Search Results (3)

A large amount of multi-layer ceramic capacitor (MLCC) is mounted inside a printed circuit board (PCB) constituting electronic components. The use of MLCC in electric vehicles and the latest mobile phones is rapidly increasing with the latest technology. Environments in which electronic components are used are becoming more diverse and conformal coatings are being applied to protect mounted components from these environments. In particular, MLCCs in electronic components mainly have voltage applied. They might be used in environments where humidity exists for various reasons. In a humid environment, electrochemical migration (ECM) will occur, with the cathode and anode on the surface of the MLCC encountering each other. This can result in product damage due to a short circuit. In this study, the effects of voltage, NaCl concentration, and distance between electrodes on a non-mount MLCC, surface mount MLCC, and solder pad pattern were evaluated using a water drop test (WDT). Based on the analysis of the effects of the presence of conformal coating, applied voltage, concentration of NaCl, and the distance between electrodes, a mechanism model for ECM behavior in MLCCs was proposed. Full article

The escalating component density in radio frequency (RF) systems presents a growing challenge related to the coupling of adjacent microstrip lines in high-density printed circuit boards (PCBs). As a result, to tackle this prominent issue, there is a continuous pursuit of innovative techniques to effectively minimize the coupling effects among closely spaced microstrip lines. This paper proposes a reduction in the coupling of adjacent lines by utilizing a coating (stiffener) layer, which is commonly used in rigid-flex PCB fabrication. For this purpose, a reference 50 Ohm coupled line performance was compared to three coupled lines with track widths of 1.39 mm, 1.30 mm, and 1.25 mm, respectively, all at a fixed distance between the tracks. These decreasing widths were used to achieve the same 50 Ohm impedance for the coupled lines when covered with different coating layers. Each of these three coupled lines was covered with different coating (stiffener) layers, measuring 0.1 mm, 0.3 mm, and 0.5 mm in thickness, respectively. The manufactured device under test (DUT) structures underwent time-domain reflectometry (TDR) and S-parameter measurements. The TDR measurements of the DUT structures with coating layers demonstrated excellent conformity to the 50 Ohm reference coupled line. Meanwhile, the S21 measurements indicated a significant decrease in the crosstalk. For example, for a coating layer thickness of 0.3 mm, the crosstalk decreased by approximately 5–6 dB within the frequency range up to 5 GHz. When the coating layer thickness was 0.5 mm, the crosstalk decreased by approximately 10 dB or more. Full article

The stability of print circuit board (PCB) conformal coating is critical to guarantee the long-term performance of electronic components on PCB boards. Coating exposure to thermal shock or temperature cycles may initiate cracks, a common failure mechanism of conformal coatings. Different simplified approaches are compared to help identify desired mechanical profiles for coatings to be used in a harsh environment, focusing on silicone characterized by low rigidity and high deformability compared to alternative chemistries. Evaluation of the bi-material strip bending test method appears not to be effective in the conformal coating selection. The large difference between the coating’s elastic modulus of silicones compared to substrate modulus allows the use of a simplified formula to calculate the stress associated with the coefficient of thermal expansion (CTE) mismatch, the silicone accommodating displacement imposed by thermal changes. Both lateral tensile stress and local shear stress near the edge are estimated, with local shear stress decreasing quickly and moving apart from the edge with the stress relaxation preventing coating delamination. Predictions of simplified models agree with both results of grid-independent finite element analysis (FEA) models and observations of test pieces submitted to temperature cycles. This demonstrates the ability to use simplified models to predict coating’s performances under thermal aging and help in product selection depending on the working environment. Full article