SMD soldering fine pitch - Page 1
Forum section: electronics / beginners

author: Lusu
author_rank: Contributor
timestamp: July 11, 2019, 07:13:57 pm
content: While THT soldering is OK for me, is is possible (within reason) for an SMD soldering noob like me to solder a fine pitch IC like Wiznet W5100 or W5100S? I keep staring at an arduino ethernet shield (W51000) and I don't see any way to solder this by hand without proper tools (microscope, hot air gun etc.) and a ton of SMD soldering experience.I would like to build my own boards (ATMEGA328P +W5100S + lots of other stuff) but while I can use the -PU PDIP version of ATMEGA, there is no real alternative package for W5100S... I can of couse use a pre-made ethernet board, but I want PoE and there sheems to be quite a shortage of those...Edit: Should I use an socket such as one of thosehttps://www.aliexpress.com/w/wholesale-lqfp48-socket.html? Are those reliable enough for a "permanent" installation or just for brief programing type scenarios?

author: KL27x
author_rank: Super Contributor
timestamp: July 11, 2019, 09:12:47 pm
content: Doesn't really matter how fine the pitch is. A QFP can be soldered to the proper PCB footprint with just an iron. If you're soldering 1 a week/month, a microscope is not really necessary. You can inspect your work with a magnifier or a loupe if you are farsighted.Half the forum probably insists to solder something like this with a needle tip, pin by pin. And using angle hair solder wire. But SMD IC's are all universally designed so they really don't bridge unless you get too much solder on there (can be removed with wick if this happens). As long as the PCB footprint is properly adhered to, you should not have any major problem.You should put plenty of liquid flux on the pads.Most all you have to worry about is making sure the pins line up with the pads after your first tack. Then zip it up by, say, carefully cleaning off the iron tip and putting just a tiny amount of solder on it, then touching it to the pins. Rinse repeat as needed. If the first few pins bridge, just spread it along and it will be fine. (And if not? Again - solderwick will fix anything).You can carefully dab multiple pins at a time then slide out off the pin ends, rather than dragging along the pins, until you feel more comfortable. If you are ham-handed you could bend a pin while drag soldering, and now you have a problem if you ahve already soldered more than one row... it will be hard to remove with just an iron.A conical is not ideal, and you might need to use solderwick, at worst, if you get too much solder on there. But just about any tip can do this. If you wanted to "make a job of it," a largish bevel/hoof or variant of such is pretty much the best. The difference between a good and bad tip for drag soldering: a good tip will be faster at heating the pins, efficiently, it might work with a greater degree of slop without having to get the angle just so, and it will be more forgiving of the amount of solder applied on it. With a conical, you might need to use a tiny bit of solder and reapply that amount for each row of legs. With a "good tip," you might be able to put a bigger dollop on there and drag solder 2-3 of these chips without stopping. A microscope will reduce the eye strain of doing something like this regularly and/or for long stretches.The big problem with designing your own stuff with SMD IC like this is when you make a mistake and have to rework it with bodge wire. But if you're just buying a dev board, you stand a good chance to get it on there fine, as long as you have flux and solderwick.But sure. Buy that chip socket, too, if it strikes your fancy. Let us know how well it works, or doesn't.

author: rbm
author_rank: Regular Contributor
timestamp: July 12, 2019, 03:55:24 am
content: Agree with KL27x. The Wiznet 5100 uses a 0.5mm pin pitch. That is possible to hand solder with moderate care and with your through hole experience you should be fine. Lots of flux as suggested.

author: Lusu
author_rank: Contributor
timestamp: July 12, 2019, 06:52:24 am
content: Thank you for encouraging me. It is just for few ICs/boards, so far I'm at design & prototyping stage and had success with THT version of it and knock-off ethernet shiedls with bodged wires...I will definetely get a better iron and tips, what I have is like a hammer used to brush your hair... But a full SMD rework station with microscope it's a little overkill.I'm not in favor of the socket, because there are diferential pairs going in&out and this calls for trouble... plus, they are huge.I plan to go with the new variant, W5100S... smaller, firmware compatible, still 0.5 mm pitch and better of all, less heat output.

author: TheHolyHorse
author_rank: Regular Contributor
timestamp: July 12, 2019, 07:15:20 am
content: I soldered a LQFP48 a few days ago for the first time ever with no prior experience with smd soldering. The first two rows got a bit messy but the last two was a no problem at all. As people have already mentioned, lots of flux and and make sure you have solder mask between the pads.As long as you have some feeling and don't go butcher on the thing you'll no doubt handle it just fine.

author: TheHolyHorse
author_rank: Regular Contributor
timestamp: July 12, 2019, 07:22:37 am
content: As for tools I had a el cheap iron with "temperature control" one of those old circular desk lights with a magnifying glass in the middle, not an insane amount of magnification but certainly more comfortable than doing it by eye. Some chipquick 0.38mm 60/40 solder. You definitely don't need any advanced gear.

author: mayor
author_rank: Regular Contributor
timestamp: July 12, 2019, 10:08:59 am
content: Hi, as was stated above, don't use a conical tip and use lots of flux. I think a common mistake for people who haven't soldered fine pitch stuff before is thinking that because the pitch is fine, the tip should be small. That's not the case. As long as the tip can reach the pins, it really doesn't have to be small. Let the flux do its job.See around the 8 minute mark here, an older EEVBlog video (I'd use more flux than what Dave is using there):

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 12, 2019, 10:47:23 am
content: few days ago i soldered LFCSP16 with conical tip... first time try i suggest using cheap/old/non working chip until feel comfortable, you can also practice desolder (using low melt solder or heat gun) and clean existing IC from pcb during the time and re-solder it back to the pcb, will be a good learning experience. solder flux and braid and tweezer is a must and IPA alcohol to clean later and microscope/magnifying glass if you have degraded eyes like me. first time try with new chip you may screw it. with the right amount of solder on the tip, it also can be done on unmasked/diy pcb but can take longer time fixing shorted bridge with solder braid if it does happen.in dave's video above, he created bridge because his iron didnt have enough heat, so heat must be correct as well... this is another tutorial...

author: Lusu
author_rank: Contributor
timestamp: July 12, 2019, 11:06:41 am
content: Saw the video(s) several times, but looking IRL at a (soldered) W5100 chip with 0.5mm pitch and 0.2mm terminals looks way too small (and scarry) for me...I will get a better iron + tips + thin solder + liquid flux for the job (have to do this anyway) and give it a try. I'm not afraid that I will damanage the ICs during soldering, I'm more afraid of solder bridges and solder misses... if a pin is not properly soldered is bad enough to ruin my day...And I will definetly use PCBs with solder mask...

author: ptricks
author_rank: Frequent Contributor
timestamp: July 12, 2019, 11:12:32 am
content: Your first priority should be a good soldering iron. If you don't have good temperature control then you will lift pads, burn flux, burn chips, etc.Good temp control, decent amount of flux and drag soldering with some solder wick afterward and you can do most SMD easily.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 12, 2019, 11:20:13 am
content: Quote from: Lusu on July 12, 2019, 11:06:41 amironically, with enough flux, its harder to make intentional bridge, i have to pull the iron quickly before the solder fully melt to create a bridge, once they are fully melted, the hope to make bridge will diminished dramatically. i'm using conical no temp control anyway, with a button to increase power momentarily. with over power yes you can lift pads and damage IC too, but cheap crap usually under power, mine is about right. so with my case, having a cheap crap iron is not an excuse... given it has enough heat to melt a solder. with experience, and bad experience before, you should have a feeling when solder is too hot or too cold. too hot you'll need to lift your iron quickly.

author: KL27x
author_rank: Super Contributor
timestamp: July 12, 2019, 10:32:46 pm
content: QuoteYeah, this. On a QFN, it's nearly impossible to make a bridge that you can't just wipe away by going back over it. But with gull wing leads, like on a QFP, there's a tipping point where too much solder on the iron allows solder to wick up into the shoulders of the pins and bridge/blob. The shape/size of the iron tip affects where the tipping point will happen. Technically, you could wipe the tip clean and touch it to the fluxed bridge and pull a little solder out of the bridge. But with a pointy conical tip this could be highly impractical, requiring 10-30 go-arounds and plenty of re-fluxing. With a 2-3mm bevel tip, you can be a lot more sloppy with how much solder you use, and if/when you cross the line 1. this tip works great with solderwick, and 2. you can often just touch the tip to the solderwick and then used the cleaned tip to suck out many bridges, rather than using the solderwick directly on the pins. Or you can lay the solderwick next to the pins without even touching, and use the bevel tip to bridge the gap between the pins and the solderwick. So you don't really have to worry about solderwick freezing to and pulling on pins.Quote+1. With a bevel tip, in particular, the size of the cut face is important. And up to a certain point (around 2.5-3mm), bigger is better. The cut face of this tip acts like a solder reservoir. The fuller/rounder the solder bead hanging off the bottom, the more solder it wants to leave on a given pad. The more empty/clean, the less solder it will want to leave (or the more solder it will suck away off a full pad). So the larger the size of the tip compared to the size of the pad, the bigger your target for how much solder to load it with, and the less the tip will change over time as solder is deposited to the board. It will just keep chugging along.There is a similar effect for many tips shapes, but the bevel has one of the strongest effects because the cut face where solder hangs down is round and tends to wet out very easily/fully.The shape of the bevel also can get right into 90 degree corners, like on a QFN. The rim is sharp/crisp, and depending on the angle you go at, you can get an adjustable edge/wedge angle anywhere between say 45-90 degrees on a bevel that is cut to 45 degrees, for good thermal contact onto the side pad and the PCB pad. The round shape glides over pins without catching and it also acts like a preheater, giving the most heat to just one or 2 pins, and getting good preheating on the surrounding pins. Whereas if you place a big chisel or knife along the pins, you are outputting potentially huge amount of heat along that entire area to get the solder to flow.If you have a Hakko, you can even try the CF bevels, which are only wettable on the cut face. The entire sides of the tip are chromed. The bridge sucking effect is way more dramatic with these tips. They are way better at drag soldering and essentially just as good or better at any SMD soldering other than QFN, IME. And because solder doesn't wrap around the side, the beads maintains a relatively small surface area, which keeps the solder wet the longest between refreshing with flux or new solderwire before the tip "dries out."IME, the dedicated drag soldering tips with the hollow face (spoons, well tips, also called gull wing tips) are gimmicky and don't have much advantage over regular bevels. OTOH, they have reduced thermal transfer due to the hollow. So you generally have to bump up the temp, and the tip dries out faster.

author: ratatax
author_rank: Regular Contributor
timestamp: July 20, 2019, 12:19:53 pm
content: Without much experience I solder any SMD pitch quite easily, and with cheap tools. You just have to use a lot of flux, put a tiny amount of solder on the iron's tip and apply to the whole pin row -- the solder will go where it needs to go. Bridges may appears, they can be removed easily by putting the tip on them, then cleaning the tip, then repeat until all the excess solder is removed (large amount of flux helps). If you design your own pcb you can put pads near the IC pins to make drag soldering easier.