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First-Level Packaging
Published in Mitel G. Pecht, Rakesh Agarwal, Patrick McCluskey, Terrance Dishongh, Sirus Javadpour, Rahul Mahajan, Electronic Packaging: Materials and Their Properties, 2017
Mitel G. Pecht, Rakesh Agarwal, Patrick McCluskey, Terrance Dishongh, Sirus Javadpour, Rahul Mahajan
The common hermetic case materials and their properties are listed in Table 29. One of the most widely used materials for the fabrication of metal cases, especially lids, is Kovar, a proprietary metal alloy composed of 54% Fe, 29% Ni and 17% Co. Kovar has a coefficient of thermal expansion of 5.1-5.9 ppm/°C; this closely matches those for the many commonly used sealing glasses, which vary from 5.25 to 6.96 ppm/°C (refer to Table 30). However, the thermal conductivity of Kovar is only 15.5-17 W/m-°C, which is low compared with that for copper alloys. As a result, the package case is not very effective in dissipating the heat generated during component operation and is not a suitable case material for high-power applications. In such applications, copper alloys are more suitable because of their high thermal conductivity. For example, the conductivity of a commonly used copper-tungsten alloy is 209.3 W/m-°C. However, it is very difficult to seal the lid in a copper case. Large thermal stresses are generated in sealing glasses because of the CTE mismatch, while electrical resistance welding (the preferred process for hermetic sealing) is difficult because the high thermal conductivity of copper causes the heat generated during the welding process to dissipate very quickly. A low-cost alternative that offers easy weldability is cold rolled steel (CRS), although it is more susceptible to corrosion.
Movable Contacts
Published in Frank W. Kussy, Jack L. Warren, Design Fundamentals for Low-Voltage Distribution and Control, 2017
Frank W. Kussy, Jack L. Warren
Copper-tungsten (Cr-W) alloys are made by a sintering process. The tungsten content can be 20 to 80%. Cr-W alloys are stronger than pure copper. The tensile strength increases with tungsten content from 110 kg/mm2 for 50% tungsten to 240 kg/mm2 for 80% tungsten. The conductivity ranges from 30 to 50% that of copper. Cu-W is more susceptible than pure copper to oxide formation. The principal advantage of this material is excellent resistance to arc erosion. Cu-W contacts are used in oil-immersed circuit breakers or contactors. They may also be used in arcing contacts, but heavy wiping action is needed. Despite the resistance to arc erosion, extended usage will eventually erode the alloy; eventually, the arc will fail to transfer to the arcing contact. Before that occurs the Cu-W arcing contact must be replaced.
Contact Materials
Published in Milenko Braunovic, Valery V. Konchits, Nikolai K. Myshkin, Electrical Contacts, 2017
Milenko Braunovic, Valery V. Konchits, Nikolai K. Myshkin
Cu–W. Contacts made of copper–tungsten materials have superior properties such as wear resistance, resistance to welding, melting at high currents and voltages, and similar mechanical characteristics to that of silver–tungsten contacts.215,216 Due to a strong susceptibility to oxidation, the copper–tungsten materials are used in contacts operating in oil at high contact pressures such as in high-voltage oil switches. The W–Cu materials with the tungsten content of 40–70 wt% are effective arc-breaking contact materials for high-power contactors with an excellent electric wear resistance of up to 3,00,000–4,00,000 switching operations at currents up to 1000 A.
Review on tools and tool wear in EDM
Published in Machining Science and Technology, 2021
Deepak Sharma, Somashekhar S. Hiremath
Copper, graphite and some of their alloys like Brass, Silver, Copper-Tungsten (CuW), Silver-Tungsten (Ag-W), and steel are the common tool electrode material. Graphite with the fine grain is the better choice for larger MRR, less TWR, and superior surface quality. But due to its high brittleness, it cannot be used to fabricate micro-tools, which makes it unsuitable for micro-EDM applications (Kumar et al., 2009). F. Klocke et al. (2016) used bronze infiltrated graphite electrode (C-Bz) for the machining of tungsten carbide. Presence of bronze decreases the brittleness of the electrode. Further the tool cost (tool material and fabrication cost) of the (C-Bz) tool was compared with the CuW tool for machining of a square cavity of cross-section 12.3 mm2 and depth 4 mm. C-Bz was approximately half as cost intensive as W-Cu (20 €/cavity vs. 41 €/cavity). By considering the high melting point of graphite, it is used for high-temperature alloys, and other metallic tools are used for low-temperature alloys. After the graphite, copper is the most commonly used EDM tool material. It is ductile, i.e., easy to fabricate and also have high electrical and thermal conductivity (Uhlmann and Roehner, 2008). Copper is three times cheaper than the fine graphite, and it has better machinability, which makes it a perfect tool material for EDM applications (Blanford et al., 2007).
Examinations concerning the electric discharge machining of AZ91/5B4CP composites utilizing distinctive electrode materials
Published in Materials and Manufacturing Processes, 2019
Ranjith R., Tamilselvam P., Prakash T., Chinnasamy C.
Figure 2 depicts the effect of pulse duration on MRR. It was found that MRR was minimal at lower pulse duration and reaches the maximum at 75 µs and MRR start to reduce with further amplification in pulse on time. Short pulse on time prompts low vaporization and melting of materials which ends up in lower MRR. Two factors were culpable for reducing MRR at longer pulse duration. The key factor that reduces MRR was plasma channel expansion which induces superfluous residual heat.[31,32] It results in heat dissipation problem and MRR is incredibly low under these circumstances. The secondary factor was that when excess material is removed, debris dissipates between the spark gap and can disrupt electrical sparks to bomb the surface of the workpiece. When the peak current and pulse on time is low, MRR is almost the same for all the electrode. However, GRAL-20 attains larger MRR at higher peak current. Copper also offers good MRR with only small rate of reduction in MRR as contrasted with GRAL-20. For AZ91/5B4Cp composites, the maximum MRR of 137 mg/min was achieved at 100 µs pulse on time, 7 A discharge current and GRAL-20 as electrode. The end result reveals that GRAL-20 electrode exhibits 5.63, 7.74 and 16.9 times higher machining speed than copper, tungsten–copper and brass electrode, respectively.
Experimental Investigation on Micro-Electrical Discharge Machining process for heat treated Nickel-based Nimonic 80A
Published in Materials and Manufacturing Processes, 2023
Piyush Pant, Pushpendra S. Bharti
Pilligrin et al.[21] employed μ-EDM process on 316L stainless steel considering capacitance, voltage, polarity, speed of tool as the process parameters and taper angle, rate of material removal, overcut, rate of electrode wear as the performance variables. The rate of removal of material was detected to be higher for the negative polarity of tool. Pilligrin et al.[22] drilled micro holes employing electro discharge micromachining technique using 316L stainless steel as the test piece and different tool electrodes of copper, tungsten, and copper-tungsten. The obtained values of overcut, EWR and rate of material removal were noticed to be maximum for copper electrode, whereas lowest for tungsten electrode.