SPRAAV1C May   2009  – March 2020 AM3703 , AM3715 , OMAP3503 , OMAP3515 , OMAP3525 , OMAP3530

 

  1.   PCB Design Guidelines for 0.4mm Package-On-Package (PoP) Packages, Part I
    1.     Trademarks
    2. 1  Using This Guide
    3. 2  A Word of Caution
    4. 3  A Team Sport
    5. 4  Be Wary of Quotes
    6. 5  Don’t Forget Your CAD Tools
    7. 6  Metric Vs English
    8. 7  PCB Fab Limits
    9. 8  Routing and Layer Stackup
    10. 9  OMAP35x 0.4mm Pitch
    11. 10 Pad Type
    12. 11 PCB Pad Dimensions for 0.4mm BGA Package
    13. 12 Multiple BGA Packages
    14. 13 Etch Traps and Heat Sinks
    15. 14 Vias and VIP
    16. 15 Laser Blind Vias
    17. 16 Filled Vias
    18. 17 Know Your Tools
    19. 18 BeagleBoard
    20. 19 BeagleBoard Views
      1. 19.1 Top Layer – Signal - Area Underneath the OMAP35x
      2. 19.2 Layer 2 – Ground
      3. 19.3 Layer 3 – Signal
      4. 19.4 Layer 4 – Signal
      5. 19.5 Layer 5 – Power (VDD2)
      6. 19.6 Layer 6 – Signal – Bottom Copper – Bottom Component Outlines
    21. 20 OMAP35x Decoupling
    22. 21 PCB Finishes for High Density Interconnect (HDI)
    23. 22 Real World Second Opinion
    24. 23 Acknowledgments
    25. 24 References
  2.   Revision History

10 Pad Type

It is important to understand the pros, cons, and unknowns concerning the two most common types of solder pads. Figure 7 shows the solder-mask-defined (SMD) and non-solder-mask-defined (NSMD) pads.

s_pads_praav1.gifFigure 7. Solder-Mask-Defined (SMD) and Non-Solder-Mask-Defined (NSMD) Pads

Industry reliability studies have revealed that NSMD-type pads are highly recommended for most 0.5mm pitch BGA applications. However, there is a problem with this approach at 0.4mm pitch.

Real-world assembly experiments with the BeagleBoard and the OMAP35x EVM revealed a tendency for solder bridging between pads when NSMD were used. There was insufficient solder mask webbing between the pads to ward off bridging. Therefore, a SMD design was used, which resulted in much better assembly yields with no solder bridging.

Talk to your board fabricator and your board assembly house and learn of their experiences and preferences before deciding which type of pad design you will use. Be prepared to change your ideas about pad definitions as your experience grows with 0.4 mm pitch parts.

NOTE

Based on experience with both the BeagleBoard and the OMAP35x EVM, the use of solder-mask-defined pads is recommended.