Calculated Steam Expansion Pressures in Reflowed Plastic Integrated Circuits
Calculated steam expansion pressures in reflowed plastic integrated circuits reach 4.69 MPa at 260°C, causing catastrophic delamination if moisture exceeds critical levels.
Clausius Clapeyron Equation
Vapor Relationship
Thermodynamic relationships describe the exponential increase of vapor pressure as temperatures rise toward reflow levels. The clausius clapeyron equation models the phase transition between liquid water and steam within a plastic package. It calculates the pressure at which a liquid exists in equilibrium with its vapor.
This relationship governs the internal forces that drive the popcorn effect during soldering operations.
Pressure Calculation
Integration of the latent heat of vaporization into the formula shows how thermal energy translates into internal mechanical load. The clausius clapeyron equation predicts that a small increase in temperature at 220 degrees Celsius results in a much larger pressure jump than the same increase at 100 degrees Celsius. Internal pressures often exceed the tensile strength of the epoxy molding compound.
Calculation of these values allows for the determination of safe ramp rates that prevent the internal pressure from rising faster than the material can vent. These forces lead to package cracking if the moisture content is too high.
Reflow Application
Moisture sensitive devices must remain below a specific saturation level to avoid the rapid pressure spike predicted by the physics of the system. Lead free soldering profiles reach higher peak temperatures than traditional tin lead processes. This shift necessitates stricter storage controls because the clausius clapeyron equation dictates that the higher heat will generate substantially more internal pressure.