Cold joints are usually the result of excess solder. The extra solder can be removed using an iron tip. If none of the remedies above are effective, follow these simple steps: Use the FS-210 Brush Tip Flux Pen to flush the cold. Cold solder joints are one of the most common — and most dangerous — soldering defects in PCB assembly. They often look harmless, but can cause intermittent failures, unexpected resistance spikes, and field returns long after a product has passed initial testing. At Best Technology, we see the. A cold solder joint happens when there is improper bonding between a solder and a solder-surface interface because of either incomplete melting or lack of fusion of the solder.