It was a wonderful day pulling teenagers on water skis, wakeboards, and tubes, but we were in a different river than normal, and I wasn’t familiar with it. At one point I got preoccupied retrieving an upended skier and didn’t notice how fast the current was pulling us towards some anchored yachts. Fortunately, we didn’t drift into anyone, but there were some fishing lines that were hastily retracted and some rather rude comments left in their place. I learned just how powerful the current could be on that day.
Current is a vital part of the operation of any circuit board, but as the current in a fast-moving river, it can also be unforgiving if not treated with the care that it deserves. When you are working with high current applications, you need to exercise an even greater amount of caution in your design. Let’s take a look at some via stitching guidelines and other tactics that are helpful in designing high current printed circuit boards.
Via Stitching Guidelines and High Current PCB Design Tactics
One of the important keys to routing high current circuits is to use a lot of metal. This can be done with wider traces, copper pours, and stitching vias. Stitching vias are used to join the routing of high current circuits on multiple layers of the circuit board. If a trace on one layer is insufficient to carry the amount of current that is needed, then the trace can be routed on multiple layers and stitched together with vias. If two different power layers have the same width trace on them for carrying the current, it will double the current carrying capacity helping to keep the board size smaller instead of having to space the trace out on a single layer.
Stitching vias do have some concerns to be aware of though. The first is that the high current traces will also be conducting heat. The stitching vias will absorb this heat, but the heat still needs to be dissipated through a thermal via to an external layer of the board for cooling. The stitching vias don’t have to be large, but there have to be enough of them to conduct all of the current and heat without being overloaded. You also need to ensure that you have provided an adequate current return path in your design. In some cases, multiple traces and stitching vias end up taking the place that was needed for a current return path and create a current loop instead.
Some other effective methods of conducting high current are to use wider traces and copper pours. If the traces aren’t wide enough to carry the current, there could be areas of high heat that could affect the board’s ability to provide the steady-state current requirements for the rest of the circuitry. This can impact the performance of other components as they push their maximum temperature constraints, and the entire board may fail to perform as intended.
There are a lot of different tactics that can be used when planning for high currents in your PCB design, and your PCB contract manufacturer can help you work through the different options.
Get Your PCB Contract Manufacturer Involved Early in Your Design
The PCB CM that you are working with will have a lot of experience in building high current circuit boards and can offer a lot of advice on what will work best for your design. These are some of the areas that they will focus on:
- Fabrication: Depending on the amount of current that your design will be handling, your CM can recommend different materials for the fabrication of the board designed for high currents and temperatures. The CM can also help you develop the layer stackup that will work the best for your needs, and recommend copper pour patterns that will help the board to not twist and bow during fabrication.
- Assembly: While high current usually dictates the use of more metal in the connections of the board, you still will need to exercise caution to ensure that the board can be assembled. Large areas of metal can cause thermal imbalances which will affect the soldering of components, such as smaller discrete parts that could tombstone during solder reflow. The use of thermal relief pads in these connections will help during assembly, and your CM can recommend their proper size and placement.
- Layout: The proper component placement and trace routing of high current circuits is also important for the best performance of the board. The PCB CM can give you different layout recommendations, and work with you on current capacity calculations for trace widths as well as high current routing and the use of stitching vias.
With their experience, your contract manufacturer can help you to avoid manufacturing problems as well as achieve the performance goals you are looking for in your design. The important thing is to choose a PCB CM that has the expertise that you are looking for.
High Current PCB Expertise at VSE
At VSE, we have been working with engineering clients like you for over 30 years. We have a deep level of experience with high current circuits, as well as with many other printed circuit board technologies. We can help you to fine-tune the high current circuitry of your design, including your power routing and stitching vias so that it can be built and operated as intended.
