SMT Pad Vias: Is it OK? | PCB Layout

  • Thread starter Thread starter Jdo300
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SUMMARY

Placing small vias on the pads of SMD components, such as 0805 bypass capacitors, is a debated practice in PCB layout using ExpressPCB. While some users, like Humber, advocate for this method due to lower inductance benefits, others, including Warren, warn that it may compromise mechanical strength and soldering quality. The consensus suggests consulting with the PCB manufacturer regarding their plating processes, as improper plating can lead to significant issues.

PREREQUISITES
  • Understanding of SMD component placement
  • Familiarity with ExpressPCB software
  • Knowledge of PCB manufacturing processes
  • Awareness of via types and their implications in PCB design
NEXT STEPS
  • Research the impact of via placement on SMD soldering quality
  • Learn about PCB manufacturing processes, specifically via plating
  • Explore techniques for reducing inductance in PCB layouts
  • Investigate alternative methods for connecting SMD components to power pins
USEFUL FOR

PCB designers, electrical engineers, and anyone involved in the layout and manufacturing of printed circuit boards, particularly those working with SMD components and via design.

Jdo300
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Hi All,

I'm working on a board layout in ExpressPCB and I am wondering if it is considered OK to place a small via on the pad of a SMD part. To be specific, I have a bunch of 0805 bypass caps that I am placing on the underside of the board for various ICs, and I want to add a via through the pad of the cap to the top layer to connect to the power pins. I am using the smallest via size the program supports (0.36mm hole) which the manufacturer says is usually filled due to the size tolerances.

Would placing these small vias in the middle of the pads present any problems, particularly when it comes to soldering the parts down? Has anyone ever tried this?

Thanks,
Jason O
 
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It probably depends on the order of steps done during manufacturing. If they plate vias after plating pads, there's a good chance such vias will not be plated properly.

I would call up whatever PCB house you're using to manufacture the board and ask them. It's definitely not normal practice, and will certainly reduce the mechanical strength of the mounting. That alone may be a reason not to do it.

- Warren
 
I often place a via within the pad, as it results in lower inductance. When this method has produced a problem, there have been others. That is, there have been no problems with an otherwise well-manufactured board.
I also use arrays of vias to connect surface mounted devices to a heatsink on the other side of the board. In this case, plated over vias rather than solder-filled are easier to produce.

Humber
 

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