EEVblog 1455 - Capacitors Produce Current During Reflow Soldering WTF - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: February 09, 2022, 01:23:38 pm
content: Electrolytic capacitors produce current when they are reflow soldered! Enough to possibly light up a high efficiency LED. What is going on?A investigation with experiments and measurements.https://twitter.com/GregDavill/status/1491235709071818752

author: f4eru
author_rank: Super Contributor
timestamp: February 09, 2022, 02:22:40 pm
content: It probably behaves as a battery (redox something something)

author: G7PSK
author_rank: Super Contributor
timestamp: February 09, 2022, 05:30:18 pm
content: Could be something to do with the forming charge, try charging and discharging the capacitor then try heating it again to see if the current goes as high as the very first heat .

author: Zero999
author_rank: Super Contributor
timestamp: February 09, 2022, 06:32:07 pm
content: Quote from: G7PSK on February 09, 2022, 05:30:18 pmThis. You'll probably find it happens again, once you've charged the capacitor. It might need to be charged for awhile, to its full voltage rating, or even slightly higher, to fully reform it.It would be interesting to measure the value before, as well as after. 407µF does sound a little on the low side for a 470µF capacitor. It might increase its value, after being recharged to reform it.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 09, 2022, 07:17:24 pm
content: Normally reforming / rebuilding of the oxide would reduce the capacitance, as the isolation layer gets thicker. Similar the heating may create additional oxide, a little similar to reforming aging. At least building up a thicker oxide could release some chemical energy. Normal charging would not reduce the oxide.Besides the build ob of new oxide (as chemical energy) there could be also a change in the surface polarizing layer, a bit like the charging part of a super capacitor.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 09, 2022, 09:04:49 pm
content: I did an a simple test with an electrolytic capacitor (470 µV 25 V THT part 85 C type), heating it up in a more controlled way and measuring the voltage with a high impedance meter.The curve is a bit confusing, as it has 2 steps of heating, first a less controlled to around 40 V and than the more controlled to a constant 75 C with some overshoot to around 80 C.The recovery from dielectric absorption part is in the normal range recovering some 5-10% of the initial voltage.In the cooling phase after the first heat up the voltage drops a little (not very visible in the graph - but visible when zoomed in) and than starts to rise again already before heating again.The effect of first heat may still be seen as some accelerated recovery of the dielectric absorption. However this picture does not really work for the later part as the voltage nearly reaches the initial 140 mV.The voltage dropping on cool down is a strange effect: the more normal behavious of electrolytic caps is the capacitance going up with temperature. So cooling the capacitor at a constant charge would normally increase the voltage and not lower it. So there must be some extra temperature dependent charge effect going on.

author: ErikTheNorwegian
author_rank: Frequent Contributor
timestamp: February 09, 2022, 09:33:08 pm
content: In Thomas Alva Edison style of testing ..How do other type capacitors behave during heatup? Ex ceramic..Do they generate a electric charge also?

author: coppercone2
author_rank: Super Contributor
timestamp: February 09, 2022, 09:49:07 pm
content: I think so long there is a thermal differential across the ceramic material you will get some kind of voltage because of a 'squishing' effect.. I think its like a BBQ starter. thermal microphonic effect?solder through hole with thermal clamps to heavily mitigate this phenomenon

author: Old Fart Analog Engineer
author_rank: Contributor
timestamp: February 09, 2022, 10:19:57 pm
content: Here is a CLUE: Nobody makes POLARIZED Aluminum Electrolytic Capacitors! All Aluminum Electrolytic Capacitors are manufactured as NON-POLARIZED. Look into the process of how they make them Polarized to find the answer. 😏

author: Old Fart Analog Engineer
author_rank: Contributor
timestamp: February 09, 2022, 10:20:54 pm
content: Kleinstein You are on the right track, but backwards. 🙂

author: BrianHG
author_rank: Super Contributor
timestamp: February 10, 2022, 03:38:57 am
content: @Dave, so, if 1 capacitor couldn't make enough voltage for the LEDs you had on hand, you could have tried 2 capacitors in series. Maybe you would get enough to light a high efficiency red or white led.

author: julian1
author_rank: Frequent Contributor
timestamp: February 10, 2022, 07:07:55 am
content: Acidic solution of the flux (in the solder paste) and dissimilar metals equals battery cell? It's hard to see where the Vforward might come from.

author: bitwelder
author_rank: Super Contributor
timestamp: February 10, 2022, 01:52:53 pm
content: Does this effect show up only on Aluminium electrolytic capacitors, or also other types of electrolytics ?

author: madires
author_rank: Super Contributor
timestamp: February 10, 2022, 02:57:12 pm
content: The current seems proportional to the surface area of the electrolytic's aluminium foil. The 220µF electrolytic generated about half the current of the 470µF one.

author: Johnny B Good
author_rank: Frequent Contributor
timestamp: October 10, 2022, 03:11:12 am
content: Quote from: bitwelder on February 10, 2022, 01:52:53 pmAlldielectrics.The lowdown is here.https://en.wikipedia.org/wiki/Dielectric_absorptionIf you do a search on "dielectric absorption" or " dielectric relaxation" or "soakage" or "battery action", you'll find plenty of articles on the subject going into finer detail than that wikipedia page. The reflow temperature effect is just a side issue of DA is all.I think the reason why Dave didn't come across information on this DA phenomenon in capacitors was simply due to not knowing what the usual descriptive terms are for this related effect. I started by DDGing "zombie voltage in electrolytic capacitors" with, of course, no luck.It took me quite a while before I finally came across those descriptive terms and matched them to my own experience when trying to select low leakage 1500uF caps to create an RC of 1000s of seconds using 10M resistors. I needed a matching response in a feedforward correction circuit to match the thermal inertia of an LPRO I was trying compensate for the parasitic heat flows that introduced unwanted variations of its internal thermal gradients despite all the insulation used to confine heat flow through only its base plate with a temperature stabilised fan cooled heat spreader to hold it to within 20mK of its set point temperature.I gave up on using an actual RC for the job and spent the next week or so looking for "digitally synthesised RC delay" and variations thereof before finally coming across this ridiculously simple C++ one liner as described in this linkhttps://www.embeddedrelated.com/showarticle/779.phpIt seems my mistake had been in failing to use the search term "Single-Pole Low-Pass Filter"Anyhow, the cost in processing cycles using an Arduino nano was very tiny with a time step of ten seconds and tau of 1000 seconds or more so it rather nicely did the trick sans the problem of DA effects in a feedforward correction cct where the tens of millivolts of DA would cause problems at the microvolt level on the ruby's EFC pin. Not a major issue in the 1200s RC LPF used by the PLL in my gpsdo as a feedBACK circuit element (2M with 500uF).BTW, the reason why I know this is related to DA effect is on account the heat of my fingers was enough to vary the the "zombie voltage" I was monitoring with an SDM3065X on a collection of candidate caps I was testing for low leakage after leaving them shorted out for hours beforehand (hence my using the phrase "zombie voltage" because it was rising up from the dead).