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38 The PCB Magazine • June 2016 substrate manufacturers. The throwing pow- er was evaluated using method A according to TPW S . As can be seen in the lower part of the chart, the new electroless copper bath outper- forms the reference system in terms of throw- ing power. The new electroless bath achieved a significantly higher absolute and relative de- position in the BMV wedges which leads to a throwing power of approx. 70–80 %, whereas the reference achieves a throwing power of about 20%. Throwing power measurements and com- parison tests for the recently developed hori- zontal e'less copper HDI are shown in Figures 8 and 9. The new electrolyte was compared with two horizontal reference systems using analy- sis method A with throwing power evaluation TPB E in horizontal mass production equipment, which is the standard production environment for high-end HDI manufacturing. Reasons for this are the constant process conditions for each panel and the excellent fluid exchange especial- ly in BMVs. During the test, the electroless cop- per thickness at the top or entrance of the BMVs was comparable for all three candidates thereby fluctuating around 350 nm whereas the abso- lute thickness at the bottom of the BMVs was significantly higher for the new bath e'less cop- per HDI compared to the reference systems. As a consequence, the calculated throwing power (approx. 73%) is higher for the new bath. In another test throwing power measure- ment method B was applied to evaluate the throwing power directly on the capture pad. The electroless copper layer of e'less copper HDI in between the electrolytic copper protection layers becomes visible after electro polishing (see Figure 10). A similar throwing power (ap- prox. 74%) compared to the result using method A at the bottom of the BMV was achieved. HIGH-THROW ELECTROLESS COPPER—NEW OPPORTUNITIES FOR IC SUBSTRATES AND HDI MANUFACTURING Figure 9: Throwing power comparison of e'less copper HDI and two reference systems. Figure 8: Throwing power measurement method A according to TPB E and the test vehicle.