Prototyping PCBs With Electrical Discharge Machining
Of all the methods of making big pieces of metal into smaller pieces of metal, perhaps none is more interesting than electrical discharge machining. EDM is also notoriously fussy, what with having to control an arc discharge while precisely positioning the tool relative to the workpiece. Still, some home gamers give it a whirl, and we love to share their successes, like this work-in-progress EDM machine. (Video, embedded below.)
Prototyping PCBs With Electrical Discharge Machining
Perhaps the best g-code method might be to just do all of your isolation cuts in order disregarding their actual electrical connections. I think I would start with all the cuts on one axis first, then do the other axis working end to end.
Standoff for the electrode needs to be 0.001" to 0.004". Open circuit ionization voltage 100 to 300 V. Machining voltage should be 20-50 V with a nominal of about 30 V. A linear approximation makes the standoff distance for a 28-32 V machining range 0.0018" - 0.0022". Electrode needs to be negative as pointed out earlier. Steel or tungsten wire electrode in the 0.003-0.004" diameter range. Steel is a lot cheaper. You want a short on pulse in the 20-50 microsecond range with lots of dieletric flood to carry away the chips before they can adhere to the electrode.. Deionized water for the dieletric needs to be treated with a resin filter preceded by a mechanical filter to recondition the water. The above is based on the information in "Electrical Discharge Machining" by Elman Jameson, SME 2001 which I read in its entirety on Wednesday. You *must* do a raster scan as a vector scan will cause you to lose the workpiece electrical continuity.
There are lots of different kinds of prototypes that you can build. In the mechanical realm, it could be cardboard, foamcore, wood, or the like, fashioned into roughly the right size and shape. In the electrical realm, it could be a microcontroller like an Arduino or Raspberry Pi connected to a breadboard with jumper wires, all stuffed in a box. In software, it could be a fake user interface, made in Photoshop or Balsamiq Mockups, or a test harness written just to test an algorithm. In each realm, there are also deeper levels of prototyping.
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The bypass capacitors are used to suppress inter-system or intra-system noise within an electrical network. All decoupling capacitors have to connect close to the power pins of IC and the other end directly to a low impedance ground plane. Short traces to the decoupling capacitors and ground vias are required to minimize additional inductance in series for this connection.
Many people underestimate the cost factors between prototyping and product design manufacturing stages. An electronic change from a mere design to a prototype still requires many development phases such as the enclosure, package, and most importantly, certifications. Opt for a local factory partner to minimize the chances of something going wrong. Collaboration with local business entities means both parties work under the same regulation, safety requirements, and quality standards. Communication is also more accessible because everyone speaks the same language.
Autodesk has created advanced multi-axis CAM software that automates part of the workflow from design to generating the computer numerical control code needed for fabrication. The CAM software helps to speed up subtractive manufacturing processes such as milling, turning and wire EDM (electrical discharge machining).
High reliability applications may require more than simple electrical testing and inspection, either during fabrication/assembly, once prototypes get into the hands of a design team, and/or by an external testing lab. An electrical stress test is just one of the possible tests that should be performed in high reliability assemblies to ensure the PCBA can withstand demanding electrical conditions.
This is sometimes lumped in with ESD as they are both forms of overstress on components. An EOS test is probably the simplest electrical stress test that can be performed: components are basically overpowered, and the DUT is monitored until the device fails. This is normally performed at the wafer level or individual device level simply to quantify when the device will fail, as well as its failure mechanism.
This test is exactly as it sounds: it tests the extent to which the PCBA can withstand ESD events. When an ESD event occurs, your PCBA will interact with a very strong electrical pulse, possibly reaching over 10,000 V and exceeding several amperes of current. Such an event can destroy components if it is not diverted back to a safety ground in your system. ESD circuits are designed to absorb and/or divert ESD pulses away from components and into the safety ground region in your system. Some digital interfaces, such as IEEE 802.3 standards on Ethernet PHYs, have their own ESD requirements that must be met at the component level.
Various industry standards beyond the IPC standards place requirements on the ability of a device to withstand electrostatic discharge. The specific test method depends on which standards will govern your product (such as IEC 62368-1/IEC 61000, ISO 10605 for automotive, DO-160 for avionics, etc.). Refer to the relevant safety standards for your product and industry to determine the level of ESD protection your product will require.
CNC machining offers many benefits over machining without CNC programmable capabilities. Significantly reduced cycle times, improved finishes and multiple features can be completed at the same time and can improve quality and consistency. It is conducive to medium and high volume requirements where accuracy and complexity are required.
A CNC electric discharge machine (EDM) uses highly controlled electrical sparks to manipulate materials into a desired shape. It can also be called spark eroding, die sinking, spark machining or wire burning.
A component is placed under the electrode wire, and the machine is programmed to emit an electrical discharge from the wire which produces intense heat (up to 21,000 degrees Fahrenheit). The material is melted or flushed away with liquid to create the desired shape or feature.
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