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The International Journal of Microcircuits and Electronic Packaging, Volume 21, Number 3, Third Quarter 1998 (ISSN 1063-1674)

8 International Microelectronics And Packaging Society

High Frequency Electrical Characterization of a High Wiring Density Organic Substrate “ALIVH” and StudBump Bonding “SBB”

High Frequency Electrical Characterization of aHigh Wiring Density Organic Substrate“ALIVH TM” and Stud Bump Bonding “SBB TM”Hideki Iwaki, Yutaka Taguchi, Tsukasa Shiraishi, Yoshihiro Bessho, and Kazuo EdaMatsushita Electric Industrial Co., Ltd.Device Engineering Development Center1006 Kadoma, Kadoma-shi,Osaka 571-8501 JAPANPhone: +81-6-6900-9628Fax: +81-6-6900-9268e-mail: [email protected]

Abstract

High frequency electrical properties of a high wiring density organic substrate “ALIVHTM”, which has any layer inner via holes structure,and Flip Chip interconnection between pads on semiconductor chips and transmission lines using SBBTM technology were characterized.The dielectric constant, the loss tangent, the transmission loss, and the via hole characteristics of the ALIVH substrate were measured from1GHz to 4GHz frequency range. Flip Chip interconnecting region using the SBB technology was also measured using a resonant method andsimulated using the FEM method of HFSS. The equivalent circuits of the via hole and the Flip Chip interconnection were evaluated. Both ofthe ALIVH substrate and the SBB Flip Chip interconnecting technology were found to be good enough to apply to high speed digital systemsup to 1GHz.

Key words :

High Frequency, High Speed Digital Circuit, Flip Chip, StudBump Bonding, and Organic Substrate.

1. Introduction

The current trend in high-performance integrated systems is to-ward achieving higher speeds. As a clock speed in a processor in-creases, properties of interconnection between semiconductor chipsand peripheral devices are significant. At high speeds, electricalparasitics limit device performance. Especially, a discontinuous re-gion on the transmission line induces partial loss and reflection of asignal. Therefore, substrates and interconnecting region between padson semiconductor chips and substrates must be characterized in highfrequency range. In addition, the determination of an equivalent cir-cuit to approximate the behavior of the discontinuous region is sig-nificant.

Flip Chip interconnecting technology and a high wiring densitysubstrate are effective for high performance systems. Both a highwiring density organic substrate “ALIVHTM” and Flip Chip inter-connection using a Stud Bump Bonding technology “SBBTM” areapplied to a high-performance and small-sized electronic packagingin a consumer electronics1,2.

In order to design high frequency circuits or high speed digitalcircuits accurately, some kinds of substrates, via hole and Flip Chipinterconnecting region have been investigated. Wansheng Su et al.3

investigated various substrate materials using stripline resonators.Daniel I. Amey et al.4 investigated Low Temperature Cofired Ce-ramic materials using T-pattern microstrip resonator. Taguchi et al.5

reported ceramic multilayer substrate. Marc E. Goldfarb et al.6 re-ported some modeling for the via hole. C. E. Free et al.7 reportedsome modelings for the via hole with electromagnetic simulator.Markus Dernevik et al.8 and Rolf Sihlbom et al.9 investigated FlipChip interconnection with anisotropically conducting adhesives.

In this paper, the researchers evaluated high frequency electricalproperties of the ALIVHTM substrate. Both equivalent circuits of thevia hole in the ALIVHTM substrate and Flip Chip interconnectingregion using the SBB technology were extracted in GHz frequencyrange.

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Intl. Journal of Microcircuits and Electronic Packaging

2. The ALIVH TM Substrate and SBBTechnology

The ALIVHTM substrate is an organic substrate with an any layerinner via holes structure. The dielectric layer consists of non-wovenaramid and epoxy resin. Inner via hole interconnections are per-formed by conductive copper paste. Details of this substrate tech-nology are described in Reference10.

The SBB technology is a Flip Chip interconnection with studbumps made of Au and conductive adhesives. The epoxy under-fillresin is inserted to fill a gap between an LSI chip and the substrate.Details of this technology are described in Reference2.

3. Basic Material Constants

The dielectric constant and the loss tangent in GHz frequencyrange of the ALIVHTM substrate were evaluated from the character-istics of a half-wavelength microstripline resonator. In general, theresonant frequency of the resonator occurs at frequencies where thelength of the resonator is approximately equal to an integral numberof half-wavelengths. In order to determine the dielectric constantand the dielectric loss tangent using the microstripline, the resonantfrequency and the quality factor Q

u (unloaded Q) of the resonator

should be measured. Schematic view of the microstripline structureresonator is shown in Figure1. The wavelengths are related to theeffective dielectric constant e

eff and the resonant frequencies f by the

expression,

kg= c / f (e

eff )1/2 (1)

where c, kg and e

eff are the speed of light in vacuum, the wavelength

at the resonant frequency of the resonator, and the effective dielec-tric constant, respectively. The Q

u of a resonator can be expressed as

follows,

1/Qu =1/Q

c + 1/Q

d + 1/Q

r (2)

where Qc, Q

d and Q

r are the terms due to the conductor loss, the

dielectric loss, and the radiation loss, respectively. The dielectricloss tangent can be expressed as follows,

tan d = 1/Qd

(3)

Qc and Q

r are determined by the dielectric constant, the conductiv-

ity, and the dimensions of the resonators.

G=0.15mm

L=85,42 ,28 ,21mm

W =3mm

Figure 1. Schematic view of the microstripline structureresonator.

The authors prepared four kinds of resonators having differentlengths (L) of 85 mm, 42 mm, 28 mm and 21 mm. The gap (G) forcoupling was 0.15 mm. The thickness of the dielectric was 0.87 mmand the linewidth (W) of the resonator was 3 mm. The resonantcharacteristics were measured using an HP8753C Network Ana-lyzer from 1 GHz to 4 GHz frequency range. The relationships amongthe resonator length, the resonant frequency, and the quality factorQ

u are shown in Figure 2. The resonant frequencies were 1.02 GHz,

2.05 GHz, 3.05 GHz and 4.03 GHz for the resonator lengths of 85mm, 42 mm, 28 mm, and 21 mm, respectively. The Q

u values were

from 36 to 41. The simulation of the resonant characteristics wascarried out using an HP85150 Microwave Design System (MDS).According to the simulation by MDS using these values, the basicelectrical characteristics of the substrate materials were estimated.

0

1

2

3

4

5

0 50 100Res onator length (mm)

Re

so

na

nt

fre

qu

en

cy

(G

H

30

40

50

Qu

Q u

R e s o n a n tfre q u e n cy

Figure 2. Relationship among the resonator length, theresonant frequency and the quality factor Q

u.

Resonant frequency dependence of the dielectric constant andthe loss tangent are shown in Figure3. The material constants of theALIVH TM substrate and the FR-4 substrate for comparison reportedby Daniel I. Amey et al.4 are shown in Table 1. This reduction of thedielectric constant is due to the difference of the aramid material andthe glass material. The loss tangent of the ALIVHTM substrate was0.024, which was the same as that of the FR-4 substrate.

(GH

z)

290




2.5

3

3.5

4

0 2 4R es onant frequency (GH z)

Die

lect

ric

co

ns

tan

t

0 .02

0 .025

0.03

0.035

0.04

Lo

ss

ta

ng

en

t

D ie lectric cons tan tLo s s tangent

Figure 3. Resonant frequency dependence of the dielectricconstant and the loss tangent.

Table 1. Basic material constants of the ALIVH substrate andthe FR-4 substrate at 4GHz.

Substrate ALIVH FR-4Dielectric constant 3.5 4.3Loss tangent 0.024 0.024

4. Transmission Line

The transmission losses in the ALIVHTM substrate as shown inFigure 4 were evaluated. The transmission loss (V

l; dB/mm) is re-

lated to the total loss (at; measured loss) as follows,

V t = V

c+ V

v+ V

l L (4)

where a c, a

v and L are the connector loss, the via hole loss, and the

transmission line length, respectively. By changing the length of thetransmission lines, one can cancel the losses caused by the connec-tors and via holes for input and output and could obtain the trans-mission line loss. The linewidth (W) was 190 µm and the substratethickness (B) was 448 µm.

Inner layer pattern

Stripline:Z0=50ƒ¶

L=80,19mm

Cross sectional view

Ground

IN OUT

W=190µm

B=448µm

Figure 4. Schematic views of the stripline structure.

The relationship between the frequency and the transmission lineloss of the stripline having about 50 W characteristic impedance isshown in Figure 5. The transmission line loss of the stripline was0.013 dB/mm at 2 GHz. The measured values show a good agree-ment with the simulated values which was calculated from mea-sured material constants shown in Table 1.

0

0 .01

0 .02

0 .03

0 .04

0 1 2 3 4Fre que ncy (GH z)

Tra

ns

mis

sio

n l

os

s (

dB

/mm

)

Me as u re dSi m u la ted

Figure 5. Relationship between the frequency and thetransmission loss.

)

291




5. Via Hole

In a multilayer substrate, via holes are inevitable to connect trans-mission lines between layers. These via holes represent the discon-tinuity on the signal propagation which results in losses and reflec-tions of the signal. Therefore, determination of an equivalent circuitof the via hole is significant to design high speed or high frequencycircuit boards. Equivalent circuits of the via hole in the ALIVHTM

substrate were extracted in GHz frequency range.In order to accurately characterize the via hole, the authors evalu-

ated the via hole characteristics in GHz range using resonantmethod11. Two resonators, the reference and target resonators wereused on the resonant method. Schematic views of the reference andtarget resonator are shown in Figure 6. The reference resonator wasa conventional stripline resonator. The target resonator was dividedinto two halves. Each segment was located in the different layer.Both segments were connected through the via hole. The length andwidth of the target resonator was the same as those of the referenceresonator. According to this method, the via hole is assumed to be alumped element. The reactance of the lumped element is given asfollows,

X = 2Z0 cot (of / 2f

n) (5)

where fn, f ,and Z

0 are the resonant frequency of the reference reso-

nator, the resonant frequency of the target resonator, and the charac-teristic impedance of the reference and target resonator, respectively.

Reference resonator

Target resonator

Ground plane

Resonator

Ground plane

448µm

448µm

L=85, 42, 28, 21mm

448µm

via

Inner ground plane

350µm

180µm

Figure 6. Schematic views of the reference and the targetresonator.

The simulation of the resonant characteristics was carried outusing MDS and High Frequency Structure Simulator (HFSS) withFEM method. Schematic view of the simulated model around thevia hole is shown in Figure 7. The length (L

V), the width (W

V), and

the height (HV) of the simulated via hole were 180 µm, 180 µm and

448 µm, respectively. The length (LL) and the width (W

L) of the via

land were 350 µm and 350 µm, respectively. The width and sub-strate thickness of the stripline resonator was 190µm and 448 µm,respectively. The thickness of the electrode was 18 µm. The innerground plane had a rectangular cutout of 6mm by 6mm for the vialand. The dielectric constant of the substrate was 3.5 and loss tan-gent was 0.024. The conductance of the electrode and the conduc-tance of the via hole were defined as 5.88x107S/m.

In n er gro u nd p lan e

V ia ho le

R eso n ator

W V =18 0 µm

W L =3 50 µmH V=4 48 µm

Figure 7. Schematic view of the simulated model aroundthe via hole.

The resonant characteristics were measured using an HP8753CNetwork Analyzer from 1 GHz to 4 GHz frequency range. As illus-trated in Figure 6, the reseachers prepared four pairs of the conven-tional resonators and target resonators having different length (L) of85 mm, 42 mm, 28 mm, and 21 mm. The diameter of the via hole inthe target resonator was 200 µm. The diameter of the via land was400 µm. The other dimensions were the same as those of the simu-lated via hole model. The top and inner ground plane were con-nected at the both sides of substrate to the bottom ground plane. Theinner ground plane had a round shape cutout of 6mm in diameter forthe via hole. The via hole resistance was less than 1 mW12. And thephotograph of the cross section of the target resonator in the ALIVHTM

substrate is shown in Figure 8. The via hole consisted of the fourstacked via hole.

292




500µm

4stacked via hole Ground plane

Ground planeresonator

Figure 8. Cross section of the target resonator in theALIVH substrate.

Figure 9 shows the relationship between the resonant frequencyand the inductance of the via hole. The line shows the simulatedvalues and closed squares show the measured values. The value ofthe lumped element was calculated from the reactance of the lumpedelement and the resonant frequency. Consequently, the reactance wasthe inductive lumped element. The inductance of the four stackedvia hole was about 0.6 nH. The measured values show a good agree-ment with the simulated values.

0 .2

0 .4

0 .6

0 .8

1

0 2 4R e s o n a n t fre q u e n cy (G H z)

Ind

uct

an

ce (

nH

S im u la te d

Me a s u re d

Figure 9. Relationship between the resonant frequency andthe inductance.

6. SBB Interconnection

A Flip Chip interconnection involves the use of metallic bumpsto connect electrically between the chips and the transmission lines.The authors evaluated characteristics of the Flip Chip interconnec-tion using the SBB technology in GHz range.

The evaluation method of the Flip Chip interconnection was thesame as that of the via hole. Schematic views of the reference reso-nator and target resonator are shown in Figure 10. The referenceresonator was a modified stripline resonator. The target resonator

was divided into two halves. One was located on the chip, the otherwas located on the substrate. Both segments were connected throughthe bump. The gap between the chip and the substrate was filledwith a under-fill resin. The simulation of the characteristics was car-ried out. Schematic view of the simulated model around the bump isshown in Figure 11. The length (L

B), the width (W

B) and height (H

B)

of the simulated bump model were 78µm, 78µm and 50µm, respec-tively. The width of the stripline resonator was 120µm. The thick-ness of the electrode was 4 µm. The thickness of both the chip andthe substrate was 250 µm. The materials of the chip and the sub-strate were defined as the same dielectric material. The dielectricconstant and loss tangent of those were 9.9 and 0.005, respectively.The dielectric constant and the loss tangent of the under-fill regionwere 3.5 and 0.02, respectively. The materials of the bump and theelectrode were defined as perfect conductors.

Reference resonator

Target resonator

Under-fill resonator

Chip

Substrate

Chip

Bump

Ground plane

L=46,36,23mm

50µm

50µm

250µm

250µm

Figure 10. Schematic views of the reference and targetresonator.

WB=78µm120µm

HB=50µm

Substrate

Chip

resonatorBump

Figure 11. Schematic view of the simulated model aroundthe bump.

(nH

)

293




The resonant characteristics were measured using HP8719D ZNetwork Analyzer from 1 GHz to 10 GHz frequency range. Thephotographs of the chip and the substrate are shown in Figure 12.Each dielectric material of the chip and the substrate was a polished99.5% pure alumina ceramic. The electrode was formed with NiCr/Au thin film. The chip and the substrate were mounted using SBBFlip Chip interconnecting technology. A cross-sectional view of theSBB Flip Chip interconnecting region is shown in Figure 13. Andschematic view of the center region of the measured target resonatorwith the bump is shown in Figure 14. The Flip Chip interconnectionconsisted of an Au bump and a conductive adhesive. The diameterof the bump was 85 µm. The other dimensions were the same asthose of simulated bump model. The DC resistance of the Flip Chipinterconnecting region was less than 10 mW13.

Chip

18mm× 16mm

Reference resonator

Target resonator

SBB

Substrate

25mm× 25mm

Figure 12. The photographs of the chip and the substrate.

Chip

Substrate

Conductive adhesive

Au bump

Figure 13. A cross-sectional view of the SBB Flip Chipinterconnecting region.

Under-fill resin Au bump

120µm

120µm

50µm

Conductive adhesive

Chip

Substrate

Figure 14. Schematic view of the center region of themeasured target resonator with the bump.

Figure 15 shows the relationship between the resonant frequencyand the inductance of the bump. Properties of one millimeter lengthwirebond are included as a reference. They were measured usingsame resonant method. The measured inductance and the simulatedinductance of the bump were less than 0.1nH. The measured valuesshow an agreement with the simulated values. And the inductanceof SBB interconnecting region was equal to about 10% of one mil-limeter length wirebond inductance value.

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 5 10

Resonant frequency (GHz)

Ind

uct

an

ce (

nH)

wire bond measured SBB measured

SBB simulated

Figure 15. Relationship between the resonant frequencyand the inductance.

7. Conclusions

The authors evaluated the basic electrical characteristics such asthe dielectric constant, loss tangent and transmission losses of theALIVH TM substrate from 1GHz to 4GHz frequency range. They alsoevaluated the equivalent circuit of the via hole in the ALIVHTM sub-strate and the Flip Chip interconnecting region of the SBB fromcomparisons of measured and simulated data.

294




Based on the above results, both of the SBB Flip Chip intercon-necting technology and the ALIVHTM substrate were found to begood enough to apply to high speed digital systems up to 1GHzhaving higher order harmonics.

Acknowledgments

The authors would like to thank Dr. Nagasawa and Mr. Ishida fortheir encouragement. The authors would also like to thank Mr.Yuuhaku, Mr. Kakimoto, Mr. Ueda and Mr. Fukuda for their sug-gestions and support for fabrications.

References

1. T. Shiraishi, K. Amami, Y. Bessho, K. Sakamoto, K. Eda, T.Ishida, and K. Fukuoka, ”Flip Chip MPU module on HighPerformance Printed Circuit Board “ALIVH” ”, Proceedingsof the International Conference and Exhibition on MultichipModules and High Density Packaging, MCM ‘98, Denver,Colorado, April 15-17, pp. 520-525, 1998

2. Y. Bessho, Y. Tomura, Y. Hakotani, M. Tsukamoto, T. Ishida,and K. Omoya, “A Stud-Bump-Bonding Technique for HighDensity Multi-Chip-Module,” Proceedings of 1993 Japan In-ternational Electronic Manufacturing Technology (IEMT) Sym-posium, pp. 362-365,1993

3. Wansheng Su, Sedki M. Riad, and Aicha Elshabini-Riad,“Microwave Material Characterization Using Stripline Reso-nators,” International Journal for Hybrid Microelectronics, Vol.14, No. 2, pp. 48-54, 1991.

4. Daniel I. Amey, and S. J. Horowitz, “Microwave MaterialCharacterization,” Proceedings of the International Sympo-sium on Microelectronics, ISHM ‘96, pp. 494-499, 1996

5. Y. Taguchi, K. Miyauchi, K. Eda, and T. Ishida, “MicrowaveCharacteristics of Alumina-Glass Composite Multi-Layer Sub-strates with Co-fired Copper Conductors,” IEICE Transactionson Electronics, Vol. E76-C, No. 6, pp. 912-918, 1993.

6. Marc E. Goldfarb, and Robert A. Pucel., “Modeling Via HoleGrounds in Microstrip,” IEEE Microwave and Guided WaveLetters, Vol. 1, No. 6, pp. 135-137, 1991.

7. C. E. Free, D. Li, P. G. Barnwell, and K. E. G. Pitt, “HighFrequency Modelling of Vias in 3D Interconnection Struc-tures,” Proceedings of 11th European Microelectronics Con-ference, pp. 84-91, 1997.

8. Markus Dernevik, Rolf Sihlbom, Zonghe Lai, Piotr Starski,and Johan Liu, “High-Frequency Measurements and Model-ling of Anisotropic Electrically Conductive Adhesive Flip-ChipJoint,” Proceedings of the Pacific Rim/ASME InternationalElectric and Photonic Packaging Conference, pp. 177-184,1997.

9. Rolf Sihlbom, Markus Dernevik, Zonghe Lai, Piotr Starski,and Johan Liu, “Conductive Adhesives for High-FrequencyApplications,” Proceedings of First IEEE International Sym-posium on Polymeric Electronics Packaging, pp. 123-130,1997.

10. S. Nakatani, S. Nakamura, and A. Wada, “Development ofAny layer IVH structure Multi-layered Printed Wiring Board,”The 9th National Convention Record JIPC, pp. 57-58, 1995

11. Robert E. Debrecht, “Impedance Measurements of MicrowaveLumped Elements from 1 to 12 GHz,” IEEE Transaction onMicrowave Theory and Techniques, Vol. 20, No. 1, pp. 41-48,1972.

12. T. Suzuki, T. Nishiyama, Y. Nakatani, M. Saida, and M.Nishiura, “Reliability of New Concept Multi-layered PrintedWiring Board ALIVH.” Proceedings of Pan Pacific Micro-electronics Symposium, pp. 211-216, 1998.

13. Masahiro Ono, Yoshihiro Tomura, Yoshihiro Bessho, TsukasaShiraishi, Kazuo Eda, and Toru Ishida, “Bonding Resistanceof SBB Technique,” Proceedings of Pan Pacific Microelec-tronics Symposium, pp. 355-362, 1997.

About the authors

Hideki Iwaki was born in Hyogo, Ja-pan, in 1971. He received the B.S. andM.S. Degrees in Physics fromKwanseigakuin University, Japan, in 1993and 1995, respectively. Since joiningMatsushita Electric Industrial Co., Ltd.,Japan in 1995, he has been engaged in theresearch and development of packagingtechnology for piezoelectric devices. Hiscurrent research interests are the packag-

ing technology for high speed circuits. He is a member of the JapanSociety of Applied Physics.

Yutaka Taguchi was born in Fukuoka,Japan, in 1964. He received B.S. Degreein Communication Engineering fromTohoku University, Japan, in 1986. Hejoined Matsushita Electric Industrial Co.,Ltd., Japan in 1986, where he has beenengaged in the research and developmentof hybrid microwave circuits. His currentresearch interests are the packaging tech-nology for high speed circuits. He is a

member of the Institute of Electrical and Electronics Engineers.

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Tsukasa Shiraishi was born inKagoshima, Japan, in 1961. He receivedthe B.S. Degree in Electronics fromKagoshima University, Japan. Since join-ing Matsushita Electric Industrial Co.,Ltd., Japan, he developed the contact typelinear image sensor for a facsimile ma-chine in Matsushita Electric ComponentCo., Ltd. And since 1995, he has beenengaged in the research and developmentof the Flip Chip mounting technology for

Multichip Module (MCM) in the current section.

Yoshihiro Bessho was born inOkayama, Japan, in 1960. He received theB.S. Degree in Electrical Engineeringfrom Okayama University, Japan, in 1983.Since joining Matsushita Electric Indus-trial Co., Ltd., Japan in 1983, he has beenengaged in the research and developmentof the mounting technology of LSI chipfor IC cards. His current interests includethe Flip Chip mounting technology forMultichip Modules.

Kazuo Eda was born in Mie, Japan, in1946. He received the B.S. and M.S. De-grees in Electronics from Nagoya Univer-sity, Japan, in 1969 and 1971, respectively.He received the Doctor Degree in Elec-tronics from Kyoto University, Japan, in1980. Since joining the Wireless ResearchLaboratory of the Matsushita Electric In-dustrial Co., Ltd., Japan in 1971, he didresearch and development work on elec-tronic ceramic devices. From 1983 to

1984, he was a visiting scholar with the University of California,Santa Barbara. Since 1983, he has been engaged in the research anddevelopment of optical devices, microwave devices, packaging tech-nology and substrate technology. He is the general manager of theplanning group and packaging technology group of the Device En-gineering Development Center of the MEI.

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High Frequency Electrical Characterization of a High ... · PDF fileBump Bonding “SBB” High Frequency Electrical ... which has any layer inner ... in a consumer electronics 1,2