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Texas Instruments Use of Polystyrene for Bare-Die Carrier-Tape Shipping Applications Application notes
Application Report
SZZA042 - November 2003
Use of Polystyrene for Bare-Die Carrier-Tape
Shipping Applications
Michael Hayden, Lee Lewis, and Lance Wright
Standard Linear & Logic
ABSTRACT
The packing and shipping of bare-die product is relatively new, especially in the tape-and-reel
packing format. Bare-die format assumes that the devices will be handled in a
clean-room-type environment and that the packing materials used to ship the dies will be as
clean as possible. Texas Instruments has developed a plan for testing multiple carrier-tape
materials from multiple suppliers. The objective was to prove or disprove that polystyrene
carrier tape could meet the same cleanliness requirements as those materials used to ship
finished wafers to internal and external customers. The tests performed indicate that the
polystyrene tape exceeds TI requirements for materials used for shipping wafers and bare
dies.
Contents
1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2
Test Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3
Test Results and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1 Ionic-Contamination Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2 Outgassing Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3 Visual Inspection Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4 Liquid Particle-Count Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4.1 ANOVA Analysis of Liquid Particle-Count Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4.2 Duncan’s Test of Liquid Particle-Count Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5
5
6
7
8
9
9
Appendix A Least-Significant Studentized Ranges rp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
List of Figure
1. Tape-and-Reel Packing Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Trademarks are the property of their respective owners.
1
SZZA042
List of Tables
1.
2.
3.
4.
5.
6.
7.
8.
9.
2
Ionic Contamination Results From Supplier A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Ionic Contamination Results From Supplier B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Outgas Test Results From Supplier A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Outgas Test Results From Supplier B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Visual-Inspection Results From Suppliers A and B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Liquid Particle-Count Data Used for ANOVA and Duncan’s Multiple-Range Calculations . . . . . . . . . 8
Single-Factor ANOVA Liquid Particle-Count Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
SSRp Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Results of Duncan’s Multiple-Range Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Use of Polystyrene for Bare-Die Carrier-Tape Shipping Applications
SZZA042
1
Introduction
The semiconductor industry ships devices to customers in many packing configurations. Most of
the devices have been ceramic- or plastic-encapsulated dies. The newest form of device is the
Wafer Scale Chip Scale package (WCSP). These devices are either bumped or unbumped dies
singulated from the wafer. Bare dies are shipped to end users using several packing methods.
For some time, conductive plastic trays with individual compartments to hold each die or special
packing material containing tacky surfaces to hold the die in place was the dominant method,
but tape-and-reel packing is becoming the norm (see Figure 1).
Cover Tape
Carrier Tape
Embossed Cavity
Bar-Code Label Area
Figure 1. Tape-and-Reel Packing Components
Bare-die format assumes that the devices are handled in a cleanroom-type environment and
that the packing materials used to ship the dies will be as clean as possible. Clean in the context
of handling the bare die means clean from ionic contaminants and clean from particles. The
industry-accepted cleanest carrier-tape base material is polycarbonate; however, the most
widely used carrier-tape base material is polystyrene. Due to cleanliness concerns, all bare-die
carrier-tape requirements at TI are being met with polycarbonate carrier-tape material.
In early 2000, TI began a concerted effort to determine whether switching from polycarbonate
carrier tape to polystyrene carrier tape for bare-die shipments was feasible. The objective was to
prove or disprove that the polystyrene carrier tape could meet the same cleanliness
requirements as those materials presently used to ship finished wafers to internal and external
customers.
Use of Polystyrene for Bare-Die Carrier-Tape Shipping Applications
3
SZZA042
2
Test Plan
Multiple groups of carrier tape from two suppliers were tested. Each supplier submitted samples
of polycarbonate and polystyrene tapes from their normal (standard tape format) process and
their clean process. The clean process has an additional air shower, and the tape is shipped to
TI on a reel enclosed in a clean plastic bag.
•
Supplier A polycarbonate carrier tape material
•
Supplier A standard polystyrene carrier tape material
•
Supplier A proposed cleaner polystyrene carrier tape material
•
Supplier B standard polycarbonate carrier tape (not cleaned)
•
Supplier B cleaned polycarbonate carrier tape
•
Supplier B standard polystyrene carrier tape
Overall, the objective was to determine if a significant difference in particle counts existed
between polycarbonate carrier tape and polystyrene carrier tape. Tapes with no dies in them
were evaluated, as well as tapes that had dies in them. Steps in the test plan were:
1. Analyze samples of empty carrier tape for cleanliness using ion chromatography, liquid
particle counting, and outgas analysis
2. Examine bare dies in a loaded carrier tape for cleanliness using visual examination
3. Examine bare dies in a loaded carrier tape by completing water extraction on samples
4. Perform statistical analysis on test results
The test methods used follow accepted industry standards:
•
Ion Analysis: Samples were soaked in deionized (DI) water for 1 hour at 80°C. The water
extract then was analyzed by ion chromatography.
•
Liquid Particle Count (LPC): Samples were soaked in DI water for 1 hour at 80°C, and a
liquid particle counter then was used to analyze the extraction.
•
Outgassing: Sample was packed in an airtight vial and baked for 16 hours at 85°C. The
resulting vapor then was analyzed by using gas chromatography/mass spectrometry
(GC-MS).
•
Visual Inspection: Sample was inspected manually at 40× magnification using a
stereomicroscope.
All tests were performed by a certified outside laboratory.
4
Use of Polystyrene for Bare-Die Carrier-Tape Shipping Applications
SZZA042
3
Test Results and Conclusions
3.1
Ionic-Contamination Data
The first data to be evaluated was from water extraction to determine ionic contamination. These
data show type and quantity of contaminants present on the carrier tape. It is important to
minimize these ionic contaminants to prevent potential corrosion. Supplier A data is shown in
Table 1, and the Supplier B data is shown in Table 2.
Table 1. Ionic Contamination Results From Supplier A
Supplier A
Normal
Polycarbonate
(mg/cm2)
Supplier A
Clean
Polycarbonate
(mg/cm2)
Supplier A
Normal
Polystyrene
(mg/cm2)
Supplier A
Clean
Polystyrene
(mg/cm2)
TI
Specification
Limits†
(mg/cm2)
Fluoride
<0.01
<0.01
<0.01
<0.01
0.02
Chloride
<0.01
<0.01
<0.01
<0.01
0.28
Nitrate
<0.01
<0.01
<0.01
<0.01
0.01
Phosphate
<0.01
<0.01
<0.01
<0.01
0.01
Sulphate
<0.01
<0.01
<0.01
<0.01
0.01
Sodium
<0.01
<0.01
<0.01
<0.01
0.1
<0.01
0.02
Contaminant
Potassium
<0.01
<0.01
<0.01
† Specification limits reflect TI specifications for plastic wafer shipping boxes.
Table 2. Ionic Contamination Results From Supplier B
Supplier B
Normal
Polycarbonate
(mg/cm2)
Supplier B
Clean
Polycarbonate
(mg/cm2)
Supplier B
Normal
Polystyrene
(mg/cm2)
Supplier B
Clean
Polystyrene
(mg/cm2)
TI
Specification
Limits†
(mg/cm2)
Fluoride
<0.01
<0.01
<0.01
<0.01
0.02
Chloride
<0.01
<0.01
<0.01
<0.01
0.28
Nitrate
<0.01
<0.01
<0.01
<0.01
0.01
Phosphate
<0.01
<0.01
<0.01
<0.01
0.01
Sulphate
<0.01
<0.01
<0.01
<0.01
0.01
Sodium
<0.01
<0.01
<0.01
<0.01
0.1
<0.01
0.02
Contaminant
Potassium
<0.01
<0.01
<0.01
† Specification limits reflect TI specifications for plastic wafer shipping boxes.
Ionic-contamination results show that both normal and cleaned tapes of both materials
(polystyrene and polycarbonate) from both suppliers show no contaminants. Because these data
are well below specification limits for packing materials, this test was eliminated as a
distinguishing factor between the tape materials. From an ionic contamination point of view,
either tape material could be used.
Use of Polystyrene for Bare-Die Carrier-Tape Shipping Applications
5
SZZA042
3.2
Outgassing Data
The second group of tests that was completed and data evaluated was for outgassing. Again,
the goal is to minimize outgassing characteristics. Supplier A data is shown in Table 3, and
Supplier B data is shown in Table 4.
Table 3. Outgas Test Results From Supplier A
Supplier A
Normal
Polycarbonate
(mg/g)
Supplier A
Clean
Polycarbonate
(mg/g)
Supplier A
Normal
Polystyrene
(mg/g)
Supplier A
Clean
Polystyrene
(mg/g)
Acrylate
ND
ND
ND
ND
Siloxane
ND
ND
ND
ND
Chlorinated solvent
ND
ND
ND
ND
Hydrocarbons
Total outgas†
ND
ND
28.8
83.56
0.58
5.69
28.8
85
Contaminant
ND = none detected
† Total outgas is slightly higher due to detection of gases not listed in the table.
Table 4. Outgas Test Results From Supplier B
Supplier B
Normal
Polycarbonate
(mg/g)
Supplier B
Clean
Polycarbonate
(mg/g)
Supplier B
Normal
Polystyrene
(mg/g)
Supplier B
Clean
Polystyrene
(mg/g)
Acrylate
ND
ND
ND
ND
Siloxane
ND
ND
ND
ND
Chlorinated solvent
ND
ND
ND
ND
14.38
13.07
5.14
6.72
14.38
13.07
5.14
6.72
Contaminant
Hydrocarbons
Total outgas†
ND = none detected
† Total outgas is slightly higher due to detection of gases not listed.
The carrier-tape materials (polystyrene and polycarbonate) are petroleum based. This explains
the existence of hydrocarbons in all cases. This test also was eliminated as a possible
distinguishing criteria between polystyrene and polycarbonate carrier-tape materials.
6
Use of Polystyrene for Bare-Die Carrier-Tape Shipping Applications
SZZA042
3.3
Visual Inspection Data
A sample of bare dies encased in carrier tape by cover tape was taken from three different tape
samples:
•
One from Supplier A normal polystyrene tape
•
One from Supplier A clean polystyrene tape
•
One from Supplier B clean polycarbonate tape
Sample size in each case was 32 dies.
One die at a time, the cover tape was removed from the samples and the die inspected under a
microscope at 40x magnification to look for evidence of contamination. If contamination was
seen, it was documented, its size checked to see if it was large enough to bridge between
bonding pads, and it then was verified as either loose or attached by using a low-pressure air
blow while holding the die in place. Results are shown in Table 5.
Table 5. Visual-Inspection Results From Suppliers A and B
Contamination
Type
Large
Enough to
Bridge Bond
Pads?
(Yes/No)
Removal
With Air
Blow?
(Yes/No)
4
Loose particle
No
Yes
Yes
4
Loose particle
No
Yes
Yes
4
Loose particle
No
Yes
Sample Size
Contamination
Seen
(Yes/No)
Amount of
Contamination
Seen
(Particles)
Supplier A
Normal
Polystyrene
32
Yes
Supplier A
Clean
Polystyrene
32
Supplier B
Clean
Polycarbonate
32
Supplier and
Tape
Composition
Visual inspection did not reveal any overt contamination that might cause bridging or significant
contamination during the solder process. This test also was eliminated as a distinguishing factor.
Use of Polystyrene for Bare-Die Carrier-Tape Shipping Applications
7
SZZA042
3.4
Liquid Particle-Count Data
The overall conclusion from evaluating and examining the unloaded carrier tapes is that no
difference exists between the polycarbonate and polystyrene materials with respect to
cleanliness. Additionally, tapes loaded with dies also were evaluated to see if one carrier-tape
material generated more particles than the other during normal shipping and handling.
Samples of Supplier A normal polystyrene (not cleaned) carrier tape and Supplier A clean
polystyrene carrier tape were analyzed. As a control, samples of Supplier B clean polycarbonate
carrier tape also were analyzed.
Particle-count data collected by a certified outside laboratory is listed in Table 6.
Table 6. Liquid Particle-Count Data Used for ANOVA
and Duncan’s Multiple-Range Calculations
Supplier and Tape Composition
Particle Size
.0.5 mm
Supplier A
Normal Polystyrene, Bottle 1
361
Supplier A
Normal Polystyrene, Bottle 2
701
Supplier A
Normal Polystyrene, Bottle 3
372
Average
478
Std. Dev.
193
Supplier A
Clean Polystyrene, Bottle 1
467
Supplier A
Clean Polystyrene, Bottle 2
608
Supplier A
Clean Polystyrene, Bottle 3
356
Average
443
Std. Dev.
79
Supplier B
Clean Polycarbonate, Bottle 1
447
Supplier B
Clean Polycarbonate, Bottle 2
369
Supplier B
Clean Polycarbonate, Bottle 3
416
Average
410
Std. Dev.
40
To help understand the particle-count data, statistical analyses, such as analysis of variance
(ANOVA) and Duncan’s multiple-range test were performed. The ANOVA test is used to
determine if there is a significant difference between the sample means. Duncan’s test
complements the ANOVA test and shows the relationship between mean pairs.
8
Use of Polystyrene for Bare-Die Carrier-Tape Shipping Applications
SZZA042
3.4.1
ANOVA Analysis of Liquid Particle-Count Data
Results of the ANOVA test are shown in Table 7. This test is not explained in detail because it is
a straightforward computation. This procedure can be found in any statistical-analysis handbook.
Data used to perform these tests are shown in Table 6.
Table 7. Single-Factor ANOVA Liquid Particle-Count Data
Data Summary
Count
Average
Supplier A,
Normal Polystyrene
Groups
Variance
6
478
29905.6
172.9324
Supplier A
Clean Polystyrene
6
443.3333
4988.667
70.63049
Supplier B
Polycarbonate
6
410.3333
1310.267
36.19761
ANOVA Results
SS
MSe
F
P-Value
Between Groups
Source of Variation
13739.11
6869.556
0.569229
0.577722
Within Groups
181022.7
12068.18
Total
194761.8
Fcritical
3.682317
Because Fcritical > F, it can be concluded that there is no significant difference in the
manufacturing processes between the carrier tapes with respect to particle count for normal
polystyrene production, clean polystyrene production, and normal polycarbonate production.
3.4.2
Duncan’s Test of Liquid Particle-Count Data
Duncan’s test, as previously mentioned, is used to determine if a significant difference exists
among the three carrier tapes. This test is explained in detail in steps 1 through 4 below for the
≥0.5-µm-particle test because it is not as well-known as the ANOVA test.
1. Linearly order the means such that u1 = 410.33 (counts/cm2), u2 = 443.33 (counts/cm2),
and u3 = 478.00 (counts/cm2). u1 is the mean for Supplier B’s process, u2 is the mean for
Supplier A’s clean process, and u3 is the mean for Supplier A’s normal process.
2. Determine the value of the least-significant studentized range, rp, for each p value or pairs
of unique data sets greater than 1. In this case, p can equal 2 or 3. The rp value is
determined by the table in Appendix A. In this table, α = 0.05, or 95% confidence level,
and γ = 15, which is the degrees of freedom associated with the error mean square in the
analysis of variance or MSe. From the table, rp = 3.014 for two sets of adjacent data sets
and rp = 3.16 for the one nonadjacent data set, based on the linearly ordered means.
3. For each p value, the shortest significant range, SSRp, must be calculated. For equal
sample sizes with n = 6 values,
SSRp + r p
Ǹ(MSeńn)
The SSRp values are shown in Table 8.
Table 8. SSRp Values
SSRp (α= 0.05), 0.5-µm liquid particle-count test
P=2
P=3
135.1725
141.7204
Use of Polystyrene for Bare-Die Carrier-Tape Shipping Applications
9
SZZA042
4. Analyze adjacent sample means. Any two population means are considered to be
significantly different if |ui − uj| > SSRp for equal sample sizes. Results are in Table 9.
Table 9. Results of Duncan’s Multiple-Range Test
Supplier and Process
Adjacent-Sample
Means
|ui − uj|
67.67
SSRp
141.7204
Supplier B and Supplier A Clean
33.00
135.1725
Supplier A Clean and Normal
34.67
135.1725
Supplier B and Supplier A Normal
Conclusion
All mean differences <SSRp, which means that all of the
processes are not significantly different, is the same
conclusion as the ANOVA test.
With regard to the data listed in Tables 8 and 9, the statistical analyses show no statistical
difference between any of the three groups. Therefore, one could conclude there is no difference
in particle cleanliness between the carrier-tape materials.
10
Use of Polystyrene for Bare-Die Carrier-Tape Shipping Applications
SZZA042
4
Summary
Polystyrene and polycarbonate carrier-tape materials from different suppliers and different
production processes were evaluated by several methods. Carrier tapes, with and without dies,
were evaluated. All of the data show results well within identified TI specification limits and
results that are not statistically different. Based on these evaluations, polystyrene is an
acceptable carrier-tape material for packing bare dies for shipment to customers.
5
Acknowledgments
Ritu Vaidya and Margaret Simmons-Matthews provided editorial assistance. Albert Escusa and
Wee Lee Ng provided test-evaluation assistance.
Use of Polystyrene for Bare-Die Carrier-Tape Shipping Applications
11
SZZA042
Appendix A
12
Least-Significant Studentized Ranges rp
Use of Polystyrene for Bare-Die Carrier-Tape Shipping Applications
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