Au-Sn SLID Bonding: A Reliable HT Interconnect and Die Attach Technology

Au-Sn SLID Bonding: A Reliable HT Interconnectand Die Attach Technology

TORLEIF ANDRE TOLLEFSEN, ANDREAS LARSSON,MAAIKE MARGRETE VISSER TAKLO, ANTONIA NEELS, XAVIER MAEDER,KRISTIN HØYDALSVIK, DAG W. BREIBY, and KNUT AASMUNDTVEIT

Au-Sn solid–liquid interdiffusion (SLID) bonding is an established reliable high temperature(HT) die attach and interconnect technology. This article presents the life cycle of an optimizedHT Au-Sn SLID bond, from fabrication, via thermal treatment, to mechanical rupture. Thelayered structure of a strong and uniform virgin bond was identified by X-ray diffraction to beAu/f (Au0.85Sn0.15)/Au. During HT exposure, it was transformed to Au/b (Au1.8Sn0.2)/Au. AfterHT exposure, the die shear strength was reduced by 50 pct, from 14 Pa to 70 MPa, which is stillremarkably high. Fractographic studies revealed a change in fracture mode; it was changedfrom a combination of adhesive Au/Ni and cohesive SiC fracture to a cohesive b-phase fracture.Design rules for high quality Au-Sn SLID bonds are given.

DOI: 10.1007/s11663-012-9789-1� The Minerals, Metals & Materials Society and ASM International 2013

I. INTRODUCTION

A. Background

HIGH temperature (HT) environments offer greatchallenges for electronic systems. In applications likeautomotive, aerospace, and drilling and well interven-tion systems, the electronic components are oftenexposed for temperatures above 500 K (~200 �C). Thenumber of commercially available HT wide band gapsemiconductors is rapidly increasing.[1] Silicon carbide(SiC) and gallium nitride (GaN) are commonly consid-ered as the semiconductors of choice for HT applica-tions.[2] SiC has a wide band gap, a high breakdown fieldstrength, a high thermal conductivity, and an operatingjunction temperature of up to 850 K (~600 �C).[2–5]However, lack of qualified HT packaging technologieslimits the market growth.[2,6–8]

The range ofHTdie attach and interconnect techniquesis restricted.[6,9,10] Alternatives include sintered nanopar-ticle Ag bonds,[11,12] liquid-based solder bonds,[13] com-posite solder bonds,[14] bismuth-based solder bonds,[15]

Au-Au thermo-compression bonds,[16] and solid–liquid

interdiffusion (SLID) bonds.[17,18] The latter, also calledtransient liquid phase (TLP) bonding,[19,20] isothermalsolidification,[21] or off-eutectic bonding,[22] has proven tobe an excellent candidate.[22–25] It utilizes a binary systemwith one low and one high melting point metal. Examplesof SLID systems include Ag-In,[17] Ag-Sn,[26] Au-In,[17,27]

Au-Sn,[22–25,27–33] andCu-Sn.[34–37] In thepresentwork, thefocus is on the Au-Sn system.

B. Processing

A combination of solid-state and liquid-state diffusiontakes place during SLID bonding.[33] First, the bondingsurfaces are brought into contact and heated to atemperature above the melting point of the low meltingpoint metal, quickly creating new intermetallic com-pounds (IMCs) by liquid-state diffusion. Second, if thetemperature is kept high enough, solid-state diffusion willcontinue until a uniformbonding layer is obtained.[27] Thesolidification is isothermal, and the final joint has a highermelting point than the processing temperature. Sinceliquid-state diffusion is approximately three orders ofmagnitude faster than solid-state diffusion,[27] the latterstep will take longer to complete.Complete wetting of the bonding surfaces is required

to create a high quality SLID bond. This can be difficultto attain for a Au-Sn alloy.[28] The main challenge isassociated with oxidation of the Sn and Au-Sn surfaces,preventing bonding.[28] Methods to achieve completewetting include scrubbing or static pressure combinedwith H2, N2, or vacuum environment during forma-tion.[38–42] A superb Au-Sn SLID bond has, e.g., beenachieved by applying a small clamp force in combina-tion with low vacuum (10 kPa).[25]

An optimization, generally minimization, of bondingtime and temperature is required to make Au-SnSLID suitable for industrialized manufacturing. Several

TORLEIF ANDRE TOLLEFSEN, Ph.D. Student, is with theSINTEF ICT Instrumentation, 0373 Oslo, Norway, and also with theInstitute for Micro and Nanosystems Technology, Vestfold UniversityCollege, 3184 Borre, Norway. Contact e-mail: [email protected] ANDREAS LARSSON, Senior Scientist, and MAAIKEMARGRETE VISSER TAKLO, Research Manager, are with theSINTEF ICT Instrumentation. ANTONIANEELS, SectionHead, andXAVIER MAEDER, Post Doc, are with the XRD Application Lab &Microscopy, Microsystems Technology Division, CSEM Centre Suissed’Electronique et de Microtechnique SA, 2002 Neuchatel, Switzerland.KRISTIN HØYDALSVIK, Post Doc, and DAG W. BREIBY,Associate Professor, are with the Department of Physics, NorwegianUniversity of Science and Technology, 7491 Trondheim, Norway.KNUT AASMUNDTVEIT, Associate Professor, is with the Institutefor Micro and Nanosystems Technology, Vestfold University College.

Manuscript submitted December 2, 2012.Article published online January 12, 2013.

406—VOLUME 44B, APRIL 2013 METALLURGICAL AND MATERIALS TRANSACTIONS B

different bonding times have been reported in the litera-ture, ranging from 4.6 minutes to 3.5 hours.[22,23,25,30,43]

In this article, the bonding time is defined as the timespent above the melting point of eutectic Au-Sn. Notethat all reported studies applied a 5-minute preheating at523 K (250 �C). In an earlier work, we found that abonding time of minimum 6 minutes is required forachieving a uniform and strong bond.[25] Shorter bondingtimes result in considerable weaker bonds. The 6-minutelimit is probably a result of the combined liquid-state andsolid-state diffusion processes occurring in SLID. Theliquid-state diffusion rapidly creates new Au-Sn IMCs,resulting in an incomplete bond. A strong and uniformbond is first realized when the solid-state diffusion isfinished.[25]

Different bonding temperatures have also beenreported, ranging from 563 K to 673 K (290 �C to400 �C).[22,23,25,30,31,43] In a previous study, we foundthat a minimum temperature of 573 K (300 �C) isrequired to achieve a uniform and strong bond.[25]

Lower temperatures resulted in through cracks and non-uniform bonds due to incomplete solid-state diffusion.

Naturally, there is a relation between bonding tem-perature and bonding time; higher temperatures result inhigher diffusion rates, causing shorter minimum bond-ing times. However, there are indications that the solid-state diffusion has a stepwise behavior.[25] Below 573 K(300 �C), there is incomplete diffusion, while it iscontinuous above.

C. Reliability and Bond Configuration

The high temperature storage (HTS) and thermalcycling (TC) capability of Au-Sn SLID have beeninvestigated in several studies.[22–24,32,43] Both HTS (upto 773 K [500 �C]) and TC reliability (e.g., in the rangefrom 308 K to 773 K [35 �C to 500 �C]) were shown tobe good.[22–24,32,43] The bond integrity has mainly beenclassified by the die shear strength. However, the shearstrength of the majority of the tested samples was abovethe equipment limit, making it difficult to detectpotential degradation.

The bond integrity and bond configuration of Au-SnSLID bonds have also been characterized by investiga-tions of cross sections and fracture surfaces using opticalmicroscopy, scanning electron microscopy (SEM), andenergy dispersive X-ray spectroscopy (EDS).[22–25,29–32,43]

There is an uncertainty in the literature regarding thecomposition of the actual bond-line, arising from thelimited precision of EDS quantitative measurements.The virgin bond-line has been suggested to either havea Au/f¢-phase/Au layered structure[30,31] or have aAu/f-phase/Au layered structure.[25,32,33] After thermaltreatment, the bond-line has been suggested to eitherhave a Au/f-phase/Au[32] or have a Au/b-phase/Austructure.[24] To design an ideal Au-Sn SLID bond-line,it is of utmost importance to know the actual bondconfiguration and thereby apply the relevant materialdata in simulations. The Au-Sn phase diagram is shownin Figure 1, while selected structural and thermo-mechanical properties of relevant Au-Sn phases areshown in Table I.

D. This Paper

In this work, an optimized bond for a HT Cu/Si3N4/Cu/Ni-P//Au/Au-Sn/Au//Ni/Ni2Si/SiC package (repre-senting a SiC transistor assembled onto a Si3N4

substrate utilizing Au-Sn SLID) was characterized.First-time identification of the Au-Sn phases present inan Au-Sn SLID bond by X-ray diffraction (XRD) wasperformed for both a virgin and an HT-exposed bond.Furthermore, the feasibility of high-spatial resolutionXRD structure determination of phases in the bond-linehas been shown.A shear tester capable of considerably higher loads

than previously applied testers (4 times higher) has beenused in order to detect potential degradation of Au-SnSLID bonds following thermal treatment. The shearstrength of virgin and thermally treated samples wasmeasured.Important design criteria for Au-Sn SLID bonds are

discussed.

II. EXPERIMENTAL

A. Sample Fabrication

Bipolar junction transistor (BJT) SiC dummy chips,delivered from Fairchild Semiconductor, were usedas chips. The chips had sputtered Ni2Si (140 nm)/Ni (300 nm)/Au (100 nm) metallization. Commerciallypurchased Si3N4 substrates from Denka Chemicalswere used as substrates. The substrates had activemetal-bonded (AMB) Cu (150 lm) and plated Ni-P(7 wt pct P) symmetric metallization (Cu/Ni-P layers onboth front and backside) to minimize warpage due tocoefficient of thermal expansion (CTE) mismatches inthe system. Both chips and substrates were electroplatedwith a uniform 10-lm Au layer (see next section forthickness justification), using a gold cyanide solution ata temperature range of 333 K to 338 K (60 �C to 65 �C)and a current density of 2.7 mA/cm2. The substrateswere diced in 6 9 6 mm2 samples, while the chips werediced in 1.85 9 3.4 mm2 samples after plating. To createthe Au-Sn SLID bond, a eutectic Au 80 wt pct Sn 20 wtpct preform (7.5 lm thick) was sandwiched between thechip and substrate (see Figure 2 for illustration of acomplete sample).Assembly was performed in two steps: First, the

substrate, preform, and chip were aligned manually on ahot plate and fastened with a clamping force. Second,the samples were bonded using a hotplate inside avacuum chamber (chamber pressure 10 kPa). The sam-ples were heated to 523 K (250 �C) and held there for5 minutes to assure a uniform temperature distributionin the bonding layers. Third, the samples were heated toa final bonding temperature of 573 K (300 �C) and keptthere for 5 minutes. The selected processing parameterswere based on an earlier optimization.[25]

B. Bond Configuration

The Au layer in a Au-Sn SLID bond has dualfunctions[25,33]: (i) diffusion barrier between chip and/or

METALLURGICAL AND MATERIALS TRANSACTIONS B VOLUME 44B, APRIL 2013—407

substrate metallization and Au-Sn and (ii) compliantlayer absorbing thermo-mechanical stress induced by,e.g., CTE mismatches in the package.[25] Previousstudies have shown that excess Au on both the substrateand chip side in the final bond is important for thelong-time reliability.[24,32] Our previous work stronglyindicates that a virgin Au-Sn SLID bond has an Au/f-phase/Au layered structure,[24,32] and that HT expo-sure transforms the f-phase into the b-phase, leaving anAu/b-phase/Au bond.[24,32] Although the experimentalevidence for this phase determination has not beenconclusive until now, an Au-Sn SLID bond designed forHT application should have a bond-line with a Sn:Auratio corresponding to max. 8 at. pct Sn.[24] For oursystem, using a 7.5-lm-thick eutectic preform, thisimplies that a minimum of 7 lm electroplated Au isrequired on both the chip and substrate to assure excessAu after HT exposure.On a global package level, i.e., substrate, metalliza-

tion, and chip, the compliant Au layer absorbs increasing

Fig. 1—The Au-Sn phase diagram. With kind permission from Okamoto,[56] Fig. l.

Table I. Structural and Thermo-Mechanical Properties of Relevant Au-Sn Phases

Crystal Structure Space Group CTE (ppm/K) E (GPa) Vickers Hardness

Sn Tetragonal[46] I41/amd[46] 22[47] 41[47] 7[47]

d-AuSn Hexagonal[48] P63/mmc[48] 14[49] 70 to 87[49,50] 146[51]

Eutectic AuSn N/A N/A 16[49] 69 to 74[49,50] —f¢-Au5Sn Trigonal[52] R32[52] 18[49] 62 to 76[49,50] —f-Au0.85Sn0.15 Hexagonal[53] P63/mmc[53] 20[49] 58[49] 100[51]

b-Au10Sn/Au1.8Sn0.2 Hexagonal[54] P63/mmc[54] — 88[50] 124[51]

Au FCC[55] Fm�3m[55] 14.4[47] 77.2[47] 36.5[51]

CTE is the coefficient of thermal expansion and E is Young’s modulus.

Fig. 2—Sketch of expected layer structure after bonding.


thermo-mechanical stress (mainly induced by CTEmismatches in the package) with increasing thickness.However, for a certain Au layer thickness, the local CTEmismatches—between pure Au and the f/b phase(DCTEAu-f/b ~ 4 ppm/K)—will dominate the thermo-mechanical stress in the bond.[25] This is a problemseldom addressed in microelectronic packaging, but isstill very important.[44] In a previous study, we per-formed finite element analysis (FEA) to calculate theideal Au layer thickness to minimize the CTE-inducedthermo-mechanical stress in our package.[25] The resultsshowed that a 3-lm-thick Au layer was optimal.Remembering that 7 lm Au will be consumed by theb-phase, the ideal initial electroplated Au layer thicknessis thus 10 lm on both the chip and substrate.

C. Reliability Testing

Bonded samples were exposed to HTS at 523 K(250 �C) to investigate the reliability of the bond. Toexamine potential degradation as a function of time, thesamples were stored in air in a Binder laboratory ovenfor 1, 3, and 6 months.

To study the effect of thermo-mechanical stress inaged samples, samples aged for 3 months were thermallycycled (TC) in a Heraeus HT 7012S2 TC chamber. Thesamples were cycled in the range 273 K to 473 K (0 �Cto 200 �C), with a gradient of 10 K/min, and a 15-minute dwell time at temperature extremes. Notice thatwe have previously demonstrated that virgin Au-SnSLID bonds (Au/f-phase/Au layer structure) can with-stand the applied TC stress.[32]

D. Characterization

All sample groups were die shear tested in a Nord-sonDage 4000Plus shear tester with a 200 kgf loadcartridge. A large number of virgin samples, 64, weretested. The four other sample groups, exposed tovarious HTS and TC treatments, consisted of 6 testedsamples each, 24 in total. A test height of 110 lm abovethe substrate and a test speed of 10 lm/s were applied.To optimize the alignment of the sample to the tool, andto minimize the sample movement during testing, acustom-made sample holder was constructed andapplied for all tested samples.

Cross-sectioning was performed on virgin, HTS, andHTS+TC samples. Cross-sectioned samples wereembedded in epoxy resin and ground (on SiC papergrade 320 through 4000, using water cooling). Thesamples were then polished (using 6 lm diamondparticles and an alcohol-based lubricant prior to finepolishing using 3 and 1 lm diamond particles with awater- and oil-based lubricant). Note that SiC and Si3N4

are very hard materials compared to Au and Au-Sn,making it challenging to prepare planar cross sections.

Fractography was conducted on all sample groups.Cross-sectioned samples and fracture surfaces wereinvestigated by optical microscopy (Neophot 32), SEM(FEI Nova NanoSEM 650), EDS (Oxford X-MAX 50),and interferometry (Veeco Wyko NT9800). The fractures

were classified by their fracture mode: adhesive—fractureat the interface between, e.g., Au and the f-phase,cohesive—fracture inside the bulk of, e.g., the b-phase, ora combination of adhesive and cohesive fracture.XRD was performed on the fracture surface of the

substrate of shear-tested virgin and HTS samples. Themeasurements were done on PANalytical X’Pert MRDPRO instruments using Cu-Ka radiation (k = 1.54 A)in the x/2h mode and the grazing incident mode (2h scanwith x = 1 deg).One cross-sectioned sample was studied by XRD

using a rotating anode source equipped with a Xenocsmultilayer mirror for monochromatization (Cu-Ka,k = 1.54 A) and a Pilatus 1M detector for collectingthe scattered radiation. This sample had been stored18 months at RT prior to the XRD studies. The verysmall scattering volume available for such a samplerequired unconventional data collection, which wasachieved by integrating the scattered intensity in reflec-tion geometry for a range of incidence angles from 5 to15 deg, using a highly collimated incoming beam ofwidth<0.1 mm kept essentially parallel to the bond-line.The total exposure time was about 2 h. The data wereanalyzed by tangential averaging, prior to backgroundsubtraction and comparison to published Au-Sn struc-tural data using SimDiffraction.[45]

III. RESULTS

A. Shear Strength

The die shear strength distribution for all shear-testedAu-Sn SLID samples is shown in Figure 3, while theaverage die shear strength for the different samplegroups is shown in Figure 4. It was very high—approx-imately 140 MPa—for the virgin samples. The averageshear strength for samples exposed to HTS for 1, 3, and6 months was considerably reduced, from approxi-mately 140 MPa to approximately 70 MPa. There areonly small differences, within the standard deviation forthe different groups, between samples aged for 1, 3, and6 months. The shear strength of samples exposed to TCafter HTS did not degrade further after TC. A smallincrease in the shear strength was observed for thisgroup.

B. Fractography

In Figure 5, the fracture surfaces of a virgin and a1-month HTS sample are shown. The fracture surfaceof the 1-month HTS sample is representative offracture surfaces of 3- and 6 month-HTS samples, aswell as for the HTS+TC samples. The fractures ofvirgin samples were a combination of adhesive Au/Niand cohesive SiC fractures. It was difficult to determinethe primary crack initiation due to the complex shapeof the fracture.After thermal exposure, the observed fracture mode

was different. The complex virgin sample fracture wasreplaced with an almost pure cohesive b-phase fracture


with only a small region of cohesive SiC fracture presentat the bond edge.

C. Bond Configuration

In Figure 6, an optical image of a cross-sectionedvirgin Au-Sn SLID sample is shown. The bond wasuniform, identified by EDS and XRD to have a Au/f-phase/Au layered structure.

A SEM image of a cross section of a 3-month HTSsample is shown in Figure 7 (this is also representativefor the other groups of thermally exposed samples).EDS and XRD studies revealed that the layered bondstructure had been transformed into Au/b-phase/Au. Acomparison of the 2h-x XRD measurements is shown inFigure 8. The f and b phases have similar crystalstructures (Table I), but with a small difference in latticeparameters. This corresponds to a small, but clearlydetectable, shift in XRD angle (~0.3 deg for the peaks inthe 2 range 35 to 41 deg). The shoulder at 2 = 35.5 degfor the HTS sample indicates that a small amount of

f-phase coexists with the dominating b-phase for thissample.Figure 9 illustrates schematically the phases as deter-

mined from XRD data obtained on the cross-sectioned

Fig. 3—The sorted die shear strengths for virgin, high temperaturestored (HTS), and HTS+thermally cycled (TC) optimized Au-SnSLID samples. Regions for different fracture modes are indicated.

Fig. 4—The average die shear strength for 64 virgin Au-Sn SLIDsamples, 18 high temperature stored (HTS) samples—at 523 K(250 �C) for 1, 3, and 6 months—in addition to six samples exposedfor 3 months HTS+1000 thermal cycles (TC) between �273 K and473 K (0 �C and 200 �C). The standard deviation is included.

Fig. 5—A SEM image of fracture surfaces of shear-tested virgin and1-month high temperature stored (HTS) Au-Sn SLID samples. Thefracture modes were identified with optical microscopy, scanningelectron microscopy (SEM), energy dispersive X-ray spectroscopy(EDS), and interferometry.

Fig. 6—An optical micrograph of a cross-sectioned virgin Au-SnSLID sample. The bond-line phases were identified by energy disper-sive X-ray spectroscopy (EDS) and X-ray diffraction (XRD).


sample. The intermetallic phase in the bond-line can beclearly identified as b-phase. This shows the feasibility ofXRD phase determination on these somewhat uncon-ventional samples and suggests that spatially resolvedsynchrotron microfocus XRD can be performed, thusallowing identification of the individual phases in Au-SnSLID bonds at various stages in the bonding/agingprocess.

IV. DISCUSSION

A. Bond Configuration and Reliability

We have demonstrated that an optimized virginAu-Sn SLID bond has a Au/f-phase/Au layered struc-ture. It is mechanically very robust and remains solid attemperatures well above the processing temperature.The latter opens a window for subsequent manufactur-ing steps without lowering the temperature for eachstep.After thermal exposure, the bond-line was trans-

formed into a Au/b-phase/Au layered structure. Theb-phase has higher E (Young’s modulus) and Vicker’shardness than the f-phase, see Table I. This means thatthe thermally exposed bond has a lower ability to absorbthermo-mechanical stress induced by, e.g., CTE mis-matches in the package than the virgin bond. The dieshear testing of HTS samples showed a decrease in shearstrength of 50 pct after thermal treatment. The fracturemode, indicating the weakest link of the package, waschanged from an adhesive Au/Ni and cohesive SiCfracture to a mainly cohesive b-phase fracture, empha-sizing the significance of the phase transformation in thebond-line.It is noteworthy that the die shear strength was still

very high after thermal treatment (more than ten timeshigher than the MIL-STD-883, 70 vs 6 MPa). Further-more, the bond was stable during additional thermaltreatment (HTS+TC). This means that a properly

Fig. 7—A SEM image of a cross-sectioned 3-month high tempera-ture stored (HTS) sample. The bond-line phases were identified byenergy dispersive X-ray spectroscopy (EDS) and X-ray diffraction(XRD).

Fig. 8—Comparison of 2h-x X-ray diffraction (XRD) measurements of the fracture surfaces of shear-tested virgin and 3-month high tempera-ture stored (HTS) Au-Sn SLID samples. Notice the transformation from Au/f-phase/Au layered structure to Au/b-phase/Au.


designed Au-Sn SLID bond is well suited for HTapplications, even in packages with large CTE mis-matches, experiencing large thermal stress. A schematicoverview of the layered structure of an Au-Sn SLIDbond at different life stages is shown in Figure 10.

As can be seen in Figure 1, there are no equilibriumphases with composition between the b-phase and theAu phase. Thus, a bond that has been transformed intoa Au/b-phase/Au layered structure is expected to be athermodynamically stable configuration. Further, ther-mal storage is not expected to give rise to new phasetransformations.

B. Design Rules

Based on our experience with Au-Sn SLID as a HTdie attach and interconnect technology—from this andprevious work in addition to a literature study—thefollowing design rules can be made:

� The minimum process temperature to achieve a uni-form and strong bond is 573 K (300 �C),[25] while theminimum process time is 6 minutes.[25]

� Excess Au on both the chip and substrate side of thefinal bond is important for the long-time reliabil-ity.[24,32,33] A virgin Au-Sn SLID bond has a Au/f-phase/Au layered structure. After HT exposure, thef-phase is transformed into the b-phase, giving an Au/b-phase/Au bond. This means that the Sn:Au ratiomust be below 8 at. pct Sn.� On a global package level—i.e., substrate, metalliza-

tion, and chip—the compliant Au layer absorbsincreasing thermo-mechanical stress (mainly induced

by CTE mismatches in the package) with increasingthickness. However, for a certain Au layer thickness,the local CTE mismatches—between pure Au and thef/b phase (DCTEAu-f/b ~ 4 ppm/K)—will dominatethe thermo-mechanical stress in the bond.[25] There-fore, FEA should be performed to calculate the idealbond-line thickness ratio.

V. CONCLUSIONS

Conclusive identification of the material phases pres-ent in the bond-line of both a virgin and a thermallyexposed Au-Sn SLID bond was performed using XRD.An optimized virgin Au-Sn SLID bond has a Au/f-phase/Au layered structure, while it was transformedinto a Au/b-phase/Au layered structure after thermalexposure.The die shear strength was halved after the phase

transformation caused by thermal treatment. However,the shear strength still remained high, approximately

Fig. 9—X-ray diffraction (XRD) data from the cross-sectioned sam-ple, compared to simulations for reported structures. The order ofthe legend corresponds to the position of the graphs (from top tobottom). In the simulations, fully isotropic structures were assumed.In this measurement geometry, the gold peaks are roughly twice asbroad as the peaks for the intermetallics. Whether this can beascribed to small-particle broadening requires further investigations.The intermetallic phase in the bond-line is best fitted by the P-phase(Au1.8Sn0.2). This shows the feasibility of XRD phase determinationand also of such unconventional samples.

Fig. 10—A schematic overview of the layered structure of an opti-mized Au-Sn SLID bond at different life stages. The different mate-rial phases were identified with energy dispersive X-ray spectroscopy(EDS) and X-ray diffraction (XRD).


70 MPa. The fracture mode changed from a combinedadhesive Au/Ni–cohesive SiC fracture to a mainlycohesive b-phase fracture after thermal treatment.

The long-time HT reliability of an optimized Au-SnSLID bond has been demonstrated. Important designrules for achieving a uniform, strong, and HT reliablebond were also presented.

ACKNOWLEDGMENTS

This work was carried out within the HTPEPproject. Funding from the Research Council of Norway(Project No 193108/S60), Badger Explorer, SmartMo-tor, Fairchild, Emerson Roxar, and Norbitech is greatlyacknowledged. The authors want to acknowledgeDr. Ole Martin Løvvik for his valuable review, helpingshape this article, and Dr. Alex Dommann for facilitat-ing XRD.

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