A CMOS-process-compatible backside inductively coupled-plasma (ICP) dry etching technology to form deep trenches underneath the inductors of RF ICs is developed to enhance the performance of RF ICs with on-chip inductors. A 1-12.6-GHz CMOS distributed amplifier (DA) was designed and implemented in a standard CMOS process. The DA exhibits good input 1-dB compression point (P/sub 1 dB/) of -2 dBm and input third intercept point of 7 dBm both at 2.4 and 5.8 GHz. The authors demonstrate that a significant improvement in power gain (S/sub 21/) and noise figure (NF) can be achieved by conducting the proposed backside ICP dry etching to selectively remove the silicon underneath the inductors of the DA. The result shows that a 1.06-dB increase in S/sub 21/ (from 9.7 to 10.76 dB) and a 0.87-dB decrease (from 5.51 to 4.64 dB) in NF are achieved at 5.8 GHz mainly due to the improvement of the quality factor of the inductors in the DA. This means that this backside ICP dry-etching technique is very promising for system-on-a-chip applications.

The precipitation-hardenable aluminum alloy 6061 (AA 6061) is favored for aerospace components and automotive parts. However, the tenacious oxide layer on the surface greatly limits the quality and applicability of joining AA 6061. In this study, the joining method of solid-state diffusion bonding was implemented for AA 6061 plates, and the effects of post-weld heat treatment (PWHT) on the joint interface were investigated. The bonding temperatures were within the range of 500–530 °C, and the time periods varied from 30 to 240 min under a static pressure of 5 MPa in a vacuum. The diffusion bonded specimens were subjected to T4- and T6-PWHT to improve the bonding quality. The interfacial microstructure of the joints was analyzed by scanning electron microscopy, and the mechanical properties were evaluated with shear tests. The experimental results showed that the shear strength of the diffusion bonded joint could reach around 71.2 MPa, which was highly dependent on bonding temperature and holding time, and T6-PWHT further enhanced it to over 100 MPa. The effects of PWHT on the diffusion bonded AA 6061 joint were investigated, and the fractography on the sheared surfaces indicated that PWHT-T6 played an important role in enhancing joint strength, which was consistent with the measured shear strength. The sequential PWHT for AA 6061 after diffusion bonding was proven to be feasible for bonding of AA 6061 parts, and the joint strength was sufficient for industrial needs.

With the development of automotive power electronics and high-power integrated circuits, ribbon bonding is currently in the spotlight for its superior properties to those of traditional heavy wire bonding. In this article, innovative ribbon materials made of Ag and Ag-4Pd are introduced. The ultrasonic bonding of Ag and Ag-alloy ribbons on direct bonded copper (DBC) substrates metallized with Ni/Pd/Au films was evaluated as replacements for Al and Cu ribbons. A continuous bonding interface with satisfactory pull strength can be obtained from substrates metallized with Pd and Au films due to their similar metallurgical properties and softer surface conditions. The footprint study of bond residuals after pull tests correlated with the failure codes and bond strengths of the modules. The reliability of Ag and Ag-4Pd ribbons with regard to pull strength after high-temperature storage tests (HTSTs) at 150 °C for 1000 h was slightly increased, and the bond interface remained unchanged. The results showed that Ag and Ag-alloy ribbons made specifically for power electronics are feasible and can be an attractive alternative to aluminum ribbons.

Stud bumping using a traditional wire bonding process followed by the severing of the wire material from the ball bond has been widely applied in flip chip packages. Traditionally, Au stud bumps were employed because of the physical properties of gold, but the mediocre reliability of Au with Al pads and the cost of gold make this material unfavorable for industrial needs. Copper stud bumps were also considered, but the intrinsic features of Cu, such as its high hardness and ease of oxidation, present no advantages over gold stud bumps. However, Ag-alloy stud bumps exhibit satisfactory bondability and have been proposed as the optimal substitute for Au stud bumps to ensure better reliability in soldering and better intermetallic growth kinetics with Al bond pads. In this article, the intermetallic growth of Ag stud bumps alloyed with 2%, 10%, and 12% Pd after high-temperature storage tests (HTSTs) is investigated. The results indicated that the Pd atoms remained immobile in the bump-side matrix without diffusing into the aluminum pad side. Alloying with higher Pd content enhanced the formation of the favorable Ag ₂ Al intermetallic compound (IMC), whereas lower Pd content resulted in severe cracking due to the formation of Ag ₃ Al IMC. Compositional analysis showed that continuous layers of Ag-Al IMCs doped with large amounts of Pd formed at the interfaces close to the Ag stud bumps, but no Pd was detected on the Al pad side. The bonding strength increased after aging at 150 °C and 200 °C for 200 h, but it decayed drastically after aging at 250 °C for 200 h. The relationship between intermetallic growth and failure mode was established.