Thermal Model
Thermal and finite element modeling software predicts component temperature profiles, thermal gradients and mechanical strain across a circuit card assembly during heat exposure. A reflow simulation models oven convection heat transfer, radiation absorption and phase changes in solder paste to optimize thermal profiles before real assembly processing. Quality guidelines in IPC-7530 recommend thermal simulation and empirical profiling to confirm solder joint formation without exceeding component thermal ratings.
Process Analysis
Complex circuit card assemblies feature unequal thermal masses, ranging from small passive chips to thick ball grid array packages. Uncontrolled thermal deltas across a board cause differential solder paste melting, leading to tombstoning on small chip components or incomplete solder wetting under large heat sinks. Virtual reflow modeling simulates heating rates across zones in a multi-zone convection oven, helping process engineers refine belt speeds and zone temperature settings.
Stress simulation modules calculate transient thermal expansion stresses inside substrate layers, via barrels and component solder joints during rapid heating and cooling phases. Identifying potential board warpage and localized strain points before building physical prototypes prevents solder bridging and trace cracking during volume assembly runs.
Acceptance Threshold
Peak temperature and time-above-liquidus targets define the thermal window required for complete solder joint reflow. Simulated heating curves must confirm that all solder connections reach liquidus temperature without exceeding peak thermal limits of heat-sensitive packages. Validation against physical thermocouple measurements verifies simulation accuracy across critical board locations.
Accurate reflow profiles ensure compliant solder fillet formation and long-term joint reliability.
