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PCBs are highly sensitive and fragile, making them prone to damage. Troubleshooting and repairing PCBs can extend the lifespan of electronic circuits. If a faulty PCB is encountered during assembly, it can be repaired based on the nature of the defect. Below are some methods for PCB repair.
Top 9 Causes of Printed Circuit Board Failure
Before discussing PCB repair, we need to first examine several causes of PCB damage. The world of electronics is complex, with many moving parts and numerous potential points of failure. One of the most common issues in this field is printed circuit board (PCB) malfunction. Below, we explore the nine most frequent causes of PCB failure.
1. Physical Damage: Dropping the circuit board causes this type of damage, even during improper handling in transit. The most common physical damage occurs when traces on the circuit board break. This can be caused by static electricity, electrostatic discharge, or other electrical energy sources.
2. Component Failure: One or more components on the PCB fail to function as intended. Circuit boards are assembled by soldering components, and solder joints can fail for various reasons.
3. Gold Finger Damage: Gold fingers are tiny, precision components connecting traces on the PCB to pads. They are designed small enough to fit in tight spaces and make connections effortlessly. However, when working on a PCB, you sometimes need to use tweezers or pliers to access those narrow spaces to ensure everything is properly connected. The more you do this, the greater the chance you might accidentally bend or snap one of these gold fingers, rendering your circuit board completely inoperable.
4. BGA Pad Damage: These are the tiny points on the board used to connect soldered components. BGA pads can become damaged if exposed to high temperatures for extended periods or if not properly isolated from heat sources like soldering irons or hot chips.
5. Damaged Through-Holes and Via Holes: When soldering components to the board, if one of these holes becomes damaged or breaks, it can cause a short circuit.
6. Corrosion: As the name suggests, corrosion is the process by which one material erodes or damages another. Most materials corrode when exposed to corrosive elements like water or oxygen. This occurs if the board is subjected to high temperatures for extended periods or in environments with high humidity.
7. Broken Traces: Printed circuit boards consist of thin, conductive copper layers. PCB traces connect different parts of the board and carry signals. When a trace breaks, it ceases to conduct electricity. Excessive heat can cause strains to fractures.
8. Damaged Edges: The edges of a circuit board are not only the most vulnerable part of the PCB but also one of the most critical. Damage to the board's edges can lead to short circuits and electrical failures, potentially causing fires and other safety hazards.
9. Solder Mask Delamination: One of the most common PCB issues is solder mask delamination, occurring when the solder mask separates from the underlying copper layer due to improper adhesion or physical damage. If left unchecked, this can cause permanent damage to individual components and the entire system due to simultaneous overheating or short circuits.
PCB Repair Methods
1. Visual Inspection Method
Employ traditional observation techniques: look for scorched areas on the circuit board, inspect for fractures in the copper plating, detect unusual odors, identify poor solder joints, and check interfaces and gold fingers for mold or discoloration.
2. Universal Replacement Method
This involves testing all components to identify and replace faulty ones, achieving repair. For components undetectable by instruments, substitution is employed—replacing them with new parts regardless of their condition to ensure all components on the board are functional. This method is ineffective for issues like blocked vias, broken copper plating, or improperly adjusted potentiometers. This method cannot be used for chips containing programs or data.
3. Comparison Method
The comparison method is one of the most common approaches for repairing circuit boards without schematics. It involves comparing the board's state with that of a known good board to identify faults and detecting anomalies by examining the waveforms at various nodes on both boards. However, often we lack a good board for comparison. This doesn't preclude using this method. For instance, we can identify circuits with identical properties on the board. Suppose a board has three identical interfaces sharing the same circuitry. We can then compare the waveforms between these three identical interfaces to diagnose issues. Even when the above scenario isn't available, we can still find circuits with common properties. For example, buses within a circuit typically exhibit identical waveforms. Additionally, when uncertain whether an IC is damaged, we can compare its waveforms with those from a functional IC to decide.
4. State Method
The state method involves verifying the operational states of components. If a component's operational state deviates from the expected normal state, the component or its affected parts are likely faulty. For instance, when inspecting a CPU, we check whether the crystal oscillator functions correctly and whether the reset signal is normal. For NAND gates, we verify the correctness of the input/output logic to assess component integrity. This method often involves forcing input signals—such as applying a signal from a signal generator to an op-amp input and measuring output amplitude and distortion with an oscilloscope to diagnose op-amp issues. By forcibly raising or lowering logic gate input levels, we measure output levels against the chip's specified logic to determine functionality.
5. Replacement Method
Replace all ICs with new ones until the issue resolves. This approach is generally less effective than the blanket replacement method, which at least involves component evaluation and can build circuit board-specific expertise over time. The success rate of this method relies entirely on luck rather than effort, and even if successful, the root cause remains unknown. However, this method still has its merits. If a circuit board or electronic device can be tested on-site for functionality, ICs can be replaced one by one. When the fault disappears after replacing a specific IC, it confirms that the newly installed IC was defective. A critical flaw of this method is the absolute necessity of ensuring the purchased ICs are functional. If defective ICs are procured by mistake, not only will the repair fail, but the fault may also worsen, thereby increasing the complexity of the repair.
6. Circuit Emulation Method
This method involves manually constructing a circuit that functions when fitted with the suspected faulty IC, thereby verifying its quality. While this approach achieves 100% accuracy, the sheer variety of IC models and complex packaging makes it impractical to build circuits for every possible component.
7. Principle Analysis Method
This approach involves analyzing a board's operational principles. For certain boards, like switching power supplies, engineers can understand their functioning and details without schematics. For engineers familiar with schematics, repairs become remarkably straightforward. However, for relatively complex or uncommon devices lacking readily available schematics, reverse engineering can be performed manually to create schematics. With these schematics in hand, repairs become virtually unstoppable.
Conclusion
DIY PCB repair requires some skill, but with patience and the right tools, almost anyone can do it. However, if you remain uncertain or lack time to start this project, iPCB may be able to assist.