How to I prevent thermal connections on 0402 packages (to, in turn, mitigate tombstoning)?

Question

For routing to 0402 parts, it is important to keep the traces balanced in terms of orientation and copper load so that both sides of the 0402 melt and solidify at the same time. Otherwise tombstoning becomes an issue. If one end of an 0402 part is connected to a polygon fill signal (e.g. ground), how do I prevent any connections from occurring? The default is 3 connections to the ground plane, but (for this package only) I want NO connections. I want to route these parts manually.

Covering the pad with a tRestrict rectangle seems to do the trick, but this results in Restrict errors under DRC when you connect traces to the pad, so it's not ideal. Are there any other solutions?

This same issue would also apply to smaller parts (e.g. 0201, 01005)

autodeskguest · Accepted Answer

On 06/20/2014 05:33 PM, Erik Blake wrote:

Covering the pad with a tRestrict rectangle seems to do the trick, but
this results in Restrict errors under DRC when you connect traces to the
pad, so it's not ideal. Are there any other solutions?

Use a thin tRestrict wire just outside the pad on three sides on as needed.

ootbrobo · Answer

1) You can approve that particular error the DRC throws, since you know it is not a problem. This approval will remain until you move the part or trace (I believe).

2) Use restrict lines around the connection you would like to make at the board level. You just have to leave a gap for the trace/thermal, so that the DRC will not throw an error.