Prevent Solder Bridging During Board Assembly
A solder bridge jumper is an unintended connection between two pads, pins, contacts, terminals, or connectors on a printed circuit board. This type of short circuit can cause serious electrical problems, requiring costly rework and replacement components. This is why it’s so important to prevent solder bridging during the PCB assembly process, especially when manufacturing boards at scale. Fortunately, there are a few steps you can take to minimize the risk of solder bridges occurring on your boards.
Fiducials are specific design markers or indicators on your PCB that allow automated machines to accurately locate and align the board, as well as place components in the correct position. A proper placement of fiducials reduces the chances of misplaced parts, which in turn reduces the likelihood of forming a solder bridge jumper. The IPC recommends using at least three fiducial marks, two in opposite corners and one in another corner.
Solder paste is a mixture of flux and particles that holds surface mount components in place during the soldering process. When too much solder is applied, it’s easy for the excess to flow into unintended locations and form a bridge. This is why it’s critical to use a pick-and-place machine, as opposed to a manual human touch, during the production process. A pick-and-place machine uses mechanical or even vacuum-based movements to take a component from a feeder, place it on the board, and then apply the necessary amounts of solder. This eliminates human error and greatly reduces costs during at-scale production.
In addition to applying the proper reflow profile and maintaining a steady temperature, it’s important to make sure that your solder paste is the right consistency and viscosity for the application and that the components you’re using have the correct lead length.
How to Prevent Solder Bridging During Board Assembly
The wrong lead length can contribute to solder bridging by creating an area where the leads are too close together, allowing liquid solder to flow between them and wet them both. Your contract manufacturer should be able to help you determine the precise lead length for your specific needs.
As we’ve discussed in other articles, a large part of the problem with solder bridges is that liquid solder tends to flow towards warmer surfaces first. Increasing the soak time for your printed circuit board can help to address this issue by giving the liquid more time to reach the pad and component leads, eliminating the tendency to flow to warm areas that could result in a solder bridge.
As we’ve mentioned, solder bridges are an all too common and frustrating occurrence during the board assembly process. The good news is that they are also relatively simple to avoid. By working with a competent electronics manufacturing services provider that is willing to discuss their assembly processes, including stencil design, inspection protocols, and more, you can minimize the chances of solder bridges and other failure modes during at-scale production.
Flux also plays a vital role in preventing oxidation during the soldering process. When metals are heated, they tend to oxidize rapidly, forming a layer of oxide that can inhibit the solder from bonding effectively. Flux creates a protective barrier that shields the metal surfaces from oxygen, minimizing the formation of oxides during heating. This protection ensures that the solder can flow smoothly and create solid electrical and mechanical connections.
