Wire Breaking, Midspan

A midspan wire break, or broken wire, is simply the disconnection of the first bond from the second bond, because of a total fracture somewhere along the length of the wire itself.  Broken wires are often due to package mishandling, particularly when the package has not yet been encapsulated or sealed. Wires being hit by the lid or cap during capping, or accidentally touched by the operator prior to encapsulation/sealing, or smashed by an equipment tool getting out of control, all suffer a midspan break after the incident.

Wire nicks and similar defects can act as crack initiation points on the wire.  Incipient cracks can easily propagate during thermomechanical stressing once they have formed from these defects.  Broken wires can also be caused by corrosion, which is often brought about by Cl contamination of the wires.  Wiresweeping during molding is another primary cause of broken wires.

Wire Depression   

Wire depression is a condition wherein one or more wires of the device are deformed or pressed downwards.  Wire depression is caused by purely mechanical means, usually by mishandling. Wirebonded leadframes prior to encapsulation are very vulnerable to wire depression, especially if these are being handled manually. Improper stacking of the leadframes, fingers coming into contact with wires, or leadframes slipping out of control prior to or during the molding process are common causes of depressed wires.

Equipment problems can also result in wire depression. For example, overcoat dispense tools that are improperly set up can land on the wires and depress them.