A Bare LED chip without encapsulation cannot meet the requirements of use. Thus, reasonable encapsulation should be designed to provide electrical connection, mechanical protection, effective heat dissipation channels, and high-efficiency and high-quality light output.
The reduction of LED chip size and display screen pitch puts forward higher requirements for encapsulation. At present, Chip-type SMD, N-in-one IMD, and COB are the commonly used encapsulation forms, as shown in Figure 2.
(1) Chip-type SMD Encapsulation
In Chip-type SMD encapsulation, a single LED pixel is die bonded on the BT board and then encapsulated using the optical resin to achieve a single Chip-type encapsulation. The Chip-type encapsulation is then attached to the PCB using SMD technology to create the LED display module to obtain the LED display module. Chip-type SMD encapsulation is a single-pixel encapsulation with small size, small solder joint area, and plenty of solder joints, which will result in the risks of water vapor erosion, poor mechanical protection, and short circuit. Based on the above analysis, Chip-type SMD encapsulation is not suitable for Micro LED displays.
(2) N-in-one IMD Encapsulation
In N-in-one IMD encapsulation, N pixel units (mostly 2 or 4) are die bonded on the BT board and then encapsulated as a whole using the optical resin. Compared with Chip-type SMD encapsulation, IMD encapsulation boasts higher integration, effectively relieving risks of water vapor erosion and poor mechanical protection. Meanwhile, IMD encapsulation inherits the advantages of the mature process, low technical difficulty, and cost of the single SMD device. However, the integration of N-in-one IMD encapsulation is still low, resulting in process issues, display effect, and reliability for micro pitch displays below 0.6mm.
(3) COB Encapsulation
In COB encapsulation, naked chips of multiple pixel unit. (mostly hundreds ) are die bonded on the PCB and then encapsulated as a whole using the optical resin. Compared with Chip-type SMD encapsulation and N-in-one IMD encapsulation, multiple chips are encapsulated as a whole in the COB encapsulation, which contributes to improved resistance to water vapor and excellent mechanical protection performance. Moreover, BT board is omitted and the naked LED chips are attached on the PCB directly in COB encapsulation, which provide s a shorter heat conduction channel and thus better heat dissipation performance. From the above analysis, it can be demonstrated that COB encapsulation is the optimum form for Micro LED displays with high pixel density.
The characteristics of the above mentioned encapsulation methods are shown in Table 2. COB encapsulation with the highest degree of integration can be used to achieve the smallest pixel pitch, the highest reliability and the longest display life theoretically and is thought to be the best packaging solution for Micro LED.
Post time: Mar-09-2022