LED bonding structures and methods of fabricating LED bonding structures
View Patent ↗An LED chip includes a bond pad suitable for thermosonic or thermocompression bonding such as Sn, AuSn or other metals. The physical dimensions of the bond pad are selected to discourage or prevent solder squeeze-out during thermocompression or thermosonic bonding with or without flux. In some embodiments, an AuSn bond pad is designed to accept 30 g to 70 g of force or more without squeeze-out.
1. An LED chip comprising:
a conductive submount ( 24 );
a bond pad ( 31 ) having a total volume less than 3×10 −5 mm 3 conductively joined to said submount;
a first ohmic contact ( 18 ) on said bond pad opposite from said submount;
an epitaxial region ( 12 ) comprising at least a p-type layer ( 16 ) and an n-type layer ( 14 );
a conductive substrate ( 10 ) on said epitaxial region opposite said first ohmic contact; and
an electrode 22 to said conductive substrate opposite from said epitaxial region.
2. An LED chip as recited in claim 1 , wherein the bond pad comprises a metal solder.
3. An LED chip as recited in claim 1 , wherein the bond pad comprises Au, Au/Sn, Pb/Sn, Sn or Sn/Ag.
4. An LED chip as recited in claim 1 , wherein the bond pad has a total volume less than about 2.5×10 −5 mm 3 .
5. An LED chip as recited in claim 1 wherein the bond pad is formed in the shape of a parallelepiped having a generally square periphery.
6. An LED chip as recited in claim 5 , wherein the epitaxial region has a width of about 250 μm or more, and wherein the bond pad has a height of about 1.2 μm or less and a width of about 150 μm or less.
7. An LED chip as recited in claim 1 wherein the bond pad is formed in the shape of a cylinder.
8. An LED chip as recited in claim 7 , wherein the epitaxial region has a width of about 250 μm or more, and wherein the bond pad has a height of about 2 μm or less and a diameter less than one half the width of the epitaxial region.
9. An LED chip as recited in claim 8 , wherein the bond pad has a diameter of about 120 μm or less.
10. An LED chip as recited in claim 1 wherein the bond pad is formed in the shape of a polyhedron having opposing parallel faces and a star-shaped periphery.
11. An LED chip as recited in claim 10 , wherein the distance from an edge of the bond pad to an edge of the epitaxial region is at least about 50 μm.
12. An LED comprising: an LED chip according to claim 1 wherein the LED chip is bonded via the bond pad onto a submount, and wherein a shear strength of the bond between the LED chip and the submount exceeds 140 g.
13. An LED as recited in claim 12 , wherein the epitaxial region comprises a perimeter and the bond pad comprises a metal solder that is located entirely within the perimeter of the epitaxial region.
14. An LED as recited in claim 12 , wherein the total volume of the bond pad is less than the space volume between the ohmic contact layer and the submount.