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62 The PCB Magazine • April 2016 for all inner layers and 1 oz. for both outer lay- ers to simulate actual design stack up for the specific application and intended use. Test coupons were designed to allow separate tests to be performed at three design regions on the board. Figure 1 illustrates the stack up used as well as the test points—X/Y test point within the plane of an inner layer across a 10 mil gap, Z-Core test point between the plane of the in- ner layer (Z-axis of a core, 5 mil span), and Z-Fill test point between the plane of the fill (Z-axis through prepreg, 10 mil span). Ten test specimens were used for each set for thermal end point testing. For each material the following test specimen quantities were used. Eight sets per temperature x 5 temperatures = 400 test specimens. Six spares per temperature x 5 temperatures = 30 test specimens. Materi- als tested include Laminate A, B, C, D and E. Twenty test specimens per material were used to establish the baseline for dielectric strength test- ing. For each manufacturing lot of material in- cluded in the test, there were a minimum of five test specimens from each manufacturing were included in the baseline dielectric strength test. Control materials with known performance were tested in conjunction with the test ma- terials. The control material configuration was in the form of 3" x 5" sheet (unclad) to match per temperature) was plotted vs. time (X-axis). From this data, 50% end of life was determined. A thermal endurance graph was generated in order to extrapolate and validate the 100,000 hour life temperature. The importance of the 25,000 hour test is based on industry practices of extrapolation of life expectancy data. In or- der to have any confidence of predicting mate- rial properties at 100,000 hours, the test length has to be 25% in duration. The following materials in Table 1 were down selected from a much longer list of PWB laminates. Press fit compatibility; comparative tracking index (CTI), flammability, dielectric breakdown voltage, and glass transition tem- perature (Tg) were used to select five laminates for thermal aging testing. Thermal aging of PCB laminates was per- formed on three manufactured lots of PCB test vehicles. Testing a processed PWB is necessary because manufacturing processes expose the laminate to a number of thermal and chemi- cal cycles. These exposures can have an effect on the material's properties and robustness. In Amphenol's study, the test vehicle consisted of a fourteen layer printed circuit board manu- factured in accordance with IPC-6012, Class 3 meeting the workmanship standards of IPC- A-610, Class 3. Copper foil weights were 2 oz. long-term thermal reliability of pCb materials Figure 1: Test vehicle stack-up and test points on test vehicle.