Solder operations

Automated soldering operations can subject the mol ding to considerable heating, and adequate heat deflection characteristics ate an important property of the plastics that ate used. Flame retardants (qv) also ate often incorporated as additives. When service is to be in a humid environment, it is important that plastics having low moisture absorbance be used. Mol ding precision and dimensional stabiUty, which requites low linear coefficients of thermal expansion and high modulus values, ate key parameters in high density fine-pitch interconnect devices. 

PCT may be used for the production of electronic and automotive components such as circuit board components, connectors, switches and relays, and alternator armatures and pressure sensors. The main application has been in the fabrication of surface-mount connectors that can withstand infrared reflow soldering operations. 

UJ Upstream Substitutions. Material substitutions upstream of the cleaning processes can also effect waste streams. Corrosive fluxes used in soldering operations remove some metal from the part. This metal will go into the waste stream after cleaning. Use of noncorrosive fluxes can prevent this problem (Egide 1989). 

Thin ( 2 /mi) layers of nickel and tin are electroplated over the silver termination, the former to act as a barrier preventing dissolution of the silver during the subsequent wave-soldering operation when the chips are surface-mounted onto a substrate. The tin layer ensures good wetting of the termina tion by the solder. In the case of the BME capacitor (see below) the termination is copper fired on under reducing conditions and covered with an electroplated layer of nickel. 

It will be easier to assemble these pieces if you can set up the thermocouple and the glass-to-metal seal so that they rotate horizontally during the silver-soldering operation. 

Which thermoplastics could be used as the body of printed circuit boards, given that a soldering operation must be carried out after the components are assembled on the board Lead tin solders melt at about... 

PI resins find use as coverlays. A coverlay is generally used to protect printed circuits during subsequent processing, primarily solder operations, or from environmental effects during use. The Pis can be used in combination with epoxies. In addition, additives, such as phosphorous-based flame retardants or adhesion promoters, may be used in the formulations. 

Such a positrol log contains complex steps, each of which might well be kept in its own log. For example, the reflow soldering operation could have a number of what steps, such as belt speed furnace zone temperatures for preheat soldering zone cool down zone atmosphere chemistry control atmosphere flow speed visual inspection for missing, misaligned, or tombstoned parts solder bridges and solder opens. 

Solder Float Resistance. This test addresses the thermal resistance of the laminate material floating on the solder bath. Becanse this method subjects the sample to a thermal gradient across the z-axis of the material similar to an actual wave solder operation, the resnlts of this test are particnlarly important and—as mentioned previously—either solder pot temperatures or exposure times should be increased if the laminates are intended for use in lead-free assembly processes. 

All component leads attach to the PCB by being inserted into holes that pass through the PCB.The components may be secured by wave soldering or by pressing into holes that result in an interference fit (press fit). Assembly involves a component placement operation followed by a wave-soldering operation. This method is still the workhorse of the low-cost consumer electronics industry. 

Simple bracket = <1 min assembly time Difficult bracket = >1 min assembly time Post-solder assembly = manual solder operation... 

ML-PWBs often have surface-mount devices on both sides of the board, and they receive three or more solder operations during the assembly of connectors and devices. In addition, because of the value of a completed assembly, the board must be able to withstand additional soldering operations needed for occasional removal and replacement of defective devices. Boards made with difunctional GF epoxy can suffer from lifted lands, cracked PTH barrels, or substrate blisters during these multiple soldering operations. The solution is to use materials with low moisture absorption and high thermal degradation temperature. 

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