Method of making a semiconductor radiation emitter package

Details Method of making a semiconductor radiation emitter package Method of making a semiconductor radiation emitter package

2001-08-23

2004-12-07

Fourson, George (Department: 2823)

Semiconductor device manufacturing: process

Making device or circuit emissive of nonelectrical signal

Packaging or treatment of packaged semiconductor

C438S028000, C438S122000

Reexamination Certificate

active

06828170

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to semiconductor radiation emitter packages such as, for example, light emitting diode (LED) packages.
Semiconductor optical emitter components such as LED devices have become commonplace in a wide variety of consumer and industrial opto-electronic applications. Other types of semiconductor optical emitter components, including organic light emitting diodes (OLEDs), light emitting polymers (LEPs), and the like may also be packaged in discrete components suitable as substitutes for conventional inorganic LEDs in these applications.
Visible LED components of all colors are used alone or in small clusters as status indicators on such products as computer monitors, coffee makers, stereo receivers, CD players, VCRs, and the like. Such indicators are also found in a diversity of systems such as instrument panels in aircraft, trains, ships, cars, trucks, minivans and sport utility vehicles, etc. Addressable arrays containing hundreds or thousands of visible LED components are found in moving-message displays, such as those found in many airports and stock market trading centers, and also as high brightness, large-area outdoor TV screens found in many sports complexes and on some urban billboards.
Amber, red, and red-orange emitting visible LEDs are used in arrays of up to 100 components in visual signaling systems such as vehicle center high mounted stop lamps (CHMSLs), brake lamps, exterior turn signals and hazard flashers, exterior signaling mirrors, and for roadway construction hazard markers. Amber, red, and blue-green emitting visible LEDs are increasingly being used in much larger arrays of up to 300 components as stop/slow/go lights at urban and suburban intersections.
Multi-color combinations of pluralities of visible colored LEDs are being used as the source of projected white light for illumination in binary-complementary and ternary RGB illuminators. Such illuminators are useful as vehicle or aircraft maplights, for example, or as vehicle or aircraft reading or courtesy lights, cargo lights, license plate illuminators, backup lights, and exterior mirror puddle lights. Other pertinent uses include portable flashlights and other illuminator applications where rugged, compact, lightweight, high efficiency, long-life, low voltage sources of white illumination are needed. Phosphor-enhanced “white” LEDs may also be used in some of these instances as illuminators.
Infrared (IR) emitting LEDs are being used for remote control and communication in such devices as VCR, TV, CD, and other audio-visual remote control units. Similarly, high intensity IR-emitting LEDs are being used for communication between IRDA devices such as desktop, laptop and palmtop computers, PDAs (personal digital assistants), and computer peripherals such as printers, network adapters, pointing devices (“mice,” trackballs, etc.), keyboards, and other computers. IR LED emitters and IR receivers also serve as sensors for proximity or presence in industrial control systems, for location or orientation within such opto-electronic devices such as pointing devices and optical encoders, and as read heads in such systems as barcode scanners. Blue, violet, and UV emitting LEDs and LED lasers are being used extensively for data storage and retrieval applications such as reading and writing to high-density optical storage disks.
Billions of LED components are used in applications such as those cited hereinabove, in part because relatively few standardized LED configurations prevail and due to the fact that these configurations are readily processed by the automated processing equipment used almost universally by the world's electronic assembly industries. Automated processing via mainstream equipment and procedures contributes to low capital cost, low defect rates, low labor cost, high throughput, high precision, high repeatability, and flexible manufacturing practices. Without these attributes, the use of LEDs becomes cost prohibitive or otherwise unattractive from a quality standpoint for most high-volume applications.
Two of the most important steps in modern electronic assembly processes are highspeed automated insertion and mass-automated soldering. Compatibility with automatic insertion or placement machines and one or more common mass-soldering process are critical to large-scale commercial viability of discrete semiconductor optical emitters (including LEDs).
Thus, the vast majority of LEDs used take the form of discrete-packaged THD (through-hole device) or SMD (surface mount device) components. These configurations primarily include radial-lead THD configurations known as “T-1” and “T-1 ¾” or similar devices with rectangular shapes, all of which are readily adapted onto tape-and-reel or tape-and-ammo packaging for convenient shipment, handling, and high speed automated insertion into printed circuit boards on radial inserters. Other common discrete THD LED packages include axial components such as the “polyLED” which are readily adapted onto tape and reel for convenient shipment, handling, and high speed automated insertion into printed circuit boards on axial inserters. Common SMD LED components such as the “TOPLED” and Pixar are similarly popular as they are readily adapted into blister-pack reels for convenient shipment, handling, and high-speed automated placement onto printed circuit boards with chip shooters.
Soldering is a process central to the manufacture of most conventional circuit assemblies using standardized discrete electronic devices, whether THD or SMD. By soldering the leads or contacts of a discrete electronic component such as an LED to a printed circuit board (PCB), the component becomes electrically connected to electrically conductive traces on the PCB and also to other proximal or remote electronic devices used for supplying power to, controlling or otherwise interacting electronically with the discrete electronic device. Soldering is generally accomplished by wave solder, IR reflow solder, convective IR reflow solder, vapor phase reflow solder, or hand soldering. Each of these approaches differ from one another, but they all produce substantially the same end effect—inexpensive electrical connection of discrete electronic devices to a printed circuit board by virtue of a metallic or inter-metallic bond. Wave and reflow solder processes are known for their ability to solder a huge number of discrete devices en masse, achieving very high throughput and low cost, along with superior solder bond quality and consistency.
Widely available cost-effective alternatives to wave solder and reflow solder processes for mass production do not presently exist. Hand soldering suffers from inconsistency and high cost. Mechanical connection schemes are expensive, bulky and generally ill-suited for large numbers of electrical connections in many circuits. Conductive adhesives, such as silver-laden epoxies, may be used to establish electrical connections on some circuit assemblies, but these materials are more costly and expensive to apply than solder. Spot soldering with lasers and other selective-solder techniques are highly specialized for specific configurations and applications and may disrupt flexible manufacturing procedures preferred in automated electronic circuit assembly operations. Thus, compatibility with wave solder or reflow solder processes are de facto requirements of an effective semiconductor optical emitter component. The impact of this requirement is far reaching because these solder operations can introduce large thermal stresses into an electronic component sufficient to degrade or destroy the component. Thus, an effective semiconductor optical emitter component must be constructed in such a fashion as to protect the device's encapsulation and encapsulated wire bonds, die-attach, and chip from transient heat exposure during soldering.
Conventional solder processes require that the ends of the leads of the device (below any standoff or at a point where the leads touch designated pads on the PCB) be heated to th

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