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Kerns Move to Machine Tools

Kerns Move to Machine Tools

A job drilling probe cards catapulted Kern into the highprecision machine tool business.

Kern Micro- und Feinwerktechnik GmbH & Co. ( started as a high-precision job shop in Germany in 1962, and its business took off about 25 year ago.

That’s when IBM approached the shop to make probe cards for the electronics industry. Probe cards are small, coinsized disks 1-mm-thick, made from highperformance, polyimide plastic resin. The material can cost around $3,000 per kilogram (about $1,360 per pound).

Kern had to drill 648, 60-microndiameter, holes in the cards, and holepositioning accuracy had to be within 2 microns, while hole-diameter tolerances were held to within 1.5 microns.

It was 1982 when it received the job, and Kern found that there were no machines that could accomplish such a task. In addition, the longest 60-micron-diameter drills available at that time were 0.6-mm in length, so the shop would have had to drill the holes from both sides of the cards – and make the holes meet in the middle – to drill them through. Besides lacking a suitable machine to do the job, the requirement that the holes be drilled through the material made the job even more of a challenge.

To tackle the probe cards, Kern built its own machine. It had excellent repeatability and a positioning accuracy of +/-1 micron.

More probe card jobs came in, and Kern’s customers started to ask about purchasing the shop’s special high-precision machine. Customer interest and markets grew, so Kern started to produce its machine for sale.

The machines have since become popular with highend mechanical-movement wristwatch companies in Europe and with U.S. shops that do medical, aerospace, electronic, and tool and die work.

To showcase the machine’s capabilities, Kern recently conducted a demonstration: it drilled a 30-microndiameter hole in a human hair.

The typical human hair measures about 60-microns in diameter. At the time of Kern’s demonstration, the smallest drilled diameter on record was 50-microns.

Usually 50-microns is the smallest unit visible to the naked human eye, so of course, a 30-micron-diameter drill is difficult to discern and is quite delicate. On top of this, Kern did not know of any tooling company that produced drills smaller than 50 microns in diameter. However, Kern found a company that made smaller drills at an EMO exhibition in Paris.

For its demonstration, Kern cut a hair from one of its employee’s head and positioned and glued the hair to a small aluminum block. The 30-micron-diameter drill produced five consecutive holes successfully without breaking.

Kern said its machine is one of few that could actually pull off such a feat, and the company credits its machine’s smooth movements in all axes, spindles that travel vertically in their own precision carriers for minimum loading, separate NC tables with +/-1-micron positioning, and glass scales with 0.1-micron resolution on all axes.

Of course, additional machine features contributed, Kern said, adding that components such as spindles, toolholders, and collets from external suppliers all had to pass strict qualitycontrol procedures. Kern rigorously tested the machine components for

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