A tunable diplexer composed of asymmetric hairpin resonators using varactors with constant passband bandwidth and high isolation characteristics has been realized. A symmetric hairpin resonator loaded with a (Ba_xSr_1-x)TiO₃ (BST) varactor is proposed as a tunable resonator. It is matched to the frequency characteristics of bandpass filter (BPF) design parameters, namely, external quality factor and coupling coefficient. This resonator has a higher unloaded quality factor below 2 GHz than one using a silicon varactor diode. Also, beyond 2 GHz, the transmission characteristics of the proposed hairpin resonator loaded with a BST varactor are more stable. A tunable second-order BPF that maintains a constant bandwidth is configured using the proposed resonator. Those frequency characteristics are realized with only two BST varactors and a DC voltage supply. Finally, a configured and fabricated tunable diplexer using the proposed resonators is shown.

A compact dual-band bandpass filter (DB-BPF) composed of chip and patterned lumped elements is realized. Two types of dual-band LC J-inverters are proposed for DB-BPF design. Also, a large amount of attenuation between two BPF characteristics is realized by the effects of the proposed dual-band LC J-inverters. The fabricated DB-BPF has both good isolation characteristics and compact size.

Benzoxazine modified BMI resin is a low dielectric curing resin obtained by synthesizing three types of benzoxazines with C36 diamine (C36DA) biomass material and reacting them with BMI having a biomass material backbone. In particular, the 2-allyl phenol/C36 diamine type benzoxazine modified C36 bismaleimid (B36-APda) resin curing compound (equivalent ratio 1:0.3) has a high 3% and 5% weight loss temperature (Td3 = 372°C/Td5 = 393°C), excellent strength (Max.stress = 1.71 kgf/mm²)and toughness (Toughness = 42.6 kgf-mm/mm³) properties, and low dielectric loss tangent, which implies the presence of the so-called ene reaction between the combined allyl and maleimide. The addition of the paraxylylene bisdiphenylphosphine oxide (PBO) phosphorus flame retardant to this resin after curing produces a flame retardancy and can further the improve heat resistance and reduce the dielectric loss tangent to 0.0015~0.0019 at 10 GHz.

Highly heat-resistant molding materials are required for manufacturing power modules. We investigated a sheet molding material where a blend of rigid and flexible maleimide resins (MA and MB, respectively) offer high heat resistance and toughness enhancement for wide-bandgap semiconductor packaging applications. We found that the MB formulation with 30% by weight of the maleimide resin enhanced toughness of the maleimide resin blend. This formulation passed -55/200°C package-level temperature cycle tests without compromising the heat resistance. We also found that the maleimide resin blend exhibited a strong adhesion strength to Cu foil (7.3 N·cm^-1). This performance maintained even after thermal storage at 200°C for 1,000 h. We think that the developed sheet molding material can be used for high-temperature-operating power modules manufactured with fan-out panel-level packaging.

It is of paramount importance to develop semiconductor packaging materials with both high heat resistance and toughness. Thus, we designed and studied various maleimide molding sheets and investigated the relationship between the amount of flexible maleimide resin and defect development, including delamination and resin cracks, during temperature cycling (TC). The stress singularity parameters computed from the interfacial stress field during the TC and die shear tests showed that delamination became more likely as the amount of flexible maleimide increased. The flexural stress criterion for crack prevention was computed using stress singularity theory. Crack formations were observed for the tested packages of the materials with measured flexural stress values below the stress values of the criterion for the TC test. Furthermore, a simple equation was proposed to determine the stress criterion from material properties.

We have developed a 5-in-1 fan-out wafer-level packaging (FOWLP) that integrates one fully operative artificial intelligence (AI) chip with approximately 2,500 pins and four memory chips for Internet of Things (IoT) modules. Three typical issues with FOWLP: (1) die shift, (2) wafer warpage and (3) fine redistribution layer (RDL) formation are solved by adopting a low elastic modulus mold resin and bonding a Si substrate on the backside of the reconfigured wafer. The developed package provides a die shift of less than ±5 µm, package warpage of 10.6 µm over 31 mm × 31 mm, and three-layer RDL formation with L/S = 10 µm/20 µm. Finally, function testing of the AI chip and memory chips using a computer circuit board are demonstrated. This study shows that FOWLP can be applied to future AI edge computing and large memory modules, and provides a direction for FOWLP process development for panel-level packaging, which may be able to ease module size restrictions.

A new heat dissipation measurement method based on an external heater and a heat flux sensor was proposed. The information of boundary conditions and thermal properties of materials, such as the thermophysical properties of printed circuit board (PCB), in the heat transfer path is not necessary for heat dissipation measurement in the proposed method. Numerical and experimental study was carried out on testing board with single component to estimate the feasibility of this method, in addition, the effects of the thermal resistance between heater and die/chip on the relative error of the proposed measurement method are investigated. This method is proved to be able to predict the heat dissipation from a single electronic component accurately, and has high applicable for the single BGA component.

Improvement of heat dissipation from electronics devices is demanded. It has been reported that heat dissipation can be improved by coating thermal-radiation material on the heat element. However, most of radiated heat from the conventional thermal-radiation material is absorbed by an external resin package, resulting in decreased heat-dissipation characteristics. In this report, we newly developed the coating- type spectrally selective thermal-radiation material (C-SSTRM) with emits infrared light through a resin package. C-SSTRM is composed of densely arranged the metallic particles with a specific particle size. The metallic particles are fixed in the resin layer. C-SSTRM was applied to the surface of a heating element, and its heat-dissipation characteristic in a sealed resin case was evaluated. The results of the evaluation confirm that the surface temperatures of the heating element and the resin case were decreased when C-SSTRM was applied compared with the temperatures when the conventional material was applied.

For the ECU that controls the electronic fuel injection system, we applied the card edge connector, which is a consumer electronics technology, and the transfer molding using a semiconductor manufacturing method. The developed ECU, all of the printed circuit board except the edge connector terminals was sealed with the specialized epoxy resin. This was the practical use of the world's first waterproof structure in the ECU alone. In addition, we have developed a waterproof card edge connector that mates with this ECU. A new insertion mechanism, multiple contact terminals, and the printed circuit board with little strength change were applied. Thus, satisfied the durability requirements for motorcycles. These technologies have been applied the ECU have achieved more than five times the productivity and 20% cost reduction compared to conventional type. The developed product has been put into practical use for small motorcycles since the 2018 model.