I’ve been making some changes and additions to the MightyOhm Wiki over the past few days.

To complement the awesome list of surplus electronics shops, I started creating wiki pages for the various projects I have previously documented on the blog.

Last night I added a list of cheap PID controllers to the wiki page for my DIY PID-controlled Soldering Hotplate.  (Backstory: the PID controller on my hotplate quit working this week and I’ve been shopping for a replacement!)

I have also  been adding more information to the PCB resources page, including where to order cheap solder paste stencils and resources for making test fixtures.

More to come…

10, 20, and 5 mil thick alumina substrates with 50 ohm transmission lines

In part 1 I gave an overview of what this project is all about. In this part I will describe the basics of the machine and some of the reasons I made the design choices I did. To start with, I wanted to do this on as small a budget as possible. The main project for which this machine serves ends up being a real money pit, so I have to budget accordingly. Hence the use of hard drive parts and scrap metal. Total spent so far is about $60.

When I first thought about how to cut these little pieces of ceramic, it seemed that there were a few elements that would be tricky on a budget. First thing I did was try and figure out how commercial dicing saws work. Certainly Intel and others have figured out a good way to slice ‘em and dice ‘em a long time ago… And they did.

Tricky thing #1: Holding the substrate while it is being cut.

After a wafer full of chips is finished being made, it is mounted onto a wide stretchy tape, creatively named “dicing tape.” The tape is pulled over a frame and then the wafer placed on top. Next the taped wafer goes into the dicing machine where it is cut by an insanely fast spinning diamond encrusted blade of blingy wafer death.

To keep the wafer from heating up (chips generally don’t like heat) water is sprayed at the cutting surface. This also helps to wash away crud generated by cutting and to prolong blade life.  Once the wafer has been diced into individual chips, the tape is exposed to UV light or heat. The adhesive on the tape is made to become less sticky when exposed, and at this point the chips can be easily removed with tweezers, or an automated pick-and-place machine.

My first thought was to try and get some of this tape and use it in the same manner, but for smaller pieces. Then someone at work told me about something far more cool, with a far better name, something called Crystalbond! Crystalbond is essentially a mounting adhesive designed for exactly what I want to do. You simply heat it up, it becomes liquid, place the part in the puddle, and then do nothing until it cools off and then solidly holds your part. I managed to find 5 lifetime’s supply on eBay for dirt cheap, but several other places sell it. Anyway after the parts are cut you wash it away with acetone and you are left with clean diced parts.

Tubes of Crystalbond mounting adhesive

Okay, so the part can be held, but I didn’t want to have to glue a part to my machine every time I wanted to cut something. So instead of gluing the part to the machine I decided to glue the part to small pieces of glass which are a convenient carrier and can be used with my hotplatethat I built for my wire bonder.

Hotplate for thermosonic wedge bonding

So now I’ve got a piece of easy to handle glass, with one or more substrates to dice which has to be mounted to the machine. I could use tape, a temporary adhesive, or clamps, but why? I just put together a digitally controlled vacuum pump for some composites work, so why not make a vacuum chuck? And even better, I mounted it to a precision X-Y dovetail slide that I purchased on eBay for cheap. Now I can easily position the glass, reposition if necessary, and make measured cuts my moving the X-Y stage and measuring at the same time with a runout gauge. This allows me to make cuts that are accurate to 0.001 inches.

X-Y positioner I bought off eBay

A note here regarding XY stages… I chose specifically a dovetail style positioner because unlike the more common linear bearing style slides, a dovetail slide has static loading.  The benefit is that there is a much greater resistance to vibration and since I am grinding, I want as solid a mount as possible.

Tricky Thing #2: The Blade

This is really a compound Tricky Thing, a combination of finding the blade, holding it, and spinning it. First a little background on dicing saws and blades…

Wafer dicing used to be done (and still is, especially in research situations) with a diamond scribe, basically a pencil with a diamond at the end. A small scratch is made along the crystal plane of the wafer and then carefully bent until a long, very straight crack is made through the wafer.

The same can be done with alumina substrates, although since it is not a mono-crystalline structure, the crack won’t be as straight or as predictable. Scribe dicing is a relatively labor intensive task and chip manufacturers HATE labor, but even more than that they REALLY HATE any time that an actual person touches a wafer.

Wafer dicing today is usually done with a very thin diamond abrasive blade that grinds away the metal or semiconductor until a cut is made. It is nearly identical to the way you might cut tiles when doing a counter top in your kitchen but on a much smaller scale. When cutting tile, if the blade wobbles a bit or is not centered perfectly, you are not likely to notice. With the alumina substrates I’m working with, the pieces are 20-40 times thinner. This implies that any vibration, wobble, or eccentricity errors can cause problems.

Commercial wafer dicing machines use high speed motors that are carefully balanced and rather than using ball bearings, employ costly air bearings. These are essentially out of reach for hobbyists and really not necessary. What is necessary though is a way to hold and spin the blade accurately. Dicing blades are thin, and the thickest ones I could find on eBay were 300 um wide. At 4.6 inches in diameter, a a very large inner diameter, they are also hard to accurately mount on a typical spindle like that found on a Dremel tool.

Diagram depicting blade mounting: Part A shows the original platter and spacer configuration, Part B shows the modifications I made, Part C shows the blade mounted.

All of these issues led me to use a hard drive motor and platters to spin and hold the blade. Hard drives have very long service lives and need bearings of the highest precision. The mounting of the platters is also done in a precise way, as any imbalance would shorten the bearing lifetime and result in undesirable operation.

To make a long story short, I removed (and reused) the spacer ring between the two platters of a hard drive, and reduced the radius of one platter to 3.5″, the inner diameter of the blade. You can see in the picture that the two platters are stacked and there’s a nice surface for gluing the blade down. Machining the platter down was not easy with my tiny lathe, and it ended up being out of round by perhaps 10 mils. It works to roughly locate the blade, but I will need to tack the blade down, measure, adjust, and finally glue into place. 10 mils out of round is really bad because the thickest substrate I’m working with is 10 mils thick. That means that one part of the blade would never actually do any cutting!

Blade test fitted to the saw.

Tricky Thing #3:  Driving the motor

This seemed to be slightly daunting at first.  Hard disk motors are typically some kind of brushless motor and require special circuitry to run.  I imagined that I would have to build a circuit, or use a motor speed control from a radio controlled plane, etc.  It turns out though that the main circuit board in the hard drive I’m using is dumb enough that even though it has had the equivalent of a frontal lobotomy, it just keeps doing it’s job.   A couple other hard drives I tore apart did not do this.

Motor Control Box

The box in the picture above shows the hard drive main circuit board and below that, a 12v/5v switching power supply.  It’s pretty basic and at the flip of the switch on the front panel, the DC supply is connected to the motor driver and voila, the motor spins up.

Schematic Diagram for the Motor Control Box

Based on the date of my first post, last Wednesday marked the one year anniversary of my blog.

While I pour a toast, here are a few highlights of the past year:

PID Controlled Solder Paste Fridge

The first project I documented on the site, my solder paste fridge was the end result of a weekend effort to turn an old beer chest into a PID-controlled Peltier cooler for storing tubes of solder paste. A year later, the cooler has a permanent home under my workbench and is still going strong, keeping its contents at a chilly 36 degrees F. Besides solder paste, I keep my POR-15 rust proofing epoxy paint and a few tubes of superglue in the fridge (they never dry out!).

Space Invaders!  Making RGB video with the PIC

I needed an excuse to learn assembly language programming on the PIC, and this project fit the bill perfectly.  Instead of slogging through yet another PIC tutorial I decided to “just do it” and the video above shows the result.  One of my favorite projects of last year, I have plans to build more of these and make some electronic artwork for the lab.

Bluetooth Handset Hack

One aging bluetooth headset plus one obsolete telephone handset equals one retro-fabulous hack that I still use today.  The best part: Look for this one in Make: volume 20!

DIY PID-Controlled Soldering Hotplate

I’m a big fan of the hotplate (aka reflow skillet) method of surface mount soldering.  Over the course of a few months I designed, machined, and assembled this PID-controlled soldering hotplate to help build the first few prototypes of my AVR HV Rescue Shield kit.  Hacking around in the garage is always fun, but creating a new tool is one of the most rewarding things I have can think of.

Here’s a video of the hotplate in action, reflowing the step-up converter on the Rescue Shield:

The AVR HV Rescue Shield

What started as a simple hack to save a crippled AVR microcontroller eventually became a kit that I’ve sold to AVR enthusiasts around the world.  The AVR HV Rescue Shield includes a cool custom PCB, integrated 5V-12V step-up power supply, and is completely open source.   I only made one batch of these, and when they’re gone, they’re gone, so head over to the AVR HV Rescue Shield product page to order one today!

Wifi Radio Project

Certainly the most famous project on the site, my Wifi Radio project has inspired many readers to start playing with cheap wireless routers and embedded Linux.  If you haven’t seen it before, the finished project sounds something like this:

I brought the Wifi Radio to the Maker Faire in San Mateo in May.  Everyone loved it, including some of the Make: staff, which got me a blue ribbon for the project.  Awesome!

Onward!

Well, that’s it for year one…  If I missed one of your favorite posts from the past year, leave a comment!  If you’re new to the blog, happy reading, you have some catching up to do. 

Here’s to another fantastic year of hacks, projects, kits, tools, and resources at mightyohm.com!

Keith of Keith’s Electronics Blog made a PID-Controlled Soldering Hotplate based on the one I fabricated earlier this year.  He’s already using it to build the stepper controller PCB for the MakerBot CupCake CNC!

He also posted a bunch of teardown photos (like the one shown below) of the CD101 PID Controller from Sure Electronics.  I suspect the CD101 is a cheap knockoff of an RKC PID controller since I can’t find the part number on RKC’s website, even though the front panel clearly says RKC on it.  I guess at $40 you can’t ask too many questions, the price is right…

Copycat PID-Controlled Solder Hotplate « Keith’s Electronics Blog.

My friend Tony created an instructable about his Heated Stage for Thermosonic Wedge Bonding, based on my PID controlled soldering hotplate design.

Tony is building a home wirebonding station so he can work with microwave MMICs and build very high frequency amateur radio transceivers.

Nice job, Tony!

Last week I posted about the DIY PID-Controlled Soldering Hotplate I designed and built to improve my surface mount soldering capabilities.

I mentioned one issue I was having with the hotplate on flickr.  Specifically, the aluminum baseplate was getting too hot for comfort (literally) when I set the hotplate to solder reflow temperatures (180-220C) for more than a few minutes.  At the time I thought it was due to radiant heat from the upper aluminum block transferring to the bottom plate.  I later discovered that the ceramic spacers I used to hold up the hotplate were much more thermally conductive than I thought and the screws I used to attach the baseplate to the spacers were burning hot before the rest of the baseplate.  It was conducted heat, not radiant, that was the primary cause of the problem!

McMaster-Carr to the rescue!

I was able to resolve the issue by reducing the diameter of the ceramic spacers from 1/2″ to 1/4″ and using all stainless hardware to attach the spacers.  Now the baseplate stays relatively cool even with the hotplate at high temperatures for long periods of time.

Click on the pictures below or view the complete set on flickr.

The right tool for this job is a stereo microscope.  Stereo microscopes use two separate optical paths to provide you with depth perception, very helpful for working with 3-dimensional objects like printed circuit boards.  Even better is a stereo zoom microscope, where the magnification factor can be changed by turning a knob instead of swapping out lenses.

Until now I assumed that a stereo zoom microscope would be way out of my price range, at least several hundred or a thousand dollars for a very basic setup.  However, some searching on eBay showed that good deals can be had, and a used microscope with a boom stand suitable for surface mount work can be found for as little as $200-$300.  New microscopes are available for $400-$500, although there is some debate regarding the quality of low-cost imported microscopes.  Caveat emptor.

For surface mount soldering, 7-30x magnification is reasonable (that’s 10x eyepieces * a 0.7-3x objective), and a 4″ or greater working distance makes using tools under the microscope a lot easier.

I ended up buying an American Optical (AO) model 569 with an illuminator and boom stand, shown below.  Total cost was just over $200 with shipping.

Combined with the PID controlled hotplate I just put together this is a very powerful setup for doing rework of very tiny components – I could probably work with 0402′s, maybe even 0201′s if I was careful.  Using this setup, 0805′s are easy. (and they look huge!)

The scope is very old, it was made in the late 1970s, but it has survived in extremely good condition.  Upon receiving it, I tightened some setscrews and regreased the slides and it’s as good as new, despite being over 30 years old!

There are a few more photos of the microscope setup on flickr.

The image quality is excellent.  Here are a couple pictures of my SYBA USB-Audio Adapter taken with the microscope and my Sony DSC-V1 digital camera.  I held the camera up to one eyepiece, set it into macro mode, and snapped the shutter – these images are straight off the camera with no retouching.

Click to enlarge.

In preparation for my Arduino-based AVR HV Programmer boards coming back, I decided to step up my home lab surface mount soldering capabilities.

Step one was to find a cheap stereo zoom microscope on ebay, with 7-32X magnification, perfect for working on surface mount devices.  One of my biggest frustrations in the past is that with a cheap magnifying ring light, I can’t actually see what I’m working on – not any more!  I’ll post some photos of the microscope when it comes.

Step two was to build a soldering hotplate.  I like using a hotplate for surface mount soldering because you can actually watch the board as the solder paste reflows, and manually add/remove/nudge components around with a set of tweezers.  This is great for engineering work where you may still be making component changes and other tweaks to the board.  Mass production is probably best left to a reflow (aka toaster) oven.

I posted a few photos of the hotplate on flickr, which ended up on Hackaday.

The hotplate:

The heater is a 1/2″ 500W, 120VAC cartridge heater I bought from McMaster-Carr for about $25.  The hotplate itself is a 3x4x1″ chunk of aluminum that I machined with a carefully sized hole just below the center for the heater to slip into, as shown.  A type-K thermocouple (top right) measures the temperature and provides a signal to the controller.  Ceramic standoffs insulate the hotplate from the bottom aluminum baseplate.  For safety, there is also a ground strap, shown on the bottom right.

This the second PID controlled project I have done, the first was my PID Controlled Solder Paste Fridge.

The controller:

The controller box contains an Omega CN77000 series PID controller and an IR/Crydom 240V 40A (overkill!) D2440 Solid State Relay (SSR), along with a power switch, fuse, and power connector.  The PID controller and solid state relay were both found at a now-defunct Silicon Valley surplus store for a few bucks each.  A 3′ umbilical cable connects the controller to the hotplate.

60/40 leaded solder reflows at about 185C, and lead-free solder is around 200-230C depending on the alloy.  (Wikipedia has a good list of reflow temperatures.)  The hotplate can easily reach these within a minute or two from room temperature and could get much hotter if necessary.

It can also be used to cure epoxy and perform any other tasks that require a precisely controlled heater – this could be the world’s most overengineered coffee warmer, if not for the dangers of lead poisioning.

Update: I just posted some more information about the microscope.