Outside of the semiconductor diode, there are several other key components of an LED that are required in order for it to function. These include the leadframe made up of the post and anvil, the reflective cavity, wire bond and the epoxy lens or case. Certain LED designs may include additional parts or have further sophistication, but all contain these basic parts. Below is a detailed list of each of these components.
Leadframe – Outside of the semiconductor die, the leadframe is the heart of an LED chip. This consists of an anvil, which is negatively charged and holds the semiconductor material itself, and the post, which is positively charged and contains the wire bond which provides current into the die. These two components of the leadframe do not physically touch, and are only connected via the wire bond.
Reflective Cavity – This is a reflective material that surrounds the semiconductor die, directing all light outwards towards the lens. It is usually many times larger than the die itself.
Wire Bond – This is the tiny filament of wire that runs from the post to the center of the semiconductor die, providing it current.
Epoxy Lens/Case – This provides protection and structural stability to the LED unit, rigidly affixing all components in place. It offers a degree of impact protection, as well as significant vibration resistance, which is critical for industrial or high performance applications.
Sub-Types
A diagram showing the primary components of an LED diode
All Light-Emitting Diodes are built on the same basic principle and components. However, there are some significant differences in the design between these different technologies, which are detailed in the following diagrams.
Standard Diode – This is the most basic form of LED, and also the oldest. It involves a relatively straightforward circuit consisting of an anvil and a post, with a wire bond electrically connecting the post to the semiconductor material in the anvil. All of these components are encased in an epoxy resin lens/housing, with anode and cathode connections ready for easy soldering to a board.
SMD LED – Short for “Surface Mount Device”, these LEDs are unique in that instead of being individual parts that are manually soldered to a board, they are actually mounted onto the board itself. One of the biggest advantages of this design is that the LED mount acts as a heat sink, allowing higher current flow and higher efficiency, generating more light.
COB LED – Standing for “Chip on Board”, this is an evolution of the SMD design. In this design, the LED chip is mounted directly to the circuit board using thermal adhesive. This allows for further efficiency in cooling, due to the direct contact between the semiconductor die and the board. The increase in cooling efficiency over SMD designs allows even greater efficiency and performance.
