By Ron Iscoff, Editor
Some 40 companies, led by vendors in Japan and the U.S., now supply IC test and burn-in sockets to the worldwide market. Additionally, new companies are joining the fray at a rate of several a year. A quick look back shows that the socket industry has undergone substantial consolidation over the past few years. Widely known brand names, such as Cerprobe, CTI, Liberty Research, OzTek and Wells, are either no more or have joined forces under the same or different owners. Even where competitors are not acquiring or merging, unusual allegiances are taking place. For example, in January, socket vendors Aries Electronics Inc. of Frenchtown, N.J., and Synergetix of Kansas City, Kan., forged an agreement to develop a new generation of test sockets. The companies announced that they will develop new socket lines based on Synergetix' proprietary spring-probe-based technology. One of the important benefits of the alliance, the companies say, will be a reduction in turnaround time from 5-8 weeks to 2-3 weeks.
'Unique Event' "Our coming together is a unique event," according to Synergetix CEO Ed Schifman. "It's the first time that two major players in the RF socket marketplace have combined forces." Socket vendors are also moving their business models in one of two generally opposite directions. They are either expanding product lines to include a range of interface products-such as the merger between Liberty Research and DCI-or they are following a highly specialized, sockets-only niche. (Representative examples of current sockets are shown in the figures.) The socket market is highly fragmented, with many privately held companies competing on a regional basis, due to very low barriers to entry, according to Andrei Berar, vice president of Integrated Products Group, Credence Systems, Fremont, Calif. (Total available market for test sockets is shown in the table on page 39, furnished by Credence.) Berar, whose company now owns DCI, notes that principal competitive factors in sockets include design, product performance, price and service. Product Weaknesses Weaknesses in the existing generation of sockets, he adds, include long delivery times, expensive per-pin cost and a lack of standardization. He further believes that spring-pin technology (frequently referred to as Pogo Pin, an Everett Charles trademark), may carry limitations for pitch reduction. ST Assembly Services (STATS), Singapore, is a major IC assembler and one that emphasizes the in-house test function. STATS owns a broad range of ATE equipment at its main Asian facility and in Milpitas, Calif., at its FastRamp test center. Yap Liop Jin, section manager for test development at STATS, is a significant user of test sockets. He is carefully watching the market, which is moving towards high-speed digital and RF applications. These applications, says Jin, call for high-performance test sockets equipped with
The future socket, he adds, should operate within a temperature range of -60°C to 150°C, without any significant variation to its electrical characteristics. The socket, he says, should be able to test pitches as small as 0.3 mm and below. "For socket maintenance, the frequency of cleaning due to solder migration should be minimized through careful selection of material as well as pin design."
'Socket Industry Keeping Pace' "The socket industry has done a great job, so far, of keeping pace with the demands of CSPs, with their extremely tight mechanical tolerances and high-performance electrical specs," observes Vijesh Unnikrishnan of Guidant Corp., St. Paul, Minn. Unnikrishnan, Guidant's advanced process development engineer, adds that the future of electronic assemblies appears to be driven by the need for thinner/low-profile final products. "Hence, the z-thickness of the various CSP is constantly being challenged." (The z-thickness is determined by the thickness of the silicon die, interposer substrate, solder-ball height and overmold thickness.) Among the variables mentioned, Unnikrishnan says, the solder ball height can be greatly varied to minimize final thickness of the assembled package, while keeping the remaining thickness parameters at their standard values. Most current design techniques in socketing rely on floating nest technology to align tight pitch (0.8-0.5 mm) packages with the contact element. In turn, he notes, this requires packages to have a solder ball with some z-height. "A novel alignment technology for tight pitch area array sockets that does not require a package with a solder ball would enable the product engineer to design extremely low profile final assemblies. This would be a big plus in products such as cell phones, PDAs, etc."
Configurable Socket New products with new technologies keep appearing in the socket market. For example, a Gilroy, Calif., firm, Signal Transfer Technology, has introduced a socket assembly for IC programming and testing that eliminates the need to retool the entire socket for different BGA packages. The company's Configurable High Insertion Count (CHIC) socket consists of two parts: a socket platform with an array of contact pads (which handle any BGA with the same contact pitch) and a "personality" nest that fits over the platform (as shown in the photo). Other companies, such as R-Tec Corp., Boise, Idaho, are pursuing the lead-free market. R-Tec has developed a proprietary GCI II socket that employs a solderless interconnect. Initial testing and use, according to R-Tech, demonstrate a tolerance of handling extremely fast signals (tested from DC to 20 GHz) in low cycle hits of 1000 or less.
At the end of the day, of course, any vendor's longevity depends on customer satisfaction. Haitham Hamed is director of strategic business development at Silicon Turnkey Solutions (STS), Manteca, Calif., and a test expert. Hamed says STS will use as many as four different socket vendors, but tries to stick with one company "unless they will not support a package that we use." STS began using its current vendor a few years ago for high pin count packages, because the company was offering competitive pricing with a large amount of reliability data. "We took their sockets based on that data, used them through HAST and burn-in. HAST was the defining test, because of the moisture and pressure involved. We have seen sockets from other vendors destroying the solder balls during HAST-actually falling out on the corners where the pressure is too high." Hamed observes that the contact on his primary sockets is placed with 50 micro-inches of gold, an important point if you're looking for a HAST socket. For a less demanding burn-in application, 30 micro-inches of gold on the contact is generally enough, he says. Additionally, says Hamed, STS looks for a customer-service driven vendor. "Our current vendor has made significant advances in customer service, while another of the vendors we have used from time-to-time has declined."
Conclusion As the socket market grows, adding new technologies, price will continue to be a significant factor. The cost of retooling a socket, for example, can run up to $100,000. Look for further consolidation among vendors and a continuing schism between "full-line" ATE vendors and highly specialized niche suppliers.
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