Method of manufacturing a circuit board

A method for manufacturing a circuit board comprising the steps of:

• forming a lower conductor connection on a substrate;
• applying a photosensitive resin on the lower conductor connection and drying the photosensitive resin to form a photosensitive resin film;
• exposing the photosensitive resin film via hole a photomask for patterning, and developing and drying the photosensitive resin film so as to form an insulating resin film including a through-hole for defining a via hole, the through-hole having an inverted-trapezoidal cross-section taken in the direction of the substrate thickness and a sloped inner wall tilted at a tilt angle θ with respect to the substrate;
• and
• forming an upper conductor connection on the insulating resin film so as to connect the upper conductor connection to the lower conductor connection through the through-hole in the insulating resin film,
• wherein the photomask has a via hole pattern including a light-shielding pattern corresponding to the bottom of the through-hole, and pluralities of light-shielding strips and translucent strips which are arranged alternately and substantially parallel to one another, the pluralities of light-shielding strips and translucent strips corresponding to the sloped inner wall of the through-hole,
• wherein the tilt angle θ, which is determined using a polynomial approximation of degree n:
• f ⁡ ( s ) = θ = φ ⁢ ∑ k = 0 n ⁢ C k ⁢ s k
• wherein s is the width of the light-shielding strips and Φ is a constant relating to the exposure conditions, is in the range of about 0.17 rad<θ< about 1.40 rad.