Help Needed - Soldering SMD Electrolytic Capacitors - Page 1
Forum section: electronics / general

author: David
author_rank: Frequent Contributor
timestamp: April 16, 2010, 10:05:41 am
content: Hi all,I am pretty much finished with assembling some PCB's but I cannot for the life of me solder SMD electrolytic capacitors! The solder just doesn't want to reflow! :S I have assembled the rest of the board (0603 caps/resistors/TQFPS etc) but these capacitors are just driving me crazy. I am using a reflow station and solder paste. Any tips?Cheers,Dave

author: jahonen
author_rank: Super Contributor
timestamp: April 16, 2010, 10:41:55 am
content: Those can be somewhat tricky with the hot air since the terminals are mostly under the plastic bottom plate. You would just need more heat.How about just using suitable tip for your conventional soldering iron and some thin solder?Regards,Janne

author: TheDirty
author_rank: Frequent Contributor
timestamp: April 16, 2010, 12:19:04 pm
content: I've never had a problem with these with hot air. I think you're just going to need to turn up the heat.

author: David
author_rank: Frequent Contributor
timestamp: April 16, 2010, 12:43:34 pm
content: Quote from: TheDirty on April 16, 2010, 12:19:04 pmIs it normal for the plastic base to melt slightly? I really can't see why they don't want to go!

author: Waifian
author_rank: Regular Contributor
timestamp: April 16, 2010, 12:59:53 pm
content: More Flux FTW!

author: jahonen
author_rank: Super Contributor
timestamp: April 16, 2010, 01:14:00 pm
content: BTW, are your caps on a multilayer board and terminals connected to internal planes? If that is the case, they are much more stubborn than the two-sided boards. A heating plate under the PCB is almost mandatory if there are enough ground vias.Regards,Janne

author: TheDirty
author_rank: Frequent Contributor
timestamp: April 17, 2010, 12:23:10 am
content: Are you using no lead solder or something? Warm the board first and the area around the component, don't just blow air on the cap itself.

author: David
author_rank: Frequent Contributor
timestamp: April 17, 2010, 10:20:30 am
content: I am actually using lead free paste but I do have some lead stuff too.Its a 4-layer board and yes the capacitors connect to internal planes.What sort of temperature should I be using?Dave

author: TheDirty
author_rank: Frequent Contributor
timestamp: April 17, 2010, 01:25:06 pm
content: The lead free paste is the issue. I gave up on it a while ago, but I only gave it a half hearted try.I'm assuming this is a hot air station. The temperature is different based on what air pressure you are using, the size of the board, the size of the part you are using, and obviously the melt temperature of the solder. I just use cheap dealextreme paste and I've been using around 375.

author: mrflibble
author_rank: Super Contributor
timestamp: June 03, 2013, 07:02:15 pm
content: I knew there'd already be a topic on this very subject.Yesterday I had to solder a few of those smd electrolytic caps, and those were a tad annoying. At first I tried to do it with paste + hot air. Maybe the temperature I used was too low, but that didn't exactly get me the result I was looking for. Since I was only doing a few parts I couldn't really be bothered to get out the hot plate, but reading the other posts in the thread maybe I should have... In the end I just went "ah, sod it" and soldered the pads and capacitor leads, fluxed the crap out of it and applied Ye Olde soldering iron. That did the trick alright, but there probably is an easier way.So I was wondering what other people's methods were.PS: oh yeah, what probably didn't help either is that the caps that I used were slightly bigger than the original footprint. DOH!

author: marshallh
author_rank: Unknown
timestamp: June 03, 2013, 07:29:03 pm
content: They are designed to be reflow soldered. If you aren't using a reflow oven then I would just use a very hot iron manually. If you are careful you can reach the pins.Hot air is not what you want. You'll heat the crap out of the cap and just melt the plastic spacer under it.Also, lead free paste is not made equal. It's worth buying quality stuff and makes rework a lot less painful.

author: mrflibble
author_rank: Super Contributor
timestamp: June 03, 2013, 07:59:41 pm
content: Thanks! No reflow oven I'm afraid. The best I can do over here to get close to that is hot plate + hot air. Well, maybe infrared lamp to help the top side preheat. In any event, seems like hot air is out then. Because as you say it gets pretty hot. I stopped well before the point of damaging (I hope), but that didn't get me even close to getting a decent joint. Even when directing the air flow mostly from the sides. So I guess I'll just have to do those with the iron. And note to self: use larger pads to make the job easier.Incidentally, this was with 63/37 solder paste so no lead free torture. Well, and a tiny bit of 60/40 solder to touch up after I decided hot air wasn't going to cut it. But I guess most of it was the original paste.

author: JuKu
author_rank: Frequent Contributor
timestamp: June 04, 2013, 08:11:22 am
content: By hand, conventional iron is how I do these. PCB design is also crucial.Rant on: Many PCB packages by default connect the pad directly to a plane (pad with four traces connecting to the plane) as a default setting. This is wrong! For electrolytics this doesn't work well; the plane heats so much that by the time the solder would flow correctly, the plastic under the part is starting to go as well, and the fumes and pollutions under the part don't go well with flux.The direct connection to a plane is a no-go for other parts, too. For resistors, that is the recipe for tombstoning. For ICs, the temperature profiles between pins will be uneven. If you get the plane connected pad to solder fine, you put uncomfortable thermal stress to the package.My factory rejects a PCB design with these. Their guidelines say (among other things) one track only from a pad to a plane, and at the end of that track, a thermal relieved via. Violate the guidelines and they make you sign a waver. Rant off.