GPU solder from hell - Page 1
Forum section: electronics / beginners

author: macross
author_rank: Contributor
timestamp: June 20, 2014, 05:10:39 pm
content: So i'm trying to desolder blown caps on my GPU, but i can't melt solder no matter what i do! I have temperature controlled weller whs40 soldering station (40w). Tried cranking up the heat to 450c still it just won't melt. I know that i'ts not the ground plane that takes all the heat away because i have just tried desoldering few caps from old motherboard which had huge ground planes and it worked just fine even with 350c. On the other hand that gpu has small ground planes and yet it's impossible to melt the solder. Anyone have any ideas on how to remove those damn caps?

author: mariush
author_rank: Super Contributor
timestamp: June 20, 2014, 05:22:30 pm
content: Add liquid flux, add LEADED solder to the pins because leaded solder lowers the melting temperature of the existing lead-free solder. 60/40 or 63/37 will do. Add a blob of solder on each pin, don't be shy, the blobs of solder will cool down slowly so it works great. Warm up both blobs of solder and gently wiggle the capacitor loosening the leads.If you have to, you can get a hair dryer and carefully warm up the whole pcb area around the capacitor for a few minutes.Alternatively if you don't care about the capacitor, get some pliers and carefully twist the capacitor back and forth a few degrees (keep it up for a few minutes) and eventually the leads will weaken and break. You'll be left with a few mm of leads. Now the capacitor no longer sucks heat from the iron so do as above and when you think it's right, grab some tweezers and PULL the leads or PUSH them through the board.

author: Neilm
author_rank: Super Contributor
timestamp: June 20, 2014, 06:15:15 pm
content: If you want to reuse the caps I wouldn't use leaded solder - you don't know if the unleaded solder will form an unreliable joint when reused.

author: rob77
author_rank: Super Contributor
timestamp: June 20, 2014, 07:15:21 pm
content: if you're sure the board has Pb-free solder then you can try the bismuth solder Sn42Bi58 - it has a very low melting temperature (138celsius if i remember correctly).but after using bismuth solder you can't even think about using a standard 63/37 solder for soldering the new caps - your joints will be unreliable (Pb + Bi => 95celsius melting point => unreliable joints).the best way would be to heat the board with hot air and add the last temperature kick only with the soldering iron.and actually it's the ground a power plane sucking the heat - but in case of Pb-free solder you need to reach a higher temperature - that's the reason why it's not working like on the MB you was mentioning.

author: peter.mitchell
author_rank: Super Contributor
timestamp: June 20, 2014, 08:18:55 pm
content: Quote from: macross on June 20, 2014, 05:10:39 pm40w you don't have a snowflake's chance in hell. You need more like 100w.GPUs have a massive number of layers, take a look at this picture, courtesy of @TiN;A motherboard may look like it has a huge number of layers, but by comparison, it doesn't. Most budget motherboards for low-mid range chipsets are only 4 layers, compared to that GPU cross section which shows 12! layers, even an expensive, top of the line, enthusiast chipset on a tiny motherboard is only going to be an 8-6 layers board. That is twice the amount of copper right there. You're practically soldering to a block of copper.

author: jetwolfk2
author_rank: Contributor
timestamp: June 21, 2014, 06:25:02 am
content: Quote from: Neilm on June 20, 2014, 06:15:15 pmthe military still uses lead solder in their applications, they have not transitioned to lead freethe 40w iron may not be enough for lead free soldering, typically 70 watt or higher is used especially with the multi layer boards and all the copper

author: rob77
author_rank: Super Contributor
timestamp: June 21, 2014, 06:32:00 am
content: Quote from: jetwolfk2 on June 21, 2014, 06:25:02 ami'm using my 48W soldering iron with Sn99.7Cu0.3 solder-wire without issues on multilayer boards while soldering, but i'm heating the boards with hot-air before de-soldering a THT component.EDIT:sorry it's SN99.3Cu0.7 solder-wire not as i written above.

author: exxon
author_rank: Newbie
timestamp: June 21, 2014, 07:01:10 am
content: Heat up the board. Slowly, till it is quite hot. Do the same with the cap on the other side. Don’t be worried, you can heat the board a lot without any damage: 100 °C is not a problem for any component if the board is not powered up. Use a 80 W min. tool.I suggest you NOT to pull, push and/or twist the component if it isn't totally loose: the stress on the metalized hole could break the connection with the internal layers causing an unrecoverable damage.

author: macross
author_rank: Contributor
timestamp: June 21, 2014, 07:19:30 am
content: Thanks for suggestions i'm going to try preheating the board first if that doesn't work then i'm going to get a more powerful soldering iron.

author: rob77
author_rank: Super Contributor
timestamp: June 21, 2014, 07:54:06 am
content: Quote from: macross on June 21, 2014, 07:19:30 amuse some holder for the board while heating or clamp you board into a vise - CAPs to be un-soldered facing down (but be carefull when using vise to not damage anything on the board). the board will get all hot - even if preheating only the area with the cap. and don't be shy to heat up the board to even 150-160celsius. and keep the hot air going - pointing at the cap's leads even when you start heating with the soldering iron (i usually even crank up the hot air to 250-300C at this stage). you don't need a third hand to pull the cap off - it will fall of the board without touching it (gravity is a good guy)and last but not least - don't use a paint stripper hot air gun when unsoldering a single component. (if you don't care about the PCB board , just want to salavage all the components from it, then paint stripper is usable )

author: firewalker
author_rank: Super Contributor
timestamp: June 21, 2014, 09:41:55 am
content: If there is no other option, cut away the old capacitor and solder the new one to the pads directly.Alexander.

author: jetwolfk2
author_rank: Contributor
timestamp: June 22, 2014, 05:37:31 pm
content: Quote from: rob77 on June 21, 2014, 06:32:00 amyes as i mentioned its not enough, which is why im glad you said your heating the board with air and using the iron