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94 PCB007 MAGAZINE I AUGUST 2021 Figure 1 shows the various stages of the through-hole fill process in 250 µm diameter x 800 µm thick panel. e plating starts out con- formal followed by bridging and filling the vias formed aer bridging. e bridge formation is achieved by using a PPR waveform and the subsequent via fill is achieved using DC plat- ing. Bridging and via fill time are optimized for the specific through-hole dimension and panel thickness. One Bath, One Step Technology Bridging and filling the through-holes is achieved by using PPR and DC plating all in one plating bath. Bridging in the through- holes is achieved by using phase shi PPR. Phase shi waveforms are generated by ap- plying the same waveform on either side of the plating panel but are offset by a certain degree. e complex waveforms are generat- ed by advanced rectifiers which are commer- cially available. e phase shi waveforms are also referred to as asynchronous wave- forms. ese waveforms enable selective plat- ing at the center of the through-holes, thereby bridging the center. Aer bridging, the plating mode is switched to DC plating for filling the vias formed aer bridging. e time for bridg- ing and filling depends on the specific through- hole diameter and panel thickness. e waveform for bridging included a long DC step followed by a pulse train. e entire sequence of this DC step is followed by a pulse train which is repeated for a specific period to achieve bridging in the specific through-hole as shown in Figure 2. e pulse parameters for Figure 1: Various stages of through-hole fill plating: Conformal, bridge formation, and subsequent via fill to fill the entire through-hole in 250 µm diameter x 800 µm thick panel. Figure 2: Phase shift waveform used for bridging the through-holes.

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