Hey guys,
I just got my PCB delivered. I made this PCB to solder some neopixels on it (WS2812B). These neopixels are very small, and the footprints of these neopixels (the footprints I found in a library in KiCad) have very small pads. I barely have space to solder the ‘pins’ of the neopixels on the pads (see picture). How can I solder these neopixels on the PCB? Does anyone has any tips?
Thanks!!
I’d use a soldering iron to place small blobs of solder on the pads (which should be easy because of the solder resist), then use a hot air gun so all four blobs remain liquid. Take away the heat gun and immediately drop the LED on top.
Since none of the pads are connected to large planes you might get away without the hot air gun if you’re fast enough, just swipe across the pads with a drop of solder on the iron, and then immediately drop the LED on top.
The WS2812 plastic cases have an annoyingly low melting point, so avoid pointing the hot air gun at them. If you have to, use a low temperature setting with a high flow rate.
Thanks for your reply. I will try this this approach. In the future, I will make a footprint with larger pads.
For a bunch of Footprints, versions with larger pads are already available in KiCad’s libraries with the suffix “Handsoldering” 
For the PCB’s you already have, the tracks are pretty wide and go to the side. You can use the tip of a knife to scrape of a little bit of soldermask to expose more copper.
For hand-soldering SMD, the use of extra flux is almost mandatory.
I usually start with taking the bare PCB and put a little bit of solder on one of the pads of each component. After that I put a bit of flux on all pads of the footprints, and then I use the soldering iron in one hand and tweezers in the other hand to place components on the PCB, and I only solder the single pad that already has solder on it. Make sure the components are centered, and all pins touch the pads.
If you have done this properly, then the next step is to have a soldering iron with the right temperature and tip size, and thin solder (0.5mm or at most 0.8mm).
If the soldering iron is too cold, you can’t heat the pads (fast enough), if it is too hot, you burn away the flux before you are finished with soldering.
With the small pads you need a soldering iron with a fine tip.
Sometimes it works to first heat the pad and the component pin, and then add the solder directly to the pin or pad. Try to not have direct contact between the solder and the soldering iron, because the flux evaporates fast after the solder melts.
Sometimes it works to first put the solder against the pad and the pin and then heat everything at the same time with the soldering iron.
Some people have success with first distributing solder paste on the PCB with a syringe, then placing the components in the wet solder paste and then heating the whole board from the underside, believe it or not, in a frying pan. A layer of dry and fine sand helps with keeping the temperature evenly distributed.
There are also other ways of soldering SMD components, and you can find them on Youtube. Some are quite nice tutorials. Some people with lots of experience make it look easy
To be nitpicky: The correct suffix is HandSoldering (Camel-case as english has no compound nouns)
See https://kicad.org/libraries/klc/F2.1/
But there are still a lot that use HandSolder as we did not codify this until very recently. (I might be the reason for most of these HandSolder ones as my IPC script for two terminal devices like resistors uses this suffix.)
Regarding the topic at hand:
Should be doable with a bit of solder on the pads and a fine tip (plus a steady hand). Just place a the tip of the solder iron on top of the lead (It is after all a gullwing part. Would it be a no lead part then you would be truly in trouble.) Maybe use a bit more heat in the iron than you would otherwise (It is better to go hot and reduce the time your component is exposed to heat than to go too cold and have the iron in contact for ages.)
A lot of flux will also help a lot. (Don’t forget to clean the board afterwards)
Some magnification can make it easier as well.
In the world of SMT components, that part is somewhere between “large” and “huge”.
Of course, SMT components are mostly placed onto board assemblies and soldered into place by automated machinery. Make a note to yourself: If you expect to manually solder SMT components to a PCB assembly, consider using footprints that are designed for that sort of process. In the KiCAD libraries there are some footprints with the designation “_Hand_Solder” in their name. Can you guess why? Load a few of rhem in the Footprint Editor, and compare them to equivalent footprints without the “_Hand_Solder” designation. What are the differences?
How large is this board assembly? Can it fit into a table-top electric skillet, or a toaster oven? If so, it’s a candidate for a crude reflow soldering process, where the small pad sizes won’t matter very much. Additional details can be found in this Forum and across the 'web.
OK, so much for the “Why didn’t you say something sooner?” answers.
To solder that package by hand you will need:
A desktop lighted magnifier (Mag-Lamp UN1030 or similar). If you can’t find one in a second-hand office supply store, expect to pay US$75 - US$100 for a suitable tool. The cheap ones from the discount store are frustrating because they don’t maintain focus across the visual field and distort colors.
A decent temperature-controlled soldering iron. A lot of folks swear by the Hakko FX-888, but there are other good ones. Sometimes you can find them on promotional prices from US$60. Some surplus industrial units are quite usable; some are repairable; and some are trash. In hobby service, a decent unit will last at least half a lifetime.
Fine-pitch tip(s) for your soldering iron. The optimum tip depends on a convolution of your work tasks with your personal work style and habits. Consider sizes and shapes similar to Hakko T18-BR02, T18-C05, T18-C08 or T18-C1. (I often have two soldering irons going on my work table simultaneously, with two different tips, and it’s not unusual to see me with one in each hand when I’m doing repairs or rework.)
Stainless tweezers, preferably non-magnetic. Reverse-action tweezers like Testor 8942T are useful after you learn to use them.
Consider doing this job with solder paste, dispensed from a syringe, rather than fine-diameter, flux core, wire solder.
Practice, practice, practice.
Patience. Don’t put off getting this - you need it NOW!
Dale
Thanks for posting that link! Reading that page increased my appreciation for the thought and effort that went into creating a well-structured, comprehensive, KLC.
It is comforting to know the Austrian Grammar Police are on duty, monitoring the usage of my first (and, regrettably, only) language.
Dale
Paulvdh has a similar approach to mine. I start with some flux around the footprint. Then I put a small dab on one pad, put the LED down and put the iron up against that pad. Then I put small dabs on the other pads, and put the iron on them. There should be a small piece of the footprint exposed and with the flux it should give a good connection. I’ve done several pcbs with the 2812 and haven’t had that many issues, but I’ve had a lot of practice as well.
You’ve got lots of board room so the hot air gun approach should work. but you have to be careful as GyrosGeier pointed out, the cases will melt easily. I’ve melted them with the iron as well.
Anyone tried the 2812 with a reflow oven?
To oven solder good temperature control is necessary. The white material is a plastic.
Also I have found some failed WS2812 in a commercial production, where the clear epoxy has fractured, disturbing the fine internal wires. About a 5% failure rate ! Thankfully the manufacturer accepted responsibility.
With this approach, the key to getting a good solder joint (while not damaging the component) is being able to touch a portion of the copper pad - even the slightest sliver - with the hot soldering iron tip. In my experience, a “bent” or “crooked” tip geometry helps:
I don’t recall when I added extra flux for soldering SMT parts. With a small tip (clean and well-tinned), good heat, and small-diameter wire solder, the flux in the solder seems adequate. Your personal technique will likely be different. But for the task presented by @hilmi28 in this thread, I’d place a small bit of paste solder on each pad, put the part in place, and touch the soldering tip to the pad. Paste solder is a mixture of finely-ground solder particles in flux. The slightest touch by a hot tip melts the whole drop, and the flux carries the solder throughout the entire joint.
Dale
I’ve been soldering parts for a long time. For me the following works the best:
1: I use a soldering tip with a flat at the end (see below) the tip is capable of holding a small amount of solder on the flat.
This is a Weller LT4 tip.
2: Pick up the part with a tweezers.
3: I usually put a little flux on the SMD part lead as the solder on the tip no longer has the flux that was in the solder it picked up. The boards I use are fresh (new) so solder readily wets the pads.
4: Hold the part to the board, and hit the lead/pad with the solder tip. Solder transfers to the joint and you should be good.
The next 3 pads should be easier because you don’t have to position (hopefully) the device as it should already be in the correct position held by the one lead. You could hold it down with a toothpick if you wished.
Good luck.
I am not convinced that the manufacturer was to blame.
These LED’s and lots of other components are moisture sensitive. Some of the components you buy from shops as Mouser are packages in a hermetically sealed bag (Not just plastic, but also with an aluminimum barrier layer) and have a dessicant bag inside, and even indicator paper which discolors if any moisture enteres the bag despite these measures.
The reason for this is that any mosture absorbed by the plastic turns into steam at solderig temperatures, and this can build up enough pressure to crack the housing.
If there is doubt about packages having absorbed moisture from the air, there are ways to recover, which involves “baking” the chips in an oven at specific temperature profiles (Usually just below 100C and after some time just above 100C). At 120C or so steam pressure is managable, and the steam has an opportunity to diffuse out of the plastic again. At soldering temperatures however, the steam pressure is so high that it exceeds the strength of the plastic ( which is also weakened at those temperatures).
For more info, do a search like:
https://duckduckgo.com/?q=semiconductor+baking+humidity&ia=web
Guys, all your replies contained so much new words and information for me. I did my research on all of your replies and learned a lot of new things. I made this PCB to make a Wordclock. The PCB is about 35x35 cm and contains 90 LED’s. The second time I order the PCB’s, I will definetely use the footprints with the HandSolder suffix. But for now, the idea of solder paste is very attractive to me. Because I don’t have a hot air gun, I will do it with my soldering iron. I will put some solder paste on the four pads, put the LED on top of it and then put my iron on the pad/solder paste. After I have tried this, I will let you guys know. Thanks so much!!
I tried solder paste some time ago. I couldn’t dispense a small enough amount of solder paste to get a good joint. The solder went everywhere. So try to get solder paste with a method of dispensing a small amount of solder.
Another thought, perhaps you can find a solder stencil that applies solder to one of you LED footprints at a time.
For dispensing solder paste by hand, somtimes a small dish, (or a coin, small, but heavy metal) is used with a blob of paste, and a toothpick or thin screwdriver dipped into the blob.
Some commercial systems work with air pressure, and there are also systems with a steppermotor. There are lots of options, from very simple to very expensive.
https://duckduckgo.com/?q=solder+paste+dispenser&t=opera&iax=images&ia=images
A note about the paste itself:
Very often it has a very limited shelf life of only a few months (Which is the main reason I never bought any) Apparently shelf life can be extended to a few years when it is kept in a fridge, but it has to be warmed to room temperature before it can be used.
Again, no personal experience but the SC10 From Loctite has apparently a long shelflife without refrigiration and I’ve read multiple posts on forums that this is about the best solder paste available. It is also one of the most expensive solder pastes (and Pb Free).
Lots of practice will make this easier no matter what you have. I might be able to solder that with a piece of copper wire and matchstick; not entirely joking.
First thing to make your life easier is good quality solder containing lead, that is of small diameter; just don’t eat the stuff. If the fab house provides an ENIG finish on the copper pads a solder with 2% Silver in it will make the solder flow to the pad differently; and possibly to the finish on the SMD part (not likely with a Neopixel).
Second thing to make your life easier is an iron tip that you prefer; a nice small chisel tip is a good starting point. It is suggested to stay away from a conical tip if you have not tried some of the other tip shapes before hand.
Third thing to make your life easier is a decent temperature controlled iron.
It is my opinion that there is a lot of good value to this iron at it’s price point. If money is not of concern, then I’d get a Metcal station.
A simple tip:
If the solder joint is not smoking prior to the tip being released from the joint, then the flux has burned off. I often do not use any extra flux other than what is in the core of the solder itself; but experience with contact time and thermal management while creating the joint do matter significantly; just because I can do it does not mean that every else can.
A general challenge with SMT assembly - whether working with solder paste or wire solder - is getting a small enough amount of solder onto the joint. A stencil definitely helps; at least, the results tend to be more consistent and uniform across an assembly versus applying paste to each pad (or each footprint) one at a time. Even with a stencil the amount of paste applied depends on how you specify the paste apertures in KiCAD (sometimes called the “paste shrink” parameter), the stencil thickness and material, the paste formula you are using, the temperature in your workspace, how you hold and operate the squeegee, etc. When you hand-stencil a board you can visually inspect the results (under your toolmaker’s microscope) and repeat the operation (without wasting solder paste) with a slightly modified technique until you are satisfied.
In the fall of 2017 I started using stencils for manually populating and soldering PCB assemblies. It’s definitely faster than any of the other methods I tried for placing solder paste. More significantly, the number of soldering errors (bridges, starved joints, and tombstone parts) is around an order of magnitude less.
I don’t know of anybody who sells a stencil containing just the most common SMT footprints, that you could use manually when placing solder paste. The practical problem is that you would unavoidably drag the stencil across other footprints as you applied paste to each footprint. But the idea seems to have merit and probably worth a little thought.
A small plastic syringe is less messy but the solder paste thickens up over time in the syringe.
Yes, even at 40F (5C) the manufacturers typically suggest 6 months or less. I have been using a jar of Kester EP256 at work, which was purchased about 18 months ago and kept on a shelf beside my work table. This spring it was noticeably thicker than it should be and didn’t want to spread uniformly on the stencil. I thinned it out with a few mL of pure isopropyl alcohol. That made it spread much more easily and uniformly, though I had to re-calibrate my wrist for spreading it. I’ll let you know in a month or two whether that was a viable solution, a stop-gap measure, or a bad idea from the beginning.
By the way, that 150g jar of solder paste has been used to populate and solder about 125 - 150 boards roughly 4"x6" (10cmX15cm), and it’s only about 1/2 gone. The stuff goes a long ways when used properly.
Dale
Hi.
I can recommend using a ceramic heat plate with temperature control, bringing the pcb to temperature applying very little (!) solder and placing the component on the pcb with fine pincers… Worked well ever so often already. You might want to use a silicone matt for protecting your hand.
The wattage of the iron has very little to do with the equation if it is well temperature regulated; and in fact one could easily argue that more power (wattage) is better then less.
Overall, good and experienced technique is more important than any hard and fast rule about how long in time a joint should be soldered. What happens when one of the pads on the board is connected to a copper pour with 4 times the thermal mass than the other pads?
