Thin fine pitch indoor LED displays have caught on the market in recent years, but a big challenge for the industry is miniaturizing LED suitable for display smaller than 100-inch, said Min-Hsun Hsieh, Vice President (VP) of R&D Center at EPISTAR during a recent interview with LEDinside.

“Fine pitch indoor LED displays have a lot of advantages in the 100-150 inch display range, but the minimum size of LED package made of widely-used PLCC, plastic leaded chip carrier, is limited to 0505.” said Hsieh. “It becomes very costly to further miniaturize the LED package and to reach the request of the uniformity of wavelength for displays smaller than 100-inch.”

To break this technical bottleneck, EPISTAR has turned to a solution that sprays quantum dots (QD) onto CSP LEDs.

By using the QD enhanced CSP LEDs, the leading Taiwanese LED manufacturer has taken advantage of the wire-bonding free chips to make LED packages smaller than 0.5mm, miniaturizing package sizes down to 0303 and 0202.

Moreover, the resulting indoor fine pitch QD LED displays can be smaller than 60-inch, said Hsieh.

According to Hsieh, the advantages of the QD solution is that it not only improves the uniformity of blue and green emission, but also solves the issue from producing expensive AlInGaP (red) LED flip chips. The QD LED chips are also more efficient in blue and green range compared to conventional LEDs.

The wavelength variation of EPISTAR’s mass produced blue LED chips is 5 to 12nm, which is still far from the aim of achieving the goal of 3 to 4nm in request of fine pitch display.

Additionally, it is very costly to convert red LED chips from vertical structure to flip chip which is needed in smaller sized LED displays.

“Blue and green LEDs are grown on sapphire substrates, which is transparent to let light come through. But red LEDs are gown on opaque GaAs substrates and they have to be transferred to glass or another transparent substrates in order to make them flip chips.” explained Hsieh about the more costly manufacturing process for red LEDs.

EPISTAR’s R&D VP Min-Hsun Hsieh will be speaking more about QD LEDs at the upcoming LEDforum 2016 hosted by LEDinside that will take place on Sept. 30, 2016 at Room 201, National Taiwan University Hospital International Convention Center in Taipei.

(Authors: Philip Chang, Analyst, LEDinside and Judy Lin, Chief Editor, LEDinside)