Aries Electronics - Your Best Source for Interconnection and Packaging Solutions

Technology Update November 2001

(Appeared in Connector Specifier)

by Bruce DeChillo, Product Manager, Aries Electronics, Bristol, PA USA

The frequent changes to radio frequency (RF) package designs in products such as cell phones, pagers and personal digital assistants are typically driven by consumer needs. The packages are constantly redesigned to be smaller, faster and less expensive. The enhancements to the packages trickle down to every component of the RF device, and can be seen especially in the rapid developments that have taken place in the RF test socket market.

Defined as sockets that can operate above 1GHz with little signal degradation because of the socket design, RF test sockets have been commonly used for over a decade. They have changed quickly over this time period as several new designs have been employed to meet demand. As these changes take place, sockets must still maintain quality performance and work properly without signal degradation.

Some of the critical elements of impedance that current RF test socket designers seek to improve include lower inductance, lower capacitance and controlled impedance. Smaller contacts, spring-loaded lids and low dielectric strips that hold the contacts in place are some of the more recent developments that help to control impedance and improve overall performance of the socket.

Although RF test sockets can be developed to custom specifications, a growing trend is to use ones that are constructed to meet existing standard packaging designs. Recent developments include sockets that are compatible with MicroLead Frame (MLF) packages as well as handlers for quad-sided packages, including Leadless Plastic Chip Carriers (LPCCs) and Quad Flat Packages (QFPs).

As the race to have the shortest signal path at the smallest pitch continues, another RF test socket design that is becoming increasingly popular is the Chip Scale Package (CSP) array socket. The CSP is usually an area array configuration, with either pads or small solder balls as the input/output (I/O). With the new CSP design, there is a variety of ways to achieve the shortest signal path including spring probes, elastomeric strips, dendritic plating and stamped contacts.

There are other elements of RF test sockets that a package designer can explore including repairability, self-cleaning, and life cycle. As RF package design continues to advance, these sockets will continue to meet the new design requirements while striving for minimal degradation and increased bandwidths.