Issue link: https://iconnect007.uberflip.com/i/521718
June 2015 • The PCB Magazine 13 the same substrate as the ICD coupon and con- tained 0.25 mm and 0.38 mm PTHs and 0.15 mm micro vias (MV). All coupons were pre- cycled at 260°C six times to simulate the as- sembly process. The IST equipment was set to cycle between 25°C and 150°C (PTH) or 25°C to 190°C (MV) with three minutes of heating and two minutes of cooling. Coupons were tested for 1000 cycles or to failure defined as a 10% increase in resistance. Failure mode was evaluat- ed and documented. This coupon is comprised of two circuits, S1 being PTH and S2 being MV, with S1 being evaluated first followed by S2. These IST coupons were electroplated in a com- mercially available sulfuric acid based copper plating solution to increase the total copper de- posit thickness to 28–30 microns. A picture of the IST coupon is shown in Figure 1. Results and Discussion The effect of the additives on the electroless copper deposit was first evaluated using PI sub- strates that historically have been problematic for electroless copper processing. These materi- als are all PI substrates found commonly in the manufacturing of flexible PCBs. Comparative studies were visually performed with and with- out the additives to determine their effective- ness at reducing or eliminating blistering and peeling of the copper deposit. Figures 2 and 3 A HIGH-RELIABILITY, STRESS-FREE COPPER DEPOSIT FOR FPC, POLYIMIDE AND RIGID-FLEx continues FeAtuRe Figure 2: Sequentially laminated rigid-flex PI window cut-outs exposed to electroless copper processing. Electroless copper (left) and electroless copper with stress reducing additives (right). Figure 3: Flexible PI PTH. Electroless copper (left) and electroless copper with stress reducing additives (right).