Incredibly, the number of transistors in integrated circuits (ICs) has tracked Moore’s law, doubling every two years. Equally amazing is the recent jump in IC device operating frequency into the mmWave spectrum. The emergence of 5G, next-generation WiFi protocols, and automotive radar have pushed ICs into these extreme frequency bands to take advantage of the additional available bandwidth. The need for instantaneous data transfer has driven the increasing demand for these new mmWave devices, whether for safety concerns in automotive radar, enormous data networks for 5G cellphone backhaul, or simply the expectation to instantaneously stream 4K video from your tablet to your flat screen. Historically, 6 GHz was the high end of the frequency band for the majority of ICs. Operating frequencies have jumped to 30, 40, 60, and 80 GHz to get the necessary bandwidth for next-generation 5G, WiFi, and automotive devices, respectively. This equates not to a doubling in frequency, but to a gigantic leap that in some cases is greater than an order of magnitude. An additional challenge beyond the rapid growth in operating frequencies is caused by 5G applications driving an emerging need for production over the air (OTA) test of antenna in package (AiP) devices.
Today cmWave (3-30 GHz) and mmWave (30-300 GHz) applications have become mainstream. The wafer is becoming the new final test package. Testing automotive radar on wafer at 80 GHz and 150 °C was previously a fantasy, but is now a reality. With high tech electromagnetic simulation tools and 110 GHz VNA’s it’s possible to design and fabricate hardware for these extremely high frequency, extreme temperature applications.
A recognized standard for evaluating the CCC (current carrying capacity) of an interconnect used at wafer probe has been the ISMI Probe Council Current Carrying Capability Measurement Guideline, published by International SEMATECH Manufacturing Initiative in 2009. The ISMI test is a relatively simple way to observe the interconnect force degradation as a function of current applied. The guideline evaluates at what point the contact sees a 20% force reduction. This 20% force reduction, means that the contact has been permanently deformed, and this is therefore a truly destructive test.
Effective thermal management has become mandatory for testing devices with faster switching speed transistors that are increasing in numbers in smaller packages. These devices are dissipating more heat while being held at steady test temperature extremes. In most cases, the heat will exit the device-under-test by conduction through the probes in the contactor. Newer probe technologies incorporate in-probe radiation features to support convection for thermal management along with two-point contact for effective conduction heat removal.