PCB007 Magazine

PCB-May2017

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88 The PCB Magazine • May 2017 term reliability at the post interconnect. Yes, there is a three-point connection shown in the right section of Figure 1. However, with such deep etchback, there is a great risk of copper plating folds (Figure 2). 2. Wedging Description: The resin is preferentially at- tacked along the edges of the innerlayers. Characteristics: Can lead to plating folds, barrel cracking, wedge voids, and uneven cop- per plating in the holes. Possible Causes: a) Too much caustic in the solvent and/ or permanganate step. b) Improper bonding (oxide or oxide alternative) process. With respect to improper bonding, one should also pay close attention to the actual multilayer bonding process itself. Some ques- tions to ask are: 1. What is the rate of heat rise in the multilayer stack? 2. Are there concerns with moisture, in the laminate or prepreg? 3. What is the optimum cure of the resin material? 3. Wicking Description: The resin does not encapsulate the glass bundles near the hole wall and appears as glowing glass bundles when illuminated. Characteristics: Can lead to plating folds, barrel cracking, glass voids, and uneven copper plating in the holes. Figure 2: Excessive etchback leading to plating folds. Etchback exceeds 0.003 inches. Figure 3: Note deep wedging between B-Stage and copper foil—wedging leads to plating void. Figure 4: Plating along glass fibers, also known as wicking. (Source: IPC-9121 Process Effects Guide) THE DESMEAR DEFECT GUIDE

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