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(10/10/00, 2:55 p.m. EST)
SMT shift revs up for aluminum caps
By
Gina Roos EE
Times
http://www.eet.com/story/OEG20001010S0041
Like their counterparts in film capacitors, suppliers of aluminum
electrolytic capacitors are moving in a big way to surface-mount
packaging technology. It's a move that vendors say will improve voltage ratings, equivalent series resistance (ESR), capacitance
range and the operating-temperature performance of aluminum
electrolytics.
The transition to surface mount for aluminum electrolytic caps has
heated up tremendously, said Rich
Schuster, president of NIC Components Corp. (Melville, N.Y.). The market had been slow to accept
surface-mount technology because of the high capacitance values and
higher voltages involved with aluminum electrolytics, Schuster acknowledged. But, he added, it's only natural that OEMs want to
switch all of their devices over to surface mount when possible to
eliminate a soldering process.
A key reason why the electronics industry has not shifted as fast to
surface-mount technology for aluminum electrolytic caps as it did for
tantalum and ceramic capacitors is cost. Engineers can expect to pay
30 to 50 percent more for a surface-mount device (SMD) compared with
a leaded part.
When SMD versions of aluminum electrolytic capacitors were first brought to the marketplace several years ago, the most compelling
issue was survivability.
On the technical side, the only drawback to using aluminum electrolytic capacitors is that they still have a relatively high
profile compared with tantalum and ceramic caps. For that reason they
aren't used in cell phones, PDAs or portable wireless products, said
Schuster of NIC Components.
Another more recent challenge that engineers face is availability.
Since interest in surface-mount aluminum electrolytic capacitors has
started to pick up, manufacturers have limited production capacity.
They are only just now gearing up production to meet demand. This has
resulted in lead times as far out as 20 weeks. For instance, lead times for leaded aluminum electrolytics
average six to eight weeks, compared with 20 weeks
for some SMDs. For many space-constrained applications, packing more capacitance or
higher voltages in the same size package is a growing requirement. In
response, cap makers are developing products with a wider capacitance
range and higher voltage ratings.
NIC can supply surface-mount aluminum electrolytic capacitors with a
capacitance range of up to 6800uF. They are also available in
low-ESR, low-leakage and extended-temperature ranges of up to 125 degrees C. The company says it has achieved higher performance
ratings because of higher magnification foil and better production
techniques.
NIC also offers its surface-mount product in 4-mm-high profiles.
"We're getting much better volumetric efficiency so that we're able
to put more capacitance into small packages," Schuster said. Most recently, NIC has introduced a larger aluminum electrolytic in a
surface-mount configuration that offers a capacitance range as high
as 6,800uF, and a high-voltage surface-mount aluminum electrolytic with voltage ratings up to 450
VDC, which can replace large-can, radial-leaded and possibly snap-in types.
Some suppliers-including BC Components, NIC and United
Chemi-Con-are moving to polymer or solid-aluminum
capacitors, which allows them to
achieve lower ESR ratings as well as a smaller footprint. They are
very popular for next-generation microprocessors, Schuster said, because they feature much longer life and better performance.
Although they have been available for about four or five years, they've really taken off in the past two years, Schuster said. "The
only drawback is limited production, but we're expanding production
and coming out with a couple of new series over the next 30 to 60 days."
The new radial-leaded and surface-mount solid-aluminum capacitors
will feature low ESR, very low impedance and very high ripple current. "This will be the first time that we offer the technology in
a radial-leaded configuration, which will allow for a wider range of
capacitance and lower loss," Schuster said.
Innovation with older technologies is not lost on some aluminum electrolytic cap makers. They have beefed up their older axial-leaded
aluminum electrolytic lines by offering a higher temperature range
and low ESR/impedance. Axial-leaded devices offer low mounting heights that are desirable in automotive applications.
COMPANY CONTACTS
NIC Components Corp.
(631) 396-7500
www.niccomp.com
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