My SMD soldering is terrible. Any suggestions what's wrong? - Page 1
Forum section: electronics / general

author: julesh
author_rank: Newbie
timestamp: January 29, 2025, 11:05:47 pm
content: I'm really struggling with soldering SMD devices, especially those with pins that have tight spacing (e.g. TQFP chips and similar). I have a couple of specific problems, which may or may not be related:* I find it hard to get solder to wick onto device pins properly. The solder typically takes a while to melt (much longer than I see in youtube videos, for example), and when it does it's more likely to just stick to my iron rather than flow onto the pad or the device pins.* If solder is in the wrong place, or I have too much of it on a pad, I struggle to get it to flow into the right place. Solder frequently just turns into partially solid balls that I can push around a pad, rather than properly flowing. When this happens, it seems the only thing I can do is use solder braid to remove as much of it as possible and start again.* Trying to clear solder bridges between pins of chips is nightmare. The solder just won't clear in the way I see other people can do it just by reheating it and letting it flow to a more useful place. Instead it hangs around, just getting pushed around by the end of my iron tip and not flowing away.My equipment, in case any of it is completely wrong:* Pinecil soldering iron, with the default conical tip (e.g.https://pine64.com/wp-content/uploads/2020/11/Pinecil-ST-B2.jpg)* I've tried a variety of different types of flux, e.g. a "ChipQuik" branded flux pen and a similarly branded syringe, along with solid rosin flux* Unbranded 0.5mm tin/lead solder (don't recall exactly where I got it from, buthttps://www.ebay.co.uk/itm/193323632242looks very similar)* PCBs from JLCPCB.I've been using the soldering iron set to a variety of temperatures, but even at the highest temperature I sometimes get the issues described above (but not always).Any ideas what I'm doing wrong?

author: TERRA Operative
author_rank: Super Contributor
timestamp: January 30, 2025, 12:05:36 am
content: Go buy some real solder, and use more flux.

author: jayx
author_rank: Regular Contributor
timestamp: January 30, 2025, 12:10:17 am
content: Have you watched any tutorials on youtube? Surely there's plenty, perhaps someone can recommend a good one.Other than that:* Conical tips are useless. Use chisel, roughly 1.5-2mm wide. No, it doesn't matter if it's larger than the gap between fine pitch IC leads, it's actually an advantage.* I don't have experience with fluxes other than rosin, it's pretty good. But can't be thin like water, need to be thick like honey. Use decent amount, aka Louis Rossmann amount.* Highest temperature doesn't mean it's best. Don't exceed 350°C for leaded solder. If you have high thermal mass (large component, large coller pads), preheat the whole PCB and / or use larger chisel tip.

author: IanB
author_rank: Super Contributor
timestamp: January 30, 2025, 12:11:14 am
content: Conical tips are bad for most types of soldering as they can only deliver a small amount of heat though such a small tip. A larger horseshoe tip would likely work better.

author: thm_w
author_rank: Super Contributor
timestamp: January 30, 2025, 12:37:23 am
content: Show photos or video if possible.I wouldn't use no-name solder as stated above.

author: johnboxall
author_rank: Unknown
timestamp: January 30, 2025, 01:14:57 am
content: Just in case you glossed over previous posts - buy real solder.Next, a very smart person made a great video on SMD soldering:

author: DavidAlfa
author_rank: Super Contributor
timestamp: January 30, 2025, 04:36:14 am
content: First, as they say, AliExpress solder is often garbage, though I've read several times that Mechanic brand is pretty decent.Better to get some good 60/40 leaded stuff.There're many terrible fluxes out there! I have a bunch of them that burn my tips or perform worse than not using flux at all.This one works really well for me:https://www.aliexpress.com/item/1005001424090098.htmlI apply flux over the pins and put a really small blob of solder on the tip, then I perform a drag operation.Try a chisel or flat style tip, they're great for this purpose!Use a thick tip that covers at least 3-5 pins at once.

author: JohanH
author_rank: Frequent Contributor
timestamp: January 30, 2025, 07:53:34 am
content: I occasionally solder SMD parts. I like chisel tips as well. Just for fun, I tried some Aliexpress solder and it was absolute garbage. I stick to a 20+ year old roll of 60/40 that I have and newer Polish Cynel 60/40 (SW26 rosin flux 2.5%). I like the flux that you apply with a syringe, almost any brand works better than the flux pens I have. Though some brand quality is probably better.

author: armandine2
author_rank: Frequent Contributor
timestamp: January 30, 2025, 08:00:54 am
content: ... I found a bent conical gets used more than a straight one..and lots of practice on discarded boards/chips - watch others - have good gear

author: asmi
author_rank: Super Contributor
timestamp: January 30, 2025, 02:44:06 pm
content: Chisel tips are the best for SMD soldering, also good flux makes a world of difference. I use this one:https://www.chipquik.com/store/product_info.php?products_id=310040And there is no such thing as too much flux - at least for manual soldering, so use plenty of it.

author: SMTech
author_rank: Frequent Contributor
timestamp: January 30, 2025, 04:31:01 pm
content: Quote from: asmi on January 30, 2025, 02:44:06 pmJust don't say that near an IPC trainer....

author: IanB
author_rank: Super Contributor
timestamp: January 30, 2025, 04:37:00 pm
content: Quote from: SMTech on January 30, 2025, 04:31:01 pmIt depends:

author: asmi
author_rank: Super Contributor
timestamp: January 30, 2025, 04:43:11 pm
content: Quote from: SMTech on January 30, 2025, 04:31:01 pmI don't really care what they think about it, I'm just saying what works for me. Besides, the flux I use and recommend is water-soluble so it's very easy to clean it up once soldering is completed.

author: julesh
author_rank: Newbie
timestamp: January 30, 2025, 11:01:58 pm
content: Thanks for all the great suggestions. I've looked at all the above, and a few other resources, and found a few things that may help:* My board has a reasonably large ground plane and no thermal relief, so definitely preheating the board is a good idea.* I discovered that the brass cleaning pad I bought is actually an electroplated steel cleaning pad, which seems to have scratched off a lot of the coating on my iron tip and let it oxidize, so I've bought replacements (along with a couple of different size chisel tips, as suggested).* Will look into better quality solders if these suggestions don't work.

author: eTobey
author_rank: Super Contributor
timestamp: February 01, 2025, 08:05:54 pm
content: This is some proper education. Its old, but it explains important things! Whatch the other ones too!

author: janoc
author_rank: Super Contributor
timestamp: February 01, 2025, 09:46:44 pm
content: Quote from: julesh on January 30, 2025, 11:01:58 pmIf you are working on boards with large ground planes and no thermal reliefs (oof, good lesson what not to do next time!),do get a proper soldering iron. Your Pinecil most likely has nowhere near sufficient power to deliver enough heat into such joints, especially if you use the conical tip that came with it.These portable mini irons are great if you need to do some small fix somewhere in the field or on the road - but not for working at the bench. Get an iron that takes the T245 JBC-style cartridges, get a properly sized cartridge for the job - and it will make all the difference even without a preheater. Thermal capacity and thermal transfer are thing, if you are trying to heat a joint like that with the pointy end of your conical tip, then no wonder your soldering is terrible - the iron could be showing 380-400 degrees C on the display but the actual temperature at the joint is maybe 200 degrees less because of the poor thermal transfer through that tiny tip.And do buy a good quality solder as the first thing, not only "if these suggestions don't work".