read barcode scanner in PRINTED CIRCUITS HANDBOOK in Software


QR Code ISO/IEC18004 Recognizer In None
Using Barcode Control SDK for Software Control to generate, create, read, scan barcode image in Software applications.
Draw Quick Response Code In None
Using Barcode drawer for Software Control to generate, create QR Code image in Software applications.
Recognizing QR Code ISO/IEC18004 In None
Using Barcode reader for Software Control to read, scan read, scan image in Software applications.
Print QR Code In Visual C#.NET
Using Barcode creation for Visual Studio .NET Control to generate, create QR Code ISO/IEC18004 image in VS .NET applications.
When the PCB is thermally saturated and the component temperatures are still too high to be tolerated at the maximum obtainable system air velocity, other means of conducting heat from the PCB to even larger area system structures are required. The chassis of the system is often the largest surface area structure in the system, is exposed to the ambient air, and often makes a good sink for heat that cannot be dissipated by the PCB alone. Mechanisms to conduct heat into the chassis include chassis screws, gap fillers, connectors, and side rails. Sometimes, radio frequency (RF) shields that are appropriately connected to components can provide additional heat sinking.
QR Code Maker In .NET
Using Barcode drawer for ASP.NET Control to generate, create QR Code image in ASP.NET applications.
Encode QR Code ISO/IEC18004 In VS .NET
Using Barcode creator for .NET Control to generate, create Quick Response Code image in .NET applications.
Chassis Screws A properly designed chassis screw thermal sink connection in a PCB includes connection to the thermal spreading plane of the PCB, through hole plating, and a thermal contact area for the screw and stand-off sleeve to clamp onto. This configuration is shown in Fig. 17.10. The thermal screw should be as close to the hot electronic component as possible to minimize thermal resistance into the chassis. As well, the chassis where the thermal screw attaches should have a high thermal conductivity to spread the heat away from the screw. Preferably, the chassis should be made of metal. If a plastic chassis is used, molding a plate of aluminum (Al) into the plastic will improve its thermal heat spreading capability. A plastic chassis alone is usually a poor thermal spreader and may not provide substantial thermal performance enhancement.
QR Code JIS X 0510 Drawer In VB.NET
Using Barcode creation for .NET Control to generate, create Denso QR Bar Code image in .NET applications.
GS1 - 13 Encoder In None
Using Barcode creation for Software Control to generate, create EAN-13 image in Software applications.
Thermal contact area Through hole PCB
Encode Barcode In None
Using Barcode encoder for Software Control to generate, create barcode image in Software applications.
Creating Barcode In None
Using Barcode generation for Software Control to generate, create barcode image in Software applications.
Drawing Code128 In None
Using Barcode printer for Software Control to generate, create Code 128 Code Set B image in Software applications.
Print Code 39 Full ASCII In None
Using Barcode generator for Software Control to generate, create Code 39 image in Software applications.
Universal Product Code Version E Creator In None
Using Barcode drawer for Software Control to generate, create UPC - E1 image in Software applications.
Generating 2D Barcode In Visual Basic .NET
Using Barcode creator for .NET framework Control to generate, create Matrix 2D Barcode image in VS .NET applications.
FIGURE 17.10 Schematic of a chassis screw implementation for sinking heat to the chassis. The thermal screw mounts through a plated through via that is shorted to the thermal plane as shown. The thermal plane conducts heat from the thermal balls of the PBGA package.
Print Matrix Barcode In Visual Studio .NET
Using Barcode encoder for VS .NET Control to generate, create Matrix 2D Barcode image in VS .NET applications.
Reading EAN / UCC - 13 In C#
Using Barcode reader for .NET Control to read, scan read, scan image in .NET applications.
How much improvement might be expected from using the chassis of an enclosure for cooling This depends substantially on the enclosure construction and the location of the chassis screw with respect to the hot component. In one example, a device was cooled with a thermal screw that connected between a hard drive PCB and the hard drive enclosure. Connecting the device thermally to the hard disk drive resulted in a 10 percent thermal enhancement. 17.4.2 Gap Fillers It is sometimes not possible to use screws for conducting heat to the chassis. In other cases, large areas of high-power density might need to be sunk into the chassis. In these instances, another type of thermal conduction path is available that lends itself to conducting heat to the chassis: gap fillers. Gap fillers are thermal compounds that fill the gap between the PCB and chassis whose sole purpose is to conduct heat to the chassis. There are many different types of
UPC A Maker In Objective-C
Using Barcode maker for iPhone Control to generate, create Universal Product Code version A image in iPhone applications.
Code 128C Generator In Objective-C
Using Barcode maker for iPad Control to generate, create Code 128B image in iPad applications.
Paint GS1 - 13 In None
Using Barcode generator for Online Control to generate, create European Article Number 13 image in Online applications.
DataMatrix Encoder In Java
Using Barcode creation for Java Control to generate, create Data Matrix image in Java applications.
gap fillers.The most common is a soft, flexible silicone rubber material that has been filled with thermally conducting particles to enhance its bulk thermal conductivity. Sometimes, thermally filled foams are used. When the soft, compliant material is compressed between the PCB and chassis, it conforms to the protruding components on the PCB, making a good thermal connection. Important criteria to consider in selecting elastomeric gap fill materials are the thickness needed, the thermal conductivity required, and the pliancy of the material. A variety of materials with varying compositions are readily available on the market. There is normally a trade-off between the pliancy of the material and the thermal conductivity, with higher thermal conductivity materials exhibiting less compliancy. Plastic sacks filled with a thermal fluid are sometimes used as gap filler materials. The fluid is usually optimized to produce convection in the gap of interest. The convection in the fluid can give an effective thermal conductivity that is substantially higher than the conductivity of the fluid alone. 17.4.3 Connectors Connectors can either provide a direct or indirect means of conducting heat from the PCB. Direct conduction occurs in those system configurations where the PCB is plugged into an edge connector or back plane socket, or is held in place with an edge guide. To take advantage of these direct connect thermal features, it is necessary to extend thermal planes into the areas where the connection or clamping occurs. The connector, clamping, or edge guide should have as large a contact area as possible to optimize thermal conduction of heat from the low thermal conductivity PCB material. In some military applications, the PCB is built around a thick Cu core that is clamped by the edge rail of the card cage. The thick Cu core provides very effective thermal conduction from the PCB into the edge rail, which is then cooled by a system of channels containing either moving air or moving water. Indirect conduction of heat from the PCB can occur when cables are plugged into connectors on the PCB. These indirect conduction paths are much harder to include accurately in systemlevel thermal analyses, but can provide some margin in a PCB thermal design. Care must be taken, however, to ensure that these plug-in cables don t block critical airflow paths that would lead to overheating. 17.4.4 RF Shields RF shields are used over sensitive RF and analog circuits to minimize electrical interference with the circuit function or to minimize electrical radiation from the circuit into the surrounding environment. RF shields are usually made of a thin metal which is soldered to ground on the PCB. In most instances, the RF shield is a continuous plate or box that encloses the circuits. Unfortunately, this continuous box creates a dead zone in the air flow directly above the components within the box, degrading natural convection for those components. To enhance the thermal performance of components within RF shields, perforations or meshing of the RF shield cage is recommended. If these perforations are kept less than 1/10 the wavelength of the shielded electromagnetic radiation, the RF shield will function adequately to quiet the circuit and block out extraneous signals while allowing air flow through the shield to cool the interior components. If additional steps are taken, the shield can be used to spread heat from hot components inside the shield over a larger section of the PCB, thereby maximizing convection and radiation cooling for the heated components. Figure 17.11 shows a schematic of a shield over a stacked package component. It is normally difficult to conduct heat from the top device in such a stack to the PCB, but when the RF shield is brought into contact with the top device, heat can conduct into the shield and down to the PCB. It is suggested that the thermal connection between the shield and the electrical components be made with a thermal epoxy or thermal grease after the shield is soldered in place to avoid issues with mechanical tolerances
Copyright © . All rights reserved.