BY J. R. SCHENK and KEN KOLDEN
Driven by growth of the worldwide wireless revolution, electronics component manufacturers are increasingly being faced with new challenges when it comes to reliably producing high-performance radio frequency (RF) devices in large quantities. In addition to spurring innovative new designs at the front-end of the semiconductor process, the migration toward more RF content is also driving revolutionary changes in back-end handling, testing and finishing processes.
As advanced RF devices move into multi-GHz frequency ranges, they generally require both longer test times and more robust interfaces to test equipment. Back-end test-handling processes must be able to simultaneously accommodate higher throughput levels while also ensuring consistent test integrity. In addition, in order to control overall costs, streamline production flow and conserve factory floor space, device manufacturers are increasingly turning to comprehensive back-end finishing systems that can combine test handling, inspection, marking and output to tape. This article will explore some of the specific processing challenges and the comprehensive system solutions that have emerged to meet them.
Challenges of RF Testing
Various factors are placing new demands on manufacturers of RF components (see “Driving Factors for the RF Component Market”).
Deploying an effective, efficient and adaptable test methodology has become one of the major challenges with volume manufacturing of new high-performance RF devices. Several converging factors are both driving up test times and constraining test interface parameters.
 Figure 1. Plunge-to-board part presentation interface. |
To achieve the high data rates and responsiveness needed in today's wireless applications, RF devices are increasingly operating at multi-GHz frequencies, which means that even very short circuit traces can take on the characteristics of transmission lines. For instance, at 2.4 GHz, traces as short as 2 mm can present critical concerns with managing skew, delay times and jitter. In some cases, product designers address these challenges by bringing more functionality into the chip-level devices, thereby eliminating external traces. In other instances, they focus on minimizing trace lengths in the board or module level product designs.
Both approaches present significant challenges for the effective design of IC test handling equipment. Packing in more chip-level functionality invariably results in longer test times, which can pose severe production throughput issues, especially if other production processes have to slow down to accommodate testing bottlenecks. Secondly, if the RF products are designed for use in environments with very short trace lengths, then they must also be tested under similar conditions. In many cases, this precludes the use of flexible cabling between the test machine and the handler's test-nests because the signal delay along the cable lengths could invalidate the test results.
Combining Multi-Function Handling with Plunge-to-Board Testing
A new generation of back-end handling equipment has become available to address the aforementioned issues by bringing together comprehensive multi-function back-end operations that include efficient plunge-to-board test presentation mechanisms.
In plunge-to-board testing (Figure 1), the handler system moves each device under test (DUT) to the test socket and makes consistent electrical contact in a controlled, accurate and repeatable manner. By ensuring electrical contact and minimizing cable lengths, plunge-to-board testing can avoid the “signal ringing” and interference concerns that could otherwise compromise RF testing integrity at multi-GHz frequency rates. Effective plunge-to-board presentation requires a precisely controlled range of motion on the part of the test handler and the ability to ensure consistent lead positioning, insertion force and contact deflection.
 Figure 2. Plunge-to-board four-up pick-up head. |
To accommodate longer RF test times while still maintaining acceptable throughput rates, these new generation multi-function back-end finishing platforms are designed for a high degree of parallel processing, which allows them to perform as much useful work as possible on every cycle, while minimizing unnecessary movements. By integrating multiple functions, such as inspection and laser marking, into the same platform along with RF test handling, multi-function systems can improve overall efficiency.
Traditional handling machines have typically made use of single-device pick-up heads to move parts one at a time between sequential operations. The newer system designs significantly improve efficiency by integrating multiple synchronized pick-up heads to simultaneously pick and move multiple parts between different operations within the machine. In some instances, specialized heads can even be used to pick several components from a tray or wafer in a single pass, thereby allowing parallel processing to deliver maximum throughput for inspection operations. An example is shown in Figure 2.
The interleaving of plunge-to-board testing and other functions in the same machine, facilitated by multi-head parallel operations, allows optimal throughput rates for the entire back-end cycle, from feeder through test to tape-and-reel output. For example, even with RF test cycle times as long as 400 milliseconds per part, a multi-function system, such as the one shown in Figure 1, can provide sustained throughput rates as high as 10,000 parts per hour.
Besides optimizing RF testing integrity and throughput, the combining of multiple back-end operations within a single platform also allows much more efficient use of production floor space by offering a much smaller footprint than is possible when using separate machines for each process. Complete multi-function back-end finishing systems can effectively combine inspection, laser marking, plunge-to-board test handling, and tape-and-reel output, all within a footprint as small as 1 square meter – not including a tester. In addition to conserving floor space, such a compact form factor also enables the back-end handling system to be closely co-located with the test equipment to minimize cabling and to further ensure test integrity.
System Configurability and Process Versatility
In today's dynamic IC manufacturing environments, it is critical that back-end processing and test handling platforms also provide optimal flexibility for fitting smoothly into overall production line requirements. This is especially true in contract manufacturing scenarios where constantly changing requirements and high-mix production flows have become a routine requirement for staying competitive.
 Figure 3. Various input formats used for back-end handling. |
Comprehensive back-end handling platforms must be able to efficiently accept components from a variety of input formats, including tubes, trays, multi-track, direct from wafer or raw bulk inputs (such as vibratory feeders) (Figure 3). Even though each feeder technology has its own advantages and disadvantages, the most important consideration is to give each manufacturer the flexibility to mesh system input mechanisms with their other production processes, as well as with accepted industry standards.
On the downstream side, the test handling and finishing system needs to be able to provide continuous output to standard tape-and-reel formats, including support for a variety of tape widths ranging from 8 to 56 mm and conforming to all applicable EIA Standards, including 481-1-A, 481-2 and 481-3.
The Bottom Line
In today's complex wireless designs, the integration of RF functionality can span a wide array of packaging types, ranging from small bumped chip scale packages or flip-chip die up through a variety of small outline devices and also including relatively large ball grid array packages. To accommodate these diverse requirements, it has become imperative that manufacturers have access to configurable back-end platforms with maximum flexibility for integrating a variety of different input formats with configurable handling and testing capabilities.
In particular, it is critical that new back-end finishing systems be able to blend handling flexibility with efficient plunge-to-board testing in order to ensure both optimal throughput and consistent high-integrity RF test results. In the final analysis, such comprehensive back-end testing and finishing capabilities will provide a vital part of the foundation for supplying the huge volumes of RF components that are necessary to fuel our increasingly wireless world.
AP
J. R. Schenk is engineering manager and Ken Kolden is marketing manager at Ismeca USA Inc. For more information, contact Ken Kolden at Ismeca, 2365 Oak Ridge Way, Vista, CA 92083-8341; 760-305-6224; Fax: 760-305-6294; E-mail: [email protected].
Driving Factors for the RF Component Market
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Wireless Devices
The demand for smaller and more powerful mobile devices is driving the wireless revolution and spurring the convergence of a widening range of functions into next generation wireless devices. Users around the globe already have put billions of mobile products to routine use in their daily lives. Now, in addition to constantly demanding smaller form factors and faster performance, consumers also are pushing for merging all of their separate devices into compact unified wireless products. Instead of juggling cell phones, personal digital assistants (PDAs) and pagers, users want to be able to handle all of their mobile communications and organizer functions within a single device.
Cell Phone Requirements
In parallel, the cell phone industry's evolution from current second-generation (2G) handsets to 2.5G and 3G capabilities is boosting both functionality and bandwidth requirements by adding features, such as Web-browsing and integrated GPS tracking, and raising wireless communication bandwidths to multi-gigabit broadband levels. Because of the multiple cell phone standards currently in use around the world (GSM, CMDA, TDMA, etc.), some manufacturers are also building so-called “worldphones” with versatile RF tuners capable of roaming between different cellular environments. To pack expanded applications, broadband connectivity and multi-standard compliance into ultra-small form factors, the RF components used in new generation cell phones have become increasingly complex and powerful, thus further raising the bar for manufacturers of RF ICs.
Bluetooth Requirements
A new wave of RF component requirements also is being driven by the relatively recent emergence of the Bluetooth wireless standard as a potentially universal mechanism for embedding short-range wireless connectivity into any device. Bluetooth operates on an unlicensed 2.4 GHz radio frequency and incorporates self-aware networking software with auto-recognition capabilities to support connectivity between all Bluetooth-enabled devices, thereby both eliminating the need for hardwired cabling and opening up a whole new realm of innovative application possibilities. For example, embedding Bluetooth RF capabilities in PDAs and laptops could allow all participants in a meeting to share electronic calendars or files. Bluetooth-enabled digital cameras could automatically link to photo-printing kiosks wherever the user might want to get pictures printed.
According to Merrill Lynch's Bluetooth Handbook, the market for Bluetooth chips will reach $4.3 billion and 2.1 billion units in annual shipments by 2005, however it also cautions “the key barrier to entry is low-cost radio-frequency (RF) silicon technology.” Therefore, providing a reliable supply for ultra high volumes of Bluetooth-compliant RF devices will be both a key enabling factor for Bluetooth to realize its full potential as a ubiquitous communications link as well as representing a major market opportunity for IC manufacturers.
Other Applications
In addition to 3G cell phones and Bluetooth-enabled applications, RF components also will continue to play a major role in military, industrial, aerospace, scientific, automotive and consumer electronics applications, as well as in relatively new arenas such as home networking. For any of these applications, high-performance RF capabilities may be incorporated into the final products at a variety of levels, which can range from die-level integration, such as chip scale packages, up through large monolithic RF ball grid arrays or system-on-chip devices.