Bond Testing of Wire Bonds within LEDs

Light emitting diodes (LEDs) provide a low maintenance and energy efficient form of illumination. These solutions are increasingly becoming the choice for lighting design, from display systems and architectural lighting systems through to automotive lighting, street lighting and medical equipment. Most LEDs exhibit a natural lifetime. Although degradation failures could not be prevented, proper LED manufacturing processes make sure that they do not fail within the intended life of the product. Figure 1 shows a standard LED device.

Typical LED device.

Figure 1. Typical LED device.

However, one key issue of LEDs is the amount of heat they generate. Heat affects the die attach and also the wire bond and this in turn causes displacement in the bulk of moulding compound. If the heat is not eliminated efficiently from the die, both the quality and performance of the light produced would be affected adversely. In addition, mechanical and thermal stress impairs the wire bond and gradually leads to failure.

As a result, wire bonds within LEDs have to perform in all potential environments throughout the duration of the LED lifespan. In view of these factors, the manufacturing process should be carefully controlled and optimized to ensure an extended operating life of the product. Generally, LEDs are divided into two main categories such as general high volume LEDs and high-performance LEDs. Although the testing requirements differ for both sets of LEDs, the requirements are both met by the Nordson DAGE bondtester.

Test Methods

The Nordson DAGE bondtester can be used for the entire range of test methods such as:

  • Die shear
  • Low profile die shear
  • Wire pull
  • Ball shear
  • Tweezer pull
  • Wafer level LED

Wire Pull Test

The wire pull test (Figure 2) assesses the quality and integrity of the wire bond. It is also utilized for wire bonding process optimization and process control during assembly manufacturing. Since LED wire loops tend to be short and low, the Nordson DAGE wire pull cartridge provides 360° rotation of the test hook in addition to a variety of tools to meet various geometries. The loop height measurement feature not only helps in detecting the height of the loop, but also aids in monitoring its consistency. For future analysis, the loop height and wire breaking force are saved in the database.

Wire pull test.

Figure 2. Wire pull test.

Ball Shear Test

The Nordson DAGE ball shear cartridge offers ball shear test capabilities (Figure 3), which can be carried out using cavity or chisel tools. This cartridge comes with an extra feature of tool rotation of up to 1800 to allow precise alignment as well as operator convenience. A touchdown sensor in the Nordson DAGE ball shear cartridge enables precise and smooth landings on the fragile LED die. The touchdown force is very sensitive and offers precise step back repeatability of more than +/-1.0µm.

Ball shear test.

Figure 3. Ball shear test.

Tweezer Pull Test

To obtain a complete test on an LED wire bond after the shear testing of the ball bond, it is possible to test the wire on the wedge side by means of tweezers (Figure 4). It is also possible to control the Nordson DAGE tweezer and pull cartridge parallel closing tweezers to apply the closing force precisely to the interface. This provides reliable and precise testing in all LED die bond applications.

Wedge bond shear test.

Figure 4. Wedge bond shear test.

Die Shear Test

GaAs and other types of LED die materials are extremely fragile and hence a complete parallel alignment of the shear tool to the die’s edges is needed, so that the die does not break prior to applying the necessary load for interface testing. The Nordson DAGE self aligning shear tool is designed to ensure complete parallel alignment. Operators can simply place the tool to one edge and the self aligning adapter applies the load evenly to the entire width of the die (Figure 5).

LED die shear test.

Figure 5. LED die shear test.

Low Profile Die Shear Test

Continuous developments over the years have made dies thinner and thinner. This ensures that the heat is transferred efficiently to the package. However, the areas are also becoming larger and larger due to the requirement for higher light output. To meet these testing demands, the Nordson DAGE die shear cartridge offers exceptional step-back repeatability and a work holder, which enables co-planarity leveling and also guarantees the high repeatability of shearing low profile dies.

Wafer Level Ball Shear Test

Tests can be carried out on LED wafers. Thanks to the high step back precision of the Nordson Dage bondtester, precise shear tests can be conducted at wafer level. The bondtester features a wide range of both standard and application-specific wafer chucks, which are capable of accommodating single/multiple wafers depending on their diameter. This along with semi-automatic test routines enables consistent, efficient and repeatable bond testing for high throughput.

Paragon™ Intelligent Bond Testing Software

Paragon, an advanced bond testing software from Nordson DAGE, sets a new benchmark in bond testing. With its highly configurable and intuitive interface, the software provides fast and easy access to state-of-the-art functionality, and thus increases efficiency and provides confidence in the bond testing results (Figures 6 and 7).

Paragon™ Intelligent Bond Testing Software

Figure 6. Quick and easy test set-up intuitive design ensures test set-up parameters are easily accessible with the start-up check list enabling a quick start.

Paragon™ Intelligent Bond Testing Software

Figure 7. Advanced Data Presentation Extensive charting functionality allows several graphs to be displayed at once and to resize and zoom in easily.

Conclusion

Wire bonds within LEDs have to perform in all kinds of environments and hence it is important to monitor and optimize the manufacturing process so that a long operating life is ensured for the LEDs. Although the testing requirements differ for high-performance LEDs and general high volume LEDs, the Nordson DAGE bondtester is designed to meet these requirements.

About Nordson DAGE

Dage was founded in 1961 and is a market leader in its chosen markets of Semiconductor and PCBA Manufacture. It has an award winning portfolio of Bondtester and X-ray Inspection Systems for destructive and non-destructive mechanical testing and inspection of electronic components.

Dage was acquired by the Nordson Corporation in 2006.

Nordson DAGE has a strong portfolio of award winning products for destructive and non-destructive mechanical testing and inspection of electronic components. It has an excellent, wholly owned distribution and support network of seven offices covering Europe, Japan, China, Singapore, and the USA, and maintains representative offices in other territories.

With its self-contained R&D facilities, Nordson DAGE has developed world-leading products for testing wire bonds on semiconductor packages such as BGA, Chip Scale Packages (CSP) and other electronic components. More recently Nordson DAGE has been heavily involved in the testing of the newest technology 300 mm wafer bump shear.

Nordson DAGE has developed an excellent suite of award-winning X-ray inspection equipment targeted at both the Semiconductor and PCBA markets.

Control of the patented core technology of X-ray tube manufacture ensures that the high-resolution X- ray will detect, identify and measure even the smallest of features. Nordson DAGE's high precision, state-of-the-art inspection equipment when joined with their sophisticated software offerings, ensure that the equipment is simple to use.

Our core strategy:

  • To support our customers wherever they do business,
  • To continually develop new products that provide its customers with enhanced competitive advantages,
  • To develop products which bring new advantages to its customer base
  • To control the core technologies that underpin its products.

Nordson DAGE

This information has been sourced, reviewed and adapted from materials provided by Nordson DAGE.

For more information on this source, please visit Nordson DAGE.

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