By Ron Iscoff, Editor Combine the shrinking IC with its shrinking package, and you've invoked a formula sure to cause some sleepless nights among the community of test and burn-in socket suppliers.
It's like anything in the micro-world: smaller package sizes demand sockets able to handle tighter I/O pitches. How do you design a new socket? Very carefully, as most socket makers will tell you, since the socket's basic task is to ensure reliability through burn-in. A Market in Motion From a business standpoint, the socket supply market has been in motion for the past two years. Although there are still more than two dozen socket suppliers, over the last few years, there has been a continuing consolidation. Several well-known firms have acquired new owners (see table), including DCI, Liberty Research, OzTek and PrimeYield Systems. What buyers want in sockets, of course, varies by application. Vitesse Semiconduc-tor, Camarillo, Calif., produces SONET compliant ICs that operate at 2.5 and 10 GHz. These must be tested to very high performance specs to meet Vitesse's quality standards. "The first item I consider is frequency bandwidth," reports Jerry Droney, an associate engineer at Vitesse. "Next I consider mechanical reliability in the production setting. That is, how many insertions can the socket take before it needs to be cleaned or otherwise maintained before problems develop?" Further considerations, he adds, include socket life span, cost and the reliability of the vendor. In selecting sockets for CSPs, Roberto Dossi, package development manager for the Wireless Flash Memory Div. of ST Microelectronics, near Milan, Italy, has a different shopping list. He looks for good electrical contact, good reliability (especially at higher temperatures), low impact on solder balls, open top sockets (on lower pitches, too) and a balance between price and quality.
Greater Flexibility Drossi says that he would like to see greater flexibility with future sockets, as well. "Currently we need new tooling for each package change, at high cost." He also wants a socket that can test packages with solder balls (such as BGA), and packages without, such as LGA). Buyers unfamiliar with sockets can be forgiven if they are confused by the numerous socket types, technologies, specs and sizes. While unintentional on the part of the vendors, the competitive atmosphere (and the growing number of package types) has escalated the diversity and number of sockets. We asked some socket vendors to tell us what the key challenges are in producing sockets for a technologically explosive market.
• Aries Electronics Die shrinks are causing package engineers to design smaller and smaller IC packages. As package size decreases, socket manufacturers are faced with alignment issues, which may cause intermittent functionality. Shrinking package size requires tighter I/O pitches and these sometimes demand new contact designs from socket manufacturers, which makes it more difficult to satisfy time-to-market requirements. -Frank Folmsbee, Sales & Marketing Manager • DCI (Division of Credence Systems) One major trend, which will impact socket and contactor designs, is increasing edge speeds. To accommodate expanding memory bandwidth and increased network traffic, new generation devices need to be designed at the "edge" of the network. This year, device bandwidth is increasing to OC-192 line rates of 10 Gbps. These new devices are exhibiting edge rates faster than 90 ps and jitter less than 35 ps. When these signals are impressed on the contacts and sockets, the wire interconnects behave as transmission lines. Without careful design, the sockets can cause ringing, crosstalk and excessive delays-as well as excessive error rates. -Nick Langston, Product Line Manager • Everett Charles Technologies Advances in CSP and near-CSP packages have enabled smaller footprints for high-performance devices. The nature of these packages, high volume, small size and high frequency, makes achieving a high level of performance with existing contactor technologies extremely difficult. Achieving higher frequencies requires transparency of the contactor-interconnect path. This directly contradicts the need for adequate compliance, necessary for reliable test hardware setup and use. Fortunately, however, recent advan-ces in Pogo pin* technology are enabling many IC manufacturers to achieve the needed compromises for successful test interfacing. -Brian Crisp, District Sales Manager • Johnstech International RF and high-speed digital needs are changing the requirements for contacting solutions. Both low electrical parasitic of the contact and the need to provide close termination to the DUT are important drivers for the contactor configuration, which will require close partnering with the tester and load board manufacturers. Supplying a contactor alone will not meet the customer's needs; we must be able to understand the mechanical interface and electrical requirements for a total test solution. -Randy Knudsen, Product Marketing Manager • Kulicke & Soffa Test Division The key challenges in designing and producing test sockets for the next generation of CSPs requires having the expertise and flexibility to address the diverse needs of different applications quickly and cost-effectively. -Karen Lynch, Marketing Director • Loranger Inter-national Corp. Smaller pitches (below 0.5 mm) will require smaller pad sizes. This trend will necessitate design and engineering advances to maintain reliability and longevity of contacts. Sockets with Kelvin connections to packages will require additional materials, design and engineering considerations. -Ariane Loranger, Sales Manager
• Plastronics Socket Co. The key challenges for next generation devices are heat dissipation and controlling the temperature of the silicon. Currently, we and others are including heat sinks on the sockets to help dissipate the additional heat provided by devices operating in the 1-20W range. However, without dynamically controlling each position, the temperature difference in a device on one side of the oven will vary ąplusmn;10°C from another device. Since burn-in boards are loaded in series in the ovens, the air temperature and velocity are not consistent across a chamber, which makes it difficult to keep the device at the specified burn-in temperature. With the mass installed base of traditional burn-in systems, the changeover to new systems that can control each individual position is a huge expenditure. The economic picture will inhibit newer systems and processes to add in the heat dissipation arena. With the wattage increasing to over 50W, new systems or methods are, however, not an option, but a requirement. -David Pfaff • Texas Instruments Interconnection Business Handling, size, I/O count, power and cost are the key challenges facing suppliers of burn-in sockets for next-generation packages. The move to flip-chip packages, where the backside of the die is bare, provides a small, thin package with excellent electrical characteristics. The potential for damaging the bare die is high, and handling of the package is an important detail. The most significant challenge facing suppliers, however, is cost. -Larry Furman, Sales & Marketing Manager
• Yamaichi Electronics Designing for finer pitch (0.5 mm<) and higher densities (I/Os reaching over 2,000) is becoming more and more difficult, as the limits of physical logistics begin to come into play (i.e., insulator wall thickness, etc.). Testing higher-and-higher-speed ICs is also becoming quite challenging, as one begins to assume a tradeoff between the smaller deflection of miniature-type contacts with lower inductance and the needed long-term cycling reliability. -Robert Million, Marketing Manager One thing's for certain. The industry slowdown that struck in the last quarter of 2000, will now force buyers to scrutinize the specs of new and expensive burn-in sockets very carefully before making a purchase. * Registered trademark of Everett Charles Technologies. |
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