BGA Partitioning Calls for Special Steps
High-pin count, fine-pitch BGAs with pins ranging upwards of 1,052 and beyond are increasingly being used. This means routing signals becomes more difficult. Thus, precise BGA partitioning on a PCB is a crucial design aspect to minimize or eliminate crosstalk and noise, as well as manufacturing issues.
Experienced high-speed PCB design and layout engineering is a major requirement for correctly partitioning a BGA on a PCB. Ideally, this expertise should be inextricably intertwined among chip vendors, OEMs, and PCB designers to create efficient BGA-based designs. However, that’s not practiced at times, and the end result is a less than efficient designs full of cross talk and noise.
Here are some important considerations for effective BGA routing:
- Correct BGA partitioning first takes into account uniformity of the partitioning, itself. This means evenly distributing power and ground pins on the four quadrants as much as possible.
- Smooth and straight connections must be created at PCB layout.
- Assure return paths are properly designed. Poorly developed return paths create unclean signals.
- For lead-frame packages with no return paths, design in a power supply return path through the pads’ thin leads.
- Ensure that traces don’t run parallel to each other to avoid line-to-line coupling.
- Via locations and how close they are placed next to BGA paths play an important role in reducing noise.
- Place decoupling capacitors as close as possible to the BGA pads while routing is being performed.
- Memory signals need special consideration during BGA partitioning. They need to be away from oscillating signals and power supply switching.
It’s important to assure pin-configurable BGAs be partitioned properly using the correct ground and power pins outs. These BGAs should also be routed with utmost care to make sure decoupling is properly implemented, and noise has been suppressed. At the manufacturing level each BGA should be properly mounted with a precise vision placement system and then its connections verified by powerful X-ray equipment.