Production Validation of SERA Solderability Test Method

Abstract

The sequential electrochemical reduction analysis (SERA) method was evaluated in production and demonstrated to provide a non‐destructive, objective measure of the solderability of production printed wiring boards. Approximately 1000 boards were analysed just before wave soldering and the SERA parameters were correlated with the soldering defect occurrence rates. The data show that PWB solderability is determined primarily by the nature of the surface tin oxide, as reflected in the corresponding SERA plateau voltage, rather than by the oxide thickness. By proper choice of the value of the plateau voltage used as the criterion for solderability, the most advantageous trade‐off between the costs of rejected boards and the rework of defects can be made.

Sn-Cu Intermetallic Grain Morphology Related to Sn Layer Thickness

“…[4][5][6][7][8][9][10] This technique has been described in detail by other researchers. [11][12][13] In this study, we apply the procedures for the technique used in those studies to measure the layers of pure tin and intermetallics. This simple electrochemical method easily measured the thickness of the tin layer and intermetallic layer, allowing us to evaluate the growth rate of intermetallics and the depletion rate of the tin layer during high-temperature aging.…”

Characterization of tin oxidation products using sequential electrochemical reduction analysis (SERA)

“…Low energy electron loss spectroscopy (LEELs) can distinguish between Sn, SnO and SnO 2 , and several studies have found both species to be present (Powell, 1979;Bevolo et al, 1983;Hoflund and Corallo, 1992). The use of electrochemical techniques to quantitatively determine the thickness of a specific tin oxide species on a surface have shown considerable promise, with good agreement being obtained when compared to results determined by the LEELs technique (Tench et al, 1995b;Hillman and Tench, 1992). A relatively new analytical technique, termed sequential electrochemical reduction analysis (SERA), has made it possible to determine the amounts of specific oxide species on metallic surfaces.…”

Sequential electrochemical reduction analysis (SERA) as a viable method for characterizing tin oxidation products formed by accelerated conditioning techniques

“…The impact of poor soldering process yields of electronic assemblies in the electronics industry due to tin oxidation is substantial. Nearly 50% of solder defects can be traced to surface oxidation problems [3]. An accelerated conditioning methodology or figure-of-merit to assess the resistance of tin-based surface finishes to oxidation and to predict the amount of natural oxide prior to soldering has been highly sought by technologists.…”

“…As previously discussed, there is an agreement within the published literature that humidity increases the oxidation rate of tin. The possibility of a hydroxide species has been previously suggested by Tench[3] and Okamoto[25]. None of the reviewed published literature documented the incorporation of a hydroxide in the tin oxide morphology.…”

“…The plateau voltages for the tin species are listed inTable 2. The tin oxide thickness values calculated by the SERA instrument were computed based on the oxide parameters listed inTable 3[3]. :i Difficult to reduce outer crust (e.g., SnO2 ) i' /_j Reduction of well-defined phase (e.g., SnO) Reduction of second well-defined phase (e.g., SnO 2 ) / Reduction of mixed oxide or amorphous phase (e.g.…”