How to Repair Printed Circuit Boards

Printed circuit boards are the core control components of electronic devices, and they are usually quite expensive. Therefore, when a fault occurs, the first thing we think about is how to repair it. PCB repair is an effective way to control costs and maximize economic benefits. This article will detail the causes of PCB problems and the steps to repair them.

What Are the Causes of PCB Failures?

The main causes of PCB failures include manufacturing defects, environmental factors, non-specific design issues, and improper handling during the operation process.

Manufacturing Defects: This is one of the common reasons for PCB damage. It may include poor substrate, incomplete inner layer development, incomplete inner layer etching, inner layer scratches, blowholes, incomplete film removal, and other issues. These problems may arise from scratches during transportation, mechanical impact, improper chemical infiltration, low resin content in adhesive sheets, too rapid temperature and pressure rise during lamination, high chlorine ion concentration, low pH value, insufficient etching pressure, too fast etching rate, and improper board placement during browning.
Environmental Factors: These include heat, dust, moisture, and physical vibration. These factors can affect the performance and lifespan of the PCB. For example, high temperatures may cause solder joints, substrate materials, or even the casing to crack; dust and moisture may lead to short circuits or circuit damage; physical vibrations may cause mechanical performance issues.
Non-Specific Design Issues: This includes improper pad design, unsuitable component orientation design, and issues like automatic plug-in bending feet, which can lead to short circuit failures. Additionally, oversized substrate holes, low solder bath temperatures, poor board solderability, solder mask failure, and board surface contamination are also common causes of failures.
Improper Handling During Operation: This includes unfavorable environmental conditions, incorrect operational steps, or improper maintenance measures, all of which can lead to PCB failures. For example, adverse environmental conditions may damage the PCB, while incorrect operational steps may result in too brittle solder joint structures or excessively high temperatures, affecting the PCB’s performance and lifespan.

How to Ensure PCB Safety During Repair

Industrial circuit boards are expensive, and while we cannot guarantee a 100% success rate in repairs due to various objective reasons, we must ensure that we do not make the board worse. To ensure the safety of the circuit board, please implement the following measures:

Implement Anti-Static Measures

Static electricity can invisibly damage components. If the relative humidity is above 50%, static electricity is not very noticeable in daily life. However, if the relative humidity is below 40%, the frequency of feeling static discharge increases significantly. Therefore, it is crucial to take anti-static measures: use anti-static mats on the workbench, wear anti-static clothing and gloves, and store the circuit board in anti-static bags during transfer.

Avoid Damaging the Circuit Board During Desoldering

Pay attention to temperature and technique when soldering or desoldering components. The temperature should neither be too high nor too low; do not forcefully pull the leads when removing components; avoid blowing hot air at one small spot continuously when heating components; and mark the orientation of polarized components such as capacitors and diodes to prevent mistakes when resoldering.

Avoid Damaging the Circuit Board During Power-On Testing

Before powering on the circuit board, confirm the voltage and set an appropriate current. Use an adjustable power supply as shown in the following steps:

Adjust the voltage to the appropriate level required by the circuit board and set the current knob to a low level.
Clip the power supply wires to the positive and negative terminals of the circuit board, ensuring the correct polarity.
Plug the power supply into the adjustable power supply socket, again ensuring the correct polarity.

If the current protection activates, adjust the current slightly higher. Never set the current knob to the maximum at the start, reverse the power supply connections, or apply the wrong voltage (e.g., applying 24V to a 5V circuit board), as these errors can cause irreversible damage to the board.

Prevent Loss of Program Data on the Circuit Board

Some circuit boards have batteries that supply voltage to RAM chips. If the battery loses power, the data in the RAM will be lost. Certain machines rely on this data for operation, and if there is no backup and no way to manually restore the data, the machine will not function even if other faults are repaired. This can lead to customer dissatisfaction, potential claims, and the inability to collect repair fees, causing significant issues.

How to Detect PCB Faults

1.Visual Inspection
Visual inspection is the first step in checking for PCB faults. Focus on the following aspects:

● Inspect Components
Check all components on the circuit board, including resistors, capacitors, inductors, diodes, and transistors. Ensure they show no signs of damage, burning, or detachment.

● Inspect Solder Joints
Carefully examine solder joints to ensure there are no cold solder joints, dry joints, or fractures. Cold and dry joints can lead to unstable connections, while fractured joints can cause complete disconnections.

● Inspect PCB Surface
Look for signs of corrosion, oxidation, or burning on the PCB surface. These issues can lead to decreased performance or total failure of the board.

● Check Power and Ground Connections
Ensure power and ground connections are correct. Incorrect connections can cause damage or faults in the PCB.

2.Measure Voltage and Current
Use a multimeter or oscilloscope to measure key node voltages and currents on the PCB to identify any anomalies.

● Measure Voltage
Check power supply voltage, signal voltage, and reference voltage to ensure they are within normal ranges. Abnormal voltage values may indicate faulty components or connection issues.

● Measure Current
Measure the current of critical components such as transistors and motors. Abnormal current values may indicate component damage or overload.

3.Resistance Testing
Resistance testing is an effective method for detecting PCB faults. Use a multimeter’s resistance measurement function to check the following:

● Component Resistance
Measure the resistance of components like resistors and inductors to ensure they are within normal ranges. Abnormal resistance values may indicate damaged components.

● PCB Trace Resistance
Measure the resistance of PCB traces to ensure there are no breaks or shorts. Broken traces can interrupt circuit connections, while shorts can damage the circuit.

4.Capacitance Testing
Capacitance testing is used to detect faults in capacitors on the PCB.

● Measure Capacitance
Use a capacitance meter or a multimeter with capacitance measurement functionality to measure the capacitance of components. Abnormal capacitance values may indicate damaged or aged components.

● Charge and Discharge Testing
Perform charge and discharge tests on capacitors to check their performance. Poor charge and discharge performance may lead to circuit instability or failure.

5.Signal Tracing
Signal tracing is an advanced fault diagnosis method used to pinpoint the exact location of a fault.

● Use an Oscilloscope
Observe signal waveforms on the PCB using an oscilloscope, analyzing the amplitude, frequency, and phase of signals. Abnormal signal waveforms may indicate faulty components or connection issues.

● Use a Logic Analyzer
Observe digital signal logic states using a logic analyzer, analyzing high and low levels and pulse widths. Abnormal logic states may indicate faulty components or connection issues.

6.Use Professional Tools
In some cases, you may need to use professional tools to diagnose PCB faults.

● In-Circuit Tester (ICT)
An in-circuit tester is an automated test device that can quickly detect faults on the PCB by applying test signals and measuring response signals to determine fault locations.

● X-ray Inspection
For complex multilayer PCBs, X-ray inspection can help detect hidden internal faults. X-rays can penetrate the PCB, revealing internal structures and potential issues.

● Thermal Imaging Camera
A thermal imaging camera can detect hotspots on the PCB, which may be due to overheating components or short circuits. By identifying hotspots, you can quickly locate fault areas.

Specific Steps for PCB Repair

Before starting the repair, you need to gather a PCB repair kit and materials. For general repairs, you will need:

A sharp knife or flathead screwdriver
A soldering gun
Adhesive copper tape
Scissors or craft knife
A hot air gun
Tweezers
Paper clips
A pen
Cotton swabs
Rubbing alcohol

Once all the tools are ready, follow these PCB rework and repair guidelines:

Step 1: Remove Damaged Components or Pads

To prevent the PCB from moving while you work, use tape to secure the board to the workbench. If the PCB pad is damaged, use a sharp knife or flathead screwdriver to remove the component for PCB pad repair.

Step 2: Clean the Tracks and Remove Solder

After repairing the PCB, use tools like scissors, a sharp knife, sandpaper, or cotton swabs dipped in alcohol to remove solder from the traces. Ensure that the traces are clean and exposed regardless of the material used.

Step 3: Place Copper Tape on the Tracks

After cleaning the traces, place adhesive copper tape on top of the traces, ensuring it aligns with the traces. Some current in the existing vias and surrounding areas will be covered, providing a good connection for the pads or new components.

Step 4: Solder the Joints

After completing the copper tape PCB repair, solder the new copper tape to the connection points of the existing traces on the repaired PCB. Ensure you complete this process in one go, as the copper tape melts quickly at soldering temperatures. Work quickly and minimize heating time.

Step 5: Restore PCB Vias

Use a round-tipped hard material, like a pen, to press and rub the newly soldered areas, ensuring the copper tape adheres firmly to the pad area. The adhesive remains tacky after heating the pad area. Once you locate the via, use a paper clip or a similar tool to create the hole.

Step 6: Place and Solder the Components

After completing the previous steps, place the new components on the PCB and solder them. Insert the leads of the new parts into the vias, then flip the PCB. Apply solder to the pads and heat until the solder melts, then hold the leads in place until the solder cools. Repeat the same process for other pads, minimizing heating time to ensure smooth soldering.

Step 7: Trim Excess Tape from the Repair Area

Once the new components are in place, use a craft knife or scissors to cut off any excess copper tape from the repair area. These steps should restore the printed circuit board. While the traces, pads, and joints may not be structurally perfect like the original PCB, you have given new life and purpose to something many would consider trash.

LST strictly controls the quality of each step in PCB manufacturing to avoid unnecessary rework and repairs. Our state-of-the-art facilities allow us to perform our duties efficiently and accurately. We have a professional design team and quality control team to ensure the quality of each product. We offer one-stop PCB services to meet all customer needs.