if anyone wants to try : here is the footprint i was trying to make in DEX. I can't figure it out. my limitation..
http://www.st.com/web/en/resource/technical/document/datasheet/CD00000956.pdfIt's not like it is that complicated a part but it has a few quirks. The thermal slug under the part is not a rectangle.
I will try to describe as best as i can and give you the numbers ( i don't want you to spend time figuring them out )
Draw the two rows of pads bottom row: 1 to 10 , top row 20 to 11. Pads are all 0.6mm wide and 2.2 mm tall.
Pin one is a rectangle, all others are 'oblongs' (rounded rectangle where the outer edge makes a 180 degree arc, so there is no 'flat' portion on the short side of the pads)
Pin pitch is 50 mils
Row pitch is 14.2mm
The center thermal pad is number 21 and measures 6.3mm by 9.5mm
For simplicity : All pads have a solder mask opening of 4mils over the edge of the pad.
the package is a silkscreen rectangle of 10mm by 16mm. no need for anything fancy here. Silkscreen rectangle center coincides with center of thermal pad.
Now, I need a piece of copper 1cm 'over' both sides of the package , we'll call em wings. so left side of package + 1 cm and right side of package + 1cm. The height is from the toe of the top pad to the toe of the bottom pad. Don't ask me what that number is. the datasheets don't give it. use the cad tool to adjust the edge to coincide (actually that height is the pad pitch + 1 height of the pad but i want you to try to adjust it without punching numbers. basically using snap operations like snap to edge , snap to near object, snap to center and the likes. basic CAD operations i have trouble in finding in DEX.
the 'spoke' ( the piece of copper that connects the thermal pad to the two outer 'wings' ) has a height of 170 mils
The backside of the board should have a pad that is the size of the entire structure on top. Basically take the top left corner coordinate of the left wing and the bottom right corner coordinate of the right wing. that size. i don't know what the numbers are. simply use the cad tool to make coinciding points. no need for calculations, leave those to the computer.
this back structure has a solder mask opening of 4 mils over its side.
Note that neither the wings nor the back structure are 'pads'. they are simply pieces of copper and have no pin number assigned to the, ,only the center thermal pad has a number
For manufacturability we need two soldermask 'dams' just outside the package so solder cannot wick onto the top 'wings'. The dam should be 15 mils wide. (roughly, i don't mind if it's 18 or 14 so you can position it as you see fit to avoid complex calculations) . This dam sits at the edge of the thermal pad. it will not overlap the thermal pad nor leave a piece of copper of the wings exposed to the thermal pad ( so one edge of the soldermask sliver must coincide with the edge of the thermal pad. again , i have no numbers to give you. Use basic operations like snap to point, snap to edge to make coinciding structures.
We need an array of 3 x 6 thermal via's in the main portion of the heatslug. Via hole : 10 mils. Spaced 50 mils apart horizontally and 75 mils vertically . The array is placed around the center of the thermal pad. (The center of the array coincides with center of the thermal pad )
A paste lattice is to be applied with a minimum distance of 5 mils from the thermal via holes and a lattice spoke width of no less than 20 mils ( to avoid the mask 'curling')
I know DEX does not have Paste layers so i'm fine if you can draw this structure on the silkscreen layer or on a mechanical layer or documentation layer. At least i can export it to Gerber and use a gerber editor to throw it on a different layer (or-ing the two layers) .
Paste shall be retracted 4 mils from the pad edge.
The courtyard shall be 8 mils over the edge of the entire structure including the soldermask gaps.. so the left side of the courtyard is at the left edge of the left wing + 4 mils of soldermask opening + 8 mils of space and so on.
for visual reference i have added a couple of pictures what that looks like.
First two are with step file and without ( no need to do that for this exercise , they are so you can understand what this package is. many stepper motor controllers or H-bridge drivers come in this package. Even the L298 is available in this package )
Picture two shows the thermal via lattice in the thermal pad and the solder solder mask dams at the edge of the thermal pad. We don't want paste bleeding out.
Picture 3 shows the solder mask (purple) so you can clearly see where the dams are.
Picture 4 shows the paste mask. i know dex does not have this, but draw it as rectangles on the silkscreen layer if you must. Just to experience the level of difficulty to create such a thing.
My workflow :
I heavily rely on things like snap-to-point, snap-to-edge , from-to copying. once i have the centerpoint established i place the origin there and then start playing with grid spacing . Having snap-to grid on makes positioning and scaling of objects really easy. Making a from-to copy of a collection and pasting it mirrored around x or y axis. Scaling of groups and other typical stuff found in CAD programs ( not just PCB cad. ) Entering numerical data in fields where one field reads mm and the other mils. That is my way of working. I rely on the CAD tool to crunch the numbers and come up with the actual coordinates.
I can't find the CAD operations is seek in DEX. Maybe they are there and i am too stupid to find em, maybe they are not there. Maybe that way of working is not compatible with DEX. I don't know. I give up. It is too time consuming to figure it out and we have known limitations like group moves (both graphically and numerically) that don't work like a traditional CAD program, so they hamper this workflow and make designing this footprint harder than it should be.
One important thing : do NOT use the wizard, not even to create a base structure of the two columns. This is not an exercise in running the wizards. I know that you could take advantage of running the wizard and then build on that, and in real life that is what i do too. But that is not the point here.
The goal of this exercise is to get a feel of what base object manipulation toolset is available in DEX ,and find out where the necessary controls and commands are located to efficiently play with grids , scale and position objects and set their properties.