Soldering Impact
Thermal event occurring during the surface mount assembly process subjects electronic components to intense physical strain as they pass through the liquidus phase of the solder alloy. This reflow thermal shock occurs when the ramp rate exceeds the material tolerance of the sensor package or the internal semiconductor die. Temperatures typically peak between two hundred and forty and two hundred and sixty degrees Celsius, causing rapid expansion of any trapped moisture or mismatched materials.
This event is the extreme thermal event a component will face before it enters service.
Material Strain
Differential expansion between the plastic mold compound and the silicon chip creates mechanical stress that can lead to internal cracking. If the heating rate is too steep, the outer layers of the package expand while the core remains cool, resulting in a shear force at the interface. This force can sever wire bonds or cause the die to delaminate from its lead frame.
Moisture Sensitivity
Vaporization of absorbed water within the package creates internal pressure that can rupture the housing in an effect known as popcorning. High temperatures during the reflow thermal shock turn liquid water into steam instantly, expanding the volume by over a thousand times. Components are graded by moisture sensitivity level to define how long they can be exposed to ambient air before they must be baked dry.
Failure to follow these storage guidelines results in catastrophic package failure during the soldering cycle.
Calibration Shift
Permanent changes in sensor output can occur even when no visible physical damage is present. Testing the device before and after the soldering process allows for the identification of these characteristic shifts.
