| T O P I C R E V I E W |
| rmorris |
Posted - 05 Dec 2011 : 09:32:34
Is there a way to control the way Thermal Reliefs are applied to Surface mount pads ? I am having a problem in that when I pour copper on the same layer as the pads ( typically for a copper 0V fill ) the thermal relief settings typically result in thermals on eg 3 sides of a pad on an 0805 footprint.
Whilst this is expected from the design settings and is fine for through hole pads I don't want it for SMT pads as it might result in excessive heatsinking relative to the pad area making soldering unreliable.
It seems to me that the easiest solution might be to define a keepout layer in the footprint itself but I can't see that this is available ?
I can of course define Keepout areas on the layout itself but then if I move the footprint I also have to manually move the keepout area which becomes very time consuming when making minor adjustments.
R Morris |
| 8 L A T E S T R E P L I E S (Newest First) |
| rmorris |
Posted - 06 Dec 2011 : 11:50:01
Yes - that would sort out the SMT pad issue. Ideally I'd like thru hole pads to connect via thermal reliefs automatically and also vias to connect automatically ( generally I don't have thermal reliefs on vias but the option is good to have ). But it seems Easy PC isn't (yet?) capable of that yet eg different rules applying to different pad styles etc.
As I have mixed SMT / thru boards I guess it's a balance of which way is the more efficient / less prone to error ( in this case my errors!)
atm I've added keepout layers to the layout which works fine but is time consuming to modify.
This is probably the best option for me right now as the boards are probably more thru hole than SMT.
For boards with more SMT I think I’d use the unassigned pour / net joining workaround that you outline. Thanks.
R Morris |
| edrees |
Posted - 05 Dec 2011 : 14:40:40
OK, so why not do as Iain suggests, -pour a flood plane first, with sufficient spacing clearance (netname=flood) and then manually add the tracks of your specification to connect the flood net to the individual component pad. EasyPC will warn you "do you want to connect Net X to Net Y?" and in your case confirm Yes. |
| rmorris |
Posted - 05 Dec 2011 : 14:05:07
yes - the heatsink is indeed the pour area and/or spokes. I write
"I wouldn't need to be concerned with the heatsinking effect on the pads" referring to the heatsinking effect as it acts on the pad rather than being caused by the pad itself.
re: "Normal connections are usually made by fixed copper tracks." Yes - that's what I mean - I'd rather the copper pour didn't attach to SMT pads at all except by means of any copper tracks I intentionally place.
R Morris |
| edrees |
Posted - 05 Dec 2011 : 11:54:54
The component pad is NOT the heatsink, -the copper pour area and/or the thermal spokes are the heatsink! I don't understand what you are trying to achieve when you state to put in normal connections to complete the net connectivity as I wish
Normal connections are usually made by fixed copper tracks. |
| rmorris |
Posted - 05 Dec 2011 : 11:29:20
Thanks. Yes - I understand the principle but was trying to get what I wanted on the pcb. It seems to me that it would be a useful feature to be able to define Keepout areas in a pcb footprint model itself but I don't think this is possible in Easy PC ?
One problem with making the spokes too thin to survive etching is that I believe the spoke setting is global for the whole pour so wouldn't be good for thru hole pads where I do want connectivity.
I guess if spokes were feasible at 1 thou then I wouldn't need to be concerned with the heatsinking effect on the pads.
R Morris |
| Iain Wilkie |
Posted - 05 Dec 2011 : 11:02:10
If your pad is on the same net as the copper pour, then it has to connect via thermal relief or no thermal relief. If you dont want a connection they would need to be put on dfferent named nets. Only other way may be to make the spoke very thin (i.e. 1 thou) and it will be removed during etching. Bu be sure to tell your manufacturer this or they may beef the spoke up.
Iain
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| rmorris |
Posted - 05 Dec 2011 : 10:29:52
I will be hand soldering the first of these at least which shouldn't be a problem for me. I'd rather the Copper Fill didn't attach to SM pads at all - leaving it for me to put in normal connections to complete the net connectivity as I wish. But I can't see a way to set that in Easy PC ?
R Morris |
| edrees |
Posted - 05 Dec 2011 : 10:07:30
I don't use thermal reliefs for SM components as the pcb will be oven processed anyway. If hand soldering use a decent thermally controlled iron with a good thermal bit mass and you shouldn't have too many problems. But if you are hand soldering sm components you cannot expect 100% reliability (especially MLCC caps which tend to go S/C when overheated). |
