Safe way to desolder SMT electrolytic caps? - Page 1
Forum section: electronics / repair

author: JoeN
author_rank: Frequent Contributor
timestamp: May 03, 2015, 09:26:05 pm
content: For some reason around here everyone is turning in not extremely old 2-Wire DSL routers at Goodwill. I bought a couple for $2 and they have a lot of good parts on them. Lots of inductors and signal transformers, a couple of memories each, a crystal, two oscillators, gas discharge tubes, regulators, lots of 0805 caps. Also they contain a number of SMT electrolytic caps. Everything else I was taking off with hot air. Are these caps safe to take off with hot air too or are they going to blow up on me? How would you take them off? Thanks.On closer inspection, the leads protrude a bit. I apply heat from a chisel tip and they come off. Maybe hot air isn't the best solution here. But, can I use it or will I blow the cap up?Caps in question:Caps in question:

author: wraper
author_rank: Unknown
timestamp: May 03, 2015, 09:31:06 pm
content: With 2 soldering irons simultaneously. But reusing Electrolytic capacitors is not a good idea in the first place.

author: and101
author_rank: Contributor
timestamp: May 03, 2015, 09:34:17 pm
content: The way I normally remove them is to heat one pin with a soldering iron and carefully lift that side of the cap up enough so it breaks away from the board. Let the pin cool so the solder solidifies and then repeat with the other pin. It should come away without causing any damage to the cap.Or if you have two soldering irons use them like tweezers and heat both pins at the same time until you can lift the cap away from the pcb.

author: JoeN
author_rank: Frequent Contributor
timestamp: May 03, 2015, 09:45:22 pm
content: Quote from: wraper on May 03, 2015, 09:31:06 pmI bet you are right. Normally I wouldn't. Certainly not a big old cap off of old piece of equipment. These boards just look so new and modern I am tempted to take them. Have a look at the image I added.

author: JoeN
author_rank: Frequent Contributor
timestamp: May 03, 2015, 09:47:06 pm
content: Quote from: and101 on May 03, 2015, 09:34:17 pmExactly the way I just did it. I guess no hot air for these is probably best. This is on my list of things to buy at some point:http://www.ebay.com/itm/902-SMD-Hot-Tweezers-Soldering-Iron-ESD-Station-Frm-USA-/120887412585It's just not high enough on the list to have bought so far.

author: wraper
author_rank: Unknown
timestamp: May 03, 2015, 09:48:46 pm
content: Quote from: JoeN on May 03, 2015, 09:45:22 pmFor me it looks almost 9 years old according to the date codes.

author: AlphZeta
author_rank: Regular Contributor
timestamp: May 03, 2015, 10:38:13 pm
content: My method of removing these caps (or larger SMD parts), is to blow hot air from the reverse side of the board. This way, you can use slightly higher temperature (given that you are not planning to use the board again) and the components won't be overheated.

author: mskobier
author_rank: Regular Contributor
timestamp: May 03, 2015, 11:06:12 pm
content: A while back, I purchased a set of soldering tweezers that work great. Its actually two soldering irons in a tweezer shaped configuration with different size replaceable tips. That's what I used to remove the caps and some resistors from my 2445B A5 board. Worked great. Do a -bay search for soldering tweezers to see an assortment of models and styles.Mitch

author: JoeN
author_rank: Frequent Contributor
timestamp: May 03, 2015, 11:18:21 pm
content: Quote from: mskobier on May 03, 2015, 11:06:12 pmI will have to move my purchase up.I have my heart set on these. They aren't the cheapest, and they aren't Hakko either, but they seem to be a nice mid-range model that appears to be very popular:http://www.ebay.com/itm/902-SMD-Hot-Tweezers-Soldering-Iron-ESD-Station-From-USA-/120887412585

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 04, 2015, 12:42:35 am
content: They can be walked off, like any leaded part. Heat one side (apply fresh leaded solder if possible to reduce melting point and enhance the transfer area of the iron's tip), apply pressure to lift that pin, switch sides and repeat.The base wafer thing might get a bit melted in the process, but that's fine if you're replacing things.Tim

author: mariush
author_rank: Super Contributor
timestamp: May 04, 2015, 02:13:28 am
content: Drop of flux on each side, put solder on the tip, move tip from side to side on the tabs until they get hot and then bump the capacitor and should lift by itself.Someone on Youtube norcal removes surface mounted capacitors by simply twisting the capacitors in both directions with a bit of downward pressure until the leads just break, as the leads are flat and very thin. He then puts solder tip on the tabs stuck to the pcb and lifts them easily from pcb.Here's his procedure, jump to 10:35

author: lm3baker
author_rank: Contributor
timestamp: May 05, 2015, 12:14:45 pm
content: Quote from: mskobier on May 03, 2015, 11:06:12 pmSoldering tweezers are worth their weight in gold!Used these at work for repair / removal / replacement of SMD parts (from big caps down to 0603), easiest method by far.

author: mzzj
author_rank: Super Contributor
timestamp: May 05, 2015, 12:38:22 pm
content: Quote from: mariush on May 04, 2015, 02:13:28 amThis is my standard procedure as well. But the OP wanted to collect those capacitors for further use.

author: jlmoon
author_rank: Unknown
timestamp: May 05, 2015, 04:46:20 pm
content: Quote from: JoeN on May 03, 2015, 09:26:05 pmIf only for salvage purposes, try using a precisely controlled hot plate heat board upto around 405 degrees F and wait a few seconds until the solder changes texture, then all the parts will fall off like magic.

author: JoeN
author_rank: Frequent Contributor
timestamp: May 05, 2015, 07:58:39 pm
content: Quote from: jlmoon on May 05, 2015, 04:46:20 pmSo is that a hot plate with a PID controller or what is that? Can you reveal the specific parts?

author: Howardlong
author_rank: Super Contributor
timestamp: May 05, 2015, 08:23:57 pm
content: Quote from: mariush on May 04, 2015, 02:13:28 amIs there a reason he replaced them with wire ended caps rather than SMD ones?Not sure about the destructive method of removal, solder tweezers is the the right tool for that job. Too much chance of damaging the board IMHO with that twist method.

author: jlmoon
author_rank: Unknown
timestamp: May 05, 2015, 08:32:54 pm
content: Quote from: JoeN on May 05, 2015, 07:58:39 pmJoe,That is a sandwich heater (1/2 - bottom portion) like the egg McMuffin heaters. You can get one at Walmart for like $25.00 and then you rip it apart, mount a Type K thermocouple in the plate, feed the heater element with a solid state relay controlled by a Solo PID controller. I had no problem reaching more than the needed temp to remove parts from a board. The thermocouple feeds the temp from the plate back to the PID which regulates the heater through the SSR device based on a temp profile set in the PID. It works really well! The one you see in my picture was a mock-up (not the safest way possible, but I am aware of the hazards) that I used to remove some 240Pin FPGA chips that needed to be reapplied due to manufacturing problems. The Solo controller is quite intelligent and will learn what you need as you go, it has 8 steps or set-temps you can set it to along with time sets on each. Personally I am very impressed with this controller.

author: jlmoon
author_rank: Unknown
timestamp: May 05, 2015, 08:34:55 pm
content: Quote from: Howardlong on May 05, 2015, 08:23:57 pmI sure wouldn't want to bend on those parts either just doesn't sound like a good plan.

author: JoeN
author_rank: Frequent Contributor
timestamp: May 06, 2015, 12:58:21 am
content: Quote from: jlmoon on May 05, 2015, 08:32:54 pmThat's really good information and I appreciate it. I may look at that controller. It turns out that about 2-3 weeks ago I was in a surplus store and they had these matched PID controllers and SSR units (new, never used, old stock, a manufacturer of commercial ovens had too many) for a song and I bought a few of each. I think that these may be able to be set up to do the same thing. I am not sure of the PID controller, I am going to have to figure it out, that's not something I have worked with before but I understand the concept. So thanks for the information, I will try to find a good hotplate and apply that to my situation. I actually have a few FPGAs I picked up a while back at a very, very good price that I would like a crack at someday too. This is very "aspirational" at this point. It is beyond my ability to design a board for this part yet but I would like to get them off and reball them.Please have a look at the controller and SSR below. Good stuff? Junk? I have no expertise but it looks pretty damn good to me for the price. I bought several of each.

author: jlmoon
author_rank: Unknown
timestamp: May 06, 2015, 03:34:21 pm
content: Those SSR's and Virtex-6 look like some interesting items. Great find! The PID, not sure about that one I have not looked up the datasheet. As I stated earlier, the one I use has 8 profiles you can operate or create a ramp which is important when working with reflow / smt devices. When you reach in excess of 400 F you don't want to stay there any longer than you have too or you can damage boards or parts to heat exposure. When I did some FPGA rework, abiding by the temperature specifications of subject parts, I was up there in temp for only 20 or so seconds and had zero flaws in the process. Another way to do this is to use a toaster oven if you desire to remove all of the parts from board, they will fall off. Warning, be sure to use as I have a good thermocouple and controller to control your heat and heat time. Stuff gets hot fast!!! Best of luck!Jon

author: Shock
author_rank: Super Contributor
timestamp: May 07, 2015, 04:43:32 am
content: If you have a Hakko 888 or 936 or clone you can buy a cheap Chinese tip and do something like this SMD tweezers hack. You might want to buy an extra tip enclosure and nut, that way easy to get on and off. Should cost you about $5.Here is a video of it as well, obviously temp control is important for longer tweezers but you can make a custom tips to get in at any angle.

author: JoeN
author_rank: Frequent Contributor
timestamp: May 07, 2015, 07:51:32 am
content: Quote from: Shock on May 07, 2015, 04:43:32 amI have received some cheap chinese boards on eBay that I think were *made* with that tip. Figures.