Tag: LED display industry, dead LED, LED lamps lights out

It is often we encounter the situation of dead LED lamps are lights out. Especially in packing companies, application department and units or personal use might encounter this situation often. This is what people in the industry say that the phenomenon of dead LED.

Two reasons resulted in dead LED

Reasons 1: the PN junction failure is because the excessive leakage current of LED lamps. However, this will not have any impact on other LEDs.

Reason 2: the inside connection leads of LEDs are disconnected, which make LED lamps out of light because of no current through.

Verypixel believe that the key point is how to reduce or eliminate the situation of dead LEDs so that improve the quality and reliability of our products.

Here are several reasons & analysis caused the dead LED lamps.

1. Damage to LED chips caused by static electricity. The excessive leakage current of LED lamps cause PN junction failure. And it turns to be a kind of dangerous element- static resistance, which has caused thousands of electronic components damage and great loss. Therefore, it is a priority to protect electronic components from electrostatic damage in this industry. Any damages will happen during the process, so we need to pay highly attention to every step.

As we all know that our body can make a 3000v ESD, which is high enough to breakdown LED chips.  During the process of LED packing production, it is important to require the ground resistance as 4 Ohm and some other places require it as low as 2 Ohm. These are the rules in electronic industry, and every department should have record of all the tests. However, according to the general private enterprises, most of anti-static measures are substandard. This is why there are no records of ground resistance testing in many factories. Even though companies had made records, they were only test once a year or a few years a time.  Everyone knows this ground resistance testing is a very important job; it has to be done forth a year or once a month.

Soil resistance will change with different seasons; generally, the ground resistance is easier to reach in wet soil conditions like spring& summer. On the contrast, the ground resistance might exceed the set value in the dry seasons like autumn or winter.  Making record is to preserve the original data, so that we can have a good documented in the future days.

Staff should wear anti-static clothing, equipped with an anti-static wrist strap to protect LEDs from body static electricity damage. We are not suggesting the worker wear anti-static strap without grounded. Anybody breaks the rules will accept a warning or punishment. How much static electricity a human body has depends on the wearing materials, body physique and situation like when we undressed clothes in winter night it’s easy to see the discharge phenomenon, which generates 3kv electrostatic voltage.  However, na SiC substrate chip LED’s ESD is only 1100v and a Sapphire chip LED’s ESD is 500-600v.  Therefore, we have to always keep our body with universal precaution when you get a LED in hands. This is the only way to protect LEDs damaged from electrostatic.

If the package enterprises not act strictly accordance with the ground rules, they would take the consequences.  The same, if the application department not abbey the rules, it will also cause damages both in LEDs and economy. According to the requirements of LED standard brochures, the distance between leads and colloid should be more than 3-5mm or have them soldered.  But there are many factories can not operate by the rules, they always solder the LEDs with a 2mm ply, and this will also cause damages. Because exorbitant solder temperature have bad impact on chips or make it worse, such as decrease the luminance efficiency of the chips or destroy them.

Some of the small companies adopt manual soldering, using 40w soldering iron, which can not take good control of the temperatures then result in dead LED lamps owing to high weld temperature.

The expansion coefficient of LED leads under 150°C will be much bigger than in normal temperature. The gold spot inside the LEDs will cut out because of the high temperature and that I why it makes for lead lights.

2. Analysis the reasons why cut the inside LED leads would cause dead lights situation.

2.1 The direct causes of dead LED lights are imperfect technology and backward incoming inspection at package enterprise. Generally, we adopt bracket to pack LEDs. This kinds of bracket are made by copper or iron material precision mode, therefore, they are cost more than other metal materials in the competitive market. In order to reduce the manufacturing cost, many purchasing departments would use cold-rolled carbon steel for instead to press LED bracket row. Verypixel only offer quality LED display.

Iron bracket row should have to sliver on the surface. There are two intentions to sliver, the first one is to prevent the oxidation of rust; the other one facilitates to welding. It is an important step to keep the good quality of bracket, it relative to the life span of LED lamps. Strictly obey the standard procedure before plating. Making these preparations (Rust cleaning, oil removing, and phosphorization) step by step, controlling the current and the thickness of sliver probably. Most packing enterprises are unable to inspect the quality of plating, which gives the plating companies has the opportunity to take advantage of. In addition, packaging companies IQC are lack of members to test the bracket and there is no specific instrument to check the fastness and thickness of sliver coasting.

The editor has met many bracket rows storage at the warehouse for months and then gets rusty. From this we can notice how badly the quality of the electroplating. We can tell the bracket rows made out like this are certainly not for long-term use rather than write on the instruction can use for about 30-50 thousand hour.

It would be easier to cause dead light phenomenon in spring or summer day. We all know that summer is humidity season and are easier to get the mental rusty and then damage the LED components. Even though the LEDs are packed, the welding spot and support would also get apart caused dead LED lamps are all because of the thickness sliver coasting.

2.2 Every step should be operated strictly during the solid crystal process. Any little mistakes might cause damages to the LED lamps. Silver colloids has to be sticked appropriately, if you add more, it would cause short circuit; while you use less, the chip can not stick thus cause LEDs out of light because of poor soldering. Therefore, it requires manufacturers to stick the sliver colloids just right in the process of production.

Welding is also an important process in production. It has to take the pressure, timing, temperature and power into consideration. The other three factors should be adjustable except time is fixed.

For pressure it requires probably moderately because heavy press is easier to crush the chips and light press will cause poor soldering.  For temperature it is generally adjust to 280°C. And for power (Ultrasonic power regulation) it is also adjust in middle. In a word, when adjust the parameters of gold wire bonder; a qualified one is with a spring torque tester detects six grams.

In order to make sure the welding parameters are optimal, the gold wire bonder should be inspected and regulate every year. Besides, there are principles for wire curvature, for single- chip solder joints, the sagitta would be 1.5-5 chips ‘thickness and 2-3 chips’ thickness for double-chip solder joints. Curvature will cause the level of the quality of LED. It is easy to cause dead light during plating when the sagitta is too low, while it will decrease the current anti- shock under high sagitta.

3. Methods of identifying poor soldering dead light: make a LED leads heated to 200-300°C by a lighter; and then connect the positive and negative of an LED with a 3V button battery, if the LED was light and gradually turned to light out as it getting cold, which shows poor soldering. This experiment using the principle of mental thermal expansion and contraction. LED leads get expansion in heating condition and then put through the power it light normal. As the temperature gets low, the leads contracted, the inside spot cut out then the LED turns to light out.

Put two leads of dead LED together and soaking with oil of vitriol, so that the surface colloid dissolved. After that, using a magnifying glass or microscope to find out the problem comes from and make improvement prevent these things happened again.

However, we sometimes can encounter the dead light phenomenon happened during the electronic exhibition. There are two reasons of this, one is the poor technology of welding or the quality of bracket plating. Another is the leakage current of LED chip increased, cause LEDs light out. There are many manufacturers not add additional antistatic protection to LED products to low their cost. That’s why there comes out the phenomenon of sensor static damaged the chips. Especially easier to happened on rainy or thunder day.

Overall, there are many reasons caused LED dead lamps, can not being enumerated. It would happen in every step from package to application. How to improve the quality of LED products will become a highly attention and seriously research problem for relative enterprises. We have to operate the whole production in accordance with the ISO2000 Quality System.

Only in this way can we improve the quality of LED light products comprehensively. Only in this way can we make a longer life span and highly reliable products. Choosing varistor & PPTC components to protect the circuit; adding parallel connections; adopting constant current switches and add temperature protection are all the efficiency measures to improve the reliability of LEDs. Packaging companies and application enterprise can certainly put the quality of LED products to a new stage by operating strictly as the ISO2000 Quality System.