Current Issue The International Reference for Chip-Scale Electronics, Flip-Chip Technology, Optoelectronic Interconnection and Wafer-Level Packaging October 2002 Email the editor

Infomation on products or services covered in this article

By Ron Iscoff, Editor

Johnstech's new Pad Series 2mm socket displays the company's new insert technology. The inserts are a copper insert with Johnstech's center body contacts (in the contact and to the left), a solid copper insert (lower left) and a Torlon insert with S-shaped contacts.

Test socket makers are rushing to stay ahead of a product technology curve that demands ever-higher performance and the ability to handle shrinking pad pitches. But that's just the beginning of the story for the socket industry and its customers.

There are no fewer than 40 test socket providers, as shown in the directory that accompanies this article. Each time we look at the test and burn-in socket industry (which we'll refer to as test sockets for simplicity), there are several new entrants, and some of the former vendors disappear by acquisition.

The reason for the growth, of course, is that the cost of entry to produce sockets is small, compared to most types of test gear. Most of the materials, such as the spring probes used to construct most socket types, can be sourced from several vendors.

Bringing out a truly new socket, however, can require a substantial amount of R&D, something often reflected in a new socket's high cost.

DCI, now a subsidiary of Credence Systems, is selling the Model 1560 Thermal Socket System for thermal management in test. The unit is suitable for all package types.

Electrical Performance

On the electrical performance front, the key driver for test sockets is always higher performance, says Jim Brandes, engineering manager at Gryphics, Plymouth, Minn.

"This concerns the ability to handle higher edge rates, higher current and higher frequencies or data rates. These requirements," he adds, "demand lower parasitic impedances."

Mechanical issues, Brandes says, involve smaller pitches, higher densities, lower insertion forces, thermal access for heating and cooling and the ability of the contact to withstand solder build-up.

Regarding socket types, demand is growing for spring probe test sockets, according to Thomas Rein, market manager semiconductors for Yamaichi Elec-tronics USA, San Jose.

"The test and burn-in socket market for BGA/CSP and LGA packages with 0.4 to 1.27mm pitch-in all package variations-is evolving positively," says Rein. "The market share for these packages is predicted to rise steadily over the next period."

In general, he adds, BGA/CSP pitch sizes are shrinking, and there is a tendency toward larger ball matrices.

Test sockets are "squarely in the middle of a serious conflict in direction" from their customers, the chip makers, according to Jon Diller, international business development manager for Synergetix, Kansas City, Kansas.

Diller observes that while devices are becoming smaller and pad widths are shrinking, the growth of leadless packages means that sockets can no longer align devices by their leads.

At the same time, he adds, edge-to-edge tolerances have remained much the same as in the past. Unhappily, this may result in sockets less able to align devices reliably.

Chip makers are also moving toward gravity-fed handlers to achieve higher throughput, Diller notes. Gravity-fed machines appear to present more problems with alignment in the X-Y and Z axes than pick-and-place handlers. "Ultimately," says Diller, "devices will be optically rather than mechanically aligned."

Signal speed and power dissipation are additional concerns to some socket vendors.

The SER 1mm-pitch FBGA socket accepts up to 2K I/Os.

"In addition to higher pin counts, smaller packages and tighter pitches, test sockets must also handle greater signal speeds and power dissipation," observes Guy Delisle, vice president of marketing for package test at Kulicke & Soffa Inc., Willow Grove, Pa.

Delisle sees an increasing demand for test sockets that can handle speeds of 10 GHz and higher.

Today, Delisle believes, chip makers are looking for more than just a socket. Now, he reports, users are looking for a single company that can design and produce a total interconnect package that includes contactors, test sockets, ATE boards and thermal management systems.

Although it appears that socket makers have not been hit quite as hard as equipment vendors by the current recession, it has been a difficult time for them, too.

"Having been in the high-performance contactor business for more than 10 years, the past 12-18 months have proven to be both difficult and enlightening for Johnstech," reports David Johnson, president and CEO of Johnstech Inter-national, Minneapolis, Minn.

"In the boom times of 2000, our customers' number one concern was getting product on time so they could meet their customers' delivery needs." In today's economy, however, Johnson reports that the top concern is reducing the cost of test while still meeting all end-user test criteria.

Obtaining contacts and spring pins from U.S. sources has been problematic, according to Nick Langston Sr. of DCI, Santa Clara, Calif.

Langston believes that onshore suppliers of these parts have been unable to keep pace with suppliers in Japan, Korea and Thailand. "We have been able to get 50W probes and very fine pitch probes from CSP sockets that run in excess of 25 GHz very readily from several Asian suppliers."

The socket industry veteran also notes that many probe suppliers are now plating their product with palladium and other noble metals to help reduce the solder migration to the pin, which causes early socket failure due to high resistance.

Thermal management is an important factor in socketing. This system, developed by Kulicke & Soffa Inc., interfaces via manual latch or optional pneumatic actuator to the device under test.

"For strip-test users," declares Langston, "high resistance on the contact pins is the leading cause of socket failure."

As China becomes the center of IC packaging and test, test socket sales (and soon socket manufacturing) will follow, says David Pfaff, president of Plastronics Socket Co., Irving, Texas. "This will bring more Asian competition into the socketing business." Additionally, observes Pfaff, domestic socket suppliers are increasing which will fuel the trend towards "price erosion across the board in the socket industry."

What motivates a buyer to select a particular socket brand?

Yap Liop Jin, section managerÐtest development at IC packaging foundry STATS, Singapore, says the selection is based on both electrical and mechanical specs.

"Take for example, an RF test socket. Besides having the desired bandwidth, we are looking for inherent losses, such as the cross talk and other parameters that may affect signal integrity-capacitance and inductance.

"To be production worthy," adds Jin, "the socket must be durable and reliable and able to perform hundreds of thousands of insertions with minimum maintenance."

For applications that don't need high frequency test, Jin will usually select a standard off-the-shelf unit. "The key focus will be on the life span (number of insertions) and the cost."

Conclusion

Suppliers in the highly competitive socket test and burn-in market are faced with many of the same challenges common to the rest of the semiconductor industry, including "smaller, faster, cheaper."

Additionally, they must address highly complex mechanical and technical issues to deliver products that work across a growing range of package types and test handlers. And, with no letup in sight in chip feature sizes or package densities, socket quality demands can only get tougher.