Spring probes have now been widely adopted as an alternative to well-known probe card technologies in testing WLCSP packaging. Several studies have been presented on this topic at BiTS and other conferences, and will be summarized.
Manufacturing spring probes at this scale is very challenging, and various suppliers have taken different approaches to building spring probes. This presentation will explore the various probe architectures that are commercially available, and present detailed mechanical and electrical lab performance of each style. Each contact technology will be presented from a mechanical and electrical reliability standpoint, as well as cost and complexity.
The WLCSP spring probe is not the only factor that influences the performance of the probe head. The socket housing design and materials used are very important aspects that need to be understood and optimized. Many, if not most, WLCSP applications have DUT pitches that drive the requirements to fan out the footprint to a reasonable layout that can be readily manufactured in an ATE board. Approaches to fan-out space transformers will be discussed, whether they are direct-attached to the ATE board or use a secondary compliant interface socket (tower).
Lastly, new technologies will be introduced that have the potential to lower the cost of WLCSP testing without reducing the performance. This includes innovative probe designs using one-piece architectures and space transformers that are manufactured in an entirely new method.