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August 2017 • The PCB Magazine 85 er will show characteristic physical properties. These properties also depend on the plating rate or current density, temperature at which the plating is done, and the morphology. For in- stance, a densely packed equiaxial deposit will have better physical properties than a columnar deposit. Most important to PCB manufacturing are tensile strength and elongation %, where these properties show the tolerance of the de- posit for thermal stress. Physical properties were measured according to the IPC TM-650, 2.4.18.1 test method. Sam- ple strips were extracted and baked in an oven at 125°C for four to six hours. An industry me- chanical test instrument was used to test the strips. The measurements were used to calculate tensile strength and elongation % using equa- tions 2, 3, and 4. Table 2 shows the results at two different bath ages, fresh bath and bath aged around 50 Ah/L. According to the results prop- erties did no change much with the bath age. Further, to evaluate thermal characteristics of the deposit, the 6X solder shock resistance test was performed on plated through-holes in accordance with IPC TM-650 2.6.8. Solder shock (SS) conditions were 10 seconds float at 288°C for six times on the same side of the test cou- pon. Results are shown in Figure 7. After 6X SS testing, no corner cracks, barrel cracks, or hole wall pull-away was observed. HIGH-THROW DC ACID COPPER FORMULATION FOR VERTICAL CONTINUOUS ELECTROPLATING PROCESSES Figure 5: Cross-sections of through-holes plated at a) 10 ASF; b) 20 ASF; c) 30 ASF; 1.6 mm test panel. Figure 6: Scanning electron microscopy (SEM) of IST 22-layer through-holes plated at 10 ASF with 2.4 mm test panel. Table 2: Physical properties. Mean average cross-sectional area (in2) = Weight of the sample (lbs) Length of tensile sample (in) x density of copper (g ⁄ in3) Eq. 2: Eq. 3: Tensile Strength = Maximum load (lbs) Mean cross-sectional area (in2) Eq. 4: Elongation = (Length at break – Original gage length) Original gage length