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It is extremely challenging to create an animatable clothed human avatar from RGB videos, especially for loose clothes due to the difficulties in motion modeling. To address this problem, we introduce a novel representation on the basis of recent neural scene rendering techniques. The core of our representation is a set of structured local radiance fields, which are anchored to the pre-defined nodes sampled on a statistical human body template. These local radiance fields not only leverage the flexibility of implicit representation in shape and appearance modeling, but also factorize cloth deformations into skeleton motions, node residual translations and the dynamic detail variations inside each individual radiance field. To learn our representation from RGB data and facilitate pose generalization, we propose to learn the node translations and the detail variations in a conditional generative latent space. Overall, our method enables automatic construction of animatable human avatars for various types of clothes without the need for scanning subject-specific templates, and can generate realistic images with dynamic details for novel poses. Experiment show that our method outperforms state-of-the-art methods both qualitatively and quantitatively., To appear in CVPR 2022

We introduce DoubleField, a novel framework combining the merits of both surface field and radiance field for high-fidelity human reconstruction and rendering. Within DoubleField, the surface field and radiance field are associated together by a shared feature embedding and a surface-guided sampling strategy. Moreover, a view-to-view transformer is introduced to fuse multi-view features and learn view-dependent features directly from high-resolution inputs. With the modeling power of DoubleField and the view-to-view transformer, our method significantly improves the reconstruction quality of both geometry and appearance, while supporting direct inference, scene-specific high-resolution finetuning, and fast rendering. The efficacy of DoubleField is validated by the quantitative evaluations on several datasets and the qualitative results in a real-world sparse multi-view system, showing its superior capability for high-quality human model reconstruction and photo-realistic free-viewpoint human rendering. Data and source code will be made public for the research purpose. Please refer to our project page: http://www.liuyebin.com/dbfield/dbfield.html.

The automation of neural architecture design has been a coveted alternative to human experts. Recent works have small search space, which is easier to optimize but has a limited upper bound of the optimal solution. Extra human design is needed for those methods to propose a more suitable space with respect to the specific task and algorithm capacity. To further enhance the degree of automation for neural architecture search, we present a Neural Search-space Evolution (NSE) scheme that iteratively amplifies the results from the previous effort by maintaining an optimized search space subset. This design minimizes the necessity of a well-designed search space. We further extend the flexibility of obtainable architectures by introducing a learnable multi-branch setting. By employing the proposed method, a consistent performance gain is achieved during a progressive search over upcoming search spaces. We achieve 77.3% top-1 retrain accuracy on ImageNet with 333M FLOPs, which yielded a state-of-the-art performance among previous auto-generated architectures that do not involve knowledge distillation or weight pruning. When the latency constraint is adopted, our result also performs better than the previous best-performing mobile models with a 77.9% Top-1 retrain accuracy., Accepted for publication at the 2021 International Conference on Computer Vision (ICCV 2021)

Durafuse™ LT paste was designed as an alternative low temperature solder targeting at enabling hierarchy design for portable devices with good temperature cycling and superior drop-shock performance. It is formulated with the mixed solder powder technology to allow the paste reflowable at around 200°C or above. Durafuse™ LT formed solder joints with a melting temperature above 189°C and a plateau type reflow profile was recommended. Impact of reflow profiles on both drop shock and temperature cycling performance was investigated. The drop number increased with increasing peak temperature up to 210°C, presumably due to an improved homogeneity of solder joint. It also increased with increasing plateau time at peak temperature for temperature below 210 °C. At 210 °C, the drop number decreased with increasing plateau time, presumably due to increasing IMC thickness at pad interface. Homogeneous solder joints were more resistant to drop failure than mixed alloy system, and could be attributed to better homogeneity for the former system. Regardless of reflow profile impact, Durafuse™ LT showed at least two-order-of-magnitude higher drop shock resistance than Bi-Sn-Ag solder. Using the optimized reflow profiles, Durafuse™ LT outperformed SAC305 in drop-shock test. For LGA with homogeneous solder joint, Durafuse™ LT exhibited a characteristic life about 2.5X of BiSn0.4Ag. For chip resistor reliability in TCT, no significant difference in reliability could be discerned when comparing ENIG with OPS. Durafuse™ LT was slightly lower in reliability than SAC305. Higher peak temperature resulted in a better reliability for Durafuse™ LT. The chip size appeared to be an insignificant factor.

3D face shape is more expressive and viewpoint-consistent than its 2D counterpart. However, 3D facial landmark localization in a single image is challenging due to the ambiguous nature of landmarks under 3D perspective. Existing approaches typically adopt a suboptimal two-step strategy, performing 2D landmark localization followed by depth estimation. In this paper, we propose the Joint Voxel and Coordinate Regression (JVCR) method for 3D facial landmark localization, addressing it more effectively in an end-to-end fashion. First, a compact volumetric representation is proposed to encode the per-voxel likelihood of positions being the 3D landmarks. The dimensionality of such a representation is fixed regardless of the number of target landmarks, so that the curse of dimensionality could be avoided. Then, a stacked hourglass network is adopted to estimate the volumetric representation from coarse to fine, followed by a 3D convolution network that takes the estimated volume as input and regresses 3D coordinates of the face shape. In this way, the 3D structural constraints between landmarks could be learned by the neural network in a more efficient manner. Moreover, the proposed pipeline enables end-to-end training and improves the robustness and accuracy of 3D facial landmark localization. The effectiveness of our approach is validated on the 3DFAW and AFLW2000-3D datasets. Experimental results show that the proposed method achieves state-of-the-art performance in comparison with existing methods., Comment: Code available at https://github.com/HongwenZhang/JVCR-3Dlandmark

A novel lead-free solder alloy 90.6Sn3.2Ag0.7Cu5.5Sb, designated as Indalloy276, was developed targeting for high reliability with a wide service temperature capability. The alloy exhibited a melting temperature range of 223 to 232°C, reflowable at profile with peak temperature 245°C and 255C, with ambient temperature Yield stress 60MPa, UTS 77 MPa, and ductility 28%, and a higher stress than both SAC305 and Innolot, the latter two alloys were used as controls. When tested at 140°C and 165°C, the die shear stress was comparable with Innolot but higher than SAC305, and the ductility was higher than both Innolot and SAC305, with Innolot exhibited distinct brittle behavior. When aged at 125 °C and 175°C, the die shear strength was comparable or higher than both controls. When pretreated with a harsh condition, TST −55°C/155°C for 3000 cycles, the die shear strength of 276 was 8 times of that of Innolot and SAC305. When preconditioned at TCT (−40°C/175°C) for 3000 cycles, the die shear strength of 276 was 11 to 20 times of Innolot and SAC305, depending on the flux type used. For SMT assembled BGA solder joints with both ball and paste using the same alloy, 276 showed higher Eta value than Innolot and SAC305 when tested at TCT with −55°C/125°C and −40°C/150°C. For 1% failure, 276 was 2 to 3 times higher in cycling life than Innolot, mainly due to the Beta value of 276 being much higher than Innolot. SAC305 performed the poorest in these two tests. Both 276 and Innolot are alloys based on SnAgCu, but reinforced with precipitate hardening and solution hardening, with the use of additives including Sb, Ni, and Bi. 276 exhibited a finer microstructure with less particles dispersed, while Innolot exhibited more particles with some blocky Ag 3 Sn plates or rods. 276 is rigid and ductile, while Innolot is rigid but brittle, Under the harsh test condition where ΔT was high, the dimension mismatch between parts and substrate became very significant due to CTE mismatch. This significant dimension mismatch would cause a brittle joint to crack quickly, as seen on Innolot. The challenge was more tolerable for a ductile joint, as shown by 276. Accordingly 276 showed a much better reliability than Innolot under harsh condition, including high testing temperature and large ΔT. Overall, to achieve high reliability under a wide service temperature environment, a balanced ductility and rigidity for solder alloy is critical for success.

A novel lead-free solder alloy 90.6Sn3.2Ag0.7Cu5.5Sb, designated as Indalloy276, was developed targeting for high reliability with a wide service temperature capability. The alloy exhibited a melting temperature range of 223 to 232°C, reflowable at profile with peak temperature 245°C and 255C, with ambient temperature Yield stress 60MPa, UTS 77 MPa, and ductility 28%, and a higher stress than both SAC305 and Innolot, the latter two alloys were used as controls. When tested at 140°C and 165°C, the die shear stress was comparable with Innolot but higher than SAC305, and the ductility was higher than both Innolot and SAC305, with Innolot exhibited distinct brittle behavior. When aged at 125°C and 175°C, the die shear strength was comparable or higher than both controls. When pretreated with a harsh condition, TST −55°C/155°C for 3000 cycles, the die shear strength of 276 was 8 times of that of Innolot and SAC305. When pre-conditioned at TCT (−40°C/175°C) for 3000 cycles, the die shear strength of 276 was 11 to 20 times of Innolot and SAC305, depending on the flux type used. For SMT assembled BGA solder joints with both ball and paste using the same alloy, 276 showed higher Eta value than Innolot and SAC305 when tested at TCT with −55°C/125°C and − 40°C/150°C. For 1% failure, 276 was 2 to 3 times higher in cycling life than Innolot, mainly due to the Beta value of 276 being much higher than Innolot. SAC305 performed the poorest in these two tests. Both 276 and Innolot are alloys based on SnAgCu, but reinforced with precipitate hardening and solution hardening, with the use of additives including Sb, Ni, and Bi. 276 exhibited a finer microstructure with less particles dispersed, while Innolot exhibited more particles with some blocky Ag 3 Sn plates or rods. 276 is rigid and ductile, while Innolot is rigid but brittle, Under the harsh test condition where ΔT was high, the dimension mismatch between parts and substrate became very significant due to CTE mismatch. This significant dimension mismatch would cause a brittle joint to crack quickly, as seen on Innolot. The challenge was more tolerable for a ductile joint, as shown by 276. Accordingly 276 showed a much better reliability than Innolot under harsh condition, including high testing temperature and large ΔT. Overall, to achieve high reliability under a wide service temperature environment, a balanced ductility and rigidity for solder alloy is critical for success.

High-Pb solders have been used as die-attach and interconnect materials since long time for discrete power packages, including MOSFET, smart power ASICs, IGBT modules and integrated power modules, operating under high-power and high-current operation environments. Due to the known harmful effects of Pb to human health and the environment, alternative Pb-free solders and other Pb-free solutions have been studied for decades. But, Pb-free alternatives to replace high-lead solders are still in the infant age and no recognized drop-in solution is available yet. The exemption of using high-Pb solders has been extended again to 2021. iNEMI initiated a project and conducted an industry-wide survey to benchmark the availability of Pb-free die bonding materials, the technological feasibility for the same and the ongoing industrial trend. Based on the survey results, this paper presents the insights on the industrial preferences and the potential lead-free materials.

High lead solder has a long history of use in the semiconductor industry as a die attach and interconnect material within high-current-density discrete power packages. The main reason high Pb solder is still an ideal material and cannot be replaceable until today because of its low resistance, high thermal conductivity for improved electrical performance, ductility to accommodate thermal expansion mismatches between joining materials, and a high melting temperature to sustain multiple reflow cycles. Typical high Pb die-attach materials are PbSn, PbSnAg or PbInAg alloys with the formation of intermetallic compounds which builds an adhesion layer between substrate or die metallization and bulk solder is critical for giving a strong reliable joint. Both Ag3Sn and Cu3Sn IMC layer are the common interface formation for TiNiAg backside die metallization on bare Cu leadframe. IMC interface Ag3Sn layer spalling with discrete structure embedded in the Cu3Sn IMC on the die side is not desirable as it may weaken the interface structure and thus leading to solder crack formation. It can happen at both the die side as well as Cu lead side. Spalling is associated with (1) the Sn content inside the solder, (2) the reflow profile being used (over heating). The overleaching Cu and the formation of Cu3Sn or Cu-rich particles inside the joint or even along the Ag3Sn layer at die side would make the joint harder and more brittle. In fact, vertical crack and the localized circular crack at the SiC die top was found right beneath the clip dimple during the reflow process. The localized circular cracking right beneath the dimple clip indicates a compression stress there along X and Y directions. Meanwhile, the vertical crack indicates the tensile stress along the X and Y directions inside the die. The CTE match between the substrate and Die or the clip and Die may warp the Si die. The hardened solder did not absorb the strain caused by the CTE mismatch and finally the stress from the mismatch strain lead to the crack of the Si die. The focus of this study is to investigate the die cracking and correlation between the BLT and IMC thickness formation will be explored as a part of this study as well throughout a series of DOEs performed to characterize the reflow process.

Considering the three dimensional (3D) channel with elevation effect, a two dimensional (2D) antenna array was employed in a generic ray-based 3D multi-input multi-output (MIMO) system. Through utilizing the channel spatial correlation between antennas at the transmitter side, we propose a cascaded MMSE channel estimation with low computational complexity. Numerical results show that the proposed cascaded MMSE channel estimation has comparable MSE and BER performances with traditional MMSE channel estimation with significantly decrease in computational complexity. The results also demonstrate that the channel estimation in spatial domain can be decomposed into horizontal domain and vertical domain.

The paper introduces lightning protection for electric vehicle charging infrastructure. It analyzes causes of lightning damage and introduces overall protection solution for electric vehicle charging infrastructure, including protection against direct lightning, earthing system, equipotential bonding, shielding, routing and installation of SPDs.

In the current work, a mixed powder BiAgX solder paste system with the melting temperature above 260°C and comparable, or better, reliability to the high lead-containing solders has been studied. The mixed powder solder paste system is composed of a high-melting first alloy solder powder as a majority and the additive solder powder as a minority. The additive solder is designed to react preferentially with various surface finish materials before, or together with, the melting of the majority solder to form a controllable IMC layer. The IMC layer of the mixed powder system is controllable by the species and quantity of the additive solder, and it is observed to be insensitive to thermal aging and thermal cycling in current tests, while the high lead-containing solders show a considerable increase in IMC layer thickness. Both micron-sized Ag-rich particles and AgSn phases along the Bi colony boundaries in the joints have been observed. The exposed Ag-rich particles and the surrounding stepwise pattern in the Bi matrix on the fracture surface indicate that these Ag-rich particles constrain the dislocation movement in Bi matrix, and thus enhance the strength and the ductility of the joint.

Although lead free soldering has been the main stream of industry since 2006, with the replacement of eutectic SnPb system by SnAgCu system, the development of drop-in lead-free alternatives for high melting high lead solder alloys is still far from mature. BiAg alloy exhibits acceptable bulk strength but very poor ductility and wetting, therefore is not acceptable as an option. In current work, a mixed powder BiAgX solder pastes system has been developed as a viable alternative high temperature lead free solder. The metal powder in the paste is composed of a high melting first alloy powder as majority and the additive powder as minority. The additive contains a reactive element to react with various metallization surface finishes. The additive will melt and react on the parts before or together with the melting of the majority solder. The reactive element in the additive is designed to be converted completely into IMCs during the reflow process, hence results in a high melting solder joint. In the mixed powder paste system studied here, a melting temperature above 260°C was verified by both DSC and TMA data. The mixed powder solders show a significantly improved wetting comparing to Bi11Ag. The voiding and TCT performance are comparable with high lead solders. The IMC layer thickness of the mixed powder system is insensitive toward thermal aging at 175°C while the high lead ones do show a considerable increase.

Lead free soldering has been the main stream of industry since 2006, with eutectic SnPb system phased out by SnAgCu system. However, development of lead-free alternatives for high melting high lead solder alloys is still struggling, thus hampering the completion of full lead-free conversion. BiAg alloy exhibits acceptable bulk strength but very poor ductility and wetting on copper, therefore is not acceptable as an option. In this work, a mixed powder BiAgX solder pastes system has been developed as a viable alternative high temperature lead free solder. The metal powder in the paste is composed of a high melting first alloy powder as majority and the additive powder as minority. The additive contains a reactive element to react with various metallization surface finishes. The additive will melt and react on the parts before or together with the melting of the majority solder. The reactive element in the additive is designed to be converted completely into IMCs during the reflow process, hence results in a high melting solder joint. In the mixed powder paste system studied here, a melting temperature above 260°C was verified by DSC and TMA data. The mixed powder solders show a significantly improved wetting comparing to Bi 11Ag. The voiding and TCT performance are comparable with high lead solders. The IMC layer thickness of the mixed powder system is insensitive toward thermal aging at 175°C while the high lead ones do show a considerable increase.