Without Clean Rooms, There'd Be No Smartphones

When you're making a tiny electronic system, dust particles can be massively destructive.

They thought there was something wrong with the dust counter. It was showing levels of tiny particles close to zero.
It was the early 1960s, at Sandia National Laboratory in Albuquerque, New Mexico. The room itself was small, just 10 feet by 6 feet. Every minute, all the air in the room flowed out and was replaced 10 times. To a person sitting in the room, this exchange would be barely perceptible—the feeling would be the same as walking through a room of still air.
Before the new air came into the room, it went through a filter good enough that if a smoker exhaled the exhaust of a cigarette through it, the air would come out clean on the other side. Pulled through vents, it was recycled back through. It was the world's first clean room.
The idea of all this, the first really good clean room, was to keep dust, microbes and other small particles from settling in the space. But no one expected that the simple idea—circulate the air through and through—would work as well as it did. When the designer of the room, Willis Whitfield, started presenting his results, people didn't believe him. From The New York Times:

“People said he was a fraud,” recalled Gilbert V. Herrera, the director of microsystems science and technology at Sandia National Laboratories in Albuquerque. “But he turned out to be right.”

Before Willis's design, the air in the best clean rooms available were 1,000 times more choked with particles than in his. They usually involved sealing the room off entirely, dressing people in protective clothing, and cleaning diligently. (Some companies apparently paid extra-close attention to doorknobs.) This did not work very well, and the tiny particles in the air were increasingly becoming a problem for ever-smaller technology.
Once he understood the issue, Wills later said, it took him only a few minutes to come up with the basic idea of his design. "I thought about dust particles," he told Time in 1962. "Where are these rascals generated? Where do they go?"
Sandia, where Willis worked, was concerned about the circuitry that controlled nuclear weapons—tiny bits of dust could throw off the delicate machinery. But the clean room he designed has been adopted by hospitals—to keep, for instance, patients on chemotherapy at lower risk for infections—pharmaceutical companies, and the manufacturers of semi-conductors (once those were invented).
Today's tiny electronic devices are often manufactured in clean rooms; even a tiny particle of dust, trapped inside your phone, could make it start wheezing, coughing, and eventually die. And while there have been some improvements to Willis's original idea—he himself tweaked it so that the air came through the ceiling and was pulled out through the floor—it's still the basis for clean room design today.