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May 2014 • SMT Magazine 95 anatomy of a LED lamp Now let's look at the anatomy of a LED lamp (Figure 2). Most LEDs are driven by a DC con- stant-current supply (LED driver). Energy effi- ciency of LEDs is very high (typically 6–8 watts for a LED lamp versus 60 watts for an incandes- cent lamp with comparable luminosity). How- ever, since the dimensions of a LED package are typically much smaller, local heat dissipation (below the LED package) per unit area will be higher. Special measures are needed to cool the LED board and hence safeguard long LED lamp lifetimes: substrate material selection (insulated metal substrate or FR-4 with thermal vias) and a heat diffuser (connected to both LED board and driver board). IMS consists of a core of aluminum sheet material covered by circuit layers. In most cases, the circuit material is white to ensure good light reflection. Since IMS material is a factor 8–10x more expensive than FR-4, low-cost consumer appliances more frequently use FR-4. Since SMT TrenDS & TeChnologieS LED THE SUNSHINE IN continues Figure 1: packaged leD market by application (source: yole Développement, September 2013). figure 2: Anatomy of a leD drop-in replacement lamp.

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