Compressed Air for Electronics Manufacturing

Do electronics factories use oil-free machines or oil-flooded machines with oil removal filters? This question has been argued for years.

Oil-Flooded Machines: Argument for oil-flooded machines is straightforward: cheap. Same output capacity, oil-flooded screw is one-third or more cheaper than oil-free screw. Add three-stage oil removal filtration downstream, coarse filter, precision filter, activated carbon, total investment still saves money. Plus oil-flooded machines are mature technology. Low failure rate. Simple maintenance. Any random compressor repair tech can handle it.

Oil-Free Machines: Argument for oil-free machines is also plenty compelling: risk. Oil separator element has a lifespan. Normal use, three to four thousand hours and it should be changed. Problem is many factories don’t change on schedule, or change to cheap knockoff elements. Once oil separator element ruptures, massive oil mist blasts downstream. Oil removal filters behind it simply can’t handle this kind of shock load.

From technical standpoint, oil-free machines really are the safer choice. Water-lubricated screw machine compression chamber only has water. Dry oil-free screw machine, screw surfaces have Teflon coating, no lubricating fluid at all. Eliminates oil contamination possibility at source. Atlas Copco AQ series and Gardner Denver Ultima are water-lubricated representatives. Ingersoll Rand Sierra and Sullair DSP are dry oil-free representatives. Electronics factory installed base for all of these is quite large.

Water-lubricated machines have one hassle: water quality management. Machine has conductivity requirements for water. Too high affects bearings. Need water treatment system. Northern factories in winter also need freeze protection. Shutdown must drain water completely. Dry oil-free machines don’t have these worries. But discharge temperature is high. Energy efficiency slightly worse than water-lubricated. Electricity cost year after year is also cost.

-40°F pressure dew point is standard requirement for electronics factories. Chip fabs want -94°F. Refrigerated dryers can’t reach these numbers. Must use desiccant dryers.

Adsorbent’s worst enemy is oil. Gets contaminated with oil and it’s poisoned. Adsorption capability drops dramatically. Regeneration can’t recover it. Can only replace the entire bed. So the oil removal filter in front of desiccant dryer is absolutely critical. This money can’t be saved. Seen a factory where desiccant dryer used two years and dew point started climbing. No matter how they adjusted, couldn’t fix it. Finally discovered upstream oil removal wasn’t done well. Adsorbent was poisoned. Replacing one bed of molecular sieve, several thousand dollars.

On whether -40°F is over-design, some engineers think shop temp is 70-something degrees, piping won’t go below this temperature either. Dew point at -4°F already absolutely no condensation. But electronics manufacturing fears more than just liquid water. Solder paste printing is humidity sensitive. High relative humidity causes voids in soldering. Wafer must be baked to remove moisture before molding. If blowing air is humid, baking was for nothing. So -40°F wasn’t randomly picked.

Pick and place machine is the SMT line’s highest air consumer and most demanding equipment. Nozzle system uses compressed air to create vacuum to pick up components. Orifice diameter fractions of a millimeter. Too many particles and it clogs. Clogged means either can’t pick up or picks up and places inaccurately. Panasonic, Fuji, ASM pick and place machine manuals all write inlet air requirements. Particles, oil content, dew point. Three parameters, none can be sloppy.

Many factories’ approach is SMT shop has its own dedicated air line. Splits off right after the dryer. Filtration grade one level higher than general shop. Some factories go further. Install a small filter at each pick and place machine air inlet. Called POU filter. Prevents pipe secondary contamination.

Carbon steel pipe is banned in electronics factories. Carbon steel rusts. Iron rust particles ride the airflow. Filters can’t catch all of it. Will continuously contaminate downstream equipment. Old factories doing air source upgrades, first thing is replace the piping.

Stainless steel pipe is standard. 304 grade sufficient for general applications. 316 has better corrosion resistance. Highest cleanliness requirement locations use electropolished stainless steel pipe. Inner wall roughness Ra below 16 microinches. Shiny as a mirror. Dirt can’t adhere.

Installation matters more than material selection. Stainless steel pipe welding needs TIG, with argon purge inside the pipe. Otherwise weld seam oxidizes. Inside is all weld spatter. No amount of blowing cleans it out. Weld one joint, inspect one joint. After installation do a blowout.

Chip packaging compressed air requirements approach wafer fabrication levels. Wire bonding process. Gold wire diameter 0.8-1.2 mil. Bond head driven by cylinder runs back and forth between chip and lead frame. Anything dirty enters the cylinder, motion precision can’t be guaranteed. Bond position offset, bond strength insufficient, both are batch defects.

Cleanrooms need positive pressure maintained. Must continuously supply makeup air. This air can’t just be randomly tapped from shop piping. Cleanliness must match cleanroom classification. Proper approach is cleanroom supply air gets its own dedicated piping. Splits off from dryer outlet. Piping standard higher than general shop.