<azonenberg> lol duct tape
<azonenberg_lab> Woot
<azonenberg_lab> Testing use of 1000nm evaporated Cu over 5nm Cr as a hardmask for KOH wet etch of <110> Si
<azonenberg_lab> early experiments are promising
<azonenberg_lab> but i need to leave it in the etch bath longer
<azonenberg_lab> the Cu isnt attacked visibly but the Si isnt etched by much either :P
<azonenberg_lab> surface is roughened, which indicates that etching is happening
<azonenberg_lab> (of the Si)
<azonenberg_lab> If this works out i may be able to ditch that Ta2O5 for good
<azonenberg_lab> Its been the main thing killing my yields lately :P
<azonenberg_lab> too finicky
<azonenberg_lab> aww... it didnt work, there are bubbles in the film
<CIA-67> homecmos r114 | trunk/lithography-tests/labnotes/azonenberg_labnotes.txt | Today's lab notes
<bart416> azonenberg, I think I have it ifgured out
<bart416> Conductive ink
<azonenberg> For?
<bart416> Then I can copper plate whatever I want
<azonenberg> Ooh
<azonenberg> Thats what i tried for via plating
<azonenberg> but i tried using it bare
<bart416> If I find one that can be diluted in water
<azonenberg> i didnt try electroplating over it
<azonenberg> Doesnt have to be water - any common solvent
<azonenberg> ethanol, isopropanol, acetone
<azonenberg> find one that can be thinned with any of them
<bart416> I'd like something that I could remove again though
<azonenberg> Same solvent again?
<azonenberg> i dilute my PR in acetone before spin coating it
<azonenberg> and strip with acetone after etching
<bart416> So I can coat the plexiglass in it
<azonenberg> as long as its a solvent-evaporation process and not curing you're fine
<bart416> copper plate
<bart416> lithography
<azonenberg> acetone isnt compatible with plexiglass but some of the other solvents may be
<bart416> remove copper with H2SO4 or another acid
<bart416> then kill the ink with something that doesn't kill the plexiglass
<azonenberg> I like what you're thinking but must caution you that you may have adhesion problems
<azonenberg> copper is hard to stick to things sometimes
<azonenberg> if the ink peels off the surface it may not work well
<bart416> well yeah, it'll be sandwiched between two layers of plexiglass
<bart416> So it only needs to stick for a few hours
<azonenberg> Hmm
<azonenberg> Explain your process again?
<azonenberg> From beginning to end
<bart416> ok, get the circuit on the plexiglass
<bart416> drill holes where necessary, plate vias, etc...
<bart416> then stick the plexiglass together
<azonenberg> So you want to use a single sheet of PMMA as your board substrate
<bart416> That's easy enough
<azonenberg> this is two layers only?
<bart416> no
<azonenberg> top and bottom of the sheet?
<bart416> two layers / sheet
<bart416> You can smash together several sheets though
<azonenberg> How thin are these sheets
<bart416> How thin do you want them?
<bart416> I was thinking of starting with 1mm
<azonenberg> Hmm, even that is a bit thick
<azonenberg> you really want like 250um
<bart416> I'd rather first get the process to work than start with a fragile material ;)
<azonenberg> True
<azonenberg> But that means you have to deal with really high aspect ratios in vias
<azonenberg> or make the vias gigantically wide
<bart416> that's why the ink needs to be diluted as well
<bart416> so it can get in the via through a bath
<bart416> I want it so I can throw the sheet in the bath for an hour
<bart416> And it's coated
<azonenberg> Hmm
<azonenberg> An hour?
<azonenberg> You want something with low surface tension
<azonenberg> maybe mix a little surfactant in there
<azonenberg> submerge, pull out, blow dry, done
<bart416> Just giving a random number :|
<bart416> yeah ideally you'd have something that chemically binds with the acrylic
<bart416> I was considering it
<bart416> But how do I remove it again afterwards eh
<azonenberg> First of all, why do you want to remove it?
<bart416> You want a conductive substrate on a pcb?
<bart416> Looks like a bad idea
<bart416> That's why to use plexiglass azonenberg
<bart416> It won't die if you try to solder it
<azonenberg> Let me get this straight
<bart416> and you can bond layers together with chloroform
<azonenberg> Isnt the idea, lay down conductive layer
<azonenberg> Electroplate copper
<bart416> Etch
<azonenberg> spin/dip coat photoresist, expose, develop
<azonenberg> etch all the way through to the plexiglass
<bart416> yes
<bart416> I want the ink gone
<bart416> or whatever I use to make the plexi conductive
<azonenberg> So you're talking about removing it from exposed areas
<azonenberg> It still seems like the best solution is to have your initial layer be evaporated copper
<azonenberg> a micron or so
<azonenberg> then electroplate that up to working thickness of 30um ish
<bart416> Evaporation is expensive
<bart416> And hard on large objects
<bart416> + you can't get copper to stick to acrylic by evaporation
<azonenberg> Its not that expensive to run if you have the equipment already
<azonenberg> But define "large"
<azonenberg> are we talking PC mobo size/
<bart416> Yes
<bart416> Anything smaller is pointless
<azonenberg> pointless??
<bart416> Yes
<azonenberg> Are you planning mass production or prototypes here?
<bart416> Cause then you can stretch it out over a larger dual layer board
<bart416> prototypes
<azonenberg> If you're doing prototypes, develop a 6- or 8-layer process
<azonenberg> and make 'em 3-4 inches across
<bart416> 10 cm is already big
<azonenberg> The evaporator i've used has around a 6" wide disk as the usable area for coating
<azonenberg> if i were to build one of my own it'd be around the same size
<bart416> I don't have access to an evaporator
<bart416> And I'm not going to build one
<bart416> We don't all go to some american university that gets 50 000 / year / student
<azonenberg> Building one doesnt have to be expensive
<bart416> And most of the funding we do have goes to the stupid management & economy department for their stupid pointless trips
<azonenberg> Cheap vacuum pump as a roughing pump
<azonenberg> Homebrewed diffusion pump
<azonenberg> or off ebay
<bart416> that alone would cost me over 200 euro
<bart416> Not in the budget
<bart416> chemicals I can get
<azonenberg> how?
<bart416> plexiglas, how much square meter do you want?
<azonenberg> The more obscure chems have been my biggest expense
<azonenberg> or among the biggest alt east
<bart416> Normal-ish chemicals (not for semiconductor use) I can get through college/university with academic discount
<bart416> So that's not expensive at all
<azonenberg> Just out of curiosity
<bart416> But a vacuum pump alone costs roughly 100 euro here
<azonenberg> See what it'd cost you to get 4 fluid ounces of 16% tantalum chloride in ethanol :P
<azonenberg> I'd be willing to bet a few hundred USD
<bart416> now in milliliter like the civilised world uses?
<bart416> the homebrew diffusion pump would set me back another 100 euro in materials at least
<bart416> Not to mention toolbits to machine the materials
<azonenberg> You dont have anything suitable in the engineering department?
<azonenberg> To machine it, i mean
<bart416> I have access to a cnc machine shop, just need to pay for the toolbits myself
<azonenberg> interesting
<azonenberg> they dont charge us for bits here
<azonenberg> just stock
<azonenberg> as in, we're expected to supply our own
<bart416> Not at college/university
<azonenberg> oh, i see
<bart416> Their cnc machines there are constantly in use and time on them is reserved from here till 2040 or something like that :S
<bart416> Same for the rapid prototyping machines
<bart416> + my point still holds
<bart416> You can't evaporate copper on plexiglas
<azonenberg> diff substrate?
<bart416> Name one that's readily available, cheap, easy to machine and heat resistant?
<azonenberg> stripping PR ont ork, you need acetone
<bart416> the chloroform will attack the photoresist as well normally
<bart416> so while bonding layers it will destroy the remains of the photoresist if there are any
<bart416> maybe mylar
<bart416> But that again brings the issue of how to coat it
<bart416> Then again, mylar I could probably buy coated
<bart416> buy coated mylar, electroplate with copper
<bart416> etch
<bart416> attack with whatever I want really
<bart416> Actually that's the best thing I can come up with
<bart416> buy mylar with a metal coat on it already
<bart416> That's cheap, readily available and strong
<bart416> Actually I'll settle on that
<bart416> Mainly cause I can electroplate it
<bart416> side bonus is that I could potentially laser cut thin sheets of mylar
<bart416> never ever try to laser cut plexiglas ;)
<azonenberg> lol
<bart416> what do you think about using mylar that already comes with a metalic layer?
<azonenberg> liek
<bart416> azonenberg, side bonus is that the industry actually uses mylar for this :P
<bart416> My only issue with this is how to do vias
<bart416> But maybe the fact that there are already metals available might act as a seed for the plating process
<bart416> also tantalum chloride azonenberg
<bart416> high purity powder?
<azonenberg> yes
<bart416> So >99.8%?
<azonenberg> yep
<bart416> Bit more than 100 euro / 10g
<bart416> and with bit more I mean like a few cents, lol
<azonenberg> so 4 fl oz @ 16% solids =?
<bart416> meh, that's up to you :|
<bart416> catalog doesn't list liquid solution
<azonenberg> ondr if i got ripped off lol
<bart416> academic pricing though
<bart416> I doubt you can easily get this
<bart416> A bit less pure it's 74 euro / 10g
<bart416> (still 99.9%)
<bart416> also, if I use regular electroplating I can finally get rid of that damned copper tubing I've been wanting to get rid off for ages
<azonenberg> ll
<bart416> azonenberg, I think I found something suitable to power a portable railgun cheaply http://be.farnell.com/epcos/b41231a9568m000/capacitor-snap-in-100v-5600uf/dp/1839296
<bart416> I just did something scary
<bart416> Mathz!
<bart416> with 50 of those capacitors I should be able to speed up a bullet sized projectile to speeds in excess of a hunting rifle
<bart416> total weight would be about 4kg
<bart416> (this is assuming a gross lack of efficiency)
<berndj> bart416, i always thought you want to drive railguns with *thousands* of volts just to get over the inductance
<bart416> berndj, depends on the design really
<berndj> and your level of ambition!
<bart416> That too
<bart416> lol
<bart416> Nah, but the induction of a railgun isn't nearly as bad as you think
<berndj> oh? ok
<berndj> maybe it's more applicable when you're building one you hear about on the news
<bart416> at least, haven't really had any trouble with that before
<berndj> as in, a very big one
<bart416> Yeah, that's probably going to be bad
<berndj> i was doing some calcs for a spot welder the other day, that's also a bit depressing
<berndj> you need either a huge transformer or loads of copper
<bart416> Yeah, and cooling is pretty nasty as well
<berndj> is it?  i assumed you could manage that with a low duty cycle
<berndj> since the xformer windings are your first heat sink!
<bart416> well yeah, I meant of the capacitor bank :P
<bart416> We've tried to build some rapid fire coilguns at college
<bart416> and the main point of failure is always the capacitor self destructing due to heat
<berndj> i was just gonna cheat and do mains -> bridge -> igbt crowbar as the "switch"
<berndj> self destructing due to one shot or a duty cycle issue?
<bart416> well yeah, you're pretty much short circuiting a lot of them close to each other through a rail of copper
<bart416> what do you expect to happen? :P
<berndj> to warm up, of course, but i've always assumed that a single discharge isn't enough to kill it?
<bart416> with cheap chinese capacitors it is
<bart416> Or it won't be able to build up enough charge until its cooled down again