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Circuit-Board-Integrated TransformersDesign and Manufacture
R. Matz1, T. Rabe2, J. Töpfer3, S. Ziesche4
1 Siemens Corporate Technology, D-81730 Munich, Germany (retired)
2 Federal Institute for Materials Research and Testing, D-12203 Berlin, Germany
3 Ernst Abbe University of Applied Sciences, D-07745 Jena, Germany
4 Fraunhofer Institute for Ceramic Technologies and Systems IKTS, D-01277 Dresden, Germany
received November 5, 2019, received in revised form Januar 7, 2020, accepted Januar 17, 2020
Vol. 11, No. 1, Pages 44-61 DOI: 10.4416/JCST2019-00071
Abstract
Transformers couple two sections of a circuit by electromagnetic induction. They are widely used to either transform alternating voltage levels or to transmit power or signals across galvanic isolation. Both of these functions are essential for the operation of sensors and controllers. Covering all aspects from idea to circuit performance and from design to manufacture, this paper presents the first comprehensive description of the making of miniaturized, rugged, up-to-100 W transformers for embedding into multilayer circuit boards. For circular coils, the well-manageable Ampere-Laplace law is shown to yield reliable designs, predicting correctly the performance of manufactured hardware. This enables fast design without lengthy finite element modelling. In the low-power linear regime, basic relations describe how the device's characteristics evolve from the material properties and device structure. While scattering parameters are useful for the analysis of isolated transformers with their intrinsic parasitics, the interaction with the components of the final circuit and the aspects of power and efficiency are addressed by chain matrixes.
While these design rules are similar for multilayer boards of different material (like epoxy, Teflon, ceramics), the manufacturing of ceramic board transformers is considered here in detail. Low-temperature-cofired ceramic (LTCC) boards being sintered at 900 °C are particularly suited for harsh environments with chemical or thermal stress as frequently found at sensor positions. The transformer performance usually benefits from or even requires an integrated ceramic core of higher permeability, a ferrite, to shape the magnetic flux. Methods to sinter ferrites inside a dielectric ceramic multilayer and to measure their performance are therefore described in detail. As the sintering behaviour of dielectric and magnetic ceramics differs considerably, their simultaneous sintering is challenging. However, the sintering temperatures of the useful MnZn and NiZnCu ferrites can be lowered to that of the dielectric material with only moderate loss of permeability by glass additives. Furthermore, thermal mismatch between materials causes catastrophic failure or at least stress and loss of magnetic performance during cooling to room temperature after sintering. This is avoidable by either adjusting the thermal expansion coefficient of the ferrite or by enclosing the ferrite between stress-releasing separation layers. We present the state of the art in materials development according to the first approach as well as fully functional devices made with the second technique.
Other applications not directly addressed but well related to this work are characterized by low load resistance in relation to the coil resistance of the transformer. Efficient power transmission then requires that technological solutions are applied to achieve the lowest possible resistive loss inside the coils by an enlarged conductor cross-section. As this is particularly challenging for LTCC boards, a technique is discussed to fabricate conductor traces with a thickness larger than their width.
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Keywords
Multilayer ceramic technology, LTCC, transformer
References
1 Jiang, H., Wang, Y., Yeh, J.L.A., Tien, N.C.: On-chip spiral inductors suspended over deep copper-lined cavities, IEEE Trans. Microwave Theory Techn., 48, 2415 – 2423, (2000).
2 Zou, J., Liu, C., Trainor, D.R., Chen, J., Schutt-Ainé, J.E., Chapman, P.L.: Development of three-dimensional inductors using plastic deformation magnetic assembly (PDMA), IEEE Trans. Microwave Theory Techn., 51, 1067 – 1075, (2003).
3 Rais-Zadeh, M., Laskar, J., Ayazi, F.: High performance inductors on CMOS-grade trenched silicon substrate, IEEE Trans. Comp. Pack. Technol., 31, 126 – 134, (2008).
4 Karmazin, R., Dernovsek, O., Ilkov, N., Wersing, W., Roosen, A., Hagymasi, M.: New LTCC-hexaferrites by using reaction bonded glass ceramics, J. Eur. Ceram. Soc., 25, 2029 – 2032, (2005).
5 Matters-Kammerer, M., Mackens, U., Reimann, K., Pietig, R., Hennings, D., Schreinemacher, B., Mauczok, R., Gruhlke, S., Martiny, C.: Material properties and RF applications of high k and ferrite LTCC ceramics, Microelectr. Relia., 46, 134 – 143, (2006).
6 Macrelli, E., Romani, A., Wang, N., Roy, S., Hayes, M., Paganelli, R.P., Tartagni, M.: Design and fabrication of a 29µH bond wire micro-transformer with LTCC magnetic core on silicon for energy harvesting applications, Proc. Eng., 87, 1557 – 1560, (2014).
7 Lahti, M., Lantto, V., Leppävuori, S.: Planar inductors on an LTCC substrate realized by gravure-offset-printing technique, IEEE Trans. Comp. Pack. Technol., 23, 606 – 610, (2000).
8 Dick, C.P., Hirschmann, D., Plum, T., Knobloch, D., De Doncker, R.W.: Novel high frequency transformer configurations – amorphous metal vs. ferrites. In: Proc. 39th Annual IEEE Power Electronics Specialists Conf. (PESC), 4264 – 4269. Technical University of Athens, Rhodes, Greece, (2008).
9 Ludwig, M., Duffy, M., O'Donnell, T., McCloskey, T.P., Ó Mathùna, S.C.: PCB integrated inductors for low power DC/DC converter, IEEE Trans. Power Electr., 18, 937 – 945, (2003).
10 Waffenschmidt, E.: Design and application of thin, planar magnetic components for embedded passive integrated circuits. In: Proc. 35th Annual IEEE Power Electronics Specialists Conf. (PESC), 4546 – 4552. Aachen, Germany, (2004).
11 Tada, N., Tabuchi, T., Ikezaki, H.: Inductor part and method of producing the same. European Patent Application EP 1 367 611 A1, (2002).
12 Barth, S., Bechtold, F., Müller, E., Mürbe, J., Töpfer, J.: Low sintering Ni-Cu-Zn ferrite tapes for LTCC integrated inductors. In: Proc. 1st IMAPS/ACerS Int. Conf. Ex. Ceramic Interconnect and Ceramic Microsystems Technol. (CICMT). Baltimore, USA, (2005).
13 Hahn, R., Sommer, G., Dörr, I., Schwerzel, S., Reichl, H.: Design of integrated inductances based on ferromagnetic LTCC layers, Ad. Microelectr., 33, 8 – 16, (2006).
14 Lim, M.H., Liang, Z., van Wyk, J.D.: Low profile integratable inductor fabricated based on LTCC technology for microprocessor power delivery applications, IEEE Trans. Comp. Pack. Technol., 30, 170 – 177, (2007).
15 Lim, M.H., van Wyk, J.D., Lee, F.C., Ngo, K.D.T.: A class of ceramic-based chip inductors for hybrid integration in power supplies, IEEE Trans. Power Electr., 23, 1556 – 1564, (2008).
16 Slater, C., Maeder, T., Ryser, P.: Fabrication and test of high-temperature ceramic transformer, Solid State Phenomena, 216, 233 – 238, (2014).
17 Lin, Y.-C., Gabler, F., Tsai, Y.-C., Tanaka, S., Gessner, T., Esashi, M.: LTCC-based three dimensional inductors with nano-ferrite embedded core for on-chip tunable RF systems. In: Proc. 17th Int. Conf. on Solid-State Sensors, Actuators and Microsystems, University of Barcelona, Barcelona, Spain, (2013).
18 Maric, A., Radosavljevic, G., Blaz, N., Zivanov, L.: Fine tuning of 3D LTCC inductor properties using combination of different ferrite and dielectric tapes, Int. J. Appl. Ceram. Technol., 12, 1034 – 1044, (2015).
19 Jao, J.C., Li, P., Wang, S.F.: Characterization of inductor with Ni-Zn-Cu ferrite embedded in B2O3-SiO2 glass, Jpn. J. Appl. Phys., 46, 5792 – 5796, (2007).
20 Lipkes, Z.: Core and coil structure and method of making the same. US patent 5 945 902, (1999).
21 Sato, T., Yokoyama, H., Yamasawa, K., Toya, K., Kobayashi, S., Minamisawa, T.: Multilayered transformer utilizing mn-zn ferrite and its application to a forward-type DC-DC converter, Electr. Eng. Jpn., 135, 1 – 8, (2001).
22 Yu, Q., Wang, H., Geng, Y., Liu, Z.: Research of LTCC NiCuZn transformer prototype. In: Proc. 6th World Congr. Intelligent Control and Automation, 5272 – 5276. Dalian University of Technology, Dalian, China, (2006).
23 Waffenschmidt, E., Jacobs, J.: Planar resonant multi-output transformer for printed circuit board integration. In: Proc. 39th Annual Power Electronics Specialists Conf. (PESC), 4222 – 4228. Technical University of Athens, Rhodes, Greece, (2008).
24 Abel, D.A.: Multi-layer transformer apparatus and method. US patent 6 198 374 B1, (2001).
25 Wahlers, R.L., Huang, C.Y.D., Heinz, M.R., Feingold, A.H., Bielawski, J., Slama, G.: Low profile LTCC transformers. In: Proc. 2002 Int. Symp. Microelectronics, 76 – 80. Denver, Colorado, (2002).
26 Slama, G.: Low-temp co-fired magnetic tape yields high benefits, Power Electr. Technol., 1, 30 – 34, (2003).
27 Lebourgeois, R., Laboure, E., Lembeye, Y., Ferrieux, J.-P.: LTCC magnetic components for high density power converter, AIP Advances, 8, 047901, (2018).
28 Matz, R.: Integration technologies for ferrites and power inductors in ceramic circuit boards. In: Ceramic Integration and Joining Technologies, 233 – 265. Ed. M. Singh, T. Ohji, R. Asthana, S. Mathur. John Wiley & Sons, New York, (2011).
29 Küpfmüller, K.: Introduction to Theoretical Electrical Engineering, in German, 10th edition, Springer, Berlin, (1973).
30 Matz, R., Götsch, D., Gossner, T., Karmazin, R., Männer, R., Siessegger, B.: Power inductors in ceramic multilayer circuit boards, J. Microelec. Elec. Pack., 5, 161 – 168, (2008).
31 Pozar, D.M.: Microwave Engineering, 2nd edition. John Wiley & Sons, New York, 211, (1998).
32 Matz, R., Götsch, D., Karmazin, R., Männer, R.: Ceramic multilayer integration of power electronic inductors, J. Ferroelec., 387, 77 – 84, (2009).
33 Ferrite type Fi328 by Sumida Corp., Tokyo, Japan; or ferrite type N27 by TDK Europe GmbH, Munich, Germany.
34 Matz, R., Götsch, D., Karmazin, R., Männer, R., Siessegger, B.: Low temperature cofirable MnZn ferrite for power electronic applications, J. Electroceram., 22, 209 – 215, (2009).
35 Ferrite type 3F4. In: Soft ferrites and accessories, data handbook. Ferroxcube International Holding B.V.
36 Nakamura, T., Okano, Y.: Low temperature sintered ni-zn-cu ferrite, J. Phys. IV, 7 C1, 91 – 92, (1997).
37 Yasuda, K., Mochizuki, Y., Takaya, M.: Multilayer ferrite chip component for growth of microelectronics. In: Proc. 8th Int. Conf. Ferrites ICF8, 1162 – 1164. Kyoto, Japan, (2000).
38 Mürbe, J., Töpfer, J.: Low temperature sintering of sub-stoichiometric ni-cu-zn ferrites: shrinkage, microstructure and permeability, J. Magn. Magn. Mater., 324, 578 – 583, (2012).
39 Mürbe, J., Töpfer, J.: Ni-Cu-Zn ferrites for low temperature firing: II. Effects of powder morphology and Bi2O3 addition on microstructure and permeability, J. Electroceram., 16, 199 – 205, (2006).
40 Jeong, J., Han, Y.H., Moon, B.: Effects of Bi2O3 addition on the microstructure and electromagnetic properties of NiCuZn ferrites, J. Mater. Sci., 15, 303 – 306, (2004).
41 Rabe, T., Naghib-zadeh, H., Glitzky, C., Töpfer, J.: Integration of Ni-Cu-Zn ferrite in low temperature Co-fired ceramics LTCC modules, Int. J. Appl. Ceram. Technol., 9, 18 – 28, (2012).
42 Hesse, J., Naghib-zadeh, H., Rabe, T., Töpfer, J.: Integration of additive-free Ni-Cu-Zn ferrite layers into LTCC multilayer modules, J. Eur. Ceram. Soc., 36, 1931 – 1937, (2016).
43 Naghib-zadeh, H., Hesse, J., Reimann, T., Töpfer, J., Rabe, T.: Effect of oxygen partial pressure on co-firing behavior and magnetic properties of LTCC modules with integrated ni-cu-zn ferrite layers, J. Electroceram., 37, 100 – 109, (2016).
44 Priven, A.: General method for calculating the properties of oxide glasses and glass forming melts from their composition and temperature, Glass Techn., 45, 244 – 249, (2004).
45 Naghib-zadeh, H., Rabe, T., Karmazin, R.: Integration of MnZn-ferrite tapes in LTCC multilayer, J. Electroceram., 31, 88 – 95, (2013).
46 Glitzky, C., Rabe, T., Eberstein, M., Schiller, W., Töpfer, J., Barth, S., Kipka, A.: LTCC-modules with integrated ferrite layers – strategies for material development and co-sintering, J. Microelec. Elec. Pack., 6, 1 – 5, (2009).
47 Rabe, T., Glitzky, C., Naghib-Zadeh, H., Oder, G., Eberstein, M., Töpfer, J.: Silver in LTCC – Interfacial reactions, transport processes and influence on ceramic properties. In: Proc. 5th CICMT, 85 – 93, Denver, Colorado. (2009).
48 Provided by Tanaka Paper Industry Corp., 1426 Tono-Machi, Mino-City, Japan 501 – 3742 (2013).
49 Bartsch, H., Albrecht, A., Hoffmann, M., Müller, J.: Microforming process for embossing of LTCC tapes, J. Micromech. Microeng., 22, 015004, (2012).
50 Bartsch, H., Geiling, T., Müller, J.: An LTCC low-loss inductive proximity sensor for harsh environments, Sens. Act. A, 175, 28 – 34, (2012).
51 Ziesche, S., Ihle, M., Eberstein, M.: High current conductors in LTCC. In: Proc. IMAPS/ACerS 8th Int. Conf. Ex. Ceramic Interconnect and Ceramic Microsystems Technol. (CICMT). Erfurt, Germany, (2012).
52 Welker, T., Gutzeit, N., Müller, J.: Enhanced heat spreading in LTCC packages utilizing thick silver tape in the co-fire process. In: Proc. 21st Eur. Microelectronics Packaging Conf. (EMPC). Warsaw Technical University, Warsaw, Poland, (2017).
53 Ihle, M., Ziesche, S., Gierth, P.: LTCC technology for active eddy current turbocharger speed sensors. In: Proc. 21st Eur. Microelectronics Packaging Conf. (EMPC). Warsaw Technical University, Warsaw, Poland, (2017).
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