With the beginning of production of the first SMD-mOhm current-measuring resistor in the world in 1987, we have developed a variety of high 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 sensing: 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 environmental temperature.
 

The production process of ISA-PLAN resistors begins with 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 electrical 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 4-wire resistance.

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. 

ISA-PLAN® resistors: SMD assembly, Hybrid assembly, braking resistors, printed circuit- and heat sink assembly

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 designer.

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.

ISA-WELD® resistors: SMD assembly, Hybrid assembly, precision resistors for high-current applications and energy measurement