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76 The PCB Magazine • March 2017 part of the testing, Bob offered to benchmark the performance of the ionic liquid-ENIPIG finish against existing finishes applied in industry. The test boards are highlighted in Figure 1, showing a 15.3 cm x 10.2 cm panel with a cop- per finish which includes smaller pop-out cou- pons. A single board contained 18 test coupons for solder spot wetting and wetting balance measurements. The test boards were plated at the UoL with an ionic liquid-ENIPIG finish. The thickness of the finish was measured using an X-ray fluorescence (XRF) device at Merlin Circuit Technology, Deeside. The plating outcome is displayed in Figure 2, showing a plot of the metal thickness measured tangential to the surface of the board for the different metals applied in the ionic liquid– ENIPIG and on different pad sizes. Two pads were measured. One was a 10.5 mm2 rectangular pad and the other was a 1.8 mm2 circular pad. The plating behaviour typically varied for the immersion palladium and gold plating processes, depending on the area and shape of the pad plated. The general trend showed that pads of a larger surface area produced thinner deposits. The ionic liquid-ENIPIG was no different, showing a variation in plated thickness dependent on the pad feature size. When processing the panels, the amount of metal plated was deposited down to within the standard set by the IPC, and as outlined for ENEPIG plating, which stipulates Ni, 3−6 μm, Pd, 50–150 nm and Au, 25 nm or larger [4] . The measured thicknesses were within the guidelines, showing that the ionic liquid chemistry could be made to perform comparably to the existing processes. The Pd thickness failed to measure on the large pad due to the detection limit of the XRF device, although independent measurements, not shown, confirmed that Pd had deposited to within minimum specification. After plating, the first quality test was a sol- der wetting balance measurement. The solder wetting balance test evaluated the ability of sol- der to adhere to the test panel, as it was verti- cally submerged with flux on its surface into a bath of molten solder. Once submerged, the sol- der climbed up the panel and the quality of the Figure 1: Test board for solderability evaluation. 18 test coupons for solder spot and wetting balance measurements. Six rows of tracks for spot patterning of 22 paste dots and seven pads for wetting balance measurement. MACFEST: BENCHMARKING A NEW SOLDERABLE PCB FINISH