SEMICONDUCTOR LIGHT EMITTING DEVICE

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to a methodology of forming optical lens on support structure for semiconductor light emitting device by applying low surface energy barrier band or surface onto said support structure. BACKGROUND OF THE INVENTION

A semiconductor light emitting device such as light emitting diode (LED) is a semiconductor light source which has been used for over the past few decades in a multitude of applications. Improvements to LEDs continue to be made in the area of efficiency, brightness as well as its manufacturing process. In a surface mount LED, there is a LED die being mounted on a support structure and being encapsulated in an optical dome lens to protect it from mechanical damage, environmental influence as well as to shape & extract light out of the LED die.

There are few methods which are mainly used in the industry to form optical lens. A common type of lens for a surface mount LED can be formed by using overmolding or compression molding process. This is a simple process to bond with a package in which the LED die is mounted. However, this process requires mold which is still relatively expensive and is only cost effective for high manufacturing volume.

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In addition to this, there are many disadvantages of using overmolding to form optical lens for encapsulation. One of them is the generation of piano area which obliquely creating issue during singulation process and hence reduce the speed of cutting, regardless of either using dicing or laser cutting, as a relatively soft material on top versus a hard material at the bottom has to be balanced. The blade used for dicing process need to be re-sharpened after certain cycles as encapsulant material tends to stick to the dicing blade. Furthermore, yield loss issue arises due to delamination of encapsulant material at piano area or chip off the support structure. Other disadvantages are light output loss due to coupling of light out to unwanted area through piano area as well as the unnecessary waste of expensive encapsulant material at piano area.

It would hence be extremely advantageous if the above shortcoming is alleviated by using a non-molded technology to form optical lens on support structure whereby said non-molded technology is being conducted by applying low surface energy barrier band or surface onto the support structure prior to adding of the encapsulant. Hence, no piano area can be seen in between units and at the same time it is a cost effectiveness methodology. SUMMARY OF THE INVENTION

Accordingly, it is the primary aim of the present invention to provide a methodology of forming optical lens for semiconductor light emitting device wherein molding machine is not required as it involves only normal dispensing to form an optical dome and hence the manufacturing cost can be reduced, besides creating much more flexibility in manufacturing.

It is yet another object of the present invention to provide a methodology of forming optical lens for semiconductor light emitting device wherein high surface energy or high thixotropic encapsulant and low surface energy barrier band is created.

It is yet another object of the present invention to provide a methodology of forming optical lens for semiconductor light emitting device wherein output yield of manufacturing said semiconductor light emitting device is increased due to the absence of piano area in between said devices.

It is yet another object of the present invention to provide a methodology of forming optical lens for semiconductor light emitting device which is flexible and hence creates fast turnaround in either designing and developing sample or actual products. It is yet another object of the present invention to provide a methodology of forming optical lens for semiconductor light emitting device wherein said methodology can be extended to develop as semiconductor light emitting module.

It is yet another object of the present invention to provide a methodology of forming optical lens for semiconductor light emitting device wherein said methodology can be applied for chip on board directly.

Other and further objects of the invention will become apparent with an understanding of the following detailed description of the invention or upon employment of the invention in practice.

According to a preferred embodiment of the present invention there is provided,

A methodology of forming optical lens (103) for semiconductor light emitting device (100) comprising steps of: i. providing at least a die (102) attached to a support structure (101); characterised in that said methodology of forming optical lens (103) for semiconductor light emitting device (100) further comprising the following steps after Step i: i. applying low surface energy material (104) onto said support structure (101); ii. dispensing encapsulant material onto said support structure (101) with said low surface energy material (104) to form at least one optical lens (103) over said die (102); iii. curing of said encapsulant (103) to convert the liquid mass to solid encapsulant (103). wherein said step of applying low surface energy material (104) can be done at any stage as long as prior to said step of dispensing encapsulant material.

In a second embodiment of the present invention, there is provided, A semiconductor light emitting device (100) comprising at least a die (102); at least an optical lens (103); a support structure (101) characterised in that said optical lens (103) is formed without the presence of piano area. In a third embodiment of the present invention, there is provided, A semiconductor light emitting module comprising at least a semiconductor light emitting device (100) comprises of at least a die (102), at least an optical lens (103) and a printed circuit board which also act as the support structure (101) characterised in that said optical lens (103) is formed without the presence of piano area. BRIEF DESCRIPTION OF THE DRAWINGS

Other aspect of the present invention and their advantages will be discerned after studying the Detailed Description in conjunction with the accompanying drawings in which:

FIG. 1-A shows a diagram of the conventional methodology of forming optical lens for semiconductor light emitting device by using overmolding process.

FIG. 1-B shows a diagram of the new methodology of forming optical lens for semiconductor light emitting device using non-molded technology. FIG 1-C and FIG 1-D shows a diagram on examples of application of low surface energy barrier band or surface onto said support structure. FIG. 2 shows a comparison on the presence of piano area for conventional methodology and new methodology.

FIG 3 shows a flowchart of the conventional methodology of manufacturing semiconductor light emitting device and light emitting module.

FIG 4 shows a flowchart of the new methodology of manufacturing semiconductor light emitting device.

FIG 5 shows a flowchart of the new methodology of manufacturing semiconductor light emitting module. DETAILED DESCRIPTION OF THE DRAWINGS

In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those or ordinary skill in the art that the invention may be practised without these specific details. In other instances, well known methods, procedures and/ or components have not been described in detail so as not to obscure the invention. The invention will be more clearly understood from the following description of the embodiments thereof, given by way of example only with reference to the accompanying drawings which are not drawn to scale.

Referring to FIG 1-A, there is shown a diagram of the conventional methodology of forming optical lens for semiconductor light emitting device by using overmolding process. A certain amount of encapsulant material is dispensed onto a mold which has indentations or cavities corresponding to a desired shape of lens. A plurality of dies are mounted onto a support structure which is placed at the upper part of the mold before the said mold is closed by applying pressure to force the said encapsulant material into contact with all mold areas. The said mold will be opened upon completion of overmolding process by having resulting structure with a molded lens over each dies. As mentioned, the existing overmolding process not only increases the manufacturing cost for preparing mold with predetermined shape, but also creates the piano areas which eventually causing loss of light output due to the light refracting effect.

Referring to FIG 1-B, there is shown a diagram of the new methodology of forming optical lens (103) for semiconductor light emitting device (100) using non-molded technology. For the new methodology, there is no need for the steps of preparing a mold for overmolding process, as needed in the conventional methodology. The said conventional step is being replaced by creating low surface energy barrier band or surface (104) onto a support structure (101) using low surface energy material. The idea is to create a high enough surface energy difference between the support structure (101) and the encapsulant

(103) used so that the encapsulant (103) will be retained in the lowest possible energy state to form the required optical lens (103) automatically. The surface energy of any substance is a direct manifestation of the intermolecular forces between molecules. In order to achieve this, the said low surface energy material is formulated in such a way to prevent wetting when the said encapsulant (103) is dispensed onto said support structure (101) which contains low surface energy barrier band or surface

(104) surrounded the said encapsulant (103) dispensed. There are certain fluorocarbon groups of optical grade silicone in the market which have low forces and can be applied for low energy barrier band or surface (104). In this invention, the barrier band (104) with surface energy in the range of 5 mN/ m -18 mN/ m could be used and preferably, it is at 15 mN/ m.

Referring to FIG 1-C and FIG 1-D, there is shown a diagram on examples of application of low surface energy barrier band or surface (104) onto said support structure (101). The said low surface energy barrier band or surface (104) can be in the shape of circular, square, rectangular or any other desired shape which will barricade the said encapsulant (103) from flowing further out and hence forms a desired shape of optical lens (103) . In addition, it is flexible to design the said low surface energy barrier band or surface (104) with different size and quantity based on the needs either for R&D purposes or for manufacturing purposes. It can be formed by any methods such as dispensing, drawn, stencil printing, inkjet printing, transfer stamping, dipping entire support structure (101) onto the solution, wafer fabrication photo resist process and etc onto the said support structure (101). Alternatively, the said low surface energy barrier band (104) could be stamped or molded as a separate piece of material and then adhere on the said support structure (101) by means of adhesives.

In the current invention, the said encapsulant (103) could be comprises of silicone, epoxy or hybrid of silicone and epoxy. The surface energy of the said encapsulant (103) shall be more than 20 mN/m. Here, the surface energy of the encapsulant (103) is increased by adding of high surfactant material or high thixotropic material in the said encapsulant (103).

The said encapsulant (103) is then being dispensed onto the said support structure (101) with low surface energy barrier band or surface

(104) directly to form the optical lens (103) shape required and cover over the die (102) upon completion. The said encapsulant (103) can be cured to convert the liquid mass to solid encapsulant (103) by either externally or within the dispensing process by means of applying heat, moisture, UV light or any combination of those above mentioned. Referring now to FIG 2, there is shown a comparison on the presence of piano area for conventional methodology and new methodology. By using of the conventional overmolding methodology, there is a presence of piano area with thickness of approximately 0.050 mm. During the overmolding process, the encapsulant material not only fills in the cavities of the mold but further extend across the region between and surrounding the cavities leading to the presence of piano area. By applying the current non-molded technology, no piano area could be observed after the completion of the process. With the absence of the piano area, the difficulties encountered during singulation process can be eliminated as well as reducing the light output loss due to light refracting effect. In addition to this, it was found that the thermal resistance for the said semiconductor light emitting device (100) produced by using current invention is low, and herein heat will be able to disperse through printed circuit board to heatsink much efficiently.

Referring now to FIG 3, there is shown a flowchart of the conventional methodology of manufacturing semiconductor light emitting device. Generally the manufacturing process comprises of Level 1 Process and Level 2 Process wherein the output of the said Level 1 Process is single unit of semiconductor light emitting device and the output for the said Level 2 Process is semiconductor light emitting module. The Level 1 manufacturing process begins by having the said die being mounted on the said support structure wherein the said support structure includes a substrate comprises of ceramic or silicon with metal leads or any other structure. Electrical connection may be formed by attaching a wire bond, preferably gold wirebonding to connect the said die to a contact portion of the said support structure. The said support structure is compression molded by pressing two pieces of mold against each other, with a predetermined amount of encapsulant material dispensed onto one part of the mold to form an optical lens over the said die. The support structure with lens formed is then removed from the mold. Upon formation of desired shape of lens over the said die, all the workpiece is proceeded for testing, followed by singulation. The said semiconductor light emitting device thereafter is tape and reel packaged for shipment.

In the Level 2 process, it begins by having solder printing for printed circuit board (PCB) and thereafter followed by SMT mounting wherein multiple units of output from Level 1 process are mounted onto the surface of PCBs. Other electrical components might also be SMT mounted at the same time. The boards are then conveyed to reflow soldering to melt the solder and to heat the adjoining surfaces of the board or module. After reflow soldering, the boards or module then proceed for testing and followed by singulation. The Level 2 process end with packaging of the semiconductor light emitting module for shipment.

Referring now to FIG 4, there is shown a flowchart of the new methodology of manufacturing said semiconductor light emitting device (100). Same as per conventional methodology, the manufacturing process begins by having the said die (102) being mounted on the said support structure (101). The said support structure (101) may be a ceramic substrate, silicon substrate or any type of support. Electrical connection is then formed by attaching a wire bond, preferably gold wirebonding to connect the said die (102) to a contact portion or metal pads of a support structure (101). In this current invention, a plurality of low surface energy barrier band or surface (104) is formed by low surface energy material on the said support structure (101) prior to the dispensing of encapsulant (103) which comprises of high surface energy material. The formation of this low surface energy band or surface (104) by low surface energy material can be performed at any of the process steps so long as it is prior to the dispensing process step. After the dispensing and curing process, upon formation of desired shape of lens (103) over the said die (102), all the workpiece is transferred for testing, followed by singulation. The said semiconductor light emitting device (100) therein is packaged in shipping tray or tube for shipment.

In another embodiment of the present invention, the said methodology of forming lens (103) can be applied on semiconductor light emitting module, which includes LED Chip On Board Device. The said Chip On Board substrate could be either Metal Core PCB, normal PCB (FR or CEM) with or without thermal via, polyimide flex board, glass substrate, silicon substrate, ceramic substrate, plastic substrate or leadframe etc. In this case, the support structure (101) is the PCB itself. Formation of optical lens (103) can be applied directly onto the said semiconductor light emitting module without the needs of mounting every single units of semiconductor light emitting device during SMT mounting. Hence the manufacturing process can be simplified to less steps as shown in Fig 5.

While the preferred embodiment of the present invention and its advantages has been disclosed in the above Detailed Description, the invention is not limited thereto but only by the spirit and scope of the appended claim.