Technical Library | 2018-08-15 17:27:28.0
Smartphones and tablets require very high flexibility and severe bending performance ability of the flexible printed circuits (FPCs) to fit into their thinner and smaller body designs. In these FPCs, the extraordinary highly flexible, treated rolled-annealed (RA) copper foils have recently used instead of regular RA foil and electro deposited foils. It is very important to measure the Young's moduli of these foils predicting the mechanical properties of FPCs such as capabilities of fatigue endurance, folding, and so on. Even though the manufacturers use IPC TM-650 2.4.18.3 test method for measuring Young's modulus of copper foils over many years, where Young's modulus is calculated from the stress–strain (S–S) curve, it is quite difficult to obtain the accurate Young's modulus of metal foils by this test method.
Technical Library | 2016-10-20 18:13:34.0
Pad cratering failure has emerged due to the transition from traditional SnPb to SnAgCu alloys in soldering of printed circuit assemblies. Pb-free-compatible laminate materials in the printed circuit board tend to fracture under ball grid array pads when subjected to high strain mechanical loads. In this study, two Pb-free-compatible laminates were tested, plus one dicycure non-Pb-free-compatible as control. One set of these samples were as-received and another was subjected to five reflows. It is assumed that mechanical properties of different materials have an influence on the susceptibility of laminates to fracture. However, the pad cratering phenomenon occurs at the layer of resin between the exterior copper and the first glass in the weave. Bulk mechanical properties have not been a good indicator of pad crater susceptibility. In this study, mechanical characterization of hardness and Young’s modulus was carried out in the critical area where pad cratering occurs using nano-indentation at the surface and in a cross-section. The measurements show higher modulus and hardness in the Pb-free compatible laminates than in the dicy-cured laminate. Few changes are seen after reflow – which is known to have an effect -- indicating that these properties do not provide a complete prediction. Measurements of the copper pad showed significant material property changes after reflow.
Technical Library | 2013-04-18 16:46:42.0
Conformal coatings are considered a method of providing corrosion protection to electrical assemblies used in high-humidity or harsh environments. They are applied to PCBs for various reasons: to protect from moisture and contamination, to minimize dendritic growth, to provide stress relief, and for insulation resistance. These contribute to more durable handling, enhanced device reliability, and reduced warranty costs. Increased miniaturization of new circuit board designs requires flexible, low stress coating material to protect delicate components and fine-pitch leads. Silicone conformal coatings offer many advantages that address the general trend of ongoing PCBs designs, such as: high flexibility and low modulus to reduce stress on delicate or small components... First published in the 2012 IPC APEX EXPO technical conference proceedings.
Technical Library | 2019-03-06 21:26:14.0
Electronic assemblies use a large variety of polymer materials with different mechanical and thermal properties to provide protection in harsh usage environments. However, variability in the mechanical properties such as the coefficient of thermal expansion and elastic modulus effects the material selection process by introducing uncertainty to the long term impacts on the reliability of the electronics. Typically, the main reliability issue is solder joint fatigue which accounts for a large amount of failures in electronic components. Therefore, it is necessary to understand the effect of polymer encapsulations (coatings, pottings and underfills) on the solder joints when predicting reliability.This paper presents the construction and validation of a thermo-mechanical tensile fatigue specimen. The thermal cycling range was matched with potting expansion properties in order to vary the magnitude of tensile stress imposed on solder joints
Technical Library | 2020-10-14 14:49:14.0
In this study, the modification of an epoxy matrix with different amounts of cube-like and rod-like CaCO3 nanoparticles was investigated. The effects of variations in the morphology of CaCO3 on the mechanical properties and thermal stability of the CaCO3/epoxy composites were studied. The rod-like CaCO3/epoxy composites (EP-rod) showed a higher degradation temperature (4.5 _C) than neat epoxy. The results showed that the mechanical properties, such as the flexural strength, flexural modulus, and fracture toughness of the epoxy composites with CaCO3 were enhanced by the addition of cube-like and rod-like CaCO3 nanoparticles. Moreover, the mechanical properties of the composites were enhanced by increasing the amount of CaCO3 added but decreased when the filler content reached 2%. The fracture toughness Kic and fracture energy release rate Gic of cube-like and rod-like CaCO3/epoxy composites (0.85/0.74 MPa m1/2 and 318.7/229.5 J m
Technical Library | 2020-10-14 14:33:36.0
Epoxy based adhesives are prevalent interface materials for all levels of electronic packaging. One reason for their widespread success is their ability to accept fillers. Fillers allow the adhesive formulator to tailor the electrical and thermal properties of a given epoxy. Silver flake allow the adhesive to be both electrically conductive and thermally conductive. For potting applications, heat sinking, and general encapsulation where high electrical isolation is required, aluminum oxide has been the filler of choice. Today, advanced Boron Nitride filled epoxies challenge alternative thermal interface materials like silicones, greases, tapes, or pads. The paper discusses key attributes for designing and formulating advanced thermally conductive epoxies. Comparisons to other common fillers used in packaging are made. The filler size, shape and distribution, as well as concentration in the resin, will determine the adhesive viscosity and rheology. Correlation's between Thermal Resistance calculations and adhesive viscosity are made. Examples are shown that determination of thermal conductivity values in "bulk" form, do not translate into actual package thermal resistance. Four commercially available thermally conductive adhesives were obtained for the study. Adhesives were screened by shear strength measurements, Thermal Cycling ( -55 °C to 125 °C ) Resistance, and damp heat ( 85 °C / 85 %RH ) resistance. The results indicate that low modulus Boron Nitride filled epoxies are superior in formulation and design. Careful selection of stress relief agents, filler morphology, and concentration levels are critical choices the skilled formulator must make. The advantages and limitations of each are discussed and demonstrated.
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