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IC Decapping: The Process

As I’ve been posting some photos of decapped ICs lately, I thought I’d share the process I use personally for those that might want to give it a go šŸ˜‰

The usual method for removing the epoxy package from the silicon is to use hot, concentrated Nitric Acid. Besides the obvious risks of having hot acids around, the decomposition products of the acid, namely NOĀ² (Nitrogen Dioxide) & NO (Nitrogen Oxide), are toxic and corrosive. So until I can get the required fume hood together to make sure I’m not going to corrode the place away, I’ll leave this process to proper labs ;).

The method I use is heat based, using a Propane torch to destroy the epoxy package, without damaging the Silicon die too much.

TMS57002 Audio DSP
TMS57002 Audio DSP

I start off, obviously, with a desoldered IC, the one above an old audio DSP from TI. I usually desolder en-masse for this with a heat gun, stripping the entire board in one go.

FLAMES!
FLAMES!

Next is to apply the torch to the IC. A bit of practice is required here to get the heat level & time exactly right, overheating will cause the die to oxidize & blacken or residual epoxy to stick to the surface.
I usually apply the torch until the package just about stops emitting it’s own yellow flames, meaning the epoxy is almost completely burned away. I also keep the torch flame away from the centre of the IC, where the die is located.
Breathing the fumes from this process isn’t recommended, no doubt besides the obvious soot, the burning plastic will be emitting many compounds not brilliant for Human health!
Once the IC is roasted to taste, it’s quenched in cold water for a few seconds. Sometimes this causes such a high thermal shock that the leadframe cracks off the epoxy around the die perfectly.

All Your Die Belong To Us
All Your Die Belong To Us

Now that the epoxy has been destroyed, it breaks apart easily, and is picked away until I uncover the die itself. (It’s the silver bit in the middle of the left half). The heat from the torch usually destroys the Silver epoxy holding the die to the leadframe, and can be removed easily from the remaining package.

Decapped
Decapped

BGA packages are usually the easiest to decap, flip-chip packages are a total pain due to the solder balls being on the front side of the die, I haven’t managed to get a good result here yet, I’ll probably need to chemically remove the first layer of the die to get at the interesting bits šŸ˜‰

Slide
Slide

Once the die has been rinsed in clean water & inspected, it’s mounted on a glass microscope slide with a small spot of Cyanoacrylate glue to make handling easier.

Some dies require some cleaning after decapping, for this I use 99% Isopropanol & 99% Acetone, on the end of a cotton bud. Any residual epoxy flakes or oxide stuck to the die can be relatively easily removed with a fingernail – turns out fingernails are hard enough to remove the contamination, but not hard enough to damage the die features.

Once cleaning is complete, the slide is marked with the die identification, and the photographing can begin.

Microscope Mods

I had bought a cheap eBay USB microscope to get started, as I can’t currently afford a proper metallurgical microscope, but I found the resolution of 640×480 very poor. Some modification was required!

Modified Microscope
Modified Microscope

I’ve removed the original sensor board from the back of the optics assembly & attached a Raspberry Pi camera board. The ring that held the original sensor board has been cut down to a minimum, as the Pi camera PCB is slightly too big to fit inside.
The stock ring of LEDs is run direct from the 3.3v power rail on the camera, through a 4.7Ī© resistor, for ~80mA. I also added a 1000ĀµF capacitor across the 3.3v supply to compensate a bit for the long cable – when a frame is captured the power draw of the camera increases & causes a bit of voltage drop.

The stock lens was removed from the Pi camera module by careful use of a razor blade – being too rough here *WILL* damage the sensor die or the gold bond wires, which are very close to the edge of the lens housing, so be gentle!

Mounting Base
Mounting Base

The existing mount for the microscope is pretty poor, so I’ve used a couple of surplus ceramic ring magnets as a better base, this also gives me the option of raising or lowering the base by adding or removing magnets.
To get more length between the Pi & the camera, I bought a 1-meter cable extension kit from Pi-Cables over at eBay, cables this long *definitely* require shielding in my space, which is a pretty aggressive RF environment, or interference appears on the display. Not surprising considering the high data rates the cable carries.
The FFC interface is hot-glued to the back of the microscope mount for stability, for handheld use the FFC is pretty flexible & doesn’t apply any force to the scope.

Die Photography

Since I modified the scope with a Raspberry Pi camera module, everything is done through the Pi itself, and the raspistill command.

Pi LCD
Pi LCD

The command I’m currently using to capture the images is:
raspistill -ex auto -awb auto -mm matrix -br 62 -q 100 -vf -hf -f -t 0 -k -v -o CHIPNAME_%03d.jpg

This command waits between each frame for the ENTER key to be pressed, allowing me to position the scope between shots. Pi control & file transfer is done via SSH, while I use the 7″ touch LCD as a viewfinder.

The direct overhead illumination provided by the stock ring of LEDs isn’t ideal for some die shots, so I’m planning on fitting some off-centre LEDs to improve the resulting images.

Image Processing

Obviously I can’t get an ultra-high resolution image with a single shot, due to the focal length, so I have to take many shots (30-180 per die), and stitch them together into a single image.
For this I use Hugin, an open-source panorama photo stitching package.

Hugin
Hugin

Here’s Hugin with the photos loaded in from the Raspberry Pi. To start with I use Hugin’s built in CPFind to process the images for control points. The trick with getting good control points is making sure the images have a high level of overlap, between 50-80%, this way the software doesn’t get confused & stick the images together incorrectly.

Optimiser
Optimiser

After the control points are generated, which for a large number of high resolution images can take some time, I run the optimiser with only Yaw & Pitch selected for all images.

Optimising
Optimising

If all goes well, the resulting optimisation will get the distance between control points to less than 0.3 pixels.

Panorama Preview
Panorama Preview

After the control points & optimisation is done, the resulting image can be previewed before generation.

Texas Instruments TMS67002
Texas Instruments TMS67002

After all the image processing, the resulting die image should look something like the above, with no noticeable gaps.

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Co-Op Bank Card Reader

Keypad
Keypad

This is a little security measure you get with Internet Banking with the Co-Op, generates codes to confirm your identity using your bank card. About the size of a pocket calculator, this is the keypad & screen.

Card Slot
Card Slot

The rear of the unit, the card slots into the top, manufactured by Gemalto Digital Security.

Card Contacts
Card Contacts

Outer back cover removed, showing the 8 contacts for the chip on the bank card, the 2 contacts below that switch on power when a card is inserted. Power comes from 2 lithium coin cells in the compartment on the lower left.

PCB Rear
PCB Rear

PCB removed from the casing, showing the internal components. Two large pads at top left are battery connections, while the only IC on the board is the main CPU, under the card connector. 6MHz oscillator & 32Khz crystal on board for processing & timekeeping. LCD screen connection at far right.

Keypad Contacts
Keypad Contacts

Reverse side of the PCB, with the keypad contacts. LCD on right, with programming interface pads at side of keypad.

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Nokia 7110

Front
Front

Another phone from the mid 90s. This is the nokia 7110.

Slider Open
Slider Open

Here the slider is open showing the keypad.

Battery Removed
Battery Removed

Here the battery is removed, a Li-Ion unit.

Battery
Battery

The battery cell & protection circuit removed from the casing.

Rear Of PCB
Rear Of PCB

This is the rear of the PCB removed from the housing. Data & charging ports on the right hand side f the board.

Front Of PCB
Front Of PCB

Front of the PCB with the RF sections at the left hand side & the keypad contacts on the right.

RF Sections
RF Sections

Closeup of the RF sections of the board, big silver rectangular cans are VCO units.

SIM Connector
SIM Connector

Closeup of the top rear section of the PCB, with SIM cnnector, battery contacts, IR tranciever at the far left. Bottom centre is the external antenna connector.

CPU
CPU

The logic section of the board, Large chip is CPU, to right of that is the ROM storing the machine code. Other chips are unknown custom parts.

Mic & Speaker
Mic & Speaker

The Mic & the loudspeaker removed from it’s housing.

LCD
LCD

LCD from the front of the unit, SPI interfaced. Flex PCB also contains the power button, loudspeaker contacts & a temperature sensor.

Scroll Wheel
Scroll Wheel

The scroll wheel removed from the front housing.

Vibra-Motor
Vibra-Motor

Tiny vibration motor removed from the rear housing, alerts the user to a text or phone call.