Failure Diagnosis in RF Boards and Mitigation Techniques

Abstract: Surface mount technology is preferably employed for higher throughput and better circuit reliability. PCB board for radio frequencies imposes certain challenges due to incompatible material as well as non-uniform material height. Other requirements such as PCB size, ESD sensitivity, warpage, thermal profile also plays important role for having the higher process yield. Critical devices such as VCO,PLL,Amplifiers chips are having body grounding and are also prone to ESD failures. The requirements for RF boards are different from the standard digital circuits for SMT process. Various boards populated with miniature and special devices are also employed for RF boards and this requirement impose restrictions on the process line. This article details the challenges imposed by the RF boards and the mitigation techniques employed to overcome the same using the SMT line. X-ray and optical inspection are the main characterization tools in the SMT line. X-ray has been effective in detecting defects in non-destructive way and hence enhanced the product quality. The inspection system ensures there are no defects such as solder shorts; Wire breaks, PTH damages,Loose particle/conductive debris inside the packages, Micro-D connector assemblies etc. The system is continuously used to inspect solder joints of QFNs, BGA & CCGAs which cannot be inspected with visual methods. This article details various failures observed using X-ray inspection system and corrective methodology adopted to avoid the future occurrence of the phenomena.