Influence of Thermal-Cycling-Induced Failures on the RF Performance of Ceramic Antenna Assemblies

In this paper, the high-frequency behavior of ball grid array solder interconnections during thermal cycling tests (TCTs) was investigated. This interconnection type was used in ceramic antenna modules that were attached to printed wiring boards thermo-mechanically equivalent to commonly used FR-4 material. The tests were carried out in a TCT chamber operating in the 0-100 °C range. To observe TCT-induced failures in the interconnections, scattering parameter measurements (return loss) were performed both during the TCT and at room temperature during cycling breaks. These measurement data were contrasted with imaging results obtained with scanning acoustic microscopy (SAM), and scanning electron microscopy (SEM) was used to verify the failure mechanisms in the interconnections. The results indicate that degradation of interconnection(s) can be seen both during cycling and in room-temperature measurements in a wide frequency band. The degradation was seen best in deteriorating out-of-band characteristics of the antennas. Measurements during cycling gave a more comprehensive picture of the assemblies´ electrical response to fractures in interconnections than did off-cycle measurements. SAM imaging showed indications of cracking much earlier than they were observed in S-parameter measurements. SEM results suggested that the main failure mechanism was cracking in solder.