Repairing circuit boards

Thread Starter

Travm

Joined Aug 16, 2016
356
I repaired a small board today, and it was terrible.
I used too much flux and it was a mess to clean.
I damaged/ripped off two pads, there were 10 in total.
I've tested it with a multi meter and it looks like the pins have good continuity, but the two damaged ones don't look like they should work, it's bad.
Could the reason i suck at this be due to a cheap iron? It was 2 3.5mm audio Jack's.

How did I screw this up? I've noticed with my iron sometimes I have to turn up the temperature for no apparent reason, it just quits melting solder, then I don't turn it back down so I'm likely always running hot.
 

Papabravo

Joined Feb 24, 2006
17,230
These are not skills that are acquired cheaply or easily. The best PCB technicians I have ever seen, besides all the ones I haven't, learned from bitter experience over a long period of time. You are on the right track.
 

dl324

Joined Mar 30, 2015
13,490
How did I screw this up? I've noticed with my iron sometimes I have to turn up the temperature for no apparent reason, it just quits melting solder, then I don't turn it back down so I'm likely always running hot.
It would be helpful if you posted pictures and gave information regarding your soldering iron. What wattage, temperature, tip size/shape? What type of solder? Leaded or no lead?

Most of us practiced on junk boards to perfect our technique before working on something important. In my case, I was trained at an HP manufacturing facility because my first job was troubleshooting refrigerator size computers using TTL to the component level.
 

absf

Joined Dec 29, 2010
1,962
Is the PCB single sided or double sided?

To unsolder parts like audio sockets or USB sockets, certain points that are connected to ground plan is tough to unsolder if the iron is not hot enough.
 

AlbertHall

Joined Jun 4, 2014
11,587
Temperature controlled iron; solder braid; practice; practice; practice.
If you are doing this as a hobby use lead solder. It is easier to use than lead-free.
 

Thread Starter

Travm

Joined Aug 16, 2016
356
IMG_20180719_170741894 1.jpg IMG_20180719_170517206.jpg IMG_20180719_170401023.jpg

So my iron cost about $50 on amazon, Stanz 48w adjustable. It doesnt seem to hold a consistent temperature, but it works (i think?).
The board is from a computer case, totally replaceable for under $20, but I thought i'd have a go at fixing it rather than scrapping the little thing.
I think it will work, but omg i'm not happy with the workmanship. Granted its the first time ive ever used solder braid, about the 5th time ive used my iron, but I feel like I suck at it.
I'm really wondering more than anything what % of this garbage is because my equipment is super cheap? Its not like I'm going to go and buy a new (or used) weller station because I'll so rarely use it and it will never make me any money, but if its a skill gap thing primarily at least i'd know I should expect to get better at it. If its mostly because my equipment is crap, and this is the best it will ever be, then thats fine too, i'll know enough not to work on anything worth more than $50.

Sorry for the huge images, my computer (linux powered chromebook) is starved for software I know how to use, and I took the poor pictures wiht my phone.

The lowest pin in the picture showing pins has no pad, and the 4th from the top also has no pad. Coincidentally(or not) this is the last pin on each component I desoldered. Possibly that was part of my problem?
 

Thread Starter

Travm

Joined Aug 16, 2016
356
Get some broken board and practice removing and replacing parts on it. Practice is the key.
So its reasonable to expect I should be able to do better than this with practice? I"m not even sure what went wrong, I didnt notice the missing pads until after I started melting the flux and resoldering the new parts.
 

dl324

Joined Mar 30, 2015
13,490
So my iron cost about $50 on amazon, Stanz 48w adjustable. It doesnt seem to hold a consistent temperature, but it works (i think?).
If it can't hold a consistent temperature, it's not working or it's underpowered for the job. What kind of tip does the iron have? Tip size and shape can be important.
Granted its the first time ive ever used solder braid, about the 5th time ive used my iron, but I feel like I suck at it.
You'll probably have more luck if you use a solder sucker to remove most of the solder, then use braid, if necessary, on what's left.
The lowest pin in the picture showing pins has no pad, and the 4th from the top also has no pad.
Don't know what you're referring to. I see 6 holes with no pads.
upload_2018-7-19_15-14-7.png
All of the joints on the right half of the board have too much solder. What diameter solder wire are you using?
 

AlbertHall

Joined Jun 4, 2014
11,587
So its reasonable to expect I should be able to do better than this with practice? I"m not even sure what went wrong, I didnt notice the missing pads until after I started melting the flux and resoldering the new parts.
Absolutely. It is a skill. To avoid damaging pads you need to be quick and gentle. I started using a solder sucker but they do have a tendency to damage pads due to the jerk when you trigger them. Braid is kinder but clearly it is consumable so will end up being more expensive than a sucker but it's not going to break the bank.
 

Thread Starter

Travm

Joined Aug 16, 2016
356
If it can't hold a consistent temperature, it's not working or it's underpowered for the job. What kind of tip does the iron have? Tip size and shape can be important.
You'll probably have more luck if you use a solder sucker to remove most of the solder, then use braid, if necessary, on what's left.
Don't know what you're referring to. I see 6 holes with no pads.

All of the joints on the right half of the board have too much solder. What diameter solder wire are you using?
I only did the right side of the board. I likely put too much solder on, basically I kept adding until it appeared to flow over the pad. The two ground pins on the far right soldered far easier than everything else (possibly because i didnt damage the larger pads).

As for tip size, iron came with 3 tips, I would say its about 1/16" dia at the tip, and conical increasing to about 1/4" @ 3/4" from the tip (from memory).

Is there really 6 pins with no pads? The picture isnt great.
 

dl324

Joined Mar 30, 2015
13,490
Is there really 6 pins with no pads?
I said 6 holes with no pads; marked in red below:
upload_2018-7-19_22-6-38.png

For solder, more isn't necessarily better. You should have emulated the joints to the left.

The way your joints are, we can't tell if they're good.

You should have heated the pad and lead and applied solder away from where the iron was contacting pad and lead. I would have applied the tip to the pad opposite of where the trace leaves. Applying solder to the pad near the trace and let the solder wick up the lead.
 

ebp

Joined Feb 8, 2018
2,332
The holes with no pads are alignment holes. Plastic parts that need to align accurately often have little plastic "pins" molded in for just this purpose. The alignment pins can be accurately positioned in the molding process but the electrical pins are often less consistent in position relative to the body of the part. The holes for the plastic pins can be made with very little clearance, but the holes for the metal pins need to have more generous clearance to avoid making it difficult to insert the part. Tradeoffs - always tradeoffs.

Desoldering braid makes a mess. I use it on rare occasions and I really don't like it, but I have power vacuum desoldering equipment, which is nice but rather expensive. If you use desoldering braid, I recommend cleaning the board after removing the part and before soldering in the new one. Cotton-tipped swabs with 99% isopropyl alcohol works moderately well. I sometimes resort to "lacquer thinner" (the type I use is mostly toluene) which is more aggressive against the base constituents of the flux but poor for the "activators." I also sometimes use acetone. All of these are highly flammable and acetone and lacquer thinner attack many plastics, so great care is needed. There are non-flammable commercial flux removers that are definitely safer. If the mess from the solder braid is cleaned up, usually there is no need to clean after soldering in the new part.

Braid usually works best if you have a nice, cleanly-cut end that can be gently pushed down into intimate contact with the pad and the pin with the iron tip. After doing one joint, clip the braid so that there is just a tiny length that still has a little solder in it using sharp cutters. This keeps the strands together. It can be difficult to get good heat transfer through the braid to the joint. Becoming proficient with braid really does take a good deal of practice. You need a range of widths for different sizes of joints.

Key to much soldering is getting adequate heat without excessive temperature. A good temperature controlled iron is helpful. Matching the tip size to the work is important. With many temperature controlled irons, the control mechanism regulates the temperature well away from the actual working part of the tip. A large tip will be more uniform in temperature just because there is more thermally-conductive copper. Large tips also are better heat reservoirs so they don't cool as quickly when applied to something. It is a tradeoff - if the tip is too small you can't get heat into the joint effectively and if it is too big you can't get the tip where it needs to be. Selecting the right tip size is also something that comes with practice and observing what is happening and thinking about what you are doing.

Your joints may have a bit of excessive solder, but not a gross amount. Usually what you want to end up with is a "cone" with slightly concave sides. If they are a little convex, you have a little more solder than necessary, but the reality is that it does no harm whatsoever. If you end up with something approaching a ball, you definitely have too much solder, and/or the joint was not adequately heated which is a a problem. With lots of experience you will get to the point where you can make joints very quickly with just the right amount of solder. Hand-soldering boards that are double-sided or multi-layer can be quite difficult because the top or inner layers of copper suck heat from the joint, making it difficult to get the desired filing of the "barrel" of the hole with solder. You often get one part where some of the pins have a lot of copper on the top side or inner layers and others don't, so you have to watch carefully how each joint takes solder as you go.

As others have said, practice Observe carefully and think about what you are seeing as you go. Too many people never get much beyond what they have been taught because they omit the observation and thinking. A good teacher is unquestionably a great help and will pass along all sorts of little details. If you don't have a great teacher, you will advance only if you think critically about what you are doing and constantly strive to become better. I often say it takes me three tries to get some newish process reasonably close to what I want. The first try is more-or-less experimental. The second try advances on what was learned in the first try. By the third try, I'm usually getting things pretty close to the way I want them. But that is for things where I may already have lots of related experience. Something really new might take another round or two.
 

Thread Starter

Travm

Joined Aug 16, 2016
356
The holes with no pads are alignment holes. Plastic parts that need to align accurately often have little plastic "pins" molded in for just this purpose. The alignment pins can be accurately positioned in the molding process but the electrical pins are often less consistent in position relative to the body of the part. The holes for the plastic pins can be made with very little clearance, but the holes for the metal pins need to have more generous clearance to avoid making it difficult to insert the part. Tradeoffs - always tradeoffs.

Desoldering braid makes a mess. I use it on rare occasions and I really don't like it, but I have power vacuum desoldering equipment, which is nice but rather expensive. If you use desoldering braid, I recommend cleaning the board after removing the part and before soldering in the new one. Cotton-tipped swabs with 99% isopropyl alcohol works moderately well. I sometimes resort to "lacquer thinner" (the type I use is mostly toluene) which is more aggressive against the base constituents of the flux but poor for the "activators." I also sometimes use acetone. All of these are highly flammable and acetone and lacquer thinner attack many plastics, so great care is needed. There are non-flammable commercial flux removers that are definitely safer. If the mess from the solder braid is cleaned up, usually there is no need to clean after soldering in the new part.

Braid usually works best if you have a nice, cleanly-cut end that can be gently pushed down into intimate contact with the pad and the pin with the iron tip. After doing one joint, clip the braid so that there is just a tiny length that still has a little solder in it using sharp cutters. This keeps the strands together. It can be difficult to get good heat transfer through the braid to the joint. Becoming proficient with braid really does take a good deal of practice. You need a range of widths for different sizes of joints.

Key to much soldering is getting adequate heat without excessive temperature. A good temperature controlled iron is helpful. Matching the tip size to the work is important. With many temperature controlled irons, the control mechanism regulates the temperature well away from the actual working part of the tip. A large tip will be more uniform in temperature just because there is more thermally-conductive copper. Large tips also are better heat reservoirs so they don't cool as quickly when applied to something. It is a tradeoff - if the tip is too small you can't get heat into the joint effectively and if it is too big you can't get the tip where it needs to be. Selecting the right tip size is also something that comes with practice and observing what is happening and thinking about what you are doing.

Your joints may have a bit of excessive solder, but not a gross amount. Usually what you want to end up with is a "cone" with slightly concave sides. If they are a little convex, you have a little more solder than necessary, but the reality is that it does no harm whatsoever. If you end up with something approaching a ball, you definitely have too much solder, and/or the joint was not adequately heated which is a a problem. With lots of experience you will get to the point where you can make joints very quickly with just the right amount of solder. Hand-soldering boards that are double-sided or multi-layer can be quite difficult because the top or inner layers of copper suck heat from the joint, making it difficult to get the desired filing of the "barrel" of the hole with solder. You often get one part where some of the pins have a lot of copper on the top side or inner layers and others don't, so you have to watch carefully how each joint takes solder as you go.

As others have said, practice Observe carefully and think about what you are seeing as you go. Too many people never get much beyond what they have been taught because they omit the observation and thinking. A good teacher is unquestionably a great help and will pass along all sorts of little details. If you don't have a great teacher, you will advance only if you think critically about what you are doing and constantly strive to become better. I often say it takes me three tries to get some newish process reasonably close to what I want. The first try is more-or-less experimental. The second try advances on what was learned in the first try. By the third try, I'm usually getting things pretty close to the way I want them. But that is for things where I may already have lots of related experience. Something really new might take another round or two.
This is a fantastic post, thank you sir.
Cleaning after the braid is a good tip that might have taken me a couple more failures to figure out. Cheers
 
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