Wirebond-related Shorts

          

 

Wirebond-related shorts refer to failures that involve the occurrence of unintended electrical shorting between two wires.  The point of shorting may be at a bond of the wire (first or second bond), or along the span of the wire itself. Below are the three most common types of wirebond-related shorts.   

     

Bond-to-Bond Shorting

     

Bond Shorting is the presence of an unintended electrical connection between two bonds.  The electrical connection may be in the form of bonds touching each other, or stray conductive materials bridging one bond to another.  Bond placement problems involving adjacent wedge bonds with long tails in a die with tightly-packed bond pads are the most common form of touching bonds.

                

Design rules for bond pad size and spacing, bond size, bond position, and bond deformation can easily prevent touching bonds. Die attach material that accidentally falls or drips on the die surface, or reach it in whatever way, can bridge one bond to another. Stray wires that somehow get into hermetic packages can also bridge one bond to another. Eutectic flakes or balls from highly oxidized eutectic die attach material can get loose inside the package and likewise act as bridges between bonds.  Aluminum squeeze-outs around the wedge bonds can also get loose and short bonds.

  

Wire-to-Die Shorting

  

Wire-to-die shorting is the presence of an unintended electrical connection between one or more wires and the die.  The electrical connection may be in the form of a wire directly touching an edge of the die, or stray conductive materials bridging a wire to the die edge. Mishandling of packages prior to encapsulation/sealing can result in depression of the wires, shorting them against each other and to an edge of the die.  Excessively low loop profiles and very short wires increase the likelihood of, if not lead to, wire-to-die shorting.  Die attach material that accidentally falls or drips on the die surface, or reach it in whatever way, can short the bond and wire to the die edge. Stray wires and loose eutectic flakes inside the package can also short the wires to the die edge.

 

    

  

Figure 1.  Wire-to-wire short (left) due to a swept wire and wire-to-die short (right) due to depressed wires

  

Wire-to-Wire Shorting   

  

Wire-to-wire shorting is the presence of an unintended electrical connection between two wires.  The electrical connection may be in the form of wires directly touching each other, or stray conductive materials bridging one wire to another. Stray wires that somehow get into hermetic packages can bridge one wire to another. High loop profiles and excessively long wires increase the tendency of wires to get shorted. Wire sweeping during molding may lead to wire-to-wire shorts, although it often breaks the wires first before shorting occurs.  Mishandling of packages prior to encapsulation/sealing can result in depression of the wires, shorting them against each other.

       

See also:   Package Failure MechanismsWirebondingFailure Analysis

            

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