Good practices for hand assembly of SMD board? - Page 1
Forum section: electronics / beginners

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: February 26, 2021, 01:13:20 pm
content: I'm just about to receive my first ever SMD PCB design - so this question definitely belongs in BeginnersI will be hand soldering and would appreciate guidance on the best order of assembly. I understand the "lowest profile first" but, as you can see in the image, there are a lot of resistors and capacitors around the ICs. Is there a preferred approach? Any other words to the not-so-wise?One thing I plan to do is assemble the LDO regulator circuitry first (the four smaller ICs) and test it before adding the main IC (a LTC2357 4-channel SS&H ADC).[ Specified attachment is not available ]

author: Mike_GFY
author_rank: Newbie
timestamp: February 26, 2021, 01:30:54 pm
content: Hi, i am new to this fourm but there are some ideas for your board about hand soldering.if you only have the solder iron and tweeze, you can try to add the soldeirng to only one pad on the board for the resistor/capacitors or any part multiple legs parts, make the pads full of soldering first, and then use the tweeze hold the parts on the right position and use the solder iron touch the pad you just added soldering, and the parts can soldering fixed on the board, and then you use the soldering iron to add the soldering on the rest parts. it will be good to do the 1-leg holding first because even you did not solder them on the right position, espescilally for the multilegs IC long thru hole pin headers, you can modify them esily by using the soldering iron to touch the 1-leg holding point.of course, the most suggesting way is to use the stencil to solder paste the board correctly and hand pick&place the parts on the boards and go thru the reflow. you can also use the hot air station to melt the soldering. But it seems too much for the beginner, i heard someone use the oven to reflow the board, need practice the temp and time control, haha.hope it can help.

author: wraper
author_rank: Unknown
timestamp: February 26, 2021, 01:32:30 pm
content: In this case IMHO you should solder IC5 before components surrounding it. Otherwise it may become a little bit troublesome. Also solder C23 before capacitor on the left side of it, since it obstructs solder joint of C23. C18 before C26. In the nutshell you should solder possibly obstructed parts first.

author: jpanhalt
author_rank: Super Contributor
timestamp: February 26, 2021, 01:45:21 pm
content: Low to high is the standard, but don't be a slave to it. Think of access with your soldering tip too. (Assuming by hand soldering you mean with a soldering iron, not hot air.)For anything with just 2 pads (e.g., resistors and capacitors), I tin one pad, place the component, heat the pad and let the part settle, then solder the other pad. Return to the first pad, if more solder is needed. Rather than tweezers, I use a short (2" or so) piece of thin music wire (about 0.031" dia.) to apply pressure and move parts when necessary. I grind a dull cone shape on each end.With lots of parts, I will often modify that procedure by adding a small microdot of cyanoacrylic adhesive (CA, super glue) between the pads. Add the component, let stand awhile, and solder away. The same needle used for positioning is used for the microdot, estimated at < 0.1 ul. Bare copper will not usually set off the CA, so I put a small drop on a piece of spare bare PCB as my reservoir for the CA. Older CA that may be a little thicker works best.For IC's, I will do a corner pad the same way. Then fix any error in positioning, and do the remaining pads.

author: Capernicus
author_rank: Frequent Contributor
timestamp: February 26, 2021, 01:48:38 pm
content: Quote from: jpanhalt on February 26, 2021, 01:45:21 pmThats a cool idea, using the super glue.

author: wraper
author_rank: Unknown
timestamp: February 26, 2021, 01:58:18 pm
content: Quote from: jpanhalt on February 26, 2021, 01:45:21 pmUsing CA is insane. It emits toxic eye and nose irritating fumes when heated. Also it's a little bit conductive. Not to say if it accidentally gets on a pad or terminal, it becomes a problem of another level.

author: mvs
author_rank: Frequent Contributor
timestamp: February 26, 2021, 02:05:38 pm
content: Quote from: Capernicus on February 26, 2021, 01:48:38 pmSolder paste + hot air soldering is much better then CA + hand soldering.Surface tension will self-align components, so there is no need to place them very precise.If you order a paste stencil with PCBs, then it also much faster.

author: Capernicus
author_rank: Frequent Contributor
timestamp: February 26, 2021, 02:17:04 pm
content: Quote from: wraper on February 26, 2021, 01:58:18 pmFunny you should say that, because solder fumes are bad as well, when it all gets up my nose like evil butter, its probably on par with super glue fumes. =)

author: jpanhalt
author_rank: Super Contributor
timestamp: February 26, 2021, 02:30:55 pm
content: Quote from: wraper on February 26, 2021, 01:58:18 pmImaginary problems. Have you ever tried it?If you have, I suspect you used way too much CA. But then again, if you feel its use is "insane," you don't have to use it. Millions of people use CA adhesives everyday. Not aware of anyone who used it properly being blinded or having to go to the hospital.As for getting a little on a pad, it actually acts as a flux.

author: wraper
author_rank: Unknown
timestamp: February 26, 2021, 02:31:08 pm
content: Quote from: Capernicus on February 26, 2021, 02:17:04 pmFlux fumes are not even 5% as bad.

author: wraper
author_rank: Unknown
timestamp: February 26, 2021, 02:40:01 pm
content: Quote from: jpanhalt on February 26, 2021, 02:30:55 pmI have attempted heating CA in the past, say when repairing torn off pad on PCB. It decomposes when heated, and if you get some fumes in your face, prepare for pain.QuoteUsing random stuff on a PCB to compensate for lack of soldering skill is not smart as minimum.QuoteMillions of people use blender everyday, it does not mean they should stick their finger into it. Nor those people heat CA.QuoteYou are suggesting improper use.QuoteIt acts nothing like that.

author: jpanhalt
author_rank: Super Contributor
timestamp: February 26, 2021, 03:10:18 pm
content: Quote from: wraper on February 26, 2021, 02:40:01 pmI guess you have to say something.You first point is exactly why I chose CA. It distills at relatively low temperatures, which is why it doesn't interfere with soldering, which argues against your earlier assertion that it does interfere.My choice was hardly random for the reason just given and the fact that Henkel used to make (maybe still does) a CA product for exactly that purpose.Of course, later generations of CA are more heat stable. I use the more heat-labile versions often used in modeling and sold in small tubes, such as 4/$1.

author: perieanuo
author_rank: Frequent Contributor
timestamp: February 26, 2021, 03:50:41 pm
content: for hand soldering, first comes the micro, u5, with his co-workers (nearby caps etc)then the rest, like reg, passives, actives, big stuff in the endwell, this is how i'll do ityou're sure after the big ones you can be at ease putting in line u5? it's rethorical

author: Siwastaja
author_rank: Super Contributor
timestamp: February 26, 2021, 04:17:26 pm
content: wraper is completely right, you don't want that chemical attack on your eyes and respitory system. BTDT, BTW; it's not an imaginary problem but something I have experienced. Painful. And it was just a tiny blob of superglue on a PCB!Millions of people using superglue do not heat it over 300degC.A carefully administred tiny spot may be OK if completely dried, you avoid heating it too much, and have good exhaust, but I wouldn't do it because it doesn't solve any problem here. Just don't. If nothing else, it tends to flow where you don't want it.If you seemingly "need" superglue in holding SMD parts for soldering, please explain whatexactlyyou are doing, so we could help you to find the standard procedures which do not require superglue.

author: tooki
author_rank: Super Contributor
timestamp: February 26, 2021, 05:51:45 pm
content: Regardless of whether CA is safe to use in this application, it shouldn’t be needed either way. If you are soldering with hot air, the solder paste is sticky enough. If you’re soldering with an iron and want to stop components from blowing away before you tack solder a corner, just use tacky flux paste.

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: February 26, 2021, 06:11:36 pm
content: I have one of these:https://www.amazon.com/Adjustable-Absorber-Remover-Extractor-Soldering/dp/B00RLEB6AGBut I do miss the phantom smell of rosin all day.

author: jpanhalt
author_rank: Super Contributor
timestamp: February 27, 2021, 11:02:18 am
content: Needed or not, adhesives -- usually CA or epoxy it seems -- are/were used to hold components during assembly. There is even a standard for it:IPC-SM-817A Adhesives .Review with list of various suppliers and products (free if registered):https://www.academia.edu/25529756/An_adhesive_selection_advisor_for_PCB_assembly_using_surface_mount_technologyMSDS Henkel/Loctite 3608 (acrylic)https://docs.rs-online.com/6e58/0900766b8001f4b5.pdfIf one uses Eagle, glue mask is layer t-35 and b-36 for top and bottom, respectively. It is the center hashed rectangle in this image:My original statement was conditioned on using a manual soldering iron and solder, not reflow or solder paste. Moreover, if only doing a few components, I usually use the method described of tinning one pad. However, with a whole board, using adhesive speeds assembly. It appears others feel the same.

author: wraper
author_rank: Unknown
timestamp: February 27, 2021, 11:46:19 am
content: Quote from: jpanhalt on February 27, 2021, 11:02:18 amI don't see any CA thereQuoteThis adhesive has nothing to do with CA.

author: bd139
author_rank: Super Contributor
timestamp: February 27, 2021, 11:49:01 am
content: Don't use CA. Ignoring the fumes which aren't much of a problem really, the vapour gets on everything and it crystalises and it also via capillary action gets under everything including on pads if you're not careful. It's fine for commercial application but forget it for hand assembly.

author: jpanhalt
author_rank: Super Contributor
timestamp: February 27, 2021, 12:03:34 pm
content: Quote from: wraper on February 27, 2021, 11:46:19 amIt's a very similar methacrylate adhesive. Did you check the MSDS? Did you check out any of the other adhesives in the review? Apparently not.Loctite 3608 contains:1) hydroxyethyl methacrylate2) hydroxypropyl methacrylate3) acrylic acid dimer4) acrylic acid monomerThe "2,2-dimethoxy-2-dihenylethane-1-one" which is probably 2,2-Dimethoxy-2-phenylacetophenone (#1) and t-butyl peroxybenzoate (#2) are probably there as a photosensitizer (#1) and polymerization promoter (#2).

author: wraper
author_rank: Unknown
timestamp: February 27, 2021, 12:21:52 pm
content: Quote from: jpanhalt on February 27, 2021, 12:03:34 pmI checked MSDS and exactly because of that I wrote it has nothing to do with CA. In no way it is similar. Having -acrylate in the name in no way makes it anything like.QuoteI did check at least half of them, but you apparently either did not or made wrong conclusions.

author: wraper
author_rank: Unknown
timestamp: February 27, 2021, 12:32:17 pm
content: Please tell me what in particular adhesive which is cured by exposure to UV with further heating has common with CA which is cured by moisture?

author: Siwastaja
author_rank: Super Contributor
timestamp: February 27, 2021, 01:07:14 pm
content: Using dispensed glue to hold SMD parts is a very commonly used and decades old process when THT and SMT are combined in wave soldering process. Obviously there are standards for it. So you can cite a standard, great!Except this has absolutely nothing to do with prototyping, or cyanoacrylate superglue.Typical internet forum discussion. Bring up completely random technical words, random points and random links to supposedly "prove" something. Please just stop misguiding and confusing beginners. When you are just so utterly and completely wrong, you can't win the argumentation game anyway, not that it makes any sense to play such games regardless of whether you can win or not. You know, we don't care, it's OK to be accidentally wrong, we all sometimes are, just move on. Trying to twist it further only adds to the awkwardness which initially wasn't that bad.You certainly are able to do electronics despite shitting your boards with cyanoacrylate. But is it a "good practice" or does it serve some real purpose? No. Is it recommendable? No.

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: February 27, 2021, 01:16:07 pm
content: I've become a spectator to my own questionAs a professional chemist, I will add my agreement that the commercial adhesives referred to are not CA. I used to make acrylate nanoparticles and was very careful to avoid inhaling the fumes, no matter what kind of acrylate monomer it was. I would not put uncured CA in close proximity to my face (i.e., when soldering) and subject it to 100s of degrees (C or F!).I'll also add that if I have the dexterity to put a microdrop of liquid between the pads of a 0806 component, I probably have the dexterity to solder the component successfully anyway.

author: jpanhalt
author_rank: Super Contributor
timestamp: February 27, 2021, 01:20:47 pm
content: Quote from: wraper on February 27, 2021, 12:32:17 pmThey are both acrylic adhesives. Ordinary acrylic adhesives existed long before CA and were generally 2-part adhesives, one part of which was usually a peroxide. Photoinitiation was also common using a photosensitizer such as benzophenone. That reaction is really quite similar to radical induced polymerization. Kodak developed CA's as adhesives for optical lenses that would not require addition of an initiator. Source: GoogleOn the left is atypical radical-induced polymerization initiated by attach on the methylene carbon. On the right is polymerization for a CA. The nitrile group is strongly electronegative and facilitates attack on the methylene carbon by a nucleophile. In water it is OH^; however almost any nucleophile will work. The final polymers are very similar in backbone structure. CA's have the advantage of not requiring a radical initiator. Aside from that, the adhesives are quite similar.Now, you seem to have gone from calling the use of an adhesive as insane and toxic to wondering about the mechanisms. How about documenting your assertions. In the days of wave soldering adhesives were used quite commonly.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 27, 2021, 04:12:30 pm
content: Assertions of wraper (and myself, too) were completely clear, unchanging, logical, and correct:* Cyanoacrylate aka superglue creates eye and respitory irritation when heated with soldering iron temperatures* That was not said about proper wave soldering adhesives (which are not cyanoacrylate)* Do not use cyanoacrylate aka superglue to glue down SMD components pre soldering.* You don't need to glue down SMD components for hand assembly.* There are at least three reasons not to glue down SMD components with superglue: 1) it's unnecessary, 2) the fumes, 3) other problems such as glue flowing where you don't want it, covering pads, etc.* There's nothing wrong mentioning multiple reasons for the same advice, quite the opposite.I think you are probably the only one struggling with this. You can keep posting random non-related images and put chemistry words together to sound fancy.

author: tooki
author_rank: Super Contributor
timestamp: February 27, 2021, 10:37:31 pm
content: Quote from: jpanhalt on February 27, 2021, 11:02:18 amForwave soldering, where the board isupside downduring soldering. That has nothing at all to do with hand soldering, which is the topic of this thread. (It says “hand assembly” right in the title.)Advocating using CA glue to hold down components before hand soldering them is silly; it’s like arguing that jet fuel would work great in your car, since it’s widely used in aviation. But it doesn’t, since they’re different applications.

author: jpanhalt
author_rank: Super Contributor
timestamp: February 27, 2021, 11:23:09 pm
content: Quote from: tooki on February 27, 2021, 10:37:31 pmTalk about being OT. Spark ignition and compression ignition have nothing to do with this subject or what I said. It seems more like trolling.Acrylic polymers "unzip" at high temperatures (usually at <200 °C). That is well known. They can revert to the monomers and other pyrolysis products. That applies to methacrylates as well as cyanoacrylates. Rather than buy a relatively huge amount of purpose-made methacrylic or epoxy adhesive, I suggested and use a CA to fix small parts while soldering. (BTW, fumeless cyanoacrylates have been available for decades.) It's faster for more than a few parts. Give it a try before claiming otherwise. Period. As the adage goes, those who say it can't be done shouldn't stand in the way of those doing it.Aside from some outrageous claims of toxicity (did you bother to calculate how much is released by <<1 ul and check the PEL's?), there is no reason not to do it as an aid to unsteady hands. As I clearly stated, there are other ways to compensate, but for lots of small SMD resistors and capacitors, it works.NB: I did not say they were needed. Using CA is merely a cheap and readily available option to consider. Take it or leave it.

author: tooki
author_rank: Super Contributor
timestamp: February 28, 2021, 08:35:46 am
content: Quote from: jpanhalt on February 27, 2021, 11:23:09 pmIt’s ananalogy, which is deliberately different to illustrate the absurdity of recommending something that’s appropriate for industrial use but not for home.Trolling doesn’t mean “someone said something I don’t like”, dude.Nobody said it can’t be done. It certainly can. It’s just a bad idea, and above all, one that is completely unnecessary. I think the people calling you out might be more understanding if there were any need for it, but there isn’t.

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: March 03, 2021, 09:30:02 pm
content: Update - so far, so good. Lots of little electrons whizzing around and photons flying out.

author: Buriedcode
author_rank: Super Contributor
timestamp: March 03, 2021, 10:33:31 pm
content: Looks good dudeShiny fillets. Don't be afraid to touch up joints with just flux if needs be - often there's more than enough solder, perhaps too much, so you shouldn't add solder just for its flux core. I don't see any joints with too much solder, or that need touching up, maybe C13s right joint could use a touch more. But to me that just looks like a well hand soldered SMT board. That SOT23-5 is pretty much spot on.Whilst you could eventually go to reflow with stencils, paste etc.. I find hand soldering boards of this kind (= number of parts/passives) almost theraputic. The novelty wears off if I have to make >4 though.Whats with this topics wild tangent about glues?!

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: March 04, 2021, 12:03:02 am
content: Assembly all done and installed on an Arty Z7 development board. Now I just need to write the code to communicate with the chip to see if it even works!

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: March 04, 2021, 01:28:50 am
content: And just because...Amazing what free software can do.

author: tooki
author_rank: Super Contributor
timestamp: March 04, 2021, 06:36:35 am
content: Quote from: JohnnyMalaria on March 03, 2021, 09:30:02 pmA very decent first attempt!A lot of the passives (esp. the ceramic caps) have far too much solder. It should be a decidedly concave fillet. If the fillet surface is flat or convex, it’s too much.Many of the IC legs have spikes, which is usually indicative of excessive soldering time. The solder gets “overcooked”, in that it a) oxidizes with the air while hot, and b) dissolves more copper into it. The first point is ameliorated by using more flux and reducing the temperature, but the second one really just requires the old solder to be sucked off and replaced with new. With practice, you’ll get faster and this will become less of a problem. But also, resist the temptation to rework an OK joint, especially without adding flux: it’ll only get worse.The other potential cause of this (well, tangential, in that it just makes the above happen much faster) is using an excessively hot iron: the extra heat accelerates both oxidation and copper dissolution, while at the same time burning off the flux before it can do its job.

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: March 04, 2021, 03:53:10 pm
content: Thank you @tooki and @Buriedcode for your feedback. I was very pleasantly surprised how straightforward this was.Here are some observations...MishapsAmazingly, only one. The very first component I picked up with my tweezers to place on the board went flying across the bench and I heard it land on the floor. I bought two of everything, so that wasn't a problem but certainly didn't bode wellAfter that, I didn't lose any more.Soldering capacitorsOne of the reasons there's a lot of solder on the capacitors (esp. compared to the resistors) is that the solder simply wouldn't take to the pad. Instead, it would bead up on the end of the capacitor. If you look in my first photo where I had only installed the power supply section, LED D3 isn't as bright as D1 and D4 on either side. They should be the same - I calculated the necessary resistor values so that each LED would get the same current from each LDO. So, I was a little surprised but initially thought that perhaps I'd got the calculation wrong.When I measured the output voltages of each LDO, U3 was only giving 2.6V instead of the intended 3.3V. I was using one of the exposed GND holes on the left-side of the board for the DMM's low input. But when I put the low lead of the DMM on the ground side of C12 (connected to D3), D3 became a lot brighter and the LDO output was 3.3V. So, the solder joint for C3 was poor. Even with a lot of extra flux, I could only get the solder to wet the pad on the PCB by using a lot of solder. I found I had to do this for most of the capacitors.The PCB has Pb-based HASL treatment and I use Tamington 0.8mm Sn63 Pb37 with rosin core solder. For additional flux, I use Kester 951 no-clean flux. I have a Hakko 888D iron with a 1.2D tip at 650F/343C. I tried a conical tip but found it difficult to use (poor heat).The capacitors were from three different manufacturers:https://www.mouser.com/ProductDetail/AVX/06035D105KAT2A/?qs=jHkklCh7amj4RS3QGB%2FJvQ%3D%3Dhttps://www.mouser.com/ProductDetail/Murata-Electronics/GRM188R61E106KA73J/?qs=5aG0NVq1C4xEV8YyiSS7mg%3D%3Dhttps://www.mouser.com/ProductDetail/KEMET/C0603X103K3GECAUTO/?qs=Mv7BduZupUjgb3CWNXLH%252BQ%3D%3DTouching up jointsFor the 0603 passives, my general procedure was:1. Do all the same value components together and don't have any others out of their bags Mouser so kindly put them in2. Put a small amount of solder of the iron's tip3. Briefly touch one of the pads on the board for each component to transfer a small amount of solder4. Place the component in position and bring the iron to the tinned padThis worked well for resistors (I could see the solder quickly flow) but less so for the capacitors.5. Having tacked on the components in place, put flux on the other pads and apply some solder. Again, this worked very easily for the resistors.6. Go back around the first pads to touch them briefly and make them shiny.I noticed that the solder applied for tacking the first pad in position would look quite grainy before retouching the joint.The main ICThis was surprisingly easy. I had to wick excess solder away a couple of times.Final power-upI slowly turned up the supply voltage in order to check the current and determine if I had any shorts. Amazingly, no.As an aside, I am amazed that I could do this. It was indeed quite therapeutic but also something of a milestone. For 13 years, I had been on a medication that created microtremors in my hands as a side effect. I could barely write with a pen, let alone do any soldering. Even TTH was challenging. I was able to stop taking it in 2020. So, psychologically, building this is really important.Now it's hooked up to my logic analyzer and Arty Z7 board - time to test the SPI and see if this thing actually works.For reference, the IC is an Analog Devices LTC2357-16 4-channel 350ksps/ch 16-bit simultaneous ADC. I got two of them as free samples.

author: Buriedcode
author_rank: Super Contributor
timestamp: March 04, 2021, 10:27:20 pm
content: Regarding SMD caps.I tin the pad (by heating the pad with the iron, and bringing the solder to it, rather than dabbing the pad with solder already on the iron. Then with the iron back on that pad (to melt the solder again) bring the SMD cap to the joint so it is touching the iron and of course the pad. Then put the iron on the other pad (also touching the cap!) bring the solder wire to that. I'm pretty sure thats just what you did.Now that first joint might not be that great, as the solder has been heated twice, so it probably won't have any flux left in it. But it can always be "touched up" just with a bit of flux and reheating it (not more solder). Really the amount of solder one needs on a 0603 or 0805 pad is tiny, it should barely make a dome/bump on the first one. Thats where having thin solder wire is handy - more control. But frankly I've done it with 0.8mm solder, its just about using it sparingly.There are so many variables, but generally, if you have- flux-cored solder, and preferably extra liquid/gel flux- a reasonable tip shape - a shape that allows you to have good contact with both the pad and the parts terminal at the same time. I use the 1.6mm D, 1/2mm D or B for 0805 and 0603. A chisel bit is fine.- tip temperature thats hot enough to get the job done quickly, but not so hot you burn off the flux before you finish the joint. Mine is set at 350C, which some see as hot but I haven't had issues.there's a good bit of slack there. Temperature controlled iron is pretty much a must, but that doesn't mean to say the absolute temperature has to be within a very narrow range, just controlled.It'll be easy.Mistakes - a solder sucker is ok for larger joints but solder wick is your best bet. I don't like plugging brands, but the only one I've enjoyed using (read: works, doesn't oxidize and doesn't make me want to kil things) is Goot wick.And yeah, I found that IC's were pretty straight forward. SOIC its almost impoosible to create bridges, unless you dont have any kind of flux (or flux in the solder). 0.5mm pitch TQFP is in some ways easier, its too fine to do each pin individually, so you can do several pins at once, and let flux work its magic. You don't have to "drag solder" that just risks bending pins, but it's not difficult. Again, did I mention flux?Edit: I realise this just echos what you've said, and wha tothers have said, but I didn't want to remove it all, because it might help someone.

author: tooki
author_rank: Super Contributor
timestamp: March 05, 2021, 04:33:48 pm
content: Quote from: JohnnyMalaria on March 04, 2021, 03:53:10 pm(Replying this way because editing the quotes is too fiddly on a phone)Caps’ one pad not wanting to take solder: I can already tell you what caused that effect. Go back and look at the caps and see what the difficult sides have in common. Ok, have you figured it out? That’s right: they all go to the ground plane. Even with thermal reliefs, the ground plane is a freaking heat vampire, sucking it all away. For such pads, you need to be super conscientious about heating the pad,not the component. (Ceramic caps already hate hand soldering due to the one-sided heat, so you wanna keep that down to an absolute minimum.) So use the flat side of your chisel on the pad, without even touching the cap. Make sure your tip is perfectly clean, freshly tinned, and with an appropriate dab of solder on the tip as a thermal bridge. And you may need to raise the iron temperature a couple of degrees. Alternatively, if you have a hot air device or IR preheater, this is a perfect example of when it makes sense to preheat the board. That way the iron only needs to add amuchsmaller amount of heat to the pad to get it up to soldering temperature.0603 passives, #2: Kick the habit of transferring solder from the tip ASAP. Even if you’re using external flux (you didn’t say), it’s just bad practice, as the solder on the tip is already a bit oxidized. Get yourself some thin solder for these, so you can feed in a tiny amount offreshsolder.#6 Yes, the grainy appearance is because the flux was already gone. You might wanna try a lower temperature if possible, it’ll give you more working time. Or consider using gel flux up front (at least until you’ve got more practice), as it’ll give you a LOT more working time. It’s just a bigger cleanup job at the end.ICs: try adding gel flux. You may find that you won’t need to use wick, because the flux will help the excess solder flow back onto the soldering iron tip. This effect is more pronounced with a large tip, so paradoxically, what at first seems like a comically oversized tip, compared to pin size, is actually ideal!Also (and this is good practice in general), give your boards a wipe with IPA before beginning. It’ll ensure there aren’t any contaminants that can reduce soldering performance. Along the same vein, clean your tweezers with IPA (they frequently get gummed up with flux), and wash your hands before beginning.Therapeutic: That’s awesome! I am so happy for you!Quote from: Buriedcode on March 04, 2021, 10:27:20 pmOverall good advice. But if you’re bending pins during drag soldering (which is an accepted, routine technique), then you’re applying FAR too much force. The tip barely even touches the pins. It’s meant to just glide across them on a pillow of molten solder.

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: March 05, 2021, 05:30:19 pm
content: Thank you - wonderful advice, tookiQuote from: tooki on March 05, 2021, 04:33:48 pmOf course! Yes, this is a 4-layer board with a dedicated ground plane. I'm not used to that.QuoteI'll be sure to do this.

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: March 05, 2021, 08:48:31 pm
content: Yay! It works...

author: TimNJ
author_rank: Super Contributor
timestamp: March 06, 2021, 03:12:30 am
content: Congrats! At work, when we do hand assembly of prototypes in the lab, either by soldering iron or toaster over reflow, we always use soft-termination/flexible-termination SMD caps. Some may argue it's overkill, given they are usually at least 2x the price. But, if you have a lot of SMD caps on your board, and you wind up inadvertently cracking one of them due to too much heat or playing with the solder joint too much, it's often a real pain to troubleshoot. Latent failure is also a possibility. Soft termination caps gives you some piece of mind and gives you some leeway for re-work and touch-up. NP0 caps are usually not as problematic as X7R or X5R types.

author: nigelwright7557
author_rank: Frequent Contributor
timestamp: March 06, 2021, 03:30:00 am
content: Not sure how smart super glue is but what about when you want the component removed ?If you buy quality smd tweezers then you wont have many problems.If something needs sticking down like an IC I use a little flux paste.

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: March 06, 2021, 01:35:42 pm
content: Quote from: nigelwright7557 on March 06, 2021, 03:30:00 amTo be honest, this was so much easier than I was expecting, especially given a lot of the tales of woe I'd read. My tweezers aren't anything special but nor are they junk. Good lighting, comfortable location, a decent stereo microscope and endless supply of tea were the order of the day.After I had designed the board and printed it out at actual size, I did think, "You've got to be kidding. How can anyone do that?"

author: tooki
author_rank: Super Contributor
timestamp: March 06, 2021, 02:41:46 pm
content: Quote from: JohnnyMalaria on March 05, 2021, 05:30:19 pmGlad to be of help!4 layer board? Oh yeah, they're a PITA to work on! (The worst is desoldering through-hole components from 4+ layer boards, especially if you can't apply heat to the component side, like when desoldering an electrolytic cap. The inner layers just suck heat away horribly.)Rather fittingly, my big reply above was 99% written (on my phone) on the train to work, but I didn't get to post it until I was on the train back home in the evening. And during that very day, 1) I taught an apprentice how to desolder from a board with two big ground planes (The problem pin was to ground, so connected to the ground pours onboth sidesof the board. I showed him how to preheat the whole board, so as to avoid needing to feed enormous amounts of heat into a single spot on the board, causing damage.), and 2) we ordered a new IR board preheater, since we've got a lot of those boards to fix, not to mention new boards to assemble!Quote from: JohnnyMalaria on March 06, 2021, 01:35:42 pmSMD isn't nearly as daunting as it appears at first glance! I think a lot of folks get themselves worked up about it, and then end up screwing up because of their agitation. But in fact, in many ways it's easier than THT soldering, and it's often a lot faster to hand assemble in practice. (The amount of time spent cutting off component legs, and in flipping the board over and over, really adds up!)

author: Siwastaja
author_rank: Super Contributor
timestamp: March 06, 2021, 03:32:09 pm
content: 4-layer boards can be preheated to around 100-120degC which does not cause any degradation issues on the board or components even if you work on it for a long time, but makes it behave more like a 2-layer board when soldering. The only issue is that you need gloves to handle the board making it a bit of hassle.Obviously, leaded solder melts at lower temperature than lead-free, making prototype soldering a bit easier.

author: Howardlong
author_rank: Super Contributor
timestamp: March 06, 2021, 09:25:10 pm
content: Two immediate comments...Avoid applying solder directly to the iron and then transferring the molten solder to the component or pad.Instead:o Place the tip on one PCB pad for the part and tin that pad with solder;o Holding the part with tweezers in place, reheat that pad to let the solder reflow, holding the component to anchor the part;o Solder the remaining part's pad(s).You should only need to apply heat to an SMD pad for a second or so before the solder melts: if you leave the heat on, the flux inside the solder evaporates, and you'll end up with a rocky road style joint, or even a dry joint.Your tip should typically be clean from solder, use a wet sponge and/or brass wool to remove any excess solder from the tip very frequently.Secondly, super glue: the only time I use super glue when soldering is if I'm flip soldering a BGA or WLCSP for a quick and dirty prototype to keep it in place. It's nasty stuff when heated. Otherwise there should be no need at all for glue when hand soldering, either use the above method or paste/stencil. For very small runs of one or two boards personally I find stencils and paste unnecessary, and hand solder. For larger runs, yes, stencil and paste is the way to go as you place parts on multiple boards at once, as well as reflowing them in batches too.Regarding tea, IME I would avoid more than one cup if you want to avoid the shakes, which is very noticeable under a microscope.

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: March 06, 2021, 09:45:39 pm
content: I thought I'd share some initial results of testing the ADC. It's a relatively new one (2017, I believe).I chose it because I need to measure 4 instrumentation signals simultaneously. Two are an IQ pair from which I calculate amplitude and phase, so simultaneous sampling is essential. (I'm measuring movement of nanoparticles in liquids with sub-nanometer resolution.)The photo shows the arrangement - a 200Hz AM signal 3Vpp with a 1.5V offset from a function generator fed to all four inputs. The graphs show: (L) the channel 0 signal - confirming the numerical accuracy of the measurement; (R) the deviation of each channel from the mean response of the four. Note that the vertical scale is mV. One LSB for this ADC on the +/-10.24V input range is 3mV. So, I'm very impressed with this ADC!https://www.analog.com/en/products/ltc2357-16.html