17 Common Defective Solder Joints in SMT Assembly

This Gold Phoenix PCB Knowledge Center article describes 17 common defective solder joints encountered in SMT assembly, including their characteristics and causes.

1. Solder connection. In the SMT assembly process, solder connection is also known as a tin bridge. Parts that should not be connected, such as component ends, adjacent component solder joints, or solder joints and nearby wires or vias, become soldered together. The SMT assembly industry refers to this as solder connection.

2. Stand tombstone, also known as the Manhattan phenomenon, refers to a component with two solder ends where, after reflow soldering, one solder end leaves the surface of the solder pad and the entire component becomes tilted and upright. The SMT assembly industry calls it stand tombstone.

3. Side standing. This is the phenomenon in which the side of a chip component comes into contact with the PCB pad. The SMT industry calls it side standing.

4. Offset. The component moves horizontally, causing the solder joint or pin to no longer be directly attached to the PCB pad.

5. Highlight. This is the phenomenon in which a chip component faces the front of the PCB while its bottom faces upward.

6. Tin beads. Tiny bead‑like pieces of solder that attach to the chip component or become scattered near the solder joint after reflow soldering.

7. Cold soldering. An incomplete reflow phenomenon in which the solder does not reach its melting point or the soldering heat is insufficient, causing the solder to solidify before wetting and flowing. No metal alloy layer is formed, resulting in the solder being completely or partially amorphous and simply accumulating on the surface of the soldered metal.

8. Core suction. Solder crawls up from the solder pad along the pins and between the pins and the chip body, resulting in insufficient soldering or an empty solder joint.

9. Reverse. The polarity direction of a polarized component is inconsistent with the actual required direction after soldering.

10. Bubbles. Gas in the solder fails to escape in time before solidification, resulting in the formation of voids inside the solder joint.

11. Pinhole. A small pin‑shaped hole formed on the surface of a solder joint.

12. Cracks. Solder joints crack due to mechanical or internal stress.

13. Solder tip. Solder protrudes outward from the soldering point in the shape of needles or thorns.

14. Excessive solder. The amount of solder at the soldering site is much higher than normally required, resulting in poor visibility of the soldered part or the formation of accumulated solder balls.

15. Open soldering. All pins or solder ends of components are detached from or deviated from their corresponding solder pads without proper soldering.

16. White spot. A phenomenon that occurs inside a laminated substrate in which glass fibers separate from the resin at the vertical and horizontal intersections. This appears as discrete white spots or “cross‑shaped” areas beneath the surface of the substrate and is usually related to stress caused by heat.

17. Grey soldering. Due to high soldering temperature, excessive volatilization of soldering flux, and repeated soldering, the surface of the soldering area becomes gray, and the solder crystal becomes loose, porous, and slag‑like.