{"id":311369,"date":"2023-10-13T08:50:47","date_gmt":"2023-10-13T08:50:47","guid":{"rendered":"\/forum\/forums\/topic\/multilayer-pcb-modal-analysis-first-mode-natural-frequency-related\/"},"modified":"2023-10-13T08:50:47","modified_gmt":"2023-10-13T08:50:47","slug":"multilayer-pcb-modal-analysis-first-mode-natural-frequency-related","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/multilayer-pcb-modal-analysis-first-mode-natural-frequency-related\/","title":{"rendered":"Multilayer PCB modal analysis first mode natural frequency related."},"content":{"rendered":"

Hello All<\/p>\n

I have a query related to boundary conditions for my vibration simulation test carried out on multilayer PCB.<\/p>\n

I have fixed the PCB on vibration fixture using 4 Nos. of M3 screws+ Plain washer+ Spring Washer using aluminum spacer (ID:3.5 mm , OD: 7mm & Length 10mm) between PCB bottom and vibration fixture top and a torque of 58N-cm is applied on the screws. (refer attached figure)<\/p>\n

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In actual vibration test first mode natural frequency observed is 136Hz.<\/p>\n

When i am simulating the same in Ansys workbench my first mode natural frequency is 156 Hz.<\/p>\n

Equivalent mechanical properties of PCB are:<\/p>\n

E =28.45 GPa & Poisson’s ratio : 0.13 density : 2420 kg\/m^3<\/p>\n

PCB dimensions are : 200 x 150 x 2.404 mm<\/p>\n

Base PCB mass : 175 gm<\/p>\n

For my simulation , i have assumed isotropic material for PCB with above properties and hole edges (neglecting the aluminium spacers) are taken as fixed boundary condtion in place of washer area , frequency obtained is 152 Hz.<\/p>\n

I tried with PCB trace mapping technique also. In that case , I used Ansys FR4 & copper properties for the PCB and again fixed boundary condition is taken as hole edges , again natrual frequency observed is <\/p>\n

I have not done pre-stress modal analysis and no damping assumed.<\/p>\n

I think there is something wrong in my boundary condition that the reason my simulation results are not matching with actual vibration test.<\/p>\n

Should i consider aluminium spacer also in simulation?<\/p>\n

please let me know where i am doing wrong.<\/p>\n

Thanks in advance.<\/p>\n","protected":false},"template":"","class_list":["post-311369","topic","type-topic","status-closed","hentry"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t