PCBs (printed circuit boards) are used to mechanically support and electronically connect electronic components. They consist of copper traces laminated onto a non-conductive substrate. Pads are the copper areas on the PCB that electronic components are soldered to. Pads can become damaged due to manufacturing defects, component removal, or long-term use. When a pad is damaged, it can prevent components from being soldered properly to the PCB. This article will cover multiple methods for repairing damaged PCB pads.
Identifying Pad Damage
Carefully inspect the pad to determine the type and extent of damage. Common pad damage includes:
- Missing copper – All or part of the copper pad is missing. This often occurs when components are improperly removed.
- Cracks/breakage – The pad copper has cracked or broken off from the board. This is usually caused by mechanical stress or impact.
- Corrosion – The copper pad has corroded, often causing high resistance or intermittent connections.
- Holes/voids – There are holes, voids, or missing copper within the pad area. This is typically a manufacturing defect.
- Lifting – The pad is detaching or lifting up from the PCB substrate. This happens due to weakness in the copper-substrate bond.
- Scratches – Deep scratches in the copper pad that may cause high resistance or open circuits.
Before attempting pad repairs, prepare the work area properly:
- Use a microscope or magnifying glass to get a close view of the damaged pad.
- Clean the area around the pad thoroughly with isopropyl alcohol to remove any grease, grime or solder flux.
- Remove any lingering solder on or around the pad using desoldering braid. The pad should be as clean as possible.
- Carefully scrape away any conformal coating from the pad area using a plastic pick. Coating residue interferes with repair procedures.
Wear safety glasses and gloves to protect yourself from debris while scraping and cleaning the PCB. Work in a well-ventilated area.
Pad Repair Methods
There are various methods available for repairing damaged PCB pads. Select the best option based on the type and extent of damage involved:
When to use: Minor damage, scratches, voids in pad.
This simple technique involves using additional solder to fill in holes, voids or missing sections in the copper pad.
- Apply a small amount of solder slowly to the pad area using a soldering iron.
- Allow the solder to flow onto the missing sections.
- Visually inspect the area and reapply solder until the pad is built back up.
- Take care not to create solder bridges to other areas.
When to use: Missing sections or large portions of the pad copper.
Use adhesive copper foil to replace any missing copper on the pad area.
- Cut a piece of adhesive copper foil slightly larger than the damaged section.
- Carefully align and place the foil over the pad area.
- Use a soldering iron with minimal solder to attach the foil to the remaining copper pad.
- Trim any overhanging edges of the foil.
Wire Soldered to Pad
When to use: Severely damaged or completely missing pad.
- Strip and tin the ends of a small gauge insulated wire.
- Solder one end of the wire to the component lead, pin or hole where the pad is missing.
- Use an ohmmeter to test connectivity between the soldered wire end and the original pad on the PCB.
- Protect the wire from shorting to other areas.
When to use: Missing pad section or complete pad rebuild.
Use copper foil tape to recreate missing pad sections or rebuild the entire pad.
- Cut copper tape to size to cover the pad area. Remove any adhesive backing.
- Align the tape over the pad area and carefully solder it into place.
- Use multiple layers if needed to match the pad height/thickness.
- Solder component leads directly to the new copper pad area.
When to use: Damaged pads on flex PCBs or high density boards.
2-part conductive epoxy can rebuild missing pad sections on delicate boards when soldering is not practical.
- Thoroughly clean and abrade the pad area to improve epoxy adhesion.
- Apply conductive epoxy over the missing copper area using a toothpick.
- Allow the epoxy to fully cure as per manufacturer instructions.
- Solder component leads carefully to the cured epoxy area.
Testing Repaired Pads
Always test pad repairs before putting the PCB back into service.
- Visually inspect for proper alignment, clearance from other pads, and look for any shorts or foreign material.
- Use a multimeter to check electrical continuity between the repaired pad and surrounding copper traces.
- If possible, solder a test component or wire onto the repaired pad, applying heat for approximately 5 seconds. The solder joint should form smoothly and cleanly.
- Check pad repairs at 5x magnification to ensure successful wetting and flow between the solder and pad.
- Functionally test repaired boards for proper operation once populated with components.
Preventing Future Pad Damage
To avoid pad damage on future boards:
- Use an appropriate soldering iron tip size and temperature for the pad size and location.
- Apply the minimum soldering time and heat needed to avoid trace or pad lifting.
- Allow adequate cooling time before removing soldered components. Never pry up on heated components.
- Handle boards carefully by the edges and avoid mechanical shocks or flexing.
- Use foam supports underneath boards during assembly and servicing.
- Apply organic or urethane conformal coating to protect pads and traces from corrosion or abrasion damage.
Frequently Asked Questions
What is the easiest PCB pad repair method?
The solder build-up method is generally the easiest pad repair for small amounts of damage. Just reflowing a small amount of solder over scratches or voids in the pad can often successfully restore connectivity.
Can I use copper tape on multilayer PCBs?
You should avoid using copper tape for pad repairs on multilayer boards. The thickness of the tape can create an uneven surface and cause issues with subsequent PCB layers. Use wire or conductive epoxy repairs instead.
Is conductive epoxy stronger than soldering?
Properly cured conductive epoxy can provide very strong and durable repairs that are resistant to shock/vibration. However, soldering forms superior electrical connections between components and PCBs in most cases.
How do I prevent damaging pads when removing components?
Heat component solder joints thoroughly before attempting removal. Use a solder sucker or wick to clear solderfirst. Gently rock or twist the component to loosen the solder joints rather than pulling or prying.
Should I scrape the solder mask off around a damaged pad?
Scraping the solder mask is not necessary for most pad repairs. Removing the mask increases chances of shorts and contamination around the pad. Leave the mask intact unless you are rebuilding the entire pad area.