Thermal Cure
Polymeric materials used in electronic assembly require a structured thermal treatment to complete their cross-linking process after the initial dispense. Following a post cure baking schedule ensures that underfills, encapsulants, and conformal coatings reach their full chemical and mechanical stability. This procedure involves holding the assembled boards at a specified elevated temperature for a set duration.
The heat drives out remaining volatile components and completes the polymer network.
Material Properties
Uncured resins can suffer from poor adhesion and low glass transition temperatures, making the board vulnerable to moisture and mechanical stress. Adhering to the post cure baking schedule optimizes the physical properties of the protective materials, maximizing their resistance to thermal shock. The cured material exhibits a stable coefficient of thermal expansion that matches the surrounding board materials.
This matching prevents stresses that could lead to solder joint cracking during thermal cycling. Fully cured underfill also distributes the shear stresses experienced by ball grid arrays during drop testing, ensuring a reliable mechanical connection.
Process Control
Insufficient baking time or incorrect temperature settings can result in incomplete polymerization and latent failures. The post cure baking schedule must be carefully monitored using calibrated batch ovens or conveyorized thermal tunnels. Thermocouples attached to the boards verify that the assembly remains at the target temperature for the required duration.
