Wafer Level Package using Pre-Applied Anisotropic Conductive Films (ACFs)

Recently, wafer level package (WLP) has become one of the promising packaging technologies due to its advantages such as fewer processing steps, lower cost, and enhanced device performance compared to single chip packages. Many developments on new WLP design, materials and processes have been accomplished according to the electrical, mechanical performance and reliability requirement of the devices to be packaged.

For lower cost, higher performance and environmentally green packaging process, anisotropic conductive films (ACFs) flip chip assembly has been widely used such as ultra-fine pitch flat panel display (FPD) and general semiconductor packaging applications. However, there has been no previous attempt using ACFs on WLP. In this study, wafer level packages using pre-applied ACFs on an entire 6 inch wafer for flip-chip assembly on organic substrates have been investigated, and the effect of process parameters, such as ACFs lamination, wafer dicing, and ACFs flip chip assembly, on the ACF wafer level package performance were investigated. After ACF lamination on Au stud bumped 6 inch wafers, and subsequent singulation by diamond sawing, and then singulated chips were flip-chip assembled on an organic substrate using a thermo-compression bonding method. Au stud bumps were well assembled on Ni/Au pads of organic substrates.

ACF joints between Au stud bumps and substrate pads using ACF-WLP method showed stable bump contact resistance of 8~9 milliohms per a bump which is the same as the typical thermocompression-bonded ACF joint. Reliability of the ACF-WLP joints are under investigation. As a summary, new wafer level package method using pre-applied anisotropic conductive films was successively demonstrated on an organic substrate for flip chip assembly. Based on these results, the newly developed WLP using pre-applied ACFs can be widely used for many non-solder flip chip assembly applications such as LDI(LCD Driver ICs), CMOS image sensor chips, memory chips and so on.