Bonding Resistance
A mechanical measurement quantifies the force required to slide or separate two joined material layers along their parallel boundary. This interfacial adhesion shear determines the structural integrity of the laminated surfaces inside electronic packages. If the adhesive strength is insufficient, the layers can separate under thermal and mechanical loading during operation.
The strength of this bond is influenced by surface preparation and curing parameters.
Stress Distribution
Shear stresses are typically concentrated at the edges of the bonded region where material properties change abruptly. High temperature cycling increases these stresses due to the mismatch in thermal expansion coefficients between the joined materials. Controlling the uniformity of the adhesive layer helps distribute these forces evenly.
Measurement Procedure
Testing utilizes a precision shear tester to apply a controlled lateral force to the bonded assembly until failure occurs. The maximum force recorded at the moment of separation is used to calculate the shear strength per unit area. This test must be conducted under repeatable angles and speeds to ensure consistent results.
Failed surfaces are then examined under magnification to analyze the failure mode.
Adhesion Improvement
Roughening the surfaces or using chemical primers enhances the mechanical interlocking and chemical bonding at the interface. Proper baking cycles remove volatile contaminants that would otherwise weaken the joint. These steps ensure robust adhesion that resists moisture and heat.
