47 By Juan Saiz-Ipiña1, Miguel Angel Solano1, Constantino Perez-Vega2 and Angel Mediavilla2 Jose-Maria Zamanillo2 Modelling parasitic effects of plastic encapsulated microwave devices This paper shows a new and accurate electrical modelling technique for low cost active plastic microwave encapsulated devices. The method employs analytically derived expressions, and is based on the analysis of measured S-parameters over an appropriate frequency range. The approach produces a good fit between measured and simulated S-parameters for plastic packaged devices, as demonstrated in the results for PHEMT devices up to 26.5GHz and for low-cost LNAs up to 6GHz. ZUSAMMENFASSUNG Low cost hermetical plastic package Bond wires Modellierung parasitärer Effekte bei Mikrowellen-Bauteilen in PlastikGehäusen (P.E.M.) Dieser Beitrag zeigt eine neues und genaues Verfahren für die elektrische Modellierung von preisgünstigen Mirowellen-Bauteilen in Plastik-Gehäusen. Die Methode benutzt analytisch gewonnene Beziehungen und basiert auf der Analyse von gemessenen SParametern über einen entsprechenden Frequenzbereich. Diese Lösung gibt eine gute Übereinstimmung zwischen gemessenen und simulierten S-Parametern für Bauteile in Plastik-Gehäusen, demonstriert an den Ergebnissen für PHEMTs bis zu 26.5 GHz und billigen LNAs bis zu 6GHz. SOMMAIRE Modéliser les effets parasites des dispositifs micro-ondes en boîtier plastique (P.E.M.) Cet article montre une technique nouvelle et précise de modélisation électrique pour des dispositifs micro-ondes en boîtier plastique à prix réduit. La méthode emploie des expressions évaluées analytiquement, et est basée sur l’analyse des paramètresS mesurés dans une gamme de fréquence appropriée. L’approche produit une bonne correspondance entre les paramètres-S mesurés et simulés pour des dispositifs en boîtier plastique. Les résultats ont été démontrés pour des dispositifs PHEMTS jusqu’à 26.5GHz et pour les LNA à faible coût jusqu’à 6GHz. MMIC (die) External pads o meet the ever-increasing demands of today’s communications systems, die technologies such as silicon FET (including SiGe) and GaAs are being used, either separately or combined. In this way, monolithic microwave GaAs ICs (MMICs) are usually used in wireless, airborne and space applications. A few years ago, only two options were possible for the microwave designers: hybrid circuitry using unpackaged MMICs directly bonded to the circuit, or expensive ceramic hermetically packaged MMICs. Advances in packaging technology during the last decade have made it possible for plastic packages to be used at RF and microwave frequencies, typically at L-band (0.39-1.55GHz) and S-band (1.55-5.2GHz), and different authors have studied these applications [1-2]. At higher frequencies, parasitic elements make the use of this type of packaging difficult, and electromagnetic theory, including methods of moments or finite differences, must be applied [3]. For space applications, plastic packages appear as a very interesting implementation option given the important associated mass and size reduction, and several authors have studied the effects of operating in space such as outgassing, thermal effects and reliability [4]. On T Figure 1(a): Schematic diagram of a SOT-23 plastic package, showing its internal parts the other hand, the cost of these plastic packaged MMICs is considerably lower than that of ceramic ones, because they use industrial standard processes to manufacture them. Figure 1 shows a schematic section of a standard hermetic plastic SOT-23 package showing its internal parts. Brown and Hiller [5] have modelled this package for microwave diodes up to 10GHz. However, designing MMICs for use in such packages is difficult due to the poor grounding characteristics of the elevated paddle (MMIC ground), and also to the lack of generally applicable circuit models for the package. This difficulty is exacerbated for designs at frequencies higher than 10GHz, and for packages with a great number of pins. The purpose of this paper is to show the accurate modelling of these effects, in order to use low cost plastic encapsulated microcircuits (PEM) at higher frequencies (up to Ku Band). The results shown in this paper are focused on two types of plastic packaged CFY77-08/10 PHEMT devices from the Infineon foundry. These transistors are low noise (0.8 and 1dB respectively) small signal devices, usually used for front- Microwave Engineering ● May 2001● www.mwee.com 48 PACKAGE MODELLING Packaged device Packaged device CIn-Out Cpgd Lpd Rpd Gate Die device Cpg Rpd Lpd LpIn Drain In RpIn Die device CpIn Cpd LpOut Out CpOut Ground Source end amplifiers up to 20GHz and for DBS down-converters in die form (without package). Both devices use the same plastic package, designated by the foundry as MW-4. Figure 1(b) shows the electrical diagram used to model such package. The same technique has been used for modelling commercial plastic packaged LNAs from the Agilent Technologies and Mini-Circuit foundries up to 6GHz with very good results. The electrical model used for these amplifiers is shown in Figure 1(c). One of the main objectives in the characterisation of MMIC packages involves accurately determining the values of parasitic elements - loss resistance, capacitance and inductance for each pad - either theoretically or experimentally. This data can be used to describe an equivalent circuit that explains the electrical behaviour of PEM devices. At microwave frequencies these parasitic elements mask the electrical characteristics of die devices and the connections between package pins and chips begin to behave as transmission lines rather than as simple wire connections [6-7]. Parasitic capacitances, inductances and resistances, such as pin-to-pin capacitance, as well as wire inductance and resistance, become significantly higher. For the different plastic packaged devices investigated here, parasitic elements are typically of the order of pF, nH, and m for the capacitances, inductors and resistances respectively. This paper shows a new and accurate electrical small signal modelling technique called DICOMPAK, developed by the authors for low cost plastic encapsulated devices. In order to summarise, system configurations, as well as the hardware and software used to make laboratory measurements possible, will not be discussed. On the other hand, some high performance tools (boxes, chip carriers and boards) specially developed to measure the devices under study have are discussed. Experimental results for the measurements of RpOut scattering matrix parameters and using, if necessary, optimisation algorithms to minimise the error function, it can be used to finally compute a unique set of parasitic values. To make the electrical characterisation of these parasitic elements possible, it is necessary to have the same type of component, either packaged or unpackaged dies, in order to make the necessary measurements of the device under both conditions. Figure 1b (above left) and 1c (above right): Electrical model used for the characterisation of (a) CFY77-08/10, and (b) Agilent MODAMP devices in MW-4 plastic packages the different types of devices are also be presented. The DICOMPAK technique The DICOMPAK method uses the scattering parameters measured at different bias points, under the hypothesis that the parasitic elements do not change with bias because of the plastic packages. This technique can be applied in two different forms called DICOMPAK I and DICOMPAK II. The intrinsic equivalent circuit at each bias point of the active circuits has been computed using conventional techniques introduced by Dambrine [8] and later modified by our group [9]. DICOMPAK II The DICOMPAK II technique is very similar to the DICOMPAK I. The main difference between the two techniques is that DICOMPAK II uses only the measured scattering matrix from the packaged device, under the assumption that all parasitic elements are null at the first iteration. Afterwards, using an optimisation algorithm and an iterative method, the plastic parasitic extrinsic elements are computed using the variance of the intrinsic elements. Values of the parasitic elements are updated in order to minimise the error vector e using the sequential quadratic programming (SQP) method [10]. A computer program using the flowchart shown in Figure 2 has been written using MATLAB [11]. At the moment a powerful version of this method is being developed using Microsoft Visual BASIC 6.0 [12]. DICOMPAK l The DICOMPAK I algorithm is based on the measurement of the scattering parameters at two or three different bias points for the same type of component, packaged and unpackaged die. It is assumed that both devices are identical during the whole characterisation process, and that the plastic package does not vary with the bias point. Parasitic elements at these bias points can be evaluated by a conventional de-embedding process. By comparison between modelled and measured Microwave Engineering ● May 2001● www.mwee.com Table 1: Results obtained applying the DICOMPAK-I technique to the CFY77-08 PARASITIC ELEMENTS FOR CFY77-08 DEVICE Resistances () Inductances (nH) Capacitances (pF) Rpg= 3.53 Lpg= 0.608 Cpg= 0.235 Rpd= 15.5 Lpd= 0.630 Cpd= 0.252 - - Cpgd= 0.00076 50 PACKAGE MODELLING Extraction of parastic elements using DICOMPAK technique [S]Unpak bias1[S]Unpak bias 2 [S]Unpak bias3 DICOMPAK-I of them use the die model MSA-0600 manufactured by Agilent Technologies. The 7-element electrical model shown in Figure 1(c) has been selected in order to characterise the parasitic effects introduced by the plastic package all types of plastic and ceramic packages of this family of amplifiers. Table 3 shows the results obtained by the application of the DICOMPAK techniques to these devices. Figures 4(a) and 4(b) show the comparison between modelled and measured scattering parameters for a plastic package MSA-686 device. Figures 5(a) and 5(b) show the same comparison for a ceramic package MSA-670 device. In both cases, a very good fit is observed. Figure 2: Flowchart of the DICOMPAK technique. DICOMPAK-II Type of technique? All parasitic elements are set to zero at the first iteration. Compute initial estimation of the values of plastic packaged parastic elements for 3 bias New values of parastic elements [S]Unpak-modeled Optimization process [S]Pak-modeled No [S]Pak-modeled=[S]Pak-measured? Yes End The 7-element electrical model shown in Figure 1(b) has been selected in order to characterise the parasitic effects introduced by the plastic package of devices presented in this paper. Table 1 shows the results obtained by the application of the above mentioned techniques to a PHEMT device CFY77-08 from Infineon. Infineon CFY77 PHEMT devices In order to validate the electrical model developed for the plastic package, measured scattering parameters of the packaged device have been compared with measurements of the same device without packaging and the addition of the electrical model extracted for the capsule. This comparison offers good agreement for different devices. As an example, Figure 3(a) and Figure 3(b) show the results for the CFY77-08 device, biased at Vds=2V, Vgs=-0.1V, and Id=15mA up to 26.5GHz. silicon bipolar MMIC process which utilises self-alignment, ion implantation and gold metallisation to achieve excellent uniformity and reliability. This characteristic is enough for operation at L- and S-bands for this kind of amplifier. In our study we have measured different types of devices: die devices, three types of plastic packaged devices - SOT-143, 85mil (2.16mm) model and 86mil (2.18mm) model - and a ceramic packaged device - 70mil (1.79mm) package model. This 70mil device has been studied in order to evaluate the differences between plastic and ceramic packaged versions, and to verify if the DICOMPAK technique is suitable for application to ceramic packaged devices. This type of amplifier with different plastic packages is commercialised by Mini-Circuits. Therefore the electrical model developed for this set of PEM devices is valid for both brands of amplifiers. Table 2 shows the cross-reference between Agilent part numbers and those of Mini-Circuits. All Agilent Modamp and Mini-Circuits devices The MODAMP MSA series amplifier is fabricated using a 10GHz fT and 25GHz fMAX Table 2: Cross reference between Agilent MODAMP and Mini-Ciruits devices, using MSA-0600 die Validation AGILENT PART NUMBER MINI-CIRCUITS PART NUMBER Conclusions A novel method of extracting the electrical values of parasitic elements from plastic packaged devices has been presented, along with experimental results for commercial plastic-packaged PHEMTs . The method could easily be generalised for other MMIC PEM devices, and has been tested for several different microwave packaged GaAs MESFET and HEMT transistors. Furthermore, it has now been extended to MMIC packaged devices with a large number of pins. As a conclusion of this work, several different models for plastic packaged devices have been developed using the 7element custom model. The models that have been developed work very well up to 3GHz in terms of scattering parameters and figures of merit (FOM), for the economy package SOT-143. For 85/86mil plastic packages, the results are very close to the equivalent 70mil ceramic package up to 6GHz. For Infineon devices, the model has excellent performance up to the Ku band and beyond. As a consequence of this study, it can be stated that the electrical model works reasonably well for AgilentMODAMP and Mini-Ciruits devices up to 6GHz, more than achieving the frequency targets of their applications, which are usually centered at L- and S-bands. However, the PACKAGE TYPE PACKAGE OUTLINE MSA-0685 MAR-6 Plastic 85mil MSA-0686 MAR-6SM Plastic 86mil MSA-0611 VAM-6 Plastic SOT-143 MSA-0670 - Ceramic 70mil MSA-0600 - Die None Microwave Engineering ● May 2001● www.mwee.com PACKAGE MODELLING 53 MODFET MEAS MODFET EE D F F F F E MEAS BB D C S11 S22 0.2 AA C 0.5 1 2 S21 5 A FF 1 EE D D A 2 C C 3 4 5 6 B Frequency [GHz]: 0.5-26.5 Frequency [GHz]: 0.5-26.5 study made here is not comprehensive enough to develop a general purpose model for the plastic packages studied. Furthermore, an extension of the model must be developed in the future to make possible the use of the model at higher frequencies. In summary, the possible solutions to higher frequency plastic packages are: 1) To extract a new set of values for the model by imposition of a best fitting in the frequency band of interest between measured and modelled scattering parameters. 2) To develop a non-linear model for plastic packages in order to increase the validity bandwidth of the model, using the nonlinear techniques developed by us [13]. 3) To develop a new model taking into account second order effects like the increase of temperature and moisture level of the plastic package during operation. 4) To repeat this study for another family of devices (GaAs MESFET, HEMTs, and Figure 3a (above left) and 3b (above right): Comparison between the measured and modelled (a) S11 and S22, (b) S21 parameters for the Infineon PHEMT transistor CFY77-08 GaAs MMICs amplifiers) with the same packages, in order to generalise the models developed within this work, and in order to see if the behaviour of these new packaged devices is similar to the behaviour presented by the devices studied here. Acknowledgments This work has been supported partially by ESA-ESTEC project contract No. 161487 and Tecnologías de Telecomunicaciones y de la Información (TTI). wireless communication applications."1998 Radio Frequency Integrated Circuits (RFIC) Symposium 98. (1998 [RFIC]): 127-130. [2] D.R.Green, J.P. Beccone and R.B. Crispell. "Packaging Requirements for High Volume Wireless Communications." 1992 MTT-S International Microwave Symposium Digest 92.3 (1992 Vol. III [MWSYM]): pp.15011501. [3] H.-Y. Lee. "Wideband Characterisation of a Typical Bonding Wire for Microwave and Millimeter-Wave Integrated Circuits." 1995 Transactions on Microwave Theory and Techniques 43.1 (Jan. 1995 [T-MTT]): pp.63-68. [4] B. Johnson and V. Verma. "Reability assessment of fielded plastic and hermetically packaged microelectronics". IEEE Transactions on Reability, vol 45, No.1, March 1996. References [1] V. Krishnamurthy, E. Balch, K. Durocher, J. Rose, R. Saia, D. Lester and D. Sherwood. "Plastic microwave multi-chip modules for Table 3: Results obtained applying the DICOMPAK II technique to the AgilentMODAMP amplifier series PARASITIC ELEMENTS OF MSA-600 SERIES Model Package MSA-0611 SOT-143 MSA-0685 85mil MSA-0686 86mil Model MSA-0670 Package 70mil - Plastic Package Resistances () RpIN=3.38 RpOUT=13.13 RpIN=5.37 RpOUT=6.52 RpIN=4.70 RpOUT=7.64 - Ceramic Package Resistances () RpIN=1.78 RpOUT=1.90 - Inductances (nH) LpIN=0.934 LpOUT=0.731 LpIN=0.455 LpOUT=0.485 LpIN=1.059 LpOUT=1.047 - Inductances (nH) LpIN=0.328 LpOUT=0.327 Capacitances (pF) CpIN=0.053 CpOUT=0.320 CpIN-OUT=0.264 CpIN=0.221 CpOUT=0.116 CpIN-OUT=0.024 CpIN=0.002 CpOUT=0.116 CpIN-OUT=0.192 Capacitances (pF) CpIN=0.291 CpOUT=0.113 CpIN-OUT=0.182 Microwave Engineering ● May 2001● www.mwee.com PACKAGE MODELLING 54 MODFET MODFET MEAS MEAS ? ? EE D B D ? O DD E E OO S11 DD BB 0.8 S22 0.5 B B A1 FA ?? 2 ? 3 ? ?? F C C 2D 4 6 8 10 Frequency [GHz]: 0.88-1.6 Frequency [GHz]: 0.88-1.6 [5] B. Brown and G. Hiller. "Circuit Models for Plastic Packaged Microwave Diodes." 1996 MTT-S International Microwave Symposium Digest 96.3 (1996 Vol. III [MWSYM]): pp.1779-1782. [6] S.-K. Yun and H.-Y. Lee. "Parasitic Impedance Analysis of Double Bonding Wires f or High-Frequency Integrated Circuit Packaging." 1995 Microwave and Guided Wave Letters 5.9 (Sep.1995 [MGWL]): pp.296-298. [7] C. Amrani, M. Drissi, V. Fouad Hanna and J. Citerne. "Packaging and Interconnection Mutual Coupling Effects in Planar Structures and Discontinuities." 1993 MTT-S International Microwave Symposium Digest 93.2 (1993 Vol II [MWSYM]):pp. 843-846. [8] G. Dambrine, A.Cappy, F. Heliodore, E. Playez. "A new method for determining the FET small-signal equivalent circuit". IEEE Transactions on MTT vol 36, nº 7, July 1988. B Figure 4a (above left) and 4b (above right): Comparison between the measured and modelled (a) S11 and S22, (b) S21 parameters for the Infineon PHEMT transistor MSA-686 [9] J.M. Zamanillo, T. Fernández, Y. Newport, A. Mediavilla, A.Tazón. "Wideband Technique Models P-HEMT and GaAs MESFETs". Microwaves & RF, pp. 60-68,Vol 35, No.2 Feb. 1996. [10] J.M. Zamanillo, C. Pérez Vega and A. Mediavilla "Modelling Parasitic Effects of Plastic Encapsulated Microwave Devices". Microwave Symposium 2000 (MS’2000) Proceedings, pp.39-42, Tetouan , May 2000. Figure 5a (below left) and 5b (below right): Comparison between the measured and modelled (a) S11 and S22, (b) S21 parameters for the Infineon PHEMT transistor MSA-670 MODFET MODFET MEAS MEAS [11] Using MATLAB Version 5. By Mathworks Inc. June 1997. [12] Visual Basic™ 6.0 User´s Guide. Microsoft Corpration 1998. [13] T. Fernández, Y. Newport, J.M. Zamanillo, A. Mediavilla, A. Tazón "Extracting a Bias Dependent Large Signal MESFET Model from Pulsed I/V Measurements". IEEE Transactions on MTT vol 44, pp.372-378, March 1996. AUTHOR INFORMATION Group of Electromagnetism Communications Engineering Department1 Group of Microwaves and Communication Systems2 ETSII y Telecommunication, University of Cantabria, Av. de los Castros s/n 39005 Santander, SPAIN. Tel:+34 942-201391 Fax:+34 942-201488 jose.zamanillo@unican.es BB ? ? ? DD S110.8 S22 ?? ? 0.8 00 00 BB DD 1 ?? ?? 2 3 D ?2 ?? 4 6 8 10 ? Frequency [GHz]: 0.88-1.6 Frequency [GHz]: 0.88-1.6 Microwave Engineering ● May 2001● www.mwee.com