(Georgia Institute of Technology, 2021-05-01)
Gupte, Omkar Deepak
OEM Microprocessors have conventionally been packaged using Land Grid Array (LGA) designs, press-fitted into sockets for ease of reworkability. However, Ball Grid Array (BGA) packages have recently become mainstream for surface mount (SMT) applications, driven by the need for miniaturization of electronic systems. While SMT processes and applications with BGA are becoming more widespread, the market need for sockets is also expected to increase significantly over the next decade. While microprocessor companies would benefit from producing a single BGA package design applicable in both socketing and SMT applications, this raises challenges for the OEM supply chain as no BGA-compatible socket is currently available. Enabling universal BGA packages compatible with both socketing and SMT processes is, therefore, critical to this industry transition.
Current BGA architectures are not compatible with socketing applications as the mechanical contact between the Au paddle and the solder sphere leads to undesirable reactions, increasing the contact resistance and degrading reworkability over time. To address this challenge, surface modification of BGA spheres with multilayered thin-film metallic coatings such as Ni-Au and Bi-Au is proposed to maintain a non-reactive noble metal interface when used in a socket. This presentation provides details of the studies conducted in this research, including (1) design, diffusion modeling, and finite element modeling of such coatings with a fundamental understanding of the trade-offs between SMT and socketing applications, (2) the development, characterization and optimization of the coating on solder spheres and attach processes using an in-house developed, hybrid sputtering/electroless deposition process and conventional mass reflow with solder paste, respectively, as well as (3) reliability characterization of the modified BGA packages in socketing and SMT applications. The results establish the proposed approach as a promising technology towards the development of a reliable, universal BGA solution.
(Georgia Institute of Technology, 2020-08-06)
Mohan, Kashyap
To address the demand for higher electrification and efficiency in automobiles and aviation, there is an increasing focus on developing new power electronics packaging technologies which can enable the wide-bandgap devices to operate at their full potential. In particular, new die-attach interconnection materials are needed with thermal stability at temperatures greater than 250°C, superior thermal and electrical conductivities for higher thermal dissipation and power handling. In this thesis, low-temperature, low-pressure sintering of nanoporous copper (Cu) films to form all-Cu die-attach joints is proposed as the next-generation die-attach technology capable of addressing the above-mentioned challenges. To realize the above objectives, two research tasks were identified and demonstrated. In the first task, fabrication o nanoporous Cu by chemical dealloying of amorphous Cu alloy ribbons and electroplated Cu-Zn films was explored. Fundamental relationships between the Cu-Zn electroplating parameters, composition of the electroplated films, morphology of the dealloyed films, and residual Zn after dealloying were established. Based on the results, guidelines were also framed for large-scale fabrication of nanoporous Cu films. In the second task, the effect of the sintering temperatures and sintering atmospheres on the sintering kinetics of nanoporous Cu film was explored, followed by the development of assembly parameters to enable good metallurgical bonding between nanoporous Cu and Cu metallizations. The initial assembly trials gave promising results and Cu-Cu joints with shear strengths>40MPa were achieved.