In electronics production, conformal coating is crucial for quality control, but a complication known as overmasking presents unexpected challenges. In this blog, we’ll discuss tips for reducing overmasking when coating printed circuit boards.
What Is Overmasking?
Overmasking means using too much conformal coating masking tape during the coating process. In this situation, areas that need to be free of coating are inadvertently covered, leading to issues in circuit board functionality. This is a problem because it reduces the efficiency of printed circuit boards. The additional areas covered by the masking tape can act as a barrier, preventing electrical currents from flowing correctly. As a result, the circuit board might fail to perform at its optimal capacity.
Common Causes of Overmasking
Overmasking can occur due to:
Inadequate Masking Techniques
One of the primary causes of overmasking is improper masking techniques. If the masking materials, such as tapes or liquid maskants, are not applied accurately or securely, they fail to protect the designated areas effectively. This can result in conformal coating seeping beneath the masking material and onto unintended regions of the PCB.
Increased Safety Hazards
One of the biggest concerns associated with traditional coating methods is the health and safety hazards they pose to operators. Spray coating, for instance, releases volatile organic compounds (VOCs) into the air, which can have adverse effects on the respiratory system and overall well-being of workers. Moreover, brush and dip coating methods often involve the handling of hazardous chemicals, increasing the risk of skin irritation, burns, and exposure to toxic substances.
Inconsistent Coating Thickness
Inconsistent conformal coating thickness also contributes to overmasking. If the coating application is uneven or too thick in some areas, it can easily breach the mask and extend onto other parts of the PCB. Maintaining precise control over coating thickness is crucial to prevent overmasking.
Electronic components on a PCB can vary in size and shape, making it challenging to achieve uniform masking. Smaller parts require more delicate masking techniques, while larger ones need special attention to prevent coating seepage.
Mask Material Compatibility
The choice of masking materials is essential. If the mask materials are incompatible with the conformal coating material, they can react or degrade over time, leading to overmasking. It’s vital to select materials that are compatible with the coating.
The skill and training of operators involved in the conformal coating process play a significant role in preventing overmasking. Lack of training can result in improper masking and coating techniques, leading to quality issues.
What Are the Effects of Overmasking?
Overmasking can have significant consequences on the quality of printed circuit boards, including:
When conformal coating extends beyond its intended boundaries, it can create unintended connections between conductive traces on the PCB. This results in electrical shorts that disrupt the normal flow of current and data, leading to circuit failures, malfunctions, and damage to sensitive components.
Reduced Heat Dissipation
Overmasking can cover thermal vias, which are essential for dissipating heat from components on the PCB. This trapped heat causes temperature build-up, leading to component overheating, reduced performance, and in extreme cases, component failure.
Conformal coating protects PCBs from moisture, but overmasking can have the opposite effect. If moisture gets trapped under the coating due to overmasking, it can lead to corrosion, short circuits, and compromised performance over time.
Interference With Connectors
Overmasking can obstruct connectors, making connection with cables or other devices challenging. This delays assembly and maintenance and sometimes damages connectors during forceful attempts to make connections.
How Does Automated Conformal Coating Reduce Overmasking?
Precision and Consistency
Automated systems are programmed to apply conformal coating with precise control over the application rate, ensuring a uniform coating thickness. This precision prevents coating from extending beyond the intended areas, which is a common cause of overmasking in manual processes.
Automated systems are equipped with digital controls and sensors that monitor the coating process in real time. If there are any deviations or irregularities in coating thickness, the system can make immediate adjustments to keep the coating within the specified boundaries.
A Repeatable Process
Automation ensures that each PCB receives the same treatment, eliminating the variability introduced by human operators in manual processes. This repeatability reduces the chances of overmasking due to inconsistent application.
Eliminating Conformal Coating Masking Tape for Multiple Industries
Invention House’s Raphael 4040 is streamlining coating processes for companies across industries. Visit our case studies page to see who we’ve helped.
Eliminate Overmasking With the Raphael 4040
Spray coating and other traditional methods increase the risk of overmasking. Invention House understands the importance of delivering a consistent product, which is why we created the Raphael 4040, our automated conformal coating robot. Our innovative approach to conformal coating offers unmatched protection against dust, moisture, and other external threats, delivering the following benefits:
- Increased quality
- Improved productivity
- Enhanced operator safety
The Raphael 4040’s Conformal Coating Process
Step One: Importing Board Image
The first step is to import either a Gerber file or board image. Next, the imported file’s X, Y, and Z dimensions are configured. This process is performed separately for both the front and back of the board.
Step Two: Path Creation
The operator controls the coating process by using a joystick, keyboard, and click/drag actions. They create a set of coating segments around the PCB’s X, Y, and Z axes starting from a designated “home” point. The initial path is tested in dry-run mode and adjusted until the operator is happy with it. Once satisfied, the optimized path can be applied to all boards in the layout.
Step Three: Wet Run
Once the dry-run path is done, the operator chooses a single board, starts the pumps, and opts for “Coat Single Board” to begin the wet-run phase. It’s crucial for them to closely monitor the coating flow and adjust brush height, flow rate, and speed as needed.
Step Four: Production
Once the conformal robot is following the preferred path, production conformal coating can begin. We recommend carefully inspecting early samples and making incremental path changes once production starts.
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