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{1317}
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ref: -0 tags: tantalum chromium polyimide adhesion date: 06-24-2015 23:20 gmt revision:1 [0] [head]

Tantalum and chromium adhesion to polyimide. Part 2. Peel and locus of failure analyses

  • CF4 etch followed by Ar sputter yielded the strongest bond to the PI.
  • Suggest that failure may be within the PI (cohesive), not between the PI and metal (adhesive).

Tantalum, tantalum nitride, and chromium adhesion to polyimide: effect of annealing ambient on adhesion

  • The peel adhesion at T-0 (initial) shows the following order: TaNx∼ TaN < Ta∼ Cr, with all samples failing in apparently virgin PI.
  • After ten thermal cycles to 400°C
    • in forming gas the peel adhesion showed the following trend: TaNx < TaN∼ Ta ∼ Cr,
    • whereas if the annealing was done in N2 the order changed to TaNx∼ TaN « Ta < Cr.
  • The peel locus of failure was
    • always in the apparently virgin PI in the Cr/PI samples,
    • while the Ta/PI samples failed in the modified PI,
    • and the TaN/PI and TaNx/PI samples failed between the Ta-nitride and the Cu peel backing film after thermal cycling.

{1316}
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ref: -0 tags: polyimide adhesion chromium copper tie layer upilex date: 06-24-2015 23:14 gmt revision:3 [2] [1] [0] [head]

Adhesion Evaluation of Adhesiveless Metal/Polyimide Substrate for MCM and high density packaging

  • Adhesion degradation after thermal and humidity stresses can occur for a number of reasons.
    • Copper diffusion can promote adhesion loss at elevated temperatures and can be inhibited by coating a barrier layer of metal – tie layer2.
    • Oxygen diffusion through polyimide film to the metal/polyimide interface plays a critical role in promoting degradation too3. Adhesion of Cr/polyimide interface is degraded significantly upon exposure to high temperature and humidity environment due to the hydrolysis of polyimide4,5 .
    • Catastrophic adhesion loss has been linked to moisture induced oxidation of chromium interfaces based on studies using radioactively tagged water4, 5.
  • That said, most of these vendors use Cr (20nm) as and adhesion layer, and Cu (200nm) as the conductor.
  • Upilex A faired very well after the pressure cooker test -- > 60% retention after 192 hours.
  • Seemingly Ta and Cr both adhere similarly to PI -- {1317}
    • Though Ta is much more ductile, and forms a stronger carbide, Cr is preferred... cheaper?

{1306}
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ref: -2008 tags: tantalum chromium polyimide tungsten flexible neural implants adhesion layer date: 06-24-2015 22:53 gmt revision:2 [1] [0] [head]

PMID-18640155 Characterization of flexible ECoG electrode arrays for chronic recording in awake rats.

  • Yeager JD1, Phillips DJ, Rector DM, Bahr DF.
  • We tested several different adhesion techniques including the following: gold alone without an adhesion layer, titanium-tungsten, tantalum and chromium.
  • All films were DC magnetron sputtered, without breaking vacuum between the adhesion layer (5nm) and gold counductor layer (300nm).
  • We found titanium-tungsten to be a suitable adhesion layer considering the biocompatibility requirements as well as stability and delamination resistance.
  • While chromium and tantalum produced stronger gold adhesion, concerns over biocompatibility of these materials require further testing.
    • Thought: use tantalum directly, no Ti needed.
    • Much better than Cr -- much more ductile and biocompatible.
    • Caveat: studies showing reduction to stociometric Ta results in delamination.
  • Ta conductivity: 1.35e-7 Ohms * m; Ti 4.2e-7; 3x better (film can be 3x thinner..)