What issues exist in LED SMD packaging technology?

1. LED (Light Emitting Diode) packaging refers to the encapsulation of the light-emitting chip; it differs significantly from the packaging used for integrated circuits. LED packaging requires not only the ability to protect the light-emitting core (die) but also the capacity to transmit light. Consequently, LED packaging imposes specific requirements on the packaging materials used.

2. Most LED packaging technologies have evolved and developed from existing discrete device packaging technologies, yet they possess distinct characteristics. Typically, the die of a discrete device is hermetically sealed within the package body, where the primary functions of the packaging are to protect the die and facilitate electrical interconnection. In contrast, LED packaging serves to facilitate the output of electrical signals, ensure the die functions properly, and—crucially—enable the emission of visible light. This involves design and technical requirements pertaining to both electrical and optical parameters; therefore, packaging solutions designed for discrete devices cannot simply be applied to LEDs.

Packaging Process

1. The objective of LED packaging is to connect the external leads to the electrodes of the LED chip while simultaneously protecting the chip and enhancing light extraction efficiency. The key process steps include die bonding (mounting), wire bonding, and encapsulation.

2. LED Packaging Formats: The formats for LED packaging are remarkably diverse, with specific dimensions, thermal management strategies, and light emission characteristics selected based on the intended application environment. Classifications based on packaging format include Lamp-LEDs, TOP-LEDs, Side-LEDs, SMD-LEDs, High-Power LEDs, and others.

3. LED Packaging Process Flow

a) Chip Inspection

Microscopic Inspection: Checking the material surface for mechanical damage, pits, or craters; verifying that the chip dimensions and electrode sizes meet process specifications; and confirming the integrity of the electrode patterns.

b) Wafer Expansion (Die Spreading)

Since LED chips remain tightly packed with very narrow spacing (approximately 0.1 mm) after the dicing (cutting) process, they are difficult to handle during subsequent manufacturing steps. We utilize a die expander machine to stretch the adhesive film holding the chips, thereby increasing the spacing between the LED chips to approximately 0.6 mm. Manual expansion is also possible, but it carries a high risk of adverse issues, such as chips dislodging or being wasted.