Today’s electronics manufacturers are becoming increasingly trickier. In pursuit of greater profits, they often neglect to provide circuit diagrams along with their equipment when it leaves the factory. This lack of information creates significant obstacles for repair work, as technicians are unable to determine crucial details like the load voltage of specific components, leading to the need to purchase new replacements rather than performing repairs.
As electronics become more ubiquitous, a growing number of individuals are seeking for circuit board repairs. However, for beginners, many of these tutorials can seem daunting and challenging to implement. At TechSparks, we understand these pain points, and that’s why we’ve crafted this article to assist you in understanding all the essential details you need to pay attention to when repairing PCB.
Which circuit board failures are repairable?
When a circuit board fails, the first thing to do is to check the type of failure and analyze whether it can be repaired to avoid unnecessary time wasting. Common detection methods include:
- Comparison method: Detecting each unit of the circuit board frame by frame and comparing the detected current, voltage, resistance, and VI curve parameters with their normal values.
- Current method: Technicians apply current to the faulty circuit board and carefully observe the current situation.
- Replacement method: Entails systematically replacing components multiple times to identify and determine the damaged components causing the fault.
- Voltage method: Measure the voltage of the main terminals and the voltage of the components in the circuit board, and compare and analyze with the normal value, so as to find the fault point.
- Resistance method: Using various instruments measuring the resistance of suspicious components and each pin of the chip to the ground. This approach aids in identifying the exact fault point within the circuit board.
Based on the above methods, we can determine which situations can be repaired and which cannot:
- Repairable situations: Soldering Problems (broken solder joints, poor soldering, solder bridging), Broken Paths, Shorted Paths, Damaged Components, Burnt-out Components, and Power Supply Problems.
- Non-repairable situations: Physical Damage (broken, shattered, severely bent, or large area burned), Lnner Layer Circuit Damage , PCB layer connection Damage , Key Components Damage (integrated circuits, microprocessors), High Density Circuit. In non-repairable situations, it may be necessary to purchase a new circuit board to replace the damaged one, as the extent of damage and complexity of repairs may exceed the capabilities of typical users.
How to repair circuit board?
Step 1: Prepare the materials needed for repair
- Solder wire/solder paste: Used for touch-up soldering or connecting wires and pads.
- Alcohol/detergent: Used for cleaning before repairs.
- Handy Paper/Cleaning Paper: Used for wiping circuit boards and components.
- Adhesive: Used to fix or attach small components or parts.
- Cable/Wire: Used to connect broken or damaged wires in an electrical circuit.
- Electronic Components: Used to replace damaged or faulty components.
- Soldering Station/Soldering Iron: Used for soldering and desoldering components and connections.
- Solder Picker/Solder Mesh: Used to desolder old solder or correct soldering errors.
- Hot air gun/hot air blower: Used for hot air rework of circuit boards or heating solder joints.
- Tweezers/Pliers: Used for grasping and mounting electronic components.
- Wire strippers: Used to remove wire insulation.
- Magnifier/Microscope: Used to inspect details on circuit boards and components.
- Multimeter: Used to measure voltage, current, resistance, and other electrical parameters.
- Brazing Pen: Used for fine soldering.
- PCB bracket: Used to secure the circuit board for easy operation and maintenance.
- Knives: Used to trim cables or cut circuit boards.
Step 2: Remove the faulty area
After confirming the fault area, the first step is to remove the faulty component or pad. Avoid using brute force to remove the components, as they are fixed on the board through soldering. Applying excessive force may cause secondary damage. It is advisable to use a heating tool to melt the solder, followed by a tin aspirator to absorb the melted solder. Finally, use tweezers or other appropriate tools to remove the faulty component.
If the pad is damaged during the removal process, TechSparks recommends using sandpaper to gently smooth the surface of the pad. This will help remove any uneven solder or excess debris, ensuring a clean and even surface for subsequent repairs.
Step 3: Clean the track
After removing components or pads, it is crucial to promptly clean the tracks to avoid any issues with the electrical connection of newly installed components or pads due to residual molten solder solidifying again. The cleaning process involves the following steps:
- Use a fine-bristled brush to remove any large, granular residues from the surface of the board.
- Dip a small piece of cotton or a cotton swab in a small amount of anhydrous isopropyl alcohol and gently wipe the tracks and the surrounding area. Anhydrous isopropyl alcohol is a commonly used PCB cleaner, but other suitable options are available as well.
- After cleaning, carefully inspect the tracks and pads to ensure there are no residual solder slag, loose solder, or any other dirt.
- Use a marker pen to mark the specific location of the repair, ensuring clarity and precision.
- Finally, use compressed air to blow the tracks and pads, ensuring the board surface is thoroughly dry before proceeding with the repair.
Step 4: Place copper tape on repaired area
When conducting repairs, carefully examine the damaged area and cut a piece of copper tape that matches the size and shape of the track. Copper tape is a conductive sheet used to repair damaged or missing wires and reconnect broken circuits. Apply the copper tape directly onto the top of the damaged track, ensuring a secure and proper connection. This technique effectively restores the continuity of the circuit and allows for a reliable repair without the need for soldering or additional components.
Step 5: Solder the joints
Once the copper tape is positioned, the next step is to create a permanent connection between the new track and the pads on both sides. The process is as follows:
- Apply a small amount of solder to one of the pads to prepare it for the connection.
- Utilize a soldering iron with a fine tip to heat the solder on the pad until it melts and becomes molten.
- Carefully place the copper tape onto the molten solder, ensuring it adheres securely to the pad.
- Hold the soldering iron’s tip against the copper tape and pad junction until the solder cools and solidifies. This creates a strong and reliable bond between the copper tape and the pad.
- Repeat the process on the other pad to complete the connection. Ensure that both connections are secure and free from any solder bridges or excess solder.
Step 6: Fix the through hole
If a via is damaged during the repair process, it is essential to address it before proceeding with the soldering of components. This applies to both plated through holes and unplated through holes. The repair process varies depending on the type of via:
For unplated through holes, a simple completion is sufficient, as they primarily serve a mechanical fixing purpose. Using a needle point, a knife, or a drill, carefully clean any residue or obstructions from the via.
For electroplated copper holes, a more comprehensive repair is required, involving re-plating the via. The following steps outline the flow for this process:
- Begin by cleaning any residue or debris from the via using a needle point, knife, or drill.
- Prepare the necessary materials for repairing the via, such as hole connector sleeves or copper tape.
- If using a via connector, insert it directly into the via and ensure it fits tightly against the via wall, providing a secure connection.
- If using copper tape for the repair, insert an appropriate length of copper tape into the via, ensuring it fits snugly against the via wall. Then, connect one end of the copper tape to the circuit that requires repair.
- Proceed with re-plating the via using an appropriate electroplating method to restore its conductivity and ensure its functionality is fully restored.
Step 7: Check repair quality
Once the electronic circuit board repair is completed, reinstall the functioning components back onto the board. However, the process does not end there. A comprehensive inspection is essential to ensure the board’s proper functioning. This post-repair inspection involves the following steps:
- Machine Testing
- Identifying Faults
- Noting New Issues
- Assessing Peripheral Interfaces
What should be paid attention to in PCB rework process?
Prevent electric shock
During the printed circuit repair process, it is of utmost importance to prevent any potential electric shock situations. TechSparks highlights two critical protection measures:
- Ensuring Proper Grounding: When disassembling the electrical casing, technicians may encounter a tingling sensation caused by the AC loop formed by the common-mode filter capacitor and resistor on the circuit board. To prevent such situations, it is vital to ensure that the grounding wire is well connected during maintenance.
- Handling High-Voltage Capacitors: Circuit boards may contain high-voltage capacitors that can pose a safety risk if touched. To avoid any discomfort or potential danger, it is essential to safely discharge these capacitors before starting the maintenance process.
The desoldering process is a critical step in circuit board repair and involves using high-temperature heating elements, such as soldering irons, soldering stations, soldering stoves, heat guns, dryers, etc. It is crucial to exercise caution while using these tools and take necessary safety measures to prevent burns and injuries. Wearing protective gloves is essential to shield hands from direct contact with hot surfaces and solder, ensuring the safety of technicians during desoldering.
Additionally, one detail that is often overlooked but of significant importance is wearing an eye mask. During the desoldering process, heavy smoke and fumes can be produced, posing a potential risk to the eyes. Wearing an eye mask provides a protective barrier, preventing any damage to the eyes caused by smoke.
Circuit board security
It is of utmost importance to approach printed circuit board repair with utmost care and precision, ensuring that the process is focused on restoration rather than causing further damage. Industrial control boards can be costly, and as technicians, extra precautions must be taken to protect and preserve the board during the repair process.
First and foremost, anti-static measures are crucial. Although static electricity may seem harmless in daily life, it can pose a significant risk to sensitive components. Even a small static discharge can cause electrical breakdown and permanent damage to delicate electronic parts. To mitigate this risk, technicians should always take anti-static precautions by wearing an electrostatic wrist strap or anti-static clothing during maintenance, especially in environments with low relative humidity.
Another critical aspect is preventing data loss. Some circuit boards contain batteries that power RAM chips, storing important data necessary for the proper operation of the equipment. If the battery loses power, the data in the RAM can be lost, potentially leading to the malfunctioning of the machine. For this reason TechSparks recommends backing up data before repairs start.
Additionally, attention to detail is paramount. Many components on the circuit board are sensitive and delicate. During the desoldering process, care must be taken to avoid breaking pins, damaging pads, or causing chip failures, which could result in secondary damage and complicate the repair further.
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