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June 2016 • The PCB Magazine 39 Dry Film Adhesion Performance The application of the dry film during pat- tern plating is a critical factor for the overall yield of the manufacturing process. In order to ensure an acceptable yield, the adhesion of the dry film on the electroless copper layer needs to be sufficient to survive the subsequent process steps of the pattern plating. Insufficient adhe- sion could otherwise lead to opens and shorts resulting in yield loss. Several parameters are in- fluencing the dry film adhesion and need to be considered. Two of the most important factors are firstly the lamination conditions of the dry film and secondly, the surface morphology of the electroless copper layer. For an optimal re- sult, the lamination parameters need to be opti- mized to the specific electroless copper deposit. Dry film adhesion on the new e'less copper IC bath is demonstrated by using the "line adhe- sion test" on electroless copper deposits plated on ABF GX-T31 laminate. After copper surface treatment with H 2 SO 4 , production series dry film line structures with a width of 6 µm respec- tively 8 µm are evaluated after exposure and de- velopment by a UV microscope. The percentage of dry film lines that survived the development process is an indicator for the adhesion on the tested electroless copper deposits. As illustrated in Figure 11, the new electroless copper process outperforms the reference system in dry film adhesion for both repetitions of the test. Nearly all 8 µm dry film tracks are in good shape after the development process whereas the 8 µm dry film lines for the reference process are visibly damaged. The result for the 6 µm dry film tracks with e'less copper IC in this test set-up is not per- fect, but still significantly better than the refer- ence that failed completely in both test runs. HIGH-THROW ELECTROLESS COPPER—NEW OPPORTUNITIES FOR IC SUBSTRATES AND HDI MANUFACTURING Figure 10: Throwing power measurement of e'less copper HDI applying method B. Figure 11: Production series dry film adhesion test of two different electroless copper deposits on ABF GX-T31.