UB 12.0.1: Part Spacing WRT Shoving

[Who_Knew]

Hi,

I've been trying to use part spacing on a portion of a design to try and keep myself from placing the parts too close together.  It's been a particularly difficult circuit and I'll likely have to rework it often.  My problem is that spacing seems to have conditions for which enforcement is relaxed.  For example, if two 0603 resistors share a common net, and the pads that are on that common net face each other, then spacing constraints seem to fly out the window.  These parts may overlap without any DRC error.  In general, if two parts share a common net, they may be placed closer together than two similar parts that do not share a common net.  If a part already has traces routed to one or more of its pads, then parts that are completely un-routed may be moved in closer to the parts with routed traces without generating a DRC. 

Is there a guide to this behaviour in the Help section somewhere?  If part spacing isn't supposed to be hard and fast part spacing, it would be nice to know what to expect.  It would also be nice to be able to control all of these conditional reductions in part spacing enforcement.

[Tien_P]

Hi,

I was able to replicate the behaviour and also found a way to make it work, please try these steps:

1. Select Options>>Global Preferences >>PCB Design

2. Click the down arrow and select Full Real time check beside DRC&netlist check frequency

3. Click Apply then OK

I've discovered that when No-real time check is selected, no warning message will not appear even though you run the check from Design>>DRC and netlist check

[Who_Knew]

Hi Tien,

Yeah, I already had those settings.  Thanks, though. 

I was getting warnings and DRCs per normal.  What doesn't seem acceptable is the variation upon which spacing is enforced.

For example, if I set spacing to 1mm for some parts, and take two of those parts and put them near each other, and both parts have no nets in common, then I will get errors if they are placed so that less than 1mm clearance is between them. 

Now take two SMT resistors that have one net in common and try to place them near each other.  The same spacing isn't enforced, apparently due to them having a net in common.  Resistors with a net in common can have the common pads from each part overlap each other and this somehow will not violate the spacing rule.   

If a chip resistor is placed next to an IC and it has no nets in common with the IC, then it can only be placed within the set distance amount.  If the chip resistor has one net in common with the IC, then it can be placed closer.  If that net is routed, closer still.  If the chip resistor has both of its possible nets in common with the IC, then it can be closer still.  If both nets are routed, closer still. 

It doesn't seem arbitrary as if by mistake.  It seems remarkably complex and by design, just not what I'd expect or want in part spacing controls unless I could control all of these variables (turn them all off for the most part).

[Tien_P]

I can't seem to be able to replicate the problem, have a look at the attached file.  There are two nets, net 1 and 2 both net clearances are set to 0 mil.  The pad from U1 and U4 are part of net 1 while U3 pad is net 2.  Both components U1 and U3 are very close to U4 but there is no DRC.  If you change the net clearance for both nets to 10 mils, I will get DRC error and this is coming from the net and not the component.  I think this is what happen in your file but I could be wrong.  Post an example and I will investigate.

[Who_Knew]

Hi Tien,

The board house has a 7mil space/trace limit, so as a minimum, I set all copper clearances to 0.1778mm (traces, pads, etc.).  For all parts in the design, I set the part spacing to zero. 

Then for a particular group of parts (had difficulty with this circuitry before, so I wanted to make rework easier on myself) I set the part spacing to 1mm.  This circuitry is a SOIC28 surrounded by several Rs and Cs.  So I placed the IC about where I thought I wanted it, then started placing the Rs and Cs around it.  Was surprised to see how much enforcement of part spacing varied depending on what net the parts belonged to, etc. as described before.  

If you're not able to replicate this, I'll start a support ticket so I can send in my working file to you.  Let me know.  And, thanks as always. 

[Tien_P]

If you have an example, please send it to me and I'll have a look.

Thanks