A multi-pronged approach to low-pressure Cu sintering using surface-modified particles, substrate and chip metallization

Abstract High temperature power electronics based on wide-bandgap semiconductors have prominent applications, such as automotive, aircrafts, space exploration, oil/gas extraction, electricity distribution. Die-attach bonding process is an essential process in the realization of high temperature power devices. Here Cu offers to be a promising alternative to Ag, especially because of thermal and mechanical properties on par with Ag and a cost advantage by being a factor 100 cheaper than Ag. With the aim to achieve a low-pressure Cu sintering process, a low cost wet chemical etching process is developed to selectively etch Zn from brass to create nano-porous surface modifications to enhance sinterability, enabling sintering with low bonding pressure of 1MPa and at temperatures below 300°C. However, high tendency of Cu to oxidize poses a major challenge in realizing stable interconnects. For this purpose, in this contribution, we present the use of polyethylene-glycol 600 as reducing binder in the formulation of the Cu sintering paste. Finally, we propose a multi-pronged approach based on three crucial factors: surface-modified substrates, nanostructured surface modifications on micro-scale Cu-alloy particles and use of a reducing binder in the Cu particle paste.

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Improved sinterability of particles to substrates by surface modifications on substrate metallization

Additional Conferences (Device Packaging HiTEC HiTEN & CICMT) ◽

10.4071/2380-4491.2019.hiten.000066 ◽

2019 ◽

Vol 2019 (HiTen) ◽

pp. 000066-000070 ◽

Cited By ~ 2

Author(s):

Sri Krishna Bhogaraju ◽

Omid Mokhtari ◽

Jacopo Pascucci ◽

Fosca Conti ◽

Gordon Elger

Keyword(s):

High Temperature ◽

High Power ◽

Low Cost ◽

Surface Modifications ◽

Bonding Pressure ◽

Light Emitting ◽

High Temperature Electronics ◽

Die Attach ◽

N2 Atmosphere ◽

Surface Modified

Abstract Sintering under pressure has been in the forefront of the research and development over the past decade as an alternative to high temperature soldering and die-attach bonding for high temperature electronics. However, high bonding pressure is a deterrent to mass industrialization due to the high costs involved in the design of special tooling and complex process control parameters. Further, it can cause device cracking, especially while working with sensitive high power optoelectronics devices (e.g. high power light emitting diodes). Therefore, alternatives to enhance sinterability are highly requested. Substrate metallization is observed to play an important role while sintering. An innovative low cost method to have nanostructured surface modifications on the substrates is realized and presented here. The method is applied to enhance sinterability of Cu particles to substrate. Shear tests on samples with surface modified substrates are promising with results of ca. 25 MPa, which is 24% better than sintering on unmodified bare Cu substrate. Sintering was enabled by in-house developed hybrid Cu paste under pressureless sintering conditions of 300°C, for 60 min, and under N2 atmosphere.

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Impact of Metallurgical and Mechanical Properties of Sintered Silver Joints on Die-Attach Reliability of High-Temperature Power Modules

Journal of Microelectronics and Electronic Packaging ◽

10.4071/imaps.506 ◽

2016 ◽

Vol 13 (3) ◽

pp. 121-127 ◽

Cited By ~ 4

Author(s):

Hiroaki Tatsumi ◽

Sho Kumada ◽

Atsushi Fukuda ◽

Hiroshi Yamaguchi ◽

Yoshihiro Kashiba

Keyword(s):

Mechanical Properties ◽

High Temperature ◽

Thermal Cycling ◽

Tensile Tests ◽

High Heat ◽

Bonding Pressure ◽

Die Attach ◽

Power Modules ◽

Bandgap Semiconductors ◽

Sintered Silver

Sintered silver bonding processes are expected to offer bonding solutions with high heat endurance for power modules using wide bandgap semiconductors. This study reports the die-attach reliability of the bonding process under thermal cycling tests, focusing on the metallurgical and mechanical properties of sintered silver joints. A nanocrystalline (NC) structure with 150-nm-sized grains was observed in the as-sintered state, while a coarsened structure with microsized grains and pore coalescence was observed after annealing at 350°C for 1 h. In addition, the increase of bonding pressure reduced the number of coarse pores. Transmission electron microscope observations showed favorable crystalline structure along the grain boundaries. Tensile tests at room and high temperature revealed that the sintered silver materials showed the inherent mechanical properties of NC metals. Thermal cycling tests of die-attached specimens demonstrated the temperature dependence of crack resistance at constant amplitude. Furthermore, coalescence of pores and coarsening of grains reduced bonding reliability. It can be inferred from the results that NC structure and minute pore dispersion improves bonding reliability.

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Microstructural Evolution and Thermal Stability Characterization of a High Temperature Die Attach Lead-Free System

Additional Conferences (Device Packaging HiTEC HiTEN & CICMT) ◽

10.4071/hitec-ta22 ◽

2012 ◽

Vol 2012 (HITEC) ◽

pp. 1-11 ◽

Cited By ~ 1

Author(s):

Rogie I. Rodriguez ◽

Dimeji Ibitayo ◽

Pedro Quintero

Keyword(s):

High Temperature ◽

Melting Point ◽

Microstructural Evolution ◽

Diffusion Mechanism ◽

Processing Temperature ◽

Mechanical And Thermal Properties ◽

Promising Alternative ◽

Free System ◽

Die Attach

There is a need for electromechanical devices capable of operating in high temperature environments (>200°C) for a wide variety of applications. Today's wide-bandgap (WBG) semiconductor based power electronics have demonstrated a potential of operating above 400°C, however they are still limited by packaging. Among the most promising alternative is the Au-Sn eutectic solder, which have been widely used due to its excellent mechanical and thermal properties. However, the operating temperature of this metallurgical system is still limited to ∼250°C owing to its melting temperature of 280°C. Therefore, a higher temperature resistant system is much needed, but without affecting the current processing temperature of ∼325°C typically exhibited in most high temperature Pb-Free solders. This paper presents the development and characterization of a fluxless die attach soldering process based on gold enriched solid liquid inter-diffusion (SLID). A low melting point material (eutectic Au-Sn) was deposited in the face of a substrate, whereas a high melting point material, gold in this instance, was deposited in its mating substrate. Deposition of all materials was performed using a jet vapor deposition (JVD) equipment where thicknesses were controlled to achieve specific compositions in the mixture. Sandwiched coupons where isothermally processed in a vacuum reflow furnace. SEM and EDS were employed to reveal the microstructural evolution of the samples in order to study the interfacial reactions of this fluxless bonding process. Mechanical characterization of the each individual intermetallic phase was achieved by nanoindentation. Differential scanning calorimetry demonstrated the progression of the SLID process by quantifying the remaining low melting point constituent as a function of time and temperature. Post-processed samples confirmed the inter-diffusion mechanism as evidenced by the formation of sound joints that proved to be thermally stable up to ∼490°C after the completion of the SLID process.

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Assessing the Reliability of Die Attach Materials in Electronic Packages for High Temperature Applications

Additional Conferences (Device Packaging HiTEC HiTEN & CICMT) ◽

10.4071/hitec-msousa-ta11 ◽

2010 ◽

Vol 2010 (HITEC) ◽

pp. 000001-000006

Author(s):

M.F. Sousa ◽

S. Riches ◽

C. Johnston ◽

P.S. Grant

Keyword(s):

High Temperature ◽

Low Cost ◽

Temperature Stability ◽

Temperature Limit ◽

Acoustic Microscopy ◽

Harsh Environments ◽

Electronic Packages ◽

Conductive Adhesives ◽

Die Attach ◽

Temperature Exposure

The operation of electronic packages under exceptionally harsh environments presents a significant challenge for the microelectronics industry. The traditional temperature limit for high temperature exposure of electronics system (for example, in down-hole, well-logging and aero-engine applications) has now to be extended from 125 to 250°C. The present work aims at developing understanding of how and why attach materials for Si dies degrade/fail under harsh environments. Two types of die attach materials have been studied: electrically conductive adhesives (ECAs) that offer low temperature assembly, low cost, and relatively low stresses imparted on the die and substrate but are generally considered unsuitable for harsh environments; and Au-2wt.%Si eutectic that offers elevated temperature stability and stiffness but requires high temperature processing and more complex manufacturing steps. Die attach assembly has been investigated using scanning electron microscopy and scanning acoustic microscopy (SAM) after ageing, thermal shock and thermal cycling treatments. The failure behaviour of the die attach materials included phenomena such as cracking of die and/or attach material; outgassing and voiding; and delamination. SAM images were particularly helpful in studying non-destructively die/die attach and die/substrate interfaces.

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Impact of Metallurgical and Mechanical Properties of Sintered Silver Nanoparticles on Die-attach Reliability of High-temperature Power Modules

International Symposium on Microelectronics ◽

10.4071/isom-2015-thp42 ◽

2015 ◽

Vol 2015 (1) ◽

pp. 000842-000847

Author(s):

Hiroaki Tatsumi ◽

Sho Kumada ◽

Atsushi Fukuda ◽

Hiroshi Yamaguchi ◽

Yoshihiro Kashiba

Keyword(s):

Mechanical Properties ◽

Grain Size ◽

Silver Nanoparticles ◽

High Temperature ◽

Thermal Cycling ◽

Nanocrystalline Structure ◽

Bonding Pressure ◽

Die Attach ◽

Power Modules ◽

Sintered Silver

Sintered silver bonding processes are expected to offer bonding solutions with high heat resistances for power modules using wide-bandgap semiconductors. This study reports the die-attach reliability of such a bonding process under thermal cycling tests, focusing on the metallurgical and mechanical properties of sintered silver nanoparticles. A nanocrystalline structure with a grain size of approximately 150 nm was observed in the as-sintered state, while a coarsened structure with a grain size of several microns and pore coalescence was observed after annealing at 623 K for 1 h. In addition, the increase of bonding pressure reduced the number of coarse pores. Observations with a transmission electron microscope showed favorable crystalline structure along the grain boundaries. Tensile tests at room and high temperature revealed that the sintered silver nanoparticles showed the inherent mechanical properties of nanocrystalline metals. Thermal cycling tests of die-attached specimens demonstrated the temperature dependence of crack propagation caused by plastic deformation at a constant temperature amplitude. Furthermore, pore coalescence and coarsening reduced bonding reliability. It can be inferred from the results that nanocrystalline structure and minute pore dispersion improves bonding reliability.

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MCrAlX (X = Y, Hf and Si) Bond Coats by Cold Spray for High Temperature Applications

Thermal Spray 2021: Proceedings from the International Thermal Spray Conference ◽

10.31399/asm.cp.itsc2021p0036 ◽

2021 ◽

Author(s):

Cristian V. Cojocaru ◽

Maniya Aghasibeig ◽

Eric Irissou

Keyword(s):

High Temperature ◽

Cold Spray ◽

Plasma Spray ◽

Deposition Efficiency ◽

Isothermal Oxidation ◽

Low Pressure ◽

Vacuum Plasma Spray ◽

Temperature Oxidation ◽

Promising Alternative ◽

Bond Coats

Abstract MCrAlX powder compositions (M= Ni; Co and X= Y; Hf; Si or combination) are often thermally sprayed (TS) via vacuum plasma spray (VPS); low pressure plasma spray (LPPS) or high velocity oxy-fuel (HVOF) to produce high temperature oxidation and hot corrosion resistant bond coats (BC) for thermal barrier coatings (TBCs). Cold spray (CS) technology is currently considered as a promising alternative to the traditional TS solutions having the advantage of delivering oxide-free and very dense metallic coatings at relatively lower costs compared to VPS and LPPS. Here; we first present high-pressure CS deposition of NiCoCrAlY and NiCoCrAlYHfSi and discuss the influence of feedstock properties on the deposited BCs. CFD numerical simulation is employed to tailor the spray conditions based on the feedstock characteristics. Secondly; we present the laser assisted cold spray (LACS) deposition of NiCoCrAlYHfSi BCs using a low-pressure CS system. We show that LACS can be successfully used to deposit this particular powder while eliminating nozzle erosion and low deposition efficiency disadvantages observed during conventional CS. Lastly; high temperature isothermal oxidation of a TBC architecture having LACS BC is presented.

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High Temperature Die Attach by Low Temperature Solid-Liquid Interdiffusion

ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, MEMS and NEMS: Volume 1 ◽

10.1115/ipack2011-52049 ◽

2011 ◽

Cited By ~ 1

Author(s):

Rogie I. Rodriguez ◽

Dimeji Ibitayo ◽

Pedro O. Quintero

Keyword(s):

High Temperature ◽

Melting Point ◽

Diffusion Mechanism ◽

Processing Temperature ◽

Mechanical And Thermal Properties ◽

Reflow Time ◽

Promising Alternative ◽

Soldering Process ◽

Die Attach ◽

Solid Liquid

There is a need for electromechanical devices capable of operating in high temperature environments (>200°C) for a wide variety of applications. Today’s wide-bandgap semiconductor based power electronics have demonstrated a potential of operating above 400°C, however they are still limited by packaging. Our group has been conducting research in novel interconnect technologies to develop reliable electronic packaging for high temperature environments. Among the most promising alternative is the Au-Sn eutectic solder (80 wt.% Au - 20 wt.% Sn), which have been widely used due to its excellent mechanical and thermal properties. However, the operating temperature of this metallurgical system is still limited to ∼250°C owing to its melting temperature of 280°C. Therefore, a higher temperature resistant system is much needed, but without affecting the current processing temperature of ∼325°C typically exhibited in most high temperature Pb-Free solders. This paper presents the development and characterization of a fluxless die attach soldering process based on gold enriched solid liquid inter-diffusion (SLID). A low melting point eutectic Au-Sn was deposited in the faces of two substrates, followed by the deposition of a subsequent layer of high melting point material, gold in this instance, in one of the substrates. Deposition of all materials was performed using Jet Vapor Deposition (JVD) equipment where thicknesses were controlled to achieve specific compositions in the mixture. Sandwiched coupons where isothermally processed in a vacuum reflow furnace. Scanning electron microscopy (SEM) was employed to reveal the microstructural evolution of the samples in order to study the interfacial reactions of this fluxless bonding process. EDS analysis was used to identify the intermetallic formation and to characterize the joint in an attempt to study the kinetics of this diffusion couple. Post-processed samples confirmed the inter-diffusion mechanism evidenced by the formation of sound joints between the two substrates. As expected, it was observed that the Au was dissolved into the eutectic Au-Sn as the reflow time and temperature were increased.

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