An illuminator ( 1 ) has bare semiconductor die light emitting diodes ( 7 ) on pads ( 11 ) of Ag/Ni/Ti material. A Si wafer ( 13 ) has a rough upper surface, and this roughness is carried through an oxide layer ( 12 ) and the pads ( 11 ) to provide a rough but reflective upper surface of the pads ( 11 ), thus forming a diffuser. Epoxy encapsulant ( 9 ) is deposited in a layer over the diodes ( 7 ) and the pads ( 11 ), and it is index matched with a top diffuser plate ( 8 ) of opal glass.
1. A method of producing an illuminator comprising the steps of:
providing a base layer of substrate material having a rough upper surface;
applying a top layer of substrate reflective material over the base layer so that surface roughness of the base layer upper surface is carried through to the top layer upper surface;
etching the top layer to define pads;
placing light emitting diodes in the form of bare semiconductor die on the substrate; and
applying encapsulant over the diodes and the substrate.
2. A method as claimed in claim 1 , wherein the base layer comprises silicon.
3. A method as claimed in claim 2 , wherein the base layer further comprises silicon dioxide.
4. A method as claimed in claim 3 , wherein the silicon is a wafer having a rough upper surface, and the silicon dioxide is grown on said rough upper surface.
5. A method as claimed in claim 1 , wherein the top layer comprises Ag.
6. A method as claimed in claim 1 , wherein the pads have a size such that the ratio of footprint of the diodes to that of the pads is equal to or less than approximately 1:50.