This feature of Eagle, which I’m struggling with, runs on-the-fly. It doesn’t let me route a connection, if it contains via in pad. Like you, I’m used to DRC, which allows me to draw what I like, and highlights the errors, when I ask it to.
Attached is a small Eagle project, which allows to reproduce my problem. There isn't anything unusual about it. Here are the steps, which in the end give me the error:
- Select “Route” tool
- Left-click the air wire. Eagle shows the draft trace between the SMT pad and the mouse pointer. The draft trace is red, because it’s in the top layer, like the SMT pad.
- Middle-click. The draft trace becomes blue.
- Left-click to complete the trace. If everything were to go well, a via would be placed into the pad. But instead, I get an error message “can’t set via to layer 1”.
If you could look at this, I'd really appreciate it! If you need more info, I'd be glad to provide it.
Best,
- Nick