New Evaluation Methods for Pressure Sensitive Adhesive (PSA)
Tapes Used in the Semiconductor Industry
by Tomoyuki Aogaki * , Hidefumi Miyagi * and Yoshihisa Kano *We propose new evaluation methods for pressure sensitive adhesive (PSA)
tapes using a high-resolution tester for shearing adhesion and a pendulum-typemechanical apparatus, by means of which we can evaluate the mechanical properties of thepressure sensitive adhesion (PSA) layer, and of products, in the form of PSA tapes. Using thesemethods we evaluated the adhesion of a blend of acrylate copolymer with UV-curable urethane
acrylate oligomer, and two kinds of UV-curable acrylate copolymers. The high-resolution tester
for shearing adhesion made it possible to clarify differences in the properties of PSA tape thatcannot be evaluated by the usual methods, and the pendulum-type mechanical apparatus
made it possible to detect differences in the mechanical properties of adhesion before andafter UV irradiation. We expect that these methods will clarify the relations between the practicalproperties and mechanical properties of PSA tapes utilized in the semiconductor industry, andwill prove useful to the design and quality control of PSA tape.

ABSTRACT1.

INTRODUCTION

1.1

Semiconductor Manufacturing Processes Where
PSA Tape Is Used
Figure 1 shows processes used in semiconductor
manufacture. Pressure-sensitive adhesive (PSA) tape isused in the back-grinding process and dicing process.
These PSA tapes must have strong adhesion during
processing, and weak adhesion after processing ends,
and to meet this need, UV-curable tape has beendeveloped and marketed. These PSA tapes must havebeen higher quality and more advanced features forthin-film wafers, and semiconductor device of a larger
scale of integration. For example, in the wafer backgrinding process, the PSA tape is required to ease the������������

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Backgrinding process and dicing process.

* Ecology & Energy Lab., R&D Div.

unevenness of the wafer surface and to grind thinly andflatly. In the dicing process, the PSA tape is required toreduce chipping (breakage of a chip) and to be able topick up a chip easily. Although the cause of chipping
is not certain, various factors, such as mechanicalproperties and adhesion properties, are considered
to have had a complex influence. In designing the
PSA tape, we have carefully studied semiconductor
manufacturing conditions and have met the abovementioned requirements by optimizing the thickness andthe mechanical properties of PSA tapes.
1.2 Composition of PSA TapeUV-curable PSA adhesive is composed of a blend ofadhesive acrylic copolymer, UV-curable resin, and photopolymerization initiator. The adhesive acrylic copolymer
is obtained by the copolymerization of acrylates (butyl
acrylate, 2-etyl hexyl acrylate, etc.) and/or acrylic acid(and/or vinyl acetate). The UV-curable resin is a monomer
or oligomer, which has at least two doubled carboncarbon bonds, such as the acryloyl group (for example,
polyester acrylate, epoxy acrylate, urethane acrylate,etc.) A UV-curable adhesive acrylic copolymer may
also be used, which introduce the functional group of
UV reactivity into a side chain of the acrylic copolymer.
UV-curable adhesive acrylic copolymer can also be
used independently as a UV-curable adhesive. To obtaincohesion, as in an adhesive acrylic copolymer for thisuse, it is common to blend a crosslinking agent. Adhesion
can be adjusted by the type of acrylic copolymer,
the value of a polar factor (such as acrylic acid), themolecular weight, and the amount of crosslinking agent.
The backing film of PSA tape uses polyolefin resin

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New Evaluation Methods for Pressure Sensitive Adhesive (PSA) Tapes Used in the Semiconductor Industry(for example, polyethylene, polypropylene, etc.), andhas been designed to have appropriate thickness andmaterial composition.
1.3 Evaluation Methods for PSA tape
As methods of evaluating PSA tape, Japanese Industry
Standards mentions adhesion, holding power, tackiness,
etc., which are specified in JIS Z 0237. Although theseevaluation methods are used widely and considered
to be effective as quality control techniques, they may
not satisfy design and development requirements andare not necessarily effective. Moreover, holding poweris the method of measuring the power by which a PSA
tape bears shearing stress when the tape is applied
to a test panel and fixed. Since the holding power isrepresented by the displacement in a predetermined timeor by the elapsed time required to fall from the test panel,measurement accuracy is not enough for the properties
of PSA tape utilized in the semiconductor industry. On
the other hand, viscoelasticity is measured to determine
the dynamic mechanical properties of a PSA layer. But
since the thickness of the specimen needs to be about
2 mm, this method is not suitable for the measurementof practical PSA tapes which consist of a PSA layer anda backing film layer, making it difficult to be used for
quality control. Researchers and manufacturers of PSA
tape have therefore developed various equipment andmethods for the testing of PSA layer, and have been
performing evaluation and analysis of PSA products 1).
1.4 New Evaluation Methods for PSA Tape1.4.1 Measuring Shearing Adhesion of PSA Layers
Equipment for measuring the shearing displacementof PSA layer has been proposed by Miyagi andothers 2). Displacement is detected using laser, and withresolution in the 10-6 to 10-3 meter order, performanceis sufficient. The equipment is shown in Figure 2. The
laser detector measures displacement when the angleof reflection from a target changes. The displacementof PSA layer due to load is measured by detecting thedisplacement of the target block which is placed on a
PSA tape fixed on the test panel. Since the elasticity of����� ������������ �����

PSA layer is sufficiently lower than that of the backing
film, it virtually has no influence on the displacement of
the backing film. In addition, the equipment can change
the test panel and the weight. The advantage of thismeasuring method is that it can evaluate a PSA layerusing practical PSA tapes. What is more, the measuring
technique can evaluate viscoelastic properties based ona static model, from which elasticity, viscous property,
etc. can be calculated for analysis. Since this equipment
has sufficient measuring accuracy and can evaluate
viscoelasticity while measuring shearing adhesion, we
consider it is effective for evaluating PSA tapes used in
the semiconductor industry.
1.4.2 Pendulum-type Mechanical Apparatus
Figure 3 is a schematic diagram of a pendulum-typemechanical apparatus. The edge is placed on a specimen
and the pendulum is drawn near with an electromagnet.
The magnetism is then released allowing free movementof the pendulum. At this time, attenuation of thependulum and change of cycle arise from the resistanceresulting from the mechanical properties of specimen andedge. By evaluating the temperature dependence of therate of attenuation, the glass transition temperature of apolymer material can be measured, and by evaluating
the time dependence, knowledge of the UV-curing and/or
crosslinking conditions of the PSA layer can be obtained.
In addition, we also used this measurement techniqueto evaluate the coating material of optical fibers, andevaluation of the hardening state in the two-layer coating
material of optical fibers is reported 3).

2.

EXPERIMENTAL

2.1 Materials
Three kinds of samples were used as UV-curable
PSA adhesive: specimen A is composed of a blendof adhesive acrylic copolymer (Mw=400000) andurethane acrylate oligomer (Mw=3000); specimen B is a
UV-curable adhesive acrylate copolymer (Mw=800000);and specimen C is a UV-curable adhesive acrylate
copolymer (Mw=200000). Each of the specimens hasa crosslinking agent added. In addition, specimen A������ �����
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High-resolution tester of shearing adhesionof PSA layers.

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Schematic diagram of pendulum-type dynamic
mechanical apparatus.

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New Evaluation Methods for Pressure Sensitive Adhesive (PSA) Tapes Used in the Semiconductor Industry

has large amounts of crosslinking agent to take a highly
crosslinked structure, and B and C have only a small
amount of additive. The three abovementioned kindsof adhesion agents were coated on backing film of apolyolefin to make PSA tape.
2.2 Measurements
PSA properties were measured according to JIS Z 0237.
The probe tack of PSA tapes was measured by a TACII probe tack tester made by RHESCA Co., Ltd. An ARES
dynamic mechanical analyzer made by Rheometrics
Co., Ltd. measured the temperature dependence of the
dynamic viscoelasticity of PSA at a frequency of 1 Hz.
The shearing adhesion of PSA layer was measured athigh resolution. Changes in mechanical properties before
and after UV irradiation was measured by a pendulumtype mechanical apparatus.

3.3 Shearing Adhesion of PSA Layer
Figure 5 shows the change in shearing behavior for the
specimens, each of which differs greatly. Specimen A
is a blended urethane acrylate oligomer, while B andC have the structures of acrylic copolymer only, but
despite being of the same structure, their molecularweights differ greatly. The difference among thesestructures is conjectured to have influenced the action of
displacement. In other words, the degree of crosslinking
������RESULTS AND DISCUSSION

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3.1 PSA Properties
Adhesion and tack of each PSA tape are shown in Table
1. Values differ according to the composition of the
PSA, or the molecular weight of the acrylic copolymer.
Specimen A (before UV irradiation) has the maximum
adhesion. The mobility of the urethane acrylate oligomer,
and the interface chemical characteristic and dynamic
characteristic of the base polymer are considered tohave contributed to this. In terms of tackiness, specimen
C provides the maximum and A the minimum. Whereas
tackiness shows the ease of adhesion for a short time, itis thought that this is a result of the crosslinking of PSA
and the participation of the glass transition temperature
and/or the complex effects of molecular weight.
Holding power could not be measured, since neither
displacement nor fall was observed on all specimens.

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3.

the glass transition temperature and room temperature.
However, in the temperature range beyond room
temperature, specimen B has a small change in G’ andits value of tan δ is small. It is assumed that the differencein the molecular weight of the acrylic copolymers has
affected the behavior of the G’ vs. temperature curve andthe tan δ vs. temperature curve.

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Table 1

Adhesive properties of UV-tapes.

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Figure 4

Temperature dependence of dynamic
viscoelasticities.

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3.2 Dynamic Viscoelasticity
Figure 4 shows the temperature dependence of thestorage modulus G’ and loss tangent tan δ . Below room
temperature the value of G’ for specimen A is higher thanthat for B and C, but lower than B at high temperatures.
Moreover, the peak value of tan δ , equivalent to the glasstransition temperature, occurs at 5°C. It is assumed that
this results from the use of a blend comprising an acrylic
copolymer with a high glass transition temperature
and a urethane acrylate oligomer of a low molecularweight. When specimen B and C are compared, theglass transition temperature of the acrylic copolymer islower than for A, and the change of G’ is small between�������� �

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Figure 5

Change in shearing displacement of adhesive layer.

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New Evaluation Methods for Pressure Sensitive Adhesive (PSA) Tapes Used in the Semiconductor Industryof PSA and/or the degree of intertwinement of thepolymer chain resulting from molecular chain length
influence the behavior of displacement. Consequently,
PSA with low degree of crosslinking and/or shortmolecular chain length would have a large displacement.
3.3.1 Static Model of Viscoelasticities of PSA Layer
Static model of viscoelasticity is thought to be best suited
to understand the shearing adhesion of PSA tapes.
According to this model, PSA is a typical viscoelastic
body and is considered to have the properties of botha Newtonian viscous body and an ideal elastic body.
In this report, PSA is analyzed using a static model ofviscoelasticity shown in Figure 6 whereby a Maxwell
element and a Voigt element is combined 4), 5). In thisviscoelastic model strain γ and stress σ are related by theequationγ = σ {(1 / G1)+[1-exp(-t / τ )] / G2+(t / η 3)}
where τ is relaxation time (τ = η / G).

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Figure 6

Viscoelastic model ofshearing adhesion of PSAs.

The parameter that contributes to the initial stageof displacement is G 1 , and η 3 is the parameter that
represents the displacement in proportion to time.
Although displacement in the interface between thetest panel and a PSA layer is also assumed to exist, it isincluded in η 3 in this report. Figure 7 shows agreement
between analytical results and actual measurements foreach sample. In all results, the displacement behavior
obtained by actual measurement and by the static modelof viscoelasticity was in good agreement, so that it isjudged that the model used in this report is appropriate.
Of these specimens, specimen B showed the largest
value for all parameters, and specimen C the smallest
value.
3.4

Measurement of Mechanical Properties by
Pendulum-type Dynamic Mechanical Apparatus
The pendulum was placed on the PSA tape, and UV was
irradiated from the upper and lower sides, carrying out
free attenuation of the pendulum oscillation. Behaviorof mechanical properties (logarithmic attenuation factor
and oscillating period) in UV-tape before and after UV
irradiation is shown in Figure 8. UV irradiation caused
the oscillating period to fall and saturate at a fixed value.
This suggests that molecule movement is restrained by
the formation of crosslinked structures. On the other
hand, the logarithmic attenuation factor increased under
UV irradiation, fell after that, and was saturated at a fixedvalue. It is thought that the logarithmic attenuation factor
increased during the formation of crosslinked structures
since the structure was not stable, and that it is stabilized
after formation of the crosslinked structures since thestructure became stable.
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Viscoelastic properties of UV-tapes.

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New Evaluation Methods for Pressure Sensitive Adhesive (PSA) Tapes Used in the Semiconductor Industry������������ �����������
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Figure 8

4.

Behavior of mechanical properties in UV-tapes before
and after UV irradiation.

CONCLUSION

We proposed new evaluation methods for UV-PSA tapeusing a high-resolution tester of shearing adhesion anda pendulum-type mechanical apparatus. The shearing
adhesion of PSA can measure the minute action ofmodification of PSA, which has not been evaluated by
the usual holding power test, and can be quantified
using the viscoelastic model. Moreover, the pendulumtype dynamic mechanical apparatus can evaluatemechanical properties by changes in the logarithmic
attenuation factor and oscillating period, and can evaluate
the characteristic before and after UV irradiation. Since
these evaluation methods are able to evaluate easily
the PSA tape in the form of products, it is also expectedthat they are applicable to quality control methods. In
future, we will accumulate data using these techniques
in order to clarify causal relationships with the practicalcharacteristics, adhesion properties, or dynamic
mechanical properties.

REFERENCES
1) M.Hayakawa and S.Akemine: Adhesion, 47 (2003), 367 (inJapanese)2) Z. Miyagi and K. Yamamoto: J. Adhesion, 21 (1987), 243
3) H.Miyagi and Y.Kano: The 40th Annual Symposium on Adhesion by
the Adhesion Society of Japan, pp63-64 (2002) (in Japanese)
4) Y.Kano: “Characterization and Applications of Adhesives”, Polymer
Publishing (2002) (in Japanese)5) Edited by The Society of Polymer Science Japan: “Fundamentals of
Polymer Science”, Tokyo Chemistry Coterie Publishing (1978) (inJapanese)

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