Library checker: Ref. designations

[jdupre]

I'm starting to construct some decals and noticed the following:
PowerPCB Library Construction Doc. #1 says to place reference and part type silkscreen labels at -1.35, .05 while the Decal & Part Type Checklist Specification says -1.3, .1.

Chklib.exe doesn't seem to care either way. But the Library Checker does report an error if the silkscreen ref. label falls on a pad.

So what is the intent here? And why these locations? Why not put them all on 0,0?

- Joe

[petehouwen]

since they always get moved anyway,

I put all of my labels at 0,0 with Center Center justification, Orthogonal right reading.

[Tom]

Joe,

Here are the stats on the pcbstandards ref des size, layer, location, Justification, etc. and the reasoning behind it.

Size: 1.5mm x 0.15mm
Reason: This size has been found to be very manufacturable and at the same time small enough for very dense PCB's. It also is approved by IPC to be the minimum. If you do a PCB design that has low density, you can automatically change the size of all the ref des by RMB/Filter/Nothing/Labels/Close/RMB/Select All/RMB/Query Modify/Change Size.

Layer: Layer_1
Reason: Because PowerPCB has "Layer Association" a ref des assigned to Layer_1 will automatically move to what ever layer you place the part on. So if you have a 6 layer board and place the part on layer_6, the Layer_1 ref des will move to automatically Layer_6.

Location: 1.3 x 0.1
Reason: The 1.3 is to move the ref des off the center so that when the red des grows to 4 characters (R100) it will still be inside the part boundaries and if your placement is too dense and cannot move the ref des outside the part, you can leave it right where it is and have it look good. The 0.1 is to center the ref des. Because PowerPCB allows you to use Upper and Lower case characters (but only UPPER Case for Ref Des) the text font is slightly shifted to comensate for the lower case characters. So we compensate back by moving the ref des 0.1mm up to center the ref des perfectly.

Jusification: Left / Center
Reason: The ref des justification is set to Left / Center. This is really important when "Renaming" the ref des (back annotation). When you place each ref des outside the part, place the ref des on the right side of the part (default). When you place the ref des on the left side, rotate the ref des 180 degrees so that the origin is on the right side of the ref des. This way you can change all the ref des assignments to new names (short or long) and you will not have to perform any cleanup.

We have run extensive tests on every possible combination of variables and this seems to work the best. Good Luck!