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I am using a component with LGA package. Should I use a solid connection or use thermals between pads and GND plane?

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    \$\begingroup\$ You mean the datasheet has no recommended lands, mask and stencil \$\endgroup\$
    – Tony Stewart EE75
    Feb 12, 2018 at 20:51
  • \$\begingroup\$ If the datasheet doesn't have a recommendation, I would go with thermal relief connections for GND, of the same width as the other traces connecting to the part. I don't think that it's a big deal on this part, but others may have better advice. \$\endgroup\$
    – Daniel
    Feb 12, 2018 at 21:20

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If it is an SMT pad, and is meant to go through a commercial reflow oven, don't use thermal relief on the pads. The reflow oven will provide the even heat needed to melt the solder consistently.

This will admittedly make manual rework more difficult, but manufacturers I've worked with are confident enough that reflow will solder everything effectively, that they don't insist on thermal relief on SMT. Given that, I'd prefer to have the solid connection to ground.

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    \$\begingroup\$ I completely disagree with the first part of your comment. In my personal experience when you don't use thermals the pour will pull heat away from the pad being reflowed and there is an increased chance that the solder won't flow properly on the pad. On smaller components like capacitors and resistors this can lead to tombstoning. Regardless of whether the parts are being reflowed or hand soldered, thermals are a must. \$\endgroup\$
    – DerStrom8
    Feb 13, 2018 at 11:56
  • \$\begingroup\$ @DerStrom8 My own personal experience is that the effect you describe has not been a problem. Perhaps we are both dealing with too many absolutes here. You claim thermals are always needed, and I say they are unneeded with SMT. I would argue thermal relief is not necessary for the part in question above due to the number of terminals, and that they generally benefit more from a solid connection to ground. I concede that tombstoning on two-terminal parts is a known phenomenon, although we've never had any issues with it in practice. AOI is meant to spot such things. \$\endgroup\$
    – 1N4007
    Feb 13, 2018 at 14:48
  • \$\begingroup\$ AOI is used to catch errors after they happen, but preventing them from happening in the first place is preferred. I have a feeling the difference between your experience and mine may be the manufacturers. If the solder profile is even slightly off or if the board isn't allowed to "soak" for the proper amount of time, I can see how that would lead to the issues I'm referring to. I guess it comes down to how much you trust your manufacturer. The way I see it, thermals are free. May as well put them in there just to make sure. \$\endgroup\$
    – DerStrom8
    Feb 13, 2018 at 14:51
  • \$\begingroup\$ What are the advantages of a solid connection? \$\endgroup\$
    – Gustav Sanchez
    Feb 13, 2018 at 21:38
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Rule of thumb: If it'll be soldered, use thermals. Period.

In my designs I always give my component pads thermals when connecting to a copper pour. Otherwise the heat will be wicked away as I am trying to apply solder (or as it is being reflowed) and you'll get uneven heating, leading to poor solder flow. I do not use thermals on vias, however, because they generally are not soldered. If I plan to use a via as a test point, only then would I give it a thermal connection to the pour because I may need to solder a jumper to it.

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Thermal pads for copper to prevent misalignment bridging DFM issues.

Segmented or crosshatch pattern for solder stencil.

Thermal barrel at least 25 um - will need more plating thickness. ( ask supplier)

More are better.
example
enter image description here

  • optimum final diameter 350 um
  • ideal distance from hole to hole (pitch) is 800 um
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    \$\begingroup\$ I think the OP is referring to thermal relief on the pads around the perimeter, not a thermal pad in the middle of the part. \$\endgroup\$
    – Daniel
    Feb 12, 2018 at 21:25
  • \$\begingroup\$ I was referring to all 3 issues \$\endgroup\$
    – Tony Stewart EE75
    Feb 12, 2018 at 21:43
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    \$\begingroup\$ Hehe, "35 mm Cu plating", I hope your board fab is on the ball that day, else your shipping costs are going to raise an eyebrow :) \$\endgroup\$
    – user98663
    Feb 12, 2018 at 22:02
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    \$\begingroup\$ good thing not gold plating \$\endgroup\$
    – Tony Stewart EE75
    Feb 12, 2018 at 22:41

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