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Unraveling the mysterious BGA routing mess
- by Matt Stevenson
A Ball Grid Array (BGA) device can be a daunting component to route especially as they get more pins and tighter pitch. We know that smaller, denser, and finer pitch devices are becoming more common and are not likely to go away. BGAs do require some focused attention and a plan—but they are not impossible to route, by any means!
Start with a little research
There are many resources available that can give some guidance so you do not have to reinvent the wheel. The device manufacturer will often have helpful information on their website such as routing examples and land patterns. There are also likely other online resources that can be very helpful, such as YouTube videos, blog posts, and technical papers. Most of these resources are free to access and just require you to sift through a multitude of noise and distill it down to something that will be useful to you.
Planning is the key
A BGA of any size requires a lot of room around it for all of the wires and vias that you will need to effectively make all of the desired connections. Make sure that the critical signal paths and decoupling capacitors are well situated to maintain signal integrity and reduce inductance. Start with the vias escapes and fan-outs. Some tried and true tricks to keep in mind that will allow you to utilize real-estate on all of the layers (but can have added expense and complexity for PCBs) are vias in pad, high aspect ratio vias, micro-vias, or buried vias. These are especially critical in the very large and fine pitch devices. Traces required to route between these pads and vias can also be reduced to provide an escape. You may need to use traces and spaces considerably smaller than the rest of the board in this area. Adding signal layers is another trick to effectively routing—typically one signal layer is needed for every two rows of pins.
Make sure that you are working with a PCB manufacturer upfront and understand their capabilities, especially as it relates to these aspects for the BGA routing. It is never fun to spend a lot of time and resources on a design and find your preferred vendor simply cannot manufacture it.
Use your Design Tool
Many of the design tools today have features to help make you more successful. Explore some of these functions and use them when they make the most sense for your design. Often you can assign specific rules around your BGA that may differ from the rest of the board, saving you the time and effort of doing it on a trace by trace basis.
Good luck out there!
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