Help with soldering smd chips - Page 1
Forum section: electronics / beginners

author: spacedementia87
author_rank: Contributor
timestamp: November 02, 2016, 03:42:45 pm
content: So I am relatively new to smd soldering but have been getting on reasonably well with sot-23 and some chips like the ATtiny 8.My new project involved some chips with smaller pin distances and I have messed up.Here is a picture of two attemptsAs you can see I am just making solder bridges all over the place.I have watched videos online that suggest "dragging" the solder. Tried that and it just balls up between 2 or 3 pins.I have tried to wick away the excess solder and it just doesn't work. The solder doesn't go anywhere so I can't even get the ship off.I have never had to use solder wick but I assumes it would remove solder! I tried solder sucking and it worked to some extent but still left loads of bridges.This is really stressing me out now so I have had to walk away for now.Sent from my ONE A2003 using Tapatalk

author: suicidaleggroll
author_rank: Super Contributor
timestamp: November 02, 2016, 03:48:46 pm
content: What iron and what solder are you using? If it's a temperature controlled iron, what's the temperature set to?

author: spacedementia87
author_rank: Contributor
timestamp: November 02, 2016, 03:57:31 pm
content: Quote from: suicidaleggroll on November 02, 2016, 03:48:46 pmI don't know the brand of iron or solder.They are generic. The solder is a rosin core On free solder though.I have tried the iron between 250 and 450 °C.I couldn't manage either way.Sent from my ONE A2003 using Tapatalk

author: suicidaleggroll
author_rank: Super Contributor
timestamp: November 02, 2016, 04:10:30 pm
content: Just looking at your pictures, it looks like there isn't any flux in the solder, or if there is, it's crap/insufficient. You do not want to skimp out on solder. I spent years soldering horribly, it wasn't until I discovered that the solder I was using was a POS and I actually bought something decent that everything turned around.I use Multicore, but there are several good options. This is my standard one:http://www.mcmelectronics.com/product/21-2280They have some smaller ones for finer pitch, but that should get most jobs done. Don't let the price scare you, a 1 lb spool will last you for years/decades depending on usage.It could also be the iron, but I'd start with the solder. You could also try manually adding flux with a flux pen, eg:http://www.mcmelectronics.com/product/21-2260Though I've found that if you use a solder with enough flux inside, a flux pen is mostly redundant.

author: bktemp
author_rank: Super Contributor
timestamp: November 02, 2016, 04:16:25 pm
content: You can never have too much flux. Adding a good flux makes soldering so much easier. Flux pens are ok, but the gel type works better.

author: Ian.M
author_rank: Super Contributor
timestamp: November 02, 2016, 04:25:41 pm
content: Trying to hand-solder fine pitch SMD chips without good flux is very difficult even for an expert. Personally, I like a liquid R or RMA (rosin) flux, applied with a small brush, as applied sparingly the residue does not need to be cleaned up, but many will swear by synthetic or rosin gel fluxes applied from a syringe with a needle. I don't like flux pens much for rework as the tip tends to get torn up on rough surfaces like existing joints. Whatever you do, don't use paste flux in a tub or tin from the hardware store as most such fluxes are far too aggressive and their residues will corrode the tracks off your board and the pins off your chip.With flux, the surface tension of the solder acts to pull it back to the pin/pad area, breaking any bridges unless far too much solder was used. Simply applying flux to the pins and pads and reheating them several at a time with a freshly tinned and wiped bit, removing it outward with a dragging motion towards the tips of the pins should leave you with no bridges and, if there was an appropriate amount of solder present, with acceptable joints.If you need to remove excess solder, wick it off with a fluxed fresh piece of wick. When cutting back the used end of the wick to get to fresh wick, always bend it to find how far the solder wicked up it and cut it back leaving a couple of mm, but no more, that has solder wicked into it at the end for better quicker heat transfer when you apply the iron to it and the joint. Wick oxidises readily and if its too old may be unusable. A year or so isn't a problem, but if its visibly tarnished or decades old its useless for fine work.350 deg C, or maybe slightly hotter would be a good temperature to start with. 250 deg C is far too cold and 450 deg C is far too hot. Except under exceptional circumstances stay in the 315 to 375 deg C range. Cheaper irons with poorer thermal coupling to the tip or less power delivery tend to need a slightly higher setting within that range, as do many unleaded solders.Search Dave's EEVBLOG videos for 'drag soldering' to find out how to do it right in the first place.

author: senso
author_rank: Frequent Contributor
timestamp: November 02, 2016, 05:38:22 pm
content: You have a severe lack of flux, just wet all the pins and the board with flux, then you just touch the tip of the iron after staining it and BAMM, its soldered, in the end drench in with IPA and its clean and shiny.Also, if it is for personal use, get some eutectic lead solder and avoid crappy lead free solder.

author: GreyWoolfe
author_rank: Unknown
timestamp: November 02, 2016, 08:34:36 pm
content: I use a liquid RMA flux in one of the cheap eBay squeeze bottles with the hypo needles on them. I squeeze the tip down until almost closed so it dispenses without going all over the place. Like Louis Rossman, I believe in that there is no such thing as too much flux. Really good solder is important. Kester 44 with 66 core, 63/37. Worth every penny.

author: JaseG
author_rank: Contributor
timestamp: November 02, 2016, 08:41:26 pm
content: As other have said, flux is your friend here.I'm a noob as well, and with a generouse amount of flux I was able to solder some SOP-16's on my first go using the drag technique. I spent more time trying to line it up nicely and get the opposite corners tacked down so I could use both hands easily.Also, with the resistors & caps I found it easier to solder when I used a footprint that was bigger than the part. The pads for the passives in your photo look like they'd be great for reflow soldering with paste, but a PITA for hand soldering.

author: spacedementia87
author_rank: Contributor
timestamp: November 02, 2016, 08:45:32 pm
content: Quote from: JaseG on November 02, 2016, 08:41:26 pmI only had issues with one or two of the passives. Basically because I put them too close together!Thanks for all the tips. I have ordered some flux and will see how that goes.Sent from my ONE A2003 using Tapatalk

author: amitchell
author_rank: Regular Contributor
timestamp: November 02, 2016, 09:42:10 pm
content: Quote from: spacedementia87 on November 02, 2016, 08:45:32 pmFlux paste is the way to go I think with IC packages. It will hold the package in place for you while you get the first pins going.MG Chemicals 8341 No Clean Flux Pastehttp://www.mgchemicals.com/products/solder-and-solder-related-products/fluxes/no-clean-flux-paste-8341

author: spacedementia87
author_rank: Contributor
timestamp: November 02, 2016, 09:43:52 pm
content: Quote from: amitchell on November 02, 2016, 09:42:10 pmSomeone else here said no to flux paste...Who to believe!Sent from my ONE A2003 using Tapatalk

author: Ian.M
author_rank: Super Contributor
timestamp: November 03, 2016, 02:31:41 am
content: That would be me. I've never been fond of the cleanup required after using electronics grade paste fluxes. Non-electronics grade acid fluxes are just a disaster waiting to happen which is why I cautioned against hardware store flux.Some of the electronics grade paste or gel fluxes may be no-clean in a production environment, but when prototyping, before applying power, you want the solvent to be fully evaporated from their residues leaving hard rosin which doesn't happen quickly if your flux left blobs of goop wherever you put it so you end up having to scrub supposedly no-clean flux off your board.I also don't believe in using flux as an adhesive as I find tacking a corner pin, and reheating to tweak the alignment as required then tacking the opposite corner pin works well for me, and the more goop you put under a part the worse your cleanup problems.However fluxes have improved since I learnt my skills so by all means give paste or gel fluxes a try. Louis Rossmann swears by Amtech flux NC-559-V2-TF and if it works for him repairing Apple notebook mainboards . . . However you should note that he has a swept frequency ultrasonic cleaner tank permanently setup for cleanup and if you don't have that sort of facilities, you'll be drastically increasing your solvent exposure if you need to clean flux residues off manually.

author: Doofenshmirtz
author_rank: Contributor
timestamp: November 03, 2016, 03:29:55 am
content: If you're doing many SMD, I'll suggest using a syringe of solder paste instead of solder wire.Lay down dots of the solder paste, position the component, solder one corner pad, fine-tune alignment, solder the opposite corner, then move along each edge with the iron. Work your way around so the next pin pre-heats while you solder the current one. It takes very little time on each pin with this technique, which is kind to the chip, and the results are very clean.For the resistors and caps, hold smaller ones in position with a dental pick while the first end is soldered, to keep them aligned.

author: amyk
author_rank: Super Contributor
timestamp: November 03, 2016, 10:46:52 am
content: I suggest investing in a hot air station if you're going to be doing lots of SMD. Also, flux.

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: November 03, 2016, 11:16:01 am
content: I looked at your photos. This is a completly diferent technology. I have come across the problem on 2 computer related boards and a modem board. They cant be soldered using a simple soldering iron. It is wave soldered. The solder wount melt.

author: jonovid
author_rank: Super Contributor
timestamp: November 03, 2016, 11:47:17 am
content: see how a pro works with SMD , Louis Rossmann good microscope , use lots of flix & do not cook your chips

author: Dave
author_rank: Super Contributor
timestamp: November 03, 2016, 12:27:42 pm
content: Killing a chip by overheating it isn't that easy. You can easily damage sensitive passives, plastic connector parts, but you'd lift the copper off the PCB much sooner than you could kill an integrated circuit.I've done some pretty shitty solder jobs back when I was starting out, but I honestly can't recall ever killing a chip because I fiddled around with a soldering iron for too long.

author: zzattack
author_rank: Regular Contributor
timestamp: November 03, 2016, 12:55:41 pm
content: Quote from: blueskull on November 03, 2016, 12:14:38 pmI find it just as amazing how he can remove chips so quickly, yet his passives never fly around even though he doesn't tape anything down. I'd guess he uses a low blower speed with high temperature.

author: tautech
author_rank: Super Contributor
timestamp: November 03, 2016, 01:13:04 pm
content: Quote from: spacedementia87 on November 02, 2016, 08:45:32 pmYou did.Layout is crucial to success for hand population and soldering, it's preferable to populate a PCB with the passive devices first and still have enough room to solder the IC's etc later.When doing layouts keep in mind the method of PCB population AND access to components for any possible rework.Quote from: zzattack on November 03, 2016, 12:55:41 pmYep, that's the trick.Each of us has limits of what we are comfortable doing and if I don't need to use paste, I hand solder.... SMD rework....out comes the hot air station.

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: November 03, 2016, 01:28:56 pm
content: These are the best video I have seen on the web for SMD drag soldering.I like the statement :"solder wick is for the undeveloped hand and eye" in the second video.

author: gnavigator1007
author_rank: Unknown
timestamp: November 03, 2016, 03:32:14 pm
content: Didn't realise my soldering was so bad until I watched those videos! Now I feel ashamed but motivated

author: anker_by
author_rank: Contributor
timestamp: November 03, 2016, 03:36:28 pm
content: Quote from: jonovid on November 03, 2016, 11:47:17 amHe has alot of tutorials for macbooks and you can learn alot about soldering too!!

author: Watth
author_rank: Frequent Contributor
timestamp: November 03, 2016, 08:22:48 pm
content: I'm a n00b, but I adhere to the Luis Rossman's ethics on flux usage: USE MORE! It works!

author: P90
author_rank: Frequent Contributor
timestamp: November 03, 2016, 09:19:31 pm
content: Quote from: anker_by on November 03, 2016, 03:36:28 pmYes, he has a lot, he also talks a lot, a lot.a lot.

author: zzattack
author_rank: Regular Contributor
timestamp: November 04, 2016, 12:15:59 am
content: Quote from: tautech on November 03, 2016, 01:13:04 pmSo what kind of temperature range would this be? Well over 350°C? Over 400?

author: tautech
author_rank: Super Contributor
timestamp: November 04, 2016, 12:32:45 am
content: Quote from: zzattack on November 04, 2016, 12:15:59 amDon't know and don't really care.For my "dumb" rework station the hot air pencil I use the smallest tip I have, ~3mm, max heat and blower speed ~1/2. Too much flow especially if not directly above will shift components and if the nozzle is too close to your work.It's not a reflow oven where temp profiles need be right for a satisfactory result, you need to "drive" a rework station based on some small experience. Practice and learn.Get some broken PCB's and have a fiddle, just be aware anything modern is likely be be made with that Pb free muck that seems to have been invented to make SMD rework a nightmare.

author: tggzzz
author_rank: Super Contributor
timestamp: November 04, 2016, 09:13:01 am
content: For my techniques and experiences, seehttps://entertaininghacks.wordpress.com/2015/03/25/assembling-pcbs-with-surface-mount-components/Given it was my first SMD board, I was pleasantly surprised at the degree of success.TL;DR: the minimum special equipment is solder paste, jeweller's screwdriver, tweezers, head-mounted magnification visor, saucepan, and some sand. Note the lack of a soldering iron. Mistakes (e.g. bridges) can be rectified with a soldering iron, solder wick, and liquid flux.If you want todesolder and solder individual SMD devices, a hot air gun and polyimide tape is desirable. The tape is used to deflect air away from components that are not to be changed. After practice, I've used them to successfully replace the infamous caps and R2013 shown inhttps://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/msg614937/#msg614937

author: spacedementia87
author_rank: Contributor
timestamp: November 10, 2016, 10:08:44 pm
content: Thank you everyone for your advice.I seem to have managed to good solder joint today!Sent from my ONE A2003 using Tapatalk