UV Curable Adhesive
Generally, UV curable adhesive consists from four components that are Acrylic Polymer, Crosslinker, UV Oligomer, Photoinitiator.
Before UV irradiated UV adhesive has high adhesion strength by high molecular Acrylic Polymer.
By irradiating UV light to this UV curable adhesive, the Photoinitiator will be activated by UV energy, then activated Photoinitiator attack the UV Oligomer. Attacked UV Oligomer also will attack the next UV Oligomer. Then, again and again…. This is the chain reaction of UV Oligomer.
By this chain reaction, UV Oligomer will make a 3 dimension formation with high molecular network. Which will cover Acrylic Polymer. At the same time, the adhesive has quite level of volume shrinkage. By this shrinkage, adhesion will degrease, hardness will raise.
During UV reaction, the adhesive will be getting harder along with volume shrinkage. This volume shrinkage will cause a micro shift between the adhesive surface and the backside of die. By this micro level shift, the adhesive strength will degrease.
UV reaction require particular condition of UV light. Must be considered carefully about wavelength, intensity, and quantity of UV.
UV light will be irradiated via base film, therefore some portion of wavelength was eliminated by base film before it reach to the adhesive. Will be used about from 300 to 400nm wavelengths one for reaction which are effective wavelength for UV adhesive and also permeated wavelength of base film.
LINTEC has been offering the UV irradiator, AdwillR RAD-2000 series for to finish this UV reaction completely.
Figure 4. shows the dependency of quantity of UV for different type of adhesive. Final adhesion level depends on the type. However, in any case, its going to be stable at more than 70mJ/cm2.
Figure 5 shows the difference of adhesion at different UV intensity. Its indicating that at low intensity, adhesion is degreasing in dully, then required more quantity of UV.
From these results, LINTEC has been setting that UV irradiation condition should be more than 70mJ/cm of quantity of UV at more than 120mW/cm2 of intensity.
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