Six common problems with LED display chips
Publish Time: 2024-07-22
LED chips are the heart of LED products. Their main function is to convert electrical energy into light energy. During use, LED display chips will also have various problems. Now let's take a look at the six common problems with LED chips!
01. Forward voltage reduction, dark light(1) One is that the electrode and the luminescent material are in ohmic contact, but the contact resistance is large, which is mainly caused by low concentration of the material substrate or electrode defects.(2) One is that the electrode and the material are in non-ohmic contact, which mainly occurs during the chip electrode preparation process when the first layer of electrode is evaporated, and the distribution position is caused by extrusion or clamping.In addition, the packaging process may also cause a decrease in forward voltage. The main reasons are insufficient curing of silver glue, contamination of the bracket or chip electrode, etc., resulting in large or unstable contact resistance.When the chip with a low forward voltage is tested at a fixed voltage, the current passing through the chip is small, thus showing a dark spot. Another dark light phenomenon is that the chip itself has low luminous efficiency and normal forward voltage drop.02. Difficulty in pressure welding(1) No sticking: Mainly because the electrode surface is oxidized or has glue(2) There is a loose contact with the luminescent material and the thickened wire layer is not firm, among which the thickened layer falls off.(3) Punching through the electrode: Usually related to the chip material. The material is brittle and the strength is not high. It is easy to punch through the electrode. Generally, GAALAS materials (such as high red and infrared chips) are easier to punch through the electrode than GAP materials.(4) Pressure welding debugging should be adjusted from the welding temperature, ultrasonic power, ultrasonic time, pressure, gold ball size, bracket positioning, etc.03. Luminous color difference(1) The luminous color of the same chip has obvious differences mainly because of the problem of epitaxial wafer material. The quantum structure of ALGAINP four-element material is very thin, and it is difficult to ensure the consistency of components in each region during growth. (The component determines the bandgap width, and the bandgap width determines the wavelength).(2) For GAP yellow-green chips, the luminous wavelength will not have a large deviation, but because the human eye is sensitive to the color of this band, it is easy to detect yellowish or greenish. Since the wavelength is determined by the epitaxial wafer material, the smaller the area, the smaller the color deviation concept, so there is a neighbor selection method in M/T operation.(3) Some GAP red chips have an orange-yellow luminescence color. This is because its luminescence mechanism is an indirect jump. Affected by the impurity concentration, when the current density increases, it is easy to produce impurity energy level shift and luminescence saturation, and the luminescence begins to turn orange-yellow.04. Thyristor effect(1) The light-emitting diode cannot be turned on under normal voltage. When the voltage is increased to a certain level, the current suddenly changes.(2) The reason for the thyristor phenomenon is that a reverse interlayer appears when the epitaxial wafer of the light-emitting material grows. The forward voltage drop of the LED with this phenomenon is hidden when IF=20MA is tested. During use, it is because the voltage between the two poles is not large enough, which shows that it is not bright. The test information instrument can be used to test the curve from the transistor diagram instrument, or it can be found through the forward voltage drop under a small current IF=10UA. If the forward voltage drop under a small current is obviously too large, it may be caused by this problem.05. Reverse leakage current IRUnder limited conditions, reverse leakage current is the basic characteristic of the diode. According to the conventional regulations of LED before, it refers to the reverse leakage current when the reverse voltage is 5V. As the performance of light-emitting diodes improves, the reverse leakage current will become smaller and smaller. The smaller the IR, the better. The cause is the irregular movement of electrons.(1) The quality problem of the chip itself may be caused by abnormal cutting of the chip itself.(2) Too many silver glue points, which may cause short circuit in severe cases. The reverse leakage caused by epitaxy is mainly caused by internal structural defects of the PN junction. During the chip manufacturing process, the side corrosion is not enough or there are silver glue threads attached to the test surface. It is strictly forbidden to use organic solvents to mix silver glue. To prevent the silver glue from crawling to the junction area through capillary phenomenon.(3) Static electricity damage. Epitaxial materials, chip manufacturing, device packaging, testing generally have a reverse leakage current of 10UA under 5V, and the reverse voltage can also be tested under a fixed reverse current. The reverse characteristics of different types of LEDs vary greatly: the reverse breakdown of ordinary green and ordinary yellow chips can reach more than 100 volts, while that of ordinary red chips is between 10 and 20 volts.(4) Improper control of wire bonding pressure causes chip collapse and IR increase.Solution(1) The amount of silver glue should be controlled within 1/3 to 1/2 of the chip height;(2) The static electricity of the human body and the machine should be controlled below 50V;(3) The pressure at the first point of the wire bonding should be controlled between 30 and 45g.06. Dead light phenomenon(1) The excessive leakage current of the LED causes the PN junction to fail, making the LED light not light up. This situation generally does not affect the operation of other LED lights.(2) The internal connection lead of the LED lamp is disconnected, resulting in a dead light without current passing through the LED. This situation will affect the normal operation of other LED lamps. The reason is that the working voltage of the LED lamp is low (the working voltage of the red, yellow and orange LED is 1.8v-2.2v, and the working voltage of the blue, green and white LED is 2.8-3.2v). Generally, they are connected in series or parallel to adapt to different working voltages. The more LED lamps are connected in series, the greater the impact. As long as one of the internal connections of the LED lamp is open, the entire string of LED lamps in the series circuit will not light up. It can be seen that this situation is much more serious than the first situation.The above is Shenzhen Desheng Display Technology Co., Ltd.'s explanation of the six common problems of LED display chips.Dear customers, our company supports the customization of various models of LED indoor and outdoor display screens, LED transparent screen grille screens, welcome to consult and customize! If you have any questions and needs, please consult and visit our website.Shenzhen Desheng Display Technology Co., Ltd. is dedicated to serving you!
