Surface mount parts

The use of surfaee mount parts is widespread. Surfaee mount parts ean rid themselves of heat only through their leads whieh are soldered to a printed eireuit board. The thiekness and surfaee area of the eopper island beeome the heatsink system. The thermal resistanees in surfaee mount deviees are mueh higher, therefore their designs have mueh less margin and room for error. Table A-3 has nominal values for thermal resistanees of eommon surfaee mount paekages. Please refer to the individual part data sheet for the exaet value. 

In surfaee mount printed eireuit board applieations, more than one issue usually must be eonsidered. Heatsinking must be eonsidered, along with signal and EMI/RFI eonsiderations. The traee that must dissipate the greatest heat within a switehing power supply is also the node that has the largest dv/dts whieh eouple very easily to the surrounding traees. 

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Moisture absorption in uncured and cured adhesives is important for reliable adhesive bonding. Absorbed moisture in adhesives, particularly those used in surface-mounted parts, may result in voids in the bond hne due to moisture desorption or entrapment. Absorption of moisture after cure also affects reliability. Popcoming, the cracking of plastic parts during solder reflow, is due to the rapid vaporization and expulsion of moisture retained by the die-attach adhesive or the plastic encapsulant. 

This type of package is made up of only surface-mount parts aU mounted on the same side of the PCB. Assembly is a one-step process that involves placing all components and soldering them in place using some form of solder reflow. 

As the name imphes, this package type contains surface-mount parts on both sides, as well as through-hole parts such as connectors. In most cases, the surface-moimt components on one... 

Yet another disadvantage of surface-mount parts stems from their small size. It is more difficult to remove heat from SMT packages than it is for their through-hole equivalent. In some cases, such as high-performance processors, the heat generated by the IC is too high to permit proper operation in an SMT package. 

There are very few surface mount capacitors with the desired value, voltage rating, and low ESR all in one part. It would be more conservative to parallel two capacitors of no less than one-half the desired capacitance value. This allows many more second sourced capacitors to be used and lowers the ESR. Lets use two 330 pF, 10 V tantalum capacitors in parallel. The Candidates now become ... 

The class of polyester-based liquid crystal polymers (LCPs) represent one of the most attractive materials in the field of engineering thermoplastics because of their superior mechanical properties, heat resistance, accuracy of dimensions, moldability and the excellent balance of these properties [1-5]. LCPs have been recently expanding their applications, in particular, those for precision electronic parts appropriate for surface mount technology (SMT). 

Generally, some improvement in Tg will be required, partly because this will help retain the mechanical properties over a wider temperature range, and partly because the soldering of surface mounting components often puts a large heat load on the entire board and not just on one surface. 

CIRCORTech provides the parts needed to construct a pMS3 system, build to order complete systems, and a wide range of SP76 surface mount components for NeSSl systems. They also provide services for designing and installing their pMS3 systems according to customer specihcahons. 

The modular nature of the surface-mount components makes it very easy to assemble or reconfigure a fluidic system to meet the requirements of a particular analyzer or sensor. Figure 10.19 shows three simple examples of surface-mount component systems being used to provide all, or part, of an analytical interface. 

To get complete coverage of the surface, the gun is moved about and directed to various areas by the sprayman in case the operation is a hand spray one. When arranged as an automatic application, the gun or guns may be mounted on a mechanical manipulation device to produce the desired motion over the surface. The part is often carried on a conveyor to be moved past the spray gun position to further create the desired relative movement of the surface with respect to the spray. 

Single part epoxy presents another option. Some materials, such as surface mount adhesives, have the curing catalyst locked in a phase change material that is released with heat. Cure temperatures range from 100 to 150°C. The material supplier controls the mixing process, and these materials have excellent shelf life. 

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