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I typically use 2 ounce copper as rule for all my PCBs. On a recent board I am using a 0.5mm pitch, relatively large micro, and noticed the pads aren't very flat. Assembly went fine with the protos, but I'm wondering if 1 once copper would provide for a flatter landing service. Does anyone have any experience with using 1 and 2 ounce copper with small pitch devices and/or any advice on assembly reliability related to copper thickness for such devices?

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  • \$\begingroup\$ I try to use 0.5oz copper for home-made small pitch features (<15mil). \$\endgroup\$ – tyblu Jan 8 '11 at 18:03
  • \$\begingroup\$ Why do you usually use 2oz copper? I know there are many valid reasons for using it, I'm just curious to your particular application. \$\endgroup\$ – W5VO Jan 8 '11 at 18:05
  • \$\begingroup\$ I wish I had a good answer but basically because that's how we've always done it. I've always been a schematic guy. I'm just getting into actual layout side of things, and so am learning. From the responses so far, it looks like using 2 ounce is not the norm, so I guess I should think about switching to 1 once unless there is a valid reason for 2, especially with small pitch SMDs. \$\endgroup\$ – bt2 Jan 9 '11 at 4:31
  • \$\begingroup\$ 2oz copper also makes hand soldering and rework more challenging than it needs to be. \$\endgroup\$ – Cybergibbons Apr 25 '12 at 10:10
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Unless you need high-current capability, 1 oz is the default thisckness. Line definition can be impaired with increased thickness, so only use when necessary.

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  • \$\begingroup\$ I've used 2oz copper several times for increased heat dissipation for components that sink heat to the ground plane. Just as another reason (other than current) that one may need 2oz copper. Never used it on a layer that wasn't a solid plane though. \$\endgroup\$ – Mark Jan 8 '11 at 18:33
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1 oz (35 um) copper is much more suitable for SMD. Most board suppliers provide it as standard.

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You don't seem to have a good reason to use the 2 oz copper ("I wish I had a good answer but basically because that's how we've always done it.") The main reason to use it is for high currents. If you don't have that, use 1 oz, it's the standard thickness and should be a lot cheaper than 2 oz.

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I summarize PCB fab capabilities at the PCB manufacturers page. (You can help -- it's a wiki).

Capabilities are different for every PCB fab, but they often publish "preferred" capabilities that look something like

  • 0.30 mm track/gap on 2 oz boards
  • 0.15 mm track/gap on 1 oz boards
  • 0.10 mm track/gap on 1/2 ounce copper boards

and "minimum" capabilities that are a bit tighter.

Thicker copper makes it more difficult to properly fabricate footprints for fine-pitch SMT components.

If you don't need lots of copper to provide a good heatsink or to handle high currents, you might be able to save a few dollars by using exactly the same board layout and specifying 1 oz or 1/2 oz copper instead of 2 oz copper -- especially if it results in the board being able to use one of their standard "preferred" processes rather than one of their more expensive "minimum" processes.

If you do need lots of copper to provide a good heatsink or to handle high currents, then a single PCB with 2 oz copper will likely to minimize your net costs. However, I've seen a few cases where designers were able to save a few dollars by re-designing the system to use 2 PCBs -- one small PCB with thin copper and narrow traces and multiple layers to support the fine-pitch SMT components, plugged into another PCB with one or two layers of thick copper and wide traces to handle high-current stuff.

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If higher current handling is needed only in specific traces, I've often seen the use of a tin reinforcement on the copper. It seems to be quite effective, as explained here.

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