The first step in final assembly is mounting the individual light-emitting diodes (LEDs) and any secondary optics onto the aluminum-based printed circuit board (MCPCB). For high-volume production, pick-and-place machines combined with reflow soldering are used. However, for DIY prototypes or small-batch repairs, a temperature-controlled soldering iron (set to approximately 320°C) is recommended for quick spot soldering. The operator must ensure that each LED is correctly oriented (cathode/anode matching the PCB layout) and that solder joints are shiny and concave – a dull or bulging joint indicates a cold solder or excess heat.
Using a 320°C iron is a practical compromise: it melts lead-free solder quickly enough to avoid prolonged heat exposure, which can degrade the LED chip or the MCPCB's dielectric layer. For example, when mounting 3W high-power LEDs, a skilled technician will pre-tin the pad, place the component with tweezers, and touch the iron for no more than 1–2 seconds per joint. After mounting, a visual inspection under magnification helps catch bridges or misalignments. This careful step directly influences the electrical reliability and thermal performance of the finished light.
