SMT007 Magazine


Issue link:

Contents of this Issue


Page 49 of 99

50 SMT Magazine • November 2016 • Accurate body dimensions, preferably with tolerances • Component standoff from PCB • Lead type • Pitch • Smaller form packages are more susceptible to design and manufacturing issues • Land pattern optimized for manufacturing • TH pin diameter and length • Solder mask-defined pads Third, take into account the manufacturing processes used to produce the PCB: • Conventional or sequential lamination • Mechanical drill, laser drill or backdrill • Number of panels stacked for drill • Solder mask-defined pads • Route or vscore singulation • Flying prober or ICT • Reflow, wave, or selective soldering • Flow solder direction • Conveyed edge for assembly • SMT, auto-insertion, pressfit, or manual placement • Stepped stencil • Rework candidate Manufacturing is a process, and processes also have tolerances. A reliability analysis needs ture and features of the assembled PCB, includ- ing the solder-paste connection to the compo- nents. First, measure and count the critical features of the PCB to assess the reliability of a custom component: • Type of PCB—rigid, flex, flex-rigid, packaging substrate • Size of PCB • Number of layers • Number of vias • Size of vias • Minimum annular ring • Microvia stackup • Number of component packages • Double-sided SMT • Range of package sizes • Copper weight • Copper distribution • Test-point density • Singulation method • Zero-offset devices • Gold fingers • Vias in pad • Embedded devices • Aspect ratio Second, list the electronic component and padstack details to be used to assess the reliabil- ity of a PCB assembly: HOW TO IMPROVE PCB RELIABILITY Figure 1: Close spacing over an extended length affects yield and reliability. Figure 2: Starved thermals prevent proper heat containment, affecting the quality of via solder connections. Figure 3: Manufacturing process tolerances can cause a same-net short, potentially affecting circuit behavior.

Articles in this issue

Archives of this issue

view archives of SMT007 Magazine - SMT-Nov2016