The need for high power density and high temperature capabilities in today's electronic devices continues to grow. More robust devices with reliable and stable functioning capabilities are needed, for example in aerospace and automotive industries as well as sensor technology. These devices need to perform under extreme temperature conditions, and not show any deterioration in terms of switching speeds, junction temperatures, and power density, and so on. While the bulk of research is performed to source and manufacture these high temperature devices, the device interconnect technology remains under high focus for packaging. The die attach material has to withstand high temperatures generated during device functioning and also cope with external conditions which will directly determine how well the device performs in the field. This literature work seeks to review the numerous research attempts thus far for high temperature die attach materials on wide band gap materials of silicon carbide, gallium nitride and diamond, document their successes, concerns and application possibilities, all of which are essential for high temperature reliability.

Die Attach Materials for High Temperature Applications: A Review

Mechanical properties of nano-silver joints as die attach materials

High temperature power electronics has become possible with the recent availability of silicon carbide devices. This material, as other wide-bandgap semiconductors, can operate at temperatures above 500 °C, whereas silicon is limited to 150-200 °C. Applications such as transportation or a deep oil and gas wells drilling can benefit. A few converters operating above 200 °C have been demonstrated, but work is still ongoing to design and build a power system able to operate in harsh environment (high temperature and deep thermal cycling).

/pdf/state-of-the-art-of-high-temperature-power-electronics-3qyx36fnso.pdf

State of the art of high temperature power electronics

Recently, high-temperature power devices have become a popular discussion topic because of their various potential applications in the automotive, down-hole oil and gas industries for well logging, aircraft, space exploration, nuclear environments, and radars. Devices for these applications are fabricated on silicon carbide-based semiconductor material. For these devices to perform effectively, an appropriate die attach material with specific requirements must be selected and employed correctly. This article presents a review of this topic, with a focus on the die attach materials operating at temperatures higher than 623 K (350 °C). Future challenges and prospects related to high-temperature die attach materials also are proposed at the end of this article.

A Review on Die Attach Materials for SiC-Based High-Temperature Power Devices

A review is provided, which first considers low-temperature diffusion bonding with silver nanomaterials as filler materials via thermal sintering for microelectronic applications, and then other recent innovations in low-temperature joining are discussed. The theoretical background and transition of applications from micro to nanoparticle (NP) pastes based on joining using silver filler materials and nanojoining mechanisms are elucidated. The mechanical and electrical properties of sintered silver nanomaterial joints at low temperatures are discussed in terms of the key influencing factors, such as porosity and coverage of substrates, parameters for the sintering processes, and the size and shape of nanomaterials. Further, the use of sintered silver nanomaterials for printable electronics and as robust surface-enhanced Raman spectroscopy substrates by exploiting their optical properties is also considered. Other low-temperature nanojoining strategies such as optical welding of silver nanowires (NWs) throu...

/pdf/joining-of-silver-nanomaterials-at-low-temperatures-507vh15pcd.pdf

Joining of Silver Nanomaterials at Low Temperatures: Processes, Properties, and Applications

Die-attachment solutions for SiC power devices

This work is devoted attaching technology between SiC structures and DBC substrates for creating SiC devices able to work at temperature up to 350°C. Our current work was concentrated on finding so called “pressure sintering” procedure in air using Ag micro particles. A special test samples with a size corresponding to the dimension of the SiC structures were assembled to DBC substrates with different surface finishing by Ag micro powder sintering. In the first series of experiments DBC substrates with Cu electroplated by Ni (3÷5 µm) and Au (above 1 µm) were used. It was found that by modifying application procedure of Ag micro powder onto DBC substrate with Cu/Ni/Au metallization, it is possible to obtain good adhesion between attached samples. The sintering is performed in air at temperature of 400°C for 40 min and pressure of 10 MPa. In the second series of experiments the SiC structures with Ni/Au metallization were assembled to DBC substrate with Cu/Ni/Au metallization. The adhesion higher than 10 MPa was obtained for such prepared samples.

Silver micropowders as SiC die attach material for high temperature applications

There are two main technical problems which should be overcome for practical applications of SiC power devices One of them is the formation of reproducible ohmic contacts and second one is creation connection system between SiC ohmic contacts and package leads The paper presents a compatibility of materials system for metallization of ohmic contacts to n-SiC and metallization of DBC substrate pads which both are well-suited and able to create stable connection system using wire bonding or flip chip bonding techniques Such materials systems should work at temperatures up to 350°C or higher Al and Au were applied as materials for wire bonding or flip chip bonding Our experiments allow to conclude that for high temperature applications the Al wire bonding to SiC/Ti ohmic contacts with Al top metallization and DBC substrate with Ni metallization should be good in devices working up to 350°C Moreover, Au wire bonding to the SiC/Ti ohmic contact with Au or Pt top metallization and the DBC substrate covered Ni/Au can be applied in devices working up to 400°C For Au balls flip chip bonding a good solution is the SiC/Ti ohmic contact with Au or Pt top metallization and the DBC substrate with Ni/Au metallization Such system can work up to 350°C

Overview of materials and bonding techniques for inner connections in SiC high power and high temperature applications

In this work, thermal properties of Al 2 O 3 , AlN, SiC as well as some of SiC die attachment materials are characterized by the laser flash method. The thermal diffusivity, specific heat and thermal conductivity were measured or calculated for the systems consisted of Al 2 O 3 or AlN substrates and SiC structures with die-attach layers between them. The experiments for single materials were carried out within wide temperature range of 50°C ÷ 800°C in argon atmosphere. Firstly, the thermal diffusivity and conductivity of Al 2 O 3 , AlN and SiC bulk material were extracted to increase the final results accuracy within full temperature range. Then 8×8 mm2 SiC chips were attached to 8×8 mm2 Al 2 O 3 or AlN substrates by silver-glass composition. Thermal properties of SiC - ceramics connections were measured from room temperature up to 350°C. The connection quality was investigated by X-ray microtomography. The thermal conductivity of the interfacial silver glass composition between SiC and Al 2 O 3 decreases from 120 W/mK at room temperature to 45 W/mK at temperature of 350°C and between SiC and AlN from 270 W/mK to100 W/mK, respectively. These values strongly depend of interface quality and thickness of interfacial layer.

Thermal properties of SiC-ceramics substrate interface made by silver glass composition

This paper describes the study on flexible connections application in IR detector package. Such a connection is used between two modules in single package. One module is IR detector operating at -73 °C, other is electronic controlling circuit operating at room temperature. Flexible electrical connection must provide good electrical parameters in both DC and RF regime as well as poor thermal conductivity. 35 μm epoxy-phenolic foil with 5 μm Ni film and special RF compatible Ground-Signal-Ground geometry was successfully applied as connection. Low eutectic temperature InSn solder was used for soldering flexible connection to both IR detector and electronic circuit. Two types of soldering processes were investigated: bump and lap type. Flexible connection was tested for DC operation with long term stability test and RF parameters were determined. Authors found that both joining techniques are suitable for application in IR photodetector devices. However lap type joint is easier to apply in technological process, therefore it will be applied in final assembly.

Zbigniew Szczepański

Papers

Die-attachment solutions for SiC power devices

Silver micropowders as SiC die attach material for high temperature applications

Overview of materials and bonding techniques for inner connections in SiC high power and high temperature applications

Thermal properties of SiC-ceramics substrate interface made by silver glass composition

Challenges in packaging of IR detectors - technology of elastic electrical connections