There are a large number of techniques and structures used over many years for creating repeatable temporary electrical contact between electrical and electronic circuits, and more recently integrated chip circuit packages, and testing devices. The interface between the chip and the tester is called the contactor, and it typically is comprised of individual contacts that have a set spring rate to create an even amount of pressure between each lead on the chip and each contact point on the contactor.
The principal problem with such contactors, however, is the fact that the spring rates that must be achieved, typically 30-50 grams of force over 0.5 mm of motion, result in the need for a long thin metal element. This creates an inherent antenna that makes the contactor more susceptible to noise, particularly as the frequency of test increases. When one sets out to design a short flexible multi-layered laminate beam, with sufficient distance between the current carrying central conductor and the outer ground layers to maintain a 50-ohm environment, for example, one soon realizes that there are more design constraints than design variables that can be adjusted. The result is that it has heretofore been deemed virtually impossible to design a laminated beam that can serve as a shielded electrical contact while maintaining typically desired spring rates necessary to make good electrical contact. The principal problem is that the stress imposed on the outer ground layers on the laminate quickly causes it to yield, causing the contacts rapidly to fatigue and fail.
The present invention, therefore, addresses the need for development of flexible shielded ground components for electronic applications, with particular application to semiconductor testing contactors. A critical element of semiconductor testing, which is often designed without regard for other components, is the contactor. The contactor is the key interface between the testing equipment and the part being tested (i.e., the integrated circuit package, chips, or DUT, the "device under test"), and it has many functional requirements including ideal electrical properties (50 ohm impedance, multi gigahertz bandwidth, no cross-talk between leads and grounds), and ideal mechanical properties (small footprint, controlled spring rate, cause no fatigue with the tester electronics board interface, and resistance to solder build-up on the contact points). Currently available contactors may satisfy some of these needs, but many functional requirements are only partially fulfilled. As a result, the rest of the mechanical system (i.e., principally the handler) is often large and bulky, and system reliability is less than desirable.
One current contactor for these purposes uses an in-line extension/compression spring, often referred to as a pogo-pin. This is usually configured as a tube with an internal coil spring that provides controlled compliance to protruding tips. Kruger, U.S. Pat. No. 4,773,877, shows such a pogo-pin with the spring integral with the tip. In this case, the system is a simple linear compression spring, and does not provide any shielding or impedance control.
With respect to bending beams, Doemens et. al., U.S. Pat. No. 4,897,598, shows a single curved beam system. This beam, however, also has no shielding, and in addition, a single curved beam will have far too much scrub, which is relative motion between the tip and the chip lead.
Another typical problem with contactors is the improper use of ground planes. U.S. Pat. No. 4,866,374 shows a ground plane and an insulating layer (dielectric) which actually encourages crosstalk between the lead. Furthermore, this type of contactor, with its long exposed lead tips is very susceptible to picking up electrical noise, and to damage of the exposed leads.
In addition, it is not just the contactor itself that creates difficulties in test; the size of most existing contactors requires their center-to-center spacing to be much larger than the center-to-center spacing of the chips in the storage trays. Consequently, the handling devices that take the chips from the trays and press them into the contactors become more complex. That is, the handlers must have complex robotic motions to spread the chips apart, which often require an intermediate station, further increasing complexity.
For the first time, the present invention satisfies all the functional requirements for an ideal contactor by combining technologies from different disciplines, not normally used in the art of contactor design and manufacture, along with novel new physical component shapes. The contactor is an assembled system with mechanical beams, that form the electrical contacts, and which are packaged in a structure that allows it to be mounted to the test system. The heart of the contactor, however, is the mechanical beam structure involving laminations with a contoured ground cover, which effectively shields high frequency signals, remains flexible being positioned on top of a coextensive insulating layer on a core conductor, and with the same lamination structure provided on the opposite side. Soldered-in-place or monolithic plated contact points project from the tips of the mechanical contacts to engage the electrical connections on chips or other devices that are being tested.