Select Page

Meeting the Rising Reliability Demands in Automotive Electronics Applications

By Watson Tseng, General Manager, SHENMAO America Inc.

While the future of autonomous vehicles is promising, demands and requirements continue increasing on automotive devices. Automotive devices are expected to be smaller, lighter, multifunctional and featuring with quick response communications. Reliability is emerging as a top priority since it related to safety of drivers and passengers. Reliability requirements for automotive are higher than for consuming electronic products while taking into consideration the impact of the extreme environment, season alternation and vibration while driving. As a result, extremely high-reliability devices are necessary.

 Thermal cycle test (TCT) is a method used to evaluate the reliability of electronic products. Thermal cycling is performed under harsh conditions of extreme high/low temperature cycling. The critical failure factor in TCT is thermal stress comes from coefficients of thermal expansion (CTE) mismatch during the temperature cycle. The CTE mismatch within assembly structure is significant. Failures occur under continuous thermal impact of expansion and contraction. Solder joints play an important role connecting the package and the PCB, provide electrical and a mechanical bonding in between. The thermal stress from CTE mismatch also impacting solder joints: increase the solder strength to prevent thermal fatigue. 

 There are two main ways to strengthen solder strength. The first is dispersion strengthening, which introducing a second phase like intermetallic compounds (IMC) through the addition of an alloying element such as Ag, Cu, etc. The Ag content affects solder mechanical properties. The higher in Ag content, the finer of dispersed Ag3Sn IMC and solder matrix grain size, result in high strength and fatigue resistance, and hence resulting in higher thermal cycle reliability. To date, Sn-Ag-Cu is the ideal lead-free solder alloy for most applications. Sn-4Ag-0.5Cu, also known as SAC405, is a popular candidate when thermal reliability is taken in consideration.

   The second method used to increase solder strength is solid solution strengthening, in which adding atoms of one element (additive) to the crystalline lattice of based element (Sn). The local nonuniformity in crystalline lattice, which induced by atom size difference of additive and Sn, make dislocations cannot easily move around this interruption. Larger differences in size create more distortion of the crystalline lattice, resulting in higher strength being obtained. Bi, In and Sb are common candidate of solid solution strengthening in solder alloy.

SHENMAO’s high-reliability solder alloys are able to meet the demands of automotive electronics devices.

To keep pace with the requirements and demands of the automotive electronics industry, high-reliability lead-free alloys must be developed with the goals of higher thermal cycle reliability than SAC405; similar soldering temperature to that of a typical SAC solder alloy and good soldering ability. Additionally, all hazardous substances like lead element must be avoided to meet all RoHS requirements.

SHENMAO’s new high-reliability solder alloys meet all these needs. SHENMAO’s PF916-S and PF918-S are solder alloys with Ag, Bi and other minor additive, features a similar soldering temperature window to SnAgCu alloys, allowing for easy adoption into existing packaging processes.

PF918-S has higher thermal reliability performance than typical solder alloys such as SAC305 and SAC405, and is suitable for use in automotive electronics applications. While PF918-S provides improved thermal reliability, SHENMAO’s PF916-S, which is doped by Sb, has the best performance in thermal cycle and mechanical shock. Both high-reliability alloys exhibit similar melting behavior to SAC405 as well as excellent tensile strength and ductility, making them ideal for use in high-reliability automotive soldering applications.

For more information about SHENMAO America, Inc., contact General Manager Watson Tseng at watson_tseng@shenmao.us or visit www.shenmao.com