Transient Liquid Phase Sintering Pastes Research Articles

High-temperature stability of Ni-Sn intermetallic joints for power device packaging

In this study, the feasibility and high-temperature stability of Ni-Sn bonded joints fabricated by transient liquid phase sintering (TLPS) were investigated for high-temperature power electronics applications. A 30Ni-70Sn (wt%) TLPS paste was fabricated with micro-sized pure Ni and Sn powders, and chip bonding was performed on a direct bonded copper (DBC) substrate. During TLPS bonding, Sn particles melted and reacted with Ni particles, which resulting in the formation of stable Ni-Sn TLPS intermetallic joints. During aging treatments at 150 and 200 °C, the formed Ni3Sn4 phases were transformed into the Ni3Sn2. With increasing aging treatments, the reactions between Ni3Sn4 intermetallics and remaining Ni particles increased, which resulted in the formation of the Ni-rich Ni-Sn intermetallics. Even after 1000 h at an aging temperature of 200 °C, there is no significant difference in the stable and dense microstructure of Ni-Sn TLPS joints. In addition, their mechanical strengths did not vary significantly even after long-term treatment for 1000 h at 150 and 200 °C. This means that the Ni-Sn TLPS joints have a good long-term microstructural stability and mechanical reliability at high temperatures up to 200 °C. Therefore, we conclude that the Ni-Sn paste is a promising candidate as a die-attach material for high-temperature electronic assemblies.

Pressureless transient liquid phase sintering bonding in air using Ni and Sn–58Bi for high-temperature packaging applications

High heat-endurance bonding has become an important technology requisite for the demands of SiC die attachment or other high-temperature packaging applications. Transient liquid phase sintering (TLPS), which is a promising candidate among high heat-endurance bonding technologies, has been widely studied in recent years. Because the advantages of TLPS bonding are short bonding time, low bonding pressure, and low cost. In this study, in order to bond in air condition and low temperature, TLPS pastes using Ni, Sn–58Bi, and flux were fabricated with various weight ratios. Pressureless TLPS bonding processes were conducted in an oven at 220 °C for 60 min in air. The thermal behaviors of TLPS pastes (before bonding) and TLPS joints (after bonding) were analyzed by differential scanning calorimetry (DSC). The shear test was conducted for investigate about mechanical properties. The microstructures of cross-sectional and fracture surfaces were analyzed by field emission scanning electron microscopy (FESEM). Also, the atomic distribution of cross-sectional micrographs was analyzed by electron probe micron analyzer (EPMA) and electron dispersive spectrometry (EDS). After bonding, the residual eutectic Sn–Bi lamellar structure was observed only in Ni–90(Sn–58Bi). To verify the reliability of TLPS joints, the samples were stored in an oven at 200 °C for 100, 500, and 1000 h, and the shear test was conducted. The initial shear strengths of Ni–90(Sn–58Bi), Ni–80(Sn–58Bi), and Ni–70(Sn–58Bi) TLPS joints were 23.56, 17.23, and 5.47 MPa, respectively. After the high-temperature storage test, the decrease in shear strength was smallest in Ni–70(Sn–58Bi) and largest in Ni–90(Sn–58Bi). In conclusion, the optimum weight ratio of Ni and Sn–58Bi was Ni–80(Sn–58Bi) because of increased re-melting temperature (270 °C) and high bonding reliability compared to other conditions.

Transient Liquid Phase Sintering Pastes in Heterogeneous Integration

Integrated package technologies continue to be the dominant trend in the electronics packaging industry. In particular, heterogeneous integration of logic and memory or sensing is an enormous growth segment for both mobile electronics and IoT applications. In the mobile microprocessor segment of the field, the most advanced technologies will be implemented in the early adopter class. New package architectures and interconnect schemes will be vetted and implemented without significant cost pressure, performance is the driver. In the IoT segment and downstream mobile, however; lower cost alternatives to cutting edge packaging architectures are needed to drive market growth. Sintering pastes offer an opportunity to cost-effectively enable cutting edge 3D package capability for a wider variety of applications. In this paper we will explore the use of transient liquid phase sintering (TLPS) pastes in package-on-package (POP) schemes for integrated logic with memory or sensing functions in through mold via architectures. Through mold via technology has been well established in the industry and has significantly contributed to the adoption of three dimensional packaging architectures. The advantages of using TLPS pastes in similar structures will be detailed.

Transient Liquid Phase Sintering Pastes as Solder Alternatives in High Temperature Applications

High operating temperature electronics are a growing market in the electronics industry. Most of the components and substrates necessary to support the production of these harsh environment devices are now available, but the interconnect materials for component, module and board level assembly are lagging in development. Currently the high operating temperature markets are being served by lead-bearing solders and expensive alloys such as gold-tin or gold-germanium. Lead has been banned from the majority of electronics applications in many areas of the world, but so far has been exempted in the high temperature solder applications due to the lack of an adequate replacement. Even without the impending regulatory restrictions, the melting temperature of the lead containing solders is marginal for the next generation of high operating temperature electronics. Transient liquid phase (TLPS) sintering paste compositions are a new class of solder replacement materials that can be processed at typical reflow temperatures, but which do not remelt when subjected to subsequent thermal excursions. TLPS pastes combine solder alloy particles and reactive metal particles in proportions such that the solder ‘thermosets’ during a typical solder reflow cycle. This ‘thermosetting’ behavior results in a joint that does not remelt at the original reflow temperature, and thus enables the highly reliable electrical interconnect essential for high operating temperature applications. TLPS pastes are similar to solders in many respects. The electrical, thermal and mechanical performance is similar to conventionally used tin-based solders. The TLPS pastes are stored and applied like solder pastes. The reflow cycles used to form the TLPS paste joints are also similar to those for forming solder joints. However, unlike solder, TLPS materials do not change shape during reflow or wet substrates beyond the deposition footprint. Also unlike solder, the metals within the bulk of the TLPS interconnect react with one another resulting in a stable interconnect with a thermally robust bonding structure to joining surfaces, even after subsequent thermal cycles. Though not a practical replacement for solder in common assembly operations, TLPS technology is an attractive solder alternative for specialty interconnect applications. In this paper, the nature and characteristics of TLPS pastes will be will be explored in comparison to solder paste materials commonly used in high operating temperature applications.