After powering down the device I measured the resistance across the capacitor and now I got a reading of 1K!!! I powered the PCBA and it of course it wasn't functional. I measured the resistance across the cap and it was in the MΩ region so I thought that something else was wrong in the circuit. I was doing some tests with an affected sample. On the surface of the other pad of the cap we found a great amount of carbon.īut this is getting even more perplexing. The sample we examined had this capacitor mechanically removed so that we could observe the area underneath the capacitor. We also did elemental analysis and the only thing that we found was Cl (chlorine) while observing one pad (concentration of 1.44%) and Ba (Barium) which afterwards was proved that belongs to the capacitor ceramic body (an oxide of Barium I suppose). We couldn't notice any suspicious formation of whiskers or dendrites. Today we examined a sample in a lab equipped with a SEM. My question is how fast growth of dentrites/wiskers can happen? Could this happen just in a couple of hours? Samples will be sent for chemical analysis to see if there are any residues that could cause this failure. I suspect formation of a conductive path formed only under voltage and after exposure to humidity (tin whiskers, dendrites, electrolysis of salts/residues? during production process of the PCBA). It all points to some electrochemical process that causes surface resistance to decrease so that the PSU is not functional (a compensation net is failing due to the parasitic resistance and the power supply does not start up). I cleaned the board and soldered again the same capacitor and the power supply was again functional! I also measured between the PCBA pads but the measurement was too high. It seems that the root cause is not mechanical stress on components or anything similar.Īfter measuring the capacitor on the PCBA (measured a value ~3KOhm) I desoldered it, measured it again and this time no stray resistance was apparent. I am returning to this after a while, since I had the chance to examine more failed boards. There is no electrical stress applied to the cap.Ĭan you think of any other reasons that a ceramic multilayer cap shorts in the first hours of its operation? One thought that I had was that the capacitor is mechanically stressed, cracks and after some time during operation (after a couple of hours) it fails (a resistance of a couple hundred Ohms is measured between the two terminals). I was wondering whether this failure is due to a faulty part or due to bad handling/stress during depanelization. The depanelization of the PCBA takes place in the supplier after reflow and before through-hole parts assembly. The PCB is around 150x150 and 0.8mm thick. There are no depanelization points very close to the cap (the closest point were the PCBA is attached to the PCB frame is around 6cm away). The cap is placed near (1mm) and parallel to the edge of the PCB. RF, PLC, CAD, HW Startups, Robotics, Microcomputing, DIY Audio, DIY Gear, DIY, Mindstorms, ASM, EE Books, Product Design, LabVIEW, Breadboard, RTLSDR, Manufacturing, Electronic Circuits.In a product we have an issue with a component (a MLCC cap) in the SMPS part of the PCBA.Īlthough the PCBA and the component itself are tested (ICT and FVT tests) by our supplier and also in the company I work we perform functional tests in the finished product we get this kind of failure in a sampling process where the product is tested under real life conditions and we had also a couple of incidents in the field. AskElectronics, Electronics, ECE, RPi, NiceChips, DevKit, Arduino, micro:bit, Nucleo, STM32F4, MSP430, PSoC, ARM, Amp Hour, FPGA, DSP,.How to solder: SMD Resistors, SMD ICs, SMD QFP IC, SMD Drag Solder, SMD Tips, 1980 Soldering Videos.Online: Ucamco, GerbLook, EasyEDA, MayhewLabs. Gerbv, GerberLogix, DFM Now, ViewMate, ZofzPCB, GC-Prevue, RefGerbView. Pro ($$$$): Altium, Allegro, OrCAD, PADS, Xpedition. WIKI / FAQ / PCB Review Tips / 3D models / SPICE models / Book ListĮagle, Fritzing, Horizon, KiCad, LibrePCB, ( Comparison).Links within /r/PrintedCircuitBoard subreddit: This subreddit isn't meant for repairing PCBs. Official Printed Circuit Board Subreddit - schematic capture / PCB layout / gerber / review / electronics assembly / circuit simulation.
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