Ensuring reliability of assemblies

Louise Smyth

Phil Kinner presents some new developments in conformal coatings for the most demanding environments

In a typical car today, electronic systems are critical to the smooth and safe operation of the vehicle. Electronics are at work unlocking the vehicle before the engine starts. Once you start the engine and step on the accelerator, sensors assist in getting out of your parking space, engine control units (ECUs) tune the engine performance, monitor the pressure of the tyres and safety systems are powered up in standby mode. As you pull away, adjust the air conditioning, ensure your phone is connected to the entertainment system, set your destination on the satellite navigation system and initiate your favourite music, yet more electronic systems are being utilised. 

The electronics continue to manage your interior temperature through the heating, ventilation and air conditioning (HVAC) system. Sensors and control systems detect crash situations, deploy airbags, side impact protection and can automatically notify the emergency authorities of the location of an accident. The usage of automotive electronics will continue to develop as consumers demand ever more performance, safety, comfort, convenience and entertainment from their vehicles.

Electronic systems are increasingly facing wider temperature extremes, greater degrees of humidity, condensation and yet more corrosive gases. Unlike aerospace applications where there may be two or three layers of redundancy in design, automotive designs typically must work first time, every time, throughout the life of the product.

Conformal coatings are thin, protective polymeric coatings that are often used to provide the required environmental protection, without an excessive cost or weight increase. Within automotive applications, these are categorised as either ‘in-cabin’ (situated within the passenger cabin) or ‘under-hood’ (near the engine) requirements.

The main differences between the requirements for the protection of ‘under-hood’ electronics and ‘in cabin’ electronics are due to the placement of the former.  The environment can be much less controlled, with higher maximum operating temperatures and far more opportunity for contamination by fuels, oils, cleaning fluids, corrosive gases, metal particulates and salt-water slush sprayed up after road gritting, etc.

Fundamentally, ‘under-hood’ and other non-cabin electronic assemblies are required to provide protection under much tougher environmental conditions. To meet these challenges, a new type of protective coating is required. These coatings are required to be extremely resistant to wet conditions, chemical resistant, highly flexible to survive thermal shock excursions and temperature resistant to survive the higher operating temperatures.

To meet the demands of the automotive industry for greater electronics reliability under ever more adverse conditions, Electrolube has developed a range of solvent-free, higher performance protective coatings. These coatings have been developed to be applied at greater thicknesses to overcome common application defects and improve sharp-edge coverage. The materials have been demonstrated to provide considerable performance improvements on model PCB test assemblies, in terms of resistance to thermal shock, condensing and salt-mist environments than traditional conformal coatings, ultra-thin coatings or even UV curable materials.

Phil Kinner is head of the Conformal Coatings division at Electrolube (a division of HK Wentworth). 

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