Issue link: https://iconnect007.uberflip.com/i/1383248
JUNE 2021 I PCB007 MAGAZINE 35 Prevent Unwanted Flow of Solder Paste During Soldering/Vias That Are Not Covered With A Solder Mask Move the via further away from the SMD pad, so you ensure that there is room for a solder mask in between the SMD pad and via pad. An alternative is to reduce the solder mask opening to be slightly bigger than the drilled via hole. Consult the IPC document IPC-4761 Design Guide for Protection of Printed Board Via Struc- tures, to find the solution for your design. Or just ask. Critical Signals That Require a Reference Plan Make sure the connections are sufficiently far from neighboring pads so that they really get the desired reference copper plane below or above them (Figure 6). Figure 3: Samples where it's possible to increase distance between pads and traces, also between differential pairs. Figure 4: a) Do not short pads like this; b) This is the way to do it. Figure 6: a) Signals are missing the reference plane; b) Signals have the reference plane. Figure 5: a) No solder mask web between SMT pad and via-pad. Solder paste will flow into via hole; b) Solder mask opening has been reduced to cover via pad, but is slightly bigger than the via hold; c) Via hole has been moved away from the SMT pad, so solder mask web can be kept. How Do You Connect Neighboring Pads? It should not look like a short circuit on the finished board (Figure 4). a) a) a) b) b) b) c)