Soft Error Issue and Importance of Low Alpha Solders for Microelectronics Packaging

To satisfy the ever-increasing demand for higher density (functionality) and lower power (portability), the dimensions and operating voltages of the modern electronic devices are being reduced frequently. This has brought new challenges both from the technology and materials point of view. One such issue is soft error, the temporary malfunction of device caused by the effect of radiation on the Si ICs. One such radiation is high energy alpha particle whose main source is the solders used in the packaging. The continued scaling of complementary metal oxide semiconductor device technologies has led to continued device shrinkage and decreases in the operating voltage of the device transistors. Scaling has meant denser circuitry overall, thinner silicon (e.g., silicon on insulator) in logic applications, and less charge on capacitors for volatile memory. These trends have resulted in devices being more sensitive to soft errors since now low energy alpha particles can flip a memory bit or alter timing in a logic circuit. Due to the use of flip-chip joints and developments towards 3D packaging, the solder bumps have moved very closer to the active Si devices, where even the low energy alpha ray having short range is able to induce soft error. One of the major sources of alpha particle radiation is the solders used for joining components in the packaging and they contain alpha emitters and there is increasing demand of Low Alpha activity Pb-free solders. The present paper reviews the issue of soft error in depth covering its historical background, causes and effects on electronic devices along with mitigation efforts. The importance of low alpha solders in microelectronics packaging applications is discussed in the light of soft-error issue.