Applications Engineering Notes

LED Handling and Manufacturing Precautions

(1) Storage:

         LED lamps should be stored at 30 C, or less, and 70% RH, or less, in its original sealed container (anti-static bag) in a dry location.

         Storage life is about 3 to 6 months (depending on ambient conditions).

         If the LED lamps are to be stored for more then 6 months, they can be stored for a year in a perfectly sealed container with a nitrogen atmosphere and moisture absorbent material.

         Rapid transitions in ambient temperature, especially in high humidity environments, where condensation can occur should be avoided.

(2) Static electricity control:

         Static electricity and/or surge voltages will damage LED die, LED lamps, and LED based products. Electrostatic discharge can be at times imperceptible.

         All LEDs are susceptible to ESD damage and GaN based LEDs (blue, white, green) are particularly more sensitive to surge voltages caused by ESD.

         ESD damage can vary in its degree; from very subtle to catastrophic, and invariably will affect the LED�s performance and life.

         Damaged LED lamps exhibit some unusual operating characteristics such as: increase in reverse leakage current, increase or decrease in forward voltage (VF), increase on the turning ON point  (not lighting at low currents), flickering, erratic behavior or performance, etc.

         It is recommended that anti-electrostatic wristbands and/or anti-electrostatic gloves be used when handling LED products. All personnel, devices, equipment, instruments and machinery must be properly grounded at all times.

         Test to ensure that the proper and true grounding indeed exists and check the ground path�s continuity.

         It is recommended that measures be taken to avoid surge voltage to/from the equipment that handles, touches, mounts and solders LED lamps.

         Create an anti-static environment by using electrically conductive mats (below 106W) and/or other anti-static equipment such as ionizing fans.

         Avoid any friction between LED lamps or PCB boards containing LED lamps and tools, instruments and housings made of plastics, metals, or other easily electrically charged materials.

         Electrostatic buildup occurs (and/or increases) easily in dry environmental conditions (low relative humidity). A relative humidity of 50% or higher is recommended for electronic-components manufacturing environments. Be extremely careful when the RH drops below 50%.

         Electrostatic levels should be kept below 200 V in the working area.

         Same handling care should be taken when intentionally submitting LEDs to voltages (or currents) well above the specified operating maximum ratings (be aware of surge voltages produced when power to an LED is switched ON/OFF).

(3) Heat generation and dissipation:

         Thermal design of the end product is of the most importance for long-term reliability and optimum lumen maintenance of the LED base product.

         Heat generation of the LED(s) and other components is to be considered while designing the circuit layout and the complete system.

         The thermal resistance of the circuit board and density of LEDs and other components on the board will all affect the coefficient of temperature increase per input electric power.

         Proper heat dissipation  (heat sinking and heat extraction) of internally and externally generated heat build-up needs to be included in any end product containing a large LED and component density.

         Heat generation must be lowered and should be well maintained within the limits specified.

         The operating current should be decided and adjusted (de-rating) after considering the maximum ambient temperature in which the LEDs will be operating.

(4) Lead forming:

         When forming (bending) the leads of an LED lamp, a distance of at least 3mm, from the base of the epoxy lens, should be maintained.

         Do not use the base of the lead frame as a fulcrum during lead forming. Use proper tools.

         Lead forming should be done before soldering.

         Do not apply any bending stress to the base of the lead since the stress at the base may damage the physical characteristics of the LED lamp or it may break the lens or the internal wire bond.

         When mounting the LEDs onto a PCB, the holes on the circuit board should be exactly aligned with the leads of the LEDs as to avoid stress on the leads during insertion and mounting of the LEDs and later operation. Such stress could cause damage to the epoxy resin leading to potential early failure of the LED lamp.

 (5) Cleaning:

         It is recommended that isopropyl alcohol be used as a solvent for cleaning the LED lamps.

         In case other solvents are being considered, it needs to be confirmed if such solvents will dissolve, damage or affect the lens resin. Freon solvents should not be used to clean LED lamps because of worldwide regulations.

         Do not clean LED lamps using ultrasonic vibrating devices. If it is absolutely necessary to do so, be aware that the influence of ultrasonic cleaning on the LED lamps will depend on factors such as the applied ultrasonic power and assembly conditions.

         Before performing any cleaning, a pre-test should be done to check whether any damage would occur to the LED lamp.

(6) Soldering LED lamps:

             For Automatic Soldering

         The temperature of the PCB, LED lamp, and soldering equipment should be measured, controlled and maintained before and during and soldering process.

         While soldering, if the temperature of the LED lamp is allowed to reach an exceed the glass-transition temperature (Tg) point of the lens epoxy, the internal LED bonding gold wire could potentially break once the epoxy hardens upon cooling.

         The LED lamp(s) soldered to a PCB should not be subjected to physical shock immediately after soldering is finished since the lens epoxy might still be soft inside the LED lamp. Shock may cause the gold wire to break.

         The best way to harden the epoxy is to have a cooling fan to provide gradual cooling.

(7) Safety guidelines for the human eye:

         In 1993, the International Electric Committee (IEC) issued a standard con�cerning laser product safety (IEC 825-1). Since then, this standard has been applied for diffused light sources (LEDs) as well as lasers.  In 1998 IEC 60825-1 Edition 1.1 evaluated the magnitude of the light source.

         In 2001 1C 60825-1 Amendment 2 converted the laser class into 7 classes for end products.

         Components (LED Lamps) are excluded from this system.

          Products that contain visible LEDs are now classified as class 1. Products containing UV LEDs can be classified as class 2 in cases where viewing angles are narrow, optical manipulation intensifies the light, and/or the energy emitted is high. For these systems it is recommended to avoid long-term exposure. It is also recommended to follow the ICE regulations regarding the safety and labeling of products.



copyright � 2002-2005 all rights reserved