Conformal Coatings Developments

Venkat Nandivada, Manager of Technical Sales at Master Bond Inc. talks to AZoM about conformal coatings, how the market is evolving for them and the significant progress Master Bond Inc. has made in developing new silicone conformal coatings.

Why use a conformal coating?

The major reason to use a conformal coating is to prevent the premature failure and to extend the longevity of electronic devices by protecting PC boards from diverse service conditions.

What type of protection do they offer?

Specific polymeric formulations have been developed to guard against moisture, chemical vapors, dust, dirt, airborne contaminants, temperature cycling, vibration, shock, impact, fungus. They also exhibit outstanding dielectric strength and prevent high voltage arcing, corona short, static discharge and dendrite growth.

How do you see the market evolving for conformal coatings?

The main resin chemistries for conformal coatings consist of acrylic, silicone, epoxy, polyurethane and parylene vapor phase deposition systems. Each product has tradeoffs in properties which could have a significant impact on meeting specifications needed to satisfy operational requirements. Additionally processing is a key factor in selecting the most desirable chemistry and has to be taken in consideration to optimize productivity.

Solvent free UV dual cure systems with a secondary heat cure mechanism at 80°C have shown increased usage over time consuming room temperature/heat curing conformal coating systems. They allow curing in “shadowed out” areas and have dramatically lowered manufacturing costs providing high performance in demanding, rigorous environmental conditions.

Most notable is Master Bond UV15DC80LV, an epoxy based system with an advantageous low viscosity for an easy application. This single component no mix compound has high physical strength properties, bonds well to multiple substrates, offers resistance to moisture and many chemicals and has a high Tg of >125°C. Serviceability is from -60°F to 350°F. Its rapid cure speed has been shown to be most desirable in high volume production applications especially where electronic device pricing is a primary concern.

Has Master Bond made any significant progress in developing new silicone conformal coatings?

Ultra low viscosity Master Bond MasterSil 773 is a one component silicone elastomer designed for conformal coating of electronic circuitry exposed to high humidity, shock, vibration. This easy to use compound represents a dramatic improvement in silicone technology because of its fast tack free time at ambient temperatures. This condensation curing system has a low modulus of elasticity, a Shore A hardness of 30 and is serviceable from -80°F to +300°F. It is also capable of minimizing stress from thermal/mechanical shock and after curing is repairable. Physical and electrical properties are retained after high temperature exposure.

Why use a two component epoxy for conformal coating?

Typically these 100% solids compositions are curable at room or elevated temperatures. They are available in a range of hardnesses and have superior humidity and abrasion resistance. These low viscosity systems have high dielectric strength and withstand a wide range of chemicals including solvents. Select systems have a long working life after mixing. Thermally conductive systems have superior heat dissipation characteristics.

Our comprehensive line of epoxy conformal coatings consists of special custom made grades that have unique properties. One such material is called EP41S-1 and has the ability to withstand an aggressive array of chemical such as solvents, alcohol, fuels, gasohol. It has good flow properties, adheres well to a wide range of substrates and has low linear shrinkage upon cure. Electrical insulation values and physical strength characteristics are excellent. Another noteworthy two component epoxy product is fast curing, even in thin sections. Called EP30-4 it has high optical clarity, a Shore D hardness of 75-85 and a volume resistivity of >1015 ohm-cm. It has a convenient mix ratio of 2 to 1, by weight.

Where are conformal coatings used?

Conformal coatings are used in consumer electronics, automotive, medical, industrial controls, communication, military, aerospace and maritime devices.

What are the best application techniques for epoxy, silicone and UV curable conformal coatings?

This is dependent on the type of chemistry employed, viscosity of the coating, board dimensions, how densely populated the board is, how sharp the edges of the components are, size of production run, speed of operations and amount of capital investment in equipment. Manual/automatic spraying, dipping, brushing or selective robotic coating can be used.

What makes Master Bond conformal coatings special?

Master Bond has over 40 years in technical expertise in finding solutions for challenging application needs for the electronic industry. Our unique value added products have enabled leading manufacturing companies to improve functionality, reliability of important electronic devices. We are always working on innovative products and have successfully developed, in close collaboration with our chemical suppliers, technologically advanced formulas featuring multifaceted capability. Among our most significant new conformal coatings are systems that are nanosilica filled to provide enhanced serviceability under the most demanding service conditions.

About Venkat Nandivada

Venkat Nandivada has been the Manager of Technical Support at Master Bond Inc since 2010. He has a Masters in Chemical Engineering from Carnegie Mellon University.  He analyzes application oriented issues and provides product solutions for companies in the aerospace, electronics, medical, optical, OEM and oil/chemical industries.