PLCC package with a reflector cup surrounded by an encapsulant

In an embodiment, the invention provides a PLCC package comprising first and second lead frames, a plastic structural body, a light source, an encapsulant, and an optical lens. The first lead frame comprises two tongues and a reflector cup. The first and second lead frames are attached to the plastic structural body. The light source is mounted and electrically connected at the bottom of the inside of the reflector cup. The light source is also electrically connected to the second lead frame by a wire bond. The reflector cup is surrounded on at least four sides by the encapsulant, the encapsulant having a domed portion that functions as the optical lens, the encapsulant being an integral single piece structure.

BACKGROUND

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.

DETAILED DESCRIPTION

The drawings and description, in general, disclose a PLCC package400containing a reflector cup202in which four sides (210,212,106and208) of the reflector cup202are covered in an encapsulant606. The encapsulant606has a domed portion that functions as an optical lens402; the encapsulant606being an integral single piece structure. In one exemplary embodiment, the reflector cup202is fashioned, for example by stamping, on a first lead frame102. The first lead frame102is attached to a plastic structural body302via first204and second206tongues. A second lead frame104is also attached to the plastic structural body302. In this embodiment, a light source602, for example an LED, is physically and electrically connected at the bottom of the reflector cup202. A laser may also be used as a light source602. In this exemplary embodiment, a wire bond604is connected to the light source602and the second lead frame104.

The first102and second104lead frames provide electrical connections for the light source as well as leads for mounting. In this exemplary embodiment, the first102and second104lead frames also function as heat sinks to dissipate heat created by the light source602.

After the light source602is mounted and electrically connected to the first102and second104lead frames, an encapsulant606fills a cavity304in the plastic structural body302. Filling the cavity304in the plastic structural body302with the encapsulant606covers four sides (208,210,212and106) of the reflector cup202. The encapsulant606also covers the wirebond604and the light source602in an exemplary embodiment. During the step of filling the cavity304of the plastic structural body302with encapsulant606, a domed portion that functions as an optical lens402is formed on the PLCC package400.

Because the encapsulant606covers four sides (208,210,212and106) of the reflector cup202, a CTE mismatch between the encapsulant606and the plastic structural body302will be less likely to cause problems related to thermal stress. For example, the occurrence of de-lamination between the light source602and the first lead frame102due to a CTE mismatch between the encapsulant606and the plastic structural body302, will be less likely. Also, the occurrence of de-lamination between the light source602and the first lead frame102due to a CTE mismatch between the encapsulant606and the first102and/or the second104lead frames, will be less likely. In addition, since the encapsulant606and the optical lens402are made of the same material, CTE mismatch problems between them are also less likely to cause problems related to thermal stress.

The first204and second206tongues that are an integral part of the first lead frame102. The first204and the second206tongues are substantially rigid to reduce movement of the reflector cup202. Reducing the movement of the reflector cup202lowers the probability of the wire bond604separating from either the light source602or the second lead frame104. When the wire bond604separates from either the light source602or the second lead frame104, the electrical connection is opened and the light source602will not function.

FIG. 1is an isometric drawing of a first lead frame102and second lead frame104in accordance with an exemplary embodiment of the invention. In this exemplary embodiment, the first lead frame102and the second lead frame104have J-leads. However, it is anticipated that 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. One side106of the reflector cup202is also shown inFIG. 1.

FIG. 2Ais an isometric drawing of a first lead frame102and second lead frame104in accordance with an exemplary embodiment of the invention. In this exemplary embodiment, the first lead frame comprises a first tongue204, a second tongue206, and a reflector cup202. Three sides (208,210and212) of the reflector cup202are also shown inFIG. 2A. The reflector cup202may be formed by standard methods, for example by stamping the first lead frame102. As will be discussed in more detail, the reflector cup202, is surrounded on four sides (208,210,212and106) of the reflector cup202by an encapsulant606.

The first204and second206tongues in this exemplary embodiment are substantially rigid so as to reduce movement of the reflector cup202. Reducing movement of the reflector cup, among other things, reduces the probability that the electrical connection between the reflector cup202and the second lead frame will be open. If the electrical connection between the reflector cup202and the second lead frame is open, the light source602will not function. In this exemplary embodiment an electrical connection is made by a wire bond604.

FIG. 2Bis a third isometric drawing of a first lead frame102and second lead frame104in accordance with an exemplary embodiment of the invention. In this exemplary embodiment, the first lead frame comprises a first tongue204, a second tongue206, and a reflector cup202. Two sides208and212of the reflector cup202are shown inFIG. 2B. As will be discussed in more detail, the reflector cup202, is surrounded on four sides (208,210,212and106) of the reflector cup202by an encapsulant606.

FIG. 3is an isometric drawing of a plastic structural body302in accordance with an exemplary embodiment of the invention. The plastic structural body302contains a cavity304. In an exemplary embodiment, the cavity304may be used to contain a portion of encapsulant606. In one embodiment, the plastic structural body302may be an integral single piece structure. In a second embodiment the plastic structural body302may have dimensions that conform to the PLCC-4 standard. The plastic structural body302may be made using any standard process. For example, an injection molding process may be used to form the plastic structural body302.

FIG. 4is an isometric drawing of a PLCC package400in accordance with an exemplary embodiment of the invention. The first102and second104lead frames in this drawing are shown as part of the PLCC package400. An optical lens402is also shown as part of the PLCC package400. The dome-shaped optical lens is composed of encapsulant606. The material used as an encapsulant606includes but is not limited to epoxy, silicone, a hybrid of silicone and epoxy, amorphous polyamide resin or fluorocarbon, glass and plastic. Also shown is the plastic structure body302.

FIG. 5is a top plan view of the PLCC package400in accordance with an exemplary embodiment of the invention. The first102and second104lead frames in this drawing are shown as part of the PLCC package400. An optical lens402is also shown as part of the PLCC package400. The dome-shaped optical lens is composed of encapsulant606. Standard processes may be used to form the encapsulant606. For example, an injection molding process, a transfer molding process or a compression molding process may be used. Also shown is the plastic structure body302. Lines6and7inFIG. 5indicate where sectional views of the PLCC package400are made. These sectional views are discussed below.

FIG. 6is a sectional view of the PLCC package400shown inFIG. 5in accordance with an exemplary embodiment of the invention. In this sectional view, the plastic structural body302is shown to have a cavity304which contains a portion of the encapsulant606. This sectional view also shows that the reflector cup202is surrounded on four sides by the encapsulant606. During the step of filling the cavity304of the plastic structural body302with encapsulant606, a domed portion that functions as an optical lens402is formed on the PLCC package400.

Because the reflector cup202is surrounded on four sides by the encapsulant606, a CTE mismatch between the encapsulant606and the plastic structural body302will be less likely to cause problems related to thermal stress. For example, the occurrence of de-lamination between the light source602and the first lead frame102due to a CTE mismatch between the encapsulant606and the plastic structural body302, will be less likely. Also, the occurrence of de-lamination between the light source602and the first lead frame102due to a CTE mismatch between the encapsulant606and the first102and/or the second104lead frames, will be less likely. In addition, since the encapsulant606and the optical lens402are made of the same material, CTE mismatch problems between them are also less likely to cause problems related to thermal stress.

FIG. 6shows a wire bond604connected to the light source602and the second lead frame104. The first102and second104lead frames provide electrical connections for the light source as well as leads for mounting. In this exemplary embodiment, the first102and second104lead frames also function as heat sinks to dissipate heat created by the light source602.

FIG. 7is a sectional view of the PLCC package400shown inFIG. 5in accordance with an exemplary embodiment of the invention. In this sectional view, the plastic structural body302is shown to have a cavity304which contains a portion of the encapsulant606. This sectional view also shows that the reflector cup202is surrounded on two sides by the encapsulant606. During the step of filling the cavity304of the plastic structural body302with encapsulant606, a domed portion that functions as an optical lens402is formed on the PLCC package400.

This sectional view also shows a light source602physically and electrically connected at the bottom of the reflector cup202. The first lead frame102provides an electrical connection for the light source602as 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.

FIG. 8is a top plan view of the PLCC package400with the optical lens removed for clarity in accordance with an exemplary embodiment of the invention. In this embodiment tongues204and206are supported by the plastic structural body302. The first204and second206tongues are an integral part of the first lead frame102. The first204and the second206tongues are substantially rigid to reduce movement of the reflector cup202.

Reducing the movement of the reflector cup202lowers the probability of the wire bond separating from either the light source602or the second lead frame104. When the wire bond604separates from either the light source602or the second lead frame104, the electrical connection is opened and the light source602will not function. Reducing the movement of the reflector cup202also lowers the probability of the light source602separating from the reflector cup202.

FIG. 9is a process flow diagram900of a method for making a PLCC package400with a dome shaped optical lens402in accordance with an embodiment of the invention. In this exemplary embodiment, a first102and a second104lead frame are provided as shown in box902. Next as shown in box904a plastic structural body302is formed around the first102and second104lead frames. In this exemplary embodiment, the plastic structural body302is an integral single piece structure having a cavity304that serves as a container for containing a portion of an encapsulant606.

Next as shown in box906a light source602is mounted and electrically connected at the bottom of the reflector cup202. Next as shown in box908an electrical connection is made from the light source602to the second lead frame104. In this exemplary embodiment, a wire bond604is used to make the electrical connection from the light source602to the second lead frame104.

Next as shown in box910an encapsulant606is formed that surrounds the reflector cup202on four sides (106,208,210and212) while forming an optical lens402. The encapsulant606also hermetically seals the light source602. In this exemplary embodiment, the encapsulant606is an integral single piece structure.

Often reflective walls of a plastic structural body302are 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 body302in order to improve the brightness of the PLCC package400.

In another exemplary embodiment, a black plastic material is used when forming a plastic structural body302in order to improve the contrast of the PLCC package400.

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.