Solder won't take to PCB pad - Page 1
Forum section: electronics / beginners

author: Domarius
author_rank: Newbie
timestamp: August 21, 2024, 02:23:21 am
content: A friend's video card (MSi 1080) has has a capacitor just pop off, so I'm attempting to fix it - as I feared, the capacitor next to it popped off as well, after only a slight nudge during examination, I figure it's some kind of manufacturing flaw.Here's a photo I found of the exact PCB with all the heatsinks removed, I can take a photo of mine as it is if it helps:My main issue is, no matter what I try, I cannot get the solder to adhere to the pad on the PCB. The remaining solder would not melt, and I'm afraid to overheat the PCB. I've already made this mistake on a test board, using the heat gun functionality of myDremel butane fuled soldering iron, I got a test board specifically so I could make these mistakes, I bubbled the board in one instance, and cooked the components in another case. So for the actual video card, I'm trying not to spend too long on any one area, I don't want to damage it.Since I couldn't get the existing solder to melt, I gently scraped it off, hoping to bare the original metal pad, though I can see the copper in some spots, so hopefully didn't scrape too far. I did some research and looks like they use special solder paste and cook the board, which would explain the grainy consistency of the existing solder, maybe that's why I couldn't melt it?Every time I apply a soldering iron to get a bit of solder to adhere to the pad, it just beads. The solder melts and never bonds to the boards, it just forms little beads on the soldering iron tip. I even dared tried using the heat gun functionality for a bit, and the solder beaded again, just sitting on the pad.I'm using plenty of flux paste to improve the surface area of the heating.I'm at a loss as to how to get this solder to take, if I could, I could do the technique I saw on YouTube where you put a blob down on one pad, put the component on that blob, melt that foot into place, then solder the other foot down. But I can't get that far.

author: _rushin_or_draggin_
author_rank: Regular Contributor
timestamp: August 21, 2024, 02:52:45 am
content: You may want to attach a picture of your board, especially a close up of the area you are working. Since you posted in the beginners section of this forum I am going to assume you have a basic knowledge of soldering. Usually when I am replacing a SMD component, or any component for that matter, I add solder to remove solder. Factory solder is 99% of the time lead free, which does not work very nicely when we are trying to work on these boards. Your first step is to add solder to the pad. This is where you are encountering your first problem. Usually what I would do in this case is to add a generous amount of flux to the area. The flux causes solder tocoagulatefor a lack of better words as well as clean the pad off and prepare it to solder. If you don't have any flux, get some. It can be the kind that you brush on or the kind from a syringe. Another thing that can cause the pad to not take solder is the pad itself is not getting hot enough. This can be due to the pad being part of a much larger plane on the PCB which means your iron has to heat up a lot more copper to the melting point of your solder. (Just a bit of electrical trivia as it is applicable here. When you design boards for manufacturing, there is typically a thermal relief between the pad and the trace/plane. This allows the pad to require much less heat to make the solder take. Anyway, continuing). If you have a larger iron tip, use it in combination with the flux. That should let the pad take solder. Once you get it to take solder I would recommend you add a big blob on each pad and then wick it away with some solder braid. This will give you a nice, clean surface to solder your new component to. And as how to solder it, add a tiny amount of solder to one pad, put the component close to the pad, melt it, and push it into place. Then, solder the other pad, and once that is cooled you can reflow the first pad. A good trick to see if you got the component soldered to both pads really well is the touch each side of the component with your iron, melting the solder on that pad. If you can touch both sides and the component doesn't move, then you're in business. Hope this helps.edit: Just saw that you were using flux. You may benefit from a larger iron tip combined with a higher wattage iron (nothing crazy of course). I am convinced you are not getting the pad hot enough, and any heat you do get into the pad is just boiling the flux off before it can do much of anything on the pad. The reason to use solder paste is in production they roll the PCB with components placed through a convection oven to heat the entire board up and melt the solder. For a 2-pad package like that this is unnecessary to do in your case.

author: Konkedout
author_rank: Frequent Contributor
timestamp: August 21, 2024, 04:41:19 am
content: 63/37 tin/lead solder is highly recommended. There may be issues if you have unleaded solder already there but I would try to use it if you have it. Is tin/lead solder permitted in your country? Also use an activated rosin core flux such as Kester 44.

author: PGPG
author_rank: Frequent Contributor
timestamp: August 21, 2024, 10:45:20 am
content: I remember only one case when whatever I was doing I was not able to solder a CAT5 cable wire to PCB pad. It was simply first time when I met Ethernet cable that a magnet sticks to it.I don't expect such savings to trickle down to the PCB, but, with mass production - who knows.

author: Domarius
author_rank: Newbie
timestamp: August 22, 2024, 12:31:22 am
content: I've attached some photos, a close up, and a zoomed out version for context. If you look in my original post there's a link to a photo of the full size board as well if that helps.The translucent globs in the middle are where I put nail polish to cover up some minor exposure of the copper during my scraping. I noticed the groove running vertically between the opposing pads and figured that might be an air gap between opposing polarity and I didn't want it to arc.Someone told me since that the board is designed to wick away heat and that I'll need to look into techniques for heating up the board to a base temperature so that my soldering iron can then apply localised heat to bring it up to the point where the pad will accept the solder. I'm going to research that...

author: ArdWar
author_rank: Frequent Contributor
timestamp: August 22, 2024, 12:57:08 am
content: Ah yes, heavy copper power plane. That usually means you just weren't heating it up enough to melt the solder.Either preheat more, or (not recommended) use high powered iron that can do enough local heating to overcome the plane soak.

author: Ian.M
author_rank: Super Contributor
timestamp: August 22, 2024, 01:58:32 am
content: I'm assuming you don't have a 50W or greater temperature controlled soldering station, with a >2.5mm bevel (hoof) tip, which is the sort of iron most of us would regard as the minimum for this sort of heavy duty work.Also as ArdWar points out, preheating the board vastly increases your odds of success. If you can get the whole board or at least a 5 cm radius around the area up to 100 °C (a reasonably safe temperature for most parts and PCBs) it will halve the rate of heat loss from the joint when it is at the melting point of Sn60/Pb40 solder, which is equivalent to doubling the effective power of the iron (and heat transfer capacity of the tip). How to improvise a board preheater is a whole other discussion - search the forum and you should find some good topics. Any preheat is better than none as long as it isn't so aggressive as to melt plastic parts, blister the board or start melting joints you don't want to disturb.A conical tip of the style supplied with yourDremel Versatipgenerally doesn't have enough contact area (due to its radius of curvature) to heat pads directly connected to wide tracks or power planes up to soldering temperature. If you haven't used the hot cutting knife tip yet, your best chance of success would be to tin its bevel with solder, and use it as a soldering tip, holding the iron so that the bevel face is flat on the pad for maximum contact area. Once you've got the pads tinned, even without preheat it should be possible to solder the capacitor's tabs to the pads while the nearby copper is still hot. If the cutting knife tip has been used on wood or plastic it may be very difficult to get the bevel face tinned - you may have to abrade it to get solder to wet it which isn't good as any breaks in the plating will shorten its life.Dremel do have a bevel tip for the Versatip, - the oval tip in thePyrography set, but that set isn't cheap and only two of its tips would be usable as soldering tips, so you may be better advised to get a budget temperature controlled soldering station for the actual soldering so you can use the Versatip hot air tip for local board preheating - keep it orbiting round the work area to distribute the heat and not too close so you don't blister the board again!

author: Smokey
author_rank: Super Contributor
timestamp: August 22, 2024, 08:09:27 am
content: I've tried to rework graphics cards before. I found it near impossible. And I have nice Metcal irons with appropriate tips and everything. So many layers. So many planes. So much high temp lead free solder.I had to absolutely blast the board with hot air to get a local spot hot enough to flow, and I only had the courage because that card was already scrapped. Pretty sure that section got too hot.I'd be afraid to put the whole card in an IR oven. No idea what the max profile is for the connectors and other plastic stuff.

author: Psi
author_rank: Super Contributor
timestamp: August 22, 2024, 08:10:21 am
content: Anything that size you will need a preheater.I got the Puhui T8280 from aliexpress.Build quality is a bit junky but it works fine (after I took the panels off and fixed a broken wire on the switch)

author: PGPG
author_rank: Frequent Contributor
timestamp: August 22, 2024, 08:43:12 am
content: Quote from: ArdWar on August 22, 2024, 12:57:08 amI have never worked at such PCB but I believe using soldering iron I frequently use I would have a chance. It is 100W trafo (gun) soldering iron. I am making soldering tips for it from 1.4mm diameter wire. Recently using it I soldered two 4mm² wires making soldering connection at 2cm length. I am using this soldering iron also when I de solder 0603 elements to heat (switching it on for second or two) one pad while with other iron (typical for SMD) I heat second pad.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: August 22, 2024, 06:24:45 pm
content: Your soldering equipment is the issue. You need one that doesn't use hand made wires. You need real tempature control. If you do have one, set it to about 400c and use the biggest bevel tip you have.Flux the board.Put the solder on the bevel.Touch the pad....if it doesn't immediately tin the pad, turn it up higher.If you dwell for more than or a second or so, you're just going to be heating a system that's designed to wick away a crap load of heat. You will not win.

author: Domarius
author_rank: Newbie
timestamp: August 23, 2024, 02:18:21 am
content: Thank you everyone, so much... this is disappointing but very informative.As a last ditch effort, I bought some conductive adhesive, but I'm not having any luck getting it to dry properly, it just flakes away on my test board, even after leaving it overnight and not touching it till the next day. On a 2nd test I tried heating it and it just melted away, and that was confirmed by the seller, they said not to heat it just let it dry. My current theory is perhaps it just the initial squeeze which is very runny, maybe if I keep squeezing more out of the syringe it will get to some more solid paste... I'm just being frugal with it since there isn't a lot. Does anyone have any experience with conductive adhesive? This is the one I bought:https://a.aliexpress.com/_mKoCJHI

author: Haenk
author_rank: Super Contributor
timestamp: August 23, 2024, 09:24:20 am
content: Quote from: Domarius on August 23, 2024, 02:18:21 amNo no no. That's certainly not the way to go.If you have nothing to loose, spend a couple of bucks on a chinese T12 soldering station, some flux, some isopropanol, some solder wick, some 60:40 solder. Those large caps don't require rocket science, might even get away without pre-heating. But adhesive or a butane iron is not the right tool. At all.

author: Herschel
author_rank: Regular Contributor
timestamp: August 23, 2024, 12:42:43 pm
content: I have some experience replacing usb ports and surface mount capacitors of a computer motherboard. And i have experienced the same problem as you faced here.This is because of a low power soldring iron. You at least need a 40 watt soldring iron (or a pretty powerful hot air station, if you have one), with a flat tip or point tip as you wish, and a 60/40 soldring leadAlso you should be using soldring flux for thatit takes at least 3seconds to heat up the area + liquify the solder lead, you want to solder."As a last ditch effort, I bought some conductive adhesive"I don't think conductive adhesive could last any long...I'm using these...

author: perieanuo
author_rank: Frequent Contributor
timestamp: August 23, 2024, 01:45:34 pm
content: ok, you don't have a big 120w soldering pencil. maybe you have 2 40-60w irons and a friend, works too. sometimes somebody can do stuff without 120w weller or 80w jbc pro stations.br

author: slavoy
author_rank: Regular Contributor
timestamp: August 23, 2024, 03:31:22 pm
content: Preheat the board.

author: Domarius
author_rank: Newbie
timestamp: August 26, 2024, 09:28:36 am
content: Thank you everyone. I will get a higher powered iron and try to find a board with a copper flood to practice on.

author: mikerj
author_rank: Super Contributor
timestamp: August 26, 2024, 10:38:09 am
content: Quote from: Domarius on August 23, 2024, 02:18:21 amThose one part conductive adhesives are mechanically very weak, they are primarily used for repair of traces that cannot be easily soldered such as the heating element on car rear screens, or on solar cells. Absolutely not suitable for mounting components on a conventional PCB.

author: Psi
author_rank: Super Contributor
timestamp: August 29, 2024, 07:41:27 am
content: Quote from: Domarius on August 26, 2024, 09:28:36 amWhen you reach a specific point no matter how hot your iron is you won't be able to solder things correctly without a preheating of some sort.I dunno if you're at that point yet.There are some cheats you can do, if you have a hot air rework station you can use that as a directional preheater and use it in combination with the soldering iron.