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Moisture Measurements in PCBs and Impact of Design on Desorption Behaviour

Technical Library | 2018-09-21 10:12:53.0

Moisture accumulates during storage and industry practice recommends specific levels of baking to avoid delamination. This paper will discuss the use of capacitance measurements to follow the absorption and desorption behaviour of moisture. The PCB design used in this work, focused on the issue of baking out moisture trapped between copper planes. The PCB was designed with different densities of plated through holes and drilled holes in external copper planes, with capacitance sensors located on the inner layers. For trapped volumes between copper planes, the distance between holes proved to be critical in affecting the desorption rate. For fully saturated PCBs, the desorption time at elevated temperatures was observed to be in the order of hundreds of hours. Finite difference diffusion modelling was carried out for moisture desorption behaviour for plated through holes and drilled holes in copper planes. A meshed copper plane was also modelled evaluating its effectiveness for assisting moisture removal and decreasing bake times. Results also showed, that in certain circumstances, regions of the PCB under copper planes initially increase in moisture during baking.

National Physical Laboratory

Practical Fiber Weave Effect Modeling

Technical Library | 2011-03-16 20:05:15.0

Fiber weave effect is becoming more of an issue as bit rates continue to sore upwards to 5GB/s and beyond. Due to the non-homogenous nature of printed circuit board laminates, the fiberglass weave pattern causes signals to propagate at different speeds wi

Lamsim Enterprises Inc.

New High-Performance Organophosphorus Flame Retardant

Technical Library | 2015-09-10 15:06:17.0

A new non-halogen flame retardant has been developed and is useful for a variety of high performance applications. This non-reactive phosphorus-based material satisfies fire safety needs for a broad range of resins including epoxy, polyolefin, and polyamide. The combination of excellent flame retardant efficiency, high thermal stability and exceptional electrical properties is unique to this organophosphorus flame retardant and makes it a breakthrough technology for high speed, high frequency use in fast growing wireless and wired infrastructures. Resin performance data, including formulations with synergists, are presented in this paper.

Albemarle Corporation

Novel Transmission Line for 40 GHz PCB Applications

Technical Library | 2011-02-10 16:14:34.0

In this paper, we discuss an electromagnetics based approach to transmission line design, and then explore a novel printed transmission line, Periodic Micro Transmission Line (PMTL™, Patents Pending), with improved signal integrity to 40 GHz.

Samtec, Inc.

Nanoelectromechanical Switches for Low-Power Digital Computing

Technical Library | 2017-03-02 18:13:05.0

The need for more energy-efficient solid-state switches beyond complementary metal-oxide-semiconductor (CMOS) transistors has become a major concern as the power consumption of electronic integrated circuits (ICs) steadily increases with technology scaling. Nano-Electro-Mechanical (NEM) relays control current flow by nanometer-scale motion to make or break physical contact between electrodes, and offer advantages over transistors for low-power digital logic applications: virtually zero leakage current for negligible static power consumption; the ability to operate with very small voltage signals for low dynamic power consumption; and robustness against harsh environments such as extreme temperatures. Therefore, NEM logic switches (relays) have been investigated by several research groups during the past decade. Circuit simulations calibrated to experimental data indicate that scaled relay technology can overcome the energy-efficiency limit of CMOS technology. This paper reviews recent progress toward this goal, providing an overview of the different relay designs and experimental results achieved by various research groups, as well as of relay-based IC design principles. Remaining challenges for realizing the promise of nano-mechanical computing, and ongoing efforts to address these, are discussed.

EECS at University of California

Everything You Ever Wanted to Know About Laminates... but Were Afraid to Ask

Technical Library | 2020-11-29 22:02:49.0

It has been over 25 years since the earliest edition of "Everything You Ever Wanted to Know About Laminates...but Were Afraid to Ask" was pounded out on an old TRaSh-80 Computer. It has undergone periodic review and editing, including adaption for use on our website. (When I entered the industry Al Gore had not yet invented the internet.) Before I "retired" in 2004, we did another minor revision, but it was largely cosmetic, removing most references to the old military specification and introducing IPC-4101, the "new" specification for laminate and prepreg materials.

Arlon Technology Enabling Innovation

Screen-Printing Fabrication and Characterization of Stretchable Electronics

Technical Library | 2017-03-09 17:37:05.0

This article focuses on the fabrication and characterization of stretchable interconnects for wearable electronics applications. Interconnects were screen-printed with a stretchable silver-polymer composite ink on 50-μm thick thermoplastic polyurethane. The initial sheet resistances of the manufactured interconnects were an average of 36.2 mΩ/◽, and half the manufactured samples withstood single strains of up to 74%. The strain proportionality of resistance is discussed, and a regression model is introduced. Cycling strain increased resistance. However, the resistances here were almost fully reversible, and this recovery was time-dependent. Normalized resistances to 10%, 15%, and 20% cyclic strains stabilized at 1.3, 1.4, and 1.7. We also tested the validity of our model for radio-frequency applications through characterization of a stretchable radio-frequency identification tag.

Tampere University of Technology

Method of Modeling Differential Vias

Technical Library | 2011-03-17 15:29:54.0

Accurate, models for vias in a multilayer circuit board are necessary to predict link performance in the GHz regime. This paper describes a methodology to build a high bandwidth, scalable first approximation circuit model using simple transmission lines o

Lamsim Enterprises Inc.

Electrostatic Theory of Metal Whiskers.

Technical Library | 2014-07-31 16:36:59.0

Metal whiskers often grow across leads of electric equipment and electronic package causing current leakage or short circuits and raising significant reliability issues. The nature of metal whiskers remains a mystery after several decades of research. Here, the existence of metal whiskers is attributed to the energy gain due to electrostatic polarization of metal filaments in the electric field. The field is induced by surface imperfections: contaminations, oxide states, grain boundaries, etc. A proposed theory provides closed form expressions and quantitative estimates for the whisker nucleation and growth rates, explains the range of whisker parameters and effects of external biasing, and predicts statistical distribution of their lengths.

University of Toledo

Conformal Surface Plasmons Propagating on Ultrathin and Flexible Films

Technical Library | 2013-09-05 17:44:14.0

Surface plasmon polaritons (SPPs) are localized surface electromagnetic waves that propagate along the interface between a metal and a dielectric. Owing to their inherent subwavelength confinement, SPPs have a strong potential to become building blocks of a type of photonic circuitry built up on 2D metal surfaces; however, SPPs are difficult to control on curved surfaces conformably and flexibly to produce advanced functional devices. Here we propose the concept of conformal surface plasmons (CSPs), surface plasmon waves that can propagate on ultrathin and flexible films to long distances in a wide broadband range from microwave to mid-infrared frequencies.

Southeast University (SEU)

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