Many of the defects that are seen after reflow are not necessarily due to the reflow process itself, but are the result of materials, printing or placement defects that only become apparent once the solder paste has been reflowed.
Our list of faults includes:
| burnt boards | short-circuits | ** | |
| component movement | * | solder balling | * |
| damaged ceramic capacitors | * | solder beading | * |
| dewetting | solder drainage | *** | |
| faulty self-alignment | * | solder paste spatter | * |
| “insufficient” solder | * | solder wicking | * |
| lost components on double-sided reflow | * | tombstoning | ** |
| poor wetting | unreflowed solder paste |
Of these defects, only solder drainage can be with certainty laid at the door of the designer, and no-one else. However, the designer can contribute to other types of fault, for example, by specifying components that are not capable of withstanding reflow conditions, or an inappropriate solder paste.
More subtle problems mostly relate to the design of apertures and the volume of solder paste intended for the joint, which can result in open-circuits or short-circuits, or to lack of symmetry in the design, which can result in effects such as tombstoning. Against the items in the list above, we have indicated with one or more asterisks (three being most significant), the extent to which each fault type is likely to have been caused by the designer.