Astm stp 640 1978

ADHESION MEASUREMENT
OF THIN FILMS,
THICK FI LMS, AN D
BULK COATINGS
A symposium
presented at
ASTM Headquarters
AMERICAN SOCIETY FOR
TESTING AND MATERIALS
Philadelphia, Pa., 2-4 Nov. 1976
ASTM SPECIAL TECHNICAL PUBLICATION 640
K. L. Mittal
IBM Corporation
East Fishkill Facility
Hopewell Junction, N.Y.
editor

List price $39.25
04-640000.25
AMERICAN SOCIETY FOR TESTING AND MATERIALS
1916 Race Street, Philadelphia, Pa. 19103


Copyright 9 BY AMERICANSOCIETYFOR TESTINGAND MATERIALS1978
Library of Congress Catalog Card Number: 77-84460

NOTE
The Society is not responsible, as a body,
for the statements and opinions
advanced in this publication.

Foreword
The symposium on Adhesion Measurement of Thin Films, Thick Films,
and Bulk Coatings was held at the headquarters of the American Society for
Testing and Materials, Philadelphia, Pa., 2-4 Nov. 1976. The ASTM
Publications Committee sponsored the symposium. K. L. Mittal, IBM
Corporation, presided as symposium chairman and editor of this publication.


Related
ASTM Publications
Spreading Resistance, STP 572 (1975), $3.55,04-572000-46
Surface Analysis Techniques for Metallurgical Applications, STP 596
(1976), $15.00, 04-596000-28
Composite Materials: Testing and Design (Fourth Conference), STP 617
(1974), $51.75, 04-617000-33


A Note of Appreciation
to Reviewers
This publication is made possible by the authors and, also, the unheralded efforts of the reviewers. This body of technical experts whose
dedication, sacrifice of time and effort, and collective wisdom in reviewing the papers must be acknowledged. The quality level of ASTM publications is a direct function of their respected opinions. On behalf of ASTM
we acknowledge with appreciation their contribution.
A S T M Committee on Publications


Editorial Staff
Jane B. Wheeler, Managing Editor
Helen M. Hoersch, Associate Editor

Ellen J. McGlinchey, Senior Assistant Editor
Sheila G. Pulver, Assistant Editor


Contents
Introduction

1

GENERAL PAPERS RELATED TO ADHESION MEASUREMENT

Adhesion Measurement: Recent Progress, Unsolved Problems,
and Pmspeets--K. L. MITTAL
Discussion

5

16

Locus of Failure and Its Implications for Adhesion Measurements-S. J. GOOD

Discussion

18
27

Problems in Adhesion Measurement--j. j. BIKERMAN
Discussion

30

38

Experimental Methods to Determine Locus of Failure and Bond
Failure Mechanism in Adhesive Joints and Coattng-Substrate
Combinations--w. L. BAUN

41

Thin-Film Adhesion and Adhesive Failure---A Perspective--D. M. MATTOX

Discussion

54

62

Use of Fracture Mechanics Concepts in Testing of Film Adhesion-W. D. BASCOM, P. F. BECHER, J. L. BITNER, AND J. S. MURDAY

Discussion

63

79

Techniques for Measuring Adhesive Energies in Metal/Ceramic
Systems--L. E. MURR
Discussion

82
97

ADHESION MEASUREMENT OF T H I N FILMS

Adhesion of Thin Plasma Polymer Films to Plastics-L. W. CRANE AND C. L. HAMERMESH

Discussion
Electromagnetic Tensile Adhesion Test Method--soL KaONGELB
Discussion

101
106
107
120


Measurements of Film-Substrate Bond Strength by Laser Spallation-J. L. VOSSEN
122
Discussion
131
Hardness and Adhesion of Filmed Structures as Determined by the
Scratch Technique--J. AHN, K. L. MITTAL,
AND R. H. MACQUEEN
Discussion

134
156

Threshold Adhesion Failure: An Approach to Thin-Film Adhesion
Measurement Using the Stylus M e t h o d - J. OROSHNIKAND W. K. CROLL
Discussion

158
182

Adhesion of Granular Thin FilmS---ROLAND FAURE
Discussion

184
197

Adhesion Measurement on Thin Evaporated Filmsw
KAIZO KUWAHARA,HIDENORI HmOTA, AND NOBUO UMEMOTO
Discussion

198
207

ADHESION MEASUREMENT OF T r a c k FILMS
Adhesion Measurements on Thick-Film Conduetors--T. T. HITCH
Discussion

211
231

Adhesion of Thick Films to Ceramic and Its Measurement by
Both Destructive and Nondestructive M e a n s - - s . L. MOREY
Discussion

233
250

Evaluation of Methods for Performing Adhesion Measurements
of Thick.Film Terminations on Chip Components-G. I. E W E L L

Discussion

251
267

Adhesion Measurement Technique for Soldered Thick-Film
Conductors--s. s. LEVEN
Discussion

269
283

Adhesion of Flame-Sprayed Coatings---H. s. INGHAM, JR.

285

Adherence Measurements and Evaluation of Thick-Film
Platinum-Gold--s. SCHROTER

293


ADHESION MEASUREMENT OF DEPOSITS AND COATINGS

Adhesion Testing of Deposit-Snbstrate Combinations-J. w. DINI AND H. R. JOHNSON
Discussion

Methods for Evaluating Adhesion of Photoresist Materials to
Semiconductor Deviees--r A. DECKERT
Discussion
Effect of Aspect Ratio on Tensile Bond Strength for Butt Joint of
Internal Fracture---Theoretical and Experimental Analysis-MINEO MASUOKA AND KAZUMUNE NAKAO
Discussion

Measuring the Temperature Dependence of the Strength of
Metal-Polymer Jolnts--N. I. EGORENKOV AND V. A. BELYI
Peel Test for Determlning the Adhesion of Electrodeposits on
Metallic Substrates--o. J. KLINGENMAIER AND S. M. DOBRASH
Discussion

305
326

327
341

342
359

362

369
389

SUMMARY

Summary

393

Index

399


STP640-EB/Jan. 1978

Introduction
This volume chronicles the proceedings of the Symposium on Adhesion
Measurement of Thin Films, Thick Films, and Bulk Coatings, held under
the auspices of the American Society for Testing and Materials, 2-4, Nov.
1976, in Philadelphia, Pa. Thin films ( < 1/zm), thick films (> 1 #m), and
bulk coatings ( > 25 #m) are used for a variety of purposes in electronic,
engineering, optical, biomedical, nuclear, space, and other applications.
Whatever their intended use may be, the properties, structure, functional
characteristics, and performance all depend, inter alia, on adhesion between
the coating and the substrate. So the need for reliable and quantitative
techniques for measuring cohesion is quite patent. Furthermore, the
quantitative determination of adhesion is important to discriminate between
the acceptable and nonacceptable parts or products, to optimize process
variables, for example, during film deposition, and to settle disputes
between the vendor and the buyer regarding adhesion-related performance
of products.
In the past no common forum had been provided to discuss the many
and varied so-called adhesion measurement techniques comprehensively.
However, a considerable amount of effort had been and was being devoted

to the development of new or the improvement of existing methods of
measuring adhesion. So I approached A S T M with the proposal that a
symposium on adhesion measurement was very timely and highly needed,
and the response to my proposal was both warm and affirmative.
The symposium was organized to review and assess current measurement
techniques, to provide a forum for the exchange of ideas, to define problem
areas which needed intensified efforts, and to galvanize increased interest
in developing better and more versatile techniques. The leitmotif of the
symposium was Adhesion Measurement Techniques: Their Potentialities
and Limitations. So the authors were prevailed upon to discuss clearly the
merits and limitations of the techniques they used, and also to focus on
the factors which interfere with the reliability and reproducibility of the
technique; and it is a pleasure to acknowledge their cooperation in this
regard.
The technical program contained 33 papers by 49 authors from seven
countries, but, unfortunately, three papers were not presented. The program
attracted about 80 people from Canada, Denmark, France, Germany,
Japan, Switzerland, and the United States. The papers dealt with a host of
adhesion measurement techniques for a variety of adherend-adherate
combinations. The authors represented a broad spectrum of professional

Copyright* 1978 by ASTM International

www.astm.org


2

ADHESION MEASUREMENT

affiliations, backgrounds, and interests. The technical program consisted
of both invited and contributed papers covering reviews and original research contributions.
This volume contains a total of 25 papers, divided into four sections, as
eight papers are not included for a variety of reasons. The first section
comprises seven papers dealing with such questions as are germane to
adhesion measurement. The topics addressed include: What is meant by
adhesion? What are the mechanisms of adhesion between different adherendadherate combinations? What exactly is measured when one attempts to
measure adhesion? How does the measured adhesion relate to fundamental
or basic adhesion? What is the nature and the importance of locus of
failure? and, What are the experimental difficulties and interpretational
complexities in adhesion measurement? The second section embodies
papers dealing with adhesion of thin films; adhesion of thick films constitutes
the third section. The final section contains papers concerning adhesion
measurement of deposits and coatings. The salient aspects or findings
of all these papers are embodied in the Summary at the end of the volume.
Each paper was followed by a discussion; the queries raised by the discussers
and author(s)' closure are appended at the end of the respective papers.
The symposium banquet was held in the evening of November 3rd, and
it was a distinct pleasure to have Dr. Harvey Alter as the banquet speaker.
He spoke on "The Material Science of Waste." The technical program was
followed by a panel discussion (the panelists were W. D. Bascom, J. J.
Bikerman, D. M. Mattox, K. L. Mittal, and L. H. Sharpe) in which some
of the relevant topics were discussed.
It is hoped that both the uninitiated and the veteran in the area of
adhesion measurement will find this volume a ready source of information
and guidance.
K. L. Mittal
East Fishkill Facility, IBM Corporation,
HopewellJunction, N.Y. 12533;symposium
chairman and editor.

General Papers Related to Adhesion
Measurement


K. L. MittaP

Adhesion Measurement: Recent
Progress, Unsolved Problems, and
Prospects

REFERENCE: Mittal, K. L., "Adhesion Measurement: Recent Progress, Unsolved
Problems, and Prospects," Adhesion Measurement of Thin Films, Thick Films, and

Bulk Coatings, ASTM STP 640, K. L. Mittal, Ed., American Society for Testing and
Materials, 1978, pp. 5-17.
ABSTRACT: In this paper, the term "basic adhesion" is used to signify the summation
of all interfaeial intermolecular interactions, whereas the term "practical adhesion" is
used to represent the forces or the work required for the disruption--either at the interface or in the interfacial region--of the adhering system. There are many factors
which influence practical adhesion, and these are discussed in detail. The relationship
between practical adhesion and basic adhesion is discussed. Basic adhesion cannot be
determined by the commonly used techniques for measuring practical adhesion. The
virtues of an ideal practical adhesion test are outlined. Some of the techniques for
adhesion measurement of thin films, thick films, and coatings are discussed briefly,
and references are made to the recent reviews on this topic.
For a given adhering system, different techniques yield different practical adhesion
values. The difficulties involved in adhesion measurement are highlighted, and the
unresolved problems are brought into sharper focus.
The failure surfaces should be examined using surface analytical tools to ascertain

the locus of failure, which is important in understanding the mechanism of failure.
KEY WORDS- basic adhesion, practical adhesion, adhesion measurement, thin films,
thick films, electrodeposits, coatings

Thin films (< 1 #m), thick films (> 1/zm), and bulk coatings (> 25/~m)
a r e u s e d for a v a r i e t y o f p u r p o s e s in d i v e r s i f i e d a p p l i c a t i o n s :in m a n y
technologies. Whatever their intended purpose--functional, decorative, or
p r o t e c t i v e - - m a y be, t h e p r o p e r t i e s , s t r u c t u r e , f u n c t i o n a l c h a r a c t e r i s t i c s ,
a n d p e r f o r m a n c e all d e p e n d , inter alia, o n a d h e s i o n b e t w e e n t h e a d h e r a t e
a n d a d h e r e n d . A d h e r e n d is a g e n e r a l t e r m u s e d for solid s u b s t r a t e to
w h i c h o t h e r m a t e r i a l s a d h e r e ; a n d M i t t a l [1] 2 h a s s u g g e s t e d r e c e n t l y t h e
1Staff engineer, East Fishkill Facility, International Business Machines Corporation.
Hopewell Junction, N. Y. 12533.
2The italic numbers in brackets refer to the list of references appended to this paper.

5
9

Copyright 1978 by ASTM International

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6

ADHESION MEASUREMENT

term adherate to represent the material which adheres to an adherend.
Obviously, in an adhering system of A and B, A adheres to B, and B
adheres to A, but the thinner phase is called the adherate. Examples of

adherates are thin films, thick films, paints, and coatings. Adhesive is a
special kind of adherate in that it adheres to two adherends instead of one.
In this publication, we are concerned mainly with adherates which adhere
to only one adherend. It is very important to differentiate between an
adherate-adherend combination--called adhering system--and an adhesive
joint (expressed in short form as adhint [2], because ideally in the former
there is only one interface and two bulk phases, whereas in the latter there
are two interfaces and three bulk phases. It should be pointed up, however,
that in many real situations, there are present additional interfaces and
interphases, as discussed later. The failure behavior of adhesive joints is
more complicated than that of adhering systems and will not be discussed
in the present paper.
The study of adhesion of adherates in the form of thin films, thick films,
and coatings is vital, and some examples where adhesion plays an important
role are given in the following paragraphs: The term "adhesion" simply
means sticking together of two similar or dissimilar materials.
1. Thin films (usually < 1 #m, and in some applications of the order of
50 nm) are so fragile that they must be supported by more substantial
substrate, and the degree to which the film can share the strength of the
substrate depends upon the adhesion between the two.
2. Durability, longevity, and wear of adherates depend intimately on the
degree of adhesion between the adherate and adherend.
3. Whenever adherates (paints, coatings) are used as protective overcoats for environmental protection, adhesion is very important. If the
adhesion is poor, the extent of deterioration of the substrates by environmental factors (humidity, corrosive gases, etc.) is greatly accelerated.
4. Polymeric substrates are metallized to reduce their permeability to
gases, and one can very well appreciate the importance of adhesion between
the metal and the polymer.
5. In the case of thin-films deposition (for example by evaporation),
adhesion plays an important role in governing the kinetics of the growth
and structure of the films, which in turn determine their functional performance. Whenever metal coatings are deposited on base metals, some of

the physical properties (grain structure, integrity, uniformity, etc.) are
dictated by adhesion to the base metals.
6. In the case of multilayer structures, adhesion between the individual
layers is crucial.
7. The adhesion of thick-film conductors (frit bonded and reactively
bonded) is important in microcircuits fabrication.
8. Artificial teeth are mostly made of acrylate, which often causes allergic
changes in the mucous membranes of the mouth and hence is inconvenient


MITTAL ON RECENT PROGRESS

7

to use [3]. Thin films of dental gold are used as coating to decrease this
unpleasant effect, and the adhesion of the coating to the tooth surface is
very important.
In addition to what has just been said, basic adhesion is important in
surface chemistry and physics as it depends directly on the interatomic and
intermolecular forces.
There are essentially two aspects of an adhesion study program: understanding of the factors affecting adhesion and thereby improvement of
adhesion strength, and the measurement of adhesion strength. The first
aspect has been the subject of recent symposia [4-6] and in the present
publication we are concerned primarily with the methodology of the
measurement of adhesionin adhering systems.
The measurement of adhesion is important for a variety of reasons:
(a) to assess the efficacy of changes in the process variables or of substrate
preparations, and thereby to optimize the conditions which yield the required adhesion strength; (b) to discriminate parts or products which have
poor adhesion strength from those which are acceptable; and (c) to gain
fundamental insight into the mechanism of adhesion.

So the need for reliable, reproducible, and quantitative methods for
measuring adhesion is quite manifest.
Can Adhesion Be Measured?

"Can adhesion be measured?" is one of the perennial questions in adhesion science and technology, and if one scans the literature, one will encounter discordant opinions on this issue. But the simple answer to the
question is yes and no, depending upon what is meant by adhesion. The
meaning and ramifications of the term adhesion are discussed first, followed by comments on whether adhesion can be measured.
ASTM Definition of Terms Relating to Adhesives (D 907-70) defines
adhesion as "the state in which two surfaces are held together by interfacial forces which may consist of valence forces or interlocking forces or
both." For a detailed discussion of the definition of adhesion, the reader
should consult a recent paper by Good [7].
There are various theories or mechanisms of adhesion [8-13] but there
is no single theory or mechanism which can explain all adhesion behaviors.
All these mechanisms are valid to varying degrees, however, and their relative importance depends on the adhering system in question.
In an adhering system, adhesion can be expressed in terms of forces or
work of attachment, or in terms of forces or work of detachment. If expressed in the former manner, then the correct appellation should be "basic
adhesion," "fundamental adhesion," "true adhesion," or "interfacial
adhesion;" however, the present author prefers the term "basic adhesion."
Basic adhesion signifies the interfacial bond strength and should depend


8

ADHESION MEASUREMENT

exclusively on the interfacial properties, without any contribution from any
other sources. Basic adhesion is simply the summation of all intermolecular
or interatomic interactions. These interactions could be electrostatic, chemical, or van der Waals type. Unless there is a well-defined interface between
the adhering phases, the term basic adhesion does not have any significance.
On the other hand, experimentally, adhesion is measured in terms of

forces or the work of detachment or separation of the adhering phases.
The separation may take place at the interface, or in the interfacial region
(also called interphase), or in the bulk of the weaker adhering phase.
Separation in the bulk is termed cohesive failure and is related to the cohesive strength of that bulk phase. The cohesive failure of a thin coating or
adhesive however, is unlikely to be the same as the cohesive failure of the
same material in bulk. Mechanical constraints by the adherend(s) or differences in chemical composition or morphology due to the conditions of
coating deposition or joint formation are two possible causes.
The interface is a mathematical plane and can be realized only in the case
of a nonsoluble/noncompound forming adherend-adherate combination.
On the other hand, an interfacial region or interphase possesses a certain
thickness, and its mechanical properties are different from those of the
contiguous phases. Interphases m a y be present on the adhering phases
(for example, oxide on metal, oily layer on a surface), or they may be formed
by interaction of the adhering phases (for example, diffusion type of interphase in a metal-metal system). The nature and thickness of interphases
depend on the adhering phases involved [14,15]. The presence of these
interphases would give rise to additional interfaces.
So obviously, in real adhering systems, there can be many interfaces and
interphases in addition to the two bulk phases, and separation could be at
any of the interfaces or in any of the interphases or in one of the two bulk
phases. If the separation occurs at an interface or in an interphase, then it
is suggested that the measured adhesion be labeled as "practical adhesion."
It should be noted, however, that such suggestion is not entirely satisYactory as there are still many unanswered questions:
1. As the interphase is of definite thickness, then why not call the failure
in an interphase the "cohesive failure" and the measured adhesion the
separation strength of that particular interphase?
2. If the failure occurs in one of original adhering phases but very close
to the interface, then should it be called "adhesive" or "cohesive" failure?
In such a situation, should the measured stress required for such separation be a measure of practical adhesion? In the case of very thin films, failure close to the interface may be actually deep bulk failure.
3. If the failure is mixed (interfacial, plus interphasial, plus bulk) in
nature, then should the measured stress be called practical adhesion?

There is no easy answer to these problems, but it is suggested that unless
the failure is deep in the bulk of the adhering phases, the measured stress


MITTAL ON RECENT PROGRESS

9

required to effect separation of the adhering system be labeled "practical
adhesion."
The forces required to disrupt the interface or interphase can be applied
in various forms (tensile, peel, shear, etc.) and the practical adhesion is
expressed in terms of tensile strength, peel strength, or shear strength. Peel
strength is measured in terms of force/width required to maintain the continuous detachment of a strip of adherate from an adherend at a specified
detachment rate. Peel strength is also expressed in terms of work or energy
per unit area.
Tensile strength is defined as the stress (force/area) required to remove a
specific area of the adherate when the entire area of the adherate is pulled
in a direction perpendicular to the adherend surface.
Forces of adhesion and the work or energy of adhesion can be related only
if assumptions are made about the changes in force with distance of separation, so that an integration can be performed. In other words, w, the work
of adhesion is
P

w = If(x) dx
Bikerman [16] has promulgated the nonexistence of interfacial failure in
a "proper bond," that is, in a bond where intermolecular interaction between the adherate and the adherend has been achieved. According to
him, true interfacial failure practically never occurs and what is taken for
interfacial failure is actually a separation in a weak boundary layer. Cases
are chronicled in the literature, however, where true interracial failure has

been observed [17]. On the other hand, Bikerman has recently [18] cited
some examples of noninterfacial failure to bolster his previous views. For a
critique of Bikerman's views, the reader should refer to Good [19]. What
Bikerrnan calls "weak boundary layers" are actually the interphases between
the adhering phases.
In any case, visual inspection is inadequate to ascertain the locus of failure in a separated system, and techniques like electron spectroscopy for
chemical analysis, Auger electron spectroscopy, or secondary ion mass spectrometry should be employed for this purpose, and these have been recently used [20,21].
Now the question arises, What is the relationship between practical adhesion and basic adhesion? Let us look at some of the characteristics of
both. Basic adhesion is strictly an interfacial property and depends exclusively
on the surface characteristics of adhering phases. Basic adhesion shotild be
independent of the thickness of adherate, thickness of adherend, specimen
size, specimen geometry, temperature, measurement technique, manner of
applying external forces, manner of performing the test, test rate, bulk
properties of adhering phases, etc.
However, the so-called adhesion measurement techniques measure prac-


10

ADHESION MEASUREMENT

tical adhesion, which is affected by all these factors. For example, practical
adhesion in terms of peel strength depends upon the rate of peel, angle of
peel, etc. Tensile strength depends upon the manner of performing the test
and the rate of pull.
Basic adhesion can be theoretically calculated or indirectly determined.
For example, if the adherate is in liquid form, one can calculate the thermodynamic work of adhesion in terms of its wetting behavior [11,22]. In the
case of thin-film deposition, basic adhesion between the film and the substrate can be determined by the nucleation methods, that is, by observing
the kinetics of formation of these films [23]. In essence, basic adhesion is
calculated by taking the summation of adsorption energies of individual

adatoms. Of course, nucleation methods of determining basic adhesion are
of limited applicability and are quite tedious.
An elegant approach based upon the molecular models was taken by
Taylor and Rutzler [24], but it has not been extended to a stage where it
could be used to quantify basic adhesion in a system of interest.
In summary, the relationship between practical adhesion and basic adhesion can be expressed as follows:
1. If there exists a sharply defined interface between the two adhering
phases and the separation is clearly at this interface, then
Practical adhesion = f (basic adhesion, other factors)
2.

If the separation is in the interfacial region, then
Practical adhesion = f (interatomic or intermolecular
bonding within the interfacial
region, other factors)

These other factors include intrinsic stresses (which depend, among other
things, upon the adherate thickness), presence or absence of sites of easy
failure, the mode of applying external stress, that is, the technique of
measuring practical adhesion, the failure mode, etc.
The following conclusions are made obvious by the foregoing: (a) Basic
adhesion can be determined only from practical adhesion provided the
contribution due to "other factors" can be quantitatively accounted for in
the practical adhesion. However, the existence of a clear-cut interface, and
the occurrence of clear separation at that interface are not realized in most
practical systems. (b) One can expect different practical adhesion values
by different techniques. (c) There may not be simple and direct correlation
between practical adhesion and the basic adhesion.

MITTAL ON RECENT PROGRESS

11

Methods of Measurement of Practical Adhesion

The literature is replete with techniques for measuring practical adhesion of thin films, thick films, and coatings. As these techniques have been
recently reviewed in detail [25,26], there is no need to expatiate upon them
here. So, in this paper references are made to the recent reviews, and only
salient developments subsequent to these reviews are covered.
An ideal test for measuring practical adhesion should be [25,26]: (a) reproducible, (b) quantitative, (c) nondestructive, (d) easily adaptable to
routine testing, (e) relatively simple to perform, ( f ) not very time-consuming, (g) applicable to a wide range of adherate thicknesses, (h) independent
of operator's experience, (i) applicable to all combinations of adherates and
adherends, ( j ) valid over a wide range of specimen sizes, (k) applicable to
products and processes, (l) able to measure wide range of practical adhesion strengths, (m)free from interpretational complexities, and (n)
amenable to standardization. Furthermore, machining requirements for
specimen preparation should be minimum, and no specialized equipment
should be necessary. But such idealization is not realized in practice, as
there is no technique which fulfills even half of the foregoing attributes. All
commonly used tests for measuring practical adhesion are destructive in
nature.

Adhesion Measurement of Thin Films
Mittal [25] has recently reviewed comprehensively and critically the adhesion measurement techniques for thin films. The principle, experimental
details, potentialities, and limitations of each technique are discussed, and
in many cases the practical adhesion strengths obtained using these techniques are presented. Also the interpretational difficulties, factors affecting
values of practical adhesion, and the precautions which should be borne in
mind to obtain reproducible results are discussed.
The following techniques are discussed in this review.
1. Nucleation methods. As mentioned earlier, the information derived

from the nucleation behavior of depositing thin films is used to determine
the basic adhesion. These methods are not really the techniques for measuring practical adhesion.
2. Mechanical methods. Direct pull-off, moment or topple, ultracentrifugal, ultrasonic, adhesive tape, peel, tangential shear or lap shear,
scratch or stylus or scribe, blister, and abrasion.
3. Miscellaneous techniques. This category includes those techniques
which are either of very limited applicability or whose usefulness in routine
practical adhesion measurement is not established.
Since this review was completed, a few interesting papers have appeared.


12

ADHESION MEASUREMENT

Jacobsson [27] has analyzed the direct pull-off method in detail and has
quantified the effects of variables which affect direct pull strengths. Goldstein and Bertone [28] have discussed the use of the scratch test to evaluate
metal film adhesion onto flexible substrates. Earlier, the scratch test had
been used only for rigid substrates. Recently [29] scratches have been examined by very sensitive surface profilemeter and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy, and it is observed, among other findings, that the mechanism of film failure depends
upon whether the film is ductible or brittle.
Stephens and Vossen [30a] have described a laser spallation technique
for measuring adhesion. They claim that the technique can be used to
measure interfacial bond strength--which is basic adhesion in terms of the
terminology proposed earlier. The technique involves impinging a pulsed,
high-energy, neodymium-glass laser beam (1.6 #m) onto the back surface of
a substrate (made opaque in the case of transparent substrates). The explosive evaporation of absorbing material on the back side of the substrate
generates a comprehensive shock wave in the substrate directed toward the
film-substrate interface. The magnitude of the shock wave is varied so as to
attain spaUation or detachment of the film. This obviates the need to attach some sort of mechanical device to detach the film. More recent findings using this technique are discussed by Vossen in this publication [30b].
Krongelb [31] has described a technique for measuring the adhesion of
thin films in which the interaction of an electric current and a magnetic

field (referred to as f x H) can be used to apply a known stress to a deposited thin film without requiring any mechanical attachment to the film.
The maximum achievable stress is proportional to the available magnetic
field and the current. The specimen fabrication, experimental conditions,
and results obtained on specimens of copper evaporated at various temperatures on thermal silicon dioxide (SiO2) are described.

Adhesion Measurement of Thick Films
For a detailed discussion of the practical adhesion measurement techniques for thick-f'dm conductors, the reader should refer to Hitch and
Bube [32], Jacobson [33], and Anjard [34]. The following tests have been
discussed by Hitch and Bube: uniaxial tension, wirebond, peel, soldered
wire, tensile peel, and dot.
Hitch [35] has most recently reviewed the practical adhesion measurement of thick-film conductors. The techniques for the measurement of
practical adhesion of electrodeposits have been recently reviewed in detail
by Mittal [26]. The principle, experimental details, potentialities, limitations, interpretational difficulties, factors affecting practical adhesion
strengths and the precautions which should be borne in mind for each
technique are discussed. The techniques discussed are:


MITTAL ON RECENT PROGRESS

13

1. Qualitative tests.
2. Tension tests (use of solders, adhesives and electroformed grips;
the OUard method and its subsequent modifications).
3. Ring shear tests.
4. Peel tests.
5. Knife and scribing tests (knife test, scratch, or stylus test).
6. Ultracentrifugal test.
7. Nonmechanical tests.
In addition, the ultrasonic and blister methods for measuring the practical adhesion of organic coatings are included.

Dini and Johnson [36] have recently reviewed the following tests for
measuring the practical adhesion of electrodeposits: ring shear, conicalhead tensile, modified Ollard, 1-Beam, and flyer plate. Modified Ollard
and I-Beam are tensile type tests, and flyer plate tests are shock-wave tests
used for evaluating parts under dynamic loading conditions. All have been
shown to be quite effective in providing consistently reproducible data.
Details are presented for each test, such as the shape and size of the specimen, preparation of specimens, and the manner in which the test is performed; data for various substrate-electrodeposit combinations are included.
Most recently, Dini et al [37] have discussed in detail some of the techniques for measuring practical adhesion of electrodeposits.
The most comprehensive review on the practical adhesion measurement
of thick or bulk coatings is that by Bullett and Prosser [38]. For an earlier
review on this topic, the reader should refer to Lewis and Forrestal [39].
These two reviews discuss in great detail the state of the art with respect to
practical adhesion of thick coatings. Primary emphasis is on organic coatings. There has not been any significant development since these reviews
were published.

Future Developments
It appears that there is a definite need to expend efforts in the following
areas:
1. Development of nondestructive techniques for measuring practical
adhesion.
2. Thorough understanding of the factors which influence practical adhesion measurement as determined by a given technique.
3. The existing promising techniques for measuring practical adhesion
should be standardized, so that results from different investigators can be
directly compared.
4. Cross comparison of various practical adhesion measurement techniques. Some adhering systems should be tested for practical adhesion by
various techniques.
5. Thorough understanding of the noninterfacial contribution to prac-


14

ADHESION MEASUREMENT

tical adhesion strength. If these noninterfacial contributions are understood
and quantified, then there is the possibility of determining basic adhesion
from measured practical adhesion, provided there is a clear-cut interracial
separation. It should be noted that in practical situations, one is concerned
with practical adhesion strength, not with basic adhesion. However, in the
case of clear-cut interfacial separation, the practical adhesion could be improved by improving basic adhesion by suitable interfacial treatments.

Summary and Conclusions
1. Generally speaking, an adhering system may consist of one or more
interfaces and one or more interphases, in addition to the two bulk phases.
When an adhering system is disrupted, or separated by applying external
stresses, the separation may take place at an interface, in an interfacial
region (also known as interphase), or in the bulk of the weaker of the adhering phases. If the separation occurs at an interface or in an interphase,
then it is suggested that the stresses required be taken as a measure of
practical adhesion. And since the practical adhesion value depends upon
the locus of failure, the failure surfaces should be analyzed for the locus
of failure. The information regarding the site of failure is important in understanding the mechanism of failure, and the modern surface analytical
instruments should be of immense help in examining the failure surfaces.
2. Basic adhesion signifies the summation of all interfacial intermolecular
interactions. In case of a clear-cut interfacial separation, practical adhesion is a function of basic adhesion and many other factors (intrinsic
stresses, techniques used to measure practical adhesion, etc.). Unless the
contributions due to these "other factors" can be accounted for, one cannot determine basic adhesion from practical adhesion.
3. In the case of failure in an interphase, the practical adhesion depends
upon the intermolecular or interatomic bonding within the interfacial
region and other factors (stresses, easy failure mode, mode of applying
external stresses, etc.)
4. Practical adhesion may not vary directly with changes in basic adhesion. For example, attempts to improve basic adhesion may not result in
increased practical adhesion, because of the contribution from "other

factors." On the other hand, two adhering systems may have the same
basic adhesion, but their practical adhesion could be quite different.
5. Different techniques yield different practical adhesion strengths.
Practical adhesion, for a given adherend-adherate combination, as determined by different techniques may not be directly comparable. Furthermore, different techniques yield values of practical adhesion in different
units (for example, peel strength in terms of force/length vis-a-vis tensile
strength as force/area).


MITTAL ON RECENT PROGRESS

15

6. As there are m a n y factors affecting practical adhesion, the experim e n t e r , while quoting values o f p r a c t i c a l adhesion, m u s t specify t h e exp e r i m e n t a l conditions, specimen size a n d g e o m e t r y , a n d o t h e r relevant
p a r a m e t e r s . F o r e x a m p l e , unless the rate o f peel a n d the angle o f peel are
k e p t c o n s t a n t , different e x p e r i m e n t e r s will m e a s u r e different peel strengths
for the s a m e a d h e r i n g system.
7. Some p r a c t i c a l a d h e n s i o n tests are qualitative in n a t u r e . In such
tests, there is always some subjective i n t e r p r e t a t i o n . Unless the test yields
some n u m b e r s for p r a c t i c a l adhesion, its usefulness is restricted. However,
qualitative tests can be used profitably in discerning cases of very p o o r
p r a c t i c a l adhesion.
8. T h e choice o f the test for m e a s u r i n g p r a c t i c a l a d h e s i o n should be
b a s e d u p o n the type of stresses the test s p e c i m e n is going to e n c o u n t e r in
practice.
References
[1] Mittal, K. L., Journal of Adhesion, Vol. 7, 1974, pp. 377-378.
[2] Bikerman, J. J., The Science of Adhesive Joints, 2nd edition, Academic Press, New
York, 1968.
[3] Nenadovic, T., Bibic, N., Kraljevic, N., and Adamov, M., Thin Solid Films. Vol. 34,
1976, pp. 211-214.

[4] Lee, L. H., Ed., Recent Advances in Adhesion. Gordon and Breach, New York, 1973.
[5] Lee, L. H., Ed., Adhesion Science and Technology, Vols. 9A and 9B, Plenum Press,
New York, 1975.
[6] Proceedings of Recent Conferences on Adhesion and Adhesives held in London, England. These are chronicled in the series Aspects of Adhesion. D. J. Alner, Ed., CRC
Press, Cleveland, Ohio.
[7] Good, R.J., Journal of Adhesion, Vol. 8, 1976, pp. 1-9.
[8] Allen, K. W. in Aspects of Adhesion, D. J. Alner, Ed., Vol. 5, CRC Press, Cleveland,
Ohio, 1969, pp. 11-24.
[9] Raevskii, R. J., Journal of Adhesion. Vol. 5, 1973, pp. 203-210.
[I0] Mittal, K. L., Journal of Vacuum Science and Technology. Vol. 13, 1976, pp. 19-25.
[11] Mittal, K. L. in Adhesion Science and Technology, L. H. Lee, Ed., Plenum Press,
New York, 1975, Vol. 9A, pp. 129-168.
[12] Mittal, K. L., Polymer Engineering and Science. Vol. 17, 1977, pp. 467-473.
[13] Huntsberger, J. R. in "Treatise on Adhesion and Adhesive. " R. L. Patrick, Ed., Marcel Dekker, New York, 1967, Vol. 1, pp. 119-149.
[14] Sharpe, L. H., Journal of Adhesion. Vol. 4, 1972, pp. 51-64.
[15a] Chapman, B. N., Journal of Vacuum Science and Technology. Vol. 11, 1974, pp. 106115.
[15b] Mattox, D. M., this publication, 54-62.
[16a] Bikerman, J. J., Industrial and Engineering Chemistry, Vol. 59, No. 9, 1967, pp.
40-44.

[16b]
[17]
[18]
[19a]
[19b]
[20]
[2l]

Bikerman, J. J., Journal of Paint Technology, Vol. 43, 1971, pp. 98ff.
Crocker, G. J., Rubber Chemistry and Technology, Vol. 42, 1968, pp. 30-70.

Bikerman, J. J., this publication, pp. 30-40.
Good, R. J.,JournalofAdhesion, Vol. 4, 1972, pp. 133-154.
Good, R. J., this publication, pp. 18-29.
Baun, W. L., Journal of Adhesion. Vol. 7, 1976, pp. 261-267.
Wyatt, D. M., Gray, R. C., Carver, J. C., Hercules, D. M., and Masters, L. W.,
Applied Spectroscopy, Vol. 28, No. 5, 1974, pp. 439-444.


16

ADHESION MEASUREMENT

[22] Murr, L. E., this publication, pp. 82-98.
[23] Campbell, D. S. in Handbook of Thin Film Technology, L. I. Maissel and R. Glang,
F_As., McGraw-Hill, New York, 1970, Chapter 12, pp. 12-3-12-47.
[24] Taylor, D., Jr., and Rutzler, J. E., Jr., Industrial and Engineering Chemistry, Voi.
S0, 1958, pp. 928-934.
[25] Mittal, K. L., Electrocomponent Science and Technology, Vol. 3, 1976, pp. 21-42.
[26] Mittal, K. L. in Properties of Electrodeposits: Their Measurement and Significance,
R. Sard, H. Leidheiser, Jr., and F. Ogburn, Eds., The Electrochemical Society
Princeton, N.J., 1975, Chapter 17, pp. 273-306.
[27] Jacobsson, R., Thin Solid Films, Vol. 34, 1976, pp. 191-199.
[28] Goldstein, L. F. and Bertone, T. J., Journal of Vacuum Science and Technology, Vol.
12, 1975, pp. 1423-1426.
[29] Ahn, J., Mittal, K. L., and MaeQueen, R., this publication, pp. 134-157.
[30a] Stephens, A. W. and Vossen, J. L., Journal of Vacuum Science and Technology, Vol.
13, 1976, pp. 38-39.
[30b] Vossen, J. L., this publication, pp. 122-133.
[31] Krongelb, S., this publication, pp. 107-121.
[32] Hitch, T. T. and Bube, K. R., "Basic Adhesion Mechanisms in Thick and Thin Films,"

Report from RCA Laboratories, Princeton, N. J., 31 Jan. 1975.
[33] Jacobson, L., Proceedings, IEEE and EIA Electronic Components Conference, 1971,
pp. 474-479.
[34] Anjard, R. P., Microelectronics and Reliability, Vol. 10, No. 4, 1971, pp. 269-275.
[35] Hitch, T. T., this publication, pp. 211-232.
[36] Dini, J. W. and Johnson, H. R., Metal Finishing, March 1977, pp. 42-46; April 1977,
pp. 48-51.
[37] Dini, J. W. and Johnson, H. R., this publication, pp. 305-326.
[38] Bullett, T. R. and Prosser, J. L., Progress in Organic Coatings, Vol. 1, 1972, pp. 45-73.
[39] Lewis, A. F. and Forrestal, L. J. in Treatise on Coatings, R. R. Myers and J. S. Long,
Eds., Marcel Dekker, New York, 1969, Vol. 2, Part 1, pp. 57-98.

DISCUSSION
H. E. Ashton 1 (written discussion )--First, your statement that the scratch
adhesion method was developed in the 1950s is not correct with regard to
organic coatings. Bell Laboratories developed the Bell Scrape Adhesion
Tester in the 1930s which led to Method A of D 2197. See A S T M STP 500-Paint Testing Manual, p. 320.
Second, the term "hesion" was used before Dr. Asbeck used it in the
1960s. I heard Dr. Reed Brantley of Occidental College use it in 1957. Try
Brantley et al. 2

K. L. Mittal (author's closure)--First, please note that I was referring
to the use of the scratch test for thin films, and to my knowledge it was
1Division of Building Research, National Research Council of Canada, Ottawa, Ont.,
Canada.
2Brantley, L. R., Stabler, R., and Bills, K., ACS Paint and Plastics Preprints, American
Chemical Society, Vol. 13, March 1953, p. 140.