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A simple analysis of LED electrostatic problem

Time:2015-08-22Print this paper

    Strong red LED antistatic ability


    LED PN junction is the basic structure , but because of different materials , the antistatic ability is different .


    Red, orange, yellow LED materials used primarily with GaAs and GaP mixed crystal GaAsP. These compound semiconductor bandgap between 1.8-2.2eV, PN junction easily doped low resistive material , better conductive properties which , when met , when the electrostatic charge can be more easily freed , it would be better antistatic ability .


    Green, blue LED antistatic ability is weak


    Green , blue LED PN junction near the InGaN material or AlGaNlGaN, its band gap of 3.3eV, than red, orange, yellow LED material about 50% larger , relatively high resistivity .


    Coupled with this type of LED with high resistance substrate is a sapphire (Al2O3) or silicon carbide (SiC) is made , the electrical conductivity and thermal resistance are poor.


    Al2O3 substrate such as a blue LED PN junction electrode is a V -shaped electrode ( commonly known as two-electrode type ) , the distance between the electrodes <300μm, once the accumulated electrostatic charge induction , there can easily occur in the self-excited discharge . Also, because the start- emitting layer AlGaNlGaN thin layer so that the electrostatic discharge breakdown easier .


    In the InGaN material SiC substrates , essentially L-shaped electrode vertical structure ( single electrode type , such as CREE) LED, the static mechanical mode voltage up to 600V or more, up under the Human Body Model 5000V ( although CREE official nominal 1000V ) . And generally Al2O3 substrates for LED devices are usually V-shaped electrode , its static mechanical mode voltage of about 400V or less only .


    Lights are more susceptible than chip static damage


    LED chips from the production process to all subsequent LED packaging , LED application products and the production has been static , etc. are threatened , but packaged LED lights from electrostatic damage than the chip is much smaller than the chance .


    Specific reasons are: small size of the chip , such as 12mil chip , its size is about 304mΧ304μmm, while the distance between the electrodes even smaller ( generally less than 100μm), if such a small LED chips in the electrostatic field , such a small potential difference between the pitch of the electric field is close to zero , the higher the electrostatic voltage is not formed , the phenomenon is generally not damaged static unless poor antistatic ability chip ; Further , LED chip electrodes of small area , more limits the possibilities of the LED chip electrostatic discharge electrode contact .


    The packaged LED lights , since the two are generally spaced about 2mm, the chip electrode spacing than 20 -fold in the static electric field than the chip in the static electric field is more prone to high voltage.


    Therefore , the probability of damage from electrostatic chip LED lights are much smaller than on the LED lights electrostatic protection measures should be more emphasis on the LED chips packaged in the form of static lights to be static assessment is more realistic simulation results with .


    Forward antistatic ability is stronger than the reverse


    LED reverse discharge of static electricity , discharge current is more concentrated than the forward , a greater power density and therefore the failure LED reverse discharge ESD threshold is much lower than the positive , that is, the electrostatic withstand voltage of the reverse LED is much lower, so the LED antistatic antistatic assessment of its ability to assess the reverse is the most reasonable .


    LED electrostatic breakdown after a common phenomenon


    Because LED electrostatic breakdown mechanism is the amount of Joule heat is generated due to the instantaneous pressure in the high power density applied to the PN junction of the chip , the chip so that a welded , generally firing an ' hole ' in the chip , and therefore LED is completely static electricity occurs after the breakdown :


    The most obvious is - LED reverse leakage current increases , or even close to a short circuit across the LED (about 10-30 ohms ) ;