment is a challenge to static control methods. The

high cost of production space requires equipment

occupying the space to be compact and operate at as

high a speed as practical. Product moves through small

spaces at high speed by a variety of robotic and other

mechanisms. Triboelectric charging (i.e., charge

generation due to friction or contact and separation of

dissimilar materials) and contact with ground are

almost unavoidable.

R2-9.2 Grounding of equipment parts that contact the

product presents added difficulties when the equipment

parts are moving at high speeds. Dissipating charge

from insulating surfaces and integrated circuit (IC)

packages may be difficult if the charged surfaces are

not accessible. Using ionizers in these confined spaces

presents challenges.

R2-9.3 Measuring the effectiveness of static control

methods in equipment will take some ingenuity. Test

methods are contained in SEMI E78 as well as ESD

SP10.1.

R2-10 Measurement of Charge and Potential

on Moving Objects

R2-10.1 The fundamental problem in measuring

accumulated charge on moving items in-situ is that only

the static voltage or electrostatic field can be measured

and not the actual charge. Direct measurements of

static charge can be made with a coulombmeter or

Faraday Cup (Pail), but only on stationary objects.

Therefore, any measurements or alarm limits for

moving objects can be set only in terms of accumulated

static voltage or electric field.

R2-10.2 Another difficulty in measuring the static

voltage or electric field from accumulated charge on

moving items in a manufacturing process is the

response time of the instrumentation. Non-contact

instruments measure the electric field emanating from

the surface of a charged object and this takes a finite

amount of time. While some instrument technologies

are faster than others, the measurement tools selected

for any application should consider the speed of the

process. A similar situation occurs in selection of

mitigation techniques, in particular ionizers, as speed of

neutralization depends solely on the number of ions

present in the immediate environment.

R2-10.3 Electrostatic charge on an object (has to be a

conductor to be accurate) is related to the electrical

potential between the object and ground and the

capacitance of the object relative to ground and the

surroundings. There is a measurable relationship

between an electric field measurement and the potential

of the conductive object. For insulators, electrostatic

charge cannot be determined by measuring electric

fields. The electric field measurement on an insulator

does not directly relate to electrostatic charge so

therefore it cannot be used to determine the level of

electrostatic hazard directly. A charged insulator can

only discharge from a very small area upon contact.

The electric field from a charged insulator causes

damage only when it is of sufficient strength and the

ESD-susceptible item is grounded while in the presence

of that electric field.

R2-10.4 ESD-instrument manufacturers are developing

new instruments that have improved response time over

earlier offerings. Much of this effort supports ESD

SP10.1, which describes measurement of voltage and

charge in Automated Handling Equipment. These

instruments will enable static measurements, even in

high-speed automated equipment.

R2-10.5 Non-contact voltmeters are an important

instrument type for measuring the electric field from

charged objects. Reducing the response time for this

class of instruments has been of major importance to

allow meaningful measurement in moving systems.

R2-10.6 Although the coulombmeter and Faraday Cup

can only be used to measure static charge on stationary

objects, they can still be useful in understanding the

charge generation characteristics of parts traveling

through process paths in component handling

equipment. Direct charge measurements combined

with estimates of electrical potential from the electric

field from a charged object can be used to determine

appropriate ionization levels, surface treatment needs,

grounding faults and provide insight into ESD risks

associated with component movement.

R2-11 Standards and Process Control

R2-11.1 Without any doubt, the most important aspect

of electrostatic control today is the advance made in

standardization and process control. Several industry

standards that cover the development and

implementation of an ESD Control Program were

released in the years since 1999. The four most

important standards are as follows:

• IEC 61340-5-1 — This document is a result of

international cooperation at the International

Electrotechnical Commission - Technical

Committee TC 101 – Electrostatics. The

companion User Guide IEC 61340-5-2 offers

considerable guidance that may assist the new

practitioner in ESD control.

SEMI E129-1103 © SEMI 2003 23

• EN 61340-5-1 (formerly CENNELEC100015) —

As a European Normative Standard (EN), this

document has considerable influence among the

European Common Market (ECM) countries and

those that supply products to the ECM. The

content of this document is identical to IEC 61340-

5-1.

• JEDEC JESD625 — A revision of EIA 625, this

document provides a great deal of information

regarding ESD-program planning, implementation

and auditing. The technical requirements are

harmonized fairly well with the above referenced

documents.

• ANSI ESD S20.20 — Technical requirements are

similar to those stated in the above documents but

the administrative requirements are quite different.

ANSI ESD S20.20 was written to comply with ISO

9001-2000 type requirements for validation,

verification and maintenance. Adopted by the US

Department of Defense (DoD), National

Aeronautics and Space Administration (NASA),

Food and Drug Administration (FDA), and

numerous corporations, ANSI ESD S20.20 is the

only ESD-program standard that has an official

certification program. ISO 9000 registrars have

been trained and others are in training at this time

to allow them to provide officially recognized

audits leading to certification granted by the ISO

registrar and the ESD Association.

• The ESD Association is the certifying body that

recognizes trained registrar companies. At this

time, four registrar companies have trained

personnel on staff that can support certification

audits throughout most of Asia, North America and

much of Europe. Numerous other registrars are

being asked by their ISO/QS clients about ANSI

ESD S20.20 certification so the list of certified

registrars is expected to grow over time.

R2-12 References

R2-12.1 SEMI Standards

SEMI E78 — Electrostatic Compatibility – Guide to

Assess and Control Electrostatic Discharge (ESD) and

Electrostatic Attraction (ESA) for Equipment

R2-12.2 ASTM Standards

ASTM D882 — Standard Test Method for Tensile

Properties of Thin Plastic Sheeting

ASTM D1003 — Standard Test Method for Haze and

Luminous Transmittance of Transparent Plastics

ASTM D1922 — Standard Test Method for

Propagation Tear Resistance of Plastic Film and Thin

Sheeting by Pendulum Method

ASTM E595 — Total Mass Loss and Collected Volatile

Condensable Materials from Outgassing in A Vacuum

Environment

ASTM E1235 — Standard Test Method for

Gravimetric Determination of Nonvolatile Residue

(NVR) in Environmentally Controlled Areas for

Spacecraft

ASTM F88 — Standard Test Method for Seal Strength

of Flexible Barrier Materials

ASTM F331 — Standard Test Method for Nonvolatile

Residue of Solvent Extract from Aerospace

Components (Using Flash Evaporator)

R2-12.3 ESD Association Standards and Advisories

ANSI ESD S1.1 — Evaluation, Acceptance, and

Functional Testing of Wrist Straps

ANSI ESD S4.1 — Worksurfaces – Resistance

Measurements

ANSI ESD S11.31 — Evaluating the Performance of

Electrostatic Discharge Shielding Bags

ANSI ESD S20.20 — Standard for the Development of

an ESD Control Program

ANSI ESD STM2.1 — Resistance Test Method for

Electrostatic Discharge Protective Garments

ANSI ESD STM4.2 — Worksurfaces – Charge

Dissipation Characteristics

ANSI ESD STM11.12 — Volume Resistance

Measurement of Static Dissipative Planar Materials

ANSI ESD STM12.1 — Seating Resistive

Characterization

ANSI ESD STM97.1 — Floor Materials and Footwear

– Resistance in Combination with a Person

ESD ADV11.2 — Triboelectric Charge Accumulation

Testing

ESD S6.1 — Grounding – Recommended Practice

ESD SP10.1 — Automated Handling Equipment

ESD STM7.1 — Floor Materials – Resistive

Characterization of Materials

ESD STM11.11 — Surface Resistance Measurement of

Static Dissipative Planar Materials

ESD STM97.2 — Floor Materials and Footwear -

Voltage Measurement in Combination with a Person