Besides the selection of the most suitable contact materials , the design and typeof attachment is critical for the reliability and electrical life of contactcomponents for electromechanical switching devices. The materials most important factors here are the material-saving useof high cost precious metals and the most economic economical manufacturing method forcontact parts are most important factors..

There are two basic manufacturing solutions available: One can start with singlecontact parts , such as contact rivets or tips , which then are attachedmechanically or by brazing or welding resp. to carrier parts. In the second case, a base material coated or clad with the precious contact metal - for specialapplications also clad with another non-precious material – in the form of stripsor profiles is manufactured as a semi-finished pre-material from which thecontact components are then stamped and formed. Besides mechanicalcladding other processes such as electroplating and deposition from the gasphase are utilized.Which of the following manufacturing processes is finally chosen , depends onthe final application of the contact components in their respective switchingdevices or electromechanical components. Other considerations , such as therequired number of electrical operations, the most economical use of preciousmetals and the anticipated volumes of parts are also important for the processselection.

===3.1 Manufacturing of Single Contact Parts===The group of single contacts includes contact rivets, contact tips, and formedparts such as weld buttons. Contact spheres (or balls) are today rarely usedbecause of economical considerations. <br>Main Articel: [[3.1 Manufacturing of Single Contact Parts| Manufacturing of Single Contact Parts]]

===3.2 Manufacturing of Semi-Finished Materials===Semi-finished contact pre-materials can be manufactured from solid preciousmetals, precious metal alloys, or precious metal containing composite materials. <br>Main Articel: [[3.2 Manufacturing of Semi-Finished Materials | Manufacturing of Semi-Finished Materials]]

===3.3 Main Articel: [[Attachment of Single Contact Parts===The following segments give an overview | Attachment of the usually applied attachmenttechnologies for contact parts to carrier components. They include mechanicalas well as brazing and welding methods used for electrical contact assemblies.Single Contact Parts]]

Main Articel: [[3== Evaluation of Braze or Weld Joints==The switching properties of brazed and welded contact assemblies is strongly dependent on the quality of the joint between the contact and the carrier.3 Attachment The required high quality is evaluated through optical methods, continuous control of Single Contact Parts | Attachment relevant process parameters and by sampling of Single Contact Parts]]finished products.

==Stamped Contact Parts==Stamped electrical contact parts typically consist of a base carrier material to which a contact material is attached by various methods (<xr id="fig:Plated and contact containing pre-stamped strips and stamped parts"/><!--(Fig. 3.4 Evaluation of Braze or Weld Joints===17)-->). The They serve as the important functional components in many switching properties and electromechanical devices for a broad range of brazed electrical and welded contact assemblies is stronglyelectronicdependent on applications. On the one hand, they perform the mostly loss-free electrical current transfer and the quality closing and opening of electrical circuits, while on the joint between other hand, the contact and carriers are important mechanical design components, selected to meet the carrier. Therequired high quality is evaluated through optical methodsrequirements on electrical, thermal, continuous controlof relevant process parameters mechanical and by sampling of finished productsmagnetic properties.

The increasing miniaturization of electromechanical components requires ever smaller stamped parts with low dimensional tolerances. Such precisionstamped parts are needed in the automotive technology for highly reliable switching and connector performance. In the information and data processingtechnology, they transfer signals and control impulses with high reliability and serve as the interface between electronic and electrical components.<figure id="fig:Plated and contact containing pre-stamped strips and stamped parts">[[File:Plated and contact containing pre-stamped strips and stamped parts.jpg|left|thumb|Figure 1: Plated and contact containing pre-stamped strips and stamped parts for different applications]]</figure><br style="clear:both;"/>Main Articel: [[3.4 Evaluation of Braze or Weld JointsStamped Contact Parts| Evaluation of Braze or Weld JointsStamped Contact Parts]]

===3.4.1 Brazed Joints===Despite optimized brazing parameters non-wetted defect areas in the brazejoint cannot be avoided completely. These wetting defects can mostly be tracedto voids caused by flux inclusions in the braze joint area. Depending on theshape and size of the joint areas, the portion of the fully wetted joint is between65% and 90%. In its final use in switching devices a joint area of 80% isconsidered good or excellent if the individual void size does not exceed 5% ofthe joint area. Frequently wetted joint areas >90% with voids <3% can beobtained. Evaluation of the quality of the joint can be performed either by destructive ornon-destructive methods. ===3.4.1.1 Destructive Testing===Destructive tests can be performed on a sampling basis in rather simple ways: *De-brazingThe contact tip is being removed by slow heating and simultaneous applicationof force perpendicular to the contact surface area. Visual inspection of theseparated components reveals the non-wetted defect areas as discolorationfrom either flux remnants or oxidation of the carrier material. *Milling SampleThe contact tip is milled off in layers to a depth that makes the joint area visiblefor optical evaluation. *Saw-CuttingA crossing pattern is cut with a fine saw into the contact tip. Areas that are notbonded fall off in pieces. *Metallographic Micro-sectionIn a metallographic micro-section perpendicular to the contact surface wettingdefects can also be made visible ''(Fig. 3.14)'' which however are only indicativeof the brazing temperature and brazing time. Fig. 3.14:Braze joint with voids.Ag/CdO tip on Cu carrier. *Shear testThe contact tip is sheared off from the carrier with the required shear force beinga measure for the bond quality. This method is especially suitable for hard andbrittle contact tip materials such as for example tungsten. ===3.4.1.2 Non-Destructive Test Methods===Typically the non-destructive testing of braze joints requires more elaborate testequipment. Besides this such test methods have limitations regarding theshape of the contact tips and/or carriers. The prevalent methods are ultrasoundtesting and X-ray analysis. *Ultrasonic testing This method is based on the disruption of the propagation of sound waves indifferent media. High resolution modern test systems with graphic print-outcapabilities and analytical software are capable to detect even small (<0.5 mmdiameter) voids in the braze joint. The portion of the wetted areas is calculatedas a percentage of the whole joint area. Fig. 3.15 shows an example of differentbraze qualities for a Ag/SnO₂ contact tip brazed to a copper carrier andillustrates the position and size of void areas as well as the final joint quality. Fig. 3.15: Ultrasound print-out of braze joints between Ag/SnO 88/12 tips and Cu carrier with 2different degree of wetting (dark areas = voids) *X-Ray testing X-ray testing is an additional method for evaluating brazed joints. Using finefocusX-ray beams it is possible to achieve a sufficient picture resolution. Thereare however limitations about the thickness of the contact tip compared to thesize of the void area. This expensive test method is rarely used for contactassemblies. ===3.4.2 Welded Joints===Since welded contact assemblies are usually produced in rather high quantitiesthe quality of the weld joints is monitored closely. This is especially true becauseof the high mechanical and thermal stresses quite often exerted on the jointareas during switching operations. The quality of the joints is dependent on theprocess control during welding and on the materials used to manufacture thewelded assemblies. Despite the ability to closely monitor the relevant welding parameters such asweld current, voltage and energy, simultaneous testing during and aftermanufacturing are necessary. A simple and easy to perform quality test is based on the shear force.Evaluations of welding assemblies in electrical performance tests have shownhowever that the shear force is only a valid measure if combined with the size of2 the welded area. As rule of thumb the shear force should be > 100 N/mm withthe welded area > 60% of the original wire or profile cross-sectional area. Forcritical applications in power engineering, for example for high currents and/orhigh switching frequency, a higher percentage of the joint area is necessary. During series production every weld is usually probed in a testing stationintegrated in the manufacturing line with a defined shear force – mostly 20% ofthe maximum achievable force. In this way defective welds and missingcontacts can be found and sorted out. The monitoring of the actual shear forceand size is performed during production runs based on a sampling plan. Fig. 3.16: Ultrasonic picture of a weldjoint, Ag/C tip on Cu carrier(ABB-STOTZ-KONTAKT) Besides destructive testing for shear force and weld area the non-destructiveultrasound testing of the joint quality is also utilized for welded contactassemblies ''(Fig. 3.16)''. ===3.4.3 Selection of Attachment Methods===In the preceding sections a multitude of possibilities for the attachment ofcontact materials to their carriers was described. A correlation of thesemethods to the switching current of electromechanical devices is illustrated inTable 3.2. it shows that for the same switching load multiple attachmentmethods can be applied. Which method to chose depends on a variety ofparameters such as contact material, material combination of contact andcarrier, shape of the contact, required number of switching operations and lastbut not least the required volume of parts to be manufactured. Based on the end application the following can be stated as general rules:Electroplated contact surfaces are limited to switching without or underextremely low electrical loads. In the lower and medium load range contactrivets and welded contacts are used. For high switching loads brazing,especially resistance and induction methods, are utilized. For extremely highloads, for example in high voltage switchgear, percussion welding, electronbeam welding, and copper cast-on processes are preferred. Table 3.2: Correlation between Contact Joining Methods and Switching Currents  ===3.5 Stamped Contact Parts===Stamped electrical contact parts typically consist of a base carrier material towhich a contact material is attached by various methods ''(Fig. 3.17)''. They serveas the important functional components in many switching andelectromechanical devices for a broad range of electrical and electronicapplications. On the one hand they perform the mostly loss-free electricalcurrent transfer and the closing and opening of electrical circuits. In addition thecontact carriers are important mechanical design components selected to meetthe requirements on electrical, thermal, mechanical and magnetic properties. The increasing miniaturization of electromechanical components requires eversmaller stamped parts with low dimensional tolerances. Such precisionstamped parts are needed in the automotive technology for highly reliableswitching and connector performance. In the information and data processingtechnology they transfer signals and control impulses with high reliability andserve as the interface between electronic and electrical components. Fig. 3.17:Plated and contactcontaining pre-stamped strips andstamped parts for differentapplications ===3.5.1 Types of Stamped Parts===Stamped parts are produced as single pieces, in pre-stamped strip and combconfigurations. Depending on the requirements and application the contact andbase material as well as the coating and attachment technology is carefullyselected. *Coated stamped partsStamped parts can be selectively or completely coated with precious metalcontaining materials based on gold, palladium, and silver as well asnon-precious materials such as tin, nickel and copper ''(Fig. 3.17)''. For stampedparts in high volumes like those used as electrical components in automobilesthe carrier material is mostly coated in a reel-to-reel process starting with eithersolid or pre-stamped strips (see also chapter 7.1.1.3). Frequently the prestampedstrip will be used directly in further automated assembly of the finishedfunctional component. As an alternative finished stamped parts can beelectroplated using barrel and rack plating methods. Very thin coating layers with tight tolerances are deposited by electroplating. Formany applications the high mechanical wear resistance is advantageous. Sinceeven very thin layers are mostly pore-free, these coatings also act as aneffective corrosion inhibitor. The type of coatings, the sequence of multiplelayers, and the coating thickness, for example for connectors, are chosenaccording to the requirements for the end application. *Clad stamped parts For many applications thicker precious metal surfaces or AlSi layers arenecessary. These cannot be deposited by electroplating. Besides meltmetallurgicallyproduced materials on the basis of gold, palladium and silver,also powder-metallurgical materials are required frequently. The metallurgicalbond between these contact materials and the mostly copper based substratesis achieved through various mechanical cladding methods (see also chapter3.2.1). In this way also aluminum clad strips are manufactured in which thealuminum layer serves as the bondable surface in the interface betweenelectromechanical connections and electronic circuits. These clad semifinishedmaterials can be further fabricated into pre-stamped strips, in combform, or single stamped parts ''(Fig. 3.18)''. Fig. 3.18:Examples of clad stamped parts *Welded stamped parts Welded stamped parts can be fabricated by various methods (see also Chapter3.3.3). Single contact pieces can be attached to pre-stamped or finishedstamped strips as weld buttons and wire or profile segments by electricalresistance welding. Contact parts can also be stamped from seam-weldedsemi-finished strip. Fitting the end application contact materials based on gold,palladium and silver. Depending on the contact material and the design of thefinished contact component the contact bottom surface may be consist of aweldable backing material. *Brazed stamped parts Brazed stamped contact assemblies are manufactured by two joining methods(see also chapter 3.3.2). The contact material is either attached by resistanceor induction brazing to base metal carriers as prefabricated contact tip or theyare stamped from brazed semi-finished toplay strip. It is typical for brazedcontact parts that the contact material consists of silver based contact materialand a good conducting copper base material with larger cross-sectional areafor the usually higher current carrying capacity. *Stamped contact parts with rivets Riveted stamped contact parts are manufactured with the use of contact rivetswhich are transferred over suitable feed mechanisms correctly oriented intoholes punched into the carrier ''(Fig. 3.19)''. Frequently also wire or wire segmentsresp. are used which are subsequently coined and formed into the desiredcontact shape (see also chapter 3.3.1). Both attachment methods have theirdistinct advantages. Using composite or tri-metal rivets allows limiting the useof precious metal custom tailored to the volume needed for specific switchingrequirements. For wire staking the precious metal usage is usually higher butthe staking can be performed at significantly higher production ratesand the additional rivet making step is eliminated. Fig. 3.19:Examples of riveted stamped parts *Pre-mounted component stamped parts Components stamped parts consist of a minimum of two carrier parts whichdiffer in their material composition and geometrical form and the contactmaterial''(Fig. 3.21)''. The assembly of these components as single pieces or stampingprogressions is performed in a stamping die by riveting or coining. To increasethe current carrying capacity at the joining area an additional welding step canbe added. Depending on the requirements the different properties of the twocarrier components can be combined. As an example: the high electricalconductivity of a contact carrier blade is joined with the thermal or mechanicalspring properties of a second material to form a functional component. For thisprocess both carrier base materials can also be coated with additionallayers of other functional materials. Fig. 3.20:Examples of pre-mounted stampedcomponent parts Stamped parts which are insert molded into or combined with plastic parts areused in electromechanical components (see Chapter 10). ===3.5.2 Stamping Tools===For the design of stamping tools the latest CAD software systems are used.Modern stamping tools usually employ a modular design with integrateddimensional and functional controls ''(Fig. 3.21)''. Depending on the requirementson the parts and the volumes they are built with steel or carbide (-steel) insertswhich are coated with a wear resistant material such as for example TiN forlonger life. A special stamping process is precision stamping for contact parts made fromthin strip materials with thicknesses in the range of 0.05 – 2.5 mm. With highcapacity stamping technology up to 1400 strokes/min can be reached for highvolume parts. During the actual stamping operation frequently other processessuch as thread-forming, welding of contact segments and insertion and formingof contacts from wire segments are integrated. Depending on the productionvolumes these operations can also be performed in multiples. The quality of the tools used for stamping, like progressive dies and stamp-formingtools is important for the final precision and consistency of the parts. During highspeed stamping the tools are exposed to extreme mechanical stresses which mustbe compensated for to ensure the highest precision over long production runs. Withsuch high quality progressive dies parts of high precision with a cutting width of lessthan the material thickness and with strict quality requirements for the cutting surfacescan be manufactured.To ensure the highest demands on the surface quality of precision contact parts quiteoften vanishing oils are used as tool lubricants. Cleaning and degreasing operationscan also be integrated into the stamping process. Additionally most stamping linesare also equipped with test stations for a 100% dimensional and surface qualitycontrol.During the design of stamping tools for electrical contacts minimizing of processscrap and the possibility to separate the precious metal containing scrap must beconsidered. Fig. 3.21:Progressive die for stamped contact parts[[Category:Manufacturing Technologies for Contact Parts|Category]] ===References===

th Proc. 24 ^th Int. Conf.on Electr. Contacts, Saint Malo, France 2008, 206-209