Soldering trouble due to corrosion and large ground planes - Page 1
Forum section: electronics / beginners

author: slowpoke
author_rank: Contributor
timestamp: October 02, 2014, 10:04:24 pm
content: First post, be gentle...I'm trying to repair a treadmill i recently bought, it has something wrong with wax/lift/power distribution board.(Will explain nature of troubleshooting/repair in repair section).Problem is, the item was sat in a garage for way too long. Being in UK doesnt help matters either, weather is crap most of the time, damp, etc... The board in question got gray corroded looking joints all over the place. No corrosion to vias or board itself. It doesnt stick to my iron. Its as if my iron is not powerful enough (30w).I heat joint up, solder liquifies and wont stick to iron at all. Fresh solder (60/40 mc) wont stick to it as well. I managed to desolder one very suspect cap and now cant clean the holes, braid wont wick it away. Had to pull cap forcibly just to detach it from the board while non sticking solder is liquid... Desoldered cap couldnt be resoldered by new solder. Had to knife scrape gray whatever off legs to get fresh solder to stick... Tried couple easier components - one diode and one resistor. Same there. Quit at that point... Dont want to ruin the board by my amateurish attempts to revive it by resoldering.How to remove solder if it wont wick or suck away with a plunger/sucker ? No amount of flux helps (kester 951 pen).Soldering iron in question is a cheapie 30w hot stick from some big box store... many moons ago...My soldering skills are...emmm...fair...ish... Managed to jtag an xbox360, that counts for something no ? Kynar wire and all that...Do bits and pieces here and there, fix crap my kids break etc, no smd's tho (except for a R6T3 removal on xbox)My electricity/ee knowledge is basic, i've been around computers most of my life (christmas computer fixing marathons suck), i understand very basic ee components.Anyone to help me solve this ?P.S. Cant just shove it into oven for reflow as there are relays, transformers and caps present. Not keen on wrecking it completely.

author: sleemanj
author_rank: Super Contributor
timestamp: October 02, 2014, 10:45:34 pm
content: Add a good blob of solder to the iron tip first to improve heat transfer (surface contact area) to the joint.If fresh solder won't stick to the tip, clean it.Existing solder on the board probably lead free which needs higher temp, combine that with possibly large ground plane, and you have a bit of a job on your hands with a small iron.

author: slowpoke
author_rank: Contributor
timestamp: October 03, 2014, 09:31:44 am
content: Tip is clean and freshly tinned.Also, i did suspect it being leadfree.Will post photos of the board later today.

author: Dago
author_rank: Frequent Contributor
timestamp: October 04, 2014, 09:35:14 am
content: Flux flux and flux. You can never have too much flux.

author: slowpoke
author_rank: Contributor
timestamp: October 04, 2014, 10:08:00 am
content: Nope. Flux doesnt help much.I decided to give it a good scrub with 99% IPA.Also, my new 60w Tenma soldering station (yey) came with pointy tip, so thats useless till i get my new chisels here.

author: SeanB
author_rank: Super Contributor
timestamp: October 04, 2014, 02:33:13 pm
content: If you do not care about the pointy tip just clip it to a chisel shape with electricians pliers to do the conversion. Will not have a long life but will do for a few dozen joints till the copper is eroded from the tip totally.

author: tautech
author_rank: Super Contributor
timestamp: October 04, 2014, 08:48:31 pm
content: Quote from: slowpoke on October 04, 2014, 10:08:00 amPhotos tell the story....Large power tracks will suck the heat out of all but large tips.Big iron, big tips should do the trick.3 mm Chisel tip on your 60 W iron might do it?It doesn't matter lead free or not, it is an unknown composition!!!!Mix fresh solder with that on the PCB, suck it away and start again clean with a solder you can work with.Get yourself a small amount of low temp solder for jobs like this and that will help also.

author: G7PSK
author_rank: Super Contributor
timestamp: October 05, 2014, 02:51:29 pm
content: Clean the surface with a brass wire brush apply flux, flux and yet more flux along with fresh solder.

author: slowpoke
author_rank: Contributor
timestamp: October 08, 2014, 08:14:38 pm
content: Done a lot of soldering practice. Problem persists.I can melt/mix new/old solders on underside of this board, but it acts as if i'm not heating it enough as top side will not go molten so i can pull components out. It drives me nuts.Holes are very tight too (in relation to lead sizes), cleaning is a nightmare, impossible to clean with braid, have to do toothpick trick. Components are clinched so that also introduces additional difficulty...I switched to 1.6mm chisel and upped temp to 400c, as 330-350c just wouldnt cut it...Also, big ground planes. Not sure how to deal with that. Heatsinks are no problem, but i'm afraid i will damage components while trying to get them off big planes... I would really appreciate advice on this...Ghrm...

author: RobertHolcombe
author_rank: Frequent Contributor
timestamp: October 09, 2014, 01:35:55 am
content: As already mentioned, flux, larger/higher thermal mass tip, clean the pads w/ abrasive to increase thermal couplingMy suggestion is to preheat the board with hot air - you're going to have issues achieving reflow without a fairly beefy station/iron working those large thermal mass traces and planes. Using braid will only increase that thermal mass, so having the whole board up to say 100-150C will make your life much easier.When using braid make sure you apply flux to the braid itself, even when its fresh out of the packet this can help

author: Unknown
author_rank: Unknown
timestamp: October 09, 2014, 02:12:31 am
content: Quote from: RobertHolcombe on October 09, 2014, 01:35:55 am^This^A couple of additional tips: use a solder sucker rather than wick to remove most of the solder, then if needed use the finest wick you can get. And, especially for smaller planes like in the PSU section of that board, if you don't have a hot air gun or preheater you can get often get a worthwhile amount of preheating from a hair dryer...

author: tautech
author_rank: Super Contributor
timestamp: October 09, 2014, 06:53:13 am
content: Quote from: slowpoke on October 08, 2014, 08:14:38 pm!.6 mm tip will be like pissing into a headwind.Many tips are parallel sided and just do not have the thermal mass or conduct enough heat.For heat hungry jobs like this I find a 3.2 mm tapered tip will just do the job and I would like larger sometimes but I have a selection of mains irons when the going gets tough.Hakko make up to 5.2 mm tapered chisel tips.