How Marktech does Optoelectronic Customization of Emitter Materials: Part One of Six

Table of Content

Introduction
Emitter Wavelengths
LED Drive Current and Temperature
     Forward Current vs. Ambient Temperature
     LED Lamp example
     De-rating for Longevity
Chip Mounting: Die Attach and Wire Bonding
     Die Attach
     Wire Bonding (Source: Hybond, a wirebonder manufacturer)
Thermocompression Bonding
Thermosonic Bonding
Ultrasonic Bonding
Lensing: Illumination Patterns and Output
     Spatial Radiation Characteristics
     Luminous Intensity and Directional Characteristics
Examples of Customized Products
     Custom Light Rings
     Marktech Solution
Pulse Oximeter: Oxygen and Pulse Rate Monitoring
     Marktech Solution
UV Curing and Drying of Inks, Adhesives, and Coatings
     Marktech Solution
Customized Displays
Bar Code Scanning
     Marktech Solution
SWIR Emitter Applications
     Typical Industries Served
     Common Applications
     Marktech Solution

Introduction

Marktech Optoelectronics has three decades of experience in optoelectronics, and utilizing that, its customization process focuses on customer needs and applications. Rather than employing standardized – and maybe non-optimized – parts, Marktech enables advantageous custom product variations to improve the client’s product design.

Further differentiation is offered by electrical sorting and custom packaging of products. Insights are offered to the designer concerning custom variations and optimizing optical, electrical, and thermal characteristics without the need for large volume commitments.

Marktech engineers can help with:

  • Application needs specific to a project
  • Manufacturing of exclusive end-products in support of the customer’s needs and specifications
  • Recommending optimizations for components, assembly packaging, technology, and electrical and thermal parameters

This article, the first installment in a six-part series on customization capabilities of Marktech, focuses on optoelectronic emitter materials. These materials are usually intended for mating with compatible (and perhaps customized) detectors.

Emitter Wavelengths

Available products have wavelengths varying from 280 nm (ultraviolet (UV)) through visible (440 nm to 700 nm) to near-infrared (IR) (710 nm to 1100 nm) and short wavelength IR (up to 3000 nm). Marktech’s online Product Selector Guide offers help for selecting emitter wavelengths as well as indicating compatible detectors. Uniform color characteristics are obtained, thanks to tight binning by Marktech, in order to optimize the application and matching detectors’ sensitivities. This leads to process-controlled, uniform product solutions.

LED Drive Current and Temperature

Degradation/lifetime effects are minimized by optimal drive current and temperature.

Forward Current vs. Ambient Temperature

Figures 1 and 2 demonstrate an example in which the current is de-rated to take temperature into account. In the case of LED lamps, CREE technical data often show the permissible current values against temperature. This information can be taken note of when planning a new design.

Figure 1. Specified by design (25 mA) exceeds permissible value at 70C high temperatures

Figure 2. Specified by design (25 mA) is within permissible value at 70 °C high temperatures

LED Lamp example

An example showing how to de-rate for temperature when designing is given below:

  • An LED lamp needs to be used at an ambient temperature of 25 °C
  • The LED lamp current should be set to 20 mA to obtain the required luminosity
  • The guaranteed operating temperature range for the equipment is -10 °C to +70 °C
  • If the current is de-rated for temperature at 70 °C, as shown in Figure 1, the LED lamp current should be set to ≤ 20 mA. A design that yields an LED lamp current of 25 mA is disallowed. However, as shown in Figure 2, some other types of LEDs emitting the same color have their current de-rated to take temperature into account. Since those LEDs, at a temperature of 70 °C, can maintain a current of about 30 mA, they satisfy the above design conditions.

De-rating for Longevity

The luminous intensity of an LED shows a gradual characteristic reduction over the life of the LED. The rate of reduction of the luminous intensity varies, based on the forward current at which the LED is driven and the material used. If the current is larger, greater is the diminution of luminosity. Therefore, when setting the forward current of the LED lamp, the setting should be determined from the temperature characteristics as well as the longevity characteristics. By setting the forward current of the LED lamp relatively low, the longevity characteristics can be effectively improved.

Chip Mounting: Die Attach and Wire Bonding

Simpler wire-bond techniques and conductive paste die attach are acceptable as chip-mounting options for low-power devices. However, for high-power devices, increased thermal conductivity is required to help to reduce the chip temperatures.

Die Attach

  • Eutectic solder die attach - good/very good for high power applications
  • Soft solder die attach - good/very good for low or high power applications
  • Conductive epoxy die attach - good for low/medium power applications
  • Advanced Eutectic (thermal compression bond Gold Silicon) - very good for high power applications, but difficult to apply

Wire Bonding (Source: Hybond, a wirebonder manufacturer)

Three types of wire bonding are carried out:

  • Thermocompression bonding
  • Thermosonic bonding
  • Ultrasonic bonding

Thermocompression Bonding

This bonding process involves the use of force, heat, and time to join two materials by inter-diffusion. To achieve the bond, a high force is applied to press the wire (heated in some cases) against a hot surface (at 150 °C or more) for some time. Friction is not used. This bonding process employs a gold bond surface and gold wire, and was originally associated with ball bonding. Even nowadays, some people use the phrase “thermocompression bonding”, notwithstanding the fact that ultrasonic friction is currently used.

Thermosonic Bonding

This bonding process entails the use of force, ultrasonics, heat, and time to join two materials. To achieve the bond, a low force is applied to press the wire (heated in some cases) against a hot surface (at 150 °C or less) and is vibrated for some time. This bonding process employs a gold bond surface and gold wire, and was also originally associated with ball bonding. This is due to first time ultrasonics once being used as a bonding parameter - it was performed with ball bonding.

Gold Ball Bonding

This process gets its name from the bonding of a gold wire, which initially has a ball or sphere formed on the end. A “flame-off” is employed to make the ball. Previously, an open hydrogen flame was used to carry out the flame-off, where the flame would rotate towards the end of the wire and melt it, thus creating a ball or sphere at the end of the wire. Currently, the ball is made with an electronic flame-off (EFO), which produces a spark to melt the end of the wire. This bonding process employs force, heat, time, and ultrasonics to achieve the bonds. Recently, copper wire has been used for this process, but the equipment requires modifications to prevent oxidation of the wire and the ball during its formation at flame-off.

Wedge Bonding

This process was originally used for aluminum wire alone, and heating was not required to create bonds. Eventually, gold wire was used for thermosonic wedge bonding of the gold wire and heat was added to the bonding surface. This is now commonly used for bonding gold ribbon or wire. Some people still use the phrase “wedge bonding” as a term for ultrasonic bonding and not thermosonic wire bonding. Irrespective of the original meaning of the phrase, the thermosonic wedge bonding process employs force, ultrasonics, heat, and time to achieve bonds.

Ultrasonic Bonding

This bonding process involves the use of force, ultrasonics, and time to join two materials. To achieve the bond, a low force is applied to press the wire against the surface (both at ambient temperature) and is vibrated for some time. This bonding process can be carried out with gold, copper, aluminum, silver, palladium, or platinum ribbons or wire. It can be used to bond surfaces of the same material. Previously, this form of wire bonding was carried out using aluminum wire, and therefore, some people still use the phrase “ultrasonic bonding”, even if it is now used for gold wire wedge bonding and other materials.

Wedge Bonding

This bonding process employs force, ultrasonics, and time with the bonding surface at room/ambient temperature to achieve bonds. This process was previously used for aluminum bonding applications, but today there are many other alloys and materials that can be bonded by the ultrasonic method. It was once thought that the bonding would only be effective if heat was applied.

Peg Bonding

This bonding process employs force, ultrasonics, and time with the bonding surface at room/ambient temperature to achieve bonds. Peg bonding is identical to wedge bonding, and can be carried out ultrasonically as well as thermosonically. However, the main difference with the methods explained above is that in a peg bonder, the wire, ribbon or any conductor is pre-aligned over the bond pad, or manually introduced under the bonding tool (peg).

The wire is not fed from a spool of wire by the wire bonder. This process is commonly known as tape automated bonding (TAB), or single point TAB. Hybond has given the name “peg” to this type of bonding, since naming it as TAB would lead to an incorrect assumption that a tape-feeding mechanism is included as part of the equipment. Another reason for Hybond’s reference is that the tool used for bonding resembles a peg. This is similar to the tool employed in wedge bonding, resembling a wedge.

Today’s ultrasonic bonding is different from its earlier version, as the concept of interfacial rubbing is invalid. A metal to be bonded is temporarily rendered soft and plastic when ultrasonic energy is applied to it. This makes the metal flow under pressure. Due to this acoustic energy, molecules are freed up and dislocated from their pinned positions, allowing the metal to flow under the low-compressive forces of the bond. The bond-site heat is a byproduct of the bonding process, and so external heat is not required to achieve the bond. This is also known as a “cold weld.”

Some contaminants in the weld area are swept aside when the friction of the wire breaks up, exposing clean metallic surfaces and promoting metallurgical bonds. To avoid failures or difficulties in bonding, it is important to begin with a clean surface. In some cases, such as with lubricants, the contaminants will not be removed by the ultrasonic scrubbing process.

The bonding tool cyclically moves across the top of the wire. The wire may not be adequately gripped by a regular flat tool, and due to this, the wire slips back and forth across the bond surface of the tool. For this reason, some tools are made using more porous materials, such as ceramic-metal alloys. Some possess special features such as grids or cross-grooves to help in the gripping of the wire during thermosonic and ultrasonic bonding.

Lensing: Illumination Patterns and Output

Spatial Radiation Characteristics

Lenses determine the output power obtainable, which depends on the angle. Lens characteristics dictate coverage areas and intensity peaks. Marktech products provide multiple choices in beam angle which can be matched to the sensor and application needs. To analyze these radiation patterns, Marktech uses goniometer equipment.

Luminous Intensity and Directional Characteristics

The relationship between directional characteristics and luminous intensity units.

Candela (cd) is the unit for measuring luminous intensity, and watts/steradian (W/sr) for the radiance. One steradian is the solid angle at the center of a one-meter-radius sphere subtended by a square meter of surface area; the steradian is a metric unit. The radiance of light is the amount of luminous flux propagated in a given solid angle, or the amount of incident. If the directionality of an LED lamp is narrow, then the luminous intensity of that lamp is higher, as shown by the figures below.

For an LED lamp of specific directionality, if the emission efficiency of the chip is higher, then the luminous intensity is also the higher.

Application Viewing Angle
High-Brightness LED information panel 15° to 30°
Signal applications 8° to 30°
Low-Brightness LED information panel 30° to 120°
Narrow-Direction indicator 30° to 60°
Wide-Direction indicator 60° to 120°
Automotive stop lamp 20° to 50°
Automotive dashboard narrow directionality 20° to 60°
Automotive dashboard wide directionality 60° to 120°

 

The Digikey site can be visited for a listing of specific Marktech emitter chips, ranging from deep UV to the visible range, to near-IR and short wave IR (SWIR).

The Marktech site can be visited to view a full listing of Marktech emitter chips ranging from deep UV to the visible range to near-IR and SWIR.

Examples of Customized Products

Custom Light Rings

Custom light rings applications:

  • Analytical instruments for the medical and scientific analysis, endoscopy, and biochemical industry
  • Security cameras
  • Critical illumination

Marktech Solution

Constructed with FR-4, ceramics, or metal core, Marktech’s ring/chip are available from 280 nm in the UV range though visible to near IR. White light ring options can be made with color temperatures ranging from warm (2600 K) to cool (10000 K). Detector or emitter chips – or a combination of both – can be added in custom light ring packages. In most cases, Marktech can test to ± 1 nm, and the size offerings range from 4 mm up to any required size.

Chip-on-board (COB) technology is usually used to manufacture smaller size light rings. However, standard surface mount components such as 1206, 0805, and PLCC-type packages are also available based on the required optical performance.

Pulse Oximeter: Oxygen and Pulse Rate Monitoring

The current medical physical checks include reliable and quick readings of patient oxygen levels, readings that can be replicated with home monitoring, thanks to low cost of access to the equipment. A simple pulse oximeter easily determines the oxygen levels of blood, using two different LED emitter wavelengths. While absorption of light for oxygenated blood is at 660 nm, for deoxygenated blood it is at 905 nm. By measuring and using the Beer-Lambert’s law to interpret the results, the saturated peripheral oxygen level from a patient’s fingertip is quickly determined.

The requirements are:

  • Customized packaging of emitter parts to easily fit in a small package
  • Optimization of the part wavelengths for increasing accuracy

Marktech Solution

The LED-sorting equipment needs to be designed, purchased, and modified to bin LED products into tighter than +/- 1 nm selected chips.

UV Curing and Drying of Inks, Adhesives, and Coatings

UV LED emitter light curing is used for a variety of applications such as dentistry, guitar finishes, telecommunications, automotive, graphic arts, electronics, plastic decorating, and glass. Inks, adhesives, and coatings cured with UV LED light achieves significant improvement in physical properties. Conventional curing involves environmentally objectionable and highly inefficient mercury lamps that could result in possible damage of the subject matter, if applied incorrectly.

In contrast, UV LEDs are highly efficient, and provide a longer-life alternative to standard bulbs. Heat output is easily controllable for LEDs while the time needed to cure is also shortened, reducing the potential for damage to the cured object.

Advantages:

  • Fast production speeds/increased capacity
  • Increased manufacturing efficiency
  • Significantly reduced set-up/clean-up labor
  • Less floor space needed
  • Environmental considerations for energy use and emissions

Marktech Solution

Marktech can optimize the emission wavelength for camphorquinone (CPQ) and other substitute materials, which can be used as curing photoinitiators. Optimal packaging is possible for access to, for example, small dental probes optimized for patient use.

Customized Displays

Marktech has contributed to the exciting, visually awesome area of Times Square in New York City as well as other large display applications with customized display capability. This includes:

  • Display visibility 60 feet below and 12-16 blocks away
  • Design solution of two-chip assembly with elliptical lens
  • Excellent quality – zero defects/zero failures since 1996
  • Cooperative manufacturing agreement with Toshiba

Bar Code Scanning

Bar code readers employ emitters with:

  • Repeatable wavelengths
  • Consistent power output

Marktech Solution

Equipment needs to be designed, purchased and modified to sort LEDs for power output, with selected/consistent binning.

SWIR Emitter Applications

The latest addition to Marktech’s broad line of emitters is the SWIR LED. Marktech is among a handful of manufacturers supplying emitters in the extended wavelength or SWIR range. SWIR emitters are available in various surface mounts and through-hole packages. They cater to a growing need for high-speed light emission in ranges not easily satisfied by standard detectors, and are being employed for chemical and material analyses.

Typical Industries Served

Security, military, medical, industrial, communications, and agriculture.

Common Applications

The fast growing market for SWIR includes applications such as produce inspection, surveillance, security, anti-counterfeiting, currency validation, night vision, safety equipment, biomedical bioflorescence, blood chemistry analysis, fiber optics and inspection system devices.

SWIR detectors can help achieve non-invasive imaging methods. For instance, optical coherence tomography (OCT) systems make use of SWIR to exploit the low scattering properties of >1 µm light to observe the previously inaccessible, thick parts of the cornea.

Marktech Solution

Marktech’s standard product range includes surface mount and through-hole packages with wavelengths from 1050 nm to 1720 nm and operating currents ranging from 20 mA to 350 mA for high-power applications. Specific package types have higher wavelength ranges of up to 3000 nm.

The Marktech extended wavelength standard SWIR package offerings include TO-46 lens, TO-46 flat, TOPLED PLCC4, SMD 1206 Lens, SMD 1206, and SMD high-power black. Custom package options are also offered.

This information has been sourced, reviewed and adapted from materials provided by Marktech Optoelectronics.

For more information on this source, please visit Marktech Optoelectronics.

Ask A Question

Do you have a question you'd like to ask regarding this article?

Leave your feedback
Submit