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PCB007-Aug2020

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56 PCB007 MAGAZINE I AUGUST 2020 Soldering and Bonding Performance In the following section, the solder wetting, solder joint reliability, and wire bonding per- formance of an ENEPIG finish with the new Pd-Core® layer are studied and compared with the performance of an ENEPIG finish with a conventional pure Pd process. In selective wave soldering tests applying a SAC 305 solder according to IPC J-STD 003, all through-holes were fully wetted with solder in as received as well as in aged conditions. Figure 3 shows the exemplary result for through-holes with a diameter of 0.8 mm in as received after 2x re- flow and humid aging for 8h at 72°C with 85% relative humidity. To study the solder joint reliability of the ENEPIG finish, high-speed shear tests have been performed with both the Pd-Core® and posits with constant performance over its full lifetime, and can deposit a layer with a thick- ness distribution of 5–10% CoV measured on 10 pads with different pad sizes varying from 0.25–49 mm². This thickness distribution is in- dependent of the overall palladium thickness and can be achieved for 150 nm target thick- ness as well as for 400 nm (Figure 1). Operating at mild conditions of 55°C and a pH of 5.8, the process works for 10 MTO and more with stable and constant performance without any indication for plate-out or precipi- tation. A Pd layer thickness of 150 nm can be achieved in a plating time of approximately eight minutes. The palladium layer that is de- posited is of fine crystalline structure compa- rable to other pure Pd deposits that are present in the market (Figure 2). Figure 1: Thickness distribution of Pd deposit on different pad sizes over the full bath life. Figure 2: FIB cut of the crystal structure in the Pd deposit.

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