Low-Temperature Die Bond Solder Paste for Flip-Chip Mini-LEDs

2022-04-27

Low-Temperature Die Bond Solder Paste for Flip-Chip Mini-LEDs

Low-temperature die bond solder paste is used in mini-LED packaging, including backlight and direct display. The main applications include professional and commercial displays such as command centers and cinemas, as well as display backlight products such as TVs and tablets.

The expansion of mini-LED applications depends on yield improvement and cost reduction. A 5x10cm substrate requires 20,000 pixels (P0.5) which is equivalent to the package of 60,000 mini-LED RGB dies. It requires a continuous yield improvement in all aspects of the packaging process to meet the increasing demand for efficiency improvement and cost reduction.

It is well known that the 0408 mini LED RGB die has a size of around 210x105x100μm, and the pad size is about 60x85μm. The thermal expansion coefficient of the mini-LED die is different from that of the substrate. After the mini-LED dies undergo a reflow process with the substrate, the thermal expansion coefficient differences result in different mini-LED die and substrate expansion levels, which have a significant impact on the small substrate. The thermal expansion increases with temperature. Hence, the higher the temperature, the greater differences in thermal expansion between the die and the substrate. If reflow temperatures are high, it is easy to cause misalignment of the pads, resulting in a series of reliability problems such as open circuits and pseudo soldering.

Mini LED 低温倒装固晶锡膏介绍

A fundamental solution to handle reliability problems caused by thermal expansion coefficient differences is to use low-temperature solder materials to reduce the peak reflow temperature. SnBi/SnBiAg series solder is one of the famous low-temperature solders. The melting point of the alloy is 139°C, which is nearly 80°C lower than that of SAC305.

Due to limitations of ultra-fine powder manufacturing technology, SAC305 is the main alloy used in die bond solders with particle sizes of T7 and above in the market. Fortunately, the low-temperature flip-chip die bond solder paste for mini-LED developed by Fitech makes up for the blank of low-temperature lead-free ultra-fine solder. The low-temperature solder paste for die bond is made up of SnBiAg powder with the size of T7(2-11μm), T8(2-8μm), or T9(1-5μm) and a special flux, which effectively benefits the low-temperature soldering of fine-pitch die bond chip.