Browsing by Author "Vuorinen, Vesa"

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  • Achieving low-temperature wafer level bonding with Cu-Sn-In ternary at 150 °C
    (2023-01-01) Golim, Obert; Vuorinen, Vesa; Ross, Glenn; Wernicke, Tobias; Pawlak, Marta; Tiwary, Nikhilendu; Paulasto-Kröckel, Mervi
     Letter
    In this work, a low-temperature wafer-level bonding process at 150 °C was carried out on Si wafers containing 10 µm-sized microbumps based on the Cu-Sn-In ternary system. Thermodynamic study shows that addition of In enables low-melting temperature metals to reach liquid phase below In melting point (157 °C) and promotes rapid solidification of the intermetallic layer, which are beneficial for achieving low-temperature bonding. Microstructural observation shows high bonding quality with low amount of defect. SEM and TEM characterization concludes that a single-phase intermetallic formed in the bond and identified as Cu6(Sn,In)5 with a hexagonal lattice. Mechanical tensile test indicates that the bond has a mechanical tensile strength of 30 MPa, which are adequate for 3D heterogeneous integration.
  • Acoustic emission-based prognostics of power semiconductor modules
    (2024-05-20) Leppänen, Tapio
     Sähkötekniikan korkeakoulu | Master's thesis
    In recent years, the prognostics of power semiconductor modules (PSMs) have been a subject of significant interest. Exploring acoustic emissions (AEs) as a potential early warning system for PSM failure represents a novel avenue of research. This thesis investigated the generation of AEs and evaluated whether using acoustic emission signals in the prognostics of PSMs would be viable. Previous studies have revealed that AEs primarily propagate in the solder layers, with the combined effect of electromagnetic force and thermoelastic effect being the most likely cause behind them. These findings, coupled with the finding that parameters such as cumulative acoustic emission count and energy, power spectral density, and frequency distribution can provide insight into the degradation process, offer a promising outlook for using AEs in PSM prognostics. In this study, the acoustic emissions were first measured with a new insulated-gate bipolar transistor (IGBT) module. Two IGBT modules were then aged in a power cycling test, which mainly caused bond wire fractures and lift-off. Then, the AEs of the aged devices were measured again to be compared. The sensors used included a custom-developed AE sensor package with seven resonant sensors. They can detect AEs at a few kHz range around the resonant frequency, covering the range of 50 - 250 kHz. Another sensor was also used, a commercial AE sensor with an operating frequency range of 50 - 200 kHz. The data was acquired using a double pulse tester, which applies two consecutive pulses to the IGBT. This setup ensured that the AEs were measured with a small amount of noise and that the tests were repeatable. The acquired signals were then analyzed in both time and frequency domains, and signal energy was also calculated for each pulse, providing further details. Based on the analysis, only small changes in the spectra could be detected. This indicates that AEs cannot detect bond wire fatigue reliably in the 50 - 250 kHz range. However, previous research has shown that monitoring the die attach condition would be possible in this frequency range. Therefore further research into AE-based prognostics is recommended, especially for online monitoring of die attach.
  • Analysis of UHMWPE wear particles produced in the simulation of hip and knee wear mechanisms with the RandomPOD system
    (2015) Saikko, Vesa; Vuorinen, Vesa; Revitzer, Hannu
     School of Electrical Engineering | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • LED-moduulien kokoonpano ja luotettavuus
    (2008) Kerola, Timo
     Helsinki University of Technology | Master's thesis
    The purpose of this thesis was to study inorganic LED-materials, especially InGaN and AlGaInP, and their operational principles, packaging, assembly as well as factors, which contribute to the reliability of LEDs. Also a summary of the current performance and future challenges of LED -components was made. So far the total absence of standards made especially for LEDs have slowed down the progress of LED-technology. The need for standards was evaluated and a summary of those currently under development is given. Nowadays, the reliability problems of high power LED-components tend to be package, and not chip related. Because of that, the reliability of LEDs where examined through the failure mechanisms of the package, leaving the reliability factors concerning the inner structure of the active components with less attention. Special attention was given to the thermal management and the design of first and second level packaging, which play a crucial role in the performance and reliability of light emitting devices. A probabilistic-approach-based reliability model of semiconductor light emitting devices was also given. Using this model with given initial light-emitting performance and degradation behaviour, the reliability function of the devices can be obtained. The results obtained by utilizing the model correlated well with experimental results available.
  • Biocompatible and Long-Term Encapsulation of Implantable Electronics
    (2014-10-20) Valmari, Betti
     Sähkötekniikan korkeakoulu | Master's thesis
  • Blistering mechanisms of atomic-layer-deposited AlN and Al2O3 films
    (2017-10-02) Broas, Mikael; Jiang, Hua; Graff, Andreas; Sajavaara, Timo; Vuorinen, Vesa; Paulasto-Kröckel, Mervi
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Blistering of protective, structural, and functional coatings is a reliability risk pestering films ranging from elemental to ceramic ones. The driving force behind blistering comes from either excess hydrogen at the film-substrate interface or stress-driven buckling. Contrary to the stress-driven mechanism, the hydrogen-initiated one is poorly understood. Recently, it was shown that in the bulk Al-Al2O3 system, the blistering is preceded by the formation of nano-sized cavities on the substrate. The stress-and hydrogen-driven mechanisms in atomic-layer-deposited (ALD) films are explored here. We clarify issues in the hydrogen-related mechanism via high-resolution microscopy and show that at least two distinct mechanisms can cause blistering in ALD films. Published by AIP Publishing.
  • Bonding of ceramics to silver-coated titanium—A combined theoretical and experimental study
    (2024-05) Vuorinen, Vesa; Kouhia, Reijo; Könönen, Mauno; Kivilahti, Jorma K.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    It would be very beneficial to have a method for joining of ceramics to titanium reliably. Although several techniques have been developed and tested to prevent extensive interfacial chemical reactions in titanium-ceramic systems, the main problem of the inherent brittleness of interfaces was still unsolved. To overcome this problem also in dental applications, we decided to make use of an interlayer material that needs to meet the following requirements: First, it has to be biocompatible, second, it should not melt below the bonding temperatures, and third, it should not react too strongly with titanium, so that its plasticity will be maintained. Considering possible material options only the metals: gold, platinum, palladium, and silver, fulfill the first and second requirements. To find out—without an extensive experimental testing program—which of the four metals fulfills the third requirement best, the combined thermodynamic and reaction kinetic modeling was employed to evaluate how many and how thick reaction layers are formed between the interlayer metals and titanium. With the help of theoretical modeling, it was shown that silver fulfills the last requirement best. However, before starting to test experimentally the effect of the silver layer on the mechanical integrity of dental ceramic/Ag/Ti joints it was decided to make use of mechanical analysis of the three-point bending test, the result of which indicated that the silver layer increases significantly the bond strength of the joints. This result encouraged us to develop a new technique for plating silver on titanium. Subsequently, we executed numerous three-point bending tests, which demonstrated that silver-plated titanium-ceramic joints are much stronger than conventional titanium-ceramic joints. Hence, it can be concluded that the combined thermodynamic, reaction kinetic, and mechanical modeling method can also be a very valuable tool in medical research and development work.
  • Challenges of Flexible Printed Circuit Surface Mount Assembly
    (2006) Koivunen, Mikko Antero
     Helsinki University of Technology | Master's thesis
    Tämä diplomityö selvittää yleisiä ongelmia jotka tulevat vastaan joustavien piirilevyjen kokoonpanossa pintaladottavilla komponenteilla, sekä tarjoaa mahdollisen ratkaisun. Yleensä samoja tuotantolaitteita käytetään niin jäykille kuin joustavillekin levyille, joten jälkimmäisten luonteesta johtuen ongelmia on syytä odottaa. Kun massatuotantoon ehdotetaan uusia menetelmiä, on syytä ottaa huomioon tuotelaatu, tuotantolinjan nopeus ja tuotantokustannukset. Kustannusten pienentämiseksi ja kokoonpanon nopeuttamiseksi esiteltiin uudenlainen alusta joustaville piirilevyille. Sen tärkein ominaisuus on liimamainen pintakerros, johon joustava piirilevy on tarkoitus kiinnittää. Tämän uuden alustan kuvauksen jälkeen muutama testi kyseisillä alustoilla käydään läpi. Mitään käytössä olleita prosessiparametreja ei muutettu näitä testejä varten, joten ainoa muutos oli se miten piirilevy kiinnitettiin alustaan. Uusi alustamateriaali osittain toimi osittain. Liimapinta pitää piirilevystä kiinni tarpeeksi hyvin ja jos tartunta alkaa heiketä, on pinnan puhdistus mahdollista. Ongelmat alustamateriaalin taipuessa päättivät testit. Uusi alustamateriaali ei myöskään auttanut nopeuttamaan hitainta prosessivaihetta, pastanpainoa. Lisätestit, jotka voisivat tuoda esiin lisää uuden materiaalin hyviä puolia, jätetään tulevaisuudessa tehtäviksi.
  • Chemically Stable Atomic-Layer-Deposited Al2O3 Films for Processability
    (2017-07-31) Broas, Mikael; Kanninen, Olli; Vuorinen, Vesa; Tilli, Markku; Paulasto-Kröckel, Mervi
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Atomic-layer-deposited alumina (ALD Al2O3) can be utilized for passivation, structural, and functional purposes in electronics. In all cases, the deposited film is usually expected to maintain chemical stability over the lifetime of the device or during processing. However, as-deposited ALD Al2O3 is typically amorphous with poor resistance to chemical attack by aggressive solutions employed in electronics manufacturing. Therefore, such films may not be suitable for further processing as solvent treatments could weaken the protective barrier properties of the film or dissolved material could contaminate the solvent baths, which can cause cross-contamination of a production line used to manufacture different products. On the contrary, heat-treated, crystalline ALD Al2O3 has shown resistance to deterioration in solutions, such as standard clean (SC) 1 and 2. In this study, ALD Al2O3 was deposited from four different precursor combinations and subsequently annealed either at 600, 800, or 1000 °C for 1 h. Crystalline Al2O3 was achieved after the 800 and 1000 °C heat treatments. The crystalline films showed apparent stability in SC-1 and HF solutions. However, ellipsometry and electron microscopy showed that a prolonged exposure (60 min) to SC-1 and HF had induced a decrease in the refractive index and nanocracks in the films annealed at 800 °C. The degradation mechanism of the unstable crystalline film and the microstructure of the film, fully stable in SC-1 and with minor reaction with HF, were studied with transmission electron microscopy. Although both crystallized films had the same alumina transition phase, the film annealed at 800 °C in N2, with a less developed microstructure such as embedded amorphous regions and an uneven interfacial reaction layer, deteriorates at the amorphous regions and at the substrate-film interface. On the contrary, the stable film annealed at 1000 °C in N2 had considerably less embedded amorphous regions and a uniform Al-O-Si interfacial layer.
  • Konfiguraation- ja tuotetiedonhallinta hammashoitoyksikössä
    (2012) Henriksson, Tuomas
     School of Chemical Engineering | Master's thesis
  • Demonstrating 170°C Low Temperature Cu-In-Sn wafer level Solid Liquid Interdiffusion Bonding
    (2022-03-01) Vuorinen, Vesa; Ross, Glenn; Klami, Anton; Dong, Hongqun; Paulasto-Kröckel, Mervi; Wernicke, Tobias; Pönninger, Anneliese
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The wafer-level Solid Liquid Interdiffusion (SLID) bonds carried out for this work take advantage of the Cu-In-Sn ternary system to achieve low temperature interconnections. The 100mm Si wafers had μ-bumps from 250μm down to 10μm fabricated by consecutive electrochemical deposition of Cu, Sn and In layers. The optimized wafer-level bonding processes were carried out by EV Group and Aalto University across a range of temperatures from 250°C down to 170°C. Even though some process quality related challenges were observed, it could be verified that high strength bonds with low defect content can be achieved even at a low bonding temperature of 170°C with an acceptable 1-hour wafer-level bonding duration. The microstructural analysis revealed that the bonding temperature significantly impacts the obtained phase structure as well as the number of defects. A higher (250°C) bonding temperature led to the formation of Cu3Sn phase in addition to Cu6(Sn,In)5 and resulted in several voids at Cu3Sn|Cu interface. On the other hand, with lower (200°C and 170°C) bonding temperatures the interconnection microstructure was composed purely of void free Cu6(Sn,In)5. The mechanical testing results revealed the clear impact of bonding quality on the interconnection strength.
  • Design for manufacturing of a wide range temperature probe
    (2021-08-23) von Steuben, Thomas
     Sähkötekniikan korkeakoulu | Master's thesis
    This thesis covers the application of design for manufacturing (DfM) methods to the product development of a wide range temperature measurement probe to achieve high yields. Data analysis of a product of similar function and structure, using statistical process control, was used as a starting point for the new product. All manufacturing stages are evaluated, and the identified manufacturability challenges are discussed for improvements. This was done with experts in-house as well as from suppliers for the best results. Requirements from the intended application area also caused changes to the product structure. Impact of reusing existing parts and infrastructure in time and money are discussed. Additional challenges were caused by having to compromise the design because of a short time frame, limited volume and economical feasibility. The implementation is then veryfied and further improvements are made, based on the findings after the product has been moved to manufacturing. As many ideas are based on assumptions, there are benefits of continuous development of product or manufacturing infrastructure.
  • Vismutin kemiallisen pinnoitusmenetelmän kehittäminen ja karakteriointi
    (2002) Myllymäki, Pia
     Helsinki University of Technology | Master's thesis
  • Development of Working Life Competencies in a Project Course for Master Students at Aalto University
    (2019) Millar, Robert; Keltikangas, Kirsti; Pinho, Paulo; Vuorinen, Vesa; Forsman, Pekka; Belahcen, Anouar; Kyyrä, Jorma
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Education programmes are expected to fulfil many requirements in the uncertain environment that constitutes the beginning of the 21st century. Whilst the transmission of content, the development of comprehension and analytical skills, and specific skills related to a particular discipline are still valid, it is vital to equip students for working in groups that may be diverse, situations that may be challenging, and in a work environment that is changing at an increasing rate. Attempting to rise to these challenges, this article focuses on team and multicultural working life skills, utilising a survey and group interviews of masters students in the Department of Electrical Engineering and Automation at Aalto University, who are required to participate in a recently introduced 10 ECTS project-based course. The groups were formed in terms of their suitability to perform project tasks given by research groups in the department. The efficacy of such purposive grouping of students is assessed in terms of 26 skills, adapted from the national-level TEK (Academic Engineers and Architects in Finland) feedback survey for engineering 2016 graduates, with a deeper focus on two of these competencies, skills related to the international work environment and team working.
  • Effect of CoCr Counterface Roughness on the Wear of UHMWPE in the Noncyclic RandomPOD Simulation
    (2017) Saikko, Vesa; Vuorinen, Vesa; Revitzer, Hannu
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Effect of CoCr Counterface Roughness on the Wear of UHMWPE in the Noncyclic RandomPOD Simulation
    (2017) Saikko, Vesa; Vuorinen, Vesa; Revitzer, Hannu
     School of Electrical Engineering | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • The effect of platinum contact metallization on Cu/Sn bonding
    (2018-07-16) Rautiainen, Antti; Ross, Glenn; Vuorinen, Vesa; Dong, Hongqun; Paulasto-Kröckel, Mervi
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    In this work, formation and evolution of microstructures in CuSn/Pt bonding were investigated after 320 °C reflow process as well as after high temperature storage test at 150 °C. Sputtered thin film platinum on silicon wafer and high purity platinum sheet were applied as contact metallizations for electroplated copper-tin based bonding metallurgy. As bonded microstructure showed PtSn4 intermetallic compound growth at the Pt/Sn interface, and both Cu6Sn5 and Cu3Sn phases formed at the Cu/Sn fiinterface. Both hexagonal and monoclinic Cu6Sn5 were found to coexist after 1000 h high temperature storage test. Platinum was discovered to dissolve into the Cu6Sn5 phase during soldering process and form (Cu, Pt)6Sn5 intermetallic compound exhibiting hexagonal allotropy. Meanwhile, under annealing, monoclinic Cu6Sn5 phase layer without platinum was observed to form between (Cu, Pt)6Sn5 grains and tin. Thermodynamic analysis was performed in order to reason the effects of Pt on the phase equilibria and phase stabilities. Results show that platinum has a significant impact on the stability of hexagonal Cu6Sn5.
  • Effects of free air cooling on uninterruptible power system reliability
    (2017-05-22) Karjalainen, Heikki
     Sähkötekniikan korkeakoulu | Master's thesis
    Data center energy consumption has become a global environmental issue. In 2010 computing facilities used 1,3% of the world’s electricity usage and the fraction has been growing since then. Data centers utilizing traditional air conditioner cooling spend 40% of their total energy consumption for it. Different methods are developed in order to decrease the energy required for cooling. One of these methods is free air cooling. It shows good energy reduction capabilities but exposes electrical equipment to more demanding environment and reduces their reliability. Uninterruptible power systems are normally present in data centers and are subjected to the same environment than servers. This work studies the effects of indoor air quality on the reliability of uninterruptible power system. The background part reviews factors effecting the reliability of electronics with a focus on corrosion. The experimental part includes a "Telcordia GR-63 outdoor" mixed flowing gas test which mimics the long term effects of corrosive environment. The experimental work did not produce sufficient results to compare conformal coatings, surface finishes and relay casings. Ways to improve electronics reliability are presented based on literature. The design rules are more general improvements since the test did not help to make more precise observations.
  • Electromigration Reliability of Cu3Sn Microbumps for 3D Heterogeneous Integration
    (2024) Tiwary, Nikhilendu; Grosse, Christian; Kögel, Michael; Windemuth, Thilo; Ross, Glenn; Vuorinen, Vesa; Brand, Sebastian; Paulasto-Kröckel, Mervi
     A4 Artikkeli konferenssijulkaisussa
    3D heterogeneous integration (HI) and advanced packaging (AP) technologies require small volume, high-density interconnects for stacking discrete chips for which the reliability of interconnects becomes crucial. Intermetallic compounds (IMCs) based μbumps have been shown to outperform solder-based μbumps concerning their resistance to electromigration (EM) related failures, which is a key index to assess the interconnect reliability. Cu-Sn solid-liquid interdiffusion (SLID) bonding is an attractive low-cost wafer-level bonding technology for rapid manufacturing of full Cu3Sn IMC μbumps, However, SLID requires melting of Sn during the bonding process which poses risks and design challenges in manufacturing. Due to Sn squeeze-out during the bonding process, Sn melt could react with redistribution layers (RDLs) or metallization layers and form IMCs at undesired locations resulting in early failures thereby compromising the reliability. The Sn-squeeze out issue during bonding is addressed in this work by designing test structures with equal and unequal lateral dimensions of μbumps in the top and bottom wafers. The effects of Sn-squeeze out on the EM resistance and reliability are compared in both designs. Significant improvement in the Sn-squeeze out and corresponding EM resistance was observed in the test structures manufactured with unequal lateral dimensions of μbumps in the top and bottom wafers. FE element simulations were carried out to gain insights and assess the impact of Sn squeeze-out on the reliability and functionality of the Cu3Sn μbumps.
  • Elektroniikkatuotteen toiminnallisten parametrien monitorointi luotettavuusanalyysissä
    (2019-12-20) Auranen, Olli
     Sähkötekniikan korkeakoulu | Bachelor's thesis