MULTICHIP LIGHT EMITTING DIODE (LED) AND METHOD OF MANUFACTURE
The present invention provides a multichip LED and method of manufacture in which white light is produced. A plurality of electrically interconnected LED chips is selected for conversion of light to white light. The LED chips comprise: a blue LED chip, a red LED chip, a green LED chip, and a target LED chip whose light output is converted to white light. A wavelength of a light output by one or more of the plurality of chips will be measured. Based on the wavelength measurement, a conformal coating is applied to the one or more of the LED chips. The conformal coating has a phosphor ratio that is based on the wavelength. The phosphor ratio is comprised of at least one of the following colors: yellow, green, or red. Using the conformal coating, the light output of the target LED is then converted to white light.
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This application is a divisional and claims the benefit of, co-pending and co-owned U.S. patent application Ser. No. 12/750,823, filed Mar. 31, 2010. The subject matter of the aforementioned patent application is related, in certain aspects, to the subject matter of the present invention. The disclosure of this patent application is therefore incorporated by reference in the specification of the present invention.
FIELD OF THE INVENTIONThe present invention generally relates to LEDs. Specifically, the present invention relates to the manufacture of multichip LEDs to produce white light.
BACKGROUND OF THE INVENTIONAs LEDs continue to grow in popularity as an efficient technological approach, the need for continued advancement grows as well. Along these lines, obtaining white light output from LEDs is not only needed, but also difficult to achieve. Many approaches in the past have attempted to find new ways to obtain white light. However, many of these approaches perform such processing at the chip level instead of at the wafer level. Such an approach can result in chip waste. Moreover, none of the existing approaches vary phosphor ratios based on an underlying device measurement (such as a wavelength of a light output). In view of the foregoing, there exists a need for an LED and associated method of manufacture that addresses the deficiencies of the related art.
SUMMARY OF THE INVENTIONIn general, the present invention provides a multichip LED and method of manufacture in which white light is produced. Specifically, a plurality of electrically interconnected LED chips (e.g., interconnected via red metal wire) is selected for conversion of light to white light. In a typical embodiment, the LED chips comprise a blue LED chip, a red LED chip, a green LED chip, and a target LED chip whose light output is converted to white light. A wavelength of a light output by one or more of the plurality of chips will be measured. Based on the wavelength measurement, a conformal coating is applied to the one or more of the LED chips. The conformal coating has a phosphor ratio that is based on the wavelength. Moreover, the phosphor ratio is comprised of at least one of the following colors: yellow, green, or red. Using the conformal coating, the light output of the target LED is then converted to white light. In a typical embodiment, these steps are performed at the wafer level so that uniformity and consistency in results can be better obtained. Several different approaches can be implemented for isolating the coating area. Examples include the use of a paraffin wax, a silk screen, or a photo resist. Regardless, this approach allows multiple chips to be treated simultaneously.
A first aspect of the present invention provides a method for manufacturing a multichip light emitting diode (LED chip), comprising: providing a plurality of LED chips in electrical contact with each other; applying a conformal coating to at least one of the plurality of LED chips, the conformal coating having a phosphor ratio that is based on a previous measurement; and converting a light output of a target LED chip of the plurality of LED chips to white light using the conformal coating.
A second aspect of the present invention provides a multichip light emitting diode (LED), comprising: a plurality of LED chips in electrical contact with each other, the plurality of LED chips comprising a blue LED chip, a red LED chip, a green LED chip and a target LED chip; a conformal coating applied to at least one of the plurality of LED chips, the conformal coating having a phosphor ratio that is based on a previous measurement; and wherein a light output of the target LED chip is converted to white light using the conformal coating.
A third aspect of the present invention provides a multichip light emitting diode (LED), comprising: a plurality of LED chips in electrical contact with each other, the plurality of LED chips comprising a blue LED chip, a red LED chip, a green LED chip, and a target LED chip; wherein the conformal coating applied to at least one of the plurality of LED chips, the conformal coating having a phosphor ratio that is based on a previous measurement, wherein a light output of the target LED chip is converted to white light using the conformal coating; and wherein the plurality of LED chips are interconnected with a red metal line.
These and other features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings in which:
The drawings are not necessarily to scale. The drawings are merely schematic representations, not intended to portray specific parameters of the invention. The drawings are intended to depict only typical embodiments of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements.
DETAILED DESCRIPTION OF THE INVENTIONIn general, the present invention provides a multichip LED and method of manufacture in which white light is produced. Specifically, a plurality of electrically interconnected LED chips (e.g., interconnected via red metal wire) is selected for conversion of light to white light. In a typical embodiment, the LED chips comprise a blue LED chip, a red LED chip, a green LED chip, and a target LED chip whose light output is converted to white light. A wavelength of a light output by one or more of the plurality of chips will be measured. Based on the wavelength measurement, a conformal coating is applied to the one or more of the LED chips. The conformal coating has a phosphor ratio that is based on the wavelength. Moreover, the phosphor ratio is comprised of at least one of the following colors: yellow, green, or red. Using the conformal coating the light output of the target LED is then converted to white light. In a typical embodiment, these steps are performed at the wafer level so that uniformity and consistency in results can be better obtained. Several different approaches can be implemented for isolating the coating area. Examples include the use of a paraffin wax, a silk screen, or a photo resist. Regardless, this approach allows multiple chips to be treated simultaneously.
A wavelength distribution exists due to an EPI in-line MOCVD (metal organic chemical vapor deposition) process drift and facility deviation of the LED chip between each chip within a LED wafer.
Therefore, only when the combination ratio of the fluorescent substance applied according to the wavelength of the chip is appropriate, the same target white chip implementation is possible. In the chromaticity diagram of
If the combination ratio of the coating film (fluorescent substance plus silicon) is identical for α, β, γ in which the chips are different wavelengths, then the white target color output coordinate of the three chips will be different. There is a difficulty in the BLU (back light unit), and a lamp in the LED application with the color dispersion occurrence in the product configuration if the white color output coordinate is changed. The process is implemented at the discrete chip level (not the wafer level) in the coating process of the fluorescent substance in regard to this kind of a problem (binning problem) in the LED PKG (package) process. Before implementing the dispensing process of coating the fluorescent substance, the sorting (or ranking) is made of the chips for each wavelength of the blue light output from the chips.
Referring now to
First, because of the thick coating film (over the minimum 300 um) of the fluorescent substance plus silicon, the optical mean free path is changed according to the LED chip surface location, and the color deviation is caused (in other words, binning phenomenon). When it designs optically, this color deviation occurrence brings many elements.
Second, the fluorescent substance coating process is not conducted at the wafer level, but is done at the chip level. As a result, the separate package material and process cost are additionally generated. Moreover, the chip cost of the inferior chip is generated by the white color output coordinate deviation after the package process. The sorting process is classified with chips within the wafer accompanied according to the same wavelength band because the wavelength distribution is quantified in advance according to the chip level coating. In this case, the long process time and equipment investment cost, etc., are generated. The separate sorting process is unnecessary if the fluorescent substance application process of each unit chip is conducted at the wafer level. Since it is not the package level, and the white color output coordinate is already obtained from the unit wafer level, the separate package process and material cost are not generated in addition to the inferior chip performance variation.
As indicated above, under the present invention, the white light-emitting diode manufacturing method performs the white light-emitting diode manufacturing process in the wafer level differently than the chip level packaging method. In particular, in the described lower-stage wafer level, after the wavelength data of each chip is measured in advance in order to control the fluorescent substance (yellow, blue, green) combination ratio, in which it is appropriate for each unit chip for the corresponding for each wavelength, accurately and radiate the white light in the wafer level according to each chip, the appropriately coated film is made with fluorescent substance plus silicon by using the dispensing method. In this way, the fluorescent substance conformal coating in which it has the thickness fixed, and is thin in the chip surface, is the basis of the possible method (chip level conformal coating: CLCC). In the present invention, the meaning of the wafer level points to the wafer state that discrete chips do not occur before the dicing process.
In
As seen in
These techniques will not be applied in the context of a plurality or an array of LED chips. Referring to
Regardless, referring now to
Referring to
The foregoing description of various aspects of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed and, obviously, many modifications and variations are possible. Such modifications and variations that may be apparent to a person skilled in the art are intended to be included within the scope of the invention as defined by the accompanying claims.
Referring to
The foregoing description of various aspects of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed and, obviously, many modifications and variations are possible. Such modifications and variations that may be apparent to a person skilled in the art are intended to be included within the scope of the invention as defined by the accompanying claims.
Claims
1. A method for manufacturing a multichip light emitting diode (LED chip), comprising:
- providing a plurality of LED chips in electrical contact with each other;
- applying a conformal coating to at least one of the plurality of LED chips, the conformal coating having a phosphor ratio that is based on a previous measurement; and
- converting a light output of a target LED chip of the plurality of LED chips to white light using the conformal coating.
2. The method of claim 1, the previous measurement comprising a measurement of a wavelength of the light output by the plurality of LED chips.
3. The method of claim 1, the plurality of LED chips comprising:
- a blue LED chip;
- a red LED chip;
- a green LED chip; and
- the target LED chip whose light output is converted to white light.
4. The method of claim 1, further comprising isolating an area of the plurality of LED chips to which the conformal coating is applied.
5. The method of claim 4, the area being isolated using paraffin wax.
6. The method of claim 4, the area being isolated using a silk screen.
7. The method of claim 4, the area being isolated using a photo resist.
8. The method of claim 1, the conformal coating having a phosphor ratio comprised of at least one of the following colors: yellow, green, or red.
9. The method of claim 1, the plurality of LED chips being disposed on a wafer, the conformal coating being applied to the wafer.
Type: Application
Filed: Mar 5, 2013
Publication Date: Mar 20, 2014
Applicant: Lightizer Korea Co. (Seoul)
Inventor: Byoung gu Cho (Seoul)
Application Number: 13/785,187
International Classification: H01L 25/00 (20060101); H01L 33/44 (20060101);