Ultra-thin black polyimide film and method for preparing the same

A method for preparing an ultra-thin black polyimide film for coverlay, comprising the steps of:

• (1) polymerizing dianhydrides and diamines to form a polyamic acid solution;
• (2) preparing a first carbon black having a mean particle diameter of 1 to 5 μm and a second carbon black having a mean particle diameter of 0.1 to 0.99 μm using a mill machine, where the first carbon black and second carbon black are milled at a temperature from 20 to 40° C.;
• (3) dispersing the first carbon black and second carbon black into said polyamic acid solution to form a mixture, and delivering the mixture at a speed from 150 to 300 kg/hr from a T-die onto an endless belt to form a coating on the endless belt;
• wherein the endless belt is operated at a speed from 15 to 25 mpm;
• (4) thermally treating the coating to lead imidization;
• and
• (5) cooling to obtain the film for coverlay;
• wherein the film comprises 3 to 10 wt % of the first carbon black and 1 to 5 wt % of the second carbon black based on the total weight of the film;
• wherein the film has a light transmittance of 10% or less in the range of visible light, a gloss of 10 to 40%, and a thickness of 8 μm or less, and a coefficient of thermal expansion (CTE) of 10 to 20 ppm/° C.;
• and
• wherein one of the diamines is 1,4-phenylenediamine and the film comprises 20 to 30 mol % of 1,4-phenylenediamine based on the total diamines.