Issue link: https://iconnect007.uberflip.com/i/1494346
MARCH 2023 I DESIGN007 MAGAZINE 75 • Insufficient etching: Where random copper blotches remain in the open, copper-free area, and where closely spaced conductors run in parallel for long dis- tances. is may be due to etch chemical imbalance or when the duration for the etching process is too short. • Scratch short circuit: When a short cir- cuit remains aer electroplating and etch- ing. Typically attributed to scratches in the dry film resist by mechanical, human contact, or hair and other fine fibers fall- ing on the board surface. ese particles, if not removed before imaging and electro- plating, will impede light access, resulting in copper bridging. Overall, the flying probe test is an efficient and cost-effective method for testing circuit boards aer fabrication is completed. It is accurate, fast, flexible, and safe, making it the ideal solution for many types of testing require- ments. However, when the circuit board fails during electrical testing, there are other test- ing methods that can be implemented to iden- tify defects. e 3D X-ray inspection systems can pro- vide 3D images of the circuit board by creating a series of 2D cross-sections to expose defects embedded in the board aer lamination. While removing the defect on the inner layers of the board may not be practical, identifying and discarding a specific circuit board within a multiple unit panel format will ensure that it does not reach assembly. e images shown in Figure 2 represent the isolated X-ray view of defects within the inner-layer circuit conduc- tor routing path. In addition to visual and X-ray imaging, ther- mal imaging, EMI test, and solderability test- ing is oen implemented to further certify that all boards are manufactured correctly and will be assembly process ready, and that any design flaws that would compromise product reliabil- ity are identified and corrected. DESIGN007 Vern Solberg is an independent technical consultant, specializ- ing in SMT and microelectronics design and manufacturing technology. To read past columns, click here. Figure 2: Isolating circuit defect locations using X-ray imaging. (Source: OlinaPCB)