{"id":{"repo_id":"tu-berlin","oai_identifier":"oai:depositonce.tu-berlin.de:11303/26303"},"canonical_url":"https://search.dev.ndltd.org/etd/tu-berlin/oai:depositonce.tu-berlin.de:11303/26303","repository":{"repo_id":"tu-berlin","name":"Technische Universität Berlin","base_url":"https://api-depositonce.tu-berlin.de/server/oai/request"},"display":{"title":"Development of Cu particle sintering as die attach solution for high temperature electronics applications","abstract":"This PhD thesis, “Development of Cu Particle Sintering as Die Attach Solution for High Temperature Electronics Applications”, submitted to TU Berlin, investigates innovative copper (Cu) sintering techniques for die-attach applications in high-temperature electronics, particularly for wide bandgap semiconductors like silicon carbide (SiC). The increasing demand for reliable interconnects in power electronics, driven by rapid electrification, necessitates materials that operate above 200°C. Conventional lead-free solders, with melting points of 220–230°C, are limited to below 150°C, prompting exploration of alternatives such as high-temperature solders, transient liquid phase (TLP) bonding, and silver (Ag) sintering. While Ag sintering is widely adopted, its high cost, susceptibility to electromigration, and environmental impact highlight the need for sustainable alternatives. Cu emerges as a promising candidate due to its comparable thermal, mechanical, and electrical properties, though challenges like oxidation and high sintering temperatures must be addressed. The research develops a novel Cu sintering approach utilizing micro-scale brass flakes engineered for nano-scale sintering behaviour. This is achieved through selective wet chemical etching of zinc (Zn) from α-brass flakes using hydrochloric acid (HCl), a process known as dezincification, which creates surface modifications that enhance material transport during sintering. Polyethylene glycol 600 (PEG600) is incorporated as an organic binder to reduce Cu and Ag oxides in-situ, enabling effective sintering in an open bond chamber under nitrogen flow. This method yields a Cu sinter paste that achieves a shear strength exceeding 50 MPa under industrially viable conditions: 275°C, 10 MPa bonding pressure, and 5 minutes of sintering time. The study provides a comprehensive analysis of sintering theory, covering mechanisms such as surface diffusion, grain boundary diffusion, and densification, supported by models like Herring’s scaling law and the Mackenzie-Shuttleworth equation. Material characterization, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and die shear strength testing, confirms the enhanced sinterability of the etched brass flakes. A review of current Cu sintering methods underscores the advantages of this approach over alternatives like Cu nanoparticles or reducing atmospheres. Results demonstrate that the etched brass flakes, with residual Zn, produce a sintered microstructure and mechanical performance comparable to commercial Ag sinter pastes, but at significantly lower cost. The PEG600 binder ensures process stability by mitigating oxidation, while the low-temperature, low-pressure sintering process aligns with existing Ag sintering equipment, facilitating industrial integration. The thesis concludes by outlining prospects for process scalability and paste optimization for broader applications in power electronics packaging. This work establishes a cost-effective, high-performance Cu-based die-attach solution that addresses the economic and environmental limitations of Ag sintering, contributing to the advancement of sustainable high-temperature electronics packaging.","abstract_html":"This PhD thesis, “Development of Cu Particle Sintering as Die Attach Solution for High Temperature Electronics Applications”, submitted to TU Berlin, investigates innovative copper (Cu) sintering techniques for die-attach applications in high-temperature electronics, particularly for wide bandgap semiconductors like silicon carbide (SiC). The increasing demand for reliable interconnects in power electronics, driven by rapid electrification, necessitates materials that operate above 200°C. Conventional lead-free solders, with melting points of 220–230°C, are limited to below 150°C, prompting exploration of alternatives such as high-temperature solders, transient liquid phase (TLP) bonding, and silver (Ag) sintering. While Ag sintering is widely adopted, its high cost, susceptibility to electromigration, and environmental impact highlight the need for sustainable alternatives. Cu emerges as a promising candidate due to its comparable thermal, mechanical, and electrical properties, though challenges like oxidation and high sintering temperatures must be addressed. The research develops a novel Cu sintering approach utilizing micro-scale brass flakes engineered for nano-scale sintering behaviour. This is achieved through selective wet chemical etching of zinc (Zn) from α-brass flakes using hydrochloric acid (HCl), a process known as dezincification, which creates surface modifications that enhance material transport during sintering. Polyethylene glycol 600 (PEG600) is incorporated as an organic binder to reduce Cu and Ag oxides in-situ, enabling effective sintering in an open bond chamber under nitrogen flow. This method yields a Cu sinter paste that achieves a shear strength exceeding 50 MPa under industrially viable conditions: 275°C, 10 MPa bonding pressure, and 5 minutes of sintering time. The study provides a comprehensive analysis of sintering theory, covering mechanisms such as surface diffusion, grain boundary diffusion, and densification, supported by models like Herring’s scaling law and the Mackenzie-Shuttleworth equation. Material characterization, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and die shear strength testing, confirms the enhanced sinterability of the etched brass flakes. A review of current Cu sintering methods underscores the advantages of this approach over alternatives like Cu nanoparticles or reducing atmospheres. Results demonstrate that the etched brass flakes, with residual Zn, produce a sintered microstructure and mechanical performance comparable to commercial Ag sinter pastes, but at significantly lower cost. The PEG600 binder ensures process stability by mitigating oxidation, while the low-temperature, low-pressure sintering process aligns with existing Ag sintering equipment, facilitating industrial integration. The thesis concludes by outlining prospects for process scalability and paste optimization for broader applications in power electronics packaging. This work establishes a cost-effective, high-performance Cu-based die-attach solution that addresses the economic and environmental limitations of Ag sintering, contributing to the advancement of sustainable high-temperature electronics packaging.","abstract_has_math":false,"creators":["Bhogaraju, Sri Krishna"],"institution":null,"degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Schneider-Ramelow, Martin"],"committee_chairs":[],"committee_members":[],"year":2026,"date_issued":"2026","date_published":"2026","updated_at":"2026-07-27T21:28:40Z","subjects":[],"languages":["en"],"rights":[],"rights_urls":["http://rightsstatements.org/vocab/InC/1.0/"],"identifier_entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://doi.org/10.14279/depositonce-25131"],"render_values":[{"text":"https://doi.org/10.14279/depositonce-25131","href":"https://doi.org/10.14279/depositonce-25131","code":true}]}]},"links":{"outbound_url":"https://depositonce.tu-berlin.de/handle/11303/26303","outbound_label":"Repository record","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Schneider-Ramelow, Martin"]},{"key":"dc:creator","label":"Author","values":["Bhogaraju, Sri Krishna"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2026-02-04T15:29:09Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2026-02-04T15:29:09Z"]},{"key":"dc:date.issued","label":"Date","values":["2026"]},{"key":"dc:type","label":"Dc Type","values":["Doctoral Thesis"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["en"]},{"key":"dc:rights.uri","label":"Rights URI","values":["http://rightsstatements.org/vocab/InC/1.0/"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://depositonce.tu-berlin.de/handle/11303/26303","https://doi.org/10.14279/depositonce-25131"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["This PhD thesis, “Development of Cu Particle Sintering as Die Attach Solution for High Temperature Electronics Applications”, submitted to TU Berlin, investigates innovative copper (Cu) sintering techniques for die-attach applications in high-temperature electronics, particularly for wide bandgap semiconductors like silicon carbide (SiC). The increasing demand for reliable interconnects in power electronics, driven by rapid electrification, necessitates materials that operate above 200°C. Conventional lead-free solders, with melting points of 220–230°C, are limited to below 150°C, prompting exploration of alternatives such as high-temperature solders, transient liquid phase (TLP) bonding, and silver (Ag) sintering. While Ag sintering is widely adopted, its high cost, susceptibility to electromigration, and environmental impact highlight the need for sustainable alternatives. Cu emerges as a promising candidate due to its comparable thermal, mechanical, and electrical properties, though challenges like oxidation and high sintering temperatures must be addressed. The research develops a novel Cu sintering approach utilizing micro-scale brass flakes engineered for nano-scale sintering behaviour. This is achieved through selective wet chemical etching of zinc (Zn) from α-brass flakes using hydrochloric acid (HCl), a process known as dezincification, which creates surface modifications that enhance material transport during sintering. Polyethylene glycol 600 (PEG600) is incorporated as an organic binder to reduce Cu and Ag oxides in-situ, enabling effective sintering in an open bond chamber under nitrogen flow. This method yields a Cu sinter paste that achieves a shear strength exceeding 50 MPa under industrially viable conditions: 275°C, 10 MPa bonding pressure, and 5 minutes of sintering time. The study provides a comprehensive analysis of sintering theory, covering mechanisms such as surface diffusion, grain boundary diffusion, and densification, supported by models like Herring’s scaling law and the Mackenzie-Shuttleworth equation. Material characterization, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and die shear strength testing, confirms the enhanced sinterability of the etched brass flakes. A review of current Cu sintering methods underscores the advantages of this approach over alternatives like Cu nanoparticles or reducing atmospheres. Results demonstrate that the etched brass flakes, with residual Zn, produce a sintered microstructure and mechanical performance comparable to commercial Ag sinter pastes, but at significantly lower cost. The PEG600 binder ensures process stability by mitigating oxidation, while the low-temperature, low-pressure sintering process aligns with existing Ag sintering equipment, facilitating industrial integration. The thesis concludes by outlining prospects for process scalability and paste optimization for broader applications in power electronics packaging. This work establishes a cost-effective, high-performance Cu-based die-attach solution that addresses the economic and environmental limitations of Ag sintering, contributing to the advancement of sustainable high-temperature electronics packaging.","Deutsche Zusammenfassung der Dissertation Diese Dissertation, „Entwicklung des Cu-Partikelsinterns als Die-Attach-Lösung für Hochtemperaturelektronikanwendungen“, eingereicht an der TU Berlin, untersucht neuartige Kupfer(Cu)-Sintertechniken für Die-Attach-Anwendungen in der Hochtemperaturelektronik, insbesondere für Wide-Bandgap-Halbleiter wie Siliciumcarbid (SiC). Die wachsende Nachfrage nach zuverlässigen Verbindungsmaterialien in der Leistungselektronik, angetrieben durch die fortschreitende Elektrifizierung, erfordert Materialien, die über 200°C zuverlässig funktionieren. Herkömmliche bleifreie Lote mit Schmelzpunkten von 220–230°C sind auf unter 150°C beschränkt, was die Erforschung von Alternativen wie Hochtemperaturloten, Transient Liquid Phase (TLP)-Bonding und Silbersintern (Ag) notwendig macht. Obwohl Ag-Sintern weit verbreitet ist, schränken hohe Kosten, Anfälligkeit für Elektromigration und Umweltbelastungen seine Anwendung ein. Cu stellt eine vielversprechende Alternative dar, da es vergleichbare thermische, mechanische und elektrische Eigenschaften bietet, jedoch Herausforderungen wie Oxidation und hohe Sintertemperaturen überwunden werden müssen. Die Arbeit entwickelt einen innovativen Cu-Sinteransatz, der mikroskalige Messingflocken mit nanoskaligem Sinterverhalten nutzt. Dies wird durch selektives chemisches Ätzen von Zink (Zn) aus α- Messingflocken mit Salzsäure (HCl) erreicht, ein Prozess, der als Dezinkifizierung bekannt ist und Oberflächenmodifikationen erzeugt, die den Materialtransport während des Sinterns fördern. Polyethylenglykol 600 (PEG600) wird als organisches Bindemittel verwendet, um Cu- und Ag-Oxide in- situ zu reduzieren, was ein effektives Sintern in einer offenen Bondkammer unter Stickstofffluss ermöglicht. Die entwickelte Cu-Sinterpaste erzielt eine Scherstärke von über 50 MPa unter industriell praktikablen Bedingungen: 275°C, 10 MPa Bonddruck und 5 Minuten Sinterzeit. Die Studie bietet eine umfassende Analyse der Sintertheorie, einschließlich Mechanismen wie Oberflächen- und Korngrenzendiffusion sowie Verdichtung, unterstützt durch Modelle wie das Herring’s Skalierungsgesetz und die Mackenzie-Shuttleworth-Gleichung. Materialcharakterisierungen durch Röntgendiffraktion (XRD), Röntgenphotoelektronenspektroskopie (XPS), thermogravimetrische Analyse (TGA) und Scherstärketests bestätigen die verbesserte Sinterfähigkeit der geätzten Messingflocken. Ein Überblick über aktuelle Cu-Sintermethoden hebt die Vorteile dieses Ansatzes gegenüber Alternativen wie Cu-Nanopartikeln oder reduzierenden Atmosphären hervor. Die Ergebnisse zeigen, dass die geätzten Messingflocken mit Rest-Zn eine gesinterte Mikrostruktur und mechanische Leistung liefern, die mit kommerziellen Ag-Sinterpasten vergleichbar ist, jedoch zu deutlich geringeren Kosten. Das PEG600-Bindemittel gewährleistet Prozessstabilität durch Reduktion von Oxiden, während der Sinterprozess bei niedriger Temperatur und Druck mit bestehender Ag- Sinterinfrastruktur kompatibel ist, was die industrielle Integration erleichtert. Die Arbeit schließt mit Perspektiven zur Skalierung des Prozesses und Optimierung der Pastenformulierungen für breitere Anwendungen in der Leistungselektronik. Diese Arbeit etabliert eine kostengünstige, leistungsstarke Cu-basierte Die-Attach-Lösung, die die wirtschaftlichen und ökologischen Einschränkungen des Ag- sintern überwindet und zur Weiterentwicklung nachhaltiger Hochtemperaturelektronikverpackungen beiträgt."]},{"key":"dc:title","label":"Title","values":["Development of Cu particle sintering as die attach solution for high temperature electronics applications"]}]}],"canonical_facts":{"dc:contributor.advisor":["Schneider-Ramelow, Martin"],"dc:creator":["Bhogaraju, Sri Krishna"],"dc:date.accessioned":["2026-02-04T15:29:09Z"],"dc:date.available":["2026-02-04T15:29:09Z"],"dc:date.issued":["2026"],"dc:description.abstract":["This PhD thesis, “Development of Cu Particle Sintering as Die Attach Solution for High Temperature Electronics Applications”, submitted to TU Berlin, investigates innovative copper (Cu) sintering techniques for die-attach applications in high-temperature electronics, particularly for wide bandgap semiconductors like silicon carbide (SiC). The increasing demand for reliable interconnects in power electronics, driven by rapid electrification, necessitates materials that operate above 200°C. Conventional lead-free solders, with melting points of 220–230°C, are limited to below 150°C, prompting exploration of alternatives such as high-temperature solders, transient liquid phase (TLP) bonding, and silver (Ag) sintering. While Ag sintering is widely adopted, its high cost, susceptibility to electromigration, and environmental impact highlight the need for sustainable alternatives. Cu emerges as a promising candidate due to its comparable thermal, mechanical, and electrical properties, though challenges like oxidation and high sintering temperatures must be addressed. The research develops a novel Cu sintering approach utilizing micro-scale brass flakes engineered for nano-scale sintering behaviour. This is achieved through selective wet chemical etching of zinc (Zn) from α-brass flakes using hydrochloric acid (HCl), a process known as dezincification, which creates surface modifications that enhance material transport during sintering. Polyethylene glycol 600 (PEG600) is incorporated as an organic binder to reduce Cu and Ag oxides in-situ, enabling effective sintering in an open bond chamber under nitrogen flow. This method yields a Cu sinter paste that achieves a shear strength exceeding 50 MPa under industrially viable conditions: 275°C, 10 MPa bonding pressure, and 5 minutes of sintering time. The study provides a comprehensive analysis of sintering theory, covering mechanisms such as surface diffusion, grain boundary diffusion, and densification, supported by models like Herring’s scaling law and the Mackenzie-Shuttleworth equation. Material characterization, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and die shear strength testing, confirms the enhanced sinterability of the etched brass flakes. A review of current Cu sintering methods underscores the advantages of this approach over alternatives like Cu nanoparticles or reducing atmospheres. Results demonstrate that the etched brass flakes, with residual Zn, produce a sintered microstructure and mechanical performance comparable to commercial Ag sinter pastes, but at significantly lower cost. The PEG600 binder ensures process stability by mitigating oxidation, while the low-temperature, low-pressure sintering process aligns with existing Ag sintering equipment, facilitating industrial integration. The thesis concludes by outlining prospects for process scalability and paste optimization for broader applications in power electronics packaging. This work establishes a cost-effective, high-performance Cu-based die-attach solution that addresses the economic and environmental limitations of Ag sintering, contributing to the advancement of sustainable high-temperature electronics packaging.","Deutsche Zusammenfassung der Dissertation Diese Dissertation, „Entwicklung des Cu-Partikelsinterns als Die-Attach-Lösung für Hochtemperaturelektronikanwendungen“, eingereicht an der TU Berlin, untersucht neuartige Kupfer(Cu)-Sintertechniken für Die-Attach-Anwendungen in der Hochtemperaturelektronik, insbesondere für Wide-Bandgap-Halbleiter wie Siliciumcarbid (SiC). Die wachsende Nachfrage nach zuverlässigen Verbindungsmaterialien in der Leistungselektronik, angetrieben durch die fortschreitende Elektrifizierung, erfordert Materialien, die über 200°C zuverlässig funktionieren. Herkömmliche bleifreie Lote mit Schmelzpunkten von 220–230°C sind auf unter 150°C beschränkt, was die Erforschung von Alternativen wie Hochtemperaturloten, Transient Liquid Phase (TLP)-Bonding und Silbersintern (Ag) notwendig macht. Obwohl Ag-Sintern weit verbreitet ist, schränken hohe Kosten, Anfälligkeit für Elektromigration und Umweltbelastungen seine Anwendung ein. Cu stellt eine vielversprechende Alternative dar, da es vergleichbare thermische, mechanische und elektrische Eigenschaften bietet, jedoch Herausforderungen wie Oxidation und hohe Sintertemperaturen überwunden werden müssen. Die Arbeit entwickelt einen innovativen Cu-Sinteransatz, der mikroskalige Messingflocken mit nanoskaligem Sinterverhalten nutzt. Dies wird durch selektives chemisches Ätzen von Zink (Zn) aus α- Messingflocken mit Salzsäure (HCl) erreicht, ein Prozess, der als Dezinkifizierung bekannt ist und Oberflächenmodifikationen erzeugt, die den Materialtransport während des Sinterns fördern. Polyethylenglykol 600 (PEG600) wird als organisches Bindemittel verwendet, um Cu- und Ag-Oxide in- situ zu reduzieren, was ein effektives Sintern in einer offenen Bondkammer unter Stickstofffluss ermöglicht. Die entwickelte Cu-Sinterpaste erzielt eine Scherstärke von über 50 MPa unter industriell praktikablen Bedingungen: 275°C, 10 MPa Bonddruck und 5 Minuten Sinterzeit. Die Studie bietet eine umfassende Analyse der Sintertheorie, einschließlich Mechanismen wie Oberflächen- und Korngrenzendiffusion sowie Verdichtung, unterstützt durch Modelle wie das Herring’s Skalierungsgesetz und die Mackenzie-Shuttleworth-Gleichung. Materialcharakterisierungen durch Röntgendiffraktion (XRD), Röntgenphotoelektronenspektroskopie (XPS), thermogravimetrische Analyse (TGA) und Scherstärketests bestätigen die verbesserte Sinterfähigkeit der geätzten Messingflocken. Ein Überblick über aktuelle Cu-Sintermethoden hebt die Vorteile dieses Ansatzes gegenüber Alternativen wie Cu-Nanopartikeln oder reduzierenden Atmosphären hervor. Die Ergebnisse zeigen, dass die geätzten Messingflocken mit Rest-Zn eine gesinterte Mikrostruktur und mechanische Leistung liefern, die mit kommerziellen Ag-Sinterpasten vergleichbar ist, jedoch zu deutlich geringeren Kosten. Das PEG600-Bindemittel gewährleistet Prozessstabilität durch Reduktion von Oxiden, während der Sinterprozess bei niedriger Temperatur und Druck mit bestehender Ag- Sinterinfrastruktur kompatibel ist, was die industrielle Integration erleichtert. Die Arbeit schließt mit Perspektiven zur Skalierung des Prozesses und Optimierung der Pastenformulierungen für breitere Anwendungen in der Leistungselektronik. Diese Arbeit etabliert eine kostengünstige, leistungsstarke Cu-basierte Die-Attach-Lösung, die die wirtschaftlichen und ökologischen Einschränkungen des Ag- sintern überwindet und zur Weiterentwicklung nachhaltiger Hochtemperaturelektronikverpackungen beiträgt."],"dc:identifier.uri":["https://depositonce.tu-berlin.de/handle/11303/26303","https://doi.org/10.14279/depositonce-25131"],"dc:language.iso":["en"],"dc:rights.uri":["http://rightsstatements.org/vocab/InC/1.0/"],"dc:title":["Development of Cu particle sintering as die attach solution for high temperature electronics applications"],"dc:type":["Doctoral Thesis"]},"updated_at":"2026-07-27T21:28:40Z"}