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. An illuminator comprising:
a substrate;
an array of pre-formed LED semiconductor diodes comprising an inorganic semiconductor material placed on the substrate;
a layer of encapsulant over the array of diodes and the substrate;
a lower diffuser comprising a rough, reflective upper surface of the substrate that is between the placed diodes;
an upper diffuser arranged above the layer of encapsulant, wherein the upper diffuser and the layer of encapsulant are index matched;
wherein the substrate comprises a Si layer having a rough upper surface, an Si02 oxide on the Si layer upper surface and having a rough upper surface, and at least one metal layer over the Si02 oxide layer and having a rough upper surface; and
wherein the substrate comprises conductive pads on which the diodes are placed.
2. The illuminator as claimed in claim 1 , wherein the upper diffuser is mounted on the encapsulant.
3. The illuminator as claimed in claim 2 , wherein the upper diffuser comprises an opal glass diffuser plate.
4. The illuminator of claim 1 , wherein the substrate comprises conductive pads on which the diodes are placed.
5. The illuminator as claimed in claim 4 , wherein the metal is Ag.
6. An illuminator as claimed in claim 5 , wherein the Ag is a layer over layers of Ni and Ti.
7. The illuminator as claimed in claim 4 , wherein the ratio of the footprint of the diodes to that of the pads is equal to or less than approximately 1:50.
8. The illuminator as claimed in claim 4 , wherein the pads are of rectangular shape in plan.
9. The illuminator as claimed in claim 8 , wherein there is a two-dimensional array of pads, and the diodes are connected in series along lines of the array between end rails.
10. The illuminator as claimed in claim 9 , wherein alternate lines of diodes are located at opposed ends of their pads.