Light emitting diodes (referred to hereinafter as LEDs) represent one of the most popular light-emitting devices today. Due to its small form factor, an LED finds new application in electronic infotainment display systems, which may commonly be found in stadiums, discotheques, electronic traffic sign displays and infotainment boards along streets. Most of these electronic infotainment display systems are placed outdoors and thus require specifications, such as wider operating temperature, resistance to moisture, and longer lifetime. The electronic infotainment display systems used for displaying traffic information outdoors may be required to function in inclement conditions, such as rain, snow, or hot weather—as high as 60 degree Celsius in deserts.
Unlike conventional electrical appliances, electronic infotainment system may not have a housing to protect the electronic devices in the system. This is because a housing, even a transparent one, may affect the visibility of the infotainment system due to the reflection of light from the surface. In addition, an electronic infotainment display system may be so large that making a large enough protective housing may not be a cost effective or otherwise viable solution.
Therefore, for many such outdoor electronic system applications, silicone potting is commonly utilized to protect the electronic components from the elements. Silicone potting is a process in which all the electronics devices on the display are encapsulated with a potting agent. The potting agent may be made from silicone to prevent moisture from seeping into the electronic parts.
Illustrative embodiments by way of examples, not by way of limitation, are illustrated in the drawings. Throughout the description and drawings, similar reference numbers may be used to identify similar elements.
Referring to
The light source die 140 may be attached to one of the leads 110. The leads 110 not receiving the light source die 140 may accommodate wire bonds 142. The leads 110 provide electrical connection to external circuits (now shown). Each of the leads 110 may have two bends 161-162 defining each lead 110 into multiple sections 171-173. Each lead 110 has a first 165 end and a second end 166. The first end 165 may be adapted to accommodate the light source die 140 or a wire bond 142 or both of them.
As shown in
The body 120 may encapsulate a portion of the leads 110. For example, the first section 171 and the first bend 161 may be at least partially encapsulated by the body 120. The first section 171 may not be encapsulated entirely. At least a portion of the first section 171 may be exposed, so that the light source die 140 may be attached to the first end 165. The top portion 120a of the body 120 further defines a reflective element 150 which comprises a reflective wall 152 and a bottom reflective surface 154. The reflective element 150 defines a cup shape and may be configured to direct light emitted from the light source die 140 in a specific direction 129.
The reflective wall 152 and the bottom reflective surface 154 may be highly reflective. In some instances, the reflective wall 152 may be coated with a metallic material. The cup defined by the reflective element 150 may be filled with a transparent encapsulant 130. The trans-parent encapsulant 130 may be an epoxy material, a silicon material, or other similar transparent material that encapsulates the light source die 140. The transparent encapsulant 130 may be mixed with a wavelength transforming material, such as yellow phosphorus, red phosphorus or any other similar material. For example, to produce white light, the light source die 140 may be a green or a blue LED die and the wavelength transforming material may be a yellow phosphor material, which produces white light in combination with a blue or green LED.
The height of the light-emitting device 100 is represented by line 125. In some instances, for example for silicone potting purposes, a taller device may be desired. For the embodiment shown in
However, this approach may increase the depth of reflective element 150, which may be commonly referred to as the reflector cup's depth. This may be because the height 123 of the top portion 120a is also representing the depth of the reflective element 150. A deep reflector cup may not be desirable, because this may limit the viewing angle of the device 100. Viewing angle may be one of the key specifications of any light-emitting device 100. Typically, a larger viewing angle may be more desirable in most applications.
Alternatively, a taller device may be obtained by increasing the height 124 of the bottom portion 120b but maintaining the height 123 of the top portion 120a. This may not be desirable because increasing only the bottom portion 120b may affect the reliability performance. In addition, due to other requirements from the application aspect, such as for silicone potting processes, increasing the top portion 120a may be equally desirable to prevent spill over of the potting agent 806 (See
The body 220 further comprises a top portion 220a and a bottom portion 220b, which may be made from a top mold and a bottom mold, respectively. The top portion 220a further defines a reflective element 250 which comprises a reflective wall 252 and a bottom reflective surface 254. Top portions 256 of the leads 210 exposed on the bottom part of reflective surface 254 may also be part of the reflective element 250. The reflective element 250 is also known as reflector cup because the reflective element 250 usually defines a cup shape configured to direct light in a specific direction 229. A reflective material, such as any white, shinny, or metallic material may be coated on the reflective wall 252 or the bottom reflective surface 254 to increase reflectivity. However, certain materials that may be used to form the body 220, such as PPA and LCP may be sufficiently reflective that additional reflective coating may not be necessary.
The bottom portion 220b further defines a trench or a cavity 290, which may be used to accommodate potting agent 806 (See
Although the cross-sectional view shows only two leads 210, the light-emitting device 200 may have any number of leads 210. Each lead 210 comprises a plurality of bends 261-264, i.e. a first bend 261, a second bend 262, a third bend 263, and a fourth bend 264. The bends 261-264 may define angles 281-284 respectively, which may be between 45 and 135 degree. In the embodiment shown in
Each lead 210 may have a first end 265 and a second end 266. The first end 265 may be adapted to accommodate a wire bond 242 or a light source die 240, or both. The bends 261-264 further define each lead 210 into multiple sections 271-275. As shown in
In the embodiment shown in
The first bend 261 and the third bend 263 may be partially encapsulated inside the body 220. The fourth section 274, the fifth section 275 and the fourth bend 264 may be completely exposed externally for electrical connection to other external electronic components (not shown). Usually, the light-emitting device 200 may be soldered on to a PCB by means of the second end 266 or the entire fifth section 275.
Compared to the light-emitting device 100, the additional bends 261-264 provide additional flexibility to the designer to design a taller light source package without changing the ratio of the top portion 220a to the bottom portion 220b, and also without increasing the depth of reflective element 250 represented by line 221. This may be accomplished by increasing the height (represented by line 222) of the second section 272, accordingly.
For example, when the light-emitting device 200 is to be designed two times the package height 225, the height 223 of the top portion 220a and the height 224 of the bottom portion 220b can be increased proportionately. In order not to increase the reflective element's depth 221, the package designer may opt to only increase the height 222 of the second section 272 without changing the reflective element's depth 221.
It has been observed that having an unreasonably high or low ratio of the top portion 220a to the bottom portion 220b may yield lower reliability performance. Maintaining the ratio between 0.8 and 1.2 may produce optimized reliability performance. This may be due to the reason that there may be no covalent bonding between the encapsulant material that forms the body 220 and the leads 210. Having more bends 261-263 on the leads 210 encapsulated within the body 220 or partially within the body 220 may provide an improved mechanical interlocking means between the body 220 and the leads 210, thus improving the reliability performance.
In addition to the bends 261-263, having apertures 615 in the leads 210 (See
The depth 226 of the trench or the cavity 290 may be up to 80% of the height 224 of the bottom portion 220b. The existence of the trench or the cavity 290 may be beneficial in terms of reliability performance because it reduces the overall volume and weight of the body 220, thus reducing the internal stress within the light-emitting device 200.
In one embodiment of the light-emitting device 200, the height 225 of the light-emitting device 200 may be 3.5 mm, the height 223 of the top is portion 220a may be 1.6 mm. The height 224 of the bottom portion 220b may be 1.9 mm, while the depth 221 of the reflective element 250 may be 0.8 mm. The depth 226 of the trench or the cavity 290 may be 0.9 mm, while the width 227 of the light-emitting device 200 may be 4.5 mm. The height 222 of the second section 272 may be 0.8 mm, which may be more than two times the lead's 210 thickness of 0.2 mm.
Unlike the light-emitting device 200 in which the fifth section 275 may be located beneath the body 220 as shown in
First, each of the leads 510 in the light-emitting device 500 has three bends 561-563 instead of four bends 261-264, as in the light-emitting device 200 shown in
Second, unlike the light-emitting device 200, the first section 571 of all the leads 510 may be substantially embedded inside the encapsulant forming the body 520, such that only a small portion of the leads 510 may be left exposed and adapted to accommodate the light source die 540 or wire bond 542. The reflective element 550 comprises the reflective wall 552 and the bottom reflective surface 554.
The shape and length of each lead 610 may be configured as desired to accommodate design requirements. The leads 610 may be formed in the lead frame 601 by stamping, laser, etching, cutting or otherwise forming openings in the lead frame 601 leaving the leads 610 defined by the openings. Dimples or roughened areas 617 may be stamped or formed in the leads 610 to facilitate attachment of the light source dies 640. Apertures 615 may be stamped, cut, laser, etched, or otherwise formed in the leads 610. Folding lines 618 may also be stamped or formed indicating the location for the bends 661-664.
Next, all of the leads 610 may be bent twice as shown in
After the molding process, all the leads 610 may be separated from the lead frame 601 and may go through additional bending processes, in which the third and fourth bends 663-664, and the third, fourth an fifth sections 673-675 of the leads 610 may be formed. As shown in
The next steps may be die attach and wire bond processes. As shown in
Similarly, during the die attach and wire bond processes, the lead frame 601 may hold the entire structure in place. Next the light-emitting device 600 may go through an encapsulation process in which the reflective element 650 may be filled by a transparent encapsulant 630. The transparent encapsulant 630 can be any epoxy material or any silicon material. Finally, the lead frame 601 may then be completely separated and discarded, yielding a complete light-emitting device 600, as shown in
As shown in
The silicone potting process utilizes a potting agent 806 to encapsulate electronic devices, including the light-emitting devices 200 and the substrate 805. The potting agent 806 may include pourable insulating resins, such as epoxies, silicones, urethanes, hybrids, or any other similar material. The potting agent 806 may be cast into cavities containing electronic components to insulate, protect, and hold them in place.
The potting agent 806 may thus protect the electronic components from moisture, as well as mechanical stresses, such as shock and vibration. As shown in
For larger electronic infotainment display systems 800, other non-optical components such as drivers and controller packaged integrated circuits may be attached on the substrate 805. For such non-optical components, similar packaging to that shown in
Although specific embodiments of the invention have been described and illustrated herein above, the invention should not be limited to the specific forms or arrangements of parts so described and illustrated. For example, light source die described above may be LEDs die or some other future light source die. Likewise, although a light-emitting device with three die and six leads was discussed, the light-emitting device may contain any number of die or leads, as known or later developed without departing from the spirit of the invention, The scope of the invention is to be defined by the claims appended hereto and their equivalents.