How Electrostatic Discharges Affect Computer Devices
Microprocessors and the accompanying chips that make up todays PCs, cell phones, PDAs, iPODs, and other electronic gadgets continually get smaller, faster, and cheaper. This continual shrinking has come to be known as Moore's Law, named for Gordon Moore, one of the founders of Intel Corporation. In the still early days of semiconductor devices, Moore stated that the number of transistors that could be packed onto a piece of silicon would double every 18 months. That progression still holds true today because of advances in semiconductor fabrication technology that shrink circuit dimensions to unimaginable smallness. The newest devices have circiut lines that are 45 nanometers wide, or slightly smaller than two-millionths of an inch. Compare that to a human hair, the smallest of which is about 670-millionths of an inch.
The small device geometries allow for pretty amazing processing speed. But in this world, nothing comes for free. One cost of shrinking those sizes is a decreasing ability of those circuits to withstand ESD. Just as you got a shock after walking across the carpet, workers in computer chip factories can build up the same static charge from walking across the floor. If they pick up a semiconductor device and touch the metallic pins or solder balls that connect that device to traces on a circuit board, they will cause an electrostatic discharge, or ESD event, into the device circuitry. Those very small metal lines in the device cannot handle the current spike from the ESD event, and they melt! That device is now permanently damaged and cannot be sold. That's not the worst of it. Sometimes the damage from an ESD event doesn't completely damage the device, but only weakens it; the weakness is not enough to cause the device to malfunction, so it appears to be a good device. It is only when that device is built into a product and used for a while that the weakness degrades into full failure. The product that was working just fine now stops working...right in the middle of that important cell phone call, or just when you're filing your tax return at 11:59 PM on April 14th. Nice!
Semiconductor manufacturers must design features into their chips to protect those small devices from the large voltages and currents that arise from ESD. How does the manufacturer know that this protection circuity works? They test it, just as they test the other circuitry in the chip. There is special test equipment to apply the ESD events and measure the circuit behavior to determine that the circuitry did its job. This test equipment applies ESD events to simulate the different types of events that are likely to happen during the device's lifetime, from the product manufacturing process to its end use by the customer.