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The appeal of making use of LEDs in illumination applications is growing rapidly. The numerous and significant benefits of utilizing modules that incorporate a matrix of LEDs are being recognized by design engineers in a number of key business sectors, including aerospace, architectural lighting, and the “golden egg” automotive market.

Attributes for instance design flexibility, low energy consumption, even and dependable light, and long lifetime distinguish LED modules from designs based on traditional filament lamps and fluorescent tubes. LEDs can also have knock-on benefits, such as greatly reducing the size and complexity from the module and simplifying the lens design.

A excellent example of some other advantages of LED lighting is demonstrated by an application inside the cabin of a passenger aircraft. A retrofit LED unit that replaced a fluorescent-tube lighting module enabled finely controlled dimming and also provided mood lighting effects via the use of differently coloured LEDs.

Thermal management
Possibly the most challenging issue when realizing a module layout that uses LEDs is always to manage the temperature of individual device junctions throughout normal operation. If the considerable amount of heat produced by all of the devices in a module is not managed correctly then the junction temperatures may reach a level where the LEDs’ expected life is shortened and reliability is compromised (see Links).

LED modules normally comprise a matrix of several surface mount devices. These LEDs are soldered to an etched copper layer that offers the interconnects in between the individual LEDs as well as other passive and active components which are required to complete the circuit. The small size from the LEDs and the close proximity with which they could be mounted means that designers possess a huge amount of design freedom and can achieve complex illumination patterns with higher levels of brightness.

The etched copper circuit is separated from a base plate – generally created of aluminum – by a thermally efficient, electrically isolating dielectric substance. The characteristics and capabilities from the dielectric layer are key to the design flexibility and efficiency of the overall module.

Dielectric supplies are made by blending thermally effective materials for instance alumina and boron nitride with other ingredients, to provide a flexible yet resilient coating for the base plate. An essential characteristic of the dielectric layer may be the quantity of electrical isolation it provides among the copper about the topside and the metallic base plate for the underside. That is identified as its dielectric strength. A typical dielectric material may possess a dielectric strength of around 800 V/mil and be coated onto the base plate to a thickness of 8–12 mils (1 mil = 1 inch–3 = 25.4 µm).<br>

Dielectric components employed on insulated metal circuit boards usually possess a thermal conductivity figure within the region of 3W/mK. That is approximately 10 times the overall performance achieved by FR4 (flame retardant woven glass reinforced epoxy resin) PCB substance.

A further important requirement of the dielectric layer would be to be capable to compensate for the different coefficients of thermal expansion with the copper track on the topside from the assembly and the aluminum base plate/heat spreader on the bottom side.

Going three-dimensional
Flat sheets of insulated metal circuit board comprising copper foil, a dielectric layer and an aluminum base plate have been accessible for numerous years. In the eyes with the forward-thinking LED module designer, the primary problem has been that flat sheets of insulated metal circuit board limit them to 2D shapes.

To address these limitations, new dielectric supplies are becoming obtainable that have a low modulus, meaning that they are compliant with mechanical tension and strain. These supplies not only accommodate the coefficient of expansion from the metal elements of the construction, but also enable parts to be formed into correct angles, and even by means of 360˚. This enables designers to realize complex-shaped designs and ones that form a complete circle with either internal or external copper traces.

When designing with new, formable insulated metal circuit board components it is possible to route the tracks around corners, which alleviates the need to use connectors and hard wiring. There are several advantages to this, including enhanced reliability resulting from having fewer junctions and interconnects. Despite the slightly higher cost of the new materials, the overall cost is reduced because fewer components are needed, and assembly time is reduced.

Strength and durability
LEDs themselves are inherently durable. Mounting them on metal based circuit boards only serves to enhance their robustness and that from the finished module, providing excellent resistance to vibration and mechanical shock.

Automotive lighting clusters provide a excellent example of how LED modules can supply superior overall performance compared with traditional filament lamps. On-vehicle applications experience large levels of vibration and wide operating temperature ranges that can cause premature failure of filament lamps. In some operating conditions LEDs can last up to 100,000 hours, which means that they should not require any attention for the life from the vehicle.

The long life of LEDs also simplifies the designers’ task because it is less essential to make the lighting effects module accessible for servicing inside the finished product. This can result in a neater, more integrated installation and also in potential cost savings.

Temperature modelling
Thermal analysis software packages are accessible to help prove LED based module designs before they are committed to manufacture.
These software packages gather data from an integrated database about LED efficiency and specifications along with those of other devices which are mounted about the insulated metal circuit board. This data is combined with other information about elements with the style, including the copper traces, energy and ground planes, and vias. The collated information is then processed to produce an accurate representation with the thermal overall performance from the layout.

User-friendly graphical representations with the results enable the design engineer to quickly pinpoint areas that might require attention, correct down to component and track level.

Thermal analysis software can bring significant commercial and style rewards by helping speed the time to marketplace and reducing the number of iterations needed to reach a production-ready solution.

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Gamers Notebooks