Function Of Conformal Coating In PCB Assys

Conformal coating plays a crucial role in protecting circuit boards from their operating environment, reducing failure rates and extending the life of electronic components. There are a number of different types of conformal coating, each with its own benefits and applications. Choosing the right conformal coating requires balancing its protective properties against the practicalities of application and rework.

The main function of conformal coating is to protect the components on a circuit board from damage caused by environmental factors such as moisture, dust, heat, chemical contamination and electrical currents. Coating can also prevent corrosion on metal components and connections and prevent mechanical stresses to the board and its enclosure.

Depending on the environment in which the device will be used a conformal coating can be made from a variety of materials. For instance, parylene and epoxy are popular due to their high dielectric strength and resistance to extreme temperatures.

There are a range of industry inspection standards and tests that conformal coatings must pass before being used in a production environment. These include thermal cycle testing, where the pcb assy is exposed to a series of gradual temperature changes, and thermal shock testing. Humidity and corrosion testing are also essential. This involves exposing the boards to a corrosive environment such as salt mist and ensuring that the conformal coating is sufficiently resistant to these environments.

What Is The Function Of Conformal Coating In PCB Assys?

Other tests include examining the thickness of the coating and rework and repair capabilities. These can be tested using a variety of methods, such as eddy current and ultrasonic thickness gauges. A cross-hatch test is also used to assess adhesion between the coating and standard circuit board materials. The best method for removing conformal coating is usually through the use of a soldering iron during rework, but it is possible to abrade the coating with micro blasting or grinding techniques.

Once a suitable conformal coating has been selected it is important to ensure that the process for applying it is as controlled as possible in order to get the most out of its protective properties. This is especially important for highly sensitive and expensive devices such as the ones used in aerospace and the military.

A range of application and curing techniques are available including dip, spray and brushing. The ideal method will depend on the volume of production, component type and placement and budget. For example, automated applications will be preferable for mass production and hand spray coating is more appropriate for smaller runs.

It is also vital to check that the conformal coating is effectively bonding to the substrate of the circuit board. This can be done with a variety of methods, including cross-hatch testing and an optical inspection system. Another common method is to burn through the coating with a soldering iron during rework. This can be effective, but it is important to do so carefully in order not to damage the circuit board underneath. Other rework techniques include chemical de-wetting, which uses a solvent to remove the coating; and micro-blasting, which uses a concentrated mix of soft abrasive particles and compressed air to abrade the surface of the circuit board.

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