SMD: What is easier to hand solder? A QFN or SOP package? - Page 1
Forum section: electronics / beginners

author: logancane
author_rank: Regular Contributor
timestamp: May 06, 2021, 11:15:20 am
content: In your experience, what would you say is easier to solder? I'm looking at an IC that comes in either a QFN-24 or a SOP-20 package. I don't have much experience with SMD so I don't really know which one I should choose. Looking at Youtube videos, it all looks kind of hard to be honest. Your help is much appreciated

author: Psi
author_rank: Super Contributor
timestamp: May 06, 2021, 11:31:00 am
content: QFN has the advantage of no pins so you don't really get any solder bridges. Bridging pins is a common problem for people new to SMD soldering.But the problem with QFN is you either need hot air or a small iron tip that you can drag solder across the sides of the chip. Drag soldering is easy once you get the hang of it, but might be a bit tricky to start with.Also, QFN comes in two versions, one type has the pads extending up the sides of the package a little. This makes hand-soldering possible. The other type of QFN does not have this. The pads are only under the chip so you can't solder them with an iron you need hot air + solder paste.SOP is quite large in the SMD world, so soldering each pin is easier. SOP pins are ~1.27mm pitch, (compared to something like a TQFP at ~0.5mm.)For someone new I reckon SOP will be easier than QFN.In either case, make sure you have a good quality solder wick available and some gel flux.It will make it much easier.

author: logancane
author_rank: Regular Contributor
timestamp: May 06, 2021, 11:43:00 am
content: Quote from: Psi on May 06, 2021, 11:31:00 amSweet, thank you for that detailed answer. What if they have thermal pads on the bottom? I guess the only way is by using hot air?

author: Psi
author_rank: Super Contributor
timestamp: May 06, 2021, 11:53:46 am
content: Sometimes the pad is optional and only used for mechanical strength and you don't need to solder it.If the pad is for thermal control then you need to solder it with hot air or a reflow oven, yesUnless your circuit won't be driving the chip anywhere near full power, then you might get away with leaving it unsoldered, but best to not take the risk.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 06, 2021, 12:37:43 pm
content: For the thermal pad there can be an alternaitve to solder with an iron with a rather large (2-3 mm ?) hole from the bottom. So kind of SMD through hole soldering.

author: logancane
author_rank: Regular Contributor
timestamp: May 06, 2021, 01:13:19 pm
content: Quote from: Kleinstein on May 06, 2021, 12:37:43 pmVery clever! I'll keep that in mind. Thanks

author: tszaboo
author_rank: Super Contributor
timestamp: May 06, 2021, 01:16:49 pm
content: If you aren't a experienced at SMD, then SOP is easier and you can easily fail with QFN, and ave no idea why it doesnt work. It also requires a microscope and hot air station or a gun.Once you know how to solder both, QFN is faster.I would go with SOP.

author: SuzyC
author_rank: Frequent Contributor
timestamp: May 06, 2021, 01:24:58 pm
content: Rather than soldering a QFN metal underbelly, just apply a thin coat of heat-conductive thermal (like CPU paste) paste, makes a good thermal contact and allows easy removal in case of repair.

author: tooki
author_rank: Super Contributor
timestamp: May 06, 2021, 01:36:07 pm
content: Quote from: logancane on May 06, 2021, 11:15:20 amI think SO is a much more beginner-friendly package. In particular, it’s a LOT easier to inspect the joints. With a QFN, you really need a microscope, and you have to get rid of basically any trace of flux in order to get a clear view of an iffy joint.Quote from: Psi on May 06, 2021, 11:31:00 amIt’s eminently possible to get solder bridges on a QFN (at least the kind with wettable sides). I see it all the time with the first-year apprentices at work.Quote from: Psi on May 06, 2021, 11:31:00 amDrag soldering is easy. An SO takes forever if you do it pin by pin, but drag soldering them is quick and easy.1000% agree on the gel flux recommendation. It makes all the difference.As for wick, I recommend MG chemicals: it’s cheap and it’s got a much finer weave than most, making it exceptionally suited to smd work.

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: May 06, 2021, 03:34:56 pm
content: Quote from: SuzyC on May 06, 2021, 01:24:58 pmAs long as it isn't serving an electrical purpose (e.g., GND or VEE).https://neurochrome.com/pages/soldering-ics-with-exposed-dap

author: Psi
author_rank: Super Contributor
timestamp: May 09, 2021, 12:41:28 pm
content: Quote from: tooki on May 06, 2021, 01:36:07 pmTrue, but it's trivial to clear a bridge between pads on QFN compared to clearing a bridge between pins.With QFN a bridge does not want to exist, but with pins every pin wants to bridge with its neighbors.

author: tooki
author_rank: Super Contributor
timestamp: May 09, 2021, 01:33:33 pm
content: Quote from: Psi on May 09, 2021, 12:41:28 pmTrue to a point, but the comparatively difficult inspection still makes SO the preferable package for beginners IMHO. And honestly, with flux and a freshly tinned soldering iron, it’s not hard to clear a bridge on pins.

author: Unixon
author_rank: Frequent Contributor
timestamp: May 09, 2021, 10:39:24 pm
content: That depends on what you're soldering with, but SOP is generally easier. Some people prefer microwave tip, I personally go with SK type small knife tip for SO leaded packages.QFN packages are usually soldered with hot air gun / IR heater, while SO without thermal pad could be perfectly soldered with a soldering iron with a proper tip or even with an improper one.Speaking about hard to solder pain-in-the-ass packages, there's a similar to QFN leadless package - the infamous DFN which has pins on 2 sides instead of 4 as QFN does,these suckers never have enough surface tension on the pins for self-centering/aligning, so it's much more prone to shorts under the package between pins or pins and thermal pad.

author: MathWizard
author_rank: Super Contributor
timestamp: May 10, 2021, 11:22:02 am
content: I really better get weaker flux, or a non-spitting type. I have some MCU's to solder, and it tends to make a lot of little solder balls and gunk, that spatters. Thats at 650C on a legit HakkoI never tried to solder a pin-less chip before, but my flux, (the solder is fine alone) has shorted a few things now I realize.

author: DenzilPenberthy
author_rank: Frequent Contributor
timestamp: May 10, 2021, 11:52:35 am
content: Quote from: MathWizard on May 10, 2021, 11:22:02 amIs that a typo? That's a completely insanely bonkers high temperature!250-350C for lead solder (lower for delicate stuff like ceramic caps, higher if you need it for connectors etc. 300C for general purpose work)Add 50C for lead free.

author: tooki
author_rank: Super Contributor
timestamp: May 10, 2021, 05:13:26 pm
content: I’m certain they meant 650F, which is around 345C. Still higher than I’d use — I try to stick as close to 300C for lead free as possible, since the higher you go, the quicker the solder on the tip oxidizes. 320C is a good temp for most boards. (At work, we aren’t even allowed to go above 360C, though I’ve frankly never had the need to do so.) At home, I usually use 270-280C for leaded, and 300-320C for lead free.I also seriously doubt the Hakko (or any other soldering station, for that matter) goes up to 650C anyway!Quote from: MathWizard on May 10, 2021, 11:22:02 amI suggest a gel flux. I use MG Chemicals no-clean gel at home, and Chip-Quik no-clean at work. The chip quik is exceptionally nice to work with, no clumpiness at all, and just smells sweet and nutty when heated. (Most modern fluxes are rather acrid.) I think it’s what I’ll get once my MG Chems runs out. It is, however, a smidgen more corrosive. (Even no-clean fluxes are corrosive - they must be heated up to a certain point for full activation, but the part people forget is that they must be heated beyond that to neutralize them. In a reflow oven that is guaranteed, but when hand soldering, almost guaranteed to not be the case. So be sure to clean.)What do you mean that your flux creates solder balls?!? Flux doesn’t contain solder. Do you mean solder paste?!