Semiconductor Test Contactors/Sockets

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Contactors/Sockets

The contactor is the test accessory that makes the actual physical contact with the device under test (DUT) to establish the necessary electrical connection between the ATE and the DUT so that the former can electrically test the latter. The contactor assembly is generally a part of the test handler. Thus, before production testing can begin, the test handler must first be fitted with the test contactor assembly or contactor block suitable for the device to be tested.

Fig. 1. Examples of contactors

The proper selection of contactors for electrical testing has a great impact on test yields, device grading, repeatability and reproducibility of testing, and productivity. A poor choice of contactor can eventually lead to contact problems that cause invalid failures or test miscorrelations, which in turn can result in unwarranted machine downtimes, unexplained yield problems, and even customer returns.

A contactor has a set of contact elements that are usually in the form of metal fingers (also known as 'contact fingers') or spring-loaded pins. These contact elements are the ones that come into contact with the leads or solder balls of the DUT during electrical testing. Contact elements are commonly composed of a beryllium-copper base metal with gold-plating on the surface.

The profile of a contact element is critical to contact integrity and life prolongation. Traditional test sockets are designed and manufactured with contact elements that act as cantilevers on which the leads of the DUT can rest. These cantilevers are given an inherent amount of ‘spring’ in them so that they’ll tend to oppose the forces exerted unto them by the leads of the DUT, ensuring good electrical contact. This contact force is a function of the flexing and compression properties of the contact elements.

New contactor designs use an ‘S’ structure for the contact elements which are believed to be more reliable and robust than those using the cantilever design. The contact force provided by these new designs depend on the flexing properties of the elastomeric elements supporting the contact elements, and not the properties of the contact elements themselves. As such, they are more immune to contact issues caused by contact element deformation.

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