failure modes and mechanism of cleanroom garment

Fibers and Polymers 2012, Vol.13, No.3, 397-402

397

Failure Modes and Mechanism of Cleanroom Garment

Yujin Lee, Joo Hyung Hong1, Jae Yong Lee

1, Ick Soo Kim, and Hyungsup Kim

1*

Nano Fusion Technology Research Group, Faculty of Textile Science and Technology, Shinshu University,

Nagano 386-8567, Japan1Department of Textile Engineering, Konkuk University, Seoul 143-701, Korea

2KM Corporation, Ansung 456-843, Korea

(Received October 25, 2010; Revised September 17, 2011; Accepted September 26, 2011)

Abstract: In order to provide a fundamental understanding of the cleanroom garment failure, we interviewed themanufacturers and the customers of the garment and studied its modes and mechanism under the simulated and real serviceconditions. The interviews revealed that the air-born particle was the most critical factor for the failure. The test showed thatthe abrasion between the fabrics influenced significantly on the air-born particle generation. As the garment was usedrepeatedly, the number of the air-born particles increased in the oscillating modes. The microscopic study explained the air-born particle generation mechanism.

Keywords: Failure modes and mechanism, Cleanroom garments

Introduction

Dust-proof garments for cleanroom (i.e. cleanroom garment)

are used in various manufacturing fields, such as electronic,

food and medicine industries. The demand of the garment

dramatically increased as high value added products should

be produced in cleanrooms in which the number of undesired

particles or microorganisms is controlled. Each industry

requires different functions and levels of the cleanrooms. For

an example, the cleanrooms for semiconductor manufacturer

need to be controlled as class 10, which means that the

number of the particles larger than 0.5 µm per 1 m3 should be

less than 10. Cleanroom garments require specific properties

such as breathability, antistatic, and filtration of the particles

from human body for better performances. To prevent

electrical static charge, the garment fabrics are produced

from PET (Polyethylene terephthalate) filaments and

conductive yarns. However, the conductive yarn is weaker

than the PET filament and can be easily broken. The broken

fibers can turn into air-born particles that have significant

influence on the defects of the products manufactured in the

cleanroom. In order to maintain the desired clean level of the

room, it is important to understand the garment failure

behavior. However, no studies have been published in the

reliability of the cleanroom garment.

For decades, reliability has been studied in various

industries, such as aircraft, mobile and electric industries, to

ensure the safety for the users and to maintain functions

during the service period [1-6]. Technical textile industries

started to give attention on the product reliability as the

application areas extended into various fields such as

reinforcing fibers for composites used in aircrafts and

vehicles, filters used in electronic industries, and geotextiles

[7-9]. However, reliability studies in textile industries are very

limited. Especially, there are few researches published in special

garments, such as protective clothes or cleanroom garments.

The failures of those garments can jeopardize the user’s life

and health. The understanding of the failure and life time of

cleanroom garment is critical because its failure can cause

the process break down and significantly increase the defects

of the product.

In this paper, we studied the failure modes and causes of

the cleanroom garments used in semi-conductor industry.

The study provides fundamental understanding of the failure

modes and mechanism of the cleanroom garments. Also, the

result applied to improve the reliability of the garments and

to reduce the product defects at the same time.

Experimental

Fabrics and Garments

Samples were supplied from KM corporation(Cleanroom

garments manufacturing and maintaining company in Korea)

as forms of fabrics and garments for class 10 cleanroom. They

were 2/3 twill woven from PET filament (75d/36f). Con-

ductive yarns (25d) containing carbon black were inserted

every 20 mm in weft direction to reduce the electrical static

charge on the fabrics. The specifications of the fabric and the

garment are summarized in Table 1.

Field Interview

To understand the failure modes and mechanisms of the

cleanroom garments, we have intensively interviewed the

QC managers of the 3 major customer companies (LCD and

Semiconductor companies) and the manufacturers of the

garments. The interview reveals the primary causes and the

modes of the failure.

Washing Process

The effect of the washing process on the failure was*Corresponding author: [email protected]

DOI 10.1007/s12221-012-0397-0

398 Fibers and Polymers 2012, Vol.13, No.3 Yujin Lee et al.

evaluated using the garments. Nine never-used garments were

washed for 19 times without practical usages. The washing

process was followed by the standard procedure of a

garment manufacturing and maintaining company. The

washing conditions are summarized in Table 2.

Abrasion

In order to study the failure mechanism by the abrasion

between the fabrics during the service time, the identical

fabric samples of the garment were prepared and abraded

each others using an abrasion resistance tester (Yasuda SC-

D). After several levels of abrasion (5,000-30,000 times), the

fabric samples were washed in the same washing condition

for further test.

Field Test

The failure modes and mechanisms of the garments in real

service environment were studied by the periodical examina-

tion of six garments used in a cleanroom. Six workers wore the

garment and carried out their assignments in the cleanroom at

class 10 for 4 days a week. On the fifth day, the garments were

collected, washed and examined for 19 weeks. The number of

the steps taken by the workers was counted using a step-

counter carried by each worker through whole testing period

(19 weeks). The garment of each worker was identified by the

barcode attached on the garment. Table 3 shows the assigned

job and the average number of steps recorded per week.

Characterization

After each experiment, the number of the air born particle

generated by the garments or the fabrics was counted using

an air born particle counter (MET ONE 2100) while they

were tumbled. The surfaces of the abraded fabrics were

observed using SEM (JEOL 6830) and an optical microscope

(Video Microscope ICS-P305B). The air permeability of the

samples was evaluated using an air permeability tester

(TEXTEST-FX3300).

Results and Discussion

Failure Patterns and Causes

To study the failure modes and mechanism, we interview-

ed the manufacturer and the customer of the cleanroom

graments. Based on observations and experiences, the

interviewees claimed that the garment failure follows the

typical bath tub curve and the failure modes can be divided

into three stages - infant, random and wear-out according to

failure time. The infant failures are usually caused by poor

product design or quality control of the manufactures. The

random failures are caused by mal-usage or mal-

Table 1. Specifications of fabric and garment

Category Exising condition

Fabric 2/3 Twill

Weightg/m2 75

g/yds 107

Thickness µm 150

Fiber Polyester DTY 75/72

Brightness Semi Dull

Film laminating PTEE 7 µm Film/PU 10 µm Top Coatiog

Carbon fiber

Covered Yarn 95/30

(Conductive Yarn 20/6+Polyester 75/24)

Cross-section

Table 2. Industrial washing conditions

Category Existing condition

The number of items (pcs) 80120

DetergentVolume (ml) 300

Acidity subacid

Pre-wash

Time (min)

- Volume of water (l)

Temperature of water

Main wash

Time (min) 30

Volume of water (l) 150

Temperature of water normal temperature

Rinse

Time (min) 4

The number of times 2



Spin-dry (min) 5

Distilled

water rinse

Time (min) 10

The number of times 2



DryHot air

Temperature (oC) 60

Time (min) 30

Cooling (min) 25

Table 3. Average number of steps for different workers

Participant

no.Position Difficulty

Average number

of steps

1 Leader Middle 15,000

2 Check up Middle 10,000



5 Packaging High 21,000

6 Packaging High 23,000

Reliability of Cleanroom Garment Fibers and Polymers 2012, Vol.13, No.3 399

maintenance. One of the typical random failure modes

observed during the service term was the garment tear by

sharp edges or foreign objects, such as pens and knives. The

wear-out failure is observed when the fabrics are abraded

during the washing action or the actual use. The abrasion

between the fabrics results in the fiber breakage, the loss of

conductivity and the increase of the air-born particles. The

air born particles released from the garment is one of the

most significant problems influencing the products qualities

which are produced in the cleanroom. The interview and the

user’s quality guideline also indicate that the number of the

released air born particle is the most significant failure mode

influencing on the process and quality control. These

particles cause the mal-functions of the machines and the

instruments equipped in the cleanroom or the defects in final

products. Therefore, the electronic industries such as

semiconductor or LCD panel manufacturers, strictly regulate

the number of the air born particles in the clean room. The

manufactures and the maintenance service providers usually

examine the garments using the air born particle counter

before they deliver the garments. The garment cannot be

used when the number is greater than 500, which is the

typical quality guideline for the cleanroom garments. In the

study, the number of the air born particles from the garments

is used as judging parameters of the garment failures

resulted from abrasion.

Effect of Washing Process

The garments need to be maintained periodically to extend

of their service time and better performance. One of the most

important maintaining methods for this is a washing process.

During the washing process, the stains and the order in

garments are removed by chemical and mechanical actions.

Meanwhile, the garments become weaker and weaker by the

fiber hydrolysis by the detergent and the fabric abrasion. The

polymeric fiber hydrolysis is mainly caused by the washing

solution containing detergents. To evaluate the influence of

pH and temperature of the washing solution on the fiber

hydrolysis, the fabrics were immersed in the agitated

washing solution for 24 hours. The hydrolysis can be

changed according to the pH and the temperature of the

solution. Generally, the hydrolysis rate of PET fibers can be

accelerated in alkaline condition at higher temperature. After

24 hours of the immersion, the number of the air born

particles was counted and the results are shown in Table 4.

The NaOH concentration showed a significant effect on the

number of the air-born particle while the temperature did

not. It was reported that the polyester micro structure was

deformed in NaOH [10].

To evaluate the repetition of the washing process on the

garment failure, eight new garments were washed 19 times

according to the industrial washing procedure. After each

washing process was completed, the number of the air born

particle was counted. Figure 1 shows the number of the air

born particle generated after each washing processes. The

number of the air born particles was increased with

oscillatory mode as the number of the washing processes

increased.

However, the number of the particle generated by the

washing process itself was lower than the quality guideline

of the users. It indicates that the washing action for the

garment maintenance did not show critical influence on the

failure.

Field Test

The garment failure during the real service period of the

garments was studied in terms of the number of the air born

particle generated from the garments as shown in Figure 2.

After the workers finished their 4-day assignments, the

garments were collected, washed and evaluated. This process

was repeated for 19 weeks. The number of the particles

increased with oscillating mode. The oscillating patterns

have 2-3 week period for the testing term except for few

cases. However, the number of the particles did not recover

to its initial state and the oscillation behaviors showed

irregular periodicity. The number of the air-born particles

and the increase pattern were dependent on the work types.

The number of the air-born particles from the cleanroom

garment for team leader was higher than the others. In

Table 4. Effect of pH and temperature on air-born particles

No.Concentration of

NaOH (wt.%)

Temperature

of water (oC)

Air-born particle

(>0.5 µm)

1 0 25 180.4

2 0 45 169.5

3 0 65 185.8

4 0.5 25 393.6

5 0.5 45 32.8

6 0.5 65 284.3Figure 1. Change of the number of air-born particles along washing

process.


general, the number was higher when the garments wearer

took more steps during their assignments.

Wear-out Failure Behavior and Mechanism

In order to investigate the air born particle generation

mechanism by the abrasion, the surfaces of the fabrics were

abraded using an abrasion tester. After the fabrics were

abraded with different levels, the fabrics were washed

according to the industrial washing process and then the

number of the air born particles was counted while the

fabrics were tumbled. Similarly to the results of the washing

process and the field test (Figures 1 and 2), the number of

the particles increased with oscillatory mode as the number

of the abrasion increased as shown in Figure 3.

In order to study the failure mechanism and the fiber

surface change, the abraded fabric surfaces were observed

using SEM and optical microscopy as shown in Figures 4

and 5. Both observations indicate that the fabric was

gradually worn out by friction and abrasion. The abrasion

causes the fiber breakage which may result in air born

particles and the conductivity reduction, in turns. As shown

in Figure 5, the fibers composing the fabrics were broken

and crumbled as the abrasion continued. In fact, the broken

fibers started to form clumps on the fabric surface and the

size of the clump grew (Figure 5(c)). However, the fabric

abraded at the same level (Figure 5(e)) did not show such

significant large number of the broken fiber or large size of

the fiber clumps. Comparing to the fabric shown in Figure

5(c), the fabric showed clear and smooth surface. It indicates

that the broken fibers and the fiber clumps were removed by

the abrasion. The abrasion of individual fiber was observed

using SEM and the images are shown in Figure 4. Similar to

the optical microscopic images in Figure 5, the surfaces of

the fibers began to be worn and peeled off as the number of

the abrasion increased. When the number of abrasion was

around 200,000, the fibers were broken and each fiber ends

started to make clumps. The removed fibers and clumps

from the fabric are believed to become the air born particles.

Figure 2. Change of the number of air-born particles in real service

period.

Figure 3. Effect of abrasion on the number of the air-born particles.

Figure 4. SEM images of fabrics abraded with different abrasion level (a) 15,000, (b) 90,000, (c) 210,000, (d) 300,000, (e) 360,000, and

(f) 360,000.

Reliability of Cleanroom Garment Fibers and Polymers 2012, Vol.13, No.3 401

These abrasion behaviors are repeated while the fabrics are

abraded.

From the observation, the failure mechanism of the

garment can be summarized as follows: the fibers protruded

on the yarn cross-over positions are peeled and abraded

while they are in use or washing. Consequently, it results in

fiber breakage and the formation of the fiber clumps, in

turns. The fiber clumps grows by adding more broken fibers.

When the clump size becomes a certain lever, the clump is

detached and released from the fabric and finally becomes

an air born particles.

Effect of Abrasion on Air Permeability

The effect of the abrasion on the garment air permeability

is shown in Figure 6. As similar to the results shown above,

the air permeability changed with oscillating pattern. It is

explained as the same mechanism of the air-born particles.

As the fabrics were abraded, the broken fibers formed the

clumps which covered the fabric surface. However, the air

permeability did not increase nor decrease significantly

along the number of the abrasion. It indicates that the clumps

were effectively removed by the washing process.

Conclusion

In this study, we revealed the failure modes and mechanism

of the cleanroom garments. The failure was defined by the

air-born particles generated from the abrasion between the

fabrics. The air-born particle increased with oscillation pattern

as the number of abrasion increased. The failure mechanism

can be explained as the sequence of the fiber breakage, the

clump formation and its detachment from the fabrics by the

abrasion. This research can be used for improving of the

cleanroom garment reliability and maintenance process.

Acknowledgements

This research was financially supported by the Ministry of

Knowledge Economy (MKE) and Korea Industrial Technology

Foundation (KOTEF) through the Human Resource

Training Project for Strategic Technology.

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failure modes and mechanism of cleanroom garment

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