Nordson ASYMTEK: Dispensing with Convention

As the LED market continues to experience growth, with a predicted ramped wafer capacity 74% in 2011, manufacturing technologies that reduce process variation, increase yield, and reduce cost are in hot demand. Nordson ASYMTEK has taken on these challenges, developing dispense processes based on its jet dispense technology that has won the company two technology innovation awards at this year's NEPCON China. At ECTC 2011, in Buena Vista, FL, Chip Scale Review talked to Akira Morita, business development manager, Nordson ASYMTEK, to learn more about the company's process offerings targeting side-view LED applications.

CSR: First of all, what are side-view LEDS, and how do they differ from other types of LEDS?

Morita: White LEDS are used in display backlighting for TVs, tablet PCs, and e-Readers as well as illumination LED lamps. These backlight technologies come in two types; one is top emission, mainly used for television backlighting. The second type is called 'side-view', and targets mobile applications such as notebook PCs, tablet PCs, and e-Readers; essentially any application requiring a very thin form factor. All LED manufacturing requires a fluid dispense process. Unlike high brightness LEDS used for general lighting purposes, side-view LEDS have tighter spaces to accommodate, presenting a challenge to traditional dispense processes.

CSR: You mention silicone phosphor dispense as one of the processes critical for white LEDS. What is the purpose of silicone phosphor in LED manufacturing?

Morita: The purpose of silicone phosphor is to create the white light emitted by LEDS. LED chips emit a blue light. Phosphor absorbs blue light and emits yellow light. Silicone phosphor is a mixture of silicone and phosphor powder, which, when dispensed into the package cavity between the wire-bonded LED chip and the lens filters the blue light through the yellow phosphor light and comes out as white light.

CSR: How was this traditionally accomplished?

Morita: Needle dispense has been the traditional approach to dispensing silicone phosphor into the package cavity. But due to the elasticity and sticky consistency of the silicone material it's difficult to control the exact amount of material that is being dispensed. Extracting the needle from the cavity can result in a long tail of silicone that breaks off. If the dispense amount changes, so does the amount of phosphor in the cavity. This can strongly affect the color quality of the LED, as well as the consistency across the array. A specific ratio is critical for producing white light.

CSR: Can you briefly explain Asymtek's jetting process?

Morita: Nordson ASYMTEK's jet dispense head dispenses tiny uniform dots rather than droplets to fill the cavity. Depositing the same number of dots in each cavity allows for more stable, precise and consistent dispense. Additionally, the calibration capabilities with jetting allow for scaling inside the machine. Dot size is measured on the scale to monitor its size. Once the operator puts the syringe in the machine and starts production, the dot size is automatically monitored. The operator doesn't need to intervene.

CSR: What significant improvements would you say are gained with Nordson ASYMTEK's process in comparison with other processes?

Morita: With conventional dispense processes, the quality of the LEDs has to be evaluated manually, with the feedback delivered to the dispense operator who adjusts fluid pressure by hand to make sure the right amount is going into the cavity. It's a slow process requiring several dispense heads of varying fluid pressures. Calibration is all done manually. Jet dispense is so fast, and uses automated calibration, so only one head is required. Feedback is automatic and there's no need for operator adjustment.

With LED production expected to reach volume manufacturing levels of billions of units per year, time consuming, inaccurate processes will not be cost effective. The benefits of jetting technology include speed, accuracy, and high yield; and all that means low cost.