Light Emitting Diodes

Light Emitting Diodes

Lightning, Biological and Indicators

Transceivers, Receivers, Emitters

Light Emitting Diodes

Light emitting diodes are light emitting dies that get their color or hue through the phosphor that is coated on top of the die. They are typically blue tinted and are getting their color from a combination of the phosphor, the die light intensity and the overmolded optoelectronic molding compound. There are multipl LED types for a huge variety of applications, ranging from simple through hole mono chrom LEDs to backlight, organic, miniLEDs and industrial baylights. All of these LED types have the same principle but completely different application and reliability requirements.


General Considerations For LED Encapsulants

As LED encaplants, besides general consideration of packaging materials, optical performance with long-term reliability is specially emphasized. 

Challenges & Solutions

Challenges Problem Description Encapsulation Solutions Product Recommend
Light Extraction
  • Refractive index mismatch between LED die (~1.58) and encapsulants, affecting energy output efficiency 
  • High RI (refractive index) encapsulant 
 
Delamination
  • Stress failure caused by CTE mismatch among encapsulant, die and lead frame during curing or temperature shifting;
  • Moisture absorption and ions corrosion
  • Adhesion issue 
  • Matched CTE and low modulus materials
  • Excellent adhesion to substrate
  • Moisture resistance material with high purity
 
Thermal-Yellowing
  • Thermal degradation and discoloration induced by high junction temperature between die and leadframe 
  • High Tg epoxy encapsulant with high cross-link and strong INP
  • Add anti-yellowing agents
  • Silicone based encapsulants
 
UV-Yellowing
  • Photo degradation induced by UV radiation from LED die and outdoor UV
  • UV transparent encapsulant
  • Silicone based encapsulants
 
Aging/Lifetime
  • Aging caused by thermal and UV degradation
  • Aging will result in mechanical failure, transmission decay and discoloration
Above All  
Sensor Transmission
  • High transmission within application wavelength to avoid disturbing signals
  • Add dyes as cut-off or bandpass filter
 

Application requirements


RGB SMT Display Applications:

  • Junction temperature is low; Packages are 0.2W – 0.5W; 20mA current
  • Contrast is more important than brightness (hence the black body)
  • Silicone is not used as it is clear molding compound application

Mid Power White LED Applications:

  • Junction temperature is 85°C-125°C; Package: 0.1W – 0.5W; 
  • Replaces more expensive alternative (silicone) as encapsulant
  • Stability against heat & UV
  • Highest transmittance in visible & IR wavelengths; Earliest transmittance onset (280 nm)

 

Other Considerations --- Indoor vs Outdoor Application

  • Indoor uses diffusant while outdoor uses a low reflectivity (reduce glare)
  • Indoor Packages: 1010,2121,3528; Outdoor Packages: 3535 & 5050
  • Outdoor requires UV resistance & low moisture absorption
  • Outdoor applications must pass these tests:
    • 85°C /85%RH + 3x 260°C reflow
    • Thermal Cycle tests: -65°C to 150°C for 200 cycles


LED Product overview 

 

Monochrome LEDs

HD RGB LEDs 

White LEDs

Product

TC-8020

(Star Product)

TC-8040

TC-7600

(Popular Product)

TC-7800

(In Development)

TC-8030

TC-8060

(Popular Product)

TC-8090

(In Development)

Summary

  • Good adhesion to BT substrate/metal leadframe 

  • Adequate flexural modulus/strength 

  • Excellent anti-reflow performance. 

  • Good processability and moldability

  • Great moisture resistance property

  • Enable LED display pass hash durability tests 

  • Ensures uniform colours and uniform emitting light at large angles

  • Reduce warpage

  • Excellent anti-yellowish performance at high temperature

  • Reduced light decline by blue/white light

  • Excellent adhesion to Ag/Cu and PCB substrate 

  • Good moldability and higher reliability

  • Two optional forms: cylindrical tablets, and fine powder

Applications

7-segment LED display, compact LED indicator, monochrome Chip LED, photo-link

High density (fine-pitch) RGB LED display

Decorative White LED

Backlight

High Reliability 

Backlight

Light Decline

Aging Test

-

Medium

10-50%

RT*20mA*500hrs

Medium

10-50%

RT*5mA*1000hrs

Low

<50%

RT*20mA*500hrs

High

<10%

RT*5mA*1000hrs

Reliability Tests

Reflow, TCT, 85℃@85%RH

Reflow, TCT, 85℃@85%RH, PCT

Reflow, TCT, 85℃@85%RH

Highlight

  • Low stress and filter versions available

  • High reliability

  • Mid blue-ray decay

  • Low blue-ray decay 

  • Low blue-ray decay 

  • High anti-yellowish

  • Low cost

  • Low blue-ray decay

  • Low blue-ray decay

  • Anti-moisture



Die attach for leadframe LEDs

 

Conductive

  • 8060T
  • 8037TI

Non Conductive

  • 8163F-1
  • 8035M