Degradation of digital signal characteristics due to intermediate stages of interconnect failure

This paper examines the effect of intermediate stages of interconnect failure on the characteristics of digital signals. It was found that at data rates above several Gbps, the skin effect causes eye parameters in the digital domain to deteriorate in response to interconnect damage well before the creation of an open circuit. Fatigue tests were conducted to gradually stress a solder joint while monitoring changes to the eye parameters, including rise time, eye height, jitter, and the constituent components of jitter. All of these parameters were found to exhibit measurable degradation prior to complete separation of the solder joint. The jitter component making the largest contribution to the change in total jitter was inter- symbol interference. The results support the conclusions from prior studies using time domain reflectometry and demonstrate their implications for digital electronics. Digital signal parameters offer an improved means of interconnect reliability assessment compared to traditional methods using DC resistance. The eye parameters also provide interconnect failure precursors, which may be useful as a product health monitoring tool for high speed electronics.