GPU Buck Converter replacement - Page 1
Forum section: electronics / repair

author: kallisti5
author_rank: Contributor
timestamp: April 04, 2022, 01:14:53 pm
content: So, taking a crack at my smallest SMD replacement yet. I have a GPU with a blown Buck Converter.I've looked the board over, I think this one is repairable. No burnt traces, nothing differential broken or damaged.While i'm waiting on the replacement FDMF3035 to arrive, i'm thinking of using the following process:Put the boardonabove my MHP30 heater, come up to ~150CHit the IC from the top with a small nozzle heat gun and remove it (hopefully before disrupting the small ICs on the opposite side directly underAllow the board to cool, inspect, cleanup the pads, pre-tin them with lots of flux.Bring the board back up to to temp, place IC on the pads, heat with heat gun until it setsDoes this sound like a reasonable plan? My goal with the small board heater is to try and get as close to the melting point without loosening the various components on the bottom of the board which have a high likelihood of getting knocked off via the heater.

author: wraper
author_rank: Unknown
timestamp: April 04, 2022, 01:27:35 pm
content: The chip might got welded to the copper pad. Happens quite often with these. In that case you will need to remove it forcefully, first trying to twist it horizontally. Not melting the solder on components around the chip in not realistic. This component will need a lot of heat before solder melts, by the time when it becomes loose, everything around will be melted, so just work cautiously to not disturb surrounding components.QuoteYou should rather use a large nozzle. Using smaller nozzle will not help against melting solder on the opposite side. I don't think it will melt but if you are concerned, just ensure that opposite side of the board does not touch anything in area underneath of the chip. Even if solder melts, components will stay in place regardless, unless mechanically disturbed.

author: DavidAlfa
author_rank: Super Contributor
timestamp: April 04, 2022, 01:47:00 pm
content: Good luck soldering that...

author: kallisti5
author_rank: Contributor
timestamp: April 04, 2022, 01:53:22 pm
content: > Good luck soldering that...Lol. Same pain of trying to solder a bga. At least fewer pins == less chances of bridged connections.

author: kallisti5
author_rank: Contributor
timestamp: April 04, 2022, 01:57:05 pm
content: Quote from: wraper on April 04, 2022, 01:27:35 pmI kinda misspoke on not melting components around the chip.. I mostly meant trying to not disturb the components on the bottom.Quote from: wraper on April 04, 2022, 01:27:35 pmThat's kinda my issue with the board heater. It is a plate which physically contacts the reverse side of the board. There are components under the board below the IC in question. Maybe I should be going pure air instead of using the board heater in unison... or maybe I should keep the board suspended above the board heater by a few mm and use the radiated heat to keep the board "warm"

author: kallisti5
author_rank: Contributor
timestamp: April 04, 2022, 06:17:36 pm
content: Quote from: wraper on April 04, 2022, 01:27:35 pmOof. You nailed it here :-) One bottom pad directly under the burn on the IC was welded to the board, and came off the IC on removal.I successfully otherwise removed the IC without any real damage.Anyone have pro tips on how to "unweld' a pad from another? Already tried scrubbing with fresh flux, heat, and a fine wick.

author: wraper
author_rank: Unknown
timestamp: April 04, 2022, 06:25:14 pm
content: Quote from: kallisti5 on April 04, 2022, 06:17:36 pmThat will not work unless you heat it to the temperature at which copper itself will melt. Unfortunately you can only do it mechanically like cutting, scraping, or milling the component off the board.

author: kallisti5
author_rank: Contributor
timestamp: April 04, 2022, 07:19:34 pm
content: Quote from: wraper on April 04, 2022, 06:25:14 pmHm. I do have a porcelain precision sanding pen, maybe I can grind it down enough to let the IC sit flush

author: kallisti5
author_rank: Contributor
timestamp: April 04, 2022, 09:07:02 pm
content: Here are a few pictures of the pad's post removal from a few angles.I "feel" like everything is there, but also feel like a pad is stuck to the bottom left corner.