Ultra-Fine-Pitch Soldering of Mini-Micro LED - Solder Paste, Epoxy Solder Paste, Die Bond Solder Paste and Flux for Micro LED

In 1993, the high-brightness blue LED based on GaN was born. All three primary color LEDs of red, green, and blue used to realize full-color display have been discovered. The LED display has entered the era of full-color light. LED display has developed rapidly in terms of raw materials, technologies, display effects, and applications. The pixels of LED displays are shrinking at a rate of about 1mm per year. After nearly 30 years of rapid development, LED displays have replaced LCD and DLP applications in indoor command and monitoring centers, cultural media, radio and television studios, cinema screens, and smart cities.

With the continuous development of LED display technology, the market's requirements for better picture quality and visual experience make the miniaturization of pixel units an inevitable trend in high-end applications. The ultra-high-density microLED display has many features better than traditional display technologies, such as high brightness, high definition, high color saturation, seamless infinite splicing, etc. Due to the extraordinary advantages, the companies in the industry highly value the technology of microLED.

Mini/Micro LED display refers to the display screen with an LED pixel pitch smaller than 1.0mm. The pixel pitch of 80-175 inch 4K and 8K ultra-high-definition large-size LED display products is generally between 0.4mm and 0.8mm. Light-emitting chip with a small size has been regarded as a fine display category, and dot pitch has been classified into a sub-millimeter display category. Infrared touch, human-computer interaction, and applications, microLED have entered the fields of super TV, high-end business, remote video conference, high-end medical treatment, education, and exhibition.

There are three main packaging routes for microLED display, including SMD, IMD, and COB. Flip-chip COB is regarded as the development direction of micro-LED packaging due to the advantages of higher pixel density, smaller dot pitch, higher reliability, low cost, and huge development potential of ultra-large size and ultra-high pixel density.

However, flip-chip COB packaging has several technical problems. The flip-chip LED integrated packaging technology is mainly optimized and improved in terms of chip transfer, bonding, packaging, and optical design. In terms of chip soldering, small micro-pitch display chips and small pixel pitch are the factors that influence the selectivity of solder paste. Under the microLED display design, the size of the flip-chip is less than 200um, and the distance between the chip electrodes is less than 100um. Taking a 4milx 8mil (100um x 200um) chip as an example, its pad size is about 34um × 70um. According to the eight-ball principle, the diameter of a solder ball should not exceed 4.25um. As a result, T9 solder pastes cannot meet the soldering requirements because of reduced soldering reliability. However, Fitech’s T10 solder paste and epoxy solder paste for fine-pitch soldering can still fulfill the soldering requirements. The products meet the soldering requirements of LED display chips with a minimum pad size of 24um × 24um. In addition, the ball-attach process is appropriate for small-sized microLED display chips. The highly reliable no-clean flux, water-soluble flux, and epoxy flux produced by Fitech are effective for the mico LED chip soldering of pre-evaporated solder joints.