4
\$\begingroup\$

I have boards that through a mistake of my own have a bunch of vias that should connect to the ground plane, but are actually isolated. See all of the holes that are isolated:

alt text

So, I need to bridge all of them to the ground plane. Since there is no solder mask I figured I could just use solder to bridge the connections. Here is what my solution looks like:

alt text

Not so pretty. I am wondering if there are any suggestion of what I can do to short these in a better manner. I will have it fixed in my next board revision, but it is a few weeks before I will have the boards and need to solder a few of these up now.

ADDITION: The biggest problem I was having was the ground plane heated up very slow and It didn't seem to want to stick to both the pad and the ground plane at the same time.

\$\endgroup\$
  • 2
    \$\begingroup\$ Get a bigger soldering iron. \$\endgroup\$ – Connor Wolf Nov 11 '10 at 0:54
  • \$\begingroup\$ It looks like the entire board is covered in soldermask \$\endgroup\$ – Nick T Nov 11 '10 at 6:43
  • \$\begingroup\$ @Nick T - Quite the opposite. This looks like a raw proto board, with no soldermask at all. \$\endgroup\$ – Connor Wolf Nov 11 '10 at 11:02
  • \$\begingroup\$ @Nick T It is a barebones order from advanced circuits \$\endgroup\$ – Kellenjb Nov 11 '10 at 14:58
  • 1
    \$\begingroup\$ Which layout software let that pass DRC? \$\endgroup\$ – markrages Nov 11 '10 at 15:32
1
\$\begingroup\$

Get a better soldering iron.

It's not the easiest solution, but in the long term (having a better iron improves everything), I think it is the best.

I have an OKI-Metcal soldering station, and I can easily solder D2PAK devices down to a solid copper plane with no thermal relieving at all. Any similar "Serious" iron should be able to do similar. (They generally run ~$200. It's an investment)

Also, what tip do you have on your iron? For something like that, a chisel tip (pick one for your iron, link is just an examle) is really essential to get good thermal contact between your iron and the copper plane.

\$\endgroup\$
  • \$\begingroup\$ We do have a very nice Weller WD1002. I think I do have a bigger tip to try. \$\endgroup\$ – Kellenjb Nov 11 '10 at 15:04
  • \$\begingroup\$ Metcal is in a different class than Weller. Yes, use the biggest tip you can find for this. \$\endgroup\$ – markrages Nov 11 '10 at 17:11
  • \$\begingroup\$ Try a soldering gun. Something like this doesn't require a lot of precision or a certain tip size, just a lot of power. \$\endgroup\$ – W5VO Nov 16 '10 at 15:47
1
\$\begingroup\$

you'll have a very hard time heating up that ground plane. You could put the PCB in a board heater then maybe solder.

Alternatively you can use conductive epoxy, that should work as long as the impedance to ground isn't super critical for the circuit.

Also, isn't that pad underneath that TO-220ish looking package shorting to the ground plan?

\$\endgroup\$
  • \$\begingroup\$ +1 for the board heater. Also, the package looks like a DPAK to me, and it does look like it's shorting out. \$\endgroup\$ – Kevin Vermeer Nov 10 '10 at 23:53
  • \$\begingroup\$ The regulator is fine. I have a board heater, but I was worried about this method since I already have parts on the bottom side. I think this would be apply a lot of unneeded heat directly to the parts \$\endgroup\$ – Kellenjb Nov 11 '10 at 15:00
1
\$\begingroup\$

Is soldering a requirement? Because if it's only a prototype or something, you can use conductive copper foil tape to "patch" the holes.

alt text

\$\endgroup\$
  • \$\begingroup\$ Do you know what the impedance of the tape is? \$\endgroup\$ – Kellenjb Nov 11 '10 at 17:33
  • \$\begingroup\$ @Kellenjb - it's just copper foil, like your ground plane. What's the impedance of that? \$\endgroup\$ – stevenvh Jun 26 '11 at 10:23
  • \$\begingroup\$ it may be a good idea, but the glue may oppose a good contact with the via. \$\endgroup\$ – stevenvh Jun 26 '11 at 10:25
1
\$\begingroup\$

You found out that the copper plane takes a lot of heat away, so that the temperature at the via will hardly be high enough to melt the solder. When the vias are connected to the plane they will be through thermal reliefs, which isolate most of it from the plane, leaving only a few bridges to make the connection.
I would use a Dremel Moto-Tool with an engraving tool bit

enter image description here

to cut away part of the copper around the via to emulate these thermal reliefs. This may require some patience, but I guess just trying to solder was taxing your patience as well. :-)

What also might work is to separate the bridging operation from the plane soldering. The bridge will require rather much solder before it connects to both ground plane and via. First solder a tinned wire on the ground plane, so that it runs over the via, or maybe even insert it into the via. You'll see that soldering it then to the via is a piece of cake. (The ground plane will remove enough heat from the wire that this side won't come loose again.)

\$\endgroup\$
0
\$\begingroup\$

Maybe a heat gun or hot air rework station would improve things. But you are still going to have the problem of the ground plane transferring heat away from the area you want to heat up moreso than the vias.

For everyone else: I'm envisioning something that would fix this problem perfectly - sort of a mesh (like a solder wick, but small and circular) that would be coated in solder which you could then place over the via and heat up with a hot air gun. When the solder starts to melt, it would adhere to the ground plane and via. Then just remove the heat and let it solidify. Like a drywall patch for PCBs. Does anything like THAT exist?

\$\endgroup\$
  • 1
    \$\begingroup\$ It would not adhere - you'd still get a cold joint. \$\endgroup\$ – Kevin Vermeer Nov 11 '10 at 18:16
  • \$\begingroup\$ Yeah, the heat gun and hot air rework stations are actually very effective at not getting shorts when soldering. This is great for most cases, not so great for me. \$\endgroup\$ – Kellenjb Nov 12 '10 at 14:39

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.