Meaning
Interfacial failure involving the loss of adhesion between the encapsulating material and the silicon surface leads to increased thermal resistance and potential electrical malfunction in integrated circuits. This underfill delamination creates a gap that can trap moisture and contaminants. It is a common failure mode in advanced packages that are subjected to thermal cycling.
Interface Adhesion
Bonding between the epoxy and the passivation layer of the chip depends on the cleanliness of the surfaces. If the surface is contaminated before the resin is applied, underfill delamination is likely to occur during the first few cycles of heating and cooling. Proper chemical treatment of the wafer surface is required to create a strong bond.
Moisture Ingress
Water molecules that penetrate the package tend to collect in the gaps created by the separation of the materials. During high temperature events like reflow soldering, this trapped moisture can turn into steam and expand rapidly, worsening the underfill delamination. This phenomenon is often called the popcorn effect and can cause the entire package to crack.
Failure Consequence
Loss of mechanical support for the solder bumps leads to fatigue and eventually to open circuits. When underfill delamination occurs, the stress from thermal expansion is no longer distributed evenly, and the individual interconnects must bear the entire load. This leads to intermittent electrical failures that are difficult to diagnose during standard testing.
