A collimated and uniform UV-LED exposure unit (EU) applied in a printed circuit board is investigated by the light spread function (LSF) method. To accurately calculate the source-to-source distance of collimated UV-LED sources and achieve uniform irradiance in the exposure area, we propose a regional maximally flat condition for the LSF. This regional maximally flat condition contains irradiance information from multiple positions in two dimensions. To verify the design results, we built this parameter into optical simulation software and used it in our LSF method calculations. The obtained collimated UV-LED EU results show uniformity and average irradiance values of 98.23% and 43.32 mW/cm2, respectively. Thus, we can conclude that the proposed LSF method is effective for achieving a uniform irradiance distribution.