Abstract
The ionic contamination on printed circuit boards (PCB) having different surface finishes was examined using ionograph. The study was performed at the RT on three types of PCBs covered with: (i) hot air solder leveling (HASL LF), (ii) electroless nickel immersion gold (ENIG), and (iii) organic surface protectant (OSP), all on Cu substrates, as well as two types of fluxes, namely EF2202 and RF800. In the group of boards without soldered components, the lowest average value of contamination was for the ENIG 18 µm surface (0.01 μg NaCl/cm2). Boards with soldered components were more contaminated (from 0.29 μg NaCl/cm2 for the HASL LF 18 µm surface). After spraying boards with fluxing agents, the values of contaminants were the highest. The influence of phosphorus content in Ni-P layer of ENIG finish on ionic contamination was examined. In the group of PCBs with Au coating, the smallest amount of surface contaminants (0.32 μg NaCl/cm2) was for Ni-2-5%P layer. PCBs with Ni-11%P layer were higher contaminated (0.47 μg NaCl/cm2), and another with Ni-8%P layer had 0.81 μg NaCl/cm2. PCBs without Au coating, had the lowest contamination (0.48 μg NaCl/cm2) at phosphorous content equal 11%P. Higher contamination (0.67 μg NaCl/cm2) was at 2-5%P, up to 1.98 μg NaCl/cm2 for 8% of P. Boards with Au finish have lower value of contamination than identical boards without Au layer thus contributing to better reliability of electronic assemblies, since its failures due to current leakage and corrosion can be caused by contaminants.
Highlights
The printed circuit boards (PCB) are the insulation boards with a suitable thickness and stiffness that are commonly used in many electronic devices, from consumer electronics up to specialized equipment
Among different finishes of solder mask over bare copper, there are three types, which are mostly used in practice: (i) hot air solder leveling (HASL LF), (ii) electroless nickel immersion gold (ENIG), and (iii) organic surface protectant (OSP)
The obtained results show that PCBs in delivery state had lower average value of contaminants than those with soldered components
Summary
The printed circuit boards (PCB) are the insulation boards with a suitable thickness and stiffness that are commonly used in many electronic devices, from consumer electronics up to specialized equipment. ENIG finish is deposited on Cu substrate and it is composed of two layers, i.e., a gold layer (thickness from 0.05 to 0.25 lm) over nickel containing a phosphorous layer (thickness from 1 to 8 lm) The benefits of this kind of finish are long-term experience in practice, good corrosion resistance and great solderability, as well as shelf life of about one year. OSP finish is deposited on Cu substrate, and its typical thickness ranges from 0.2 to 0.5 lm This kind of surface finish has a 1-year shelf life and can handle multiple heat cycles, but its main disadvantage is difficult inspection of the final product (Ref 5). The influence of the type of flux and PCB surface finish (HASL LF, ENIG, and OSP), as well as phosphorous content in ENIG finish on ionic contamination was examined
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