Taking a look at decapped ICs

Aside from wanting to play around with nitric acid, [Ben] really didn’t have a reason to decap a few 74xx and 4000-series logic chips. Not that we mind, as he provides a great tutorial at looking at a bare IC that isn’t covered in epoxy and resin.

Most ICs are encased in a hard epoxy shell making it very difficult to look at the circuits within. [Ben] tried to grind this epoxy off with a Dremel tool, but didn’t have much luck until he moved over to a CNC mill to remove 0.040 – 0.050″ of epoxy without breaking the bond wires.

After carving out a nice pocket above the die, [Ben] put a few drops of nitric acid on the chip to dissolve the epoxy coating.  This worked very slowly at room temperature, but after putting the chips on a hot plate the acid was able to reveal the die underneath.

After successfully removing all the epoxy and giving them an acetone bath, [Ben] took his chips over to the microscope and was able to check out the underlying circuit. He doesn’t have any idea what he could do with these decapped logic chips, but the bond wires are still intact so he could still use these chips in a build.

We’d like to see a few decapped MEMS devices, but if you have a suggestion on what [Ben] can do with his decapped chips, drop a note in the comments.

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Store your RFID transit card inside your cellphone

Check it out, this is a Boston transit pass — or at least the parts of it that matters. [Becky Stern] got rid of the rest in a bid to embed the RFID tag inside her cellphone.

The transit pass, called a CharlieCard, started out as a normal credit card shaped tag which you might use for access in the workplace. She unsheathed the chip and its antennae by giving it a generous soak in acetone. In about thirty minutes the plastic card looks more like paper pulp, and you can gently fish out the electronics. These are now small enough to fit in the back cover of a cellphone much like those inductive charging hacks.

[Becky] put hers in an iPhone. But the idea comes from [Dhani Sutanto] who used the same technique to extract the coil from a London transit pass. He then embedded the hardware in a resin cast ring.

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What the flux: buy it or brew it yourself

Flux generally makes our lives easier. It’s the best bet when trying to prevent solder bridges with fine-pitch components like you see here. But it is also indispensable when it comes to desoldering components from a board (we’re talking just one component without disturbing all of the others). But have you ever looked at what it costs to pick up a syringe of liquid flux from an online retailer? In addition to the cost of the product itself there’s usually a hazardous material handling fee that is rolled into the shipping cost. So we were happy that [Christopher] sent in a link to the DIY flux page over at Dangerous Prototypes.

The concept is simple enough. Mix some rosin with some solvent. Turns out these items are really easy to source. The solvent can be acetone (which you may have on hand for removing toner transfer from freshly etched PCBs) or plain old rubbing alcohol. And an easy source for rosin is your local music store. They sell it to use on bow hair for String players. Grind it up, throw it in a bottle and you’re good to go. Now does anyone know where we can source needle-tipped bottles locally?

For those that still just want to buy flux we highly recommend watching part one and part two of [Ian’s] flux review series.

DIY ultrasonic plastic welding

Here’s something that may be of interest to all the reprappers, vacuum formers, and other plastic fabbers out there: ultrasonic welding of plastics. If you’ve ever wanted to join two pieces of plastic without melting them together with acetone or screwing them together, [circuitguru] is your guy.

Ultrasonic welder setups are usually reserved for companies that don’t mind spending tens of thousands of dollars on a piece equipment. There are smaller versions made for heat staking – melting plastic pillars into rivets on the work piece – and [circuitguru] was lucky enough a somewhat reasonable price.

Because the heat staking gun was a handheld unit, a rotary tool drill press was put to work. The end result is a relatively inexpensive way to join two plastic parts without screws, glue, or solvents. The bond is pretty strong, too. Check out the video after the break to see [circuitguru] join two pieces of a plastic enclosure and try to tear them apart.

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Welding and casting ABS

Anybody who has a 3D printer always has a ton of useless plastic lying around. Some of that plastic may be from useless baubles, but most of it is in bad prints, short bits of filament, and general scraps. [Luke] found an interesting way to put those ABS scraps to use, and ended up turning trash into valuable plastic parts.

Commonly sold as nail polish remover, acetone will turn anything made out of ABS into a puddle of plastic. [Luke] makes glue using the same process – he fills a small container half full of acetone and half with small bits of ABS. After a day or so, he has a nice thin glue that dries into solid ABS. [Luke] used this to create a 400mm long piece of extruded t-slot. We don’t know if it would be suitable to build a child RepRap from, but it would sure be an interesting experiment.

[Luke] also did a little bit of casting with his ABS glue. With a thicker solution of ABS and Acetone, he managed to make this ‘thing’. The entire process is explained over at Thingiverse, We can’t wait to see what can be done with this stuff.

VGA Testers for the Children

Recently on our Hack A Day forums a member asked about getting some VGA testers made in our “Request and Commissions” forum for a charity called the World Computer Exchange, who take old office PC’s and freshens them up to be used by children in developing countries for their education.

I sort of wanted to do a no brainier electronics build as I had been working on that Apple II weather display for quite a while at that point. I say no brainier because I decided to use one of the many already designed vga testers out there and all I really had to do was get it to fit in whatever box we ended up with.

I choose the deogen because it was already featured on Hack A Day, supports multiple raster patterns and resolutions (640×480 through 1280×1024), is already pretty darn small, and uses an ATTiny 2313 which is good because I am already set up for AVR micro controllers. For a case I choose to use some plastic “Ice Breakers” mint boxes, which due to their oval shape makes it quite a bit smaller than an altoids tin. The challenge is on to shove a PCB, switch, 9V battery, 2 buttons and a vga connector in the cramped space.

Join us after the break for a pile of pictures and some build notes.

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Negative laser etching

[James] has been refining a method of negatively etching metal with a laser. He had been using a product called Thermark which is designed for this process, but it’s quite expensive. He found that paint designed for wood stoves works just as well. To prepare the surface he bead blasted it and then cleaned of the residue and finger prints off with acetone. The board was preheated in an oven before covering it with the spray paint. He ran the laser at 98/100 power and 90/400 speed at a step size of 0.1mm to achieve the results above. This should immediately make you think about making circuit boards. We’d love to ditch the toner transfer and we’re always looking for one more reason to get a laser cutter.