In these several years, SMD LED display types are applied more widely than that of DIP because of the excellent displaying effect of the former. Although SMD LED has such an advantage, the problem of death lamp exits in this field some times. For the death lamp, it means the LED lamps are off. Here is a photo of this problem:
How does the Death Lamp Occur?
There are many processes that may cause death lamp, for instance, SMD LED chip, LED chip packaging or LED display working period. After researching for the 5 raw materials of LED lamp, including SMD LED chip, LED holder, fluorescent powder, solid crystal glue, and bonding wire connection, we find that the last one of the bonding wire connection is one of the most important reasons to cause death lamp. Besides, as most of them are with cascade and parallel connection, this situation would affect other LED lamps.
There is another cause. The leakage current of LED lamps is too high to make the PN junction disabled, which causes death lamp. For this situation, other LED lamps are not affected.
Below is a drawing of inside connection of LED lamp:
A: The juncture of LED chip electrode and golden ball.
B: The juncture of the golden ball and the bonding wire.
C: The bonding wire.
D: The juncture of the 2nd solder joint and the bonding wire.
E: The juncture of the 2nd solder joint and the LED holder coating.
From the above drawing, we could see the C part (the bonding wire) is the key component to bridge the LED chip and the LED holder coating.
Below is the sectional view of LED death lamp caused by solder joint fracture:
In the market, there are 2 kinds of bonding wire during the LED chip packaging: copper wire and gold wire. For the copper wire, it is more widely applied because of its lower price. But compared with gold wire, there are 3 problems with copper wire packaging:
①The copper wire is much easier oxidized, thus causes the golden ball out of shape.
②During soldering with copper wire, the aluminum layer of the 1st solder joint would be damaged easier, especially for the layer with less than 1um thickness.
③Because it is not easy for the copper wire to bond with the LED holder, it could cause bad welding of the 2nd solder. Thus, there would be some risk during the application.
For gold wire, it is with the advantages of good thermal conductivity, good tenacity, good chemical stability, corrosion resistance. But correspondingly, its price is much more expensive than that of the copper wire.
How to Avoid Death Lamp Problem?
According to the above analysis, we could see the bonding wire material is essential for the death lamp problem. We suggest clients could choose better material like gold wire to make more stable products. As one of the essential part during the LED chip packaging, the pure gold wire could completely eradicate death lamp problem.
We welcome you to discuss more of this aspect.
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