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Electronics => Repair => Topic started by: I_Code_4_Hugs on July 04, 2018, 07:16:31 pm

Title: Flat-flex "dendrites"
Post by: I_Code_4_Hugs on July 04, 2018, 07:16:31 pm
My Samsung Blu-ray player had been acting up by randomly switching off.  Upon disassembly, finding nothing loose, I put the cable under the microscope and found "dendrites" shown in the attached image.

Disconnecting the flat-flex solved the problem.  Simple fix, but interesting failure mode.

Has anyone else seen something similar?
Title: Re: Flat-flex "dendrites"
Post by: joeqsmith on July 04, 2018, 07:40:44 pm
Yes, on a hard drive ribbon cable that went to the head. 
Title: Re: Flat-flex "dendrites"
Post by: kony on July 04, 2018, 07:41:32 pm
What voltage is present across those two tracks? Looks like electromigration of the printed thick film paste metal to me.
Title: Re: Flat-flex "dendrites"
Post by: In Vacuo Veritas on July 04, 2018, 08:29:31 pm
Looks like CAF.
Title: Re: Flat-flex "dendrites"
Post by: chickenHeadKnob on July 05, 2018, 03:29:47 am
Quote from: kony on July 04, 2018, 07:41:32 pm
What voltage is present across those two tracks? Looks like electromigration of the printed thick film paste metal to me.
I would agree there must be a DC voltage present, one side is clearly an anode the other cathode. As I understand tin pest is different, it generates from the surface energy of the plated tin all by itself. With even  no DC present, you would  expect whiskers coming in randomly from all directions.
Title: Re: Flat-flex "dendrites"
Post by: helius on July 05, 2018, 04:23:49 am
Quote from: In Vacuo Veritas on July 04, 2018, 08:29:31 pm
Looks like CAF.
For those playing along at home, CAF are conductive anodic filaments (https://en.wikipedia.org/wiki/Conductive_anodic_filament).
This failure mode can be very hard to detect when it migrates on interior layers.
Title: Re: Flat-flex "dendrites"
Post by: mzacharias on July 06, 2018, 05:31:43 pm
SATA connector, never used, went up in flames inside my desktop computer. Apparently they can grow these internal shorts.
Title: Re: Flat-flex "dendrites"
Post by: Ranayna on July 06, 2018, 07:42:14 pm
Those Molex to SATA adapters with the molded SATA power connector are infamous in IT.
They spawned the expressen "Molex to SATA - lose all your data"...
There are a lot of pictures of various SATA devices going up in flames, and in almost all cases, one of those stupid things was used.
Title: Re: Flat-flex "dendrites"
Post by: envisionelec on July 06, 2018, 09:20:53 pm
Yes, on a Maytag dishwasher control panel. $150 for a new one...  :--

You might be able to blow the dendrites away with a carefully controlled burst of energy between the two conductors.
Title: Re: Flat-flex "dendrites"
Post by: exit_failure on July 06, 2018, 09:57:11 pm
Has there been any real explanation for the countless instances of melted or even burning SATA to Molex adaptors? Thin wires? Bad mechanical construction? Divine retribution?
Title: Re: Flat-flex "dendrites"
Post by: german77 on July 07, 2018, 01:25:27 am
Quote from: exit_failure on July 06, 2018, 09:57:11 pm
Has there been any real explanation for the countless instances of melted or even burning SATA to Molex adaptors? Thin wires? Bad mechanical construction? Divine retribution?
Yes basically they are made as cheap and fast as possible. The cables inside are basically not in the correct position and some build failures like the flat-flex until they arc.

This video has a nice examples of the bad manufacturing https://www.youtube.com/watch?v=fAyy_WOSdVc (https://www.youtube.com/watch?v=fAyy_WOSdVc)
Title: Re: Flat-flex "dendrites"
Post by: oventech on July 13, 2018, 03:17:48 am
Are they made with a mechanical  connection?    Reminded me of tin whiskers due to ROHS.