First, let us understand the common types of PCB short circuits.
By functional cause, short circuits can be classified as:
Soldering shorts (e.g., solder bridging)
PCB shorts (e.g., residual copper, hole misalignment)
Component shorts
Assembly shorts
ESD/EOS breakdown
Inner‑layer micro‑shorts
Electrochemical shorts (e.g., chemical residues, electromigration)
Shorts caused by other reasons
By routing characteristic, short circuits can be classified as:
Trace‑to‑trace shorts
Trace‑to‑plane (layer) shorts
Plane‑to‑plane (layer‑to‑layer) shorts
Method 1: Use PCB Design Software
Open the PCB design files on a PC and highlight the shorted net. Observe which locations are closest to each other and most likely to be bridged. Pay special attention to shorts inside ICs.
Method 2: Develop Good Habits for Manual Soldering
Visually inspect the PCB before soldering, and use a multimeter to check critical circuits (especially power and ground) for shorts.
After soldering each IC, use a multimeter to check for shorts between power and ground.
Do not flick solder off the soldering iron randomly – if solder splashes onto IC pins (especially on SMD components), it becomes very difficult to locate.
Method 3: Trace Cutting
If a short is found, take a board and cut traces (this is especially suitable for single‑layer or double‑layer boards). After cutting, power up each functional block separately and eliminate possibilities step by step.
Method 4: Use a Short‑Circuit Locator (Fault Locator)
For certain specific situations, using specialised short‑circuit locating instruments can significantly improve both detection efficiency and accuracy.
Method 5: Handle BGA Chips Carefully
Since BGA solder joints are hidden under the chip and invisible, and the board is often multi‑layer (4+ layers), it is best to split the power supply to each IC during design – using ferrite beads or 0 Ω resistors as links. In this way, if a power‑to‑ground short occurs, you can disconnect the beads and quickly isolate the faulty IC. Because BGA soldering is difficult, unless done by automated machines, it is easy to accidentally bridge adjacent power and ground balls during manual soldering.
Method 6: Pay Special Attention to Small SMD Capacitors
When soldering small SMD capacitors, especially power‑supply decoupling capacitors (e.g., 103 or 104), be extra careful. They are numerous and can easily create power‑to‑ground shorts. Sometimes, bad luck may even give you a capacitor that is itself shorted – so the best practice is to test each capacitor with a multimeter before soldering.
Additional Practical Tips for Troubleshooting
In circuit board repair, a short circuit on a common power rail can be daunting, because many devices share the same power supply – and any of them could be the culprit. If there are not many components on the board, a "brute‑force" method (cutting traces or lifting pins one by one) will eventually find the short. However, if there are many components, you may need to be a bit more strategic.
For through‑hole components, you can use diagonal cutters to snip one lead (remember to cut in the middle, not flush with the board or the component body). For through‑hole ICs, you can cut the VCC pin. If the short disappears after cutting a particular pin, that component is the likely cause. For SMD ICs, use a soldering iron to melt the solder on the power pin and lift it off the pad, isolating it from the VCC rail. After replacing the faulty component, simply resolder the cut or lifted connection.
A Faster Method Using a Milliohmmeter
There is another faster method, but it requires a specialised instrument: a milliohmmeter.
We know that copper traces on a PCB have resistance. For example, if the copper thickness is 35 µm and the trace width is 1 mm, the resistance of a 10 mm length is about 5 mΩ. Such low resistance cannot be measured with an ordinary multimeter, but a milliohmmeter can.
Suppose a component is shorted. An ordinary multimeter would read 0 Ω, but a milliohmmeter would read somewhere between tens of milliohms and a few hundred milliohms. When you place the probes directly across the two pins of the shorted component, the reading will be the lowest – because if you measure across other components, the reading also includes the resistance of the copper traces connecting them. By comparing milliohm readings, the component (or solder bridge, or copper residue) that gives the lowest resistance is the prime suspect. This method allows you to quickly pinpoint the fault.
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