This application note provides basic information about flat SMT LED potting in display and signage applications to provide an introduction and description of the materials used, the appropriate equipment and process details. In addition, this article provides an overview of the typical display configuration, the impact of different LED types on the system, and the challenges. Finally, the results of the selected environmental tests are given to demonstrate their impact and the advantages of the potting protection method.
Introduction
With the advent of the digital age, outdoor signs and displays are becoming more common. Today, these electronic signs can be seen in stadiums, while street billboards and billboards are found throughout urban buildings, bus stops, gas stations, etc. (Figure 1). Because these applications are mostly related to the outdoor environment, electrical components including LED gussets must be protected.
Figure 1: Typical example of a display
There are some challenges in display and signage applications due to advances in technology and the shift from plug-in to surface mount (SMT) LED technology. One of the main topics discussed in this paper is the protective materials and methods for SMT LEDs used in outdoor displays. Specifically, LED height reduction, pixel pitch reduction, coating material selection, and coating methods have led us to continually explore appropriate protection methods. However, the actual potting tests performed by OSRAM Opto Semiconductors combined with environmental testing prove that these challenges can be solved.
The basic structure of the LED display
In most cases, large outdoor displays or signage consist of multiple modules with LEDs to outline the final product. To make an analogy, a single wall tile on a bathroom wall can be thought of as a display module, and their close arrangement is considered to be a complete display (Figure 2).
Figure 2: Basic structure of the LED display
These basic modules, also known as wall blocks, may vary in size, but are typically about 20 cm to 30 cm in length and width. According to the basic structure, they consist of a frame, a mask, and a printed circuit board with LEDs and other electronic components. Currently, masks are an integral part of display wall blocks because they act as sun blockers to increase overall contrast, especially in outdoor applications.
Advantages of SMT LEDs for displays and signs
Until recently, outdoor displays and billboards on the market were still dominated by old-style (also known as plug-in) LED technology. For such LEDs, the most appropriate description is for greater illumination intensity and long metal lead angles; while SMT LEDs are typically smaller and have no longer lead angles. There are many advantages to using SMT LEDs compared to plug-in LEDs.
Figure 3: A simplified diagram of two typical LED wall block configurations (left: plug-in LED; right: SMT LED)
One of the first advantages is technology. Most innovations and advancements in the LED industry occur at the SMT level. SMT LEDs offer the versatility of a larger package shape and are also available in multi-chip packages. The lead-in LEDs have an angle of up to 30 mm. The SMT LED package height may be less than 1 mm, while the plug-in LED lamp bead height is 10 mm and the diameter is approximately 3 to 5 mm. Therefore, the size of the LED limits the minimum spacing value for display applications. Another factor is the weight of the LED itself, which can have very different effects, especially in mobile display applications such as concerts and scene configurations.
Osram Opto Semiconductors' monolithic surface mount LEDs like DISPLIX Oval weigh only 13 mg, which is about 10 times lighter than typical lamp LEDs (Figure 4). Due to the differences in the height of the LEDs mentioned, the amount of protective material required is also different. A simple evaluation of the actual display wall tiles of size 24 x 24 cm and 16 x 16 pixels (pixel pitch 15 mm) compares the weight of the different types of LEDs with the required protective material.
Figure 4: Pictures and data of DISPLIX Oval & Blackprint with typical plug-in LEDs
For better comparison, the LED types of 3.5 mm plug-in, DISPLIX OVAL, DISPLIX Blackprint are selected, of which 3 LEDs are installed per pixel for plug-in type and DISPLIX Oval; for DISPLIX Blackprint (multi-chip RGB LED) Install 1 LED per pixel. Regarding potting materials, did you choose Dow Corning? SE-9187L, which is a single component black silicone. Depending on the configuration and LED size, it can be assumed that the typical package height of the DISPLIX Oval is 0.9mm, the DISPLIX Black is 1.9 mm, and the plug-in LED is 5 mm.
Specifically, this means that the weight of the lighting components can be reduced by up to 6 to 7 times with DISPLIX Oval and by up to 3 to 4 times with DISPLIX Black (based on the initial values ​​on the product specification) compared to typical plug-in LEDs. ). Transferring the evaluation of a wall block to a standard billboard measuring 14 feet x 48 feet (4.3 mx 14.6 m) and containing approximately 1084 blocks of the above wall tiles illustrates the important impact on the weight of the system (Figure 5).
Figure 5: Comparison of the effects of LED type and potting weight on system weight based on practical application examples
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