De-soldering help needed - Page 1
Forum section: electronics / beginners

author: Drake122
author_rank: Contributor
timestamp: February 26, 2018, 09:40:34 pm
content: Hey guys!I'm learning board level repair and started to practice de-soldering and soldering back SMD components. I'm fairly new and only practice on already junked boards, but I'm still messing up a lot of pads. They come off with the component. I obviously don't want that on a customer's boardWhat I might be doing wrong? I'm using a hot-air station for de-soldeing, with a temperature of about 300°C. Is it that I overheat the pads? but lead-free shit just won't melt

author: ogden
author_rank: Super Contributor
timestamp: February 26, 2018, 09:52:06 pm
content: Quote from: Drake122 on February 26, 2018, 09:40:34 pmIf you tear pads off the board then solder obviously isnot melted. 300oc temperature is too low for lead-free solder. Probably this is an issue. Thou you shall search youtube. There's plenty of "SMD rework" videos.

author: Drake122
author_rank: Contributor
timestamp: February 26, 2018, 09:57:42 pm
content: I searched youtube, and google, and ofc everybody has a different approach. Even with a heat-gun. I was already afraid that I was using too high of a temp, that I would melt the IC or the board. So I guess a bit higher temp with less exposure time.

author: ogden
author_rank: Super Contributor
timestamp: February 26, 2018, 10:04:33 pm
content: Quote from: Drake122 on February 26, 2018, 09:57:42 pmAs alwaysit depends- what kind of chip you are trying to desolder and on what board. There's huge difference between 14 pin soic on 2-layer board and huge BGA on multi-layer (let's say 10) board. If you are working on multilayer boards then you shall consider additional preheating of the board area where's chip located.

author: Drake122
author_rank: Contributor
timestamp: February 26, 2018, 10:10:39 pm
content: Well, it was a multi layer board, an Asrock motherboard, that I practiced on today, and removed only smaller components (2 leads, 6-8 pins).So, pre-heating you sayI thought that raising the temperature to a 100-150C constantly is bad. I thought you want to minimise the heat exposure of other components, so go in fast, with a bit bigger heat and leave.

author: ogden
author_rank: Super Contributor
timestamp: February 26, 2018, 10:20:44 pm
content: Quote from: Drake122 on February 26, 2018, 10:10:39 pmMotherboard is not the best way to start learning smd rework. You shall have some skills to do >=8 layer boards. Don't be afraid to heat other components upto 150oC or so around one of interest. After all they had been in the oven for couple of minutes when manufactured, at solder melting temperatures! If you see there's something like hand-soldered socked that can melt - use capton tape or .. dunno.. aluminium foil to shield it.

author: Neilm
author_rank: Super Contributor
timestamp: February 27, 2018, 06:19:12 pm
content: Motherboard have multiple 0V and power planes. This means it is a very large mass to heat up. If reworking one of these, you have to heat the whole board up over several tens of seconds before starting to apply heat to the specific component you want to remove.Even a 4 layer board with a solid power and 0V plane can cause issues if what you are trying to rework is a connected to one of the planes by multiple vias near the pads.

author: frozenfrogz
author_rank: Frequent Contributor
timestamp: February 27, 2018, 06:50:27 pm
content: To get into board level repair via Youtube I highly recommend watchingLouis Rossmanns videos.He has a lot of content to dig through and a lot of it is related to Apple hardware. Of course the advice on gear and basic operation applies to other boards as well.Re. 300°C hot air for component removal: You need to go up to 450°C (or there about - depending on the circumstances). 300°C will leave you heating up a large area of the board without getting proper heat in the spot where you need it. You want quick energy transfer in a more or less defined area. Also, do not skimp on airflow. More hot air == more energy transfer.

author: ogden
author_rank: Super Contributor
timestamp: February 27, 2018, 06:52:30 pm
content: Quote from: frozenfrogz on February 27, 2018, 06:50:27 pmUse flux as well.

author: frozenfrogz
author_rank: Frequent Contributor
timestamp: February 27, 2018, 06:56:56 pm
content: Quote from: ogden on February 27, 2018, 06:52:30 pmThis. +1Stannol X32-10i does a good job for small repairs and the genuine Amtech flux gels are worth the money.

author: cowasaki
author_rank: Frequent Contributor
timestamp: February 27, 2018, 10:14:56 pm
content: Use a lot of flux.A board pre heater is not expensive but if you heat the whole board to 150-170 or whatever then it makes it so much easier to simply supply the additional heat to the actual component.Consider one of the specialist very low heat soldiers designed specifically for component removal. As this mixes with the original solder it allows components to be removed at very much lower temperatures.Use more flux :-)

author: newbrain
author_rank: Super Contributor
timestamp: February 27, 2018, 11:29:43 pm
content: Quote from: cowasaki on February 27, 2018, 10:14:56 pmSorry, could not resist.Photo by Wilhelm Gierse, from Wikimedia Commons.

author: Teledog
author_rank: Regular Contributor
timestamp: February 28, 2018, 01:55:11 am
content: I've screwed up many a board when I first started (CPU/NAND BGAs)Mask all the components you don't want to blow off with kapton &/or tin shieldsPreheat the bottom of the board with a (can be cheap) pre-heater with the board clamped at the edges (use heavy base clamps or DIY/large metal units)I like to monitor the board temp with a hand held non-contact laser thermometer (cheap)Then use your hot air gun.Don't try to pull anything off..the solder shouldall of a suddenlook shiny..then "slide" it, if you can..if not..then it's not hot enough. Heat it more/bump higher temp& then pick it off with fine tweezersLarger BGA's will need a larger heat gun (modified paint stripper - really!)Experiment by clamping an old motherboard upside down above a concrete floor (garage?)Wear safety boots (gloves? your call) & heat it up with a heat gun..moving the gun back & forth, alternating heating the underside, and the top - until components drop off..really!Hence the safety boots..Bit of a learning experience..but then you'll kind of get the feel for what it takes for the solder to melt ..without charring a board or ripping up traces/pads

author: cowasaki
author_rank: Frequent Contributor
timestamp: February 28, 2018, 03:44:26 am
content: Quote from: newbrain on February 27, 2018, 11:29:43 pmAuto correct which seems to spend more time being auto make wrong!!

author: TheDane
author_rank: Regular Contributor
timestamp: February 28, 2018, 10:19:54 am
content: If youonlywant to use hot air, and not combine your skill set with a regular iron (which also can be great for small and large components),I suggest acquiring/using some ceramic tweezers.Ceramics does not act like a heat sink like metal do, and this allows you to work the component more easily when it is hot.Let the tools do the job, if something sticks - it wrecks.Gentlemen - and ladies