Jack commented on my prior post, An Unanswered Question. His point was that instead of just saying “check with the manufacturer’s datasheet”, like I so often suggest when talking about land patterns, I should give more credit to the IPC and understand that many datasheets are the result of less-than-thorough study. That’s a very good point.
The challenge is that some manufacturers do a great job of figuring out how to use their packages, such as TI with its Package-on-Package (PoP) OMAP, or Freescale with some of its ZiBee chips. u-blox has done a good job of documenting paste mask requirement for its castellated mounting configuration, too. On the other hand, some other manufacturers seem to have cut-and-paste part of an old datasheet without even giving it a once-over. As Jack mentioned, with some of the newer packages, IPC doesn’t always have the data yet. I didn’t see that IPC-7351B covers 0.4mm pitch BGAs yet. It does do a good job of covering the need to segment the solder paste stencil over a QFN center pad, which I also have written about more than a few times.
I guess my thinking is that the part manufacturer should be the best equipped to tell us how to use their components. To Jack’s point though, that would be in an ideal world. But, reality rarely holds up to the ideal. Some manufacturers do quite well and some seem to virtually forget that they even made the part once it’s out of the development labs. IPC does a very good job but isn’t necessarily the most current. Then, of course, some manufacturers don’t follow IPC guidelines. Board fab houses and stencil makers have a lot of good data too, but also aren’t always up to date (nor are assembly houses).
I suspect that I get a little cynical on this subject in general because we see so many diversions from standard come through our shop. The designers, by and large, would much prefer to lay out their boards for greatest manufacturing success, but so many of them have a very difficult time finding the necessary data.
In some ways, I think the environment is getting better. More people seem aware of the need for good standards and to follow those standards. IPC seems to be pretty quick in adding in newer packages. The IPC land pattern generator is a big help. But the proliferation of new parts in new form-factors negates a lot of that gain.
I’m not convinced that in net, this post has any actual content.