Pad Cratering: The Basics

Pad cratering, what is it?  Pad cratering is defined as a separation of the pad from the PCB resin/weave composite or within the composite immediately adjacent to the pad.  It triggers failures only if the crack propagates into a copper trace or conduction pad makes the circuit open or intermittent.

Pad Cratering Drivers:

  • Finer pitch components
  • More brittle laminates (lead-free compatible)
  • Stiffer solders (SAC vs. Sn Pb)
  • Presence of large heat sinks
  • Location
  • PCB Thickness
  • Temperatures and cooling rates

Issues with Detecting Pad Cratering

  • Companies are frequently unaware until failure occurs
    • Recalls can be frequent and painful 
  • Potential Warning Signs
    • Excessive BGA repair rates
    • High percentage of “defective” BGA’s
    • High rate of “retest to pass” at in circuit test (ICT)
  • Difficult to detect using standard procedures of X-ray, generally must use destructive testing such as dye n pry, ball shear, and ball pull
  • Expensive advanced testing methods now available to screen for pad cratering

“Band Aid” Solutions for Pad Cratering

Solutions to prevent costly damage are labor intensive, costly, or have marginal impact on the problem.

  • Expoxy fillets at BGA corners
    • Ineffective and do not prevent board flexing
  • Increase board thickness to eliminate flexing
    • Expensive
  • Changing BGA and PCB pad design
    • Limited effectiveness, limits design and sources of components, can be expensive
  • Underfill of BGA components
    • Labor intensive, prevents rework of BGA parts after assembly

Zeta Cap as a solution

 

How does it work?

  • Zeta Cap requires no special processing or equipment.  It simply replaces the outer layer foil in the PCB construction
  • When used as a cap layer, it becomes the interface between the copper pad and the rest of the PCB
  • The more pliant cap will prevent or block fractures and protect copper connections (traces) the the pad

Why does it work?

It serves as a barrier to block pad cratering with a unique combination of properties:

  • High strength without being brittle
  • Modulus allows for some flexibility
  • Very high Tg and Td
  • Very low CTE (close to copper and solder)
  • Halogen free
  • Lead free compatible
  • Used on PCB surface with convention materials

If you are interested in learning more, please contact us for additional information.  Material spec sheets and test and reliability data are readily available! 

 

Purchasing and designing printed circuit boards does not have to be difficult! 

 

A special thank you to Insulectro for working with us and compiling this information! 

 

  

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