Adhesion and Puncture Strength of Polyurethane Coating Used to Mitigate Tin Whisker Growth

Abstract

Reliability of conformal coatings used to mitigate tin whisker growth depends on their ability to contain tin whiskers. Two key material properties required to assess the reliability of a polyurethane coating are documented experimentally: adhesion strength and puncture strength. A modified blister test using a predefined blister area is employed to assess the adhesion strength and a puncture test is employed to evaluate the puncture strength of the coating. After measuring the properties at time zero, the coatings are subjected to accelerated testing conditions (high temperature/humidity storage and temperature cycling) and the degradations of the coating properties are documented.

Blister Testing for Adhesion Strength Measurement of Polymer Films Subjected to Environmental Conditions

“…where C 1 is a numerical constant, 0.518, to accommodate the volume difference of the spherical cap due to the clamped end condition of the blister [12]. Alternately, the energy release rate can be expressed just by the critical pressure, the critical blister deflection, and a constant value for both the bending dominant and stretching dominant analytical expressions…”

“…The radius dependency of the energy release rate is obvious. An accurate well-defined predefined area is critical to the sample repeatability [12]. To establish the extent of the predefined area, a stencil piece composed of flat sheet metal with 12 3/8 in.…”

“…A common adhesion strength testing method that is effective for this type of flexible/rigid interface is the blister test [2][3][4][5][6][7][8][9][10][11]. Previous challenges with this technique involving creation of a welldefined blister area have been addressed, leading to more consistent blister test results [12].…”