Soldering Capacitors and Grounding

[TheDailyToker]

Hi guys,

This is my first post on this forum, so forgive me if I have posted this incorrectly. I have searched the forums for this topic but did not find anything pertaining to my situation exactly.

I have a motherboard with a few blown capacitors that need to be replaced, and have decided to take on the task myself. This is my first soldering experience. I have a soldering station and all the necessary equipment, including a Panavise motherboard holder. I have been reading up on soldering and specifically cap replacement, but was still curious about the best way to protect the PCB from ESD. I have an ESD mat and strap, but wasn't if I should use one or the other, or a combination of the two.

I was hoping that you guys might have some suggestions on the best way to protect the board.

Thanks very much.

 

[memadmax]

Use both, won't hurt.

 

[Trenchcoat]

ESD is completely avoidable without a grounding strap or mat but you have both so use them. .... Relax.

 

[TheDailyToker]

You'll have to forgive me, I'm just a bit paranoid about destroying a board by being careless.

If I were to just use the strap, what would you guys recommend clipping to?

 

[Pinhedd]

Hi guys,

This is my first post on this forum, so forgive me if I have posted this incorrectly. I have searched the forums for this topic but did not find anything pertaining to my situation exactly.

I have a motherboard with a few blown capacitors that need to be replaced, and have decided to take on the task myself. This is my first soldering experience. I have a soldering station and all the necessary equipment, including a Panavise motherboard holder. I have been reading up on soldering and specifically cap replacement, but was still curious about the best way to protect the PCB from ESD. I have an ESD mat and strap, but wasn't if I should use one or the other, or a combination of the two.

I was hoping that you guys might have some suggestions on the best way to protect the board.

Thanks very much.

Use both, won't hurt.

No need to use an ESD mat or a wrist strap. Seriously. The biggest risk of damage will be from your soldering, not ESD. Using a wrist strap is likely to just get in your way and hinder you.

Here's some soldering tips (edit: pun not intended):

1. Before you even think about starting make sure that you are working in a well ventilated area. The flux used in solder is corrosive and toxic. You do not want to breathe it in any more than you half to.

2. Make sure that you're using the right kind of solder. The solder should have a low thermal EMF, such as Pb90Sn10, Sn95.5Ag3.9Cu0.6 (my favorite), or Sn99.3Cu0.7. Preferably, you want something lead free. The ones that I just listed are suitable for electronics. Other solders such as Pb60Sn40 are for other applications such as plumbing or automotive, not electronics. Whatever solder you use, having a flux core will make things easier.

3. If you've never soldered before, practice a bit. It's not nearly as easy as it looks.

4. If you have a fine point heat gun, use that in combination with a pair of pliers to desolder and remove the blown cap(s). If you use a soldering iron to extract the damaged part you may burn the PCB, which can ruin the pad that the capacitor connects to. Construct a foil shield around the joint to concentrate the heat from the heat gun and keep it away from nearby components. Don't yank on the capacitor, when the solder liquefies it will come out easily.

5. When you get around to soldering the new capacitor in, apply the solder to the opposite side of the wire from the iron itself after the joint has had an opportunity to heat up. Solder is attracted to metal, and it is really attracted to hot metal. Few things are hotter or more attractive than a soldering iron so if you don't do this properly you'll simply end up with a big wad of solder dripping from the end of the iron.

6. The final joint should be flat and shiny. If it's bulbous, the flux and heat didn't have enough time to do their job. Apply more heat until it melts and wiggle the iron around until it forms a nice joint. If it's dullish, the joint didn't form properly, apply the iron until it melts thoroughly and then remove it quickly.

 

[TheDailyToker]

Hi Pinhedd,

Thank you very much for these tips! I do have a junk board that I plan on practicing on first, as soldering makes me pretty nervous! I picked up some cheap caps to practice with as well. Sadly, I won't be able to tell if it was a success because the junk board was a victim of a surge. I inherited most of these tools and just the sheer amount of different items is a bit intimidating.

My plan was to work on a table next to a screen door with a fan blowing across the board out of the screen. Do you think this will be ventilated enough? Unfortunately, I'm in a small apartment and that was the best option I could come up with, short of sitting on the balcony.

I am unable to find the EMF rating on the solder I have, but I can tell you that it is Alpha Fry 60/40 Electrical Rosin Core Solder. Would this be okay to use, or should I hold off until I am able to pick up something better?

So I just shouldn't worry about ESD? I've never personally shocked anything, but I've always taken cautionary measures when handling PCB's and components. You certainly sound like you've done this a few times though, so I'll trust you.

 

[Pinhedd]

Hi Pinhedd,

Thank you very much for these tips! I do have a junk board that I plan on practicing on first, as soldering makes me pretty nervous! I picked up some cheap caps to practice with as well. Sadly, I won't be able to tell if it was a success because the junk board was a victim of a surge. I inherited most of these tools and just the sheer amount of different items is a bit intimidating.

My plan was to work on a table next to a screen door with a fan blowing across the board out of the screen. Do you think this will be ventilated enough? Unfortunately, I'm in a small apartment and that was the best option I could come up with, short of sitting on the balcony.

I am unable to find the EMF rating on the solder I have, but I can tell you that it is Alpha Fry 60/40 Electrical Rosin Core Solder. Would this be okay to use, or should I hold off until I am able to pick up something better?

So I just shouldn't worry about ESD? I've never personally shocked anything, but I've always taken cautionary measures when handling PCB's and components. You certainly sound like you've done this a few times though, so I'll trust you.

You shouldn't worry about ESD at all. Empirical tests have shown that in order to damage a board you'd have to shoot it with a 50,000 volt taser, or rub the board all over a cat. Even then, the damage will come from the pissed off cat rather than the ESD. I've tossed plenty of components resulting from various electrical or mechanical failures; I've never tossed one as a result of ESD.

As far as the solder goes, yours appears to be 60% lead 40% tin based on the Amazon listing. For electronics, Hobbyists normally use 60% tin and 40% lead, the other way around, or some other mixture. The lead is really used to lower the melting point, but can impact other electrical properties. Fortunately this is not a high power or high strength application so you can probably use your existing solder, but practice with it a bit first. It's imperative that you practice getting the joint right. A "ball" joint is a very common and very easy mistake to make; these can appear to be jointed, but will either be structurally weak, non conductive, or both. I recommend purchasing a solder sucker or some solder wick first to help correct any mistakes.

 

[TheDailyToker]

Wow, now I feel pretty foolish for taking so many precautions. At least I wasn't driving a copper stake into the earth.. although I was getting pretty close.

I will definitely get as much practice as I can before taking on the real deal. I guess I should be more worried about the 800 degree piece of metal pressed against the motherboard rather than ESD. I do have some solder wick, and have read a little about how to use it, but the entire process of soldering is still a bit of a mystery to me. I will have to order a solder sucker right now; I definitely want to do this right.

On a non-bootable board, (assuming that my joint looks good) should I test for resistance on the joint to see if it has been soldered correctly? Should I give the cap a little wiggle to test integrity?

Thank you very much for all of this information, this is extremely helpful.

 

[Pinhedd]

Wow, now I feel pretty foolish for taking so many precautions. At least I wasn't driving a copper stake into the earth.. although I was getting pretty close.

I will definitely get as much practice as I can before taking on the real deal. I guess I should be more worried about the 800 degree piece of metal pressed against the motherboard rather than ESD. I do have some solder wick, and have read a little about how to use it, but the entire process of soldering is still a bit of a mystery to me. I will have to order a solder sucker right now; I definitely want to do this right.

On a non-bootable board, (assuming that my joint looks good) should I test for resistance on the joint to see if it has been soldered correctly? Should I give the cap a little wiggle to test integrity?

Thank you very much for all of this information, this is extremely helpful.

You won't be able to test for resistance on a capacitor, but you can test for continuity. The traces themselves are covered in an insulating protective coating so it'll be nearly impossible to test from the trace itself. However, you can test continuity between the joints and across the capacitor if you wish. If it's a polarized capacitor be careful not to keep it in reverse bias too long as it will break down and explode from a prolonged reverse-bias continuity test if the meter isn't well designed. If the capacitor is polarized, make sure that you put it in the right way!

Giving it a wiggle is a good idea though. Give the cap a wiggle and look at the joints. If the joints move freely with the cap they're probably not very good joints.

 

[TheDailyToker]

Ah, I see. Forgive my ignorance. I had no idea! Perfect, I'll test for continuity and give them a wiggle. I want to make sure that I'm doing it correctly before working on a functioning board.

I won't be able to give this a try until the weekend, but I will post back when I undoubtedly run into issues.

One more question if you don't mind... I've heard about people recommending discharging capacitors before desoldering... I was under the impresssion that capacitors only held their charge for a matter of seconds. Have you ever had to do/done this? If so, how would you recommend doing this? I've seen people who have built their own discharge tools, and others that recommend just using a screwdriver.

 

[Pinhedd]

Ah, I see. Forgive my ignorance. I had no idea! Perfect, I'll test for continuity and give them a wiggle. I want to make sure that I'm doing it correctly before working on a functioning board.

I won't be able to give this a try until the weekend, but I will post back when I undoubtedly run into issues.

One more question if you don't mind... I've heard about people recommending discharging capacitors before desoldering... I was under the impresssion that capacitors only held their charge for a matter of seconds. Have you ever had to do/done this? If so, how would you recommend doing this? I've seen people who have built their own discharge tools, and others that recommend just using a screwdriver.

Capacitors that have been removed from a circuit will hold their charge for a very, very long time. Capacitors that are connected to a circuit but have a non-conductive path due to a semi-conductor placed between the two nodes will slowly discharge due to leakage current. Strictly speaking, any board that has been off and unplugged for more than a few seconds should be fully discharged. Even then, the total charge on the capacitors on a motherboard is pretty negligible.

 

[genz]

Wow, now I feel pretty foolish for taking so many precautions. At least I wasn't driving a copper stake into the earth.. although I was getting pretty close.

I will definitely get as much practice as I can before taking on the real deal. I guess I should be more worried about the 800 degree piece of metal pressed against the motherboard rather than ESD. I do have some solder wick, and have read a little about how to use it, but the entire process of soldering is still a bit of a mystery to me. I will have to order a solder sucker right now; I definitely want to do this right.

On a non-bootable board, (assuming that my joint looks good) should I test for resistance on the joint to see if it has been soldered correctly? Should I give the cap a little wiggle to test integrity?

Thank you very much for all of this information, this is extremely helpful.

I would interject that that may apply for the mobo (due to it's floating ground) but it does not apply for all the components that attach to the mobo, like your CPU (the underside of which is quite sensitive). Also your car can quite easily transfer 50k volts of ES to you jut by touching it on a hot day. All ES charge is very high voltage very low amperage as a matter of fact.

As for what to ground yourself on, if you are in a cooler country, you likely have metal radiators. They are great, as the pipework goes all the way into the ground. Clip the band onto the metal directly, its useless on paint.

If not, you can use just about any raw metal source over a square foot in size. It's not really the size, it's more important that they are more conductive than your skin and therefore will carry away charge.

 

[TheDailyToker]

Ah I see. I've always been warned of the dangers of ESD, but was unaware that the board and traces were covered with a protective layer. The area that I live in is pretty hot, so my journey of finding the perfect grounding source seems to be never-ending. Working on PCs is not an issue, as I can clip to the case, but I am always a little nervous when working with laptop boards and components.

I've seen quite a few people suggesting plugging the cable from the mat into the ground in a three prong outlet, and others telling me that I would be electrocuted to death if I did. I've just been clipping to an old PC cage when working with laptop components, but this isn't very convenient. I just have not found a good way to use the mat and strap when working with laptops - would you have any suggestions?