Light emitting diodes (LEDs) have many advantages over conventional light sources, such as incandescent, halogen and fluorescent lamps. These advantages include longer operating life, lower power consumption and smaller size. Consequently, conventional light sources are increasingly being replaced with LEDs in traditional lighting applications. As an example, LEDs are currently being used in flashlights, traffic signal lights, automotive taillights and display devices.
Among the various packages for LEDs, an LED package of interest is the plastic leaded chip carrier (PLCC) package for a surface mount LED. Surface mount LEDs in PLCC packages may be used, for example, in automotive interior display devices, electronic signs and signals, and electrical equipment.
A concern with the current process for producing PLCC packages is the problem of thermal expansion between different materials used in PLCC packages. Because materials expand and contact differently, thermal stress is created between different materials. A coefficient of thermal expansion (CTE) is often used to characterize how different materials expand or contract with changes in temperature.
Thermal stress may initiate mini cracks along interfacial surfaces. Thermal stress may also cause de-lamination between a die and a lead frame for example. Thermal cycling conditions (i.e. repeated changes in temperature) that occur during normal operation may propagate mini cracks to the extent a die that is attached to a lead frame may be lifted from the lead frame.
Silicone is commonly used as a material to encapsulate a light source in a PLCC because it is soft and pliable. Because silicone is soft and pliable, it is often used to reduce cracks in a PLCC package. However, silicone is not as useful as other materials for use as an optical lens due to its softness.
The drawings and description, in general, disclose a PLCC package 400 containing a reflector cup 202 in which four sides (210, 212, 106 and 208) of the reflector cup 202 are covered in an encapsulant 606. The encapsulant 606 has a domed portion that functions as an optical lens 402; the encapsulant 606 being an integral single piece structure. In one exemplary embodiment, the reflector cup 202 is fashioned, for example by stamping, on a first lead frame 102. The first lead frame 102 is attached to a plastic structural body 302 via first 204 and second 206 tongues. A second lead frame 104 is also attached to the plastic structural body 302. In this embodiment, a light source 602, for example an LED, is physically and electrically connected at the bottom of the reflector cup 202. A laser may also be used as a light source 602. In this exemplary embodiment, a wire bond 604 is connected to the light source 602 and the second lead frame 104.
The first 102 and second 104 lead frames provide electrical connections for the light source as well as leads for mounting. In this exemplary embodiment, the first 102 and second 104 lead frames also function as heat sinks to dissipate heat created by the light source 602.
After the light source 602 is mounted and electrically connected to the first 102 and second 104 lead frames, an encapsulant 606 fills a cavity 304 in the plastic structural body 302. Filling the cavity 304 in the plastic structural body 302 with the encapsulant 606 covers four sides (208, 210, 212 and 106) of the reflector cup 202. The encapsulant 606 also covers the wirebond 604 and the light source 602 in an exemplary embodiment. During the step of filling the cavity 304 of the plastic structural body 302 with encapsulant 606, a domed portion that functions as an optical lens 402 is formed on the PLCC package 400.
Because the encapsulant 606 covers four sides (208, 210, 212 and 106) of the reflector cup 202, a CTE mismatch between the encapsulant 606 and the plastic structural body 302 will be less likely to cause problems related to thermal stress. For example, the occurrence of de-lamination between the light source 602 and the first lead frame 102 due to a CTE mismatch between the encapsulant 606 and the plastic structural body 302, will be less likely. Also, the occurrence of de-lamination between the light source 602 and the first lead frame 102 due to a CTE mismatch between the encapsulant 606 and the first 102 and/or the second 104 lead frames, will be less likely. In addition, since the encapsulant 606 and the optical lens 402 are made of the same material, CTE mismatch problems between them are also less likely to cause problems related to thermal stress.
The first 204 and second 206 tongues that are an integral part of the first lead frame 102. The first 204 and the second 206 tongues are substantially rigid to reduce movement of the reflector cup 202. Reducing the movement of the reflector cup 202 lowers the probability of the wire bond 604 separating from either the light source 602 or the second lead frame 104. When the wire bond 604 separates from either the light source 602 or the second lead frame 104, the electrical connection is opened and the light source 602 will not function.
The first 204 and second 206 tongues in this exemplary embodiment are substantially rigid so as to reduce movement of the reflector cup 202. Reducing movement of the reflector cup, among other things, reduces the probability that the electrical connection between the reflector cup 202 and the second lead frame will be open. If the electrical connection between the reflector cup 202 and the second lead frame is open, the light source 602 will not function. In this exemplary embodiment an electrical connection is made by a wire bond 604.
Because the reflector cup 202 is surrounded on four sides by the encapsulant 606, a CTE mismatch between the encapsulant 606 and the plastic structural body 302 will be less likely to cause problems related to thermal stress. For example, the occurrence of de-lamination between the light source 602 and the first lead frame 102 due to a CTE mismatch between the encapsulant 606 and the plastic structural body 302, will be less likely. Also, the occurrence of de-lamination between the light source 602 and the first lead frame 102 due to a CTE mismatch between the encapsulant 606 and the first 102 and/or the second 104 lead frames, will be less likely. In addition, since the encapsulant 606 and the optical lens 402 are made of the same material, CTE mismatch problems between them are also less likely to cause problems related to thermal stress.
This sectional view also shows a light source 602 physically and electrically connected at the bottom of the reflector cup 202. The first lead frame 102 provides an electrical connection for the light source 602 as well as leads for mounting. In this exemplary embodiment, the leads shown are J-leads; other leads such as SOJ leads, gull wing leads, reverse gull wing leads and straight cut leads may be used in other embodiments of this invention.
Reducing the movement of the reflector cup 202 lowers the probability of the wire bond separating from either the light source 602 or the second lead frame 104. When the wire bond 604 separates from either the light source 602 or the second lead frame 104, the electrical connection is opened and the light source 602 will not function. Reducing the movement of the reflector cup 202 also lowers the probability of the light source 602 separating from the reflector cup 202.
Next as shown in box 906 a light source 602 is mounted and electrically connected at the bottom of the reflector cup 202. Next as shown in box 908 an electrical connection is made from the light source 602 to the second lead frame 104. In this exemplary embodiment, a wire bond 604 is used to make the electrical connection from the light source 602 to the second lead frame 104.
Next as shown in box 910 an encapsulant 606 is formed that surrounds the reflector cup 202 on four sides (106, 208, 210 and 212) while forming an optical lens 402. The encapsulant 606 also hermetically seals the light source 602. In this exemplary embodiment, the encapsulant 606 is an integral single piece structure.
Often reflective walls of a plastic structural body 302 are used to achieve a certain brightness needed for a specific application. In one exemplary embodiment, a white plastic material is used when forming a plastic structural body 302 in order to improve the brightness of the PLCC package 400.
In another exemplary embodiment, a black plastic material is used when forming a plastic structural body 302 in order to improve the contrast of the PLCC package 400.
The foregoing description 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 other modifications and variations may be possible in light of the above teachings. The exemplary embodiments were chosen and described in order to best explain the applicable principles and their practical application to thereby enable others skilled in the art to best utilize various embodiments and various modifications as are suited to the particular use contemplated. It is intended that the appended claims be construed to include other alternative embodiments except insofar as limited by the prior art.
Number | Name | Date | Kind |
---|---|---|---|
5444726 | Kitamura et al. | Aug 1995 | A |
5614735 | Kitamura et al. | Mar 1997 | A |
5825794 | Ogino et al. | Oct 1998 | A |
6061160 | Maruyama | May 2000 | A |
6335548 | Roberts et al. | Jan 2002 | B1 |
6344689 | Suzuki et al. | Feb 2002 | B1 |
6345903 | Koike et al. | Feb 2002 | B1 |
6355946 | Ishinaga | Mar 2002 | B1 |
6376902 | Arndt | Apr 2002 | B1 |
6407411 | Wojnarowski et al. | Jun 2002 | B1 |
6486543 | Sano et al. | Nov 2002 | B1 |
6603148 | Sano et al. | Aug 2003 | B1 |
6621223 | Hen | Sep 2003 | B1 |
D494938 | Kamada | Aug 2004 | S |
6809261 | Ng et al. | Oct 2004 | B1 |
6830496 | Lin et al. | Dec 2004 | B2 |
6849867 | Roberts | Feb 2005 | B2 |
6862305 | Nishiyama | Mar 2005 | B2 |
6879040 | Ng et al. | Apr 2005 | B2 |
6914267 | Fukasawa et al. | Jul 2005 | B2 |
6943433 | Kamada | Sep 2005 | B2 |
D511331 | Horinouchi et al. | Nov 2005 | S |
7030423 | Chang et al. | Apr 2006 | B2 |
7183588 | Chia et al. | Feb 2007 | B2 |
7211882 | Wang et al | May 2007 | B2 |
7238967 | Kuwabara et al. | Jul 2007 | B2 |
7242033 | Isokawa et al. | Jul 2007 | B2 |
7253448 | Roberts et al. | Aug 2007 | B2 |
7282740 | Chikugawa et al. | Oct 2007 | B2 |
7335522 | Wang et al. | Feb 2008 | B2 |
D563333 | Kim | Mar 2008 | S |
7365407 | Ng et al. | Apr 2008 | B2 |
7385227 | Mok et al. | Jun 2008 | B2 |
7435143 | Anderlini | Oct 2008 | B2 |
7462870 | Nakashima | Dec 2008 | B2 |
7499288 | Tanaka et al. | Mar 2009 | B2 |
7528414 | Huang et al. | May 2009 | B2 |
7595549 | Kamikawa et al. | Sep 2009 | B2 |
7635915 | Xie et al. | Dec 2009 | B2 |
7655958 | Sanmyo | Feb 2010 | B2 |
7663199 | Lee et al. | Feb 2010 | B2 |
7675145 | Wong et al. | Mar 2010 | B2 |
7709754 | Doogue et al. | May 2010 | B2 |
20020004251 | Roberts et al. | Jan 2002 | A1 |
20030001166 | Waalib-Singh et al. | Jan 2003 | A1 |
20030168720 | Kamada | Sep 2003 | A1 |
20040052077 | Shih | Mar 2004 | A1 |
20040227149 | Ibbetson | Nov 2004 | A1 |
20040256706 | Nakashima | Dec 2004 | A1 |
20050077623 | Roberts et al. | Apr 2005 | A1 |
20050133810 | Roberts et al. | Jun 2005 | A1 |
20050242708 | Keong et al. | Nov 2005 | A1 |
20050263784 | Yaw et al. | Dec 2005 | A1 |
20050269587 | Loh et al. | Dec 2005 | A1 |
20060054912 | Murakami et al. | Mar 2006 | A1 |
20060175716 | Nakashima | Aug 2006 | A1 |
20060186428 | Tan | Aug 2006 | A1 |
20060226435 | Mok et al. | Oct 2006 | A1 |
20070034886 | Wong | Feb 2007 | A1 |
20070063321 | Han et al. | Mar 2007 | A1 |
20070081313 | Tanaka et al. | Apr 2007 | A1 |
20070181901 | Loh | Aug 2007 | A1 |
20070257272 | Hutchins | Nov 2007 | A1 |
20080079019 | Huang et al. | Apr 2008 | A1 |
20080191235 | Wang et al. | Aug 2008 | A1 |
20080224162 | Min et al. | Sep 2008 | A1 |
20080258162 | Koung et al. | Oct 2008 | A1 |
20080273340 | Ng et al. | Nov 2008 | A1 |
20080290352 | Park | Nov 2008 | A1 |
20090032829 | Chew et al. | Feb 2009 | A1 |
20090283781 | Chan et al. | Nov 2009 | A1 |
20100072506 | Bae et al. | Mar 2010 | A1 |
20100072592 | Yong et al. | Mar 2010 | A1 |
20100133560 | Kim et al. | Jun 2010 | A1 |
Number | Date | Country |
---|---|---|
WO 2007000037 | Jan 2007 | WO |
Number | Date | Country | |
---|---|---|---|
20100264437 A1 | Oct 2010 | US |