Solder Bridge Jumper Best Practices in PCB Design
A PCB variant is often simply thought of as a new layout created from an old design. However, if you’re creative with your routing and layout, you can use a solder bridge jumper to configure portions of a single PCB layout for multiple variants. This lets you quickly create variants of a PCB layout without rerouting traces or changing your schematics. If you plan to use jumpers in your PCB layout, there are some important guidelines to follow to ensure you do not create other design problems. Let’s look at solder bridge jumpers and how they can quickly create variants of your design.
What is a Solder Bridge Jumper?
A solder bridge jumper is simply a pair of pads on a PCB trace that can be easily bridged with a solder ball. You’ll get a much cleaner layout if you use 0 Ohm resistors to create the bridge; 0 Ohm resistors are very low cost and are available as surface-mount components. In some cases, a solder bridge jumper need not be solderable, as shown in the example below.
In the image below, I’ve placed bridged and unbridged jumpers at specific points in the layout. Rather than worry about soldering or placing 0 Ohm resistors, I can quickly modify my layout to create a new variant by replacing a bridged jumper with an unbridged jumper, or vice versa. Even after the variant is produced, I can still configure my device by bridging any jumpers after assembly.
The CAD tools in your PCB design software can be used to easily create a schematic symbol and a PCB footprint for a solder bridge jumper. In the example above, I’ve created two symbols and PCB footprints; one pair is for the bridged jumper, and the other pair is for the unbridged jumper. My schematic symbols for the jumpers shown in the above layout can be seen in the image below. By simply swapping the bridged and unbridged jumpers, I can easily create a new board with different circuit blocks activated or deactivated.
Why Use a Solder Bridge Jumper?
A solder bridge jumper is a great way to make a board configurable. By “configurable,” I mean that a single board design can be produced with defined layout and routing, but the signal paths involved can be chosen during assembly. A designer can create a PCB layout that is used for multiple variants by carefully selecting where to place different jumpers.
A solder bridge jumper can be placed on different signal paths to open or close a circuit, depending on if it is needed for a particular peripheral. To close the jumper, simply place a small amount of solder between the two pads to be bridged. This creates a closed circuit and allows current to flow across the jumper to a downstream component. This takes a bit of creative routing on the front end. Still, it allows the designer to create multiple variants of a single layout, rather than producing additional layouts for each variant.
You might want to use a solder bridge jumper to easily turn on a particular circuit block. In a recent project, we used multiple solder bridge jumpers to create prototype and production variants using the same layout. Merely opening or closing a bridge allows you to activate or deactivate a component, circuit block, or connection to a peripheral.
Some Best Practices with Solder Bridge Jumpers
The most important thing to think about when choosing to place solder bridge jumpers in your layout is who will assemble your board, if you need to configure your board after assembly, or if your manufacturer can accommodate variants of the same board in a panel. If you’re using 0 Ohm resistors or you plan to solder your jumper closed, your fabricator might act like the sky is falling when you ask them to DNP different components on different boards in the same panel. If you want to avoid a long explanation for your fabricator (as I recently experienced), you’re better off using the copper-bridged jumpers I’ve shown above.
You need to pay careful attention to routing in your schematic and PCB layout to make easy use of solder bridge jumpers. In addition, pay attention to the following design points.
Watch Out for Transmission Lines
If you plan to place a 0 Ohm resistor or solder on a transmission line, you should use it very close to the driver’s end. If the jumper is placed far from the driver and left open, you’ve just created an open transmission line, which will act as an antenna at specific frequencies. Placing the jumper close to the driver ensures that the leftover copper will not act as a transmission line if the jumper is left open.
Avoid Solder Bridge Jumpers on High Voltage Lines
An open solder bridge jumper on a high voltage line may violate IPC 2221B or IPC-9592B standards. This will happen if the distance between each end of the jumper is very small. For safety and reliability’s sake, you should use a rugged switch or relay rated for the voltage/power in your board.
Solder Bridge Jumpers Are Not Reusable
If you plan to use solder bridge jumpers in your PCB layout, remember that they should not be reused, meaning they should not be repeatedly soldered and opened. You might get away with multiple placements and removals of a 0 Ohm resistor since you aren’t drawing solder across a gap on the PCB surface, but these should also not be reused.
If you know, you will need to open and close jumpers repeatedly, use SMD jumper pins. You can then pull off the jumper as needed. This is a good strategy when designing a first-run prototype, and you need to experiment with different operating modes or peripherals. You can still use standard solder bridge jumpers and jumper pins in the same layout. Plastic jumpers are also useful for peripherals that will connect to your board over a pin header. You might not need to use a solder bridge jumper, depending on your routing and layout.
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