Technical Library | 2010-06-03 22:23:03.0
Strategies for successful design and manufacture of microwave multilayer printed circuit boards. All aspects from pad registration, dimensional stability, impedance fluctuation, fusion bonding, thermal ageing, z-axis expansion, reliability, to Young's mod
Technical Library | 2013-03-28 16:18:22.0
For the last couple of years, the main concerns regarding the electrical performance of blank PCB boards were impedance and ohmic resistance. Just recently, the need to reduce insertion loss came up in discussions with blank board customers (...) The paper describes the test vehicle and the testing methodology and discusses in detail the electrical performance characteristics. The influence of the independent variables on the performance characteristics is presented. Finally the thermal reliability of the boards built applying different copper foils and oxide replacements was investigated.
Technical Library | 2009-03-25 17:14:11.0
This article presents design guidelines for helping users of HDMI mux-repeaters to maximize the device's full performance through careful printed circuit board (PCB) design. We'll explain important concepts of some main aspects of high-speed PCB design with recommendations. This discussion will cover layer stack, differential traces, controlled impedance transmission lines, discontinuities, routing guidelines, reference planes, vias and decoupling capacitors.
Technical Library | 2008-02-26 15:02:19.0
More and more chip packages need multi-GHz RF structures to meet their performance targets. The ideal chip package needs to combine RF features with Digital features for these applications. They drive low-loss, controlled impedance transmission lines, flexibility in assigned signal and power layers, and clearances of various shapes in power layers. Building these features in a chip package is difficult without making the stack-up very thick or compromising the reliability of the product. In the present paper, we have designed and built a flip-chip package test vehicle (TV) to make new RF structures, using Z-axis interconnection (Zinterconnect) building blocks.
Technical Library | 2009-07-09 17:23:07.0
Sometimes you just cannot clean with water. Good examples of this are: circuits with batteries attached, cleaning prior to encapsulation, ionic cleanliness testing, and non-sealed or other water sensitive parts. High impedance or high voltage circuits need to be cleaned of flux residues and other soils to maximize performance and reliability and, in these types of circuits; water can be just as detrimental as fluxes. When solvent cleaning is called for, Hansen solubility parameters can help target the best solvent or solvent blend to remove the residue of interest, and prevent degradation of the assembly being manufactured. In short, using this approach can time, manufacturing cost and reduce product liability.
Technical Library | 2020-07-29 20:12:52.0
Aluminum is a metal that it is hard to solder due to the high surface tension difference between it and molten solder alloy. This occurs because aluminum rapidly forms a tenacious oxide layer whenever it is exposed to oxygen in the air. The oxide layer is responsible for the high surface tension difference between the aluminum and the solder and impedes the solder from spreading evenly on an aluminum surface. There are hundreds of aluminum alloys available in the marketplace; it is important to identify the form of aluminum that is being soldered. Once this is done, an appropriate soldering technique can be chosen for soldering the specific aluminum alloy under consideration. Direct aluminum soldering eliminates using expensive plating techniques to prepare the aluminum surface for soldering.
Technical Library | 2016-11-03 17:53:56.0
We present a novel method for fabricating a high-density carbon nanotube microelectrode array (MEA) chip. Vertically aligned carbon nanotubes (VACNTs) were synthesized by microwave plasma-enhanced chemical vapor deposition and thermal chemical vapor deposition. The device was characterized using electrochemical experiments such as cyclic voltammetry, impedance spectroscopy and potential transient measurements. Through-silicon vias (TSVs) were fabricated and partially filled with polycrystalline silicon to allow electrical connection from the high-density electrodes to a stimulator microchip.In response to the demand for higher resolution implants, we have developed a unique process to obtain a high-density electrode array by making the microelectrodes smaller in size and designing new ways of routing the electrodes to current sources.
Technical Library | 2019-05-01 23:18:27.0
Moisture can accelerate various failure mechanisms in printed circuit board assemblies. Moisture can be initially present in the epoxy glass prepreg, absorbed during the wet processes in printed circuit board manufacturing, or diffuse into the printed circuit board during storage. Moisture can reside in the resin, resin/glass interfaces, and micro-cracks or voids due to defects. Higher reflow temperatures associated with lead-free processing increase the vapor pressure, which can lead to higher amounts of moisture uptake compared to eutectic tin-lead reflow processes. In addition to cohesive or adhesive failures within the printed circuit board that lead to cracking and delamination, moisture can also lead to the creation of low impedance paths due to metal migration, interfacial degradation resulting in conductive filament formation, and changes in dimensional stability. Studies have shown that moisture can also reduce the glass-transition temperature and increase the dielectric constant, leading to a reduction in circuit switching speeds and an increase in propagation delay times. This paper provides an overview of printed circuit board fabrication, followed by a brief discussion of moisture diffusion processes, governing models, and dependent variables. We then present guidelines for printed circuit board handling and storage during various stages of production and fabrication so as to mitigate moisture-induced failures.
Technical Library | 2020-11-04 17:57:41.0
Residues present on circuit boards can cause leakage currents if not controlled and monitored. How "Clean is Clean" is neither easy nor cheap to determine. Most OEMs use analytical methods to assess the risk of harmful residues. The levels that can be associated with clean or dirty are typically determined based on the exposed environment where the part will be deployed. What is acceptably clean for one segment of the industry may be unacceptable for more demanding segments. As circuit assemblies increase in density, understanding cleanliness data becomes more challenging. The risk of premature failure or improper function is typically site specific. The problem is that most do not know how to measure or define cleanliness nor can they recognize process problems related to residues. A new site specific method has been designed to run performance qualifications on boards built with specific soldering materials, reflow settings and cleaning methods. High impedance measurements are performed on break off coupons designed with components geometries used to build the assembly. The test method provides a gauge of potential contamination sources coming from the assembly process that can contribute to electrochemical migration.
Technical Library | 2019-09-11 23:33:04.0
There are numerous techniques to singulate printed circuit boards after assembly including break-out, routing, wheel cutting and now laser cutting. Lasers have several desirable advantages such as very narrow kerf widths as well as virtually no dust, no mechanical stress, visual pattern recognition and fast set-up changes. The very narrow kerf width resulting from laser ablation and the very tight tolerance of the cutting path placement allows for more usable space on the panel. However, the energy used in the laser cutting process can also create unwanted products on the cut walls as a result of the direct laser ablation. The question raised often is: What are these products, and how far can the creation of such products be mitigated through variation of the laser cutting process, laser parameters and material handling? This paper discusses the type and quantity of the products found on sidewalls of laser depaneled circuit boards and it quantifies the results through measurements of breakdown voltage, as well as electrical impedance. Further this paper discusses mitigation strategies to prevent or limit the amount of change in surface quality as a result of the laser cutting process. Depending on the final application of the circuit board it may prompt a need for proper specification of the expected results in terms of cut surface quality. This in turn will impact the placement of runs and components during layout. It will assist designers and engineers in defining these parameters sufficiently in order to have a predictable quality of the circuit boards after depaneling.
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