Silicone (SR) conformal coatings are inorganic materials. They are polymers in which atoms of silicon and oxygen alternate in a chain. They differ to the organic polymers like the acrylics and urethanes.
The silicone coatings normally have a very wide temperature range of operation compared to the other conformal coatings. Typical range can be -55°C to +200°C (-67°F to +392°F). Like the organic coatings (acrylics and urethanes) they have good moisture protection. They also have good chemical resistance to polar solvents.
Curing of silicones occurs through several different mechanisms, depending on the conformal coating, including RTV (Room Temperature Vulcanisation), Heat, UV, Moisture / Condensation and Catalysed Cure.
In production they can be difficult materials to use due to the cure mechanism being difficult to control. Good housekeeping can minimise these effects. SR coatings can also require different coating equipment or options compared to the organic coatings. This should be considered as part of the holistic approach to conformal coating selection.
The different conformal coating material properties
Conformal coatings can be considered in many different ways.
This includes the different families of materials, their individual properties and the chemistries of these coatings.
The different ways we can examine conformal coatings include:
There is a vast range of options and considerations available.
Nexus are to hold a FREE conformal coating workshop in the Diamond SCH coating facility in Shenzhen China on the 17th October 2012.
Topics include Understanding Liquid Conformal Coating Materials & their Selection. This presentation will look at How to select a conformal coating, the various coating material properties, your options for selecting the coating and what can happen when you get it wrong.
Want to choose the right conformal coating for the project and protect the circuit board correctly? Don’t miss this presentation and find out more.
This One-day workshop will be held at the Diamond SCH Conformal Coating Facility. The address is 3rd Floor, A5 Building, Tianrui Industrial Park, Fuyuan Road1, FuYong Town, Baoan District, Shenzhen, China.
“It can be as basic as the coating just will not stick to the PCB or it runs away from areas on the PCB. At other times, it’s interpreting just how well the coating is stuck and determining if it’s good enough for the customer? Normally, this cannot be answered instantly and leads to some serious thinking!”
“One of the biggest issues we face is availability of the materials. As a subcontract coating house we generally have to use the coating selected by the customer. This can have dramatic issues occasionally when lead times on products can stretch into weeks or months and the customer wants the product now!”
“Conformal coating is one of the last processes on the PCB. Coating houses are normally making up the time lost in other areas. If you can plan the production to coincide with the material supply chain it’s a great help!”