Residual Stress and Warping Analysis of the Nano-Silver Pressureless Sintering Process in SiC Power Device Packaging.

Chip bonding, an essential process in power semiconductor device packaging, commonly includes welding and nano-silver sintering. Currently, most of the research on chip bonding technology focuses on the thermal stress analysis of tin-lead solder and nano-silver pressure-assisted sintering, whereas research on the thermal stress analysis of the nano-silver pressureless sintering process is more limited. In this study, the pressureless sintering process of nano-silver was studied using finite element software, with nano-silver as an interconnect material. Using the control variable method, we analyzed the influences of sintering temperature, cooling rate, solder paste thickness, and solder paste area on the residual stress and warping deformation of power devices. In addition, orthogonal experiments were designed to optimize the parameters and determine the optimal combination of the process parameters. The results showed that the maximum residual stress of the module appeared on the connection surface between the power chip and the nano-silver solder paste layer. The module warping deformation was convex warping. The residual stress of the solder layer increased with the increase in sintering temperature and cooling rate. It decreased with the increase in coating thickness. With the increase in the coating area, it showed a wave change. Each parameter influenced the stress of the solder layer in this descending order: sintering temperature, cooling rate, solder paste area, and solder paste thickness. The residual stress of the nano-silver layer was 24.83 MPa under the optimal combination of the process parameters and was reduced by 29.38% compared with the original value of 35.162 MPa.

Reliability Simulation Analysis of TSV Structure in Silicon Interposer under Temperature Cycling.

As semiconductor integration scales expand and chip sizes shrink, Through Silicon Via (TSV) technology advances towards smaller diameters and higher aspect ratios, posing significant challenges in thermo-mechanical reliability, particularly within interposer substrates where mismatched coefficients of thermal expansion exacerbate issues. This study conducts a thermo-mechanical analysis of TSV structures within multi-layered complex interposers, and analyzes the thermal stress behavior and reliability under variable temperature conditions (-55 °C to 85 °C), taking into account the typical electroplating defects within the copper pillars in TSVs. Initially, an overall model is established to determine the critical TSV locations. Sub-model analysis is then employed to investigate the stress and deformation of the most critical TSV, enabling the calculation of the temperature cycle life accordingly. Results indicate that the most critical TSV resides centrally within the model, exhibiting the highest equivalent stress. During the temperature cycling process, the maximum deformation experiences approximately periodic variations, while the maximum equivalent stress undergoes continuous accumulation and gradually diminishes. Its peak occurs at the contact interface corner between the TSV and Redistribution Layer (RDL). The estimated life of the critical point is 3.1708 × 105 cycles. Furthermore, it is observed that electroplating defect b alleviates thermal stress within TSVs during temperature cycling. This study provides insights into TSV thermal behavior and reliability, which are crucial for optimizing the design and manufacturing processes of advanced semiconductor packaging.

Effects of Side Profile on Acoustic Streaming by Oscillating Microstructures in Channel.

In microchannels, microstructure-induced acoustic streaming can be achieved at low frequencies, providing simple platforms for biomedicine and microfluidic manipulation. Nowadays, microstructures are generally fabricated by photolithography or soft photolithography. Existing studies mainly focused on the projection plane, while ignoring the side profile including microstructure's sidewall and channel's upper wall. Based on the perturbation theory, the article focuses on the effect of microstructure's sidewall errors caused by machining and the viscous dissipation of upper wall on the streaming. We discovered that the side profile parameters, particularly the gap (gap g between the top of the structure and the upper wall of the channel), have a significant impact on the maximum velocity, mode, and effective area of the streaming.To broaden the applicability, we investigated boundary layer thickness parameters including frequency and viscosity. Under different thickness parameters, the effects of side profile parameters on the streaming are similar. But the maximum streaming velocity is proportional to the frequency squared and inversely proportional to the viscosity. Besides, the ratio factor θ of the maximum streaming velocity to the vibration velocity is affected by the side profile parameter gap g and sidewall profile angle α.