Circuit card assembly

Momentum control gyroscopes and precision guidance instruments are used to control and detect movement in satellites, space probes and platforms, airplanes and missiles. They are, composed of a number of extremely complex electromechanical systems with circuit card assemblies, wire windings, lamination stacks, ball, roller, and gas bearings, and potted components which contain small voids and crevices. Tolerances on these assemblies can be in the microinch range. These instruments can contain lubricants and the previously discussed damping fluids. 

In order to predict temperature rises in electronic components, a thermal model needs to be created, which shows all of the dissipating elements and the entire heat path. Starting at the junction of each dissipating semiconductor, the model needs to include all layers in the thermal path the die attach, substrate (if used and its attachment), package, thermal interface materials (if used), heat sink and circuit card assembly (CCA). The heat dissipated in each component, physical layout, and availability of cooling air are required to calculate the temperature-rise predictions. 

A basic understanding of material performance is necessary for both the designer and fabricator of the printed wiring board (PWB). Understanding the materials available is one of the primary tasks for designing for manufacturability and performance. It is necessary to match the product end-use performance requirement as well as the environmental exposure the board experiences in the fabrication and circuit card assembly (CCA) processes with the capabilities of the material. It is common for boards to experience as many as five thermal excursions in CCA. 

For decades, the majority of PCBs have been built with epoxy resins, dicy-cured, and with bromine flame retardant.The industry has developed around this paradigm. Drills and drilling, chemistry, lamination, and circuit card assembly are all well understood with reference to standard FR-4. Although there are fabricators with processes developed to manufacture PCBs using laminates other than standard FR-4, this knowledgebase is not distributed industrywide. Especially problematic is the intersection of requirements for HF and/or LFAC with high thermal resistance and improved electrical characteristics, such as low attenuation in the material. 

Once a circuit card assembly (CCA) has been fully assembled and tested, it often needs to be protected from the environments in which it will ultimately be used. Moisture, salt, dirt, fungus, and a variety of other contaminants as well as mechanical shock and vibration will cause failure on an unprotected assembly. The CCA s last hue of defense against the elements is a thin layer of coating that conforms to the shape of all the part leads, solder joints, and other complex features on the completed CCA. This conformal coating (or flow coating) is applied as liquid to the fully assembled CCA, and is cured in place to form a protective layer of insulation for the assembly. 

Fig. 1. The different levels of electronic packaging (0) chip (1) chip carrier (2) printed circuit board (electronic card assembly) (3) rack and (4) system (2).

The sensors of the electronic nose are assembled in an array. The array is normally a small electronic unit that integrates the different sensors into a practical circuit card or another appropriate system that is easy to insert into the electronic nose instrument. If the array is to be used in a flow injection setup the unit also comprises a flow cell compartment with minimal volume. The system depicted in Fig. 2 shows how MOS and MOSFET arrays are integrated in a flow injection system [11]. Larger arrays can be integrated into silicon chips, as described for CP sensors where, for example an ASIC chip with 32 sensors has been fabricated with BiCMOS technology and having an area of 7 x 7 mm [18]. If the array is be inserted in the headspace volume of a bioreactor, the technical solution is a remote array probe that can be placed in a gas sample container [19]. 

PANI-NFA 2O5 is promising nanocomposite material for utilization as a cathode for ion-Li batteries [292,293]. PANI-NFs have been used as a cathode material for rechargeable Li-polymer cells assembled with a gel polymer electrolyte [152], and in an aqueous PANI-Zn rechargeable battery [261]. Dispersions of dedoped PANI-NFs in poly(vinyhdene fluoride-hexafluoropropylene)-based gel polymers can be used as electrolyte membranes for rechargeable Li batteries [513]. PANI-NF and PANI-NT arrays, which show superior electrochemical properties to the bulk counterpart, can be applied to Li-polymer thin-film batteries, which are shape-flexible and specifically suitable for powering integrated circuit cards and microelectromechanical systems [514,515]. 

The EMC directive allows CE marking of components that (1) have an intrinsic function and (2) are sold to the end user, but not when sold to manufacturer s or assemblers. Some components may bear CE marking under the EMC directive. Examples of components include personal computer circuit cards, computer disk drives, PLCs, stand-alone power supplies, electric motors (except induction), and electronic temperature controls. 

They provide an interconnect medium from the semiconductor devices and the passive devices to the next level of assembly — the circuit card. 

FIG. 32 PCB transportation system. Circuit cards being transported between assembly process equipment (pick and place) and a reflow oven. (Courtesy of Universal Instruments Corporation). 

The Reactor Controllers control the reactor and maintain continuity of electrical power to the spacecraft based on sensor inputs. The reactor sensors include, but are not limited to, hot leg temperature, cold leg temperature, pressure, flow, neutron flux, fission products, continuous control device assembly position, and discrete valve and control device assembly positions. Details of the mass for circuit cards, sensors and cabling are contained in Reference 4-2 and are summarized below. 

System Control The control unit operates all the functions of the extractor. It is composed of a CRT, keyboard, contact closure outputs and inputs and nine control cards each with special functions. This unit requires almost no modification since its functions are highly specialized and the circuits are delicately assembled. The most important function to the user is its ability to interface with other instruments. This is done via the contact closures. Of primary use in our design is the contact closure which controls the event end output pulse. In the Suprex Model 50, this is contact closure B. This event end contact closure is the main interface in our design to other in-... 

The electronics needed to operate six temperature sensors on each microreactor channel are located underneath these cards. The ribbon connector, which is also visible in Fig. 12.8, is used to transfer electrical signals directly from the reactor board to the heater circuit board (described below). Serial communications for the Redwood flow manifolds is provided by two, four-conductor RJ-11 jacks on the front. The front of the board has gas inlets for the reactor feed and the purge gas. In addition, there are two gas outlets, one for each reaction channel. The inlet and outlet fittings are 1/16-inch type 316L stainless steel. The tubing assembly component having the greatest pressure sensitivity is the microreactor membrane. 

Monotonic (bend-to-failure) testing is designed to simulate the assembly conditions to which a PCA is subjected in manufacturing. A variety of assembly steps impart loading conditions that are similar to a monotonic bend test, such as heatsink attachment, connector attachment, in-circuit test (ICT), handling, and card-cage installation.These assembly steps could mechanically... 

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