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Stepping Through BGA Signal Escape Routing

Signal escape routing associated with the highly advanced ball-grid array (BGA) package is definitely not an easy task. Rather it’s highly challenging and poses critical PCB designer decisions along the multitudes of routes involved in getting those signals out.

One has to keep in mind that PCBs continue to become smaller, especially those rigid-flex and flex circuits for IoT products. Consequently, the design challenges are compounded due to shrinking PCB size and growing complexity.

The top job for the PCB designer is to carefully investigate a board design and develop appropriate fan-out strategies that won’t adversely affect board fabrication. There are several major considerations involved in selecting the correct fan-out/routing strategy. Those include ball pitch, land diameter, number of I/O pins, via types, pad size, trace width and spacing, and the number of layers required to escape the BGA.

Check out our article on signal routing to get more details.

In the meantime, here are some tips and hints on getting you better acquainted with signal routing when it comes to BGA packages.

  • Dog-bone fan-out (Fig. 1) is used for BGAs with 05 millimeter (mm) and above ball pitch.
  • “Via” is a term associated with BGA signal routing. It refers to a pad with a plated hole connecting copper tracks from one PCB layer to other layers.
  • The first step in implementing dog-bone fan-out is to determine via sized needed for the BGA fan-out.
  • Trace width and minimum space required between traces define a BGA’s escape routing.
  • Number of layers required can be estimated once trace and space width, number of traces routed though one channel, and type of via to be used for the BGA layout are determined.
  • Manufacturing and functionality are two key aspect that need to be considered for BGA signal routing.

The technology of BGA packaging for PCB designs is steadily advancing. This means signal escape routing is difficult and challenging. Several major considerations are involved in selecting the correct fan-out/routing strategy. Those include ball pitch, land diameter, number of I/O pins, via types, pad size, trace width and spacing, and stack-up. Following these strategies ensures a product is correct in terms of form and fit and function.