For nearly 10 years, real-time infrared (IR) imaging systems have been a popular tool for microelectronic failure analysis, fault isolation on completed assemblies, and thermal design verification. Capable of noncontact, wide-area temperature measurement at full video frame rates, this technology offered a tool that was easy to set up and use.
These systems, however, were limited in their total recording capacity and triggering flexibility. This made the evaluation of lengthy thermal events and transitory phenomena problematic.
Today, designs with finer geometries, higher operating speeds, and tighter component placement create an environment of very rapid and unpredictable thermal dynamics. Working with these components requires true real-time data-capture analysis, accompanied by large disk capacity to store the images and thermal data.
Historically, real-time IR systems have been controlled by dedicated hardware, often equipped with limited amounts of real-time storage capacity. Most systems could not capture more than 45 seconds of recorded data for post-analysis; few could conduct live analysis as the event unfolded. Often, systems were triggered manually, or you had to predict the time of the next event when setting the system.
A new generation of products moves real-time thermal imaging to standard PC hardware while addressing the image-capture requirements introduced by the new smaller, faster electronic designs. State-of-the-art IR imaging technology, combined with high-performance multimedia PCs, provides high-resolution IR imagery, excellent temperature measurement accuracy, thermal sensitivity down to 0.1°C, and essentially unlimited real-time recording. This marriage of technologies produces systems that digitally capture thermal events that occur as often as every 16 ms without the data loss associated with data compression.
The need for this rapid-capture capability is driven by the increasing miniaturization and high clock speeds of newer electronic devices. Their size and speed create an environment where significant amounts of heat can be generated very quickly.
That heat also can have wide-ranging, possibly adverse, effects on other parts of the design. The small heat capacity of semiconductor junctions, particularly those subjected to miniaturization, makes it necessary to carefully evaluate and account for the heat generated during operation. Slower thermal-management tools may completely miss the thermal event.
A key component of the new real-time systems is a high frame-rate IR camera based on a focal plane array (FPA) detector. The FPA is a solid-state microelectronic device with individual elements approaching 20 m m2. Such high-resolution cameras use a rectangular or square matrix of more than 75,000 detectors which is read at rates up to 60 Hz.
A typical frame may be more than 165 kbytes in size, resulting in an output data stream with a bandwidth often exceeding 9 Mbytes per second. This bandwidth makes the new PC-based systems valuable for evaluating smaller circuit designs. The IR camera is interfaced to the computer through a digital video interface, while a serial connection transmits data about the current operating configuration.
The high clock speeds and extensive graphics processing power of today’s multimedia computers provide a platform that accommodates the high input data rate from the thermal camera while running sophisticated image-analysis tasks. But the benefits of a PC platform are, in some cases, more practical than technical. The Windows operating system offers a familiar and user-friendly operating environment compatible with many of the programs engineers use in their daily work.
The connectivity and data-sharing potential of the Windows/PC combination complement the team-engineering approach. Not only can a Windows PC be serviced almost anywhere, but upgrades also can be added by simply switching components or adding new software.
Applications
As researchers work on the newest generation of semiconductor lasers and RF power transistors, thermal management is one of the most significant design considerations. The relatively small size of these semiconductors, combined with their very high levels of power dissipation, requires specialized cooling strategies.
As an electronic device, the laser has many operating modes, each with significantly different design requirements and operating power levels. New real-time IR systems accurately monitor high-speed thermal events over the wide temperature ranges characteristic of these devices. They also are easily set up to evaluate evolving thermal-management strategies and different application configurations.
The triggering flexibility in these systems eliminates the need to loop the test to ensure good data capture. You can choose where the trigger occurs in respect to the laser firing and gain more information about pre-fire conditions and cool-down characteristics. A direct TTL-compatible trigger input easily integrates with other laboratory equipment. An open-collector alarm output can shut down an experiment that has gone awry.
A specially designed user interface directly controls every acquisition parameter. The system graphically displays the memory used by varying combinations of recording time, recording rate, and frame size (Figure 1). By optimizing the size of the captured area, you can increase the total available recording time.
To extend the flexibility of IR imaging in close-focus applications, collimating attachments are used with standard IR optics. They offer a less expensive optical solution than a special-built IR microscope and feature extended working distances to enhance application flexibility.
For approximately one-fifth the cost of an entire microscope objective, a collimating accessory simply attaches to a lens you already own. This strategy also produces working distances up to 10 cm as compared to less than 3 cm for traditional microscope designs.
This is especially important when specialized liquid-cooled designs are being evaluated. The height of the cooling jacket does not allow use of traditional IR microscopes because of their short focal distance.
In another application, a major electronic equipment manufacturer in Western Europe depends on IR thermography to support its thermal-management program. The manufacturer uses finite element analysis (FEA) to model complex thermal relationships at the device, board, and system level. This analysis provides theoretical information about the physical mechanics of the design.
With this information, engineers perform design margining which considers the cumulative effects of worst-case design-element combinations (Figure 2). This data helps create a design that accommodates the real-world variations found in electronic components.
Thermal imaging is an integral part of the program for several reasons. First, IR imaging verifies FEA simulations. The wide range of available optical accessories for the thermal-imaging system allows you to switch from imaging a new circuit assembly to evaluating an entire instrument enclosure in a matter of seconds. Inexpensive IR-transmissive plastics replace portions of the enclosure to ensure a faithful replication of the normal equipment operating environment.
Secondly, materials used in a new design may not yet have FEA model data available for them. When this occurs, the IR technology is used to study the new materials to help develop the data necessary for an FEA model. In the interim, IR imaging provides valuable feedback to designers who cannot wait until an FEA can be run.
The data-sharing capability of the Windows/PC platform is critical to this thermal- management program. As test engineers validate new designs, they rapidly extract numerical data that is preformatted for spreadsheet analysis and correlation with FEA output. This data can be e-mailed to the design engineers, eliminating the delays associated with transmission of paper documents through the mail.
Conclusion
As designers continue to strive for more functionality in smaller spaces, shortened design cycles, and higher levels of operating reliability, thermal management will become an even more critical component of a quality product. The marriage of high-performance IR imaging and the Windows/PC platform offers a tool that builds on the traditional popularity of the technology. It increases performance and flexibility, reduces cost of ownership, and enhances ease of use.
About the Author
Patrick Finney is a senior applications engineer at FLIR Systems. He previously held marketing and engineering positions with Schlumberger and Electro Scientific Industries. Mr. Finney has a B.S. degree from the University of Chicago. FLIR Systems, 16505 S.W. 72nd Ave., Portland, OR 97224, (503) 684-3731.
Sidebar
The Basics of IR Imaging Systems
IR imaging systems, with their capability to detect the heat emitted by all objects, are important heat-management and inspection tools for applications from thermal design verification to microelectronic failure analysis. The images produced by these systems show the relative temperature differences that are present on the observed object, with warmer areas typically appearing lighter than cooler ones.
Advanced high-resolution cameras are used to accurately measure the temperature of any pixel on the image without contacting the object.
Thermal-imaging systems detect energy from the IR band of the electromagnetic spectrum. IR energy enters the camera through a lens and strikes the detector. Specific areas of the detector correspond to individual pixels on the screen of the camera system.
As these detector areas are excited by the incoming IR energy, the corresponding pixel is assigned a temperature value, and the pixel is appropriately colorized. This process repeats up to 60 times a second in some of the most advanced thermal-imaging cameras.
Copyright 1997 Nelson Publishing Inc.
August 1997