News Column

Patent Issued for Power Surface Mount Light Emitting Die Package

May 14, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- Cree, Inc. (Durham, NC) has been issued patent number 8710514, according to news reporting originating out of Alexandria, Virginia, by VerticalNews editors.

The patent's inventors are Andrews, Peter Scott (Durham, NC); Loh, Ban P. (Durham, NC).

This patent was filed on May 25, 2012 and was published online on April 29, 2014.

From the background information supplied by the inventors, news correspondents obtained the following quote: "Example embodiments in general relate to packaging semiconductor devices which include light emitting diodes.

"Light emitting diodes (LEDs) are often packaged within leadframe packages. A leadframe package typically includes a molded or cast plastic body that encapsulates an LED, a lens portion, and thin metal leads connected to the LED and extending outside the body. The metal leads of the leadframe package serve as the conduit to supply the LED with electrical power and, at the same time, may act to draw heat away from the LED. Heat is generated by the LED when power is applied to the LED to produce light. A portion of the leads extends out from the package body for connection to circuits external to the leadframe package.

"Some of the heat generated by the LED is dissipated by the plastic package body; however, most of the heat is drawn away from the LED via the metal components of the package. The metal leads are typically very thin and has a small cross section. For this reason, capacity of the metal leads to remove heat from the LED is limited. This limits the amount of power that can be sent to the LED thereby limiting the amount of light that can be generated by the LED.

"To increase the capacity of an LED package to dissipate heat, in one LED package design, a heat sink slug is introduced into the package. The heat sink slug draws heat from the LED chip. Hence, it increases the capacity of the LED package to dissipate heat. However, this design introduces empty spaces within the package that is be filled with an encapsulant to protect the LED chip. Furthermore, due to significant differences in CTE (coefficient of thermal expansion) between various components inside the LED package, bubbles tend to form inside the encapsulant or the encapsulant tends to delaminate from various portions within the package. This adversely affects the light output and reliability of the product. In addition, this design includes a pair of flimsy leads which are typically soldered by a hot-iron. This manufacturing process is incompatible with convenient surface mounting technology (SMT) that is popular in the art of electronic board assembly.

"In another LED package design, the leads of the leadframe package have differing thicknesses extended (in various shapes and configurations) beyond the immediate edge of the LED package body. A thicker lead is utilized as a heat-spreader and the LED chip is mounted on it. This arrangement allows heat generated by the LED chip to dissipate through the thicker lead which is often connected to an external heat sink. This design is inherently unreliable due to significant difference in coefficient of thermal expansion (CTE) between the plastic body and the leadframe material. When subjected to temperature cycles, its rigid plastic body that adheres to the metal leads experiences high degree of thermal stresses in many directions. This potentially leads to various undesirable results such as cracking of the plastic body, separation of the plastic body from the LED chip, breaking of the bond wires, delaminating of the plastic body at the interfaces where it bonds to various parts, or resulting in a combination of these outcomes. In addition, the extended leads increase the package size and its footprint. For this reason, it is difficult to populate these LED packages in a dense cluster on a printed circuit board (PCB) to generate brighter light.

"Another disadvantage of conventional leadframe design is that the thick lead cannot be made or stamped into a fine circuit for flip-chip mounting of a LED--which is commonly used by some manufacturers for cost-effective manufacturing and device performance."

Supplementing the background information on this patent, VerticalNews reporters also obtained the inventors' summary information for this patent: "An example embodiment of the present invention is directed to a light emitting die package. The package includes a substrate having a first surface and a first conductive lead on the first surface that is insulated from the substrate by an insulating film. The first conductive lead forms a mounting pad for mounting a light emitting device. The package includes a lead electrically connected to the first conductive lead and extending away from the first surface.

"Another example embodiment is directed to a light emitting die package. The package includes a substrate having a first surface and a second surface opposite the first surface, a via hole through the substrate, and a conductive lead extending from the first surface to the second surface. The conductive lead is insulated from the substrate by an insulating film. The package includes a metal contact pad on one of the first and second surfaces electrically connected to the conductive lead. The metal contact pad has a light emitting diode (LED) mounted thereon.

"Another example embodiment is directed to a LED package including a substrate having a first surface, a second surface opposite the first surface, and a first conductive lead on the first surface that is insulated from the substrate by a first insulating film. The first conductive lead forms a mounting pad for mounting a light emitting device. The package includes at least one via hold formed through the substrate. A surface of the via hole is coated with a second insulating film.

"Another example embodiment is directed to a LED package including a substrate having a top surface, a bottom surface, at least one conductive element on the top surface connected to a LED and at least one conductive element attached to the bottom surface. The package includes at least two via holes formed through the substrate. Each via hole includes an electrical conductor therein which electrically connects the at least one conductive elements on the top and bottom surfaces of the substrate."

For the URL and additional information on this patent, see: Andrews, Peter Scott; Loh, Ban P.. Power Surface Mount Light Emitting Die Package. U.S. Patent Number 8710514, filed May 25, 2012, and published online on April 29, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=75&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=3704&f=G&l=50&co1=AND&d=PTXT&s1=20140429.PD.&OS=ISD/20140429&RS=ISD/20140429

Keywords for this news article include: Cree Inc., Electronics, Light-emitting Diode.

Our reports deliver fact-based news of research and discoveries from around the world. Copyright 2014, NewsRx LLC


For more stories covering the world of technology, please see HispanicBusiness' Tech Channel



Source: Electronics Newsweekly


Story Tools






HispanicBusiness.com Facebook Linkedin Twitter RSS Feed Email Alerts & Newsletters