Designing PCBs comes with various challenges, including undesirable breakouts due to drill wander, misalignment, and stress concentration. To address these issues, one effective technique is the use of teardrops.
PCB teardrops are the design features where the junction of the trace, pad, or via on a printed circuit board is tapered or gradually widened to form a teardrop-shaped connection. Sometimes, teardrops can even take the form of a snowman, featuring two rounded pads connected by a narrow trace in the middle. These teardrops serve as additional copper areas, facilitating smoother transitions and distributing stress more evenly. By improving mechanical and electrical reliability, teardrops are particularly beneficial for enhancing connections in through-hole pads and vias.
Functions of teardrops in PCB design
Reduce Undesirable Breakouts and Compensate for Misalignment
When drilling vias or holes in a PCB, there is a possibility of slight deviations from the intended position, leading to misalignment between the drilled holes and corresponding pads or traces. Teardrops address both hole misalignment and layer misalignment challenges. By incorporating teardrops, the pads or traces are gradually tapered toward the drilled holes, creating a larger landing area for the drill bit. Moreover, in situations where vias or pads connect traces on different layers, the teardrop shape provides some tolerance. If there is a slight misalignment between the layers, the tapered teardrop shape ensures that a sufficient connection area is maintained. This significantly reduces the negative effects of misalignment on the electrical and mechanical integrity of the connection.
Reduce mechanical stress and Enhance Reliability
Another important function of teardrops is to alleviate stress concentrations at the connection points, particularly where thin traces meet pads or via annular rings. Issues like solder joint fractures, pad lifting, or via cracking may occur. Teardrops effectively reduce these issues by providing a gradual transition from a wide trace width to a narrower neck. This tapered shape minimizes stress concentrations and provides stress relief by avoiding abrupt changes in geometry. Additionally, teardrops act as reinforcement, enhancing the structural integrity of through-hole pads and vias. This reinforcement ensures that the PCB can withstand various environmental factors, temperature fluctuations, and physical stressors, further enhancing its reliability.
Teardrops are particularly essential in special situations like flexible PCBs. The flexibility of the PCB can create stress points, particularly at the junctions where the traces meet the pads. By incorporating teardrops on flexible PCB layouts, the traces and pads can withstand the flexing and bending motions without experiencing significant stress-induced issues. In addition to flexible PCBs, teardrops are also applied to high-speed designs, designs with fine-pitch components and when via is in a high-stress or high-density area of the board.
