There are two things which doubts me. Please, see attached decal of one of my QFNs:
1. First advice is to associate copper in L1 and L21(solder mask top). After this calculate thermal pad area. Solder paste should be 50% of this copper. Draw some squares in L23(paste top) and associate them to thermal pad.
2. Do not put vias in the decal - put them in the design between paste squares. Usually I use via 0.3/0.55 and via grid 0.9 mm or 1 mm.
I work in this way and I don't have a problem.
SMD_QFN50P900X900X100-65N.png 128.0 KB
This issue goes back and forth on how to connect a thermal pad. People have two techniques.
I prefer to keep all the connectivity in the schmatic. I add an extra pin on the symbol in the schematlc and tie it to the thermal pad; I used to go as far as to add multiple pins and then make them through hole in the pad so the thermal vias are tied to the decal too. That has routing limitations though if you ever need to shift a thermal via so now I only define the pad. That will connect me to a top side ground plane and I'll add thermal vias as needed.
Others like to define things in the layout. They will add a copper shape for the thermal in layout, not the decal, and set it to the appropriate net (i.e. ground). This puts all the responsibility for the thermal performance on the layout designer. I like to classify that as post processing.
I'm typically the engineer that selects the parts, sets up the library, defines the circuit on the schematic, and then does the layout. That is why I like to tie it all together on the schematic, so post processing doesn't get lost during a revision change.
You have the right techniques. You need to pick which you prefer to use.
Thank you both.
It kind of sums up what I've been pretty convinced of for some time...there is no easy, cover all the bases, do it all in decal editor way to do it.
I suppose I'll continue with what I've been doing...
Pads, seems like here is one area the product could be vastly improved.
First: allow holes/vias to be added to a part without calling them "pins". This would allow a person to add thermal vias without having to add pins to the schematic symbol.
Second: allow modification of individual layers such that we can make grid squares or X-outs on the paste layer etc. as we need to without having to go through the gyrations we currently need to go through.
Thanks again for the responses.
I agree with PADS there is no all inclusive way in decal, but in all honesty if Mentor would get there act together there should be.
Expedition does have the ability to do almost anything within a Cell that you can think of. But of course get ready to mortgage your life to own it.
It's this kind of basic functionality in todays design environment that should be in ALL level CAD systems.
OK don't let us autoroute adhearing to the rules or nto be able to use soem advanced feature etc unless you pony up the big bucks,
but this kind of stuff is basic to being able to make land patterns correctly.
Just my 2cents.
Amen to that!
This is basic functionality at its...well...most basic. I shouldn't have to cough up a few extra 0's on the right side of the number to get it. I won't name names but "other" much cheaper CAD packages have it.
And since we all know inflation is alive and well...that's my 3 cents!
Thanks, I didn't want to say it but, but, agree very much YES other far less expensive CAD packages than PADS
do have much more basic & advanced level functionality than PADS for the buck in many areas.