Integrating metals and plastics is essential for lightweight structures and efficient assembly in industries such as automotive and IT device manufacturing. This study investigated how laser micro-patterning enhances the interfacial bonding strength between these dissimilar materials in metal insert injection molding. Galvanized high-strength steel and polyphenylene sulfide (PPS) reinforced with 40% glass fiber were used as the metal and plastic materials, respectively. Four micro-patterns—circular, square, diamond, and hexagonal—were machined by laser on the bonding area at the end of the steel sheet. The effect of pattern spacing on bonding strength was evaluated by tensile shear tests on injection-molded specimens. The combined effect of laser processing and plasma surface treatment was also examined. For the square pattern, wider pattern spacing increased the bonding strength 2.2-fold, and for the hexagonal pattern the increase was 1.4- fold. Combining laser micro-patterning with plasma treatment enhanced the bonding strength by factors of 1.4 to 2.3. The effect of plasma treatment was greater for the square and diamond patterns than for the circular geometry.