Optimization and quantification of “mini-LED flip chip on board (COB) package” by self-alignment with anisotropic conductive paste (ACP) and pinhole free wafer direct technology

It is desired to mount millions of mini LED flip chips on board for local dimming backlight and RGB display from now on. But mini LED flip chip on board process is facing technical difficulties such as that requires to prefer between volume and quality in mini LED mount technology. If it prefers volume of mini LED mounting, it is necessary to patient for mounting accuracy. Because mini LED mounting at high speed has reached the limit of mechanical accuracy. So, it is necessary secondary offset correction system for mini LED flip chip mounting in high speed and good accuracy. Anisotropic conductive paste (ACP) is electric conductive adhesive agent which is combination of solder and resin. ACP connects mini LED flip chip and electric pad on substrate by soldering, and covers sensitive electrodes of mini LED and electric pad on substrate by resin as under-fill. ACP has a chemical reaction of strong self-alignment. It is possible to correct offset of mini LED by self-alignment of ACP. Self-alignment becomes effective during soldering and curing. This is secondary offset correction system for mini LED flip chip mounting. It quantifies self-alignment correction value and supply volume of ACP. Further difficulty is contamination It leaves a broken piece of blue sheet on sapphire glass or at electrodes by making pinhole when mini LED flip chip mounting. This is a serious problem and requires a cleaning process. In addition, the pinhole releases the tension on the blue sheet, and the mini LED shifts from its original position, which affects mounting accuracy. Unique technology of pinhole less mini LED flip chip mounting can solve contamination and shift of mini LED together. Pinhole less mounting does not make any hole on blue sheet but can release mini LED from there. Mounting head of machinery push down mini LED with blue sheet to the mount position of substrate. Resin sticks mini LED and substrate by strong adhesive power and peels mini LED off from blue sheet. Pinhole less mounting can avoid any chip shift due to no pinhole exists. It quantifies balance of adhesive power and supply volume of ACP. And also, it compares and quantifies adhesive power of soldering and ACP.