IC Lead-related Failure

Lead Pulling

Lead pulling is the condition wherein one or more leads of a semiconductor device are yanked out of the device package completely (see Figure 1). It is actually a failure of the plastic material holding the affected leads, and not a failure of the leads themselves.

This phenomenon results if the axial stress through the lead exceeds the adhesion strength of the lead to the plastic package without exceeding the fracture strength of the lead itself. If an anchor hole is present in the lead finger, then the axial stress must exceed the sum of the lead-to-plastic adhesion strength and the flexural strength of the plastic inside the anchor hole before lead pulling can occur. Thus, putting anchor holes in lead fingers is a very effective way to prevent lead pulling.

Lead pulling does not happen in normal units, since the lead would break first in normal units before the lead-to-plastic anchoring and adhesion fail.

Lead pulling generally indicates a weakness in the attachment of the leads to the package. Leadframe design problems such as improper lead geometry, inadequate lead finger dimensions, and lack of anchoring features can result in this problem. Material problems that affect the adhesion of the molding compound to the leadframe can also result in 'pulled' leads.

Figure 1. Holes in the package from which two leads got pulled

Lead pulling may also indicate the presence of package anomalies such as cracks and delaminations. In fact, if the package is properly designed, lead pulling can only occur if there are cracks or delaminations in the plastic material surrounding the affected lead. Partial lead pulling may not produce visible cracks but may result in second bond breaks in the affected leads.

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