3D chip stacking with through silicon vias (TSVs) has been identified as one of the major technologies for achieving higher silicon packaging density and shorter interconnect. The test vehicle presented in this paper is a 3D chip stack package. Each layer of the test vehicle has two silicon flip chips mounted at the bottom of a silicon interposer with solder bumps. The flip chip has the equivalent dimensions and pad patterns as commercial memory chips. The interposer, with multiple interconnect TSVs for electrical connection and a central TSV for underfill dispensing, can function as a logic chip or as a redistribution chip in a real application. The assembly steps of the test vehicle include conductive adhesive filling for the interconnect TSVs, bonding two bumped flip chips on an interposer (to form a single layer), vertical stacking of the single layers and underfill dispensing. For the filling of the interconnect TSVs, an auger-dispensing method is first adopted to overfill the interconnect TSVs, followed by removing the excessive adhesive beyond the interconnect TSVs by squeegeeing. A jet valve continuously dispenses free dots of an underfill encapsulant into the central TSVs. The central TSVs function as an entrance for underfill dispensing and an uninterrupted point-source to provide fluid for each layer. The free dots form a capillary flow to fill the under-chip spaces of the test vehicle. The usage of TSVs rather than chip edges eliminates the presence of a wide edge reservoir, resulting in smaller ‘keep-out’ area occupation on the substrate.

A low-cost (with bare chips) and high (optical, electrical, thermal, and mechanical) performance optoelectronic system embedded into a PCB (printed circuit board) or an organic laminated substrate is designed and described. This system consists of a rigid PCB (or a substrate) with an embedded optical polymer waveguide, an embedded vertical cavity surface emitted laser (VCSEL), an embedded driver chip, an embedded serializer, an embedded photo-diode detector, an embedded tans-impedance amplifier (TIA), an embedded deserializer, embedded heat slugs, and a heat spreader. The bare VCSEL, driver chip, and serializer chip are 3D stacked and then attached on one end of the embedded optical polymer waveguide in the PCB. Similarly, the bare photo-diode detector, TIA chip, and deserializer chip are 3D stacked and then attached on the other end of the embedded optical polymer waveguide in PCB. The back-side of the driver or serializer and the TIA or deserializer chips is attached to a heat slug with or without a spreader. This novel structural design offers potential solutions for low-cost and high-performance semiconductor circuits with optical devices to realize wide-bandwidth and low-profile optoelectronic packaging for chip-to-chip optical interconnect applications. Optical, thermal management, and mechanical performances are demonstrated by simulations based on the optic theory, heat-transfer theory, and continuum mechanics.

Effective and reliable interconnections are crucial for microfluidics to connect with the macro world. Current microfluidic interfaces are still bulky, expensive, or with issues of clogging and material limitation. In this study, a novel ultraviolet (UV)-assisted coaxial three-dimensional (3D) printing approach was proposed to fabricate hollow microfluidic connectors with advantages of rapid prototyping, fixture-free, and materials compatible. An assembled coaxial nozzle was designed to enable co-flow extrusion, where the inner flow (water) served as the sacrificial layer and the outer flow (adhesive) was cured for shell formation. Furthermore, a converged UV-LED light source was attached to the coaxial nozzle for UV curing of adhesives. UV rheological characterizations were performed to study the UV curing kinematics, and the gelation time was employed to describe the state transition behaviors of UV curable adhesives used in the study. To explore requirements for successful hollow connectors direct printing, processing criteria such as co-flow regime and pre-cure time were investigated. The hollow connectors with an inner channel diameter of ~150 $\mathsf{\mu }$ m and a height of 5 mm were successfully printed on polymethyl methacrylate (PMMA) and glass substrate. The integration feasibility of the proposed method was also demonstrated by the presented microfluidic device with printed hollow connectors.

Recent advances in the development of surface plasmons (SPs) enhanced LED have provided a great opportunity to enhance either the internal quantum efficiency (IQE) or the spontaneous emission rate (SE) by employing specific metal structures. However, it is still challenging to simultaneously achieve high IQE and Purcell factor (F_p), which demonstrates the SE enhancement, without sacrificing the electrical performance of LEDs. Herein, we designed and investigated a conic metal structure applied to LEDs by comprehensively considering the electrical, optical, and data transmission performance of devices. Conic structures with various heights were implemented to investigate the variation trends of IQE and F_p with the structure design, accompanied by the planar structures as references. A more than five times increase in IQE and almost five times increase in F_p were demonstrated experimentally even with a coupling distance of 100 nm, by employing this conic structure. The theoretical analysis was verified by the experimental results and revealed the mechanism of high F_p and IQE toward high SP–photon coupling efficiency and initial IQE. This study provides a universal strategy to enhance the performance of luminous efficiency and modulation speed of LEDs without sacrificing electrical properties, making them viable for the integration of lighting, display, and communication.

Cu pillar microbumps with polymer cores have been demonstrated to effectively reduce thermomechanical stress and improve joint reliability. Fabricating polymer cores by a printing approach was proposed to overcome the limitations in conventional fabrication process. Cylindrical polymer cores with diameter of 20 $μm$ and height of 30 $μm$ were successfully printed. Surface metallization was subsequently applied on the printed polymer cores and Cu pillar microbumps with printed polymer cores with diameter of 35 $μm$ and height of 35 $μm$ were eventually achieved. To study the reliability performance of the interconnect joints made of Cu pillar microbumps with printed polymer cores, flip-chip bonding technology was successfully introduced and the interconnect joints between a designed bismaleimide triazine (BT) substrate and a silicon chip were formed. The interconnect joints made of conventional Cu pillars with identical dimensions were prepared for comparison. The reliability performance of the joints was investigated under temperature cycling condition and drop condition, respectively. Printed polymer cores increased the characteristic life by 32% in a temperature cycling test (0–100 $°C$⁠), while the drop test showed that printed polymer cores increased the characteristic life by four times due to the extra compliance provided by the printed polymer cores. It can be concluded that Cu pillar microbumps with printed polymer cores can effectively reduce stress and improve joint reliability.