Packaging and Embedded Components

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1 Packaging and Embedded Components

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3 Mater. Res. Soc. Symp. Proc. Vol Materials Research Society 0969-W01-04 Investigation of Ultralow Loss Interconnection Technique for LTCC Based System-in- Package(SIP) Technology at 60GHz Dong-Young Kim, Jae Kyoung Mun, Dong-Suk Jun, and Haechoen Kim Microwave Device Team, ETRI, 161 Gajeong-dong, Yuseong-gu, Daejeon, , Korea, Republic of ABSTRACT The effects of wire and ribbon bonded interconnection on the transmission characteristics at millimeter wave frequency range was presented. The insertion loss and return loss was closely related with the ratio of the signal line width to that of bonded wire or ribbon. The most promise condition for low loss interconnection was that the width of bonded wire or ribbon should be compatible to the width of signal lines. In the measurement of amp module fabricated using low temperature co-fired ceramics (LTCC) technique, the insertion loss due to LTCC packaging is very small which means that the loss due to bonding itself is nearly negligible. However, SI 1 and S22 degraded severely due to the interconnection. A new transition structure was introduced in order to compensate this degradation of SI 1 and S21. INTRODUCTION System and hardware investigations on the broadband wireless access at 60GHz band have been widely conducted around the world [1]. These applications required compact, high performance, and low-cost wireless equipment. Low temperature co-fired ceramics (LTCC) is one of the most promise candidates in system-in-package (SiP) at millimeter wave bands. LTCC technology has many advantages such as low loss in millimeter wave bands, high integration density, and high reliability. LTCC is a multilayer ceramic technology, which provides an ability to embed passive component in layers while the active elements are mounted on the surface layer. Despite the emergence of new packaging and interconnect technologies, wire-bonding method remains the dominant conventional chip connection technology with low cost, high reliability and high manufacturability [2]. With increasing frequency from microwave to millimeter wave frequency range, however, wire bonds exhibits increased parasitic effects that deteriorate the module performance [3]. In addition, radiation loss due to discontinuity caused by wire bends on both ends of the wire becomes significant, particularly in the millimeter wave frequency range [4]. Sutano et. el. reported the investigation on the transmission characteristic of wire and ribbon bond interconnection at millimeter wave frequency range. However, their result showed the measured characteristic under 40GHz [5]. In this paper, we present the millimeter wave transmission characteristic of wire bonding on CBCPW (conductor backed coplanar waveguide) lines with one or two dielectric layers (looum or 200um thickness). The mechanism of increased return loss of wire-bonded module will be presented, and ultra low loss configuration of interconnection.will be suggested.

4 EXPERIMENT Ferro A6S and thermally matched gold and silver conducting pastes were used to fabricate the CBCPW line patterns. Vias were formed through mechanical punching. The punched vias were filled with silver conducting pastes using screen-printing. After via filling, a conductor paste was screen-printed onto the tape, resulting in the lines, patterns and ground planes. After all tape layers had been prepared, they are collated and laminated at 70 C and 3000psi for 10 minutes. 5 layers, which is minimum requirement for LTCC process suggested by manufacturer, were used to fabricate the line patterns. One or two layers were used as dielectric layers. The other layers were dummy layers for ground planes. After the lamination process, the LTCC laminates were fired in the furnace under an appropriate temperature profiles. The thickness of each layer after firing was looum. Gold wire with diameter of 0.8mil or gold ribbon with width of 2mil and thickness of 0.5mil was used as bonding wire. Fabricated CBCPW lines and bonded lines were measured with a vector network analyzer HF8510C. DISCUSSION 50Q CBCPW lines at 60GHz were designed with the aid of a finite-element method (FEM)-based full wave simulator. Two kinds of CBCPW lines with dielectric thickness (looum and 200um) were fabricated. The gap-width between signal line and side-ground planes was fixed to 80um. The widths of signal lines with characteristic impedance of 50Q at 60GHz were 94um (looum-thick dielectric) and 140um (200um-thick dielectric), respectively. Figure 1 shows the measured millimeter-wave characteristics of two types of CBCPW lines. The insertion loss of CBCPW lines at 60GHz was very low, i.e., -0.30dB (looum) and -O.21dB (200um), respectively. SI 1 values of these lines were lower than -15dB at the frequency range between 50GHz and 70GHz. This shows that the impedance of lines was well matched to 50ft at this frequency range. cff S11 100um! S11 200um I S21 100um _L S21 200um i Fig Frequency (GHz) Measured S-parameter of CBCPW lines with different dielectric thickness (Line length is 3mm)

5 Figure 2 shows the wire- and ribbon-bonded CBCPW lines with one dielectric layer (looum). The gap between lines was fixed to 200um. Figure 3 shows the measured characteristics of these lines. The number of bonded wire or ribbon was one or two. The insertion loss of single-wire bonded CBCPW line was -0.17dB, and return loss was -21.6dB at 60GHz. These values are low enough for the application of millimeter-wave packaging. As the number of bonded wire increased two, the insertion loss decreased to -O.lOdB, and return loss decreased to -28.6dB. The insertion loss of single-ribbon bonded CBCPW line was -O.lOdB, and return loss was -27.4dB at 60GHz. As the number of bonded ribbon increased two, the insertion loss decreased to -0.09dB, however, return loss increased to -24.3dB. Because the measured insertion loss included the line loss, contact loss between line and measuring probe, and bonded wire or ribbon, the loss due to bonding itself will be ultra low and nearly negligible. Fig. 2. Photographs of wire and ribbon bonded CBCPW lines with looum of dielectric layer single wire S11 single wire S21, - - double wire S1 i e- double wire S21 m- single ribbon S11 ~-t-r- single ribbon S21 -A- dbuble ribbon S11 ^-&- dbuble rjbbon?21 Frequency (GHz) Fig. 3. Measured S-parameter of wire or ribbon bonded CBCPW lines with looum of dielectric layer In the case of interconnection with CBCPW lines with two dielectric layers (200um), the transmission characteristic shows somewhat different results. Figure 4 shows the measured characteristic of wire or ribbon bonded CBCPW lines. For the single-wire bonded interconnection, the insertion loss was as high as -0.78dB, and the return loss was over -lodb. In the case of double-wire or single-ribbon bonding, the insertion losses were -O.35dB and ldb, and return loss were -14.5dB and -15.4dB, respectively. In the case of one dielectric layer (looum), the measured SI 1 and S22 are very low, which means the impedance of bonded wire or ribbon was nearly 50Q. As the dielectric thickness increases, however, the impedance of

6 boned wire or ribbon increases because the distance from the ground plane increases. In order to compensate this increment of impedance of bonded wire or ribbon, the width of wire or ribbon should be increases. The double ribbon bonding has similar effect of increasing width of ribbon. In the case of double ribbon bonding, the insertion loss was -0.12dB and return loss was db. However, the use of double-ribbon bonding is impractical because the size of bonding pad in active devices is not enough for double ribbon bonding. _ _ single wire $21 double wire S11 double wire S21 single ribbon S11 single ribbon S21 double ribbon S Frequency (GHz) Fig. 4. Measured S-parameter of wire or ribbon bonded CBCPW lines with 200um of dielectric layer For the test of the compatibility of this ribbon bonding with real active devices, power amplifier (PA) module was fabricated. Figure 5(a) shows the photographs of this module. PA chip was manufactured in our group. The detailed properties of PA chip will be presented elsewhere. Figure 5(b) shows the measured property of bare-chip and LTCC module. The insertion loss due to packaging was -O.ldB, which is very small as expected.. However, the SI 1 and S22 of LTCC module were severely degraded from those of bare-chip. This degradation of S11 and S22 is thought to be due to the difference of line types between bare chip and LTCC module. In the test pattern, two CBCPW lines were used as transmission lines, and shows very low SI 1 and S22. In the fabricated LTCC amp module, however, the transmission line of the PA chip was not CBCPW line, but microstrip line with GSG(ground-signal-ground) pad for measuring or interconnection. The transmission mode of both CBCPW line and microstrip line are the same as quasi- TEM (transverse electromagnetic) mode. [6] However, the electric field distributions of both lines are different. In microstrip lines, the electric field between the signal line and the lower ground plane is stronger than any other direction. However, the electric field between the signal line and side-ground planes are the strongest in CBCPW lines. These difference of electric field distribution retards the smooth transmission of signal, and causes extra reflection of signal at the bonded wire or ribbon, which increases SI 1 and S22. In order to suppress these degradations of S11 and S22, new transition structure from CBCPW to microstrip was introduced for smooth variation of electric field distribution. Figure 6 shows these transition structure and their measured properties.

7 -30 -Sll.chip -S21_chip -S22_chip S11_LTCC module S21_LTCC module -S22_LTCC module 40 [ Frequency [GHz] Fig. 5. Photographs and measured characteristics of PA module interconnected with singleribbon bonding to CBCPW lines with 100mm of dielectric layer This transition provides impedance matching with narrow band-gap. In this structure, the center frequency of matching was 59GHz. meaduted S11 e meadufed S21 simmulated S11 O simmulated S21 Frequency (GHz) Fig. 6. Photographs and measured characteristics of test pattern with CBCPW-to-microstrip transition structure Due to the CBCPW-to-microstrip transition, the SI 1 and S22 decreased below -20dB above 53GHz. New type of amp module with this transition was fabricated using commercial LNA chip. Figure7 shows the photograph and measured properties of this LNA module. Both SI 1 and S22 of this LNA module were smaller than those of chip above 57GHz. This shows that the transition improves input matching. The gain of module is higher than that of chip due to this improved input matching. However, the center frequency of matching was shifted to 63GHz. The impedance of microstrip line in test pattern was 50 X However, the input impedance of LNA chip is deviated from 50 Cl. This deviation makes the shift of center frequency of matching.

8 CD S o & CD i [ module S11 i.d9r.module S2.1 i -g- module S22 : --- cwps11 i - - chip S21 i -m~ chips22 j j- i- i \ / \ V : i \ i Frequency (GHz) Fig. 7. Photographs and measured characteristics of LNA module with CBCPW-to-microstrip transition structure [LNA chip was manufactured by Velocium Co. Ltd] CONCLUSIONS The insertion loss and return loss of wire or ribbon bonded interconnection was closely related with the ratio of the signal line width to that of bonded wire or ribbon. The most promise condition for low loss interconnection was that the width of bonded wire or ribbon is compatible to the signal line width. In the fabrication of PA module, the insertion loss of module was -O.ldB. However, the SI 1 and S22 severely degraded due to the difference of transmission line between chip and packaging module. A new transition structure was introduced in order to compensate this type of difference. The module with transition structure shows reduced SI 1 and S22, and improved gain above 57GHz. REFERENCES H. H. Meinel, IEEE Trans. Microwave Theory & Tech., vol. 43, no. 7, pp , July 1995 R.Tummala and E. Rymaszewski, Microelectronics Packaging Handbook, New York: Chapman & Hall, 1997, vol.11 pp R. H. Caverly, IEEE Trans. Microwave Theory & Tech., vol. MTT-34, pp , September 1986 H. Y. Lee, IEEE Trans. Microwave Theory & Tech., vol. 43, pp , January 1995 A. Sutano, N. G. Cafaro, J. Lasker, and M. M. Tentzeris, IEEE Trans. Advanced Packaging, vol. 24, No. 4, pp , November D.M. Pozar, Microwave Engineering, Reading Massachusetts; Addison-Wesley Pub. Co., 1990,pp.l83-201

9 Mater. Res. Soc. Symp. Proc. Vol Materials Research Society 0969-W01-05 Influence of Full-Filled Polymer Molding on High-Frequency Circuits Kiyoshi Nakanishi 1 and Masayuki Fujimoto 2 ^hizuoka University, Hamamatsu, , Japan 2 Shizuoka University, Jyouhoku, Hamamatsu, , Japan ABSTRACT The influence of full-filled polymer molding on high-frequency circuits in cellular phones is evaluated using computer simulations and high-frequency measurements. Polymer-molded high-frequency circuits of cellular phones increase radiation harmonics and line and antenna phase errors. High-frequency properties are degraded due to a decrease in line impedance and an increase in stray capacitance of land electrodes that are used in the assembly of components. Degradation problems caused by full-filled polymer molding can be alleviated by appropriate circuit design, such as by adjusting the distance of components and creating more effective electromagnetic shielding. Better circuit design must satisfy the specifications of several different types of cellular phones, including global systems mobile telecommunications and digital cellular systems. INTRODUCTION The cellular phone, a common mobile consumer electronic device, has become indispensable

10 in modern life. Subscribers to cellular phone service number almost 1.5 billion people worldwide. The first generation of cellular phones, the analog cellular system, has disappeared, and the second generation, the digital cellular system (global systems mobile telecommunications, GSM), is now used all over the world. Furthermore, the third generation (international mobile telecommunications-2000, IMT), which can connect to and download rich quality content from the Internet, has already been introduced in many countries. The fourth generation (EVIT-advanced) is scheduled to begin service in Japan in 2010 [1]. Camera phones, which include photographic and audio and visual (AV) functions, were introduced in the third generation of cellular phones. Such functions require not only multi-radio frequency (RF) band circuit blocks, but also extremely large memories in increasingly small phones [2-4]. To obtain a higher density of surface mounting of components, three-dimensional mounting and printed circuit boards (PCB) with buried components have already been adopted (Fig. 1). The only remaining spaces for effective mounting of components or functions are the gaps between components. The knowledge of RF circuit design has already been condensed as much as possible to fit the circuit patterns. A "black-box" covering, which is preferable, makes the design difficult to see and protects the intellectual properties. Therefore, we used the gaps between components for functions, such as shielding, noise suppression, heat sinks, and stress dispersion, as well as for functional mold materials. Carrier Substrate Thin film L,C, R via formation Composite sheet (graphite) Fig. 1. Schematic of components in buried multilayer polymer substrate. 10