SOIC-8 (de)soldering - Page 1
Forum section: electronics / beginners

author: User32
author_rank: Contributor
timestamp: August 23, 2020, 08:32:35 pm
content: Since I want to be able to unbrick GPUs, do vDroop/voltmodding and recap motherboards by myself i'm thinking of getting a proper soldering station. Problem is: where the hell do I start? Last time I tried soldering something on a motherboard (a ASUS A8N-SLI with effed caps) it didn't go so well.Do I need hot air for things like SOIC-8 IC removal or will a normal iron work?

author: jmelson
author_rank: Super Contributor
timestamp: August 23, 2020, 08:40:02 pm
content: Quote from: User32 on August 23, 2020, 08:32:35 pmWell, there are a couple ways to do it. If you know the chip is toast, nick all the leads on one side right next to the body with an X-acto knife. Why you are almost all the way through, use the blade as a pry bar and snap the lead off just enough to know it is broken. Now, nick the leads on the other side just a little bit, and pry up on the package. It will hinge up on the nicked leads and easily break off after a few bendings. Then, use a soldering iron to wipe off the remaining part of the leads and prepare the PC board to replace the component.This is my technique for removing all SOIC-style parts, and is gentlest on the PC board pads.There are also desoldering tips for various SO-type parts that heat all the leads at once, so you can lift the part off with tweezers. These are a bit trickier to use, but if you have a bunch to do, they make the job go much faster. But, you need almost a different tip for every chip size.Hot air stations with bottom preheaters are another way to do it, again you need different nozzles for each chip size. You have to be sure all leads have molten solder befor trying to lift the part or you can pull pads off the board.Jon

author: wraper
author_rank: Unknown
timestamp: August 23, 2020, 08:47:53 pm
content: Basically there are 4 ways to proceed:1. using hot air gun2. using soldering iron in combonation with low melting point alloy like Rose's metal, Wood's metal, chipquik SMD4.5 wire (expensive). Can be also done with blobs of usual leaded solder but it's very tricky.3. using two soldering irons, one on each side of the chip for removal, or using soldering tweezers.4. cut the legs from the old chip with side cutters, clean the pads from any remaining solder, then solder a brand new chip.

author: Gyro
author_rank: Super Contributor
timestamp: August 23, 2020, 09:02:37 pm
content: Here's a technique that I use when I'm feeling lazy...Cut a non-wettable piece of thin shim (a piece cut from a razor blade is ideal) that is thin and narrow enough to fit between the two rows of legs. Bend the end up so that it is easy to hold with tweezers or pliers. Slide the shim underneath the package, then blob a nice ball of solder across all 4 pins on one side of the package and carefully slide the shim under the legs to isolate then from the pads in the molten solder joints and allow to cool. Once the first side is unsoldered then just use the same blob method on the 4 pins on the other side to remove the package. Remove the excess solder from the IC pins and solder pads.I've even used this method with TSSOP flash chips.

author: User32
author_rank: Contributor
timestamp: August 23, 2020, 09:46:54 pm
content: What about irons, will a bargain basement iron do or do I need a €1000 desoldering station if I want to seriously do SMD rework?

author: BrianHG
author_rank: Super Contributor
timestamp: August 23, 2020, 09:55:18 pm
content: An SO-8 is small enough for a blob of solder added to the legs on each side to work.Then use some solder wick to clean the excess on the PCB pads.

author: bdunham7
author_rank: Super Contributor
timestamp: August 23, 2020, 10:03:26 pm
content: Quote from: User32 on August 23, 2020, 09:46:54 pmSurely there's some room in between? I get by with a Hakko FX-888, Hakko FR-301 (and a lot of tips for each, including the mosquito tips for the FR-301) and a cheap 858D hot air station. I only do occasional SMD, if I needed to do larger chips or SMD in general more often, I would certainly upgrade to a better hot air station and a preheat table. And some hot tweezers, which I may buy anyway.I typically try to cut all the leads on packages where that can be done, then suck the legs off the board with the FR-301. This is really helpful where the package has a center soldered heat sink--it prevents pulling a pad up when you are trying to cook off an especially stubborn chip while not blowing way its neighbors. I also am not averse to using a dremel tool to remove the body of the chip if it is in a difficult location.

author: BrianHG
author_rank: Super Contributor
timestamp: August 23, 2020, 10:25:45 pm
content: I know many here cringe at junk, but for SO8, even this would work:https://www.aliexpress.com/item/32618051207.html?spm=a2g0o.productlist.0.0.3e5d1bf88bZgHH&algo_pvid=d2bc40e9-e4a3-48e4-ad4c-456092eebe57&algo_expid=d2bc40e9-e4a3-48e4-ad4c-456092eebe57-41&btsid=0ab6fab215982212718361480ed248&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_I've used one for quite some time, even though the iron part hasn't the perfectly heated heat reservoir of a quality Hakko or Weller name brand, if you are replacing SO8 and even small QFP, it is functional.

author: julian1
author_rank: Frequent Contributor
timestamp: August 23, 2020, 10:35:42 pm
content: An 858D for under 100 dollars if you can manage it, will allow you to do almost anything you want, using conventional technique - eg. replicate stuff you see on youtube. Buy one in priority, after you have a regular iron and multimeter.

author: ledtester
author_rank: Super Contributor
timestamp: August 23, 2020, 11:19:22 pm
content: Some enlightening videos:https://youtu.be/CVsmwFAkf7Ihttps://youtu.be/Hb9gWodVx7Y

author: bdunham7
author_rank: Super Contributor
timestamp: August 24, 2020, 12:52:40 am
content: Quote from: BrianHG on August 23, 2020, 10:25:45 pmTry some genuine Hakko tips with it, I'll bet the tips are the biggest deficiency.

author: magic
author_rank: Super Contributor
timestamp: August 24, 2020, 08:37:17 am
content: Quote from: Gyro on August 23, 2020, 09:02:37 pmThis works. I don't even bother with a metal shim, just lift the desoldered side using tweezers and apply some flux to clean any solder bridges still remaining between the lifted pins and he board.I also nondestructively desoldered TQFP with a normal iron once. Never again

author: Ian.M
author_rank: Super Contributor
timestamp: August 24, 2020, 08:56:07 am
content: See my comments on a method similar to Gyro's shim, of using a fine wire to lift the pins here:https://www.eevblog.com/forum/microcontrollers/arduino-pro-mini-two-copies-have-different-sleep-currents/msg3139276/#msg3139276Back when SMD was coming in to the consumer market, and with most repair shops not properly equipped for SMD rework, I got quite good at that method.

author: User32
author_rank: Contributor
timestamp: August 24, 2020, 11:03:21 am
content: Would a FX-888D work? I have a dead Quadro FX 3800M to practice on.Pretty expensive at €133 w/ VAT though:https://www.eleshop.nl/hakko-fx-888d.html

author: Gyro
author_rank: Super Contributor
timestamp: August 24, 2020, 07:29:41 pm
content: Just to clarify, the reason for the shim is to interpose a non-wettable barrier between the legs and pads so that you don't need to worry about having to wick every last bit of the solder out of the gaps. You can just blob the other row of pins and float the IC off and leave the cleanup until you have decent access. Even a strip of paper works at a push.It only works with 2 row parts of course (unlike Ian's).

author: magic
author_rank: Super Contributor
timestamp: August 24, 2020, 07:41:08 pm
content: I might try katpon tape once. It's even less solderable than stainless steel (which I can totally believe is good enough already) and probably thinner.

author: User32
author_rank: Contributor
timestamp: August 24, 2020, 07:53:28 pm
content: Quote from: Gyro on August 24, 2020, 07:29:41 pmWhat if I want to reuse and re-solder the EEPROM? (ie take it off, put it in my flasher and solder it back)

author: magic
author_rank: Super Contributor
timestamp: August 24, 2020, 08:00:20 pm
content: The whole point is to slide something thin between the pins and the PCB when the solder is molten in order to1. lift the pins a bit from the PCB2. prevent solder from holding them to the PCBYou do it on one side, then on the other. If you are careful, both the board and the chip will survive. Practice on some scrap board you don't mind destroying.

author: Gyro
author_rank: Super Contributor
timestamp: August 24, 2020, 09:47:56 pm
content: You only need to use the shim on one row of pins btw. Once that row is isolated by the shim, heating the other row of pins with a nice blob of solder allows you to slide the package free of the pads.The EEPROM should be perfectly good after cleaning up the pins.

author: wasyoungonce
author_rank: Frequent Contributor
timestamp: August 25, 2020, 01:25:15 am
content: OP Just remember That computer MBs and video cards are multilayer high density PCBs usually big ground planes on inner layers.Makes it harder to solder/desolder as heat sinks away like beer drinks on hot day! So it will be more difficult. Hot air pre-heat can help.Just be aware of this if you have trouble melting joins.