Search query: sinter silver PZT

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abstract: Traditional lead free solder are widely employed for die attachment owing to low cost and easy process. The melting points of lead free solder are under the tolerable levels for silicon semiconductor devices. However, wide band gap semiconductors such as Gallium nitride (GaN) and Silicon carbide (SiC) with excellent electrical characteristics can be utilized for power electronics application at high power and high junction temperatures beyond 300degC [1] [2] Therefore, suitable die attachment materials which could bear the high junction temperatures play an important role for these wide band gap devices. However, the traditional techniques to interconnect (such as the solder alloys) are inappropriate due to the limits of operating temperatures and lower thermal conductivity. Silver sinter joining is well known for die bond material because of outstanding heat conductivity as well as excellent high temperature stability [3] [4] [5] In the study, a high thermal conductivity was obtained from the micro sized silver particles sintered at 280degC for 90 min without pressure [6] Besides, shear strength of bulk silver joint on bare copper substrate larger than 35 MPa were successfully achieved, which was produced a lower porosity less than 8.5%.In order to investigate the stability of pressure less sintered silver joints after high aging tests, we have carried out high temperature storage (HTS) at 175degC for 2000 hours. The power device characters with sinter material including the die shear strength (DSS) ratio of porosity, I V curve, surge current ability and thermal conductivity were verified in comparison to the initial state. In this study, mechanical shear over 28 MPa has been remained after aging at 175degC for 2000 hours. Furthermore, we have proven the electrical and thermal stability of non press sintered silver when environmental tests of high temperature storage. Cross section microstructure of the interface between sintered silver and copper substrate was examined by Scanning Electron Microscopy (SEM) The SEM images show that the formation of metallic bonds between the sintered joints and bare copper. Then, the sintered density of the joints were higher after high heat reliability test because of the micro silver particles composed complex porous networks as well as thick connection. In addition, it is carried out high thermal storage at 250degC for 500 hours, as well as the surge current ability still kept stable after the aging heating tests. To sum up, there is no doubt that the novel sintered silver paste without applied pressure has been one of the most promising candidates for high temperature and high power electronic applications in the future.
author_names: Yu-Wen Huang

Min-Cheng Tsai

P 4 Hsu

Hao-Chiang Hsu

Hsueh-Kuo Liao
title: Investigation of Non Pressure Sinter Silver in Power Module with High Accelerated Stress Aging Test
venue: 2018 13th International Microsystems, Packaging, Assembly and Circuits Technology Conference (IMPACT)
year: 2018

abstract: In this work we show the capabilities of non destructive testing by pulsed infrared thermography (PIRT) on large area silver sinter layers. This method can achieve a similar reliability in detecting delamination as SAM and X ray analysis. The great advantage of PIRT is its potential to become a tool for 100% in line inspections in the production line of power modules, whereas SAM and X ray are preferred as offline tools for reasons of costs, time or the need of a coupling medium. PIRT could help to replace vulnerable solder layers in power modules by much better performing silver sinter layers to enhance the reliability of those modules. By PIRT analysis on sample series with varied sinter process parameters and different sinter pastes, which will be compared to conventional failure analysis such as SAM and x ray, this work can show the quality of this method for the developing process of new sinter applications and for the following quality assessment in production lines.
author_names: Dan Ralf Wargulski

Battist Rabay

Adrian C Stelzer

Jacek Rudzki

Armin Hindel

M Bast

Dirk Busse

Ellen Auerswald

Mohamad Abo Ras
title: Paving the way for the replacement of solder interconnections in power electronics by silver sinter using pulsed infrared thermography
venue: 2019 22nd European Microelectronics and Packaging Conference Exhibition (EMPC)
year: 2019

abstract: Silver nanoparticles (NPs) coated with silver stearate [CH3(CH2)16COOAg] have been prepared using a thermal decomposition method. Near spherical Ag NPs with average size of 4.4 nm were obtained after thermal decomposition at 523 K. The effects of the organic acid and thermal decomposition temperature on the characteristics of the Ag NPs were investigated. For stearic acid and lauric acid with straight chain structure, a longer chain of the organic acid contributes to the achievement of Ag NPs of smaller size, while ascorbic acid with cyclic structure results in relatively large sized (approximately 11.7 nm) Ag NPs. Small sized Ag NPs with uniform size distribution were obtained after thermal decomposition at temperature of 473 K or 523 K. However, after thermal decomposition at temperature of 573 K, the particle size of the Ag NPs increased and obvious aggregation occurred, which may be caused by the absence of the silver stearate coating. Low temperature sinter bonding of bare Cu was realized using Ag NP paste at 623 K under pressure of 5 MPa in air atmosphere. The microstructure of the joint revealed formation of a dense sintered Ag filler layer and its favorable interfacial bonding with the Cu substrates.
author_names: Yangwu Mao

Yubo Duan

Ke Wang

Lixia Xi

Quanrong Deng

Geming Wang

Shenggao Wang
title: Preparation of Ag Nanoparticles Coated with Silver Stearate for Low Temperature Sinter Bonding
venue: Journal of Electronic Materials
year: 2019

abstract: During the experiment, pressure less silver sintering pastes that can sinter using a conventional reflow oven for die attach applications were developed. This development makes it possible to produce die attach assemblies in a continuous and high throughput fashion for mass production. Different reflow profiles such as "ramp up and peak" and "ramp up and plateau" types were tested and high shear strength joints with no voids were obtained. For each sample, the sintering time was around twelve minutes or less, which is about one order of the magnitude that is presently used for box oven sintering time. Two sintering pastes, A and B, were developed. Paste A has been used to study the relationship between processing conditions (reflow oven sintering temperature and atmosphere such as air vs nitrogen) and the die attach structures (with varied substrate materials such as copper or active metal brazing (AMB) and surface metallization such as copper, silver, or gold) Under the same combined conditions of sintering temperature, atmosphere, and substrate type, the Ag metalized substrate gave the strongest joint shear strength. In comparison, Au metalized substrate displayed the weakest strength because of the formation of a "depletion layer" as a result of the diffusion of silver on gold surface, leaving behind a weak connection between sintered silver and Ag Au layer. For the above noble metal metallized surfaces, sintering in air normally results in stronger joint shear strength than that in a nitrogen atmosphere. On the bare Cu metallized surface with nitrogen sintering, increasing the sintering temperature and changing to paste B are two ways to increase joint shear strength. Sintering on an AMB substrate displays around 10Mpa higher shear strength than that on a Cu substrate, indicating the importance of surface morphology. When sintering at 250degC in air, oxygen can help accelerate the inter diffusion between Cu substrate and sintered Ag and enhance interfacial adhesion, increasing the shear strength. A higher sintering temperature reduces the adhesion due to the formation of large amounts of copper oxide; therefore, control of the optimum temperature range is key to obtaining a strong joint in air.
author_names: Sihai Chen

Evan Wernicki

S Wright

Christine Labarbera

Ning-Cheng Lee
title: "Drop in" Conventional Reflow Oven Sinter Able Pressure Less Silver Paste for Die Attach Assembly Mass Production
venue: International Symposium on Microelectronics
year: 2019

abstract: Silver sintering become a mature interconnection technology for high reliability or high temperature electronic devices. Different sintering processes are applied depending upon application requirements, for instance pressure sintering process is optimized for elevated life time power modules. The pressure of the sintering process can be adjusted in order to modify the properties of the sinter layer. In general, higher pressure or temperature leads to higher Young's modulus. With respect to the lifetime of an interconnection, the Young's modulus, the dimension of the connected area and the CTE mismatch of the joint materials play an important role in temperature cycling. Thermo mechanical tension might not be reduced easily by the interconnection material if the Young's modulus of the material itself is high. A brittle die attach material might crack due to the bending of the package caused by the CTE mismatch of the used materials. This leads to a degradation of thermal conductivity and a reduced life time of the components, particularly on components which are operated at above 175degC. Silver sinter material with a reduced Young's modulus as well as an adjusted CTE is desired to avoid crack, especially for the interconnection of large areas. This paper shows the result of silver sinter paste with improved mechanical properties. By adding non silver particles to the sinter paste the Young's modulus became independent of process parameters and became stable against further thermal exposure. This investigation is part of the public project HHK funded by BMBF.
author_names: Wolfgang Schmitt

Ly May Chew

David Stenzel
title: Silver sinter paste for SiC bonding with improved mechanical properties
venue: 2019 IEEE International Workshop on Integrated Power Packaging (IWIPP)
year: 2019

abstract: Silver sinter joining paste has been seen as the most promising candidate for die attachment materials of next generation power devices. However, there are still technique issues to be overcome before its actual utilization such as sinterability under various atmosphere and the lack of rapid sintering ability. In this research, on the basis of reported silver hybrid paste, an optimized paste composition which is composed of silver micron flakes, silver submicron particles, silver nanoparticles and ether type solvent has been established. The newly developed paste has proper viscosity which can inhibit the leakage tendency of solvent during mask printing. Its sintering property has been systematically evaluated and an omnipotent sinterability under various atmosphere has been observed. Moreover, the rapid sintering property drastically shorten the sintering temperature from at least 30 min to 10 min. These results suggest that the modified silver hybrid sinter joining paste can accelerate the further application of next generation power devices owing to its obvious process advantage and excellent performance.
author_names: Tomoya Egawa

Hao Zhang

Takanori Kobatake

Yasuyuki Akai

Chuantong Chen

Katsuaki Suganuma
title: Sinterability improvement of hybrid silver sinter joining paste by adding silver nanoparticles
venue: 2019 20th International Conference on Electronic Packaging Technology(ICEPT)
year: 2019

abstract: Development of sinter free stretchable conductive inks is critically important to expand the range of materials and applications for flexible electronics. However, conventional stretchable conductive inks require high temperature sintering, which may damage the heat frail substrates. In this study, we developed sinter free stretchable conductive inks composed of polystyrene block polybutadiene block polystyrene (SBS) and silver flakes in tetrahydrofuran (THF) The high volatility and polarity of THF induced the densification and alignment of silver flakes in the SBS matrix, where silver flakes with large surface area and high aspect ratio were formed into the multistacked structure, resulting in the increase of conductive pathways in the stretched wiring.
author_names: Takenori Nakanishi

Kento Yamagishi

Eiji Iwase

Hiroyasu Iwata

Shinji Takeoka

Toshinori Fujie
title: Sinter free stretchable conductive inks composed of polystyrene block polybutadiene block polystyrene and silver flakes in tetrahydrofuran
venue: Applied Physics Express
year: 2019

abstract: Silver (Ag) nanoparticle based inks are frequently used in printed electronics to form conductive patterns, but often require high temperature sintering to achieve the optimum electrical conductivity, hindering their use in substrates with poor heat resistance. Herein, a three dimensional (3D) printing strategy to produce highly conductive Ag 3D architectures that can be sintered at low temperatures is reported. This strategy is based on the additive deposition of Ag nanoparticles and microflakes via extrusion based 3D printing with the Ag ink that involves poly(acrylic acid) (PAA) stabilized Ag nanoparticles, Ag microflakes, and NaCl a destabilizing agent. The designed Ag inks are stable and suitable for ink extrusion 3D printing. In chemical sintering, Cl can detach PAA from the Ag nanoparticle surface, enabling nanoparticle coalescence and sintering. An elevated annealing temperature induces increased NaCl density in the printed patterns and accelerates the surface and grain boundary diffusion of Ag atoms, contributing to enhance chemical sintering. On annealing at ~110 degC for 30 min, the printed structures exhibited an electrical conductivity of ~9.72 x 104 S cm 1, which is ~15.6% of that of bulk Ag. Complicated Ag architectures with diverse shapes were successfully fabricated on polymeric substrates. Several structural electronic applications were demonstrated by hybrid 3D printing combining our extrusion based 3D printing and conventional fused deposition modeling (FDM)
author_names: Jung Hyun Kim

Sanghyeon Lee

Muhammad Wajahat

Jinhyuck Ahn

Jaeyeon Pyo

Won Suk Chang

Seung Kwon Seol
title: 3D printing of highly conductive silver architectures enabled to sinter at low temperatures.
venue: Nanoscale
year: 2019

abstract: This study aims to utilize Simultaneous Thermal Analysis Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) along with respective differential curves to infer relative data points such as temperature and shape of peaks, duration and percentage of solvent outgassing to design and optimize curing profile with appropriate outgassing and sintering time and temperature, ramp up rate at shortest duration. Using different scan modes; isothermal and dynamic, five different curing profiles were derived and simulated to check thermal responses. The effectiveness of each profile was evaluated through curing of die attached units and the presence of die bulging and channeling voids were assessed through five point Bondline Thickness (BLT) SEM and SCAT. It was found out that gradual solvent outgassing at lower temperature and longer time, as well as choosing lower sintering temperature and ramp up rate could prevent formation of these anomalies. It was also proven that unoptimized curing profile triggers the occurrence and recurrence of die bulging and channeling voids.
author_names: Marty Lorgino D Pulutan

Bobby Johns L Villacarlos
title: On the Elimination of Die Attach Defects Occurrence Optimization of Silver Sinter Curing Profile Using Simultaneous Thermal Analyses
venue: 2019 IEEE 21st Electronics Packaging Technology Conference (EPTC)
year: 2019

abstract: Die attach on power semiconductor using leadfree technique has attracted considerable interest. Silver sinter has demonstrated significant develop over the past years to be considered one of frontrunner non lead containing die attach solution. Pressure silver sintering by far offers superior thermal and electrical conductivity properties which enables power electronics applications to operate at high temperature. Eliminating precious metal finishing on substrate would represent significant compatibility to present supply chain and lower the entry barrier to adopt silver sinter solution. This paper explores the development of a safe to use micro Ag sinter paste for pressure sintering on bare Cu for power electronics packaging. We attached Ag metallized mechanical Si dies on silicon nitride active metal brazed copper substrates with Ag and Au metallization as well as without metallization by silver sintering at 230degC with a pressure of 10 MPa for 3 min. We observed that the average initial die shear strength for Ag metallized substrate is higher than that for Au metallized and bare Cu substrates. This observation points to the self diffusion of Ag is faster than the silver/gold and silver/copper interdiffusion. The average die shear strength for all the samples increased remarkable after temperature cycling test with a condition of 40degC/+150degC and after a long term storage at 250degC. It is highly likely that the sintering process is not yet completed under the mild sintering process conditions we used in this study and consequently Ag, Au and Cu continued to diffuse during temperature cycling test and high temperature storage and as a result strengthen the sintered joint. It is strongly believed that the sintering process is completed after a certain time of storage at 250degC as we observed no further increase in die shear strength after 250 h storage. The bending test results further confirm the increase of bonding strength by thermal cycling. It is worth noting that cohesive break in the Cu layer was observed for Ag metallized and bare Cu substrates after 1000 h storage at 250degC. Elemental analysis by energy dispersive X ray spectroscopy demonstrates that interdiffusion between Ag and Cu occurred during high temperature storage in which Cu from the substrate diffused into the silver sintered layer and concurrently Ag from the silver sintered layer diffused into the substrate. In contrast, we observed cohesive break in the sintered layer after 1000 h storage at 250degC for Au metallized substrate indicating that Au metallized layer acts as a barrier to prevent Cu from the substrate from diffusion into the silver sintered layer.
author_names: Ly May Chew

Wolfgang Schmitt

Christian Schwarzer

Jens Nachreiner
title: Micro Silver Sinter Paste Developed for Pressure Sintering on Bare Cu Surfaces under Air or Inert Atmosphere
venue: 2018 IEEE 68th Electronic Components and Technology Conference (ECTC)
year: 2018