The demand for PCB-driven electronic devices has tremendously increased over the years. Thus, the printed circuit boards are becoming complex than ever before. With stringent safety and quality regulations in place, the PCB manufacturers are taking extreme steps to ensure that PCBs perform as expected. However, it doesn’t mean that PCBs never get damaged or they cannot be repaired. Do you want to know what goes into the PCB repair and rework? Read this post to know your answers.
Basic PCB Cleaning and Rework Procedures
The following are a few procedures involved in a regular PCB rework and repair.
- Cleaning: The PCBs may contain surface contaminants that may severely affect its electrical characteristics, as well as physical components such as soldering, coating, and bonding. These surface contaminants are cleaned in either of the ways – automated cleaning processes or using cleaning agents.
- Conformal Coating Removal: Removing the conformal coating is often the first task in PCB repair process. Conformal coating is defined as a protective chemical coating, which protects electronic circuits from a harsh environment that may contain several chemical contaminants. Coatings are applied on PCBs for insulations to protect them from corrosion or sometimes to hide what’s underneath. This removal can be easily done in various ways. However, the understanding of the type of coating is important before proceeding with any method.
After identifying the type of coating, it is removed by any of the following ways:
- Solvent Method: This procedure removes coatings by using solvents. This procedure is ideal for overall coating removal of solder resists.
- Peeling Method: This coating removal method is great for removing RTV silicone or other thick rubbery coating materials.
- Thermal Method: This method uses low temperature, a localized heating method to remove the thick coating from PCBs.
- Scraping Method: In this method, the scraping tools is done using a dental style scraper.
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Coating Replacement: As the name suggests, this procedure defines the different methods used to replace solder masks in BGA locations, and coatings on circuit boards.
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Baking and Preheating: The reason for baking PCBs before rework is to remove all moisture from the plastic part of the components. When SMT components go through reflow then the temperature of the components rises very quickly, causing any moisture to turn into steam. This expansion results in a crippled board. This procedure helps your product to prepare for the subsequent operations.
- Baking: Whenever possible, PCBs should be baked prior to soldering and other operation to prevent blistering and other laminate degradation. Backing removes absorbed moisture.
- Preheating: Preheating promotes the adhesion of subsequent materials to perform soldering/unsoldering operations efficiently.
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Bow and Twist Repair: Flatness of boards are important for efficient positioning the panels on the machines which are determined by two features known as bow and twist. The bow is defined as a spherical curvature of the board, whereas, the twist is a deformation of the one corner with the remaining once. If the circuit board influenced by twist and bow then it needs to be removed for the better visual appearance of the boards. Bow and Twists method is designed to reduce warping of circuit boards. This method is ideal for GF or GE substrate base materials with glass transition temperatures below 125 degrees.
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Hole Repair: Circuitry and the plated hole gets damaged during PCB processing and rework. Thus, it is important to repair plated and a non-plated hole on circuit boards. This can be achieved with two methods, one is epoxy and another is transplanted method. Epoxy covers are used to repair minor damage to a mounting hole. The hole may have pins, terminals, wires or another type of hardware run through it. Transplant method is used to modify the shape, size or location of a mounting hole.
The above-discussed are only basic rework and cleaning procedures adopted by PCB assembly services. It is important to check the credentials of the PCB assembly services provider before approaching them for work. Accelerated Assemblies is one of the leading PCB rework and repair services in the USA. The company provides BGA repair services, SMT repair services, and PTH repair services.
