Package Failure
Internal delamination and cracking of plastic packages happens during soldering when absorbed moisture vaporizes rapidly under high thermal stress. The destructive process known as popcorning mechanism occurs when the internal steam pressure exceeds the mechanical strength of the mold compound or the adhesive interfaces. This release of pressure produces a characteristic acoustic signature and destroys the physical integrity of the component.
Vapor Pressure
Soldering temperatures during surface mount assembly provide the rapid thermal input that triggers this failure mode. In the popcorning mechanism, moisture that has accumulated at the interface between the silicon die and the metal leadframe transforms into high-pressure steam. This pressure bends the molding compound upward until the interface separates and the package cracks open to release the steam.
This damage is often hidden beneath the surface of the mold.
Metrological Detection
Detection of this internal damage relies on acoustic microscopy and cross-sectional analysis of the stressed packages. Test laboratories use acoustic scans to check for delamination before and after the reflow soldering cycle to confirm that the package remains sealed. This step is critical for validating the moisture sensitivity level of new package designs.
This testing prevents damaged components from entering the final assembly line.
Prevention Level
Safe operation requires that the moisture content of the package is kept below a critical threshold before the soldering run. This threshold is maintained by strict control of the floor life and the use of protective barrier packaging.
