Comparison Of Several Pcb Surface Finish Types
At the same time, O and S parts had been also gathered on the enrichment area of the Cu component . In mixture with EDS analysis outcomes of Area A, the migrating corrosion merchandise have been mainly composed of sulfates and oxides/hydroxides of copper. Furthermore, it could also be discovered from Figure 2a that a thin layer of a shiny white substance existed on the left of the migrating corrosion products.
Two leading candidates for brand new finishes that would achieve market share sooner or later are Electroless palladium and a PTFE-type movie that is plasma deposited onto the board. Wave soldering after meeting is listed as a major issue with this finish. When the finish is exposed to elevated temperature, the skinny tin layer can become nearly completely transformed to SnCu intermetallic . Many PCB retailers in the Americas or in Asia do not have excessive volume capability with this finish.
From Figure 2b, it may be seen that an apparent ECM phenomenon occurred on Cu factor. In the meantime, the Cu component migrated toward the cathode from the anode, and almost half of the FR-4 boards had been covered.
Figure 2b exhibits that the bright white substance is metal Cu, indicating that a great amount of Cu ions have been lowered between the 2 plates and that it steadily grew toward the cathode. The growth path of the Cu crystal differs from the dendrite in earlier revealed literature . From Figure 2c,d, it can be seen that each Na and O components had been enriched on the surface of the cathode plates. Therefore, it may be deduced that the reaction on the floor of the cathode plates is especially the O2 reduction response and the compound could also be NaOH. The lack of a satisfactory surface finish to suit all functions has result in the event of recent finishes.
This leaves us with gold as essentially the most appropriate prime plating but this has its own distinctive setback. Gold can't be put immediately onto copper; it wants a barrier layer, offered either by the nickel in ENIG, the silver in ISIG (Immersion Silver/Immersion Gold) or by Palladium in ENIPIG . To observe the electrochemical migration behavior and discover the failure mechanism, elemental distribution mapping detection was carried out on the PCB floor, as proven in Figure 2.