828 IEEE TRANSACTIONS ON COMPONENTS, HYBRIDS, AND MANUFACTURING TECHNOLOGY, VOL. 16, NO. 8, DEC’EMBER 1993

An Overview and Evaluation of Anisotropically Conductive Adhesive

Films for Fine Pitch Electronic Assembly David D. Chang, Member, IEEE, Patricia A. Crawford, Joe A. Fulton, Richard

McBride, Maureen- B. Schmidt, Raymond E. Sinitski, and C. P. Wong, Fellow, IEEE

Abs?ruc?- Conductive adhesives have been used in the elec- tronics industry for several years to attach chips to package lead frames in the semiconductor industry and for general intercon- nection of components to flexible circuits for various consumer products. Generally, these materials conduct equally in all direc- tions. To obtain pad isolation, the adhesives are screen printed to the pattern of the circuit pads. In the last few years, a new class of adhesives that are conductive in a single direction have been developed. These are referred to as anisotropic conductive adhe- sive films (ACAF’s). These anisotropically conductive adhesives provide electrical as well as mechanical interconnections for fine pitch applications. The conductivity of ACAF materials is only in the 2-direction (perpendicular to the plane of the board) while electrical isolation is maintained in the X - Y plane.

Currently, at least 15 ACAF materials are commercially avail- able. We have developed a methodology for evaluating these materials for their mechanical and electrical properties and interconnection use in the 8 to 15 mil pitch range. In addition, we characterized the materials according to their physical properties and cure characteristics. This paper details our findings with a comparison of physical form to assembly/cure and final electrical properties. We include in this study data from scanning electron microscopy, thermal analysis of the ACAF’s, and cure and assem- bly studies on mixed substrate test vehicles. Information on initial electrical testing and long-term reliability testing is also given.

I . INTRODUCTION

ONDIRECTIONAL (isotropic) conductive adhesives N have been used in the electronics industry for a number of years to attach chips to package lead frames. These materials have also been used for pad interconnection by stenciling them onto the pads to be connected. In the last few years a new class of adhesives that are conductive in one direction only have been developed. These are referred to as anisotropic conductive adhesive films (ACAF’s). These anisotropically conductive adhesives can provide electrical as well a mechanical interconnections between conductive pads on parts to be permanently assembled. The conductivity of these materials is restricted to the 2-direction (perpendicular to the plane of the board) with electrical isolation provided in the X - Y plane. Thus, the ACAF materials offer an alternative method for fine pitch interconnection.

Manuscript received March 1, 1993; revised July 31, 1993. This paper was presented at the 1993 Electronic Components and Technology Conference, Orlando, FL. June 1 4 , 1993.

The authors are with the Engineering Research Center, AT&T Bell Laho- ratories, Princeton, NJ 08542.

IEEE Log Number 9213229.

The most commercially significant ACAF’s are based on the single particle bridging concept. These material! are under investigation ai numerous companies and several preliminary studies have been reported [ 11-[3]. Examples of 1 ypical in- terconnections using ACAF’s are shown in Fig. 1 Fig. l(a) shows the interconnection of a flexible circuit t ( ’ a liquid crystal display (LCD) using a narrow strip of ACN ’, and Fig. l(b) shows the attachment of a tape automated bonc ed (TAB) circuit connected to a second flexible circuit using a picture frame of ACAF. In general, the adhesive material is applied as a film to one interconnection surface, such as a display with a pad array. A part, such as the flexible circuit. is aligned to the display with standard placement equipmenl and then bonded by the simultaneous application of heat and pressure. Obviously, a wide variety of assembly options art: possible using ACAF materials.

11. MATERIALS AND COMPONENTS

A. The Anistropically Conductive Adhesive In general, the ACAF materials are prepared by dispersing

electrically conductive particles in an adhesive mi atrix at a concentration far below the percolation threshold. The con- centration of particles is controlled such that enoug li particles are present to assure reliable electrical conductivit,,? between the assembled parts in the 2-direction while too few particles are present to achieve percolation conduction in the X - Y plane.

B. ACAF Types

.When designing materials to achieve fine pitch intercon- nections, several important variables must be considered and are application dependent. These variables include adhesive characteristics as well as particle type.

Two basic types of adhesives are available: the1 moplastic and thermosetting. Thermoplastic adhesives are rigic materials at temperatures below the glass transition temperatti re (Tg) of the polymer. Above this temperature, polymer flov occurs. When using this type of material, assembly teri iperatures must exceed the Tg to achieve good adhesion. rhus, the Tg must be sufficiently high to avoid polymer flow during use conditions, but the Tg must be low enough 10 prevent thermal damage to the electronic circuits during asse tnbly. The

0148-6411/93$03.00 0 1993 IEEE

CHANG et al.: OVERVIEW AND EVALUATION OF ANISOTROPICALLY CONDUCTIVE ADHESIVE FILMS 829

(b) Fig. 1. Examples of interconnections using ACAF’s: (a) Attachment of a flexible circuit to an LCD. (b) Mounting of a TAB device onto a flexible substrate.

principal advantage of thermoplastic adhesives is the relative ease with which the interconnection can be disassembled for repair operations.

Thermosetting adhesives, such as epoxies and silicones, form a three-dimensional cross-linked structure when cured under specific conditions. Curing techniques include: heat, UV light, and added catalysts. As a result of this irreversible cure reaction, the initial uncross-linked material is transformed into a rigid solid. The curing reaction is not reversible. This fact may hinder disassembly and interconnection repair. The ability to maintain strength at high temperature and robust adhesive bonds are the principal advantages of these materials.

The principle criterion used for selecting the adhesive is that robust bonds are formed to all surfaces involved in the interconnection. Numerous materials surfaces can be found in the interconnection region including: Si02, Si3N4, polyester, polyimide, FR4, glass, gold, copper, and aluminum. Adhesion to these surfaces must be preserved after standard tests such as temperature-humidity-bias aging and temperature cycling. Some surfaces may require chemical treatments to achieve good adhesion. In addition, the adhesive must not contain ionic impurities that would degrade electrical performance of the interconnections.

The materials used as conductive particles must also be carefully selected. Silver offers moderate cost, high electrical conductivity, high current carrying ability, and low chemical reactivity, but problems with electromigration may occur. Nickel is a lower cost alternative, but corrosion of nickel surfaces has been found during accelerated aging tests. The

material that offers the best properties is gold, however, costs may be prohibitive for large-volume applications. Plated particles may offer the best combination of properties at moderate cost.

1) Frequency Response: Because of the compo.de struc- ture of ACAF’s, the possibility of signal frequency i lependent phenomena is a concern. The fundamental principle in achiev- ing high frequency performance in any interconnection system is to minimize inductance and capacitance, or hav: uniform controlled impedance. The shortest interconnectit )n length gives the lowest inductance. The interconnection lei igth of an ACAF material is determined by the diameter of [ mductive particles, which can range from 0.5 to 30 p m, sipnificantly shorter than pins or wirebonds. Therefore, the inductance of an adhesive interconnection should be negligible. The capacitance resulting from the adhesive’s dielectric is mainly dependent upon the physical layout of the intercl mnection. Only the dielectric located between the signal and ground lines will show stray capacitance. Although it has not been experimentally demonstrated, z-axis conductive kdhesive’s high frequency performance should be better than coiiventional pin or wire-bonded interconnections.

2) Current Carrying Capability: Since the amount of con- ductive metal is small and varies in ACAF’s, one muLt evaluate the current carrying capability of each material and its appli- cation. AC current carrying capability has been demonstrated using an active bipolar IC bonded with an ACAF to a flexible circuit. The results show ACAF’s filled with plaited metal particles can carry at least 20 mA root mean squ,ire (RMS) current at 2 MHz. For carrying high radio frequenLy current, it appears that the surface of the conductive particles should be smooth.

DC current carrying capability has been demons rated with ACAF’s containing silver coated nickel particles .it the 200 mA level. Other test results on ACAF’s loaded with silver coated polymer spheres showed a limited current carrying capability of less than 5 mA. In general, DC curreiit carrying capability can be increased and through resistance decreased by increasing the conductive particle loading.

C. Parts Considerations

Adhesives are often used to attach the copper conductors onto the polyimide or polyester core material of flexible circuits. These substrate adhesives have to be dimensionally stable at the bonding temperature of the z-axis adhesive. If rigid particles are used in the ACAF, the substratl: adhesive layer also has to soften enough to provide for some compliance under the conductor. This compliance is required to provide for particle size variation and, thus, assure bridging contact for all particles. Compliance can also be gained by increasing the conductor, attach adhesive thickness.

Design considerations for the substrate conducttxs include the height (or thickness), width and spacing betwel:n adjacent conductors. The width and spacing are determimd by pad size and spacings on the parts. The narrowest conductor spacing affects the maximum conductive particle $4ze for the adhesives. For a specific conductor pitch, slight increases

IEEE TRANSACTIONS ON COMPONENTS, HYBRIDS, AND MANUFACTURING TECHNOLOGY, VOL. 16, NO. 8, DI :EMBER 1993 830

TABLE I CHARACTERIZATION METHODS

Technique Information

Optical Microscopy Scanning Electron Microscopy (SEMI Energy Dispersive X-ray (EDX) Differential Scanning Calorimetry (DSC) Thermogravimetric Analysis (TGA) Dielectrometry Fourier Transform Infrared Spectroscopy (FTIR) Mechanical Push-off Assembly test (at ambient and 65’ C/65% RH)

Morphology Detailed morphology

Material identification Cure temperature and glass transition

Decomposition and stability Cure kinetics Cure time and polymer type

Adhesion Electrical properties and reliability

in conductor widths results in decreasing conductor spacing. As a result, it becomes more difficult to maintain electrical 2 - y isolation with a specific ACAF material. The primary benefits of enlarging conductor widths is to accommodate any lateral misregistration between pad and conductor during the bonding operation and increase the number of particles in the interconnection. The pad heights and particle size, together with any compliance in substrate or particles, determine the needed ACAF thickness. By matching this thickness to the final gap between parts, voids in the assembly interconnection layer can be minimized. Voids between the adhesive and the parts lower the strength of the bond and provide sites for moisture accumulation. Both of these phenomena can degrade the performance and reliability of the interconnection.

Because oxides on conductors can interfere with electrical contact, the ideal conductor surface finish is a gold layer plated over a nickel flash on the copper contact. For the adhesives studied, bare copper without any surface treatment gave poor interconnection. In general, the key is to minimize surface oxides before the bonding operation.

111. CHARACTERIZATION OF ACAFS

After an extensive review and some initial experimentation of various characterization techniques, we determine that the procedures listed in Table I would give us the best information for comparison of ACAF’s. The table also contains the infor- mation provided by the techniques. Below we describe the individual techniques in more detail and discuss the types of information that can be obtained with their use. To demonstrate the techniques, we chose four ACAF’s and subjected them to our characterization and evaluation process.

A. Microscopy

Various types of microscopy can be used to examine the ACAF materials and the type is chosen based on the type of information being sought. Overall surface detail, particle shape, particle type, and a rough measure of the loading of particles in the ACAF requires low magnification and is best done with optical microscopy or low magnification SEM. Fig. 2(a) shows this type of microscopy. For higher magnification

(b)

Fig. 2. Examples of photomicroscopy of ACAF materials: (a:] General mor- phology of the ACAF surface; (b) High magnification SEM 0 1 a conductive particle in an ACAF.

of a film SEM is ideal and gives more detailed :nformation on the conductive particles and other possible fillei 3. Fig. 2(b) shows a typical photomicrograph of an ACAF pu rticle. This data was obtained by SEM.

B. Energy Dispersive X-Ray (EDX)

EDX systems are often coupled with SEM’s, bccause they can use the electron imaging beam of the SEM tri excite X- ray emissions from elements in the sample. The idc ntity of the elements and a semiquantitative measurement of trtie amounts of those elements can be determined from the enerlgy and flux of the emitted X-rays. This technique can be used to analyze the surface composition of the conductive particles or other fillers.

Table I1 shows the types of data that can be obtained from the commercial ACAF’s we chose to examine. This information gives a general view of the types ( I € particles, coatings, and particles sizes that occur in a range of the adhesive films.

C. Fourier Transform Infrared Spectroscopy (FTIH’)

Absorption of infrared radiation is widely used in science to analyze polymeric materials. FTIR is a very serisitive tool for measuring the vibrational energy of the reactivc functional groups of the polymer films such as heat curable t poxies and silicones. Further, the presence of various polyme I types and

CHANG er al.: OVERVIEW AND EVALUATION OF ANISOTROPICALLY CONDUCTIVE ADHESIVE FILMS

~

831

1

WAVE NUMBERS (CM')

(a)

WAVE NUMBERS (CM')

( 4

I' J

400

4000 400 WAVE NUMBERS (CM')

$ 2 8

4000 400

TABLE I1 P ~ T I C L E CHARACTERINION

WAVE NUMBERS (CM')

(4 Fig. 3. FTIR spectra showing the variations in ACAF polymers.

Material Particle Size Particle Type

A 5-7pm Au/Ni B EL12pm AdGIass C 12pm NiPolymer D 20pm Au/Ni

their modification can be identified with FTIR. In addition, FTIR can be used to measure completeness of cure in some polymer systems by measuring the change in an absorption band. For example, the strong absorption of Si-H at 2100 cm-' shows the presence of an uncured silicone in a sample. During a hydrosilation cure of the sample, the decrease of Si- H absorption is an indication of curing and could be easily measured by its peak height or peak area. Stabilization of the Si-H absorption is a good 'indication of the cure state of the material.

Fig. 3 shows the IR spectra of the four polymer films and demonstrates the wide variety of polymer variations found in the films. One can, however, pick out chemical moieties that are common to all these materials and could compare those moieties to standards to determine the polymer variations present.

D. Differential Scanning Calorimetry (DSC)

Differential scanning calorimetry (DSC) measure'. the heat change in a material during a thermal change. It meawes both the heat capacity of endothermic and exothermic transitions of the sample, and provides quantitative information regarding the enthalptic changes in each material. A DSC scan plots energy supplied against average programmable temperature. The peak areas can be directly related to the mthalptic changes quantitatively. Tg (glass transition temperature) can be readily calculated and kinetic information can also be obtained. For the commercial ACAF materials, D'SC scans from ambient to 250°C were taken at a prescribed rate. Fig. 4 shows the DSC scan of a typical uncured ACAF material. A general exothermic peak, such as peal; I in the figure, provides qualitative information regarding each ACAF materials' cure temperature. When the materials are fully cured, there should be no heat loss or gain in the region of the cure temperature during subsequent DSC scans. The four ACAF's being evaluated showed cure temperatures. to be in the range of 140' to 160OC. Peak I1 shows the poini at which polymer degradation begins.

E. Microdielectrometry

Dielectrometry is the measurement of dielectric change in a sample at a particular frequency during a plhysical or

832 IEEE TRANSACTIONS ON COMPONENTS, HYBRIDS, AND MANUFACTURING TECHNOLOGY, VOL. 16, NO. 8, DECEMBER 1993

0 50 100 150 200 250

TEMPERATURE (C)

Fig. 4. A DSC scan of an uncured ACAF showing the cure exotherm (I) and a degradation isotherm (11).

chemical change in that sample. The recent development of high sensitive microdielectrometry, capable of making measurements in the frequency range of 0.05 Hz to 10 kHz, allows one to study dielectric changes in polymeric films [4]. We used a Micromet Instruments’ Eumetric System I1 microdielectrometer with a miniature IC sensor and capable of using a wide range of frequencies (from 0.05 Hz to 10 kHz) to monitor the loss factor (E”) in the ACAF films. To make the measurement, a layer of the uncurred film was placed on a miniature IC sensor and put inside a programmable oven. The temperature of the oven was set to a temperature (i.e., 130”, 140” or 150OC) and the loss factor (E”) at various frequencies (0.05, 1, 100, 1000, 10000 Hz) was monitored periodically during the curing time. Results of the microdielectric loss factor (E”) measurements are shown in Fig. 5. During an isothermal cure, using low frequency sweep experiments, we used this sensitive tool for measuring a material’s complete cure and thus determined its cure time at a given temperature. As an example, Fig. 5(a) shows an ACAF’s E” measurement versus curing time at 140OC. The initial E” s increase with various frequency scans (0.05, 0.1, 1, 100 Hz) and these increases are due to the thermal randomization of dipoles within the ACAF resin during the heating period from ambient to 140OC. When the material temperature reaches 14OoC, all E” s begin to decrease rapidly. This indicates rapid material cure at this temperature. When E“ reaches its equilibrium state, i.e., no further change in E” with time, the material is completely cured. The low frequency sweep experiments (0.05, 0.1, 1 Hz) provide a sensitive method of determining a polymer’s cure time. Fig. 5(b) and (c) show results obtained for the ACAF films “ A and “D”, respectively. With curing times of N 35 min for the “A” material and N 15 min for the “D” material at 140°C. The length of the cure time is probably due to the somewhat low temperature. In later experiments we increased the cure temperature to 160°C to decrease the cure time needed.

I‘ I I I I 0 30

TIME (min)

(a) I I I I I

Temperature

I I

0 30

TIME (min)

@)

Temperature

U

I 1 U

1 0 9

30 TIME (min)

(4 Fig. 5. Examples of microdielectrometry experiments showing the change

in dielectric loss (E”) during the curing ACAF matei-ids.

The temperature where weight loss begins is the t cmperature at which change (loss of water, degradation, elc.) of the polymer starts. Thermal gravimetric analysis (‘II’GA) is a thermal analytical technique that automates this procedure. A TGA output is displayed in Fig. 6 . As can be seen, this ACAF begins to lose weight at 14OOC and shows a large loss above 150°C. This is an example of an only partially cured resin to demonstrate the effect of low stability. When completely cured, the four materials analyzed all k,howed the start of degradation between 190” and 220°C and 1-10 material resisted major degradation above 24OoC, in air.

F. Thermal Gravimetric Analysis (TGA)

The stability of a polymer film can be evaluated by heating it through a range of temperatures and measuring its weight loss.

G. Mechanical Adhesion

Adhesion of parts connected with ACAF’s Wac3 measured using a “push off’ type tester. A set of parts is assernbled with

833 CHANG er al.: OVERVIEW AND EVALUATION OF ANISOTROPICALLY CONDUCTIVE ADHESIVE FILMS

TEMPERATURE (C)

Fig. 6. A TGA of a partially cured ACAF, showing its weight loss at various temperatures.

an ACAF and one part is securely held in the tester while a measured force is applied to the edge of the other part, and when separation of the parts occurs the force is recorded. The ACAF’s in the set of four under examination were tested using a silicon chip with circuitry connected to a FR4 printed wiring board. In all cases, the “push off force was greater than 8 lbs and in some cases greater than 16 lbs.

IV. ACAF ASSEMBLY

A. Registration Placement accuracy is a critical element in using ACAF’s.

Unlike the reflow solder bump interconnect process, con- ductive adhesives do not have the self-alignment capability that corrects minor misregistration between pad and substrate conductors. Thus, the placement accuracy is determined by the pad size of the parts to be assembled.

Particle type will also contribute to planarity variations. For compliant particles, such as plated polymer spheres, the large spheres will be compressed more than small spheres. Therefore, coplanarity between interconnecting parts can still be maintained and all spheres will have equal probability of making contact between pad and substrate conductor. How- ever, for particle types which are less compliant, such as silver coated nickel, the differences in sphere sizes can be compensated for with thicker pad metallization or by a thicker adhesive layer under the substrate conductors.

B. Assembly Parameters

Important process parameters for ACAF assembly are tem- perature, load, tacking time (the time needed for the adhesive to soften and flow), and bonding time (final cure time). One of the interconnecting parts is preheated to a temperature below the ACAF’s bonding temperature, but high enough to partially soften the film so that it has the ability to flow and fill void areas. The bonding load should be high enough to allow the conductive spheres to make good physical contact between the assembly’s conductors; but not high enough to

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Photograph of the ACAF assembly test vehicle. (a) FR4 circuit. Fig. 7. (b) Polyester circuit.

damage any of the parts. Finally, the tacking time qjhould be sufficient to give adequate time for the film to flciw before cure begins so that it seals the contact area during the final bonding process.

C. Assembly Test

To evaluate the ability of our selected ACAF’G, to form electrical interconnections and to evaluate their robustness, the four ACAF’s were used to connect a polyester film circuit to a standard FR4 printed wiring board. A photograph of the two circuits is presented in Fig. 7. When the ciircuits are successfully interconnected, they form a group of six daisy chains in three pairs. Probe points for testing the through resistance are located on the FR4 board and ha]€ of each daisy chain is located on each part. This design provides 14 contact points per daisy chain and the pairs of daisy chains are interdigitated to allow future measurements o t isolation resistance. All circuitry is copper with a nickel and then gold plate. Contact pads are 6 mils square and are separated by 6 mil spaces. Alignment is accomplished mechanicdly, using two close-fitting dowel pins in a metal fixture. Once the “stack up’’ of parts with adhesive and alignment fixture is made, we cure the assembly in a laboratory hydraulic press with heating and cooling capabilities. For all the assemblies described here the cure was run at 16OOC for 10 min at 100 lbs of load. The test vehicles were then cooled to room temperature before the load was released. Those that showed interconnection of all daisy chains (resistances per chain were normallj less than 0.5 s2 as measured with a digital multimeter) were stored at ambient conditions for a minimum of two days and in some cases for as long as seven days, before being remedsured. No change of greater than 5% was found. It is obviouk, from this experiment that short-term ambient storage is not useful for differentiating between ACAF assembly capabilitie 3.

834 IEEE TRANSACTIONS ON COMPONENTS, HYBRIDS, AND MANUFACTURING TECHNOLOGY, VOL. 16, NO. 8, DE( EMBER 1993

TABLE I11 qualitative evaluations in the evaluation and screening of ACCELERATED AGING TESTS OF ACAF commercial ACAF’s and the assembly processes associated

with them. ASSEMBLY VEHICLES AT 85’C AND 85% RH

Material ID Chain Resistance

Same Increased Open - A 1 5 1

3 6 4 6 5 4 1 1 10 6

- - - -

- - Totals 27/30 2/30 1/30

B 1 - 4 2 4 1 2 3 5 4 1 1 7 2 4 9 6 10 2 4 12 4 1 1 13 4 2

4 2 16 - 6 17

- -

-

-

- - Totals 23/60 22/60 15/60

C 1 4 2 3 2 4 5 1 5 6 1 5 7 1 3 2 8 2 4 9 2 4 10 4 2

Totals 13/48 31/48 4/48

D 1 2 4 1 5 2 2 4 4

6 6 6 7

8 - 2 4 9 2 1 3 10 2 2 2

2 4 13 -

- - - -

- -

-

- - - - - - -

Totals 4/54 12/54 38/54

D. Accelerated Life Testing

The performance of ACAF interconnections in an acceler- ated temperature and humidity environment can yield valuable information for the evaluation of ACAF’s and their use.

We conducted one such test where the samples previously assembled, using a flex to rigid interconnection, were eval- uated in an elevated temperature and relative humidity (RH) environment. These samples were subjected to an 85’C/85% RH environment for 100 h. Interconnection functionality was measured at the end of the test and circuit changes were evaluated. The results indicate that 85’C/85% RH environ- ment is appropriate for differentiating ACAF materials. A compilation of the results are shown in Table 111. While all samples showed some increase in some daisy chains, the “ A ACAF has many fewer failures than the “D” material. These extrapolations, from limited data sets, will not give completely accurate lifetime predictions. They are, however, useful for

V. CONCLUSIONS

We have outlined various evaluation techniques that are useful in the characterization of anisotropically conductive adhesive films (ACAF’s) for use in fine pitch assembly. Robust interconnections can only be achieved if both materials and processes are optimized for a particular application. A methodology for the evaluation and trial assembly of ACAF materials has been developed which demonstrates the depen- dence of interconnection reliability on material properties and morphology.

Hopefully, our findings will stimulate both si.ippliers of adhesives, as well as manufacturers of assembly equipment, to develop improved materials and methods for AC‘AF assem- bly.

ACKNOWLEDGMENT

The authors acknowledge contributions to the ACAF mate- rials evaluation program by the following people: 1‘4. R. Basa- vanhally, E. K. Buratynski, B. H. Cranston, D. W. Dahringer, A. M. Lyons, E. L. Smith, and R. E. Woods. They ihank them for their help in making this presentation possible

REFERENCES

[1] N. R. Basavanhally, D. D. Chang, and B. H. Cranston, “Direct chip inter- connect with adhesive-connector films,” in Proc. E l e c t r o ~ Components Technol. Conj. May 18-120, 1992, pp. 487-491.

[2] D. D. Chang, J. A. Fulton, A. M. Lyons, and J. R. Nis. “Design con- siderations for the implementation of anisotropic conductive adhesive interconnection,” in Proc. 92th NEPCON West, Feb. 25 -27, 1992, pp.

[3] I. Tsukagoshi, A. Nakajima, Y. Goto, and K. Muto, Hitathi Tech. Rep. 16, 1991, pp. 23.

[4] C. P. Wong, “Effect of room-temperature-vulcanized silicone cure in device packaging,” in American Chemical Society Symposium Series, vol. 346, 1987.

1381-1389.

tions. Recently, he has Dr. Chang is a men

David D. Chang (S’81-M’81), rewived the B.S. degree in physics from the Fu-Jen Catholic Uni- versity, Taiwan, in 1976, and the h4.S. and Ph.D. degrees in electrical engineering from the University of South Carolina, in 1981 and 19%, respectively.

He joined the AT&T Bell Laboratories in 1984 as a Member of the Technical Staff. Since then he has been working in many areas, inchdin!; the reliability of ceramic capacitors, ultrafine pilch IC assem- bly, flip-chip attachment, as well as anisotropically conductive adhesive for chip-on-boar d interconnec-

been focusing on the area of RF mini.iturization. iber of Tau Beta Pi and Eta Kappa Nu.

CHANG et al.: OVERVIEW AND EVALUATION OF ANISOTROPICALLY CONDUCTIVE ADHESIVE FILMS 835

Patricia A. Crawford attended Brooklyn College. She is a Senior Technical Associate of the En-

vironmental and Materials Technology Department at AT&T Bell Laboratories, Engineering Research Center, Princeton, NJ. She has worked on the ana- lytical characterization of manufacturing processes. Also, she has worked on a wide variety of en- capsulating techniques with emphasis on glob top materials for chip protection. Recently she has done extensive work on flip-chip assembly with conduc- tive adhesives. She is the coauthor of more than 15

technical papers in the field of material science and electrical interconnection.

Joe A. Fulton received the B.S. degree in chem- istry from the University of Illinois and the Ph.D. degree in analytical chemistry from Arizona State University.

He is a Member of the Technical Staff in the Assembly Technology Department at AT&T Bell Laboratories, Engineering Research Center, Prince- ton, NJ. He joined AT&T in 1979 and initial worked in the area of chemical analysis for the development of manufacturing processes. For the last ten years, he has worked in the area of interconnection tech-

nology using various types of conductive polymers. Previous to joining AT&T he was an NlH postdoctoral fellow at the University of South Alabama School of Medicine.

Richard McBride was born in 1952 in Brooklyn, NY. He received the B.A. degree in chemistry from Cheyney University, Cheyney, PA, and the M.S. degree in chemistry from Drexel University, Philadelphia, PA.

He has worked at AT&T Bell Laboratories since 1979. He is currently working on electrostatic discharge test methods, and he has worked on polymer-metal coating and adhesion, silicone encapsulation of electronic components, and also gas source molecular beam epitaxy of group 111-V compounds.

Maureen B. Schmidt received the B.A. degree in Chemistry from the University of Missouri.

She is a Member of the Technical Staff-I of the Assembly Technology group at AT&T Bell Labora- tories, Engineering Research Center, Princeton, NJ. Since joining AT&T in 1985, she has worked in the areas of material evaluation and development and photolithography. Currently, she is responsible for overseeing the manufacture of AT&T’s elastomeric conductive polymer interconnect material and is a member of the miniaturization group. She is the

Raymond E. Sinitski is a Senior Technical Assistant of the Assembly Technology group at AT&T Bell Laboratories, Engineering Research Center, Princeton, NJ. Since joining ATkT in 1970, he has worked in the areas of photo selective metal deposition, copper plating, millimeter wave guides, gold plating, and epoxies. Currently, he is involved in AT&T’s Elastomeric conductive polymer interconnect material and is ii member of the miniaturization group.

C. P. Wong (SM’89-F’92) received ihe B.S. de- gree in chemistry from Purdue University and the Ph.D. degree in organic and inorganic chemistry from the Pennsylvania State Universit! .

After his doctoral study, he was aw:i.-ded 2 years as a postdoctoral scholar with Nobel Laureate Prof. Henry Taube at Stanford University, where he con- ducted studies on electron transfer ..ind reaction mechanism of metallocomplexes. He was the first person to synthesize the first known lanthanide and actinide porphyrin complexes which represents a

breakthrough in metalloporphyrin chemistry. In 1977 he joined AT&T Bell Laboratories as a Member of the Technical Staff. He has bcen involved with the research and development of the polymeric materials (inorganic and organic) for electronic applications. He became a Senior Mcmber of the Technical Staff in 1982 and the Distinguished Member of the Te1:hnical Staff in 1987. His research interests lie in the fields of polymeric materials, high T, ceramics, materials reaction mechanism, IC encapsulation, in particular, hermetic equivalent plastic packaging, and electronic manufacturing packag- ing processes. He is one of the pioneers who demonstrated the w e of silicone gel as device encapsulant to achieve reliability without hermeticity in plastic IC packaging. He holds over 28 U.S. patents and has pubhned over 80 technical papers in the related area. He is the editor and one of 11ie authors of the textbook, Polymers for Electronic and Photonic Applicatioiis (Academic Press).

Dr. Wong is a Fellow of IEEE and an AT&T Bell Labs Fellow, a member of Phi Lambda Upsilon, National Honorary Chemical Society, .md Materials Research Society. He received the AT&T Bell Laboratories ihtinguished Technical Staff Award in 1987, the IEEE Components, Hybrids and Man- ufacturing Technology (CHMT) Society Outstanding Paper Award in 1990 and 1991, and the IEEE-CHMT Society Board of Governors Distinguished Service Award in 1991. He was the program chairman of the 30th Electronic Components Conference in 1989, and the general chairman of the 41st Electronic Components and Technology Conference in 1991. He served as the IEEE-CHMT Society Technical Vice President in 199CL1991 and as President of the Society in 1992-1993.

author or coauthor of three papers.