LED applications has been extended to various fields, including the LCD Backlight, Backlight phone, signal lights, art lighting, architectural lighting and stage lighting control, home lighting and other fields, according to DIGITIMES Reasearch survey, 2010 to 2015 the growth in demand of up to 30% , thereby promoting LED production capacity increased significantly. With the diverse and complex environment of LED application, LED downstream suppliers on the upstream grain quality requirements become increasingly stringent, such as LED static resistance test (ELectrostatic Discharge ESD) voltage requirements from 4kV, a gradual increase to 8kV in order to tolerate the harsh outdoor environment. Resistance to static testing of high-voltage LED to the LED die point measuring machine, pressing the development of key modules.
A variety of different modes of electrostatic environment, including the human body static electricity or mechanical electrostatic, both will have the LED to cause damage. When the electrostatic induction or directly touch the two pins of the LED on the potential difference will have a direct role in both ends of the LED voltage withstand value over the LED, the electrostatic charge in a very short period of time in the LED between two electrodes discharge, resulting in damage to the LED insulation parts, resulting in leakage or short circuit phenomenon. Solid State Technology Association JEDEC (Joint Electron Device Engineering Council) with JESD22-A114E, with JESD22-A115A, the development of human body electrostatic discharge mode (Human Body Model, HBM) and machine devices discharge mode (Machine model, MM) test specification to ensure the quality of LED products. Buy foreign high-voltage device with a charge-discharge switch circuitry, and integration of Prober and automated mobile platform, the main disadvantage of slow reaction speed (0 to 4kV rise time of 500ms), and did not consider the high-voltage insulation of the probe, so slow grain classification and testing of wave stability and lack of serious problems, often breakdown LED charge and discharge module, as shown in Figure 1, or the lack of high voltage test of the machine, still being high voltage electrostatic damage after delivery, directly affecting the quality of LED products. Plus 20 000 40 000 grain measurements on the wafer is often time-consuming and more than 1 hours, the need to shorten the detection time to increase capacity. Static electricity through the development of needle high speed and large dynamic range of LED wafer measurement module for high-speed multi-voltage switch high pressure to produce the component design, dynamic range control circuit with PID feedback control, the dynamic range of the high voltage (250V-8kV) and high-speed static test (80ms), as shown in Figure 2A and Figure 2B, to meet the demand for domestic LED industry to reach the purpose of reducing costs and key modules homemade.
Second, the LED wafer electrostatic measurements modular system architecture
In this paper the development of high speed and large dynamic range of the LED wafer electrostatic measurement module shown in Figure 3 for grain resistance to static voltage-wide detection test, according to the size of the LED resistance to electrostatic voltage, LED level classification. This static point measurement seized the entire module contains test high-speed multi-voltage switching high voltage to produce components, probe components, charge and discharge components, software classification component. Contact with the positive and negative electrodes of the test LED to move two probes of the test probe platform, high-speed multi-voltage switching high pressure to produce components of the electronic control according to the software program to set the human body electrostatic discharge mode or machine device discharge mode test voltage level, charge The discharge module to store the high voltage generator charge to treat measured LED static pressure test the classification component of the final software to display the static test results. Technology for existing domestic LED wafer electrostatic measurement module dynamic range (500V to 4000V) with foreign module voltage switching time is too slow (0V to 4kV rise time of about 500ms), designed for high speed and large dynamic range of LED wafer static measurement module, the output voltage can be covered by the specification static classification of the minimum voltage of 250V to the maximum voltage of 8000V large dynamic range; and reduce low-voltage switching to high voltage rise time of 80ms or less, to achieve high speed and large dynamic range of LED crystal The tablets online detection and classification purposes.
Design Considerations of the major components as follows:
A test probe assembly design part
The test probe components used to deliver voltage and current probes external insulation protection prevents the leakage current, thereby increasing the static measurement accuracy.
Insulation design is divided into divided into internal insulation and external insulation of the two categories. Within the insulation for the modules within the insulation. Including solid dielectric insulation and a combination of insulation of different media. Although the external atmospheric conditions, internal insulation basically no impact, but the aging of materials, high temperature, continuous heat and moisture and other factors internal insulation dielectric strength there are adverse effects, while internal insulation breakdown, its dielectric strength can not be self-healing. External insulation refers to work in direct contact with atmospheric conditions, the formation of a variety of different forms of insulation, including the exposed surface of the air gap and modular solid insulation. The salient features of the external insulation in the discharge stopped, the dielectric strength usually a rapid and full recovery, and has nothing to do with the number of repetitive firing. Closely related to the dielectric strength of the outer insulation and the external atmospheric conditions, atmospheric temperature, pressure, humidity, etc. will be affected by many factors; to the atmosphere, for example, the dielectric strength in the general atmosphere around 30kV/cm droplets exist about 10kV/cm, the temperature rose from room temperature to 100 degrees Celsius, the dielectric strength is reduced to 80%, so the design will be caused by the temperature and humidity to estimate material dielectric strength varies, and design pressure required to retain the safety spacing.
Probe insulation testing dielectric strength test to determine. The tests include a pressure test and puncture test two. The pressure test is to impose a certain voltage, the specimen after a period of time, whether the breakdown occurred as a judgment standard test whether or not qualified. The breakdown test voltage was gradually increased under certain conditions imposed on the specimen until the specimen breakdown occurred.
2 high-speed multi-voltage switching of high pressure to produce components with charge and discharge components
This component part of the design including the control loop stability and interference control, control loop stability including component model, stability conditions, loop stability testing. Interfere with the control method in order to reduce the parasitic capacitance, the geometric position of the size of the board parasitic capacitance value and the circuit board wiring line, the line width, the board must source material, to reduce line parasitic capacitance of the design, interference-prone point marked This shall identify the location for priority routing considerations, not easily disturbed line is the last wiring traces.
(3) the software component part
Control of the probe needle position, trigger the charge and discharge the high voltage generator module to treat the measured LED discharge and measured results show that the control input voltage charging is complete.
Third, the LED wafer electrostatic measurement module assembly and testing results
Completion of the high voltage generator AC voltage modulation circuit design shown in Figure 4, the use of high-voltage probe the actual measured AC voltage amplitude of the peak amplitude of peak 6.26kV-largest exchange: 3.13kV, testing and validation results of the DC voltage maximum value 8.08kV in 8kV voltage via a short-circuit the output short-circuit current tests on the discharge resistance: 1500 Ω + / – 1%, the peak current of 5.46A (theoretical value: 8000/1500 = 5.33). Verified in a static voltage 4Kv complete LED static point measurement module specifications and the following test conditions:
(1) at room temperature, and humidity, atmospheric environment
(2) probe: bandwidth greater than 1 GHz current probe
(3) charge capacitance: 100 pF + / – 10% (effective capacitance)
(4) discharge resistance: 1500 Ω + / – 1%
Repeated measurements the HBM short-circuit peak current results are as follows:
The peak current measurement of the theoretical value of 2.66A, one hour after the peak current of 2.70A, the offset of 1.5%, to meet the peak current of the test specification 2.40 ~ 2.96A @ 4kV and HBM load short rise time of 2.0 ~ 10ns @ 4kV.