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56 PCB007 MAGAZINE I MARCH 2025 • When gold wire bonding is required • Excellent replacement for harsh environments • High gold bond shear test results • Nonmagnetic for RF • Better wear attributes than gold Final Finishes As semiconductors (IC transistors) become smaller and have faster rise times, the signal is more sensitive to any ferromagnetic metal in its path. Many alternatives have been developed to remove nickel as a barrier metal on copper for final finishes, especially ENIG, to improve insertion loss. Everyone has their favor- ites. e simplest and cheap- est is OSP, followed by Pb- free HASL, but they have their pros and cons. Immersion sil- ver is quite popular in North America, and immersion tin is popular in Europe. ENIG has been a long-time standard, but the nickel now comes into play because it does not dissolve in the solder as these others do. Enter palladium to replace the nickel as a barrier metal to gold. e new finishes are Pd on Cu, Pd/Ag, Ni/Pd, Ni/Pd/Au, Pd/Au, and even [Sn/Ni]/Pd. All were developed to replace the ENIG for solderability, shelf-life, and wire bonding. New Applications of Palladium For electronic assembly reliability, espe- cially for harsh environments, palladium has many advantages over nickel, except cost. For improved wire bonding reliability, a minimum of 5 microinches of electroless palladium over nickel or copper will eliminate any 0.7 mil gold wire surface failures and provide over 6 grams of pull strength (Figure 1). Figure 1: Comparison of ball shear strength (gm) of four different palladium finishes and mixed gas simulation for 10 years 2 . Table 1: Soldering wetting angle for various finishes, as received and after one reflow cycle (Source: Atotech)