LED module with hermetic seal of wavelength conversion material
View Patent ↗An LED module includes a substrate having a high thermal conductivity and at least one LED die mounted on the substrate. A wavelength conversion material, such as phosphor or quantum dots in a binder, has a very low thermal conductivity and is formed to have a relatively high volume and low concentration over the LED die so that the phosphor or quantum dots conduct little heat from the LED die. A transparent top plate, having a high thermal conductivity, is positioned over the wavelength conversion material, and a hermetic seal is formed between the top plate and the substrate surrounding the wavelength conversion material. The LED die is located in a cavity in either the substrate or the top plate. In this way, the temperature of the wavelength conversion material is kept well below the temperature of the LED die. The sealing is done in a wafer level process.
1. An LED module comprising:
a substrate having a first thermal conductivity;
a plurality of LED dies electrically and thermally mounted on the substrate, wherein the LED dies are connected in parallel;
a wavelength conversion material having a second thermal conductivity substantially lower than the first thermal conductivity, the wavelength conversion material located overlying the LED dies;
a light transmitting top plate having a third thermal conductivity greater than the second thermal conductivity, the top plate being positioned over the wavelength conversion material; and
a hermetic seal formed by a sealant material between the top plate and the substrate surrounding the plurality of LED dies and wavelength conversion material,
the LED module having first flat sidewall edges around its periphery, the top plate having second flat sidewall edges around its periphery, and the substrate having third flat sidewall edges around its periphery, wherein the second flat sidewall edges and the third flat sidewall edges coincide to form the first flat sidewall edges of the LED module due to the top plate and the substrate being sealed during a wafer level process and the wafer then singulated to form the LED module,
the plurality of LED dies being located in a reflective single cavity formed in the substrate, the cavity having walls that surround all the LED dies, wherein the wavelength conversion material overlies the LED dies and at least partially fills the cavity,
wherein the wavelength conversion material is deposited into the cavity using the cavity as a mold for the wavelength conversion material, and wherein the top plate has one or more openings formed in it which are located directly over the cavity for depositing the wavelength conversion material into the cavity after the hermetic seal is formed.
2. The module of claim 1 , wherein the top plate comprises glass and wherein the sealant material comprises glass that has been melted to affix the top plate to the substrate.
3. The module of claim 1 , wherein the sealant material comprises a metal solder, wherein the plurality of LED dies are bonded to a substrate electrode using the same metal solder, and wherein the hermetic seal is formed when the substrate is heated to melt the metal solder.
4. The module of claim 1 , wherein the top plate is hermetically sealed to the substrate as a wafer, and the wafer is singulated to form the LED module.
5. The module of claim 1 , wherein the top plate has optical features that redirect light emitted by the plurality of LED dies.
6. The module of claim 1 , wherein the cavity is one of a plurality of cavities in the substrate containing the wavelength conversion material, wherein each of the cavities is sealed so that a break in the hermetic seal of one cavity does not break the hermetic seal of another cavity.
7. The module of claim 1 , wherein the wavelength conversion material comprises at least one of phosphor particles in a binder or quantum dots in a binder.
8. The module of claim 1 , wherein heat generated by the plurality of LED dies is at least partially removed by thermal conduction of the substrate, the sealant material, and the top plate, and wherein a temperature of the wavelength conversion material is kept lower than a temperature of the LED die.