Extra-Fine Pitch BGA Pads

One of the annoyances of the world of trade secrets and proprietariness is that we can’t all learn from each others’ experiences. That is important, and even generally necessary, in a competitive world. If you put in some hard work, you should get the first right to profit from it. Otherwise what incentive would you have to put in that hard work?

There are times, however, when it would be helpful for the industry or the economy in general if we can all learn from someone else’s challenges. Times when, for example, the entire auto industry and therefor the safety of the general public would benefit if all companies shared what they have learned about the reliability of electronic throttle systems.

Bb Good SMD pads Here’s another chance for open source hardware to shine. Take the Beagleboard. The TI folks who designed it pushed technology in a number of areas and by presenting what they have created as open source, we can all benefit from it. Even stepping outside of the great work in the schematic, they have done great service in the areas of manufacturing complex devices as well.

A while back, I wrote about soldermask defined (SMD pads) vs non-soldermask defined (NSMD) pads on 0.4 mm pitch BGAs. The basic idea is that while with most Bb Bad NSMD pads BGAs, you want NSMD pads for better mechanical strength, with the really small BGAs, like the 0.4 mm pitch OMAP processor, you want SMD pads to prevent shorts.

The messages that the Beagleboard team learned here are, first, it’s true that you want SMD pads and second, make sure that your PCB fab house follows your instructions in that regard.

Many fab houses have their own rules and will set the soldermask up based on what they feel is best. They may have never used your part though. Make sure the board house does what you need. By insisting on closing up the soldermask, the Beagleboard team went from 90% failure with the NSMD pads to 96% good and no BGA shorts with the SMD pads. (This info and the photos come from the Beagleboard ESC presentation by Gerald Coley.)

Duane Benson
The worms do.

http://blog.screamingcircuits.com/

About Duane

Duane is the Web Marketing Manager for Screaming Circuits, an EMS company based in Canby, Oregon. He blogs regularly on matters ranging from circuit board design and assembly to general industry observations.
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One Response to Extra-Fine Pitch BGA Pads

  1. Tom Hausherr says:

    Duane,

    Disclaimer: the views and opinions presented here are not necessarily assoicated with my employer. This is my personal opinion.

    That is a sad fact that anyone on this planet can copyright a fine pitch BGA fanout, especially if the fanout technique is the only viable solution. There are PCB fabrication shops that claim their solution for a 0.4mm pitch BGA is Proprietary Knowledge that cannot be freely shared with the industry. It’s their trade secret and it’s similar to patenting air. How is the industry supposed to prosper with this philosophy?

    Tom

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