Cold joint
Cold joint turns up in 3 fields: PCBs, concrete, waterproofing. Here is what it means to the people in each one.
Cold joint in PCBs
Solder joint that never got hot enough to flow and wet properly, leaving a dull, grainy and unreliable bond.
A cold joint forms when solder melts incompletely or the parts never reach wetting temperature, so the solder sits on the surface without a proper metallurgical bond. It looks dull, grainy or lumpy, with a poor fillet or visible gaps, and may conduct at first and then fail intermittently. Causes include a large copper plane sinking the heat, too low an iron temperature or dwell time, and oxidised or contaminated surfaces the flux cannot clean.
"That connector's ground pins are all cold joints, the plane is sucking the heat out, use a bigger tip and preheat."
Cold joint in concrete
An unplanned seam left where fresh concrete was placed against concrete that had already begun to set.
Forms when a late truck, a plug or a breakdown lets the last concrete placed stiffen before the next load arrives, so the two never knit together. The result is a weak plane, a leak path and often a visible line on finished walls. Retarders, keeping the leading edge alive and bulkheading a proper construction joint when a delay drags on are the standard defenses.
"Third truck's 50 minutes out, so either we bulkhead it now or we're looking at a cold joint halfway up this wall."
Cold joint in waterproofing
The seam where one concrete pour meets a later one, a classic leak path in below-grade walls and slabs.
Concrete placed against concrete that has already set does not fuse fully, leaving a plane of weakness that water follows. Cold joints occur at planned construction joints, wall-to-footing intersections and unplanned stops in a pour. Waterproofing details treat them with waterstops cast in, extra membrane reinforcement on the positive side, or injection after the fact.
"Water's coming in right along the cold joint at the footing, the swelling strip must have been missed."