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Circuit boards degrade over time. Whether by a factory defect or physical wear and tear, sometimes a solder joint will give out and stop the assembly from functioning.

However, there may yet be hope. If you have a soldering iron and a couple of other materials handy, you might be in a position to rescue the board from its destination at the scrap heap.

To help set you up for success, we’ll explain five easily-repairable solder joint issues, how to find them, what supplies you’ll need, and what to do to get the job done in quality fashion.

We’ll also go over 5 solder joint situations that you’ll want to steer clear of. These should only be repaired by someone with the proper tools and experience in the circuit board field.

 

 

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What It Is:
When a solder joint does not contain the industry-required solder amount, it is classified as “insufficient”. The PCB may function properly early on, but the brittle nature of this defect could trigger an intermittent or permanent failure at any point.

How to Spot:
On through-hole components, these joints usually appear as either completely lacking solder or are only partially filled with it. On surface mount components, any solder that is present may appear as a strand that is thinner than the lead it connects, or the metal pad below the solder may be visible.

What You’ll Need:

  • Soldering Iron
  • Solder Wire
  • Cleaning Agent (Recommended)

How to Fix:
An insufficient solder joint can be repaired by using the soldering iron to add small amounts of solder wire. Continue until the gap between the component lead and the PCB’s connection point is adequately filled in.

(Pro tip: If you can decipher whether tin-lead or lead-free solder was originally used on the assembly, we suggest using that same solder type to form the strongest possible connection.)

Solder wire is infused with flux that will either be water-soluble or “no-clean”. Water-soluble residue should be removed right away with water and a brush. No-clean residue can safely be left on, or if desired can be removed with alcohol or specified PCB-cleaning agents.

 

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What It Is:
a cold solder joint is a poor connection that, for various possible reasons, failed to bond properly upon cooling. This flaw often results in intermittent faults across the assembly.

How to Spot:
Cold solder joints are often challenging to find. A common visual cue on through-hole joints is solder that “sinks down” around the component’s lead, lacking a discernible solid connection. The solder may also exhibit an unusual shape such as lopsidedness or “icicle” formations.

On surface-mount joints, cold solder joints may be even less visually obvious, though they may appear rough, grainy, or even oddly-shaped as with through-hole joints.

What You’ll Need:

  • Soldering Iron
  • Flux
  • Cleaning Agent

How to Fix:
These joints can usually be refreshed. Add flux to the joint in question and reheat with the soldering iron until the joint reshapes itself into a proper solder fillet. Don’t heat for too long or you may reintroduce the defect!

Once finished, be sure to remove all remaining flux using the appropriate solvent: water for “water-soluble” and alcohol or a PCB-cleaning agent for “no-clean”. (When applied directly to the board, both flux types remain active after soldering iron use and thus could cause damage over time.)

 

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What It Is:
Excess solder that unintentionally links two or more connections together is called a “bridge”. This defect is very likely to cause erratic functionality and physical damage to the assembly.

How to Spot:
Solder bridges usually stand out as a blob between solder joints, but even a microscopic strand of solder is enough to cause a short.

What You’ll Need:

  • Soldering Iron
  • Solder Wick
  • Flux
  • Cleaning Agent

How to Fix:
First, add flux to both the bridge and a small area of the solder wick. Then, place the flux-infused area of the wick over the unwanted solder and heat both with the soldering iron. The wick will begin to absorb the solder. Repeat the process until the desired amount of solder has been removed.

Be careful! Keep the wick hot until it has been moved away from the solder joint, or it will freeze to the board and could tear off vital circuitry.

If you accidentally remove too much solder, use solder wire to fill the joint back in.

When you are finished, clean the flux off of the board using water for “water-soluble” or alcohol / PCB-specific cleaner for “no-clean”.

 

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What It Is:
Wires are often attached to circuit boards directly using either through-hole- or surface-mount-based solder connections. These connections may fail for a variety of reasons, from poor solder bonding to mechanical stress.

How to Spot:
The usual sign of this defect is that the wire has mostly or fully disconnected from the solder joint. If a cold or insufficient solder joint is to blame, the individual strands of the wire may look dull, dry, even separated.

What You’ll Need:

  • Soldering Iron
  • Solder Wire (recommended)
  • Flux
  • Cleaning Agent

How to Fix:
Hold the exposed wire against the surface mount pad or in the through-hole. Carefully add solder to the connection until a strong solder joint has been created. The wire should also fill with solder near the joint, making the strands less apparent (though they do not need to be fully hidden.)

If there is already sufficient solder at the joint, simply apply flux to it, then use the soldering iron to bond the wire back into the solder.

Careful! Don’t linger once the solder has melted. Too much heat can melt the insulation around the wire.

As with other repairs, be sure to clean off any flux that has been added to avoid solder deterioration.

 

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What It Is:
During the surface mount reflow phase of assembly, the solder may fail to flow onto both sides of a surface-mount chip. This defect leaves one side of the chip suspended above the solder pad rather than connected to it.

How to Spot:
The more obvious instance of this defect (known as a “tombstone”) is a chip component that has been pulled upright on its end. As this issue causes a guaranteed connection problem, it is rare that one would make it past the manufacturer’s testing phase.

The less visible version of this situation is known as a “head-in-pillow” defect. Instead of standing straight up, the chip will merely rest on top of one solder joint instead of connecting to it. This can cause intermittent electrical issues that are more likely to slip through the testing process.

What You’ll Need:

  • Soldering Iron
  • Tweezers
  • Flux
  • Cleaning agent

How to Fix:
If you are repairing a tombstone defect, you must essentially turn it into a “head-in-pillow” defect first. Using tweezers, carefully remove the component from the attached pad by heating up the solder joint with your iron.

Then, lay the component down against both pads. Add flux and heat up the first side to connect it to the board.

Now that the chip is in the “head-in-pillow” stage, the rest is simple. Add flux to the disconnected pad, melt the joint with the soldering iron to connect it to the chip, and you’re done!

As always, be sure to clean up any remaining flux for both safety and functionality purposes.

 

 

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What It Is:
The size of the soldering iron tip is incredibly important when doing any solder work. You may be tempted to dive right in with what you have available, but using the incorrect tip size may have damaging side effects.

How to Spot:
Your soldering tip should be nearly the same width as the metal land around the lead. If this is not the case, the tip is likely the wrong size.

Why a Soldering Iron Won’t Work:
A soldering tip that is too small will struggle to transfer heat into the solder joint fast enough. By the time the solder finally melts, any flux that has been added may be exhausted. What you end up with may be a cold solder joint.

A tip that is wider than the land runs the opposite risk of transferring heat too fast, risking damage to the component. Furthermore, it will overstep the land and can cause permanent damage to the surrounding area.

 

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What It Is:
When a lead of a component is disconnected from an otherwise well-soldered joint, it is considered a “lifted lead”. This defect is more common among components with rows of fragile leads.

How to Spot:
A lifted lead usually shows up as an out-of-place twisted or raised lead in an otherwise consistent row. The solder pad beneath it may look different from others as well.

Why a Soldering Iron Won’t Work:
While specific soldering tips may reconnect the lead to the solder joint, bending in any direction may have caused microscopic fractures to the lead, resulting in weakened (and in serious cases destroyed) connectivity. It’s best to have a qualified technician handle the rework with proper tools and, if possible, replace the component.

 

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What It Is:
Surface mount components are becoming smaller and smaller as technology progresses. Many ICs, QFPs and other common components today have leads that are incredibly small extremely close together.

Such leads are too close together for a soldering iron to successfully contact one solder joint at a time.

How to Spot:
Defects on fine-pitch components may require a microscope to find. Lifted leads, insufficient solders and solder bridges are all common defects due to the leads’ size and proximity to one another.

Why a Soldering Iron Won’t Work:
Fine-pitch components require specialized equipment to properly repair, such as hot air reflow tools and soldering tips with specialized designs. Using a normal soldering iron will likely cause more damage than good, even under the best of circumstances.

 

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What It Is:
Components may “skew” during production, leaving the leads disconnected or even connected to the wrong solder joint altogether.

How to Spot:
Leads on skewed surface mount components often sit in-between solder pads and may connect to nothing or form a bridge between two pads. In extreme cases, the component may shift far enough to form solid solder joints on the wrong leads, leaving one or more leads out in the open.

Why a Soldering Iron Won’t Work:
To correct a skewed component and create the proper solder joints, the component must first be fully removed. To do so, all solder joints on the component must be heated simultaneously.

A soldering iron cannot safely heat more than one solder joint at a time. Special rework tools must be used to detach and rotate the component.

 

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What It Is:
Certain leads of a component may be attached to what is known as a “copper plane”. These vast sections of metal can absorb major amounts of heat compared to other areas of the PCB.

How to Spot:
Copper planes usually show up in the same shade as the board’s traces, but appear as large, solid areas rather than small pathways.

Components are often connected directly to planes. If you are unable to melt a solder joint after a few seconds, it may be that the heat is dispersing into a copper plane too quickly.

Why a Soldering Iron Won’t Work:
The circuit board is likely absorbing heat faster than the soldering iron can deliver. As the iron is losing heat constantly, increasing the iron’s temperature will have little effect. Keeping the iron to the solder joint for an extended time frame risks damaging the component.

Rework on this type of solder joint usually requires preheating tools to keep the board’s temperature up.

 

 

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Faulty circuitry can’t always be avoided, but it can often be rescued. By knowing which solder joints your trusty soldering iron can handle, you may just be able to save the board right away. And, knowing when to send the struggle to the professionals may just save you the entire board altogether.

Have you ever met a solder joint your soldering iron couldn’t handle? Or perhaps you’ve found a successful trick we didn’t mention? Help us aid the circuit board medics out there by sounding off in the comments below!

Chris Meyer has been on the electronics manufacturing scene for over 15 years and has discovered plenty of ways to both fix and fry a component. He writes to help people past the learning curve and start improving their PCB quality right away.
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