a lid for a wafer - scale package includes a body having a bond area around a cavity defined by the body , an oxide layer atop the bond area and the cavity , and a reflective layer atop the oxide layer . the cavity has an angled sidewall where a portion of the reflective layer over the angled sidewall forms a mirror for reflecting a light . the lid further includes a solder layer atop another portion of the reflective layer over the bond area , and a barrier layer atop the mirror . the barrier layer is solder non - wettable so it prevents the solder layer from wicking into the cavity and interfering with the mirror . the barrier layer is also transparent to the light and has a thickness that either does not affect the light reflection or improves the light reflection .