Just Let It Slide
Engineer's steel to ceramic solution posts
yields, lowers internal costs
When engineers at power component
manufacturer Vicor Corporation, Andover, MA, got tired of
watching newly-manufactured parts jam up and/or short to the
fixtures in which they were tested, they decided to design
an in-house solution that would both lengthen the life of
the testing fixture and reduce the number of false failures
resulting from parts shorting to it. With customers in the
communication, data processing, industrial control, test equipment,
medical and defense electronics markets, the company tests
millions of components each year in stringent product qualification
processes that include testing at the beginning design stage
and continuing throughout the life of the product.
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New ceramic insert
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Worn steel version
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Test fixture
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"During the testing of control modules in a cleanroom
environment, the modules must slide through a track that uses
the edges of the devices themselves to guide them into a test
fixture," explained Vicor mechanical engineer Niko Bratsis.
This fixture is comprised of four main components: the base
is built with a groove machined in it so that parts from the
track slide into the groove; covers keep the parts from falling
out of the track; a stopper assembly holds parts in place;
and test fingers are pneumatically controlled to close on
parts in order to electrically test them.
The tested components have 30-mil-thick ceramic backs, which
are used to guide the parts through the tester. "These
ceramic backs would wear away the aluminum and steel walls
in the track, causing the parts to 'hang up,' or not feed
through," said Bratsis. He noted that some parts would
also rotate within the track, adding to alignment problems.
Further, when testing high voltage parts, the team encountered
a significant number of false failures as a result of the
parts shorting to the fixture. "This was
due to the close proximity between the leads of the tested
devices and some of the metallic parts of the test fixture,"
he explained. These lower yields combined with the cost of
regularly replacing the test fixture increased internal costs
that Bratsis knew could be lowered.
"I decided to design a replaceable portion of the base
made out of ceramic (99.5% alumina) after consulting with
engineers from Insaco," said Bratsis. Insaco, Inc., Quakertown,
PA, is a precision fabricator of ultra-hard materials including
sapphire, ceramics of all types, glass, quartz and many others.
The alumina chosen for the base is very hard and wear-resistant,
with high compressive strength, even against extreme temperatures
and corrosive environments. It is also an excellent electrical
insulator, and succeeded in solving Vicor's two main problems.
"First, as a replaceable, longer-wearing insert for
the steel base, the ceramic piece showed no significant wear
after 200,000 tests. The steel version needed to be replaced
after the same number," Bratsis said. Second, the team's
yields in high voltage applications increased, reflecting
only a small amount of true electrical failures.
Bratsis' proactive materials solution is sure to save his
company time and money. A Material Designer's Guide on
the Insaco website provides free, customized reports to engineers
who key in their own "important properties for applications,"
should a materials solution for your company be looming on
the horizon.
--KC
Circle 556 - Vicor Corporation or connect directly
to their website via the Online Reader Service Program
at http://www.OneRS.net/104df-556
