The wafer in the PMMA mask.

So, while waiting for the turbopump to arrive, my mind was left meandering around, and thinking about the PMMA masking, and the difficulty to obtain very low molecular weight masking liquid…

And I thought…If Silicon is sort of transparent to 10600nm laser light…but PMMA is not…can’t I just use laser etching to patern low resolution features on my test wafers?

With that thought, I prepared a test vector file with lines separated 100µm – 200µm – 300µm – etc… for the laser cutter:

Then proceeded to engrave some acrylic I had around, and McGyvered the shitty microscope we had at home:

That is nice!

That looks very consistent to me! Also, linewidth seems pretty constant (no micro power fluctuations in the laser supply)

For scale, a 110µm copper wire was placed in one trench:

The process idea is as follows:

First etch the PMMA with the laser, but not trying to go all the way, just to the top of the silicon wafer. Then, using PMMA solvant, you eat away some thickness from the leftover PMMA, revealing the silicon on the bottom of the trenches.
After that, an anneal step and you can etch the wafer. This should enable 100µm features, with 100µm spacing.

Advertisements

This Boring Company II

(GO TO PART I)

Finally got to install the temperature probes. I began by drilling/reaming a vertical hole from the heat face, so even if it was crooked, the start point was correct.

After that, a bigger hole was drilled on the other side to accept a ceramic separator that came with the probe:

To make space for the probe dome and cables, a sharp scrapper was used:

And it looks like this:

The ceramic retainer is attached to the metal plate with screws, with their head on the inside, so they can’t work loose. Also, dual nuts where used:

Now looks like a partial eclipse:

In the meantime, the plasma cutter arrived, and made my life much easier by allowing me to cut simple shapes with zero effort. So, a 3D model of what I wanted was made:

That was transferred to CAD, and then lasercut some MDF stencils to gide the plasma torch:


Other project stencils, but you get the point.

And panels where made.
Plasma cutting by hand (with stencils) is tricky for internal shapes, and thus, all holes had to be tweaked with a file for the modules to fit.

I am slowly getting better at welding (and thick sheet metal helps):

After power sanding:

First test fit alongside the oven:


The control box is upside down. xD

Nuts where welded to hold the cover:

And tabs where added to hold the box away enough from the oven side:

And then the integration began:

Power cabling:

A quick note on fiberglass covered power cable. You MUST crimp the ends before cutting the fiberglass, or it will unravel and create isolation issues. I did mine with some brass tube and parallel pliers:

Since I was not in the mood to make more holes in the box, I opted for the easy cable routing:

And no, the heatsinks can’t get hot enough to damage the fiberglass cable or the silicone cable, altough the second one might get sleeved up to the probes at some point. Let’s say it is workshop friendly as long as there are no kids around. XD

When you want a compact unit, things like this happen:

Testing the power section to ensure everything is ok:

I left it cooling overnight and then installed the timer. It is NOT connected to the power section, it’s just a convenient place to have a programable clock/alarm.

The controller also has a double circuit switch to deactivate the SSR’s, so the oven power is OFF but I can still monitor the temperature.
The oven now just requires some external quartz tube supports, but it can be used as is for now.

See ya!

This Boring Company I

Finally! The oven build begins.

All materials have been gathered:

  • 6x Alumina bricks. (4 needed, 2 spares/testing)
  • 2x SSR 25A+ 2x ssr radiator.
  • 2x High temperature K probes.
  • 2x Temperature controllers.
  • 2x Porcelain connectors.
  • 2x Kanthal heating filament 2000W (60cm compressed)
  • Quartz tube (45mm OD x 450mm)
  • Diamond hole saws (6.5 / 48 / 61mm)
  • 3D printed drill guides.
  • High temp electric cable.
  • Lengths of 15mm square stainless steel tube, screw rod and some washers.

First, a holey test:

Result:

If one works slowly, the cores remain intact and you can remove them without having to remove the drill from it’s mount:

Next: Big drills.

A 48mm drill digs out half of the Quartz tube channel, and a 61mm one cuts the channel to allow the heater to serpentine.

I’ll have to figure a way to align the block so the cuts are straight before actually building the thing, tough. XD


Go, go, go!

First, find a way to hold the bricks in place. Justsome press fit wood blocks will do.

This is probably NOT the worst tool in the world. Positioning is within ±0.2mm and angular alignment is good enough. Since this is a single use only (so to speak) tool, I wasn’t going to bother doing the mounting perfectly:


lol

In retrospective, I would make the pieces in such a way that they would fully reach to the base (and also have align markings) instead of this complex centering/mounting technique.

The complete tool (with short test brick):

Testing the drill-through capability before commiting with the good bricks. Everything looks nice.

The bricks are longer than the reach of the filament saw, so they have to be turned around and drilled from both sides. How good is alignment?

Good enough, I’d say:

Video of the process (not full length drilling because of reasons):

Once that is done, vacuum it good and insert the filaments (pre stretched so there are no shortcircuit between loops)

This looks so nice. ^^

Now. How should this be put together?

Metal!


I really, REALLY, need a welding table. I have zero holding devices, and the aluminium plate I use, warps with heat.

I made some “trays” out of stainless, allowing for a small gap between them and the bricks, so I could use a thin ceramic matt (4mm, compressible)

This way, I cushion everything, reducing the likelyhood of breaks.

Some length of stainless screw get soldered to the top and bottom:

And some washers hold everything together:

Looking good:

Next, heater connection. Seats are cut into the body.

 

And into the back plate:

This will make a secure connection AND hide everything.

You don’t want to clamp the canthal wire directly as a single filament. Instead, you have to bend it a few times to decrease resistance in the clamping point and allow a better connection over time.

It is also time to test the quartz glass tube fitting:

So…damn…gorgeous!

One more beauty shot:

Now, add some legs and cables:

I’m using duall controllers, one for the top filament and one for the bottom filament, because I’m a control freak, mostly.

I could not resist to test it before finishing the electronics body. First, one hour @300ºC

Then 20 minutes at 600ºC

The filament glows nice at this point, and you can very well see the heat pulses:

Let it cool down, and then, ramp it up to 1000ºC

Closeup of the inferno:


Make sure you don’t have the probes swapped, it can lead to weird temperature readings/setups (one coil heating the other to keep temperature), don’t ask me how I know.

And that’s it!

All the important bits and pieces have been done, encasing the electronics is trivial enough not to deserve a continuation of this post.

Part II

Toolroom for hell. (part 1)

There are times when I am amazed at what does people find in internet. Like all tubular ovens out there. Well, I was not able to find anything that suited my needs, so had to proceed along the hard route, build it myself.

Kilns are not difficult to build, just watch some tutorials on youtube and you are pretty much set, however, a tubular oven has slightly different demands:

  1. The glass tube must be Quartz to withstand the working environment, borosilicate won’t cut it.
  2. The filament is not NiCrom! wich is good for 900ºC max. You have to buy Kanthal, good for 1200ºC and not much more expensive.
  3. You want the heat as even as possible, hence the tubular shape of the filament guides/kiln shape.
  4. Also, since we’re at it, dual temp controllers will ensure that heat rise doesn’t generate hot/cold spots.

 


Skecth in Fusion 360.

Alumina bricks are easy to saw, but once you want precison shapes, hand carving is not going to be enough. So, what do you do?

I had lying around a 14mm sliding bar from an old scanner, so I bought some linear bearings (14x21x30mm) for it, and encaging those in 20x27x4 radial bearings (via some sleeves), I designed a support for all that (2x) to be anchored into 20mm normalized aluminium extrusions.

Since this is a low load, more or less single use tool, I decided to 3D print it instead of make it from a durable material like aluminium. 7h later, I had this:

After a few more hours of printing and designing a motor mount and such, this is what I got:


I had to add an axial bearing to this assembly, it’s shown in the videos below.

So what does this do?

The effector (rod) will have attached some apropriately sized  diamond circular saws on it’s end. Once the tool and the brick are aligned, you can handfeel the pressure and go as slow as you want on the drilling (because the material is so soft).

I know, I know, I could have used one of the guides as driver with a gear attached to the bearing, however, the motor was an afterthought. I had planned to drill it by hand, but I’m a lazy bastard I guess.

Under power (the video is in slow motion) looks like this:

But wait!
This only drills the central section and front/back coil recesses but the oven has this shape:

For the coil guides themselves, another machine has to be made, using 6mm drill guide, 6*10mm linear bearings (LM5LUU) and 15*21 ball bearings.


Failed print due to nozzle clog. (dammit, 10h lost)

But each half has six coil guides! how does this work? Magic? xD
No, not really, this adaptor works exploiting the axial simmetry. Once you have drilled three holes, turn it 180º and it will align to drill the other 3.

Since the print failed, I redesigned to be less volumetric and put the printer into another 15h shift (2x):

That’s it while I’m waiting for the rest of the pieces to arrive!

See ya!