Page 165 - Handbook of Adhesion Promoters

158 Selection of Adhesion Promoters for Different

8.15 POLYIMIDE

Dow Corning Z-6106, and Silquest A-1170, Y9627, and Y-11699 improve adhesion with
polyimide according to their manufacturers.
Copper pastes were prepared in 3-glycidoxypropyltrimethoxysilane prepolymer (1
wt%) acting as an adhesion promoter and a vehicle (15.4 wt%) composed of ethyl cellu-
lose (7.0 wt%), 2-(2-butoxyethoxy) ethyl acetate (83.7 wt%) and diethylene glycol
monobutyl ether (9.3 wt%). The paste was then screen-printed on glass and polyimide
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substrates and sintered at 275 C (polyimide) under a formic acid/N environment, result-
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ing in the formation of copper-based electrode materials (see Figure 2.26 for the effect of
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the addition of an adhesion promoter). The sintered Cu films exhibited excellent adhesion
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properties.
In another development, the copper complex ion ink that was ink-jet printed on a
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polyimide film and was transformed into copper films by thermal treatment at 200 C for 2
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h in hydrogen. The 3 wt% silane coupling agent was added to the ink as an adhesion pro-
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moter to obtain good adhesion and low resistivity.
The adhesion between polyimide and silica glass was studied using molecular
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dynamics simulations. A polyimide having a lower coefficient of thermal expansion
requires a greater pulling force but a shorter pulling distance to be completely separated
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from the silica surface. The polyimide chains near the interface dominate the molecular
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response due to their stronger adhesion to the glass surface. The energy of bonds and cou-
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lombic energy play the most significant role in resistance to deformation. The adhesive
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failure is the dominant mechanism regardless of the type of polyimide.
Adhesion of epoxy resin to polyimide was improved by amine treatment of polyim-
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ide (immersion in amine solution). There was an optimum drying temperature for maxi-
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mum adhesion strength following amine treatment. The adhesion strength increased with
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increase in the molecular weight of diamines or polyamines. Poly(amic amide) was
formed on the polyimide surface by the reaction of a primary amine of diamines and imide
group of PI, including crosslinking reaction reinforcing weak polyimide surface layers. 4
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Also, epoxy resin reacted with free amine groups on polyimide surface.
The adhesion promoter (aminosilane such as Silquest A-1100) was spin-coated onto
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the sensor (quartz) prior to the application of polyimide. The approximate thickness of
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the silane layer was 10 nm.
A polyimide copper clad laminate comprises layers of polyimide and copper foil. 6
The polyimide layer is made from a polyimide precursor comprising a diamine monomer,
a dianhydride monomer, an organic solvent, and a silane coupling agent having one or
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more organic functional groups (e.g., γ-ureidopropyltriethoxysilane). The smooth copper
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foil is used in the application.
A conductive ink includes metallic nanoparticles, a polymeric dispersant, a solvent,
and numerous performance additives including adhesion promoter (quaternized alkyl imi-
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dazolines, Cola Solv Ies). The inks are deposited on flexible substrates such as polyim-
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ide, liquid crystalline polymers, and poly(ethylene terephthalate).
Polyimide substrates are bonded to germanium wafers having an epitaxially grown
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III-V layer and a metal layer. The choice of adhesive is of paramount importance. There
are several requirements for the adhesive layer to act as a permanent carrier of the thin
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fragile multi-junction solar cell. The adhesive must remain flexible after curing and have