As sensitive inline RF performance influences new designs, designers are scrutinizing components quite differently. One popular technique being utilized by designers is “planarizing” the components so they align in the same plane as the transmission line in RF applications. Keeping the resistor and the transmission line in the same plane reduce losses and minimizes the effects of capacitance. At DC, the resistor is simply governed by ohms law. However in an RF environment, certain parasitic effects and contributions must be accounted for. The same resistor that performs termination functions adequately at DC or low frequencies can often exhibit different performance at higher frequencies due to unwanted capacitance and inductance present when utilizing various package designs. When using a wraparound, (WA) termination, the resistor forms a small series inductance and the chip terminals form a small shunt capacitance. As frequency increases the capacitance value eventually becomes dominant and must be managed. The partial wrap, PW resistors are designed to be mounted face down and therefore have better parasitic performance than the WA style under similar layout and operating conditions. The terminals are partially wrapped around the side of the chip so when they are mounted face down, the solder joint can [...]

Introduction Contemporary electronic board designs are becoming more challenging for designers than ever before. In today’s thick film, component applications designers are often faced with a trade-off between process flexibility and component performance. In terms of magnetic sensitive applications, this often requires the use of components that are sensitive to processing or attachment methods and therefore limit options for installation. At times this restricts the use of certain solders, temperatures or multiple re-flow operations. In applications where extreme processing is used with vulnerable components, failure modes can include component detachment or intermittent loss of continuity due to metal leaching of contacts and terminals. In order to understand this challenge and its factors, it is helpful to list the perfect performance characteristics of a thick film component. 1) Withstands high heat 2) Resists high Sn content solder 3) Non-magnetic 4) RoHS compliance 5) Affordability 6) Value diversity In designs where magnetism and RoHS compliance are in demand (i.e. medical imaging) resistance to high-temperature solder which can only be matched by a product similar to a freeze dryer (this is found in a science laboratory). It also has “non-magnetic” properties are critical. Unfortunately, they oppose each other from a process perspective. Traditionally, [...]

A ThermaBridge™ is a specialty thick film component developed and offered by IMS for use in the thermal management of electronic devices and modules. These products operate under the simple principle of conducting as much heat energy as possible, while simultaneously serving as an outstanding insulator of electrical energy and signal. The combination of these characteristics makes the ThermaBridge™ a very useful and flexible component that designers use to move heat either in, out, or to balance the temperature between two locations. ThermaBridges™ accomplish this without any fans, power, or moving parts making them useful for every electrical design sensitive to the effects of thermal energy. ThermaBridges™ operate by providing an electrically isolated, thermally active link between high heat generating areas and low temperature heat sinks or other locations within a circuit. According to Fourier, maximizing heat flow from one high temperature area to a lower one is made efficient by limiting the distance between the two points, maximizing the area of the conductive path and optimizing the material’s conductive heat properties. ThermaBridges™ do this by using Aluminum Nitride ceramic and offering a variety of thicknesses, lengths and widths to suit any thermal/mechanical requirement. For example if we take the [...]

Attenuators are passive two-port devices that reduce or attenuate the high level output of a signal generator. They are often used to provide a lower level signal to an antenna input of a sensitive radio receiver or similar device. Attenuator accuracy and overall effect on a system is also important to know particularly in applications for test equipment or other sensitive electronics. Improving Frequency Response The IMS A-0402WA attenuator has been characterized up to 40GHz. When this component is mounted upside down with the resistor and the transmission line in the same plane, improvements can be gained which reduces losses and minimizes capacitance effects. Face down mounting has several other advantages such as reduced current loop area, lower ESL, improved power handling and reduced overall insertion loss. Figures 1 and 2 demonstrate the improvement of physical mounting geometry with respect to insertion loss.   As seen in the plots above, the two mounting techniques provide the same level of response up to about 8 GHz, at which point the ‘face down’ attenuator begins to outperform the face up attenuator. The improvement becomes more dramatic as the frequency increases. Improvement through controlled device impedance For greater improvement to the performance, the [...]

High ohmic valued chip resistors exhibit characteristics of both insulators and normal resistors. As a result, a chip resistor may have a significant voltage coefficient of resistance, i.e., the resistance may vary with the applied voltage. This mandates that a fixed voltage source rather than a fixed current source be utilized when measuring these devices. Resistances can then be computed as volts/amperes. The applied voltage for a high ohmic value chip resistor is often specified as appropriate for the application to assure correlation. Typical values of applied voltage are 1 and 5 volts DC. This requirement leads to the measurement of very low currents and the attendant problems of such measurements. The problems of low current measurements include: 1. Noise currents generated in the connecting cables when flexed (triboelectric effect) 2. Noise from sources other than the cables 3. Cable, fixture and probe leakage currents 4. Cable, fixture and other stray capacitances 5. Radio Frequency Interference (RFI) 6. Characteristically high Temperature Coefficients of Resistance (TCRs)   These problems can be minimized by: 1. Properly connecting the resistor to the measurement system. 2. Properly guarding and shielding to reduce or eliminate electrostatic noise. IMS recommends that all meters be calibrated to [...]

The choice of mounting orientation, termination styles, pad dimensions and sizes used for surface mount passive resistive components are some of the factors that contribute to the device’s performance in an RF circuit layout. Determining the trade off between these factors in addition to ease of component-to-PCB assembly, solderability, ruggedness and other design optimization for power and RF performance could be an onerous task for RF engineers. The purpose of this technical note is to shine light on the advantages and/or disadvantages of these mounting techniques and termination styles in high frequency applications. Fig. 1A & 1B above are simple illustrations of an SMT resistor wraparound termination style. At DC, the resistor is simply governed by ohm’s law’s Current, Resistance and Voltage relationship (R=V/I) whose impedance Z is simply equal to R. However in an RF environment, certain parasitic effects and contributions must be understood and accounted for as shown in Fig 2 below. The equivalent circuit diagram of Fig 2 below is a more appropriate representation of the simple resistor described above. From the equivalent circuit, C1 is the shunt capacitor that is formed between the input and output pads of the full wraparound termination style device. This capacitor [...]

The number of high frequency, high power applications is rapidly increasing each year. The need for resistors with both high frequency performance and high power handling capability is growing. In most cases, the smaller the resistor, the better it will perform at high frequencies. At the same time, the larger the resistor, the better the thermal properties are. Many designers are making compromises when both power and performance matter. IMS has solved this dilemma with an innovative resistor that offers the best of both worlds called a SZG style termination device. Power Thermal management is becoming much more important as the density of electronic components and the applied power increases. Both factors lead to higher temperatures produced by not only the individual components, but also the entire assembly. Heat dissipation in high power electronics creates challenges for integrating material selection together with thermal designs. As a result of the power and signal combinations running through resistors, heat is generated. When more power is applied to a resistor, more heat is generated. If this heat is not properly transferred out of the part, the heat build-up can cause the part to shift in value and eventually fail electrically and mechanically. When [...]

HIPOT: What is it? The Hipot test (short for High Potential test), or sometimes called Dielectric Withstand test or Insulation breakdown test, is a test used to verify the strength of the insulation between the current-carrying path of a device and its chassis or enclosure. This is done by applying a high voltage (significantly higher than the device’s nominal operating voltage) from the input lines to the chassis of the product and measuring or monitoring the resulting leakage current flowing through its insulation. Why HIPOT? The Hipot test is the most important safety test for electronics and electrical devices. The test is done on finished goods prior to shipment to detect or verify the quality of the insulation system of the product as well as detect any latent manufacturing faults. It can also be used to verify the installation correctness or otherwise of a system for field or end user applications. The theory behind the test is that if a voltage much higher than the product would typically see is applied across the insulation of the system or product without a breakdown, the product will be able to operate safely at nominal operating conditions. The Hipot basically stresses the insulation [...]

Resistors are common devices required for today’s electronics. It is so prevalent in design, we often tend to think they do not require close attention to their inherent properties. While many applications can be designed using performance assumptions gained from years and years of experience, this is not the case for all resistors, all of the time. When using very high value resistors, there are a number of common resistor behaviors that may not apply, or in some case are backwards of traditional thinking. One such counter-intuitive relationship is Voltage Coefficient of Resistance (VCR). VCR is the relationship between the voltage seen by the resistive element and the corresponding resistance measured by a given device. One of the most important parameters of precise high-ohmic resistors is the VCR. The goal of resistor manufacturers is to try to create a resistor device that has consistent stated value of resistance, but does not have varying resistance values across broad voltage ranges. The Voltage Coefficient is the change in resistance with applied voltage over a specific voltage range. We measure the stability of the resistor with respect to changes in voltage. A resistor with a VCR of 100 ppm/V will change 0.1% over [...]