Graphic details how a small water droplet destroys an LED screen

How serious is a small waterdrop on LED products?
The moisture in the atmosphere penetrates into the interior of the packaging material of the LED lamp beads by diffusion. When the SMD LED device is mounted on the PCB through the patch, it is flowed into the reflow oven for reflow soldering. In the reflow zone, the entire device should be around 183 degrees 30-90s, the maximum temperature may be 210-235 degrees (SnPb eutectic), and the peak of lead-free soldering will be higher, around 245 degrees. Under the high temperature of the reflow zone, the moisture inside the LED device will expand rapidly, the matching between different materials of the device will be lost, and various connections will cause bad changes, which will cause the LED device to peel off or burst, so the device Electrical performance is affected or destroyed.
In the case of severe damage, the appearance of the device is deformed, cracks, etc., and in most cases, it is invisible to the naked eye. But as time goes by, the crack will crack more and more, and eventually the circuit will be bad.

How serious is a small waterdrop on LED products?

Scaling phenomenon

In order to detect that the LED lamp bead manufactured by the packaging factory has sufficient moisture resistance, avoiding the above-mentioned LED lamp bead manufactured by the inspection package to have sufficient moisture resistance and avoiding the above-mentioned lead stripping phenomenon, IPC/JEDEC defines a The standard "humidity sensitivity level" is as follows. Those who need it can also download J-STD-020D.1 from the official JEDEC website.
This document identifies the level of stress-sensitive classification of unsealed solid-state surface mount devices (SMD) that is used to determine the level of classification that should be used for initial reliability identification. Once the classification level is determined, SMD devices can take appropriate action during packaging, storage, and handling, and avoid thermal and mechanical damage during assembly solder reflow attachment and/or repair operations.

"Moisture Sentivity levels", from small to large, the smaller the number, the better the humidity resistance; the larger the number, the shorter the time it can be exposed to ambient moisture.
According to the MSL standard, the display factory and the engineering manufacturer can easily pick a qualified lamp, and have clear regulations on the packaging, storage and handling of the LED lamp in the subsequent processing. Because this standard has high requirements on the quality of LED lamp beads, there are very few packaging companies that dare to adopt. There are Curry and Nichia in foreign countries, and Mecca, Lehman and Lanke in China.
Take level 3 as an example. If the part is exposed to an environment within 30 ° C and 60% humidity, the storage time should not exceed 192 hours (including the 24-hour LED packaging factory). Exposure time, so the LED display factory only has 168 hours (=192-24) of workshop time), which means that after the level 3 LED components are removed from the vacuum package, it must be within 168 hours. Hit and finish Reflow. If Reflow cannot be completed within the specified time, it must be repacked, preferably after re-baking, because the time after re-baking can be reset to zero. If it exceeds the specified time, it must be re-baked before it can be used.
Destroying an LED display does not require strong storms, and a small drop of water is enough.