bgadatasheetpcbpcb-designpcb-fabrication
I'm trying to figure out the pad size to use for my footprint according to this datasheet.The last page in the datasheet has the package dimensions. I've also posted the relevant information in a picture below.
The bottom right has the dimension for the pad size but I cant figure out the actual measurement from the table it provides. I'm confused by the labeling, do I use eee or fff? and what is the purpose of C A B symbols next to eee and C next to fff.
If you're interested in solderability and manufacturability, then you should follow the recommended pad layout. I've never had a manufacturer's recommended pad layout give me grief, although I have run across a few vendors whose dimensioning requires a fair bit of headscratching and pencil-and-paper chicken-scratching in order to figure out offsets and spacing.
You are making some bad assumptions in your calculations though. No, pins are not often centered on the pads "lengthwise" but they are often centered widthwise. Y1 and C1 would most certainly be given by the manufacturer. The recommended land pattern will (in my experience) give more space for the pin on the "outside" of the pad and less underneath it. My guess is that that gives a good shape to the solder connection. You won't have anything in terms of heat dissipation unless there are a lot of grounds or you have a ground pad underneath. In the case of a lot of ground pins, you'll want to give them a lot of copper fairly quickly, but you'll want to connect the pad to the copper with thermals or you'll have soldering problems.
I wouldn't worry about minimizing board space, especially if you're not building a million of these. The half a millimeter you might save by shaving Y1 a little isn't worth it.
The SO8W (Wide) package dimensions are as follows:
For confirmation, the datasheet of the specific part would be of value.
For land pattern and pad dimensions, just use a SO8N package layout, and split it down the middle to fit the wide package.
For a comprehensive list of package dimensions, see this link.
Best Answer
The ball size is 'b', 0.3mm nominal which makes sense for a device with 0.65mm ball pitch.
That is shown in this picture (347 x diameter b)
The usual land pad size for a BGA is 0.8 the ball diameter for non solder mask defined (NSMD) pads, for 0.24mm in this case; we normally round this off to 0.25mm.
This application note from NXP explains their specific products, but the general rule is the same.
This presentation agrees with that.
I would use 0.25mm pads with a solder mask diameter of slightly larger than the maximum ball size (you risk stress fractures of the ball otherwise); perhaps 0.37mm in this case. This will leave sufficient area for dogbone breakouts to have solder mask (diagonal pitch ball to ball is about 0.92mm).
This does mean that breakout for all but periphery balls (or those where there is no periphery ball in the way) is through vias.