ISA-PLAN® and ISA-WELD®
With the beginning of production of the first
SMD-mOhm current-measuring resistor in the world in 1987, we have developed
a variety of precision and power resistors. They were all manufactured
based on our ISA-PLAN® and ISA-WELD® technologies.
These two technologies enable us to offer
resistors which fulfill all the characteristics expected from a precision
resistor for current measurement: high long-term stability and continuous
as well as pulse loadability, minimized power losses during high-current
measurements, low inductance values, low thermoelectric voltage against
copper as well as resistance values that are largely independent of the
Insights in the
begins withâThe production process of ISA-PLAN
the gluing of the Manganin® or Zeranin® foil with a metal substrate made
from copper or anodized aluminium. The high-temperature-resistant
connection is optimized with regard to adhesion, insulation and above all
low thermal resistance between resistance foil and substrate.
Resistance foil and substrate are pretreated and then laminated in a vacuum
under high pressure and at high temperature. This guarantees constant
gluing operations on the copies, without any inclusion of air.
After cleaning, marking and dowel hole stamping
the copies undergo a photolithography process, in which the individual
resistance structures (presently more than 10,000 units per copy) are
already defined. Together with the etching technique, this planar structure
enables the manufacture of ideal four-wire SMD resistors in the value range
of a few milliohms.
The four-wire (Kelvin) connection completely
eliminates the influence of the Cu-connection resistance on the resistance value
and TK and guarantees high reproducibility. All influences of the soldering
point quality on the resistance value are excluded through this. For the
2-wire designs, together with the layout of the printed circuit a quasi
4-wire connection can be realized, which comes very close to the ideal
After the etching process follow further chemical
treatments as well as largely automated processes such as lasing and
calibration. The separating of the resistors from the substrate is carried
out by means of lasing, stamping or sawing. Likewise fully automated
automats perform the final work: cleaning, resistance test, labeling and
packaging (in the belt for the automatic SMD assembling at the customer).
In order to detect weak points in the etched structure, every resistor is
tested under electrical pulse load with subsequent evaluation of the IR
image. The finished coils are welded in foil to maintain the solderability
and back-gassed with nitrogen. Every coil is identified with a barcode,
through which all relevant data can be traced back, such as type of
resistor, value, tolerance, date-code, quantity and coil number.
On request an additional identification with a customer-specific part
number is possible.
Insights in the
The resistors are stamped from composite material
(three longitudinal seam welded bands made from copper+resistance
material+copper). The process is very flexible: thickness and width of the
bands are also variable as are the resistance materials Manganin®,
Zeranin®, Isaohm® and Aluchrome. The relatively free shaping in the
stamping-, bending- and imprinting process increases the design options of
The composite material is welded
continuously on the band. This takes place in a vacuum using an electron
beam and without material allowance, whereby the bands are cleaned on entry
into the machine and the flanks freshly machined. That prevents impurities
or oxides in the welded seam and ensures that greatly physically or
metallurgically differing materials can also be welded economically and
without faults. A particular advantage is the narrow welding zone, with
about one third of the material thickness. Through this the transition
takes place quasi abruptly, which minimizes the influence of the alloy zone
on the resistance value and the electrical properties of the measuring
resistance. The benefit for the user: when assembling the component on the
printed circuit or in the conductor rail, he no longer needs to establish
the connection resistance material – copper himself.
The comparably low supply line resistance of the
Cu-connections ensures, that the total resistance is only insignificantly
higher that the actual measuring resistance. The total load is thus reduced
to a minimum. In addition, with its high thermal conductivity and thermal
capacity the heat generated in the resistance material is very efficiently
dissipated or stored in the adjacent Cu-connections.
Due to their extremely high electrical
conductivity, the solid Cu-connections also ensure for an even current density
and heat distribution in the resistor. As a result Hot Spots are avoided
and a high pulse- and continuous loadability is achieved.