Se-Hoon Park

Dry-film photoresists (DFRs) are susceptible to pattern collapse arising from hydrophilic water–DFR interactions after the development process. Although wet surface treatment (rinsing) has been proposed to increase the hydrophobicity and prevent collapse, the associated surface chemical and mechanical changes remain insufficiently understood. In this study, the effects of these changes on pattern collapse were systematically analyzed using rinses containing tetramethylammonium chloride (TMAC), cetyltrimethylammonium chloride (CTAC), or BHA hydrochloride (BHAC). The surface free energy decreased after rinsing, confirming the increased hydrophobicity. During photolithography, pattern collapse was worsened by TMAC or CTAC but prevented by BHAC. The mechanical strength was degraded by TMAC or CTAC but enhanced by BHAC, as observed by nanoindentation. Diffusion of cations into the DFR was confirmed by confocal Raman microscopy, while changes in the chemical structure and apparent crosslink density arising from cation–DFR interactions were evaluated by Fourier transform infrared spectroscopy and swelling tests, respectively. In particular, BHAC treatment enhanced hydrogen-bonding in the DFR, which was associated with a higher apparent crosslink density and improved mechanical robustness. Finally, the BHAC-containing rinse was selected as the optimal rinse and used to fabricate a panel-level redistribution layer interposer. The interposer was successfully fabricated, exhibiting an insertion loss magnitude below 1.4 dB over 0–40 GHz. These results highlight that pattern collapse of the DFR can be effectively prevented using a BHAC-containing rinse during fine patterning.

Recent advances in chiplet architectures, heterogeneous integration, 2.5D/3D packaging, high-performance computing, and RF applications have increased the demand for high-density vertical interconnects and low-loss packaging platforms. Glass substrates have attracted considerable attention for next-generation advanced packaging because of their low dielectric loss, high dimensional stability, smooth surface, and compatibility with large-area panel-level processing. Through-glass vias (TGVs) are essential vertical interconnect structures that enable the electrical integration of glass substrates. This focused review summarizes TGV technologies for glass-based advanced packaging from the perspectives of via formation, seed layer deposition, metallization, Cu filling, defect formation, reliability, and plugging-based alternative architectures. Representative TGV formation methods, including laser drilling, selective laser etching, laser-induced deep etching, wet/dry etching, and photosensitive glass processing, are compared. Metallization approaches based on sputtering, electroless plating, ALD/CVD, and hybrid processes are discussed together with Cu electroplating strategies such as conformal plating, bottom-up filling, pulse or pulse-reverse plating, and engineered-geometry filling. Key defects, including voids, seams, pinch-off, seed discontinuity, Cu/glass interfacial delamination, glass cracking, and Cu protrusion, are reviewed in relation to thermomechanical reliability. Finally, polymer/dielectric plugging, plugging/re-drilling, conductive paste plugging, and hybrid Cu/plugging structures are discussed as application-specific alternatives for balancing electrical performance, reliability, manufacturability, yield, and cost.

Electromagnetic interference (EMI) shielding is critical for maintaining signal integrity in high-speed electronic packaging. However, conventional shielding approaches face limitations in process complexity and spatial efficiency. In this study, an EMI shielding film based on trimodal silver (Ag) ink and low-dielectric polyimide (PI) resin was developed and comprehensively evaluated. The fabricated film exhibited an average shielding effectiveness (SE) of −99.7 dB in the 6–18 GHz frequency range and demonstrated a 50% increase in electrical conductivity after lamination (from 0.752 × 10⁵ S/m to 1.13 × 10⁵ S/m). The horizontal thermal conductivity reached 34.614 W/m·K, which was 3.4 times higher than the vertical value (10.249 W/m·K). Signal integrity simulations showed significant reductions in near-end crosstalk (NEXT, 77.8%) and far-end crosstalk (FEXT, 65%). Moreover, cyclic bending tests confirmed excellent mechanical durability, with a normalized resistance change below 0.6 after 1000 cycles at a bending radius of 4 mm. Notably, the film enabled a 50% reduction in signal line spacing while maintaining signal integrity, even without strict compliance with the 3W Rule. These results demonstrate the potential of the proposed EMI shielding film as a high-performance solution for advanced packaging applications requiring high-frequency operation, thermal management, and mechanical flexibility.

This study presents the development of a modified polyimide (MPI) with low dielectric properties and low-temperature curing capability for high-frequency flexible printed circuit boards (FPCBs). MPI was cured using dicumyl peroxide (DCP) at 80–140 °C through a radical process optimized via DSC analysis, while Fourier-transform infrared (FT-IR) confirmed the elimination of C=C bonds and the formation of imide structures. The MPI film exhibited low dielectric constants (D_k) of 1.759 at 20 GHz and 1.734 at 28 GHz, with ultra-low dissipation factors (D_f) of 0.00165 and 0.00157. High-frequency S-parameter evaluations showed an excellent performance, with S11 of −32.92 dB and S21 of approximately −1 dB. Mechanical reliability tests demonstrated a strong peel strength of 0.8–1.2 kgf/mm (IPC TM-650 2.4.8 standard) and stable electrical resistance during bending to ~6 mm radius, with full recovery after severe deformation. These results highlight MPI’s potential as a high-performance dielectric material for next-generation FPCBs, combining superior electrical performance, mechanical flexibility, and compatibility with low-temperature processing.

This study presents the development of a highly robust, pressureless, and void-free silver sinter-bonding technology for power semiconductor packaging. A bimodal silver paste containing silver nanoparticles and sub-micron particles was used, with polymethyl methacrylate (PMMA) as an additive to provide additional thermal energy during sintering. This enabled rapid sintering and the formation of a dense, void-free bonding joint. The effects of sintering temperature and PMMA content on shear strength and microstructure were systematically investigated. The results showed that the shear strength increased with rising sintering temperatures, achieving a maximum of 41 MPa at 300 °C, with minimal void formation due to enhanced particle necking facilitated by PMMA combustion. However, at 350 °C, the shear strength decreased to 35 MPa due to cracks and voids at the copper substrate–copper oxide interface caused by thermal expansion mismatch. The optimal PMMA content was found to be 5 wt.%, balancing sufficient thermal energy and void reduction. This pressureless sintering technology demonstrates significant potential for high-reliability applications in power semiconductor modules operating under high-temperature and high-stress conditions.

This study compares the characteristics and low-temperature curing properties of pastes prepared from silver (Ag) powders synthesized by either wet powder (WP) or dry powder (DP) processing. The WP synthesis of electrode particles has the advantage of controlling the average particle size and particle size distribution but the disadvantage of producing low-purity, crystalline particles because they are synthesized through chemical reduction at less than 100 °C. Conversely, the DP synthesis of electrode particles has the advantage of producing pure, highly crystalline particles (due to synthesis at high temperatures) but the disadvantage of a high processing cost. WP and DP were used to manufacture pastes for low-temperature curing, and the physical properties of the pastes and the electrode characteristics after low-temperature curing were compared between powder types. Shear stress as a function of the shear rate shows that the WP paste is a plastic fluid, whereas the DP paste is a pseudoplastic fluid, closer to a Newtonian fluid. Screen printing the Ag pastes and curing for 30 min at 130 °C produces a nonconductive WP paste, whereas it produces a DP paste with a conductivity of 61 mΩ/sq, indicating that the highly crystalline DP paste is advantageous for low-temperature curing.