There are a variety of methods for reflowing a circuit board, but they all rely on a single principle: heat up the solder paste (a mixture of flux and solder) until the flux burns off and the solder becomes liquid, and then cool it down. Accomplishing this once or twice is easy; once you’ve played with a hot plate you’ll swear off through hole. Scaling it up and doing it repeatedly with high yield is extremely challenging, though. Continue reading “Tools of the Trade – Reflow”
You need to use surface-mount technology (SMT) parts in your design. But you also need to prototype. How to fit those little buggers into your breadboard?
[Simon] came up with a general-purpose SMT-to-breadboard solution. Now, there are already myriad adapter boards for the many-pin devices: SSOP-to-DIP adapters and so on. But what do you do when you just need to work that tiny SOT223 voltage regulator into a breadboarded circuit?
[Simon]’s solution fills that gap with one breadboardable design to handle all of your small-pin-count part needs. It accommodates SOT223, SOT323, and SOT23 three-pin parts like transistors or voltage regulators, and also has pads for all of the common two-terminal parts like resistors and capacitors from 0402 on up to 1206. You could build up a full voltage regulator circuit on one of these things. He’s even included some whitespace on the back for your notes.
SMT parts aren’t even the future any more. And with the right procedure, they’re not hard to hand-assemble. So the next time you have some extra space in a PCB order, toss in a couple of [Simon]’s breakouts and you’ll be ready for your next breadboarding session.
If you are lucky enough to encounter a piece of homebrew electronics from the 1950s, the chances are that under the covers the components will be assembled on solder tags, each component with long leads, and chassis-mounted sockets for tubes. Easy to assemble with the most agricultural of soldering irons.
Open up a home build from the 1960s or early 1970s, and you might find the same passive components alongside germanium transistors mounted through holes in a curious widely spaced stripboard or even a home-made PCB with chunky wide tracks.
By the late 1970s and early 1980s you would find a more familiar sight. Dual-in-line ICs through-hole on 0.1″ spaced stripboard, and home-made PCBs starting to appear on fibreglass board. Easy to use, easy to solder. Familiar. Safe. Exactly what you’ll see on your breadboard nearly forty years later, and still what you’ll see from a lot of kit manufacturers.
But we all know that progress in the world of electronic components has not stood still. Surface-mount components have a history going back to the 1960s, and started to appear in consumer equipment from the end of the 1980s. More components per square inch, smaller, cheaper devices. Nowadays they are ubiquitous, and increasingly these new components are not offered in through-hole versions. Not a problem if your experiments are limited to the 741 and the 555, but something that rather cramps your style if your tastes extend to novel sensors for a microcontroller, or RF work.
This development has elicited a range of reactions. Many people have embraced the newer medium with pleasure, and the Hackaday.io project pages are full of really clever SMD projects as a result. But a significant number have not been able to make the jump to SMD, maybe they are put off by the smaller size of SMD components, the special tools they might require, or even the new skills they’d have to learn. When you sell a kit with SMD components these are the reactions you will hear from people who like the kit but wish it was available in through-hole, so this article is for them. To demystify working with SMDs, and to demonstrate that SMD work should be within the grasp of almost anyone who can wield a soldering iron.
But They’re So Tiny!
It’s likely to be the first reaction from a lifelong through-hole solderer. SMD parts are often very small indeed, and even those with larger packages can have leads that seem as numerous and thin as the hairs on a cat when seen with the rabbit-in-the-headlights panic of the uninitiated.
But it is important to take a step back and understand that not all SMDs are created equal. Some of them are grain-of-sand tiny and only hand-solderable by those with God-like powers, but plenty of devices are available in SMD packages large enough for mere mortals.
So don’t worry when you look at a board covered with grain-of-dust-sized components. Very few people could attempt that level of construction, your scribe certainly can’t. (We await commenters claiming to routinely hand-solder thousand-pin BGAs and 01005 chip components with anticipation, however such claims are useless without proof.)
Instead, concentrate on the SMD packages you can handle. SMD chip component packages are refered to by a number that relates to their dimension. Confusingly there are both metric and imperial versions of the scheme, but the format is the same: length followed by width.
Consider the picture above with the PCB and the tape measure, it’s the underside of a Raspberry Pi model B+, and will have been assembled by a robotic pick-and-place machine. The majority of the components are very tiny indeed, but you will notice L3 as the black component towards the bottom left that looks huge compared to its neighbours. That package is a “1008”, 0.1 inches long by 0.08 inches wide. It’s still tiny, but imagine picking it up with a pair of tweezers under a magnifying glass. Not so bad, is it. You’ve probably handled plenty of things in that size range before, do SMD parts seem so scary now? The larger components – 0805, 1008, and 1206 – are surprisingly within the grasp of the average maker.
But I need all sorts of special tools!
In a commercial environment an SMD device will be assembled by machine. Glue or solder paste will be printed in the relevant parts of the board, and a robotic pick-and-place machine will retrieve components from their tape packaging and automatically place them in their correct orientations. The board will then be soldered all-at once, either in a reflow oven or by a wave soldering machine.
If you’re new to SMDs you are unlikely to have any of this kit just lying around on your bench. There are self-built pick-and-place machines and a host of self-built reflow ovens, but it’s safe to say they’re still quite an advanced thing to have.
You’ll also see all manner of commercial kit aimed at the bench-top SMD constructor. Hot air soldering stations or SMD bits for conventional irons, all of which are very useful but come with a hefty price tag.
The good news is that you don’t need any of these special tools to dip your toe into the SMD water. You almost certainly already have everything you need, and if you don’t then very little of what you lack is specifically for SMD work. If you have the following items then you are good to go:
A good light source. Even the larger SMDs are still pretty small. Plenty of light ensures you will be able to see them clearly. A good downward pointing desk lamp should suffice. A clear high-contrast surface. Because SMDs can be difficult to see, it helps if they are manipulated over a bright white surface. A fresh sheet of white printer paper on a desk makes a suitable working area. Good hands-free magnification. Unless you are fortunate enough to have amazing eyesight, you will need a decent magnifier to work with surface-mount components. The “Helping hands” type on a stand are suitable. A very small flat-blade screwdriver. You will need this to hold surface-mount components down while you solder them. A good-quality set of precision metal tweezers. You will need these for picking up, manipulating, and turning over surface-mount devices. A fine-tipped soldering iron. If you have a standard fine tipped iron suitable for use with conventional 0.1” pitch through-hole components then you should be well-equipped.
That said there is one special tool that might be worth your consideration. Holding an SMD device while soldering it can sometimes seem like a task that needs three hands, so one or two tools can be found to help. Fortunately this is something you can build yourself. Take a look at the SMD Beak, a weighted arm for example, or your scribe’s spring clamp third hand.
I’m sorry, this is just beyond my soldering skill level
It is easy to imagine when you are looking at an SMD integrated circuit that its pins are just too small and too close together, you couldn’t possibly solder them by hand. The answer is that of course you can, you simply need to view how you solder them in a different way.
With a through-hole IC you solder each 0.1″ pitch pin individually. It is something of a disaster if you manage to put a solder bridge between two pins, and you race for your desolder pump or braid.
With a surface-mount IC by comparison there is little chance that you as a mere mortal could solder each pin individually, so you don’t even try. Instead you solder an entire row at once with an excess of solder, and remove the resulting huge solder bridge with desolder braid to leave a very tidy and professional-looking job. Surface tension and plenty of flux are your friends, and there is very little soldering skill required that you do not already have if you are an experienced through-hole solderer.
If you can hold it down onto the board and see it clearly with your magnifier if necessary, then it doesn’t matter what the component is, you can solder it. Give it a try, you’ll surprise yourself!
So we hope we’ve convinced you as an SMD doubter, that you have the ability to work with SMDs yourself. What next?
Start by reading up on the subject. Your favourite search engine should deliver, tutorials can be found from Sparkfun, from Adafruit, or from Instructables among many others. And look for videos, YouTube has a huge number of SMD soldering guides.
But there is no substitute for practice. Find a scrap board populated with reasonably-sized surface-mount components, and have a go at reworking it. Desoldering its components may be a bit difficult, but you should easily be able to rework the solder joints. Slather an integrated circuit’s pins with flux, and try running a blob of molten solder along them, then removing the excess with desolder braid. The great thing about a scrap board is that it doesn’t matter if you damage it, so you can practice these techniques to your heart’s content until you are satisfied with your new-found skill.
So you’re ready to move forward, and make your first SMD project. Well done! What you do next is up to you. Design your own circuit and get a PCB made, buy a kit, or find an SMD project you like on Hackaday.io with downloadable PCB files and order your own.
Whatever you do, be happy that you’ve conquered your SMD fears, and resolve to be first in the queue to try any new technology in the future!
Have some plexiglas (acrylic) leftovers lying around? Well, they could be put to good use in making this SMD organizer. It comes in handy if you deal with a lot of SMD components in your work. No longer will you waste your time trying to find a 15K 1206 resistor, or that BAS85 diode… or any other component you can think of soldering on the PCB. The basic idea is fairly straightforword, which helped keep this short.
SMD resistors are packed in thick paper tapes that don’t bend easily, and thus need larger containers than other components, which are packed mainly in flexible PE tapes. The first version of this organizer was built with a 96mm diameter space for resistors and 63mm diameter for other components, but it seems that there is no need for such large compartments. If I were to make it again, I would probably scale everything down to about 80% of it’s current size.
The best way to join all plexiglass parts is to use four M4 threaded rods. There is also a 1.5mm steel rod which holds SMD tape ends in place and helps to un-stick the transparent tape which covers the components. At the top of the organizer there is a notch for paper, used for components labels. Most SMD components are packed in 8mm wide tapes, making the optimal compartment width 10mm. It is not easy to cut the 10mm thick acrylic and get a neat edge – instead, you could use more layers of thin sheets to make the spacers. Using 5mm acrylic you can combine more layers for any width of tape, which contains wider components, like SMD integrated circuits. The only thing that you have to be careful about, is to keep the distance between the thin steel rod and acrylic, which is marked as “2-4mm” on the drawing. It is good if this space is just a few tenths of a millimeter wider than the thickness of SMD tapes.
The CorelDraw file that can be used for laser cutting the acrylic parts, is available for download. If you scale the profiles, don’t forget to readjust the hole diameters and some other dimensions which have to remain intact. If you have 5mm acrylic pieces, you should probably use two layers of acrylic for every tape (red parts on the drawing). The barrier layers would be made of thin acrylic — for instance 2mm (the blue parts). Edge layers (green) are once again 5mm thick, and there are also the end pieces (yellow), glued to the previous borders and used to “round up” the whole construction and to protect your hands from the threaded rods and nuts.
While you’re building this for your bench, make a vacuum picking tool for SMDs out of a dispensing syringe with a thick needle. It’s a common trick for hackers to use an aquarium air pump, just turn the compressor unit by 180°, so that it creates vacuum instead of blowing the air outside. This process is described by R&TPreppers in the video below.
Friday afternoon I had the pleasure of sitting in on a surface mount soldering workshop. I’ve done some surface mount soldering before and am quite adept with a soldering iron, but this focused on solder paste and a hot air pencil. [Bob Cogeshall] ran the workshop and went beyond the most basic information. His experience founding Small Batch Assembly, a contract manufacturer whose offices are in the Nova Labs hackerspace, has led him to learn a lot of tricks of the trade.
Do you know what a MELF is (and, yes, it is safe for work to Google it)? What’s the difference between a QFP, and LCC, and a PLCC package? Do you need a 0603 resistor or a 1206 resistor?
If you are an old hand at surface mount devices (SMDs) you probably know the answers to most of these questions. But if you’ve done most of your work with through hole, it is a confusing mess of acronyms and numbers. Sure, you can Google and find out that at 0603 resistor is .06 inches by .03 inches. [TopLine] has a great booklet that pulls many common definitions in one place available for download that can help you make sense of different SMD nomenclature.
Microcontroller Dev Boards have the main hardware choices already made for you so you can jump right into the prototyping by adding peripherals and writing code. Some of the time they have everything you need, other times you can find your own workarounds, but did you ever try just swapping out components to suit? [Andy Brown] documented his process of transplanting the clock crystal on an STM32F4 Discovery board.
Even if you don’t need to do this for yourself, the rework process he documented in the clip after the break is fun to watch. He starts by cleaning the through-hole joints of the crystal oscillator with isopropyl alcohol and then applies some flux paste to each. From there the rest is all hot air. The crystal nearly falls out due to gravity but at the end he needs to pluck it out with his fingers. We’re happy to see others using this “method” as we always feel like it’s a kludge when we do it. Next he grabs the load caps with a pair of tweezers after the briefest of time under the heat.
We’d like to have a little bit of insight on the parts he replaces and we’re hoping there are a few crystal oscillator experts who can leave a comment below. [Andy] calculates a pair of 30pf load caps for this crystal. We understand the math but he mentions a common value for board and uC input capacitance:
assuming the commonly quoted CP + CI = 6pF
So we asked and [Andy] was kind enough to share his background on the topic:
It’s a general “rule of thumb” for FR4 that the stray capacitance due to the traces on the board and the input (lead) capacitance of the the MCU is in in the range of 4-8pF. I’m used to quoting the two separately (CP,CI) but if you look around you’ll see that most people will combine the two and call it just “CP” and quote a value somewhere between 4 and 8pF. It’s all very “finger in the air” and for general purpose MCU clocks you can get away picking the mid-value and be done with it.
That leaves just one other question; the original discovery board had an in-line resistor on one of the crystal traces which he replaces with a zero ohm jumper. Is it common to include a resistor and what is the purpose for it?