Find out what solder bridging is.
Learn what causes solder bridging.
Explore how to prevent solder bridging.
I was trying to impress my son by building a trail of dominoes without toppling them over. It’s the ultimate test of concentration and precision, as each domino needs to be placed at a specific distance from the previous one. Imagine the frustration of accidentally knocking one over and watching them all tumble at once.
The same precision is necessary when assembling components on a PCB. Not only must the components be placed accurately on top of the pads, but the soldering process must be equally flawless, otherwise, you’ll stumble into all sorts of soldering issues, including solder bridging. In this article, we discuss how to prevent solder bridging through a few key methods.
What Is Solder Bridging?
The short circuit from solder bridges may damage components.
As the name implies, solder bridging is akin to having a bridge of solder built between two adjacent component pads. It usually happens on fine-pitch SMD components, such as a microcontroller on an LQFP package. When left unspotted, the short circuit created by the solder bridge can cause the circuit to malfunction and, in some cases, damage the shorted components.
Solder bridging is a common problem that occurs in prototypes that are manually soldered. One would expect that machine-assembled PCBs would be free from solder bridging issues, but such an assumption is dangerous. Solder bridging can still happen on machine-assembled PCBs, although it is less common. Therefore, you’ll always need to conduct a thorough inspection before putting any PCBs into a live test. Those tiny solder joints across the pads are hard to spot with bare eyes, which is why optical inspection equipment can be used to spot solder bridges.
What Causes Solder Bridging?
A thicker stencil deposits more solder paste, which may cause solder bridging.
It’s hard to pinpoint the root cause of solder bridging because it can be due to a multitude of factors. SMD components are tricky to work with from the start, particularly if they have a very small pitch. A slight increment in the pad width may lead to solder bridges.
The issue can be aggravated if the solder paste mask is absent or only covers a narrow area between the pads. This enables the solder paste to rest on the substrate, which causes solder bridges to easily form.
Sometimes, solder bridging is caused by stencil thickness, which affects the volume of solder paste applied onto the pad. A thicker stencil will lead to more solder paste on the pads, which may cause the paste to overflow from one pad to another.
Any imperfection in the solder paste printing process may also cause solder bridging. For example, dust or grime at the bottom of the stencil will introduce a gap during printing. This may cause the solder paste to be applied inaccurately. The same goes for misalignment, even at the slightest scale, during paste printing.
How to Prevent Solder Bridging
Fix solder bridging with a soldering iron and solder paste.
Worried about how to prevent solder bridging? While PCB designers have no control over the assembly process, there are some areas that you can work on to reduce the occurrence of solder bridging. The first thing is to ensure that the stencil thickness is not causing excessive solder paste to be deposited on the pads. If it is, you’ll need to produce a thinner stencil.
Ensure that component pads are designed with the right dimension. Pads shouldn’t be too wide or too narrow. If you’re in doubt, refer to the IPC standards on the dimension for optimum solderability. It also helps if you’re designing with component libraries that are in compliance with IPC standards.
Even with all the precautionary measures, solder bridging may still occur. To fix that, you’ll need to use a narrow tip solder iron, wet it with a solder paste, and heat up the solder bridge. Gently drag out the melted solder out of the pads. Then, test with a multimeter to ensure that the pads are no longer shorted.
Your choice of PCB design software may help to prevent solder bridging. OrCAD’s IPC web component libraries ensure minimum issues during the assembly process. If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.