Whisker Formation Induced by Component and Assembly Ionic Contamination

Abstract

This paper describes the results of an intensive whisker formation study on Pb-free assemblies with different levels of cleanliness. Thirteen types of as-received surface-mount and pin-through-hole components were cleaned and intentionally contaminated with solutions containing chloride, sulfate, bromide, and nitrate. Then the parts were assembled on double-sided boards that were also cleaned or intentionally contaminated with three fluxes having different halide contents. The assemblies were subjected to high-temperature/highhumidity testing (85°C/85% RH). Periodic examination found that contamination triggered whisker formation on both exposed tin and solder fillets. Whisker occurrence and parameters depending on the type and level of contamination are discussed. Cross-sections were used to assess the metallurgical aspects of whisker formation and the microstructural changes occurring during corrosion.

Fast formation and growth of high-density Sn whiskers in Mg/Sn-based solder/Mg joints by ultrasonic-assisted soldering: Phenomena, mechanism and prevention

“…Chason et al 27 concluded that the Sn whiskers only grew from a small number of surface sites; thus, there were certain features about these sites that caused whiskers to preferentially initiate there, e.g. , suitable grain orientations101426, weak oxide layers828, surface defects2829, and IMC formation1314. Following these findings, a Sn whisker would be prone to emerge at the interface ( e.g.…”

Whisker Formation on SAC305 Soldered Assemblies

“…The first group was cleaned using the method developed in screening experiments. 16 The samples were cleaned twice to get the level of contamination 10 times below typical acceptable industry level and did not exceed 0.062 lg/cm 2 (0.4 lg/in 2 ) Cl. The second group was contaminated with NaCl using the method developed earlier.…”

“…The second group was contaminated with NaCl using the method developed earlier. 16 The piece part level of chlorine contamination 0.465 lg/cm 2 (3 lg/in 2 ) was selected to be within the industry levels encountered (no standards exist).…”

“…Optical and SEM images and EDX elemental spectrum were used to record findings similar to the results published by authors in 2008 and 2012. 16,17 RESULTS AND DISCUSSION…”

“…The distribution of the contamination on the cleaned and re-contaminated part was distributed into the plating grooves and valleys similar to the part before cleaning. 16 Cross sectioning of the PLCC demonstrated that the Sn plating of the leads is extremely uneven. The XRF measurements reported Sn thicknesses of 8-10 lm; however, the actual thicknesses observed during cross sectioning varied from 1 to 38 lm.…”