Analytical Shear Lag Modeling for Strain Transmission into Bottom Terminated Packages
Analytical shear lag models quantify strain transfer from boards to bottom-terminated packages, showing compliant die attach drops offset drift by 98 percent.
Bottom Terminated Packages
Package Design
Surface-mount semiconductor packages with metallic contacts located exclusively on the underside of the body provide efficient heat transfer and minimize the footprint on printed circuit boards. Utilizing bottom terminated packages allows hardware designers to integrate high-power devices and high-speed chips into space-constrained designs. The absence of traditional leads reduces parasitic inductance and resistance.
This configuration enables faster switching speeds and better signal integrity.
Assembly Mechanism
Applying solder paste requires precise deposition and careful control of the thermal reflow profile to ensure reliable joint formation. When mounting bottom terminated packages, the stencil thickness and aperture design must be optimized to prevent solder bridging or extensive voiding. The absence of compliant leads means that the solder joint must absorb all mechanical and thermal stresses.
The resulting solder thickness determines the reliability of the mechanical connection.
Thermal Pathway
Heat dissipation in bottom terminated packages occurs through a large central pad that connects directly to the circuit board. Inspection of this solder joint via x-ray imaging determines the presence of voids that could impede thermal transfer.
Stress Concentration
Temperature variations in the operating environment cause the circuit board and the component to expand at different rates, introducing significant shear stress on the solder connections. The lack of flexible leads on bottom terminated packages concentrates this thermal-mechanical strain within the solder joints, eventually leading to fatigue cracks. Thermal cycling tests are used to qualify these joints by subjecting the assembly to extreme temperature swings.
These tests establish the lifetime expectations under typical operating environments.