BEST PRACTICES for SMT Design

摘要

Fine-pitch devices and automation levels are resulting in greater board density. There are mechanical and logisti-cal limits to how far these trends can go, however, and the following best practices will help ensure that an SMT device is manufacturable.rnFor fine-pitch devices, designers must be careful to ensure that no natural bridges occur. A natural bridge is a clear, straight track between leads. This creates a trace over which solder can (and likely will) run when soldered (FIGURE 1). Although the result is not technically a defect, it appears as one to automated and human testers. This causes delays and additional manual (i.e., expensive) intervention to check. To avoid natural bridges, traces should be designed to route from the ends of pads, rather than using direct, straight connections.