{1265} revision 7 modified: 10-11-2014 00:13 gmt

Adhesiveless copper on polyimide substrate with nickel-chromium tiecoat

  • Chrome works the best, with Nichrome lagging slightly behind. Thicker tie layers (20nm) work slightly better.
  • 17 nm Cr and 5nm NiCr both work well after gold plating
    • in aggressive cyanide solution -- without tie layer, the copper was released.
    • note how thin the layers are!
  • Surface benefits from oxygen plasma pre-treatment. (de-scum?)
  • Still not sure how to get second layer of polyimide to adhere to top layer of Cr.

Adhesion Between Polymers and Other Substances - A Review of Bonding Mechanisms, Systems and Testing

  • The adhesion between the polyimide, PMDA-ODA and metals such as copper or chromium has received considerable attention due to its importance in the microelectronics industries.
  • As mentioned, the PMDA-ODA is normally deposited from solution as the polyamic acid and cured in-situ to the imide form.
  • Adhesion of the polyimide deposited on a metal is therefore a different problem than adhesion of a metal deposited on the cured polyimide.
  • The former situation (polyimide on metal) tends to give stronger adhesion than the latter (metal on polyimide) but there can be problems of metal, particularly copper, dissolution.
  • Great! (is this a reliable source?)
  • The interaction between the metals and the polyimide has been studied in great detail using x-ray photoelectron spectroscopy (XPS) and other surface analysis techniques but there is not complete agreement on the form of the interaction.
    • It is clear that strong interaction and electron transfer occurs when the metal is deposited from vapour onto the polyimide.
    • When the polyamic acid is deposited on the metal and cured then reaction occurs between the acid and the metal.
  • The strong interface formed between chromium and the polyimide is clearly a result of the strong chemical interaction but there is still considerable interest in making it more resistant to water and oxidation.

High-Performance Polymers (book) Guy Rabilloud (via google books.)

  • Order of metals by increasing adhesion:
    • Cu, Pd, Ni, V, Cr, Nb, Ti [140]
  • The adhesion between chromium and polyimide is degraded sharply as the interface is exposed to temperature-humidity stressing (85C, 81% RH [612]
  • Polyimide-polyimide self-adhesion strongly benefits from partial cure of the first layer (which is not possible with lithographic processes, TMAH etches uncured film). Plasma and adhesion treatments would likely help, due to molecular tangling (?). Presumably VM-651 helps. We'll cross that bridge when we get to it.
  • PMDA-PPD or PMDA-PDA is perhaps the most rigid of all the polyimides, but due to the extremely hydrophillic nature of PMDA & associated electron affinity of the dianhydride ( E aE_a ), and the fact that it tends to crystalize & not be tough/plastic, it's infrequently used.