BACKGROUND
Some light sources use light-emitting diodes placed on leads or lead frames. The lead frames and the light-emitting diodes are encapsulated to protect the light-emitting diodes and other devices in the light source. The encapsulant keeps the components from becoming dislodged and keeps contaminants from adversely affecting the components.
One problem with light sources is that the encapsulant delaminates from components within the light source and/or cracks. The delamination and cracking may cause damage to components within the light source. The delamination and cracking may also enable contaminants to enter the light source and cause the components to fail.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top perspective view of a portion of an embodiment of a light source with the encapsulant removed.
FIG. 2 is a side view of the light source if FIG. 1.
FIG. 3 is a top perspective view of a portion of a second embodiment of a light source with the encapsulant removed.
FIG. 4 is a side view of the light source if FIG. 3.
DETAILED DESCRIPTION
FIG. 1 is a top perspective view of a portion of a light source 100. It is noted that the light source may be encapsulated by an encapsulant as described in greater detail below and which is not shown in FIG. 1. The light source 100 includes a first lead frame 110 and a second lead frame 112. During operation of the light source, current conducts between the first lead frame 110 and the second lead frame 112 as described in greater detail below. Accordingly, one lead frame 110, 112 may be an anode lead and the other lead frame 110, 112 may be a cathode lead.
Additional reference is made to FIG. 2, which is a side view of the light source 100. Both the first lead frame 110 and the second lead frame 112 may extend from a mounting surface 114. The mounting surface 114 may support both lead frames 110, 112 and may contain or be in contact with an encapsulant as described below. In some embodiments, the light source 110 may not include a specific mounting surface 114. Rather, the mounting surface 114 may be a region from which the lead frames 110, 112 extend. The mounting surface 114 is used herein as a reference surface to describe the positions of the lead frames 110, 112.
The first lead frame 110 has a first portion 120 that extends from the mounting portion 114. The first lead frame 110 also has a second portion 122 that is connected to a cup portion 124. In some embodiments, the first portion 120 of the first lead frame 110 connects directly to the cup portion 124 without the need for the second portion 122. The second portion 122 of the first lead frame 110 of FIGS. 1 and 2 includes a horizontal section 130 and a vertical section 132, wherein the vertical section 132 is connect to the cup portion 124.
The cup portion 124 has a first side 136, sometimes referred to as a cup portion first side 136 and a second side 138, sometimes referred to as a cup portion second side 138. In the embodiments of FIGS. 1 and 2, the first side 136 is located opposite the second side 138. As shown in FIGS. 1 and 2, the cup portion first side 136 is connected to the second portion 122 of the first lead frame 110. More specifically, the cup portion first side 136 is connected to the vertical section 132 of the second portion 122 of the first lead frame 110. The second side 138 of the cup portion 124 is configured to receive or hold a light emitter, such as a light-emitting diode (LED) 140. The LED 140 may be adhered or bonded to the second side 138 of the cup portion 124 using conventional techniques. A wire 144 connects the LED 140 to the second lead frame 112. Thus, a closed circuit is created from the first lead frame 110, to the LED 140, to the wire 144 and to the second lead frame 112.
In the embodiment of the light source 100 of FIGS. 1 and 2, the first lead frame 110 includes an extension member 150. The extension member 150 may provide structural support within the light source 100. It is noted that, with the embodiments of the light source 100 of FIGS. 1 and 2, the extension member 150 does not connect to the cup portion 124. It is noted that conventional light sources are configured so that the extension member connects to the cup portion and there is no second portion 122. Accordingly, the extension member is the only component connecting the first lead frame to the cup portion. As described below, the configuration of conventional light sources allows the first lead frame to flex, which causes substantial movement of the cup portion. The flexing damages the light source as described below.
The lead frames 110, 112 and other components within the light source 100 are encapsulated by an encapsulant 158. The encapsulant 158 serves to keep contaminants from damaging or degrading the components of the light source 100. For example, the encapsulant keeps the lead frames 110, 112, the LED 140, and the wire 144 from being exposed to corrosive materials and corroding. In addition, the encapsulant 158 keeps the LED 140 and the wire 144 from being damaged by preventing them from contacting other objects. The encapsulant 158 adheres to the components and may be, among other compounds, an epoxy or silicon.
Delamination of the encapsulant 158 within the light source 100 can cause failure of the light source 100. Likewise, cracking of the encapsulant 158 may cause failure of the light source 100. Either situation may enable contaminants to enter the light source 100. In addition, delamination or cracking may cause the wire 144 to disconnect from the LED 140 or the second lead frame 112, which will cause the light source 100 to fail. Delamination or cracking may also cause the LED 140 to lift from the cup 124. Either the broken wire 144 or lifting of the LED 140 will cause an open circuit, which will cause the light source 100 to fail.
One cause of cracking and/or delamination in conventional light sources is due to stresses created by thermal expansion and contraction. As stated above, conventional light sources attach the cup portion, or its equivalent, to the extension member, or its equivalent. In some embodiments, the cup portion extends a distance from the lead frame via a member or the like. The conventional light sources do not have second portions 122 as described above. The configuration of conventional light sources causes the cup portion to be on a cantilever relative to the first lead frame. This cantilever increases the flex of the first lead frame to the cup portion, which increases the amount of movement of the cup portion when it undergoes thermal expansion and contraction. This movement in conventional light sources is relatively large in the region of the cup portion and the second lead frame, which causes cracks and delamination of the encapsulant in this region. Accordingly, conventional light sources are subject to failure by the wire breaking, the LED being removed from the cup portion, and other problems associated with delamination and cracked encapsulant.
The light source 100 described herein provides more stable components, which reduces the possibility of delamination or cracking of the encapsulant 158 due to movements of the components. As shown in FIGS. 1 and 2, the cup portion 124 is supported by the vertical section 132. Therefore, when the light source 100 is subjected to thermal stresses or other forces that cause flexing within the light source 100, the cup portion 124 may move a small amount relative to a cup portion of a conventional light source. The minimal movement of the cup portion 124 keeps the encapsulant from delaminating or cracking, which prevents the above-described problems.
A second embodiment of the light source is shown in FIGS. 3 and 4 and is referenced as the light source 200. The light source include a second lead frame 112, an LED 140, and a wire 144 that are substantially the same as those used in the light source 100 of FIGS. 1 and 2. However, the light source 200 includes a first lead frame 206 that differs from the lead frame 110 of FIGS. 1 and 2.
The lead frame 206 has a first portion 210 that extends substantially perpendicular relative to the mounting surface 114. A second portion 212 extends from the first portion 210. In the embodiments of FIGS. 3 and 4, the second portion 212 includes a horizontal section 214 and an angled section 216. The angled section connects to the first side 136 of the cup portion 124 at an angle θ. The angle θ is determined by design criteria. In some embodiments, the second portion 212 is a single member that connects between the first portion 210 and the first side 136 of the cup portion 124. The second portion 212 serves as a support to keep the cup portion 124 from moving in order to reduce the likelihood that the encapsulant delaminates or cracks.
In the embodiment of FIGS. 3 and 4, the light source 200 also includes a horizontal portion 220 that connects the top of the first portion 210 to the cup portion 214. The horizontal portion 220 is connected to the periphery of the cup portion 214 in the embodiment of FIGS. 3 and 4, however, the horizontal portion 220 could connect to other regions of the cup portion 214. The combination of the second portion 212 and the horizontal portion 220 serve to stabilize the cup portion 214 when the light source 200 is subjected to thermal stresses and other forces that cause flexing within the light source 200.
Patent Application
20100072592
