In even the relatively-large masses of solder implicit in holding large (in mass or current-demand) components to a power/sweep board, the integrity of the board-to-trace or board-to-land adhesion can usually be assumed. Nonetheless, look askance at obvious messily-reworked joints, and especially if the expression "dog's-breakfast" comes readily to mind.
'Dry' joints are rather found between pigtails and pins and the solder, and/or the solder and the land or trace. The stabilizing effect of through-board holes can help, as can the use of hot-glue blobs post-soldering, to prevent movement of the solderees® during the all-important freezing of the solder after its application. Also critical to good joint formation is that the solder 'melt' should properly 'wet' and bridge the surfaces being attached. Fluxing and cleanliness (jointly, 'wettability') of surfaces, immobility of the joint, and rate of heat input and escape during freezing of the solder are important in assuring a good joint.
The frozen solder is a solid solution of malleable metals. Tension and cyclic stress can therefore, in time, affect a joint's adhesive qualities, even to the point of separation of the metals/metalloids from each other by 'crystallizing out' of the solution. Dull finish and granular appearance of a joint may be evident, but increased ohmic resistance to the point of open-circuit is the clincher.
The remedy? Remake the joints. This needs all the gear and attention of the original joint-making. It may need only a dab of fresh solder and flux, or it may need aspiration of the faulty solder and its total replacement. Adequate cleanliness, heat input/removal and stabilization of the parts is important. A resistance-check across remade joints will be useful, but the success of the complete operation may not be apparent before the job is completed and the board is back in service. None of the foregoing guarantees no shorting in an FBT, or that bung capacitors or barbecued resistors will have healed themselves. The components on power/sweep boards are big enough for physical inspection to suggest replacement, when that is needed, rather than resoldering, and rugged enough that no fear of damage from static (given normal and tasteful precautions) should be a consideration.
This peroration may take longer to read than it takes to resolder a joint, with practice. You can practise on something inconsequential, such as a current Acer PC, and be up and running in no time at all. Rots of ruck.
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