Advanced Test Sockets Meet CSP Design Requirements

A newly developed test socket design, featuring interchangable package inserts, provides a system distinguished by lower cost, improved performance and increased reliability.

An approach that meets all of the above criteria is the i2™(interchangeable insert) test socket system from OZ TEK. The i2 system features a single socket base manufactured for a specific device under test (DUT) board. The socket base accommodates a variety of interchangeable inserts, each one manufactured to meet the exact parameters of a specific package. Figure 1 is a drawing of a Delta Flex™-compatible CSP test socket (also referred to as a test contactor), designed and produced using the i2 test socket system.

A key feature of the i2 system is the universal body which houses spring-loaded probe contacts. The Delta Flex-compatible body incorporates a 144-ball count on a 12 x 12 grid pattern for contacts and is available in five pitch variations: 1.00 mm, 0.80 mm, 0.75 mm, 0.65 mm and 0.50 mm. Figure 2 shows the footprint for the 0.50 mm pitch version.

Spring-loaded probe contacts, which are employed in the i2 system, are highly accurate and reliable. They can be designed and manufactured to meet the specific requirements of different package types, avoiding the risk of inadequate performance (due to under-design) or excessive cost (due to over-design), which is often characteristic of a "one-size-fits-all" approach.

Specifications

Figure 2. Footprint of the 0.50 mm pitch OZ TEK socket

Typical electrical specifications, depending on package requirements, include insertion loss of 1 dB at five to nine GHz, contact resistance of 25 to 300 mW, self inductance of 1.0 to 3.0 mH, and capacitance of 0.01 to 0.10 pF. Typical mechanical specifications, depending on the package requirement, include contact spring force of 5 to 25 g, contact compliance of 500 µm and an expected life cycle (MTBF) of over 100,000 cycles.

Key Features

Figure 3. Delta Flex-compatible socket with four package-specific inserts

In addition to providing accuracy and reliability, the spring-loaded probe contacts can be added to, or removed from the socket body as needed. This feature works in conjunction with the second key feature of the i2 test socket system, interchangeable package-specific inserts, to provide operational §exibility. Changing inserts and contact configurations (all nonfunctioning contacts can be removed) allows users to employ the same socket to test a variety of different packages with various ball counts, as long as the packages have the same ball pitch.

This design §exibility allows the tailoring of socket and contact designs to meet a variety of CSP requirements, including high-speed RDRAM packages.

Figure 3 is a photograph of a Delta Flex-compatible CSP test socket with four package-specific inserts, each with a different ball arrangement. Figure 4 is a photograph of an HP95000 CSP test contactor with three package-specific inserts for RDRAM devices, each with an identical ball arrangement, but a different package outline.

Faster Delivery

Figure 4. Test socket for the HP95000 test system shows package-specific inserts

Because only a new insert is required to accommodate a new package design, typical delivery time is less than two weeks rather than the six to eight week delivery time required for most custom sockets, or the six months tooling time which is typical for new, off-the-shelf socket designs. In addition, replacing only a package-specific insert, rather than a complete new socket, is typically 25-40 percent less expensive than replacing a complete new test socket.

The payoff to the user with the new socket system is a reduction in time, money and inventory, as only one DUT board, one docking plate for the handler, and one socket base are required for an entire family of package designs and sizes with the same ball pitch.

This §exibility allows test areas that utilize multiple assembly vendors, or packaging foundries, to rapidly convert from package-to-package with a minimum of downtime and hardware. The result is maximum utilization of handler hardware, reduced test socket cost, smaller inventory, quicker setup times and improved part-to-socket tolerances.

Conclusion

The i2 test socket system provides one method of meeting the demands of advanced CSP package designs. This design approach incorporates interchangeable inserts and spring-loaded probe contacts housed in a universal socket body to address electrical, mechanical and cost factors in a balanced and flexible manner.

The balanced and §exible approach of the i2 test socket system may not meet all CSP test socket requirements. For example, a test application may require a specific electrical or mechanical specification that is not attainable within the framework of the i2 test socket system, and may require a custom design.

The i2 test socket system however, will provide operational, delivery and cost benefits for many CSP test applications, including high-speed RDRAM testing.

Mr. Rogers is OZ TEK's vice president of sales and marketing. He founded Bruce Rogers and Company, a manufacturer's rep for semiconductor test products, and headed that firm until joining OZ TEK in 1997. Mr. Rogers holds a bachelor's degree in business administration from the University of Nevada, Reno.