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42 The PCB Magazine • June 2016 lamination process of the film. Mass production comparison tests of e'less copper IC with the reference system on ABF GX-92 showed that the peel strength performance of the new bath is on the same very good level as the reference bath (cf. Figure 13). This result could be confirmed also on several other relevant laminates includ- ing ABF GX-T31 and ABF GY-series. Reliability During the development and mass produc- tion qualification, both new electroless copper baths have been intensively tested with all stan- dard reliability tests established in the market (see Table 2 below). The following figure illustrates the detailed IST and TCT test results for e'less copper HDI as achieved at a mass production test in Korea. Summary Two new electroless copper baths have been developed to cope with upcoming miniaturiza- tion challenges in the high-end IC substrate seg- ment as well as in the evolving HDI board mar- ket. The main challenge to be overcome is the reduction of the differential etch in the pattern plating process by decreased electroless copper thickness on the surface of the build-up layer. To this end, several requirements need to be ful- filled to ensure a safe and high yield production. First of all, the throwing power performance of e'less copper IC and e'less copper HDI [3] espe- cially in the wedges respectively at the bottom of the BMVs is crucial for the via-filling perfor- mance due to conductivity requirements. Two reliable throwing power measurement methods have been introduced and throwing power re- sults presented in this paper show that the new electroless copper baths constantly achieve sig- nificantly better throwing power performance compared to the reference systems that are industry standards in the respective markets. A minimum target thickness of the electroless copper layer in the BMV (wedges) is therefore ensured while the thickness on the surface can be reduced for improved L/S resolution. Second- ly, the adhesion of the copper layer on the bare laminate (typically ABF material) is a basic re- quirement for the high-end IC substrates manu- facturing process. Favorable internal stress char- acteristics of the copper layer of the e'less copper Figure 13: Peel strength results after acid copper plating on ABF GX-92; Annealing Parameter.: 1h at 130°C after e'less copper, 1h at 180°C after electrolytic copper. Table 2: Summary of reliability tests for e'less copper IC and e'less copper HDI. HIGH-THROW ELECTROLESS COPPER—NEW OPPORTUNITIES FOR IC SUBSTRATES AND HDI MANUFACTURING