Agilent Measurement Journal - Issue 5 - 2008 - (Page 67)

failing its RF speciﬁcations, but will have a signiﬁcant effect on insertion-loss repeatability over time. The random nature of this particle buildup also means that such failure can be intermittent — and it may not be detectable, as these particles remain trapped on the surface of the center conductor throughout the lifetime of the switch. This adverse effect is the result of an inﬂexible jumper-contact design. Consequently, it is not uncommon to ﬁnd switches with designs of this nature having loose repeatability speciﬁcations — or none at all. to withstand oxidation and environmental corrosion. However, there is an issue with this choice of plating material. Because the gold layer is plated directly on the beryllium copper surface, the copper will eventually migrate into the gold layer, and the gold will likewise diffuse into the copper layer. This migration is further accelerated by the presence of oxygen, heat and humidity. To minimize the migration and prevent diffusion of gold and copper atoms, some form of barrier material is normally used between the beryllium copper and gold layers. Beryllium copper is a metal alloy that typically contains copper with 1.8 to 2 percent beryllium. Sometimes additional alloying elements are added. In addition to possessing signiﬁcant metalworking advantages, this amalgam exhibits good electrical and thermal conductivity characteristics. For example, its good thermal conductivity and very high tensile strength allow the jumper contacts to be exposed to high temperatures without any risk of melting or deterioration — key factors that ensure consistently good pressure contact and prolong the operating life of the switch. Debris is trapped Flat surface Inﬂexible tip Jumper contact Center conductor Figure 4. The particle buildup phenomenon Adding a wiping mechanism Assessing contact-surface materials An important factor in determining the performance and operating life of an EM switch lies in the materials, plating and surface proﬁle employed at the contacting surfaces. The combination of contact ﬁnish and plating materials is also crucial to the handling of high-power signals. Contact ﬁnish affects the series resistance of a pair of closed jumper contacts, whereas plating material affects both the contact resistance and thermal conductivity of the assembly. The jumper contacts used in EM switches are often fabricated from beryllium copper alloy, followed by a thin layer of a good conductivity metal (e.g., gold) on the contact areas. A thin layer of gold ﬁnish promotes excellent corrosion resistance, low contact resistance, good RF characteristics, and acceptable wear characteristics. Gold is the preferred plating material for the contact due to its intrinsically low resistance and its capability Increasing the repeatability and operating life of a switch requires a design that essentially cleans off the center conductor tip during each switching cycle. This process eliminates the particle buildup prevalent in conventional EM switch designs. The principle of contact wiping action is widely known and has been applied in relays and keyboard switches to break through surface corrosion and debris on contacting surfaces. In the context of EM switches, a properly designed wiping mechanism plays a very important role in prolonging electrical life and maintaining repeatability. In addition to wiping action, Agilent EM switches also use suitable lubricants and smooth ﬁnishing at the contacts. This unique design produces excellent repeatability of less than 0.03 dB across the operating life of the switches, while maintaining all RF speciﬁcations. Essentially, the wiping action pushes any small particles or debris out of the contact zone, allowing the switch to self-clean. However, it is important to note that excessive wiping action combined with high contact pressures can generate debris due to excessive rubbing between the two surfaces. Therefore, the key is to generate the optimum amount of wiping action between the contacting surfaces. Agilent Measurement Journal 67

Table of Contents Feed for the Digital Edition of Agilent Measurement Journal - Issue 5 - 2008

Agilent Measurement Journal Issue 5 Finding a New Path when Assumptions Break Down Contents Testing MIPI D-PHY Protocols Oscilloscope Firmware Update DNA Replication Joining the LTE/SAE Trial Initiative Testing Proteins Praise for DC Power Analyzer Scripting Features for AMDS Testing Hybrid PCBA Systems Improving the Gene Expression System Workflow Turning a “Good Enough” Test Strategy into One That’s Reliable, Repeatable and Traceable Understanding the Effects of Limited-Bandwidth Channels on Digital Data Signals Introducing the 3GPP LTE Downlink Validating the 26 Validating the Physical and Protocol Layers in DDR Memory Interfaces Understanding Total Jitter Measurements of Low Probabilities Using Behavioral-Model Simulation to Accurately Predict First-Order PLL Performance Creating Synchronous High-Frequency Sampling across Multiple Digitizers Overcoming the Challenges of Testing FlexRay Networks Understanding Operating Life and Repeatability of Electromechanical Switches and their Effect on Total Cost of Ownership Implementing Micro and Nano LC/MS Techniques for High Sensitivity Lipidomics Analysis

Agilent Measurement Journal - Issue 5 - 2008

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