This is my first time designing an SMD part in Eagle and I'm pulling my hair out.
The Sparkfun tutorial has so far been easy enough to follow:http://www.sparkfun.com/tutorials/110
But when I got to the part where I had to design the footprint, everything went all pear shaped. I can place the pads and size them fine. Positioning them is a pain in the ass since I can't see a grid smaller than 1mm so I just have to go by eye with the alt grid set to 0.025, bit I seem to have the hang of that.
The problem I'm having though is figuring out what dimensions to use.
Here's the datasheet. It tells me what the spacing between the pins is, but the overall width and height of the package seem to list two dimensions in MM seperaed by a line and I don't know if that means I'm supposed to average them cause they're min and max or what:http://www.ti.com/lit/ds/symlink/tlc5947.pdf
But that's not really very helpful anyway. I'm supposed to look at this datasheet instead for the actual pad sizes:http://www.ti.com/lit/an/slma002g/slma002g.pdf
And I started to design the landing pattern based on that but after getting all the pins right (or so I thought) I went to place the pad for the heat sink and it was huge in comparison.
Btw, I'm building the htssop-32 here, which is a DAP package. So the heat sink pad should be 11 x 5.2.
The problem it seems is the example I based my pad landing sizes on was the 24 pin PWP package. Fair enough. But it says below the example that I should refer to the parts datasheet to get the landing pad sizes. So now I'm going in circles with one document saying I should look at the other and vice versa.
So I guess what I'm asking is how do I determine where to place the landing pads for the pins, and what size they should be? Even if I placed the center of the pads according to the measurements from the datasheet, there's no information on how large to make them or exactly where the center of the pad should be.
I also found this document which helps some with making the heat sink, but right now I just need to make sure I get those pins right:http://www.ti.com/lit/an/slma004b/slma004b.pdf