how often do you see magic shorts in circuits? - Page 1
Forum section: electronics / projects

author: coppercone2
author_rank: Super Contributor
timestamp: February 17, 2024, 09:29:34 am
content: I swear I totally disassembled this device, all the boards were ultrasonic cleaned baked and inspected. Cable harness too. Those I even flushed with alcohol and inspected under magnification.When I run it I see some LDO are over heating on the PCB. (drawing 2A when it should be nothing)I take it fully apart after playing card swap for 2 hours between two units and of course it works just fine with all the original PCB right at the end when I was going to call it a night. I was obviously inspecting the PCB under light as I was trouble shooting to find shorts.the invisible man strikes again with the transparent superconductive short.I feel like if I was working in the dirty workshop with piles of cut strands and filings with zero care about contamination, there would not be a problem. Normally its the evil ghost of otto sckorzeny haunting my work, switching polarities.. this time he leaves a wrench on the tram rails. If you don't know he was a dangerous man that drove general patton and friends crazy by flipping signs in france.Anyone else notice this tendency? when you work like a haphazard fool it ends up working fine, but when you try to do a good job of course you create some kind of problem.

author: exe
author_rank: Unknown
timestamp: February 17, 2024, 09:39:28 am
content: I had a few surprising shorts on my boards too. Like, had tiny whiskers after hand soldering that I could only see under microscope.I try to clean all the debris asap, and cut stranded wires directly above the bin and under the table so no strands can get onto my table.

author: Saqi S
author_rank: Newbie
timestamp: February 17, 2024, 11:37:26 am
content: It's a reminder that in the world of electronics, sometimes, circuits just like to play tricks on us, adding a bit of surprise magic to our tech adventures. But finding the reason behind such troubles is important to save your money from getting into the waste. The possible reasons could be faults, interference, overload, Short Circuit, Malfunction, [ineffective heat removal], Aging, and Misconnection.Moderator edit: Removed spam link/blatant advertising from user profile.

author: shakalnokturn
author_rank: Super Contributor
timestamp: February 18, 2024, 01:56:40 am
content: In many years I've had maybe 3-4 confirmed cases of tin whiskers.Now my eyesight is on the decline if I'm not more careful while reflowing and double checking when all is done I tend to get myself more surprises.The time when I could solder a QFP144 and only use magnification for the final check seems so nearby yet desperately out of reach...

author: Teledog
author_rank: Regular Contributor
timestamp: February 18, 2024, 04:23:30 am
content: Where were the boards made?Had issues years ago on large boards (hand populated), supplies were good/checked OK, but once the BGA CPU was installed, it shorted!Yanked the CPU & checked ..guess what.. the PCB mfr. didn't tent the vias under the BGA CPU.What a PITA!At least we only ordered a few boards for prototyping.Start by building up the power supply section, a component at a time & check the continuity/current as you go.Sometimes one gets a batch of defective parts (had that happen more than once)

author: CosteC
author_rank: Regular Contributor
timestamp: February 18, 2024, 01:37:58 pm
content: Is you have 2 A of current thermal camera becomes helpful. Now prices are so low it justifies saving hours of work.

author: Niklas
author_rank: Frequent Contributor
timestamp: February 18, 2024, 11:30:06 pm
content: Two things that comes into my mind:1. Cracked ceramic capacitorMight be difficult to find unless the capacitors are desoldered and checked with light from the side. Could cause high currents, but not much heat, so difficult to find with a thermal camera.2. PCB designed with too little margin between via hole and surrounding copper on internal layer.Layer-layer alignment tolerance during lamination. Small/no annular ring on layers without connection on that net together with small plane/polygon clearance. Drill positioning tolerance. Wicking of plating liquid up to 0.1 mm from the hole wall. The result could be internal connection that is triggered by thermal expansion, so very difficult to measure with a multimeter.A small short in a feedback network for a regulator could cause high current if the output voltage is increased above spec for the load. Even weak connections as dendrites or case 2 above could cause that.

author: 44kgk1lkf6u
author_rank: Regular Contributor
timestamp: February 19, 2024, 04:16:13 am
content: I had a board which accommodated QFN and QFP versions of the same chip. I used a QFP one. Some flux got under the chip and shorted the QFN pads. The board looked clean, so I only found the problem after I suspected maybe the chip was broken and removed it. Then I switched to solid rosin.

author: enut11
author_rank: Super Contributor
timestamp: February 20, 2024, 07:07:32 pm
content: How about its counterpart - the magic open.I was tracing a signal through an audio generator board when it disappeared at one end of a solid copper link. I removed the link and tested it stand alone, totally open.What appeared to be a solid piece of copper wire was open circuit.

author: SiliconWizard
author_rank: Super Contributor
timestamp: February 20, 2024, 07:56:06 pm
content: A bad contact with one pin on QFN or BGA packages can be a nice one too. Sometimes hard to see with QFNs, impossible to see with BGAs unless you have X-ray.Not in all cases will it "behave" as a complete open. Due to the proximity of the pad to the pin/ball, even if not in full contact, it'll have capacitive coupling. So if dealing with a high-freq signal, the fault may not be completely obvious.

author: jonpaul
author_rank: Super Contributor
timestamp: February 21, 2024, 12:55:45 am
content: a few times in 30 yrs: Tin whiskers esp in lead free with voltages above logiHairline shorts on PCB

author: Vovk_Z
author_rank: Super Contributor
timestamp: February 21, 2024, 06:41:32 am
content: They say there are more then 3 dimentions in our world. They say there can be 4-th and 5-th etc dimentions which we just cannot see. But those invisible dimentions interact somehow with our things. Definitely something like that happens, because otherwise I couldn't do such stupid mistakes. 😀

author: coppercone2
author_rank: Super Contributor
timestamp: February 21, 2024, 06:52:33 am
content: Quote from: Vovk_Z on February 21, 2024, 06:41:32 amblame thishttps://iaizzi.me/2020/03/18/spinons/