Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

PCB groundloops?

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PCB groundloops? | 27 March, 2013

Hi I was looking for the development board of a MCU i was asked to evaluate, but upon checking out the gerbers i found something weird

this pcb is a 4 layer stack 1 smd connections 2 gnd 3 vcc 4 thd connections

question 1) in this case, i'd place one via per IC VCC pad i found, except for those going to the decoupling caps - in which i'd place a via to the cap pad and the route to the IC vcc. same with ground. but in this board they... mmm... having too close lets say 4 VCC pads of different components, they routed them together in a sort of island but still placed one via per pad... is there any point to route them together when the via already takes them to the right plane? look at the pic, the node highlighted in white is supposed to be ground, the vias connect to that power plane...

question 2) i noticed they placed the thd in a 100mils grid, the smd in a .5mm grid AND the vias on a .1mm grid... maybe this'll help drilling but aren't the vias supposed to be close to the pads and centered on either of their sides - as long as they don't get too close to another pad-? the .5 grid doesn't quite agrees with the .1mm so the vias end a bit away from the pad they belong to and at times they arent centered in the side either... is that ok? in the picture there are also gnd vias that seem too far awar from the pads while others are almost merging into them

question 3) this pcb is mostly digital, so the pwr and gnd planes are just two big uninterrupted squares... but there's also a tiny bit of analog on one side. they routed all of it in the 1 plane since it seems small, but shouldnt there be a hole in the power planes right under it? there's just this thd connector pin joining the VSSA with the VSS... but still looks weird

so, what do you think?


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