Technical Library | 2020-03-09 10:50:17.0
A customer called the Helpline seeking advice for cleaning no-clean fluxes prior to applying a conformal coating. The customer's assemblies were manufactured with a no-clean rosin based solder paste (ROL0) and were cleaned with an isopropyl alcohol (IPA) wash. After cleaning, a white residue was sometimes found in areas with high paste concentrations and was interfering with the adhesion of the conformal coating (Figure 1). For conformal coatings to adhere properly, the printed circuit board (PCB) surface must be clean of fluxes and other residues. In addition, ionic contamination left by flux residues can lead to corrosion and dendrite growth, two common causes of electronic opens and shorts. Other residues can lead to unwanted impedance and physical interference with moving parts.
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 | 2023-06-02 14:13:02.0
This work examines the use of dual-material fused filament fabrication for 3D printing electronic componentsand circuits with conductive thermoplastic filaments. The resistivity of traces printed fromconductive thermoplastic filaments made with carbon-black, graphene, and copper as conductive fillerswas found to be 12, 0.78, and 0.014 ohm cm, respectively, enabling the creation of resistors with valuesspanning 3 orders of magnitude. The carbon black and graphene filaments were brittle and fracturedeasily, but the copper-based filament could be bent at least 500 times with little change in its resistance.Impedance measurements made on the thermoplastic filaments demonstrate that the copper-based filamenthad an impedance similar to a copper PCB trace at frequencies greater than 1 MHz. Dual material3D printing was used to fabricate a variety of inductors and capacitors with properties that could bepredictably tuned by modifying either the geometry of the components, or the materials used to fabricatethe components. These resistors, capacitors, and inductors were combined to create a fully 3Dprinted high-pass filter with properties comparable to its conventional counterparts. The relatively lowimpedance of the copper-based filament enabled its use for 3D printing of a receiver coil for wirelesspower transfer. We also demonstrate the ability to embed and connect surface mounted components in3D printed objects with a low-cost ($1000 in parts), open source dual-material 3D printer. This work thusdemonstrates the potential for FFF 3D printing to create complex, three-dimensional circuits composedof either embedded or fully-printed electronic components.
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.
