기술문서

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Mechanism of Acoustic Noise generation
Copyright. SAMSUNG ELECTRO-MECHANICS All rights reserved. SAMSUNG Mechanism of Acoustic Noise generation [1] principle of Acoustic Noise generation [2] The origin of Acoustic Noise [3] Deformation Shape of MLCC SAMSUNG Principle of Acoustic Noise generation MLCCs in the power lines result in vibration on PCB - Humans can hear "Acoustic Noise" when PCB vibration is in the range humans' audible frequency range(20Hz to 20kHz) Variation of Applied Voltage → MLCC Vibration by Its Piezoelectricity → Vibration Transfer by Soler → PCB Vibration → Acoustic Noise Generation 좌측: AP(CPU) / DC-DC Converter / Battery 가 놓여 있는 판 그림 → 우측: Voltage Variation을 중심으로 박스가 그려져 있음. 하단에 MLCC, PCB 판 놓여있음. SAMSUNG The origin of Acoustic Noise The origin of Acoustic Noise is the (Inverse) Piezoelectricity of BaTiO3 of MLCC * Structure of MLCC MLCC Cross Sectional Image 그려져 있음 선과 선 사이: ■ Dielectric Layer : BaTiO3 ( Base material of X5R, X7R) → Ferroelectrics ⊂ Piezoelectrics 선: ■ Inner Electrode : Ni 바깥쪽: ■ Termination : Cu / Ni / Sn 100% * Piezoelectricity is the ability of some materials to generate an electric potential in response to applied merchanical stress or vice versa(Inverse Piezoelectricity). * Classification of Crystal Ferro electrics (가장 작은 박스) / pyro electrics (앞의 박스를 품고 있는 더 큰 박스) / piezo electrics (앞의 박스를 품고 있는 더 큰 박스) / 32 Crystal Classes (앞의 박스를 품고 있는 더 큰 박스) SAMSUNG The origin of Acoustic Noise The origin of Piezoelectric Effect of BaTiO3 of MLCC is spontaneous polarization which induces its high dielectric constant (a) Cubic(a=b=c) / Under Tc(125℃) / (b) Tetragonal(a=b≠c) / 보라색 동그라미: Ba2+, 노란색 동그라미: O2-, 주황색 작은 동그라미: Ti4+ / 위로 올라가는 화살표: relative displacement 위의 그림 설명: Fig. The crystal structure of BaTiO3 (Perovskite-type structure) Below the Curie temperature(Tc), BaTiO3 consists of a tetragonal structure, and has a spontaneous polarization ( dipole mement) by off-centered Ti ion which induces piezoelectric effect in case of BaTiO3. SAMSUNG Deformation Shape of MLCC Mechanical vibration assessment for each face of MLCC by using scanning LDV (LDV: Laser Doppler Vibrometer) - For horizontally mounted MLCC, ( Z-vibration) vs.(X & Y - vibration) → Opposite phase! (Poisson's effect) - Curvature shapes of MLCC are different according to mounting direction 왼쪽 이미지: Deformation Shape of MLCC, MLCC 이미지가 가운데에 있고 Top(Bottom), Head, Side에 해당하는 이미지 있음 오른쪽 이미지: Vibration shape of each face of MLCC / Horizontal Mounting - mlcc가 놓여 있고 위 아래로 나가는 화살표, 위에서 아래로 파란색 반원 그어져있음 / Vertical Mounting - mlcc가 놓여 있고 안에서 밖으로 나가는 화살표, 좌에서 우로 파란색 반원 그어져있음 Copyright. SAMSUNG ELECTRO-MECHANICS All rights reserved.*