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{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..)

{1057}
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ref: Kozai-2009.11 tags: electrodes insertion Kozai flexible polymer momolayer date: 01-30-2013 04:45 gmt revision:10 [9] [8] [7] [6] [5] [4] [head]

PMID-19666051[0] Insertion shuttle with carboxyl terminated self-assembled monolayer coatings for implanting flexible polymer neural probes in the brain.

  • This study investigated the use of an electronegative (hydrophillic) self-assembled monolayer (SAM) as a coating on a stiff insertion shuttle to carry a polymer probe into the cerebral cortex, and then the detachment of the shuttle from the probe by altering the shuttle's hydrophobicity.
    • Used 11-mercaptoundecanoic acid. Details included.
    • SAM atrtacts water once inserted, causing the hydrophobic polymer to move away.
      • Why not make the polymer hydrophillic?
      • Is this just soap?
  • Used agarose brain model.
  • Good list of references for the justification of soft electrodes, and researched means for addressing this, mostly usnig polymer stiffeners.
    • "Computer models and experimental studies of the probe–tissue interface suggest that flexible and soft probes that approach the brain’s bulk material characteristics may help to minimize micromotion between the probe and surrounding tissue ({737}; {1203}; {1102}; {1200}; LaPlaca et al., 2005; {1216}; Neary et al., 2003 PMID-12657694; {1198})"
  • "However, polymer probes stick to metallic and silicon surfaces through hydrophobic interactions, causing the polymer probe to be carried out of the brain when the insertion shuttle is removed. The solution is to use a highly hydrophillic, electronegative, self-assembled monolayer coating on the shuttle.
  • Biran et al 2005 suggests that incremental damage due to stab wounds from the shuttle (needle) should be minor.
  • Probes: 12.5 um thick, 196 um wide, and 1.2cm long, polymide substrate and custom designed lithographed PDMS probes.
  • Polymer probes were inserted deep - 8.5 mm.
  • PDMS probes inserted with non-coated insertion shuttle resulted in explantation of the PDMS probe.

____References____

[0] Kozai TD, Kipke DR, Insertion shuttle with carboxyl terminated self-assembled monolayer coatings for implanting flexible polymer neural probes in the brain.J Neurosci Methods 184:2, 199-205 (2009 Nov 15)

{1030}
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ref: Parikh-2009.04 tags: BMI rats cortex layer depth date: 01-10-2012 01:09 gmt revision:2 [1] [0] [head]

PMID-19255460[0] Lower layers in the motor cortex are more effective targets for penetrating microelectrodes in cortical prostheses.

  • Aggregate analysis (633 neurons) and best session analysis (75 neurons) indicated that units in the lower layers (layers 5, 6) are more likely to encode direction information when compared to units in the upper layers (layers 2, 3) (p< 0.05).
  • DUH. Have we forgotten all anatomy?

____References____

[0] Parikh H, Marzullo TC, Kipke DR, Lower layers in the motor cortex are more effective targets for penetrating microelectrodes in cortical prostheses.J Neural Eng 6:2, 026004 (2009 Apr)

{770}
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ref: life-0 tags: RCA Thompson lyra mp3 player ARM teardown date: 09-11-2009 17:15 gmt revision:4 [3] [2] [1] [0] [head]

During the GOSH! summit there was an intensive talk about making a open-hardware USBkey-to-television converter/computer/mp4 player, an idea (patented!) by Joshua Kauffman and Gwendolyn Floyd. Since this was a very hands-on workshop, I decided to get an mp4 player in downtown Banff and take it apart to see how it works. The selected device, a RCA Lyra MC4202-A portable media player, is, in accordance with its low price, electrically simple on the inside. What follows is a rough teardown of the internals.

-- View of the Lya with the back plastic panel removed.

  • A - STMP3710 SOC & ARM9 processor @ 206Mhz, 100 pin TQFP package, Freescale logo. comparison table. Device does not have enough processing power to support full mp4 playback; you have to use a special CODEC to put video files on the device.
  • B - Hynix HY27UU08AG5A 2GB Nand flash. Probably the first few blocks are reserved for booting; these blocks must be accessible through USB, as RCA/Thompson offers firmware updates. Were I motivated, I could packet sniff the USB update procedure to allow flashing with any firmware. (I would have to be very motivated!)
  • C Mini-USB type B connector. The STMP supports both full speed and high speed USB transfers.
  • D Audio out jack. Doubles as a FM antenna.
  • E Microphone. Not really sure where the amplification / digitization for this is - it may be an all digital mic, e.g. LMV1024 and sit on the I2C bus.
  • F Inductor for the external supply - 3V.
  • G Inductor for processor core supply - 1.2V (? - Freescale documentation is less than freely available on the internet)
  • H 24 Mhz crystal (large) + 32kHz real-time-clock crystal (small). The yellow tape covers a bunch of 0402 capacitors and resistors.
  • I Keypad lock switch. This makes the device a bit (but not very) tricky to re-assemble. Yes, my player continues to work after re-assembly.
  • J Lithium-ion battery. Due to the sticky tape on it's back, I bent the battery while taking the player apart. Fortunately, it did not explode! This battery is slightly thinner than that in my LG cell phone, yet its capacity is 1/3 as much - this is a cut-rate battery.
  • K Flexible kapton lead to the sub-QVGA LCD, behind the battery.

-- View underneath the main PCB, showing the keypad PCB.

  • A STFM1000 FM demodulator & clock generator chip.
  • The main PCB is 4 layers, with about 0.005" trace / 0.007" (?) space clearance. Keypad PCB slightly rougher and only 2 payers. Capacitors and transistors on this are used to drive the backlighting LEDS on the other side.
  • If you assemble these together with the screws in the wrong holes, the keypad will only partially work, probably due to connector spacing / shorting issues. I discovered this the hard way :-)