Novel Wafer Level Packages using Anisotropic Conductive Pastes (ACPs) and NCPs

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 including ACFs have been accomplished.

For lower cost, higher performance and environmentally green packaging process, anisotropic conductive adhesives (ACAs) and non-conductive adhesives (NCAs) flip chip assembly has been widely used for ultra-fine pitch flat panel display (FPD) and general semiconductor packaging applications to replace solder bump flip chip. Previously wafer level packages using pre-applied ACFs on an entire 6 inch wafer for flip-chip assembly on organic substrates have been successfully demonstrated by our research group. 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.

In constrast, in this study, lower number of processing steps and lower cost WLP using ACPs method rather than ACFs will be demonstrated. By this new method, ACF-WLP processes such as ACF film formation and ACF lamination process can be eliminated resulting in simpler processing steps and lower cost.

In this study, new ACPs materials were formulated in terms of viscosity, thixotropy, and film formation capability to be applied on an entire wafer. ACF joints between Au bumps and substrate pads using ACP-WLP method will be investigated by comparing the previous ACF-WLP results and the typical thermocompression-bonded ACF joint.Reliability of the ACP-WLP joints will be also investigated.

As a summary, new wafer level package method using pre-applied anisotropic conductive pastes (ACPs) or NCPs will be demonstrated on an organic substrate for flip chip assembly. Based on these results, the newly developed ACPs-WLP can be widely used for many non-solder flip chip assembly applications such as LDI(LCD Driver ICs), CMOS image sensor chips, memory chips, Though Silicon Via(TSV) 3-D chip stack, and so on.