Improved polyimide/metal adhesion by chemical modification approaches
- Suggest fuming sulfuric acid (H2S04) + Ag2SO4 for 30s as the most effective treatment.
- 1 minute in 1M KOH also effective.
- Silver was magnetron-sputtered on; peel test performed with tape.
IEEE-4936772 (pdf) Studies of adhesion of metal films to polyimide
- Suggest Ar / O2 plasma treatment of surface to increase Cr/Cu adhesion (mechanical effect?)
- Used two different polyimides: one derived from (BPDAâ€PDA) polyamic acid, and pyromellitic dianhydrideâ€4,4’â€oxydianiline (PMDAâ€ODA).
IEEE-670747 (pdf) Adhesion evaluation of adhesiveless metal/polyimide substrate for MCM and high density packaging
- Adhesion of Cr / polyimide interface is degraded significantly upon exposure to high temperature and humidity environment due to the hydrolysis of polyimide.
- There is also some worry of Cu diffusion into the polyimide.
- All used a Cr tie layer, 200A thick (20nm).
- Deposited photoresist, electroplated copper, then etched to define pattern.
- Testing performed at 121C 100% RH, +15psi. (tough!)
On polyimide-polyimide interlayer adhesion:
Diffusion and self-adhesion of the polyimide PMDA-ODA (1987)
- Diffusion occurred during the curing process of the second layer and was controlled by the cure schedule.
- It was found that a large diffusion distance, at least 200 nm, was required to obtain a bond whose strength was equal to that of bulk material.
- Good protocol:
- Dry first layer at 80C for 30 minutes.
- 150C (or lower?) bake of first layer. "as the polyamic acid imidizes (and the solvent is lost) its diffusive mobility decreases rapidly; very little diffusion occurs after the first few minutes of the second bake.
- Spin coat second layer.
- 400C second bake.
- Ductility is increased for polyimide that has experienced a series of increasing cure temperatures.
- In this context it is worth noting that the contour length of a PMDA-ODA of 30,000 molecular weight is about 130nm, a value very similar to the diffusion distances measured when T1 (first layer bake) was 150C.
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