Page 59 - Handbook of Adhesion Promoters

52 Mechanisms of Adhesion Loss

The automotive coatings are com-
posed of several layers. The bulk photooxi-
dation of the clearcoat may cause the
growth of surface cracks and increase the
likelihood of peeling between clearcoat and
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basecoat. During weathering the percent-
age of clearcoat peeled areas increased and
the force required for peeling was dramati-
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cally lowered.
Adhesion between polyimide and
copper is an important for electronic pack-
aging devices, such as multichip modules
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and flexible printed circuit boards. The
elevated temperature and high humidity
Figure 3.6. Peel force of pressure sensitive adhesive, 3M environments lead to serious deterioration
Scotch Isotac 9473, vs. peel rate. [Adapted, by permis- of adhesion property, culminating in device
sion, from Brockmann, W; Huether, R, Int. J. Adh. Adh., failure. The cohesive failure occurs inside
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16, 81-6, 1996.]
the polyimide during peeling and a polyim-
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ide trace is found on the metal. If interfacial failure occurs, no trace of polyimide is
23
found on metal surface. The oxygen ion bombardment of the polyimide improves the
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adhesion strength between the two materials. The ion beam bombardment of the polyim-
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ide retards the loss of adhesion caused by thermal degradation.

o
o
Figure 3.7. Images of the cohesive zone with different peeling rates and two different peeling angles 60 and 90 ,
respectively. [Adapted, by permission, from Peng, Z; Wang, C; Chen, L; Chen, S, Int. J. Solids, Struct., 51, 4596-
603, 2014.]