From Microvias: For Low Cost, High Density Interconnects
2.5 Solder Resist Materials and Processes
IPC-T-50b defines a solder resist (mask) as a coating material used to mask or to protect selected areas of a printed circuit board (PCB) from the action of an etchant, solder, or plating. A somewhat more useful working definition for a solder resist is as follows: a coating that masks off a printed circuit board surface and prevents those areas from accepting any solder during reflow or wave soldering processing (see Fig. 2.25).
Figure 2.25: Major features of solder resist on a PCB.
The prime function of a solder resist is to restrict the molten solder pickup or flow in those areas of the PCB, holes, pads, and conductor lines that are not covered by the solder resist. PCB designers, however, often expect more functionality out of the solder resist than just a means to restrict the solder pickup. Table 2.26 lists the functions of a solder resist.
Reduce solder bridging and electrical shorts
Reduce the volume of solder pickup to obtain cost and weight savings
Reduce solder pot contamination (copper and gold)
Protect printed circuit board (PCB) circuitry from handling damage, i.e., dirt, finger prints, etc.
Provide an environmental barrier
Fill space between conductor lines and pads with material of known dielectric characteristics
Provide an electromigration barrier for dendritic growth
Provide an insulation or dielectric barrier between electrical components and conductor lines or via interconnections when components are mounted directly on top of the conductor...
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