Soldering Bridges Reasons and Suggestions

Bridging refers to soldering errors that connect two or more adjacent pads and contact between pads to form a conductive path. During the assembly process, problems at various stages of the process can lead to bridging. This article analyzes the root causes of bridging and how to solve the bridging problems in formwork manufacturing, screen printing, placement components, reflow soldering, PCB fabrication, and the use of solder paste.

PCB manufacturing

The reason that the PCB board causes bridging may be a problem with the coplanarity of the SMD pads. When setting up the printer, it caused a poor seal between the template and the pad. Removing the solder mask between adjacent pads, especially the solder mask between fine-pitch component pads, can eliminate the PCB-induced bridging.

Template design

During the stencil design phase, the size of the hole is controlled. For fine pitch components, it is strongly recommended that the opening of the hole be slightly smaller than the size of the pad to improve the seal between the template and the PCB.
The dirty template on the reverse side of the paste will contaminate the next bare circuit board to be printed, and it will become a hidden danger of bridge formation. To reduce the possibility of this problem occurring, check the zero print gap setting, the minimum necessary print pressure, increase the frequency of the wipe template, or replace the chemical cleaner.
Pattern tension can also cause print defects. If the tension of the stencil is not strictly maintained, it is impossible to maintain the consistency of the printing, and the paste pattern printed on the plate may be blurred.

Paste and screen printing

Screen printing may be the root cause of solder bridging due to poor seals, misalignment between pads and stencils, poor cleaning, uneven screeds, and inaccurate printing speeds or printed board support problems. Sealing and alignment problems can be corrected by optimizing the printing tool. Keeping the template dry before the next printing, and optimizing the order of wetting, vacuum, and drying, can solve the problem of soiling the circuit board due to bad solder paste on the template, as well as the problem of bridging.


When printing, sharp edges often appear on fine-pitch holes. In order to reduce the bridging caused by this problem, it is necessary to check the support of the circuit board, adjust the speed of separation of the circuit board and the screen, and confirm that the chemical properties of the solder paste are taken into account in each setting.

Print defects caused by solder paste may be due to the solder paste drying out. Drying of the solder paste may cause irregularities in the shape of the printed solder paste, and the volume of the solder paste printed on the pad may be inconsistent. At this time, it should be checked whether the solder paste used is expired; whether the temperature is within the temperature range recommended by the solder paste supplier; and when the relative humidity (RH) is 50%, the temperature of the printing press is about 25°C. Do not mix new solder paste with old solder paste. Unusual operating temperatures can also make solder paste seep out of the pad and connect to adjacent pads. If the temperature is normal and the temperature is maintained at the time of printing, another batch of solder paste should be inspected to confirm if the problem is related to the print lot. Cold slump and hot slump tests were performed using IPC-650 method 2.4.35.

Component placement

Inaccurate placement of components will reduce the spacing between pads and increase the likelihood of bridges. For each product, check the placement pressure of the components. Use X-rays to check that the BGA is properly aligned and use QFN for microscopic examination.

The component's placement pressure is too high to push the paste out of the pad. If this happens, check the actual height of the component based on the component height data of the input machine. The mounting height of the component should be ±1/3 of the solder paste height.

Reflow temperature curve

When the holding time is extended, the solder paste will absorb more heat and cause the solder paste to fall off. If possible, choose a temperature profile with no holding zone and temperature rising directly to the maximum temperature.