When Sparkfun visited the factory that makes their multimeters and photographed a mysterious industrial process.
We all know that the little black globs on electronics has a semiconductor of some sort hiding beneath, but the process is one that’s not really explored much in the home shop. The basic story being that, for various reasons , there is no cheaper way to get a chip on a board than to use the aptly named chip-on-board or COB process. Without the expense of encapsulating the raw chunk of etched and plated silicon, the semiconductor retailer can sell the chip for pennies. It’s also a great way to accept delivery of custom silicon or place a grouping of chips closely together while maintaining a cheap, reliable, and low-profile package.
As SparkFun reveals, the story begins with a tray of silicon wafers. A person epoxies the wafer with some conductive glue to its place on the board. Surprisingly, alignment isn’t critical. The epoxy dries and then the circuit board is taken to a, “semi-automatic thermosonic wire bonding machine,” and slotted into a fixture at its base. The awesomely named machine needs the operator to find the center of the first two pads to be bonded with wire. Using this information it quickly bonds the pads on the silicon wafer to the board — a process you’ll find satisfying in the clip below.
The final step is to place the familiar black blob of epoxy over the assembly and bake the board at the temperature the recipe in the datasheet demands. It’s a common manufacturing process that saves more money than coloring a multimeter anything other than yellow.
Continue reading “The Mystery Behind the Globs of Epoxy”
Designing and building something from scratch is one thing. But repairing fried electronics is a much different type of dark art. This video from [Mike’s Electric Stuff] is from more than a year ago, but we didn’t think you’d mind since what he accomplishes in it is so impressive. He’s got a burnt out pick and place hybrid power module which isn’t going to fix itself.
The power module construction includes a part that has chip-on-board-style MOSFETs and the circuitry that goes with them enclosed in a black plastic housing. It’s kind of like a submodule was encapsulated using the same plastic as integrated circuits. After cracking it open it appears the bonding wire has burnt away. [Mike] connects a jumper wire to one of the board traces in order to use an external MOSFET. This is much easier said than done since the module substrate is ceramic designed to dissipate heat. We’re amused by his technique of melting the jumper into the plastic housing to protect it from the heat sink that goes over the package. In the end he gets his CNC running again. This may not be the best long-term fix but he just needed to continue running until a proper replacement part arrives.
Oh, one more thing: the Metcal vacuum desolderer he uses in the video… do want!
Continue reading “Tricky Repair of Power Driver for CNC Machine”
And here we’ve been complaining about Flat Pack No-Lead chips when this guy is prototyping with Ball Grid Array in a Wafer-Level Chip Scale Package (WLCSP). Haven’t heard that acronym before? Neither had we. It means you get the silicon wafer without a plastic housing in order to save space in your design. Want to use that on a breadboard. You’re crazy!
Eh, that’s just a knee jerk reaction. The wafer-level isn’t that unorthodox as far as manufacturing goes. It’s something like chip on board electronics which have that black blob of epoxy sealing them after the connections are made. This image shows those connections which use magnet wire on a DIP breakout board. [Jason] used epoxy to glue the wafer down before grabbing his iron. It took 90 minutes to solder the nine connections, but his second attempt cut that process down to just 20. After a round of testing he used more epoxy to completely encase the chip and wires.
It works for parts with low pin-counts. But add one row/column and you’re talking about making sixteen perfect connections instead of just nine.
Often the true key to success is persistence and that holds true for this project which dumped the ROM from the current generation of Tamagotchi toys. If you’re a fan of learning the secrets built into consumer electronics — and you know we are — you’ll want to go back and watch the 24-minute lecture on Tamagotchi hacking which [Natalie Silvanovich] gave a 29C3 last year. She had made quite a bit of headway hacking the playable pods, but wasn’t able to get her hands on a full ROM dump from the General Plus chip on board processor. This update heralds her success and shares the details of how it was done.
As we learned form the video lecture it was a huge chore just to figure out what processor this uses. It turned out to be a 6502 core with a few other things built in. After prowling the manufacturer’s website she found example code for writing to Port A. She was then able to execute her own code which was designed to dump one byte of ROM at a time using the SPI protocol.
[Natalie] posted her code dump if you’re interested in digging through it. But as usual we think the journey is the most interesting part.