Technical Library | 2010-01-13 12:34:10.0
Micro-sectioning (sometimes referred to as cross-sectioning)is a technique, used to characterize materials or to perform a failure mode analysis, for exposing an internal section of a PCB or package. Destructive in nature, cross-sectioning requires encapsulation of the specimen in order to provide support, stability, and protection. Failures that can be investigated through micro-sectional analysis include component defects, thermo-mechanical failures, processing failures related to solder reflow, opens or shorts, voiding and raw material evaluations.
Technical Library | 2013-07-03 10:31:54.0
It has been demonstrated in numerous pieces of work that stencil printing, one of the most complex PCB assembly processes, is one of the largest contributors to defects (Revelino et el). This complexity extends to prototype builds where a small number of boards need to be assembled quickly and reliably. Stencil printing is becoming increasingly challenging as packages shrink in size, increase in lead count and require closer lead spacing (finer pitch). Prototype SMT assembly can be further divided between industrial and commercial work and the DIYer, hobbyist or researcher groups. This second group is highly price sensitive when it comes to the materials used for the board assembly as their funds are sourced from personal or research monies as opposed to company funds. This has led to development of a lower cost SMT printing stencil made from plastic film as opposed to the more traditional stainless steel stencil used by industrial and commercial users.This study compares the performance of these two traditional materials and their respective impact on solder paste printing including efficiency and print quality.
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.
Technical Library | 2022-09-12 14:07:47.0
Unique component handling issues can arise when an assembly factory uses highly-moisture sensitive surface mount devices (SMDs). This work describes how the distribution of moisture within the molded plastic body of a SMD is an important variable for survivability. JEDEC/IPC [1] moisture level rated packages classified as Levels 4-5a are shown to require additional handling constraints beyond the typical out-of-bag exposure time tracking. Nitrogen or desiccated cabinet containment is shown as a safe and effective means for long-term storage provided the effects of prior out-of-bag exposure conditions are taken into account. Moisture diffusion analyses coupled with experimental verification studies show that time in storage is as important a variable as floor-life exposure for highly-moisture sensitive devices. Improvements in floor-life survivability can be obtained by a handling procedure that includes cyclic storage in low humidity containment. SMDs that have exceeded their floor-life limits are analyzed for proper baking schedules. Optimized baking schedules can be adopted depending on a knowledge of the exposure conditions and the moisture sensitivity level of the device.
Technical Library | 2021-11-26 14:34:07.0
The use of desiccant bags filled with Silica Sand and or Clay beads used in conjunction with a Moisture Barrier Bag to control moisture for storage of printed circuit boards has long been an accepted practice and standard from both JEDEC and IPC organizations. Additionally, the use heated ovens for baking off moisture using the evaporation process has also been a long#2;standing practice from these organizations. This paper on alternative drying methods will be accompanied by completed independent, unbiased tests conducted by Vinny Nguyen, an engineering student (now graduated) from San Jose State University. The accompanied paper will examine the performance levels of different technologies of desiccant bags to control moisture in enclosed spaces. The tests and equipment set were reviewed by an engineer and consultant to the Lockheed Martin Aerospace Division and the IPC - TM-650 2.6.28 test method was review by engineer from pSemi. The tests were designed to mimic performance tests outlined in Mil Spec 3464, which both IPC and JEDEC have adopted for their respective standards. The test examined variables including absorption capacity rates, weight gain and release of moisture back into the enclosed area. The presentation will also address and highlight: • Similarities of PCBs and Heavy Equipment as it applies to Inspections, Causes of Failure, Types of Corrosion and Moisture Collection Points. • Performance Attributes of Different Desiccant Technologies as it applies to shape, texture, change outs, labeling and regeneration. • Venn Diagram of Electromechanical Failure with the circles 1. Current 2. Contamination 3. Humidity Presentation Available
Technical Library | 2007-08-28 20:18:06.0
A conformal coating is defined as a thin polymeric material which covers the surface of an electronic assembly. These coatings are used to provide an electrically insulative and environmentally protective seal or cover to a completed printed circuit board (PCB).
Technical Library | 2023-05-10 01:42:46.0
Zirconia ceramic PCB, for applications in the field of microwave communication
Technical Library | 2012-07-11 20:10:59.0
As technology advances, understanding thermal management issues of high frequency PCB's increases. There are many different aspects to consider for PCB thermal management. This paper will investigate thermal management issues of high frequency PCB's as it
Technical Library | 2011-03-30 21:14:33.0
The expression "multifunctional PCB", as a synonym for a PCB which is applicable with a variety of assembly techniques, is already established on the market. That means the PCB can be used for multiple reflow soldering and multiple assembly techniques lik
Technical Library | 2021-01-06 20:28:58.0
Cavity technology in a Printed Circuit Board (PCB) has existed for many years. The methodology to create the cavity in the PCB has evolved over time as technologies have advanced and the manufacturing process varies by the individual PCB
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