Analysis of dead LED lights
As a general-purpose LED lighting, the current mainly by two: one SMD LED can be carried out SMT operation; the other is integrated and array of COB and copper substrate module. Of course, there are DOB, but today we do not discuss.
Dead lights, then it should be divided into true death or suspended animation.
Suspended animation is more common when the LED back when the LED and PCB between the virtual access. The Weld is better to find and solve. Through the point of testing and aging can be found in the location of Weld, and can be heated through the hot air gun or LED gun can be modified and replaced. Another kind of suspended animation, LED internal virtual connection or gold wire fracture but also next to each other. As shown in Figure 1, is a typical LED wire inside the virtual connection (has been disconnected, but still next to the LED or can be lit, but after a while because of the stress caused by the gel head disconnected from the dead lights) .
Really die, then the situation is more, but the common gold line break (that is, in Figure 1, such as broken head is not next to a true death). There is also an over-current lead to chip and gold wire burned, the visual is very obvious, as shown in Figure 2 below. Sum up to really die of several conditions: one is the line fault, may be caused by poor bonding line failure, may also be internal stress (thermal expansion and contraction of the force) lead to line failure; one is more than the necessary current and voltage Problem; there is a static breakdown LED problem (this failure mode visual effect is not obvious, the chip PN junction breakdown, the need for aging for some time to gradually die).
The most important thing is to ensure the reliability of the welding line, the reliability of the adverse consequences are fatal. First of all, to ensure stability of the machine, as well as welding mode, and some need to tail-pressing, or re-tail to add a tail. Second, is to ensure that wire and chip keys and compatibility. Previously we used 9999 pure gold, and now use K gold (60% gold), or alloy (8% gold) and CHIP PAD bond and the compatibility and welding strength need to be taken into account.
In addition, the relationship between the hardness of the glue, if the glue is too hard, then the stress (thermal expansion and contraction of the force) will pull off the chip. This failure mode is also more common. Why? Because silicone is too expensive, sealing is not good, more people tend to use hard silicone and epoxy resin as potting. Therefore, we choose packaging materials, we must take into account the stress and package matching, not too hard, suitable for use in the environment.
For example, now 9V1W 2835 as a bulb light source, the pin temperature TS often between 105-110 ℃. So for such a high temperature, the hardness of our packaging glue must be small, or over time due to excessive stress off the gold wire and die. Of course, if it is 0.06W of the LED, epoxy resin should be cheap and practical packaging glue, the impact of stress is not too great. As for the electrostatic protection, the electronics industry, almost all of the electronic devices need to be static protection, such as the establishment of the air shower, the body away with the charge, air humidification, equipment grounding, increase plasma fans and so on.