Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration IZM

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Investigation and Modeling of Etching Through Silicon Carbide Vias (TSiCV) for SiC Interposer and Deep SiC Etching for Harsh Environment MEMS by DoE

2022 , Mackowiak, Piotr , Erbacher, Kolja , Schiffer, Michael , Manier, Charles-Alix , Töpper, Michael , Ngo, H.-D. , Schneider-Ramelow, M. , Lang, K.-D.

This article presents prime results on process development and optimization of dry etching of silicon carbide (SiC) for via formation and deep etching for SiC-based microsystems. The investigations and corresponding results of the process developments enable the first realization of a full SiC-based technological demonstrator composed of a SiC-interposer with a flip chip mounted deep etched micro electromechanical system (MEMS) SiC Device. By optimizing the process, etch depth of 200 μm with an etch rate of up to 2 μm /min can be achieved for via etching. In addition, a design of experiments (DoEs) with a total of 29 experiments with seven factors was done to characterize the deep etching of large areas into the SiC. Hereby, vertical sidewalls with low micromasking, low microtrenching and an etch rate of up to 4 μm /min could be achieved. The findings and optimized processes were implemented to develop on the one hand a 200- μm -thick SiC interposer with copper metallization. On the other hand, a SiC-MEMS Device was manufactured with a deep etched cavity in SiC bulk wafer forming by the end a 50- μm thin membrane. The results demonstrate the ability of etching monocrystalline SiC with a high etch rate, enabling new fundamental topologies/structures and packaging concepts for harsh environments MEMSs and high-power electronics. The developed etching technologies demonstrate and enable various applications for 3-D Integration with wide bandgap substrates taking advantage of the superior electrical and mechanical properties of SiC.

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Heavy copper wire-bonding on silicon chips with aluminum-passivated Cu bond-pads

2016 , Gross, David , Haag, S. , Reinold, M. , Schneider-Ramelow, M. , Lang, K.-D.

Thick electroplated Cu bond-pads have recently been shown to allow for heavy Cu wire-bonding on silicon power devices. The Cu surface oxides present on these pads are a major concern for the bonding process and for a sufficiently stable bond formation. They currently have to be removed after the die-attach and prior to wire-bonding. To avoid such removal, the application of a thin Al coating on the Cu bond-pads is investigated for its passivating ability and its suitability for the bonding process.

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Heterogeneous integration of a miniaturized W-band radar module

2015 , Becker, Karl-Friedrich , Georgi, L. , Kahle, R. , Koch, M. , Voges, S. , Brandenburger, F. , Höfer, J. , Ehrhardt, C. , Zech, C. , Baumann, B. , Huelsmann, A. , Grasenack, A. , Reinold, S. , Kleiner, B. , Braun, T. , Schneider-Ramelow, M. , Lang, K.-D.

For radar applications, the W-band frequency range (75 - 110 GHz) is a good candidate for high-resolution distance measurement and remote detection of small or hidden objects in distances of 10 cm to >> 20 m. As electromagnetic waves in this frequency range can easily penetrate rough atmosphere like fog, smoke or dust, W-band radars are perfectly suited for automotive, aviation, industrial and security applications. Additional benefit is that atmosphere has an absorption minimum at 94 GHz, so relative small output power is sufficient to achieve long range coverage. By combining and enhancing knowledge from the disciplines of heterogeneous integration technology and compound semiconductor-technology, the Fraunhofer Institutes IAF, IPA and IZM developed a miniaturized and low cost 94 GHz radar module. Result of this approach is a highly miniaturized radar module built using a modular approach. The radar components are mounted on a dedicated RF-NF-hybrid PCB while the signal processing is done on a separate board stacked below. This hybrid RF-module is combined with highly integrated digital processing PCB via micro connectors in a way that the radar system and an adapted conical HDPE-lens fit into an aluminum housing of 42x80x27 mm³ with a weight of only 160 grams for the whole module. The paper will describe the technological basis for such a frequency modulated continuous wave [FMCW] W-band radar module and describe in detail the technological features that enabled the assembly of such a miniaturized but high-performance system. The module yields an evaluated distance measurement accuracy of 5 ppm (5 mm deviation per meter target distance) while its low weight and small dimensions pave the way for a variety of new applications, including mobile operation.

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Transfer molding technology for smart power electronics modules: Materials and processes

2012 , Becker, K.-F. , Joklitschke, D. , Braun, T. , Koch, M. , Thomas, T. , Schreier-Alt, T. , Bader, V. , Bauer, J. , Nowak, T. , Bochow-Ness, O. , Aschenbrenner, R. , Schneider-Ramelow, M. , Lang, K.-D.

In recent years, within power electronics packaging, there has been a trend toward compact power electronics modules for automotive and industrial applications, where a smart integrated control unit for motor drives is replacing bulky substrates with discrete control logic and power electronics. Most recent modules combine control and power electronics, yielding maximum miniaturization. Transfer molding is the method of choice for cost-effective encapsulation of such modules due to robustness of the molded modules and moderate cost of packaging. But there are challenges with this type of package. Typically, these packages are asymmetric, and thus a substrate with single sided assembly is overmolded on the component side and the substrate backside is exposed, providing a heat path for optimized cooling. This asymmetric geometry is prone to yielding warped substrates, preventing optimum thermal contact to the heat sink and also putting thermomechanical stress on the encap sulated components, possibly reducing reliability. Such packages are truly heterogeneous, combining power ICs, wire bonds, SMDs, control ICs, substrate, and lead frame surfaces. As a result, the encapsulant used needs to adhere sufficiently to all surfaces present. Additionally, those packages need to operate at elevated temperatures for extended time periods, for example, at 150°C for 2000 h and more, so high thermal stability is of prime importance. Within this paper, a reference application is described integrating power and control logic inside a lead frame based molded package. Taking into account the challenges mentioned above, a detailed description of material selection for this module will be given, including material analysis, such as rheology, reactivity, and change in εr; and thermomechanical properties, in initial stage as f(t,T) and after media storage. Process development tools for module molding are used to ensure manufacturability and usability.

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Development and characterization of a novel low-cost water-level and water quality monitoring sensor by using enhanced screen printing technology with PEDOT:PSS

2020 , Wang, B. , Baeuscher, M. , Hu, X. , Woehrmann, M. , Becker, K. , Juergensen, N. , Hubl, M. , Mackowiak, P. , Schneider-Ramelow, M. , Lang, K.-D. , Ngo, H.-D.

A novel capacitive sensor for measuring the water-level and monitoring the water quality has been developed in this work by using an enhanced screen printing technology. A commonly used environment-friendly conductive polymer poly(3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) for conductive sensors has a limited conductivity due to its high sheet resistance. A physical treatment performed during the printing process has reduced the sheet resistance of printed PEDOT:PSS on polyethylenterephthalat (PET) substrate from 264.39 W/sq to 23.44 W/sq. The adhesion bonding force between printed PEDOT:PSS and the substrate PET is increased by using chemical treatment and tested using a newly designed adhesive peeling force test. Using the economical conductive ink PEDOT:PSS with this new physical treatment, our capacitive sensors are cost-efficient and have a sensitivity of up to 1.25 pF/mm.

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High viscosity paste dosing for microelectronic applications

2016 , Thomas, Tina , Voges, S. , Braun, T. , Raatz, S. , Kahle, R. , Becker, K.-F. , Koch, M. , Fliess, M. , Bauer, J. , Schneider-Ramelow, M. , Lang, K.-D.

Today's microelectronics packaging especially for SiPs relies on the processing of a wide variety of materials. Materials for components, for substrates, for contact materials (solder & adhesives) and encapsulants. Most materials are processed as bulk material but precision dosing of pastes is key to many assembly processes. Examples are dosing of solder paste, typically done by stencil printing, Underfilling for Flip Chip encapsulation, typically done by dispensing or jetting, or Glob Top encapsulation of Chip on Board assemblies, where also dispensing is the typical process. When working with those paste materials, viscosity is one of the key parameters for processing, and viscosities too high do not allow dosing of the materials, not even to transport the material from a reservoir to the dosing head, which may be a simple needle or a jet valve. [i, ii] To overcome this obstacle, i.e. to dose materials of high viscosity precisely and homogeneously from a syringe to the dosing head, a research program has been set up, where Vermes microdispensing as a valve manufacturer and TU Berlin/IZM as a research institute are cooperating. TU Berlin is working on material rheology effects and flow models; Vermes is researching valves modifications and material flow path optimization. Core of the research is to find methods that allow a reduction of paste viscosity without leading to irreversible changes in the material, as would be the case when simply applying heat to the paste. As reference process for material dosing, FO-WLP has been chosen, materials selected for the investigations are GlobTop dam and fill material and liquid molding compound - using both rheological experiments as well as actual material dosing and processing. Apart from temperature, mechanical and ultrasonic stimulation of the material have been evaluated to achieve optimized dosing of high viscous pastes, As a result, a first description of paste behavior during processing is given, being the basis for future work towards homogeneous precision dosing of high viscous pastes for microelectronic applications.

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Correlation between mechanical properties and microstructure of different aluminum wire qualities after ultrasonic bonding

2015 , Broll, Marian Sebastian , Geißler, U. , Höfer, J. , Schmitz, S. , Wittler, O. , Schneider-Ramelow, M. , Lang, K.-D.

Three different heavy aluminum wire qualities were investigated regarding their microstructural evolution after ultrasonic bonding by electron backscatter diffraction and nanoindentation. The results complete the findings of our recent research regarding the effect of bonding mechanisms on the wire bond microstructure and its local mechanical properties. Local elastic-plastic material parameters of the bonded wires were approximated on the basis of the elastic anisotropy of crystals and a correlation between hardness and stress.

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A numerical study on mitigation of flying dies in compression molding of microelectronic packages

2019 , Dreissigacker, M. , Hoelck, O. , Bauer, J. , Braun, T. , Becker, K.-F. , Schneider-Ramelow, M. , Lang, K.-D.

Compression molding with liquid encapsulants is a crucial process in microelectronic packaging. Material properties of highly filled systems of reactive epoxy molding compounds depend on process conditions in a complex manner, such as shear-thinning behavior, which is superimposed by a time- and temperature-dependent conversion rate, both strongly affecting viscosity. The focus is set on forces exerted on individual dice during encapsulation in fan-out wafer-level packaging (FOWLP). The presented framework consists of an analytical approach to calculate the melt front velocity and simulations carried out to capture the nonlinear kinematics, chemorheology, and to extract forces exerted on individual dice. It offers separate evaluation of pressure and shear contributions for two cases, 0° and 45° between the dice' frontal area and the melt front. Process parameters, such as compression speed, thus cycle time, and process temperature, are determined to keep the forces on the dice below the critical level, where drag forces exceed adhesive forces. As a result, process parameters are determined to minimize flying dice and thereby maximize yield. The approach is easily transferable to arbitrary geometries and is therefore well suited to face the challenges that come with the current efforts toward the transition from FOWLP to larger substrates.

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In-situ measuring module for transfer molding process monitoring

2016 , Kahle, Ruben , Braun, T. , Bauer, J. , Becker, K.-F. , Schneider-Ramelow, M. , Lang, K.-D.

While Moore's Law is slowing down heterogeneous integration and System-in-Package (SiP) are taking up the challenge towards further miniaturization. To ensure reliability of these packages often encapsulation by transfer molding is used - providing a highly productive and cost effective device housing. Though transfer molding is the dominant process for microelectronics encapsulation, the process details are typically not accessible directly but only via machine settings. To understand more of the mold process further research needs to be conducted to get inside information from the process. A sensor based system was developed to in-situ measure transient material data and process parameters. The temperature of the tool and melt front, the cavity pressure and cure related dielectric material data was measured with a first prototype. Summarized this paper presents the development of a sensor based system to in-situ measure characteristic material properties and process parameters in a transfer mold machine. The in-situ measurement tool allows a live documentation, optimization and knowledge extension of transfer mold processes parallel to FEM simulation and external measuring like DSC analysis. The sensor approach can lead to material driven self-adjusting transfer mold machines with an economized process.

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The influence of liners with Ti, Ta or Ru finish on thin Cu films

2014 , Gross, David , Haag, S. , Schneider-Ramelow, M. , Lang, K.-D.

The influence of the different liner material stacks Ti-N/Ti, Ta-N/Ta and Ta-N/Ru on the microstructure of 1 mm thick sputtered Cu films is examined prior to and after annealing. It is shown that the liner has an impact on the crystallographic orientation distribution of the Cu grains and seriously affects the defect density in the Cu films. The measured Cu resistivity shows a strong dependence on the microstrain.

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