LED assembly includes various dispensing applications such as silicone phosphor cavity encapsulation, phosphor plate attachment, and phosphor coating. The most common application is silicone phosphor cavity encapsulation for the Plastic Leaded Chip Carrier (PLCC) LED package type that makes up the bulk of the market.
LED silicone phosphor cavity encapsulation is particularly concerned with:
- Accuracy and consistency of the dispensed fluid volume to achieve the target LED color
- High throughput (units per hour; UPH) to minimize cost of ownership
- Maintaining phosphor suspension and uniformity in the fluid during a production run
In order to achieve a target LED white color temperature, a specific amount of phosphor must be evenly distributed over the LED die. White light LEDs are typically made by combining blue light LEDs with yellow phosphor (new developments may also combine red and green phosphors to enhance the light emission spectrum). It is the secondary emission from the yellow phosphor combined with the correct blue light mixture that makes white light. Variations in the amount of phosphor dispensed over multiple blue LEDs have direct impact to the resulting yield of white LEDs with a target color temperature. As such, it is very critical to maintain good control and consistency of the dispensed fluid volume in order to have a high production yield.
A mixture of phosphor and a binder (e.g., silicone or epoxy) is used to encapsulate the LED chips in their PLCC package. One of the technical challenges in this production process is to ensure uniform mixing and dispersion of the phosphor particles within the binder as the phosphor particles tend to settle out after dispensing and before curing. Less uniformity can adversely affect the color quality.
Nordson ASYMTEK’s patented Calibrated Process Jetting (CPJ) and active nozzle technology ensure dispense weight accuracy and consistency, which contribute to tight LED color quality control. Use of jet valves either in single or dual valve configurations on Nordson ASYMTEK platforms provide for the high throughput desirable in the LED market. Likewise, our optional agitation systems help to maintain the phosphor suspension in the silicone prior to dispensing.