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46 The PCB Magazine • February 2015 nal integrity becomes even more challenging. This has a direct impact on assembly, and in response future surface finishes need to accom- modate newer adaptations of thermo-compres- sion bonding as the established solder technol- ogies are also at the edge of their capabilities. Topics and Considerations for Future Final Finishes Fine-line Technology The concept of fine-line technology already has to factor in the impact of etching to arrive at the required line and space. For example, to achieve 10 µm line and space the circuit will be designed at 12 µm line and 9 µm space. After such painstaking front-end design, final finish- es are faced with the challenge of maintaining this integrity as far as possible. With future fine- line technology hinting at 5/5 and even 2/2 the final finish can no longer afford µm scale pro- tection layers such as Ni at 4–7 µm. A further pitfall of the Ni inclusive technol- ogies is their susceptibility to Ni spread and re- sultant shorting, even at an abnormally low Ni thickness (the low Ni is required to achieve the line and space criteria). High-Frequency Capabilities The widespread use of smartphones and tab- lets to support daily employment and leisure activities is tangible evidence of the future ap- petite for high data flow capabilities which ne- cessitates by virtue high-frequency capabilities. Based on history, it is clear that this insatiable appetite will continue to expand. At very high frequencies surface finishes with a nickel layer become critical. It is known that nickel plated on copper will cause an ad- ditional loss to signal propagation due to the so THE FUTURE OF NICKEL IN NICKEL/PALLADIUM/GOLD FINAL FINISHES continues feature Figure 2: the impact of established ni containing finishes on line and space.