A New EBG Structure for < 5 GHz SSN Suppression in < 10mm x 10mm high density Mixed –Signal SIP

Eunseok Song and Heeseok Lee

IPT (Interconnect Product and Technology) Team, Semiconductor Division, Samsung Electronics,

san #24 Nongseo, Giheung, Yongin, Gyeonggi 449-711, Korea Tel) +82-31-209-3559, Fax) +82-31-209-3131,

E-mail) hees.lee@samsung.com

Abstract In modern mobile hand-held phone, many kinds of

wireless services are employed. For example, there are blue tooth, mobile TV, wireless broadband internet, HSDPA, RF-ID, and etc. Since the small-form factor chip set solution corresponding to each wireless service is strongly required in ultra-thin small form-factor mobile phone, system in package (SIP) is promising solution. In mixed signal SIP (MS-SIP) integrating digital logic IC and RF-IC, noise isolation between digital and RF domain is becoming one of major concerns. To manage RF noise propagation, one of recently presented noise suppression design technology is power delivery network (PDN) with electromagnetic band-gap (EBG). In this paper, a new EBG structure employable to small form factor (<10mm x 10mm) MS-SIP will be presented.

1. Introduction In modern mobile hand-held phone, many kinds of

wireless services are employed. For example, there are blue tooth, digital multimedia broadcasting, wireless broadband internet (WiBro), HSDPA (high speed downlink packet access), RF-ID, and wireless LAN (Wi-Fi). Since the small-form factor chip set solution corresponding to each wireless service is strongly required in ultra-thin small form-factor mobile phone, system in package (SIP) is promising solution.[1] In mixed signal SIP (MS-SIP) integrating digital logic IC and RF-IC, noise isolation between digital and RF domain is becoming one of major concerns. To manage RF noise propagation, one of recently presented noise suppression design technology is power delivery network (PDN) with electromagnetic band-gap (EBG) [2-6]. In this paper, a new EBG structure employable to small form factor (<10mm x 10mm foot-print) MS-SIP will be presented.

Prior to this work, most EBG structures have been developed for large-scale backplane or motherboard applications. T. L. Wu et al. makes 0.6-4.6 GHz band-gap by using 30mm x 30mm unit cell and FR4 substrate.[5] While this work is very powerful to block broadband noise, their unit cell is too big for 10mm x 10mm area. To reduce the physical size of unit cell, J. Lee et al. have presented high dielectric

constant ( rε =16) thin film EBG power/ground network, in which they achieved 0.3 – 3.6GHz band-gap by using 10mm x 10mm rectangular patch unit cell.[6] J. Lee et al. increases electrical length by increasing dielectric constant.

Since SIP products considered in mobile phone application require very small form-factor (smaller than 10mm x 10mm x 1.4mm) and most today’s wireless service is served under 5GHz, 30mm x 30mm EBG unit-cell structure with FR4

substrate cannot be used in our MS-SIP. While the unit cell size can be reduced by usage of high dielectric constant thin film given by [6], a new material for PCB makes big cost increase. The motivation of this work is achievement of <5GHz band-gap by using a new EBG structure with normal FR4 substrate. It must be able to be implemented within 10mm x 10mm for small form-factor MS-SIP, for which the size of unit cell for EBG must be minimized.

The proposed EBG structure is a new spiral-patch EBG, unit cell, which is presented in Fig1. (a).[7] The conventional rectangular-patch EBG unit cell is presented for comparison. By using the proposed spiral EBG, band-gap behavior is found under 5GHz, which is presented by measured result. When using conventional rectangular patch, no band-gap is obtained under 15GHz. By presenting experimentally measured SSN-suppression behavior, it is demonstrated that EBG with spiral unit cell (spiral EBG) can be utilized in < 10mm x 10mm MS-SIP for mixed signal application operating under 5GHz.

2. Proposed spiral-patch EBG structure The PDN constructed by EBG/plane pair has three

metallic layers. There are top plane layer, the EBG patch layer, and the bottom plane layer. In this study, all metallic layers are made by Cu, whose electric conductivity is 5.8x107 S/m. The top and the bottom planes are the same as the ones employed in conventional multilayer packaging structures. The EBG patch layer consists of periodic lattice of square patched of M columns along x-axis and N rows along y-axis. The periodic length of one patch is d given in Fig.1. Each patch is connected to the bottom plane by a vertical metal-filled via-hole (MFVH) at the center of the patch. In this study, MFVH is made by a build-up blind-type via process. As shown in Fig.1(b), the distance between the EBG patch layer and the bottom plane is h2, and the distance between the top and the EBG patch layer is h1. The relative dielectric constant of the material filled between the top layer and the EBG patch layer is 1ε , and 2ε is the relative dielectric constant of the material filled between the EBG patch layer and the bottom plane. The diameter of vertical via is r. Although the EBG patch discussed in this paper is spiral patch presented at Fig. 1(a), the rectangular patch presented by the previous works [3-6] will be used for comparison. In conclusion, the presented EBG with spiral patch give promising SSN suppression solution for small-form factor SIP. In the next paragraphs, the dispersion diagram, bloch impedance characteristic, bandgap property, and an equivalent circuit model will be presented.

70

1-4244-0665-X/06/$20.00 c©2006 IEEE

Unit-Cell Size = 1mm x1mmd = 1mm

Via Land

Spiral Unit-cell Rectangular patch Unit-cell

d

d

Unit-Cell Size = 1mm x1mmd = 1mm

Via Land

Spiral Unit-cell Rectangular patch Unit-cell

d

d

(a)

2ε1ε1h

2h

t

d

r 2ε1ε1h

2h

t

d

r

(b)

Fig. 1. (a) Top view of unit cell patch for EBG. The power delivery network with EBG is constructed by 1mm x 1mm unit cell in this study. The period of unit cell is represented by d. In this work d is 1mm. The proposed unit cell for EBG has spiral-patch. The conventional rectangular patch is presented for comparison. (b) Cross-section view of EBG/plane pair. The period of EBG is indicated by d. In this paper, h1 = 0.2 mm, h2 = 0.1mm, t = 0.02 mm, r =

0.1mm, 1ε = 4.4, 2ε = 4.4 are used.

3. Unit-cell Approach for Dispersion Analysis of EBG To utilize an EBG for SSN suppression, the bandgap must

be easily estimated at the SIP design period. Full-wave modeling approaches are able to give accurate results. However, such approaches require very large computational resource. Several unit-cell modeling method for the electromagnetic (EM) modeling of periodic structure are very efficient. [8-10] In this paper, the scattering parameter model of unit cell calculated by HFSS is used. The dispersion diagram and band gap of EBG are found based on eigen-value analysis.[11]

d

n

n

n

n

n

n eIV

IV

DCBA

IV γ==

+

+

+

+

1

1

1

1

(1)

( )( )21

21122211

211

SSSSSA +−+= (2)

( )( )21

21122211

211

SSSSSD ++−= (3)

2cosh DAd +=γ (4)

+= −

2cosh1 1 DA

dγ (5)

In (1), the ABCD matrix of unit cell can be calculated from the simulated scattering matrix with (2) and (3). Sine the scattering parameter and ABCD matrix are frequency-dependent, (1) gives the relationship between the complex propagation constant ( ) and the frequency. The dispersion relation can be represented by (5).

0 5 10 15 20 25 30 35 40-30

-25

-20

-15

-10

-5

0

Frequency [GHz]In

sert

ion

Loss

, S12

[dB

]0 5 10 15 20 25 30 35 40-30

-25

-20

-15

-10

-5

0

Frequency [GHz]In

sert

ion

Loss

, S12

[dB

]

Fig. 2. Insertion loss (S12) of unit cell structure is presented for each type of EBG structure. Red dashed line represents S12 of unit cell structure constructed by rectangular-patch. Black solid line represents S12 of unit cell structure including spiral patch. Two kinds of EBG patch has same spatial period length d = 1mm.

In Fig. 2, the simulated insertion loss of unit-cell is given

for spiral-patch EBG and rectangular-patch EBG, respectively. The scattering parameter is calculated by the commercial finite element field solver, Ansoft’s HFSS. The intrinsic resonances are found with spiral-patch EBG. Based on (5) with the simulated scattering parameter of unit-cell, the dispersion diagrams are found as shown in Fig. 3. While the rectangular-patch EBG has band-gap over 35 GHz, the spiral-patch EBG has band-gap around 5 GHz. In Fig. 4, the attenuation constant is also presented. It is found that the attenuation constant is very large in band-gap frequency, which prevents electromagnetic wave from propagating. In this paper, the electromagnetic wave propagating through PDN is noise generated by output driver of logic circuitry. EBG gives noise suppression around band-gap.

2006 Electronics Packaging Technology Conference 71

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 10

5

10

15

20

25

30

35

40

Freq

uenc

y [G

Hz]

πβd-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

0

5

10

15

20

25

30

35

40

Freq

uenc

y [G

Hz]

πβd Fig. 3. Dispersion diagram of rectangular patch EBG given by blue dashed line and spiral patch EBG indicated by red solid line. While rectangular patch EBG has bandgap over 35GHz, spiral patch EBG has bandgap around 5 GHz. Two kinds of EBG has same spatial period length d = 1mm.

0 5 10 15 20 25 30 35 4010-15

10-10

10-5

100

105

α[N

p/m

]

Frequency [GHz]0 5 10 15 20 25 30 35 4010-15

10-10

10-5

100

105

α[N

p/m

]

Frequency [GHz] Fig. 4. Attenuation constant of rectangular patch EBG and spiral patch EBG. The line with cross represents the attenuation constant of spiral patch EBG. At the forbidden frequency region called by bandgap, attenuation constant, α, increases. There exists only evanescent mode in bandgap, which results in no electromagnetic wave propagation

The bandgap property can be determined, in terms of

impedance characteristic. In the periodic structure such as EBG/plane pair, the characteristic impedance is replaced by bloch impedance. [11] The bloch impedance is defined by (6). The ABCD matrix of unit cell shown in (1) gives the relation (7) between Zb and ABCD matrix.

1

10

+

+=n

nb I

VZZ (6)

( ) 4

22

0

−+−

−=±

DADA

BZZb

(7)

0 5 10 15 20 25 30 35 4010-5

100

105

| im

ag(Z

b) |

[Ohm

]

Frequency [GHz]

0 5 10 15 20 25 30 35 4010-20

10-10

100

1010

| rea

l(Zb)

| [O

hm]

Frequency [GHz]

0 5 10 15 20 25 30 35 4010-5

100

105

| im

ag(Z

b) |

[Ohm

]

Frequency [GHz]

0 5 10 15 20 25 30 35 4010-20

10-10

100

1010

| rea

l(Zb)

| [O

hm]

Frequency [GHz] Fig. 5. Bloch impedance (Zb) of rectangular patch EBG is given. In the case of propagation mode, real part is dominant. However, evanescent mode in bandgap has imaginary bloch impedance.

0 5 10 15 20 25 30 35 4010-5

100

105

| im

ag(Z

b) |

[Ohm

]

Frequency [GHz]

0 5 10 15 20 25 30 35 4010-20

10-10

100

1010

| rea

l(Zb)

| [O

hm]

Frequency [GHz]

0 5 10 15 20 25 30 35 4010-5

100

105

| im

ag(Z

b) |

[Ohm

]

Frequency [GHz]

0 5 10 15 20 25 30 35 4010-20

10-10

100

1010

| rea

l(Zb)

| [O

hm]

Frequency [GHz] Fig. 6. Bloch impedance (Zb) of spiral patch EBG is given. Around 5 GHz, imaginary part of Zb is large, which is the typical feature of evanescent mode in bandgap.

The bandgap property is determined in terms of impedance

characteristic. As presented in Fig.5 and Fig. 6, the imaginary part of bloch impedance is dominant in band-gap frequency region. Since the voltage wave and the current wave are out-of-phase in band-gap frequency, energy propagation is prevented. As presented in Fig 3 and Fig. 4, band-gap frequency can be found in bloch impedance diagram. The real part of bloch impedance outside band-gap is equal to parallel plate constructing EBG/plane pair.

4. Experimental Verification As well known, the band-gap property of periodic

structure can be easily found and verified using the large number of unit-cell, which approximately results in the behavior of ideal periodic structure. To study the intrinsic band-gap property of spiral-patch EBG, EBG/plane pair with 30 x 30 patch array is fabricated and measured by vector

72 2006 Electronics Packaging Technology Conference

network analyzer (HP8753E) and micro-probe. Also, a rectangular-patch EBG is fabricated with identical PCB material and fabrication process used in spiral-patch EBG. The set of physical dimension describing EBG/plane pair is given in Fig. 1. The measured insertion loss and trans-impedance is presented in Fig. 11 and Fig. 12, which determines the SSN suppression performance. While rectangular-patch EBG has no band-gap around 5GHz, presented spiral-patch EBG generates band-gap property around 5 GHz.

Fig. 11. Comparison of measure |S12| between the proposed EBG (solid black line) and conventional EBG (dotted led line with circle). Blue dotted circle represents band-gap generated by the proposed EBG structure. While conventional EBG structure makes no band-gap under 15GHz, the proposed spiral EBG structure achieves 5GHz-6GHz band gap with just 1mm x 1mm unit cell.

Fig. 12. Measured SSN suppression behavior represented by trans-impedance (Z12). The proposed spiral EBG structure has novel noise isolation around 5GHz.

Fig.11 and Fig. 12 agree well with the simulated dispersion

diagram and attenuation constant given in Fig. 3 and Fig. 4. As given in Fig.3, and Fig. 4, the band-gap frequency of spiral-patch EBG is found around 5GHz. The several peaks in measured insertion loss and trans-impedance are cased by the finite size of PDN. Under 3 GHz, rectangular-patch EBG and spiral-patch EBG gives very identical characteristic. It is explained that the propagation characteristic of unit cell corresponding to rectangular-patch EBG and spiral-patch EBG is very close under 3GHz in terms of dispersion diagram, attenuation constant, and Bloch impedance, as presented in Fig. 3-6. Based on the measured and simulated results, it is demonstrated that the proposed spiral-patch EBG is promising solution for suppression of SSN under 5GHz employable in

10mm x 10mm small-sized SIP. In addition, very efficient modeling and simulation method is also presented for EBG design, which is unit-cell approach.

5. Application to FBGA Package for SIP

In this chapter, the SSN suppression performance of spiral-patch EBG employed in several form-factor SIPs will be presented. Three cases of PDN constructed by EBG/plane-pair are fabricated in 5mm x 5mm FBGA, 10mm x 10mm FBGA, and 14mm x 14mm FBGA. In 5mm x 5mm FBGA, 4 x 4 EBG cell array is employed. In Fig. 13, the SSN suppression behavior of rectangular-patch EBG and spiral-patch EBG is compared in terms of insertion loss and trans-impedance. While rectangular-patch EBG has no band-gap, the spiral-EBG has band-gap, which results in 5GHz SSN suppression. PDN employing 4 x 4 spiral-patch arrays gives -30dB band-gap from 5GHz to 6GHz. In addition, the input-impedance is also presented in Fig. 14, which is the key feature of self generated switching noise. While rectangular-patch EBG has several resonances around 5 GHz, the spiral-patch EBG has no resonances in band-gap. The resonances around 5 GHz is removed by the spiral-patch EBG. The experimental measurement demonstrates that the proposed spiral-EBG is very promising solution for around 5GHz SSN suppression in 5mm x 5mm FBGA for SIP.

2 4 6 8 10 12 14 16 180 20

-40

-35

-30

-25

-20

-15

-10

-45

-5

freq, GHz

dB(S

(1,2

))dB

(S(3

,4))

2 4 6 8 10 12 14 16 180 20

1E1

1

3E1

freq, GHz

mag

(Z(1

,2))

mag

(Z(3

,4))

Fig. 13. Measured SSN suppression behavior of 4x4 EBG cell array in 5mm x 5mm FBGA package. The proposed spiral-patch EBG structure has novel noise isolation around 5GHz. S(1,2) and Z(1,2) are insertion loss and trans-impedance of PDN using rectangular-patch EBG. S(3,4) and Z(3,4) are those of PDN using spiral-patch EBG. The dotted circle indicates band-gap around 5 GHz.

2006 Electronics Packaging Technology Conference 73

1E101E9 2E10

1

1E1

1E-1

4E1

freq, Hz

mag

(Z(1

,1))

mag

(Z(3

,3))

Fig. 14. Measured input-impedance of PDN constructed by rectangular-patch EBG and spiral-patch EBG is represented by Z(1,1) and Z(3,3), respectively. Around 5 GHz, the resonance in input-impedance is removed by the new spiral-patch EBG, as indicated by dotted red circle.

In 10mm x 10mm FBGA, 9 x 9 EBG cell array is used. In Fig. 15, the SSN suppression behavior of rectangular-patch EBG and spiral-patch EBG is compared. While rectangular-patch EBG has no band-gap, the spiral-EBG has band-gap, which results in 5GHz SSN suppression. Also, 14mm x 14mm FBGA case is presented.

2 4 6 8 10 12 14 16 180 20

-60

-50

-40

-30

-20

-70

-10

freq, GHz

dB(S

(1,2

))dB

(S(3

,4))

2 4 6 8 10 12 14 16 180 20

1E-1

1

1E-2

1E1

freq, GHz

mag

(Z(1

,2))

mag

(Z(3

,4))

Fig. 15. Measured SSN suppression behavior of 9x9 EBG cell in 10mm x 10mm FBGA package. The proposed spiral-patch EBG structure has novel noise isolation around 5GHz. S(1,2) and Z(1,2) represents insertion loss and trans-impedance of PDN using rectangular-patch EBG, respectively. S(3,4) and Z(3,4) are those of PDN using spiral-patch EBG. The dotted red circle indicates band-gap around 5 GHz.

In 10mm x 10mm FBGA, 9 x 9 EBG cell array is used. In

Fig. 15, the SSN suppression behavior of rectangular-patch EBG and spiral-patch EBG is compared. While rectangular-patch EBG has no band-gap, the spiral-EBG has band-gap,

which results in 5GHz SSN suppression. In the case of 10mm x 10mm FBGA, PDN constructed by 9 x 9 spiral-patch array generates -40dB band-gap from 5GHz to 6GHz. The SSN suppression behavior of PDN used in 14mm x 14mm FBGA is presented in Fig. 16. For comparison, the insertion loss and trans-impedance of spiral-patch EBG and rectangular-patch EBG are simultaneously given.

2 4 6 8 10 12 14 16 180 20

-50

-40

-30

-20

-10

-60

0

freq, GHz

dB(S

(1,2

))dB

(S(3

,4))

2 4 6 8 10 12 14 16 180 20

1

1E1

1E-1

2E1

freq, GHz

mag

(Z(1

,2))

mag

(Z(3

,4))

Fig. 16. Measured SSN suppression behavior of 13x13 EBG cell in 14mm x 14mm FBGA package. The proposed spiral-patch EBG structure has novel noise isolation around 5GHz. S(1,2) and Z(1,2) are insertion loss and trans-impedance of PDN using rectangular-patch EBG, respectively. S(3,4) and Z(3,4) are those of PDN using spiral-patch EBG. The dotted red circle indicates band-gap around 5 GHz.

Since most SIP products developed for commercial sales

are less than 14mm x 14mm, a noise suppression solution in PDN must be able to be implemented in the limited area of multilayer PCB. Therefore, the previously presented EBG [4,5] cannot be employed in FBGA package smaller than 14mm x 14mm within 5 GHz. In addition, since mobile-phone market requires ultra-low cost solution, the employment of a new advanced material [6] is also hesitated. In this paper, a spiral-patch EBG is proposed to satisfy both cost and performance requirement. The SSN suppression performance of the spiral-patch EBG is demonstrated by test vehicle with 1mm x 1mm EBG unit cell.

Although the unit cell size, d, of a spiral-patch EBG is fixed to be 1mm x 1mm, the unit cell size can be modified for lower frequency application. When d is increased to be 2mm x 2mm, PDN has 2.5 GHz band-gap property. Since 2mm x 2mm EBG/plane pair is still small and can be employable to be 4 x 4 patch array in 10mm x 10mm FBGA, the proposed spiral-patch is very useful for MS-SIP supporting today’s wireless service.

74 2006 Electronics Packaging Technology Conference

6. Conclusions

A new spiral EBG is presented. The conventional

rectangular-patch EBG unit cell has a physical limit. The unit cell size of rectangular-patch EBG for 5 GHz SSN suppression must be larger than 30mm x 30mm. Since it is even larger than SIP to be considered in this study, the spiral-patch EBG is presented. In this work, unit cell size is 1 mm x 1 mm (d=1mm). By using the proposed spiral-patch EBG, <-30dB band-gap behavior is found under 5GHz.

Especially, the SSN suppression performance of the proposed spiral-patch EBG is demonstrated with 5mm x 5mm, 10mm x 10mm and 14mm x 14mm FBGA, which is presented by Fig.13, Fig. 15 and Fig. 16. By presenting experimentally measured SSN-suppression behavior and calculated band-gap property, it is demonstrated that EBG with spiral unit cell (spiral-pathc EBG) can be utilized for SSN suppression in < 10mm x 10mm MS-SIP operating under 5GHz. It is expected that the enhanced noise isolation between logic circuitry and RF circuitry is easily guaranteed by using the presented spiral-patch EBG design method and small size characteristic of the proposed spiral-patch EBG.

References 1. R. R. Tummala, M. Swaminathan, M. M. Tentzeris, J.

Laskar, G.K.Chang, S. Sitaraman, D. Keezer, D. Guidotti, Z. Huang, K. Lim, L. Wan, S. K. Bhattacharya, V. Sundaram, F. Liu, and P. M.arkondeya Raj, "The SOP for miniaturized, mixed-signal computing, communication, and consumer systems of the next decade," IEEE Transactions on Advanced Packaging, VOL. 27, NO. 2, pp.250-267, May 2004.

2. IEEE Trans. Microwave Theory Tech. (Special Issue), vol. 47, Nov. 1999.

3. G. Chen and K. L. Melde, "Cavity resonance suppression in power delivery systems using electromagnetic band gap structures," IEEE Transactions. on Advanced Packaging, vol. 29, no. 1, pp.21-30, Feb. 2006

4. T. Kamgaing and O. M. Ramahi, “A novel power plane with integrated simultaneous switching noise migration capability using high impedance surface,” IEEE Microw. Wireless Compn. Lett., vol. 13, no.1, pp.21-23, Jan. 2003.

5. T. L. Wu and T. K. Wang, “Embedded power plane with ultra-wide stop-band for simultaneously switching noise on high-speed circuits,” Electronics Lett. Vol.42, No.4, 16th Feb. 2006.

6. J. Lee, H. Kim, and J. Kim, “High dielectric constant thin film EBG power/ground network for broadband suppression of SSN and radiated emissions,” IEEE Microw. Wireless Compn. Lett., vol. 15, no.8, pp.505-507, Aug. 2005.

7. E. Song, H. Lee, and S. Lim, Korean Patent, submitted, 10-2006-0053114 (2006)

8. H. Lee and J. Kim, "Unit-cell approach to full-wave analysis of meander delay line using FDTD periodic structure modeling method," IEEE Transactions. on Advanced Packaging, vol. 25, no. 2, pp.215-222, May. 2002

9. S. and O. M. Ramahi, “A Simple and Effective Model for Electromagnetic Bandgap Structures Embedded in Printed Circuit Boards,” IEEE Microw. Wireless Compn. Lett., vol. 15, no. 10, pp.621-623 Oct. 2005

10. Long Li, Bin Li, Hai-Xia Liu, and Chang-Hong Liang, "Locally Resonant Cavity Cell Model for Electromagnetic Band Gap Structures," IEEE Trans. on Antennas and Propagation, vol. 54, no. 1, pp.90-100, Jan. 2006

11. R. E. Collin, Foundations for Microwave Engineering, Second ed. New York: Wiley, 1992.

2006 Electronics Packaging Technology Conference 75